300 Industrial Structures

AbstractSection 300 covers design for concrete and steel structures such as pipeways, pipe supports, equipment support, stairs, ladders, walkways, platforms, guyed stacks, pipeway crossings, and roadway bridges. This section does not cover buildings and offshore structural platforms, although most of the components can be used on offshore production facilities.

The guidelines in this section are written for inexperienced engineers or engineers working outside their discipline or area of expertise.

Contents Page

310 Introduction 300-3311 Background Information

312 People and Organizations

313 Industry Codes and Practices

320 Piping Support 300-6321 Design ConsiderationsElevated Pipeways

322 Design Guidelines

323 Low-Level Pipeways and Sleepers

324 Secondary Pipe Supports, Springs, and Hangers

330 Equipment Supports 300-29331 Design Requirements

332 Design Loads

333 Structural Analysis and Design

334 Design Considerations for a Corrosive Environment

340 Stairs, Ladders, Walkways, Platforms, and Handrails 300-32341 GeneralChevron Corporation 300-1 June 1997

342 Design Loads

343 Grating and Floor Plate Design and Selection

300 Industrial Structures Civil and Structural Manual344 Ladders, Cages, and Guards

350 Guyed Stacks 300-45351 Use and Layout352 Design353 Installation354 Maintenance360 Pipeway Crossings and Roadway Bridges 300-53361 General Considerations362 Buried Lines

363 Corrugated Pipe Arches364 Overhead Pipeway Crossings365 Bridges for Pipeline Crossings370 Computer Programs For Designers 300-64371 STAAD III

380 Model Specification, Standard Drawings, and Engineering Forms 300-65381 Model Specification

382 Standard Drawings

383 Engineering Forms

390 References 300-66June 1997 300-2 Chevron Corporation

Civil and Structural Manual 300 Industrial Structures310 IntroductionAs used in this section, the term industrial structure refers primarily to structures used to support piping and equipment. In addition, the section addresses guying of stacks and the design of stairs, ladders and other means for accessing these struc-tures.

Information included here will be useful for both novice engineers and engineers working outside their discipline. While this information will help you develop preliminary designs and make informed decisions, it is not a substitute for review and sign-off by a registered civil or structural engineer. To enhance the utility of this section, some major subsections have their own references. A comprehensive list of primary references can be found in Sub-section 390.

311 Background InformationIndustrial structures are required to perform a specific function, and a complete understanding of this function is critical. But, in addition to meeting functional requirements, there are other important objectives that a designer should strive to meet. These objectives include: Select a framing system and structural elements appropriate for the type of

loads involved.

Meet all safety requirements, including those in the Safety in Designs Manual (SID).

Provide a structure that can be economically fabricated and installed.

Select materials appropriate for the environmental conditions.

Give particular attention to the detailing of structural connections. Structural problems are frequently traced to inadequate or inappropriate connection details.

Provide a structure that performs satisfactorily over its intended useful life, without requiring extensive maintenance.

Provide a structure that creates minimum interferences to the normal activities of the operators.

Provide a structure with the access, clearances, work and laydown areas neces-sary for maintenance.

Present a balanced appearance consistent with the facilities being supported.

Give consideration to aesthetics whenever the structure is highly visible.

Provide space and structural capacity for changes and future loads.

Keep structural details as simple as possible to fit up and weld. Review of struc-tural steel details should take into account the accessibility for welders to perform their work.Chevron Corporation 300-3 June 1997

300 Industrial Structures Civil and Structural Manual Eliminate areas which will collect and hold moisture and other foreign mate-rial. Such areas will be subject to accelerated corrosion.

There are many standard structural details illustrated in Company Standard Draw-ings and Forms, and other structural design references. For many simple structures, these details will reduce design time and provide proven solutions. A list of these drawings and forms is included in Sub-section 380.

The Company primarily uses either structural steel or reinforced concrete struc-tures. The choice is most often an economic decision based on lowest installed cost. However, the importance of maintenance costs and flexibility for future modifica-tions and additions may also be considerations.

Design DocumentationStructural designers are responsible for documenting the design basis for structures. This documentation should assist designers involved in future additions, modifica-tions, or corrective actions. The following items should be included on design draw-ings where applicable:

Design Codes (Including Date or Edition) Company Design Standards (Wind and Earthquake) Design Operating Loads Design Loads and Moments for Foundations Soil Bearing Pressures Pile Design Loads Unusual Design Conditions

312 People and OrganizationsBe familiar with the people, organizations, regulations and requirements that provide input to your designs, or have a review and/or approval function. Here are a few of the most important:

Government AgenciesThe extent of local governmental review is closely tied to existing regulations. Where no regulations exist, follow local management perception of need and antici-pation of future requirements.

Identify applicable regulations, required permits, and government agencies with jurisdiction over the work. Determine if there are requirements that civil/structural drawings be stamped by a Professional Civil Engineer and/or Structural Engineer. Since 1986, the State of California requires that ....all final civil engineering plans, specifications, reports, or documents shall bear the seal or stamp of the registrant, and the expiration date of the certificate or authority.

Two examples of how local codes have influenced designs are:June 1997 300-4 Chevron Corporation

Civil and Structural Manual 300 Industrial Structures At one location, the applicable building code was based on an earlier edition of the Uniform Building Code. Subsequent changes to the UBC were not recog-nized by the local authorities.

Another locality enforced their own limitation on the allowable openings between rails on a handrail. This required the addition of a second midrail for all railings.

Safety EngineerThe local Company safety engineer is an important contact to establish at the early stages of design. For example, the number, location, and types of egress are critical items that should be addressed early. Periodic discussions with the safety engineer are encouraged to review required clearances, to consider special situations, and to clarify or interpret Company requirements and practices. Final review by the safety engineer occurs when the structure is complete. Items found to be in nonconfor-mance at that time can prove to be costly to correct.

Fire Protection EngineerThe fire prevention specialists in CRTCs Health, Environment, and Safety Group must be consulted to establish fireproofing requirements. Early agreement to define the vertical and horizontal fireproofing limits for specific structures or locations is desirable.

Facility OperatorsThe local operators will normally have four primary concerns relating to structures. These include: functional aspects of the structure, operator access, clearances, and servicing/maintenance requirements. They will influence size of platforms and number and types of access.

Drafting and EngineeringDivision of work between engineers and designer/draftsmen will depend on estab-lished practices at a location, level of experience for designer/draftsmen, and complexity of intended structure.

Contact with other engineering disciplines is frequently required to define intended function, anticipated loads, space limitations, access and clearances required for operations and maintenance work.

313 Industry Codes and PracticesThis section lists the applicable codes used for design of steel and concrete struc-tures.

Steel ConstructionManual of Steel Construction - American Institute of Steel Construction (AISC). Includes: AISC Specification for the Design, Fabrication and Erection of Struc-tural Steel for BuildingsChevron Corporation 300-5 June 1997

300 Industrial Structures Civil and Structural ManualStructural Welding Code - AWS D1.1, American Welding Society (AWS)ASTM Standards in Building Codes Specifications, Test Methods, Definitions Volume 1

Metal Bar Grating Manual - The National Association of Architectural Metal Manufacturers (NAAMM)

Concrete ConstructionBuilding Code Requirements for Reinforced Concrete, American Concrete Institute (ACI 318)ASTM Standards in Building Codes Specifications, Test Methods, Definitions Volume 1

Safety In Designs ManualUniform Building Code. International Conference of Building Officials. Covers the fire, life and structural safety aspects of all buildings and related structures. The UBC is commonly accepted in whole or in part by municipalities, so that review and approval of designs is frequently based on meeting UBC requirements. A sepa-rate volume, Uniform Building Code Standards, presents test, material, and special design standards which are referenced in the UBC. Guidelines for the Seismic Eval-uation and Design of Petrochemical Facilities [20] is an excellent resource as it provides commentary and guidance on how to apply the Uniform Building Code, which is mainly intended for buildings, to structures typically found in petrochem-ical facilities.

Standard Welding Symbols. A copy of the AWS Standard Welding Symbols is included at the end of this section (Figure 300-30). Incorrect or incomplete weld symbols on drawings can lead to inadequate welded connections, or to increased fabrication costs because of claimed extras by the fabricator. An example occurred when an engineer designed some critical connections as full penetration welds. However, the basic welding symbol used on the drawings could also be interpreted as a partial penetration weld. Since the notation CP (for complete penetration) was left off the drawing, and the specification did not call for full penetration welds, the fabricator made a claim for a sizable extra to the contract.

Note Figure 300-30, Standard Welding Symbols, is a foldout at the end of this section.

320 Piping SupportThis subsection on piping support discusses design considerations and applicability of three types of support: stanchions for elevated pipeways, grade-level pipeways and sleepers, and secondary supports, springs and hangers.

Stanchion supports (Figure 300-1) are commonly used in refineries and other plants where piping runs might interfere with vehicle and personnel movement. They are considerably more expensive than grade-level supports. In many instances, stan-chions remain a constant size while the piping loads and configurations they bear June 1997 300-6 Chevron Corporation

Civil and Structural Manual 300 Industrial Structuresoften change. With this in mind, it is important to ensure that stanchion design reflects potential future loadings.

Fig. 300-1 Pipeway StanchionChevron Corporation 300-7 June 1997

300 Industrial Structures Civil and Structural ManualIn addition to carrying process lines and utility/service headers, the pipeway stan-chions carry electrical and instrument distribution systems along with mechanical and safety equipment.

Another issue in stanchion design is fire protection. Generally, on-plot stanchions are either fireproofed or constructed of fireproof material, while off-plot stanchions are not. The exception will be stanchions located in near-off-plot pipeways, i.e., pipeways adjacent to or between process plants.

321 Design ConsiderationsElevated PipewaysThis section discusses 10 major considerations used to determine pipeway design parameters. These include:

1. Pipeway Capacity

Pipeway capacity, the amount of the available space to carry piping, is the critical element affecting stanchion design. The width of pipeway, number of levels, and stanchion geometry are all dependent on establishing the pipeway capacity. Require-ments for pipeway space are determined from planning studies by the piping engi-neers and designers and input from operations, and are based on estimated current space requirements plus an allowance for future lines.

2. Stanchion Geometry

After determination of design pipeway capacity, studies can begin on stanchion geometry alternatives. These studies will establish:

Overall pipeway width Number of pipeway levels Column spacing Elevation of crossbeams Extension of support beams outside the column lines Requirements for other supports at plot limit manifolds

Factors considered in these studies include:

Vehicle access Plant space limitations Proposed piping layouts at plot limit waterfalls Location of utility stations Electrical/instrument conduits Access during construction and maintenance considerations

Individuals responsible for the stanchion structural design will often get involved in these studies as the constructability and economics of various design concepts are considered.June 1997 300-8 Chevron Corporation

Civil and Structural Manual 300 Industrial Structures3. Stanchion Spacing

The horizontal distance between stanchions is normally determined from plant layout studies and is influenced by the size of lines to be supported. For acceptable piping/conduit spans, stanchion spacing between 20 to 30 feet is generally used. Smaller stanchion spacings to accommodate the small allowable span of small diameter piping and conduit are typically not used, since small lines can be supported by unistrut between two larger lines or by intermediate crossbeams. See Figure 300-2 for an illustration of intermediate crossbeams. For information on recommended spans for individual line sizes, refer to Sub-section 324.

4. Clearances

Vertical and horizontal clearances must be determined by the operating require-ments of the facility. At times there may be a need for an operating or maintenance roadway underneath the pipeway. If the roadway runs longitudinally directly below the pipeway, side clearance for the stanchion columns must be sufficient for vehicle access plus an allowance for manifolds or other equipment mounted on or adjacent to the stanchion columns.

The vertical clearance above the roadway must be sufficient to allow passage of fire protection vehicles and a hydraulic maintenance crane. A frequently used minimum vertical clearance from high point of grade to the lowest projection on the pipeway is 12 feet-6 inches, but specific plants may require a different clearance.

Fig. 300-2 Pipeway Isometric Illustration of TermsChevron Corporation 300-9 June 1997

300 Industrial Structures Civil and Structural ManualFor multi-level stanchions, the clear vertical distance between levels will vary depending on the average and maximum line sizes to be installed. Adequate clear-ance is necessary for lines to enter the pipeway and for reasonable accessibility for completing field welds, insulation, and painting. For the average case a clearance of 2 feet-6 inches is suggested, from top of lower support beam to underside of the beam above. Where small lines (4-inch maximum) are involved, the spacing may be reduced to about 2 feet. A clearance of 3 feet or more may be required if a number of large lines are proposed. For example, if there are a number of 12-inch lines in the pipeway, a 4-foot clearance might be desired so that two elbows can be used for a 90 degree jumpover of other lines in the pipeway. See Figure 300-3.

When there are only a few large lines in a pipeway, it may be desirable to consider using 45 degree jumpovers instead of 90 degrees for lines entering the pipeway. This will reduce the required clearance between pipeway levels.

Structural bracing can be a head-knocker. In areas where people walk, the lower ends of braces should intersect columns high enough to keep a 7-foot clearance above grade. However, in Seismic Zones 3 and 4, braces must extend down to grade (See Figure 300-2). A barrier should be used to prevent accidents. In Seismic Zone 2, the 7-foot clearance is acceptable, provided certain design requirements are met. See Chapters 2211 and 2212 of the 1994 UBC for details.

5. Fireproofing Requirements

Structural steel pipeway stanchions can be covered with special materials or concrete to protect them from fire. Precast or cast-in-place concrete pipeway stan-chions usually do not require special fire protection consideration. Fireproofing materials and requirements are discussed in the Insulation and Refractory Manual, Section 400. Generally, fireproofing principal members of a pipeway structure is warranted if exposure to fire could result in failure of these members and cause loss or serious damage to critical piping, or supported equipment such as air-cooled exchangers.

Fig. 300-3 Clearances for PipingJune 1997 300-10 Chevron Corporation

Civil and Structural Manual 300 Industrial StructuresOn-plot pipeway stanchions are generally fireproofed up to and including the first main horizontal member, but not less than 20 feet above grade. Knee braces for support beam extensions outside the stanchion columns are generally fireproofed when located less than 20 feet above grade. Braces provided for wind and seismic loading need not be fireproofed, as long as the structure is stable without them for gravity loading conditions. In high risk areas (equipment operating pressure over 1000 psig), fireproofing may be required for the second and higher levels of pipeway supports. Structural members supporting air coolers handling liquid hydro-carbons above pipeways in process areas should be fireproofed up to the point of applied load.

For off-plot stanchions the only fireproofing generally required is at plot limit mani-folds areas, and at other locations deemed to be fire hazard areas. If fireproofing is warranted for such areas, it would be limited in scope, such as:

Pipeway columns within 25 feet of manifolds or fire hazardous areas.

Horizontal members that support piping coming from manifolds.

Fireproofing would normally not be required for off-plot pipeway diagonal bracing or for longitudinal struts between stanchions.

InstallationFireproofing is provided for structural steel members by using either regular port-land cement concrete, gunite, or special insulating materials. Refer to the Insulation and Refractory Manual Section 400 for a discussion of surface preparation, priming, top coats, and fireproofing materials. Following are the ratings for various thickness of concrete fireproofing over steel:

For main support members that require fireproofing, it is customary to provide a 4-hour fire rating as shown on Drawing GA-N33336 (in the Fire Protection Manual). Concrete having a minimum compressive strength of 2500 psi is recom-mended for fireproofing.

Corrosion under fireproofing can be a serious problem. Flashing or caulking may be required to prevent entry of water between the fireproofing and steel. Acceptable sealants should be specified. Two products that have been used are Dow Corning No. 732 Silicone elastomeric sealer, and H.B. Fuller, Foster Products Division No. 94-95 Butyl Caulking.

(1) On the face of steel member. Thickness at edge of structural member may be 1/2 inch less. Thickness requirements are illustrated in Figure 300-4 for beams. The top flange face of beams does not require fireproofing. The flange faces for columns require full thickness coverage.

Minimum Thickness(1) Fire Rating (Hours)

2-1/2 inch 4

2 inch 3

1-1/2 inch 2Chevron Corporation 300-11 June 1997

300 Industrial Structures Civil and Structural Manual6. Steel vs. Concrete

For a new installation, the preferred stanchion materials are either steel or concrete. Some factors that influence the final choice are:

Stanchion GeometryStructural steel is usually the economic choice for complex pipeway stanchions (multi-level, cantilever beams, larger spans). These are difficult and costly to construct with precast or cast-in-place concrete. Moreover, steel structures have the additional advantage of being more adaptable for future modifications. Reinforced concrete is generally limited to simple structures that require fireproofing. A combi-nation of materials may also be used, such as reinforced concrete for the lower portion that requires fireproofing, and structural steel above.

FireproofingThe economics of steel vs. concrete depend on the fireproofing requirements. Struc-tural steel is generally the economic choice if concrete encasement is not required. However, for installations that require fireproofing, the added costs to encase the structural steel reduces the cost differential between steel and reinforced concrete.

Other ConsiderationsOther factors should be considered in the evaluation of steel vs. concrete. Some of these may require input from installation contractors.

Items that might be evaluated for specific installations include:

Relative impacts of steel vs. concrete on project construction schedule.

Fig. 300-4 Fire Proofing CoverJune 1997 300-12 Chevron Corporation

Civil and Structural Manual 300 Industrial Structures Differences in weather impacts. For example, steel might be preferred over concrete in a freeze/thaw environment.

Impact on other construction activities performed concurrently in the area.

Does stanchion geometry lend itself to precasting and use of reusable forms?

Ability to precast on-site or in contractors yard.

7. Foundations

Spread FootingsSince the axial loading imposed by pipeway columns is relatively light, spread foot-ings are an option if the soils have adequate bearing capacity. Spread footings are generally designed on the basis that the column-to-footing connection is hinged. The reasons include:

Soil conditions may preclude imposing large moments on the footing without substantially increasing the footing dimensions.

Fixed column-to-footing connections are more difficult to achieve and may be more costly.

Pile-Supported FootingsPile-supported footings can be designed to take combined axial loads and longitu-dinal and/or transverse moments from stanchion columns. A column-to-footing connection using a base plate and anchor bolts requires careful design to assure complete moment transfer. An alternative is to extend the column into the pile cap by grouting into a prepared pocket. Typical column-to-footing connections are shown in Figure 300-5.

Fig. 300-5 Typical Column-to-Footing ConnectionsChevron Corporation 300-13 June 1997

300 Industrial Structures Civil and Structural Manual8. Longitudinal Struts or Tiebeams

Longitudinal loads on stanchions result primarily from the friction forces developed by thermal expansion of the supported lines, along with possible loads from anchored lines.

It is a common practice in stanchion design to tie individual stanchions together longitudinally with structural strut members. Braced stanchions are provided at appropriate locations, every fifth to tenth stanchion along the pipeway, to resist the total longitudinal forces developed. These are strategically located to resist longitu-dinal pipeway loading and minimize restrictions to vehicle and personnel access. Diagonal bracing can be used to anchor a single stanchion, or multiple stanchions can be braced as shown in Figure 300-2.

For some pipeways, the tiebeams act as struts only, and do not carry external loads. Often, there are vertical loads imposed. These occur where:

Tiebeams serve as support for steam loops or lines that branch from the main pipeway.

Small pipeway lines or conduit are directly supported by the tiebeams between stanchions.

Intermediate crossbeams are provided between stanchions for support of small lines and electrical/instrumentation conduit. Intermediate crossbeams in turn receive their support by the longitudinal tiebeams.

9. Future Expansion

A space allowance for future lines is normally included in the determination of pipeway capacity. This allowance is frequently based on a percentage of the space proposed to meet current requirements. For example, an arbitrary 25% allowance might be chosen, to be adjusted upward or downward depending on the expecta-tions for future lines. Another factor to consider is the ease or difficulty to add pipeway capacity in the future. On-plot stanchions frequently present great difficul-ties with regard to expansion, and increased spare capacity in the initial installation is warranted.

If you choose to make provisions for modifications and expansion of the pipeway in the future, member sizes and details should be designed to support an additional level to the pipeway, the addition of cantilever crossbeam extensions, or an increase in the pipeway width by adding another row of columns and extending the cross beams.

10. Loadings

Following the conceptual development studies for the pipeway and structures, develop a consistent and realistic set of design loads.

Loadings to be considered on stanchions are:

Dead loads from pipeway structure Pipe gravity loads including fluidsJune 1997 300-14 Chevron Corporation

Civil and Structural Manual 300 Industrial Structures Electrical and control conduit loads Thermal expansion loads from piping including anchor forces Earthquake and wind loads Loads from equipment and associated platforms

Pipe Gravity LoadsPipe gravity loads may be treated as uniform loading of 35 pounds per square foot of contributory area of loading, per pipeway level for columns and transverse beams. This is equivalent to the loading from water- filled 6-inch lines (0.250-inch wall) at standard 10-inch spacing between lines. The above loading is appropriate for the typical pipeway, but a more refined determination may be justified if the majority of lines will be either less than or will exceed 6-inch diameter. Piping plans should be checked to avoid special loading situations that may exert high concentrated loads.

Longitudinal TiebeamsTiebeams that will also support lines at pipeway intersections should be designed for the full unit loading of 35 pounds per square foot of contributing area.

Tiebeams at other locations should be designed for anticipated current and future loads. It is common practice to apply the same design loads to a continuous string of tiebeams to provide uniformity in design and give maximum flexibility for adding future loads.

Thermal LoadsThermal loads result from expansion or contraction of piping from changes in both ambient temperatures and operating line temperatures. The static coefficient of fric-tion for individual lines is usually estimated at 0.3 to 0.5 (steel against steel), with the value 0.42 used for 1 or 2 pipes and 0.3 for 3 or more pipes. The horizontal force due to friction is:

Ff = fW(Eq. 300-1)

where:Ff = friction force (lbs)f = coefficient of friction

W = weight of piping and contents supported by structure

Thermal loads are usually considered internal and self-compensating for stanchions with longitudinal tiebeams. That is, if a group of stanchions are interconnected and anchored to resist longitudinal movement, thermal loads on individual stanchions can be disregarded.

Even for stanchions that do not have longitudinal tiebeams there will be some self-compensation of thermal loads. The friction forces developed by individual hot lines will tend to be offset by resisting forces from other lines in the pipeway not Chevron Corporation 300-15 June 1997

300 Industrial Structures Civil and Structural Manualexpanding at the same time. By carefully considering the load contribution from hot lines, the designer can select total thermal forces for stanchion design that are adequate but not overly conservative.

Thermal loads on pipeway stanchions should be considered at changes in pipeway direction, where expansion loops or bellows are used, or where pipes may be restrained external to the pipeway, such as where connected to vessels or equip-ment. In a long, rigidly-connected pipeway, consideration should be given to thermal stresses induced into the stanchions due to expansion of structural members. These stresses can be mitigated by subdividing the length of the pipeway into groups of individual stanchions tied together with longitudinal tiebeams. Each group is individually anchored, with no tiebeams between groups.

EarthquakeEarthquake forces (transverse and longitudinal) can be determined using procedures given in Section 100, Wind and Earthquake Design Standards. Seismic loading in the transverse direction is usually of greater concern than in the longitudinal direc-tion, as supports are restrained longitudinally by the lines themselves. Transverse seismic loading is resisted by rigid frame design of the stanchions or diagonal bracing in the transverse plane.

WindWind loading transverse to the pipeway is calculated using the projected area of the largest pipe at each pipeway level, plus the area of the support columns. Rigid frame design or diagonal bracing is the usual choice for resisting lateral wind loading. The wind force longitudinal to the pipeway is usually neglected. For wind forces refer to Section 100, Wind and Earthquake Design Standards.

Other LoadsPipeway stanchions may also be used to support operating equipment such as air coolers and miscellaneous vessels. Loads should be determined from the operating weight of equipment, platforms, and supporting structures.

322 Design GuidelinesThe purpose of this section is to review accepted design practices for stanchions, and direct the reader to references on this subject.

Design ReferenceIncluded in the References subsection is a document entitled Pipe Support Design (Reference [16]). Individuals not familiar with designs for pipeway structures may wish to obtain a copy of this manual through Chevron Research and Technology Company. In using this document the following cautions apply:

Refer to Section 100 of this manual to determine design loadings for wind and earthquake.June 1997 300-16 Chevron Corporation

Civil and Structural Manual 300 Industrial Structures In developing designs use good judgment when following the procedures given in Reference [16]. Take a critical approach to determine if unusual loadings or other conditions require modifications to the design steps.

Construction Details for Earthquake ResistanceDetails for earthquake-resistant design should give the structure the ability to absorb energy. The following general comments apply:

Reinforced Concrete Structures. Design all moment-resisting space frames as ductile frames (for seismic zones 2,3 and 4) in accordance with Section 1921 of the 1994 Uniform Building Code, and to ACI 318, Chapter 21, Special Provisions for Seismic Design.

Steel Structures. Pay special attention to connections. Ultimate strength of connec-tions should exceed the yield strength of connected members. At connections and other points of high stress in rigid frame structures, follow the requirements of the AISC Specification for plastic design regarding width-thickness ratios, lateral bracing, web stiffening, and fabrication. Design in accordance with Sections 2211 and 2212 of the 1994 Uniform Building Code.

Column Orientation (Structural Steel)Selection of column orientation is unique to each design. It is influenced by:

The geometry of the structure Relative magnitudes of transverse and longitudinal forces Limitations on the use of bracing Connection details for cross beams Moment transfer at the base of columns

To provide maximum access under on-plot pipeways, stanchions are frequently designed as rigid frame structures to take transverse pipeway loading. The strong axis of the columns is oriented accordingly as shown in Figure 300-6.

For off-plot pipeways, where transverse bracing between columns is acceptable, orientation of the strong axis to take longitudinal pipeway loading is a common practice.

Attachments and Inserts for Concrete SupportsIt is relatively easy to add miscellaneous small lines and/or equipment to bare struc-tural steel pipe support structures. However, for reinforced concrete, or concrete encased steel, it is important to establish what attachments are required to be embedded in the concrete. Examples include unistrut to support conduit or small piping and lifting inserts for handling or installation of precast reinforced concrete sections. For all reinforced concrete crossbeams supporting piping, a slide plate is required as detailed on CIV-EF-588. For all stanchions, stop plates must be provided at the ends of support beams to prevent piping from moving off the supports.Chevron Corporation 300-17 June 1997

300 Industrial Structures Civil and Structural ManualStandard Form CIV-EF-588 (A&B)Provides standard details for connections, attachments, and reinforcing for both double column and T-type precast concrete stanchions.

323 Low-Level Pipeways and SleepersTo minimize the cost of structural supports, pipeways outside of process areas are frequently installed at or near grade level. Sleeper supports are used to keep the lines clear of the ground. This helps protect pipes from corrosion, and allows the grade under the pipeway to be drained and maintained. A minimum ground clear-ance of 12 inches is suggested but additional clearance allows easier maintenance. Figure 300-7 illustrates the types of piers commonly used for supporting low level pipeways.

Pipe, new or used, is commonly used for construction of low level pipeways and sleepers. Reasons include: availability, cost, easier painting and maintenance of pipe versus beams, appearance, and pipe provides an ideal shape for the horizontal member supporting piping.

Fig. 300-6 Column Orientation for Rigid FrameJune 1997 300-18 Chevron Corporation

Civil and Structural Manual 300 Industrial StructuresRoutingIn general, pipeway routing is selected to minimize the length of piping runs. However, consideration must be given to pipeway, plant, and tankfield expansion. Cross country routing of individual lines must be avoided.

New pipeways planned for older facilities should be routed and sized so that existing lines can be placed on them as part of a future program of line and pipeway consolidation.

Pipeway CrossingsLow-level pipeways require special treatment at intersections with refinery roads, highways, and railroads. The method selected for the pipeway crossing will have to be based on economics, piping considerations, vehicle accessibility, and the clear-ances and restrictions imposed by plant operators, or by a railroad company or highway department if outside Company-owned facilities. Refer to Sub-section 360 for a discussion on alternative pipeline crossings.

Sleeper Design

Loads. Develop vertical loading requirements either using the unit pipeway loading of 35 pounds per square foot of contributory area of loading as discussed in

Fig. 300-7 Types of Piers for Supporting Low Level PipewaysChevron Corporation 300-19 June 1997

300 Industrial Structures Civil and Structural ManualSub-section 321 (stanchions), or by calculating the actual weight of proposed lines. For recommended maximum spans between supports for various line sizes refer to Sub-section 324.

Low-level sleepers are usually self-supporting and must be designed to resist over-turning forces developed by thermal expansion of lines. Section 321 discusses calculation of thermal load friction forces.

Foundation TypeSelect sleeper and pier foundation type appropriate to the local site conditions and calculated overturning forces.

Many sleeper design situations can be accommodated by the standard support details shown on Drawing GF-M-99874. Typical details and member sizes are given for single pier supports up to 3 feet in width, and double pier supports up to 6 feet in width, with height of pipe supports 3 feet or less. These same details can be adapted for wider pipeways by using multiple supports. When sleeper requirements are outside the range of load capacity and height limitations given, it will be neces-sary to proceed with detailed designs.

Selection of sleeper foundation type depends on soil conditions and applied loads. Spread footings may be appropriate in many places if the soil offers good support and economic footing sizes can be achieved. For guidance in sizing and design of spread footings and pile-supported footings, refer to Section 200. Occasionally, because of induced moments to the foundation, a pole-type footing is the economic choice. The Uniform Building Code (Reference [5]) provides the formula given in Equation 300-2. This equation, along with Figure 300-8, can be used in deter-mining the embedment requirements for pole footings in various soil conditions. Where piled footings are required, refer to Section 200.

Fig. 300-8 Allowable Foundation Pressure Courtesy ICBO

Class of MaterialsAllowable Foundation Pressure (lbs/sq ft)

Lateral Bearing (lbs/sq ft/ft of depth below lowest point of ground adjacent to foundation)

1. Massive crystalline bedrock 4000 1200

2. Sedimentary and foliated rock 2000 400

3. Sandy gravel and/or gravel (GW and GP)

2000 200

4. Sand, silty sand, clayey sand, silty gravel and clayey gravel (SW, SP, SM, SC, GM and GC)

1500 150

5. Clay, sandy clay, silty clay and clayey silt (CL, ML, MH and CH)

1000 100June 1997 300-20 Chevron Corporation

Civil and Structural Manual 300 Industrial StructuresDesign Criteria

NonconstrainedThe following equation may be used in determining the depth of embedment required to resist lateral loads where no constraint is provided at the ground surface, such as rigid floor or rigid ground surface pavement.

(Eq. 300-2)where:

A = 2.34 P / S1 b

P = Applied lateral force in pounds.

S1 = Allowable lateral soil-bearing pressure in lb/ft2 set forth in Fig. 300-8 based on a depth of one third the depth of embedment.

b = Diameter of round post or footing or diagonal dimension of square post or footing (feet).

h = Distance in feet from ground surface to point of application of P.

d = Depth of embedment in earth in feet but not over 12 feet for purpose of computing lateral pressure.

Anchors. Where pipe anchors are required, special attention must be given to the associated lateral forces on the sleeper. Drawing GB-M99653 (in Piping Manual) provides details for pipe shoe anchors suitable for anchor supports on structural steel, pipe, or reinforced concrete stanchions.

324 Secondary Pipe Supports, Springs, and HangersSecondary supports include all pipe supports other than stanchions and sleepers. These supports may be for individual lines or for multiple lines.

Vertical Design LoadsVertical design loads are computed on the basis of actual weights of pipe, fluids, insulation, valves, and fittings. As a general rule, the length of pipe supported at a given point is taken as half the sum of the adjacent spans. Where the support is close to a vertical run, it is assumed that the support carries the entire load of the vertical section. Where horizontal bends exist, a judgment is made on the contribu-tory loads to individual supports.

d A2---- 1 14.36h

A-------------++ =Chevron Corporation 300-21 June 1997

300 Industrial Structures Civil and Structural ManualHorizontal Design Loads

Thermal. For supports that carry only one or two lines, the longitudinal friction loads due to thermal expansion and steel-on-steel sliding is generally computed with a static friction coefficient of 0.42. Section 321 discusses calculation of fric-tion forces. In cases where several lines are carried by a support, a judgment is made as to the combined contribution of thermal loads. A common practice is to use the longitudinal force developed by the largest line(s) and assume that no restraint or load contribution is provided by other lines. Because of the size of the line and operating temperature for some situations, it may be desirable to consider the use of teflon pipe slides as a means for reducing thermal loads. With teflon the coefficient of friction can be reduced to about 0.1. The actual coefficient is a func-tion of the load pressure against the teflon slide, decreasing as the unit loading on the teflon increases. However, as a practical consideration, the weight of most piping is not sufficient to achieve the lowest coefficients attainable with teflon.

Wind. Transverse wind forms should be determined by the procedures given in Section 100. The projected horizontal area is based on the diameter of the largest line supported.

Earthquake. Refer to Section 100 for determination of earthquake forces.

Other LoadsIf guides or anchors are provided on supports, any lateral loads imposed by piping must be considered. Combining loads from piping flexibility studies and wind or earthquake may be necessary.

Support SpacingSpacing of supports is a function of allowable stresses and deflections in the pipe. Longitudinal flexural stresses in the pipe can generally be considered independent of circumferential stresses caused by fluid pressure. The temperature of the pipe must be taken into account, with respect to the modulus of elasticity and allowable flexural stresses. The limiting consideration for deflections is usually the require-ment that significant amounts of liquid not be trapped after draining the lines, or visually the lines do not appear to be sagging.

Figure 300-9 may be used as a guide for commonly recommended spans. Spans and recommended deflections given are for uninsulated water-filled schedule 40 pipes. For the cases shown, flexural stresses are all below 20,000 psi.

Fig. 300-9 Recommended Spans and Deflection (1 of 2)

Recommended Nominal Pipe Size (in.) Recommended Span (ft.) Maximum Deflection (in.)

3/4 10 1/4

1 15 1/4

1-1/2 20 1/4

2 20 1/4June 1997 300-22 Chevron Corporation

Civil and Structural Manual 300 Industrial StructuresActual deflection for any line in a continuous horizontal run with uniform spans may be determined from the following equation:

Deflection = 5.88 w L4 / E I(Eq. 300-3)

where:w = Wgt. of line, fluid, insulation lb/ft

L = Span in feet

E = Modulus of Elasticity (psi)I = Moment of Inertia (in4)

Vertical runs of piping should be guided as well as supported. The spacings of guides depends upon the rigidity of the piping and the wind pressures acting on the system. The following table (Figure 300-10) may be used to obtain maximum spacing of guides for various pipe sizes.

Horizontal runs of piping may require guides near expansion loops. Guide require-ments should be reviewed with the engineer or designer responsible for pipe flexi-bility studies.

HangersIn general, resting-type supports are preferred over hanging supports. However, to maintain maximum access for personnel under piping, smaller lines may be supported by hanging one pipe from another or from an overhead structural member. Ensure that excessive vertical and lateral loads are not imposed on any supporting pipe, and the operating temperature of such supporting pipes should not exceed 150F. Hanger details are shown on GF-M-99874 (Sheet 2) and CIV-EF-799C. Commercial hanger units are readily available.

3 30 3/8

4 35 1/2

6-12 40 1/2

Fig. 300-9 Recommended Spans and Deflection (2 of 2)

Recommended Nominal Pipe Size (in.) Recommended Span (ft.) Maximum Deflection (in.)

Fig. 300-10 Recommended Guide Spacing (1 of 2)

Nominal Pipe Size (in.) Maximum Spacing of Guides (ft.)

1 22

1-1/2 23

2 24

2-1/2 25Chevron Corporation 300-23 June 1997

300 Industrial Structures Civil and Structural ManualAdjustable Pipe SupportsAdjustable supports are used where design loads must remain fully supported. This generally occurs at the piping connection support closest to equipment such as at pumps and compressors. Adjustable supports are also used for alignment of equip-ment piping.

Adjustable supports are not appropriate for accommodating differential settlement at pumps or compressors. Supports for this equipment should be anchored to the pump or compressor foundation and not to an independent foundation.

Included on Standard Drawing GF-M-99874 are details and member sizes for adjustable pipe supports:

Support Design ConsiderationsThe following drawings provide standard details that may be used for secondary pipe supports:

CIV-EF-799 (6 sheets A through F) Pipe Support Details GF-M-99874 (2 sheets) Guide Sheet for Pipe Supports GB-M-99653 Standard Pipe Shoe & Pipe Shoe Anchors (in Piping Manual)Drawing GF-M-99874 provides typical details and member sizes for single post supports up to 3 feet in width, and double post supports up to 6 feet in width, with the height of pipe supports 3 feet or less. Support requirements outside the load capacity and height limitations given in GF-M-99874 will require detailed design.

Wherever practical, designers should standardize the sizes of members used for field fabricated supports. This will help to minimize the stock of material required in the field, and maintain a uniform appearance. The size selected for support members should present a balanced appearance consistent with the size of pipes

3 27

4 29

6 33

8 37

10 41

12 45

14 47

16 50

18 53

20 56

24 60

Fig. 300-10 Recommended Guide Spacing (2 of 2)

Nominal Pipe Size (in.) Maximum Spacing of Guides (ft.)June 1997 300-24 Chevron Corporation

Civil and Structural Manual 300 Industrial Structuresbeing supported. If the width of pipe supports is sufficient for lines to be added in the future, make certain that this is considered in the design loads. If open space is left on a pipe support it is natural for someone in the future to assume that the supports are adequate for line additions. If in doubt use a uniform loading of 35 psf of pipeway for such design loading.

Spring SupportsVertical thermal expansion can cause unacceptable loads on connected equipment. This problem can be overcome by providing flexible pipe supports which apply supporting force throughout the expansion and contraction cycle of the system. The most important consideration in the design of a spring support is defining the neces-sary characteristics of the unit. These are rarely set by the thermal stresses in the supported pipe, but usually are governed by permissible stresses on connected mechanical equipment specified by the manufacturer, to avoid failure or undesirable distortions in the equipment.

Spring supports should be provided with means to prevent misalignment, buckling, eccentric loading of the springs, or unintentional disengagement of the load.

Materials, design, and manufacture of spring supports are covered in ANSI/MSS SP-58 (Reference [19]). There are three basic types of spring units: Spring Cushion Supports Variable Spring Supports Constant Support

Figure 300-11 illustrates the use of these support types and the principles of their operation.

Spring Cushion Supports. This class of spring is characterized by having 2 inches or less total deflection. As the name implies it is used to reduce localized stresses in the line and dampen line vibration.

Variable Spring Supports. Variable spring hangers are used to support piping subject to vertical movement where the more costly constant supports are not required. The inherent characteristic of a variable spring is such that its supporting force varies with spring deflection and spring scale. Therefore, vertical expansion of the piping causes a corresponding extension or compression of the spring and will cause a change in the actual supporting effect of the hanger. Since the pipe weight is the same during any condition, cold or operating, the variation in supporting force results in pipe weight transfer to equipment or adjacent hangers, and consequently develops additional stresses in the piping system. When variable spring hangers are used, the effect of this variation must be considered.

Constant Support. Constant support hangers provide constant supporting force for piping throughout its full range of vertical expansion and contraction. This is accomplished through the use of a helical coil spring working in conjunction with a bell crank lever in such a way that the spring force times its distance to the lever pivot is always equal to the pipe load times its distance to the lever pivot. The Chevron Corporation 300-25 June 1997

300 Industrial Structures Civil and Structural Manualconstant support hanger is used where it is desirable to minimize any pipe weight load transfer to connected equipment or adjacent hangers.

Selection of Spring SupportsSelection of springs is usually made by piping or structural designers working with the design data given in manufacturers catalogs. Requirements for springs are generally developed from the results of a computer-generated piping stress analysis. The type of spring support unit is determined by such considerations as the amount

Fig. 300-11 Spring Supports Courtesy ITT GrinnellJune 1997 300-26 Chevron Corporation

Civil and Structural Manual 300 Industrial Structuresof head room, support above the spring or below the spring, and geometry of the support mechanism. The size of spring unit is based on operating loads, movement from cold to hot position, and direction of movement from cold to hot position.

Using the example table in Figure 300-12, you can work through the following example for selecting a variable spring support. This table has been excerpted from a more comprehensive table in the Grinnell catalogue. All spring support manufac-turers have similar tables.

Example:Thermal expansion downward is 2-1/4 inches. Total operating pipe load 4700 pounds

Steps:1. Enter hanger selection chart looking for a load of approximately 4700 pounds

(maximum load). In this example, you will find 4700 pounds under Hanger Size 14.

2. Read deflection for a figure type that allows for a full range of deflection. In this example, the deflection of the spring in the hot condition is 5-3/4 inches.

3. Check range of deflection. Hot deflection - cold deflection = 5-3/4 inches- 2-1/4 inches = 3-1/2 inches

4. Read corresponding cold load by checking chosen hanger size at cold deflec-tion = 3800 pounds (Size 14 hangar, 3-1/2 inches deflection)

5. Difference in pipe loads 4,700 hot

(3,800) cold 900 pounds

6. Hot and cold loads both within Working Range of Size 14 Figure 98 unit.

7. Order this support preset to 3-1/2 inch deflection.

Note The 900 pounds difference in loading will impose an equal but opposite loading at other supports on equipment. There may be instances where moment forces require even less deflection. In these instances, upsize your hangar selection.

Fig. 300-12 Example Load Table in Pounds for Selection of Hanger Size Courtesy ITT Grinnell (1 of 2)

Working Range (in.) Hanger Size Spring Deflection (in.)

13 14 15

1800

1875

1950

2025

2400

2500

2600

2700

3240

3375

3510

3645

0Chevron Corporation 300-27 June 1997

300 Industrial Structures Civil and Structural ManualOrdering DescriptionInformation that must be provided when ordering spring supports may vary between manufacturers, but the following data are normally required:

Support Type and Figure No. (from manufacturers catalog) Size

Desired supporting force in operating position

0 2100

2175

2250

2325

2800

2900

3000

3100

3780

3915

4050

4185

1

1 2400

2475

2550

2625

3200

3300

3400

3500

4320

4455

4590

4725

2

2 2700

2775

2850

2925

3600

3700

3800

3900

4860

4995

5130

5265

3

3 3000

3075

3150

3225

4000

4100

4200

4300

5400

5535

5670

5805

4

4 3300

3375

3450

3525

4400

4500

4600

4700

5940

6075

6210

6345

5

5 3600

3675

3750

3825

4800

4900

5000

5100

6480

6615

6750

6885

6

3900 5200 7020 7

Spring Size - lb. per in. 300 400 540

Fig. 300-12 Example Load Table in Pounds for Selection of Hanger Size Courtesy ITT Grinnell (2 of 2)

Working Range (in.) Hanger Size Spring Deflection (in.)June 1997 300-28 Chevron Corporation

Civil and Structural Manual 300 Industrial Structures Calculated amount and direction of pipe movements from installed to oper-ating position

Customers identification number

Desired factory spring preset

Spring Support Installation and MaintenanceAfter installation, and in preparation for startup, field engineers should inspect the springs and remove chocks, if any. Generally, spring supports do not require exten-sive preventive maintenance, except for inspection and repainting as required to control corrosion.

Manufacturers state that spring units are low maintenance items and that periodic checking of operational loads and deflections is generally a more important consid-eration than physical inspection and maintenance of the unit itself. A frequent problem is that actual pipe loads exceed design loads, and the support bottoms out. This could result in higher concentrated piping stresses. Replacement or readjust-ment of the spring support is required if this condition is encountered.

330 Equipment SupportsThis section of the guidelines discusses the design of elevated equipment support structures. Examples of equipment requiring support include air coolers, exchangers, horizontal vessels, catalyst handling equipment, conveyors, etc. This section is limited in scope to the following situations:

To assist engineers reviewing design work by consultants.

To provide design guidelines for relatively simple structural supports.

For more complex structures and unusual loading situations, the design work should generally be undertaken by an experienced Company or contractor civil/structural engineer.

331 Design RequirementsObtain certified vendor prints to define dry and operating weights, critical physical dimensions, foot print of support points, details of equipment supports, and location of appurtenances.

A complete understanding is required of the function of the equipment to be supported.

The following items need to be addressed:

Access stairs, platforms, and ladders required by operators

Requirements for routine maintenanceChevron Corporation 300-29 June 1997

300 Industrial Structures Civil and Structural Manual Crane access or permanent lifting equipment, (davit or monorails) required for handling equipment or parts which cannot be manually handled by two persons. (Limited to approximately 100 pounds in easy-to-reach location.)

Testing plans (hydrotest), weights and sequence Incremental platform space required as laydown area for equipment to be

cleaned or repaired

Special equipment loading conditions; for example, vibration or impact loads, or earthquake or wind loads

Additional equipment and piping to be supported from the structure

Extent of fireproofing required

Limitations on vertical or lateral deflections because of closely interconnected piping or equipment

Requirements for equipment and piping insulation. It frequently happens that the thickness of insulation is overlooked when determining structural and personnel clearances.

332 Design LoadsAll equipment, piping, and electrical loads must be accounted for. Fluids, catalyst or other operating loads must be included.

Consider special loading conditions imposed on the structure: thermal expansion, hydrotest, upset conditions, impact loads, tube bundle pulling, etc.

For wind and earthquake loading, refer to Section 100.

333 Structural Analysis and DesignTwo-dimensional or three-dimensional analysis of the structure is most easily done with a structural computer program.

Not all designers, however, will have access to a suitable program, and hand calcula-tions will be necessary. If the designer has limited experience in structural design, the Pipe Support Design Manual (Reference [16]) may serve as a guide for analysis of small support structures using hand calculations for relatively simple, braced frame structures.

In the analysis and design of structures, the following important requirements are occasionally overlooked:

1. Proper application of vertical and horizontal loads (bending about both prin-cipal axes) to get the most severe combined axial and bending forces.

2. Code check of combined axial compression and bending stresses for structural steel columns. (Refer to AISC Specification.)June 1997 300-30 Chevron Corporation

Civil and Structural Manual 300 Industrial Structures3. Consideration of biaxial bending and compression in the design of concrete columns.

4. Appropriate adjustments to allowable stresses (structural steel) for seismic or wind loading, or to factored loads (reinforced concrete).

The engineers should verify that these factors have been included in the analysis, if appropriate.

DeflectionsThe following deflection limits are suggested:

Total deflection of beams should generally not exceed 1/250 of the span.

For beams supporting closely interconnected equipment, total deflection should not exceed 1/500 of the span.

Sideways deflection of structures due to wind/earthquake loads should not exceed 1/100 of the height.

ConnectionsShop connections are generally welded.

Field connections are generally bolted. For most applications, including onshore coastal areas, no special coating is required for structural bolts.

Bolted connections for main structural steel should generally be friction-type connections made with minimum 3/4-inch diameter high strength bolts.

Bolted connections for secondary structural steel should be minimum 3/4 inch diam-eter unfinished bolts, except bolts for stair bracing and handrails may be 1/2 inch diameter, and for stair treads 3/8 inch diameter.

Beveled washers should be specified for connections where an outer face of the bolted parts has a slope greater than 1:20. Connections should be designed to provide the full strength of connected members in seismic zones. This allows for absorption of a large amount of energy during an earthquake.

334 Design Considerations for a Corrosive EnvironmentIf the expected atmosphere is corrosive or maintenance will be difficult, this fact should be taken into account when designing steel structures. For example:

For primary steel members maintain a minimum thickness for angles and flanges of beams and tees (e.g., 3/8 inch).

For secondary members and webs a suggested minimum thickness of 1/4 inch may be appropriate.

Double-angle members back to back should be avoided.

All welds should be continuous.Chevron Corporation 300-31 June 1997

300 Industrial Structures Civil and Structural Manual Provide coatings for bolts.

Where corrosion protection coatings are used for bolts, these coatings should be specified on the drawings or fabrication specifications. Following are comments on the more common types of protective coatings used for corrosive atmospheres, or for marine/coastal areas:

Galvanized. Good corrosion protection. May give some difficulty during removal in the future, as nut may jam in the bolt threads.Cadmium Plated. Good corrosion protection. Can suffer hydrogen cracking in high strength bolts (UTS over 125 ksi) due to hydrogen charging during plating. Controlled by baking out hydrogen after plating.

Teflon Coated. Good corrosion protection. Excellent for connections where a future make & break requirement is anticipated. Quality varies, the problem being the presence of holidays. Overtorqued nuts will damage threads. Double nuts are commonly used to avoid loosening. This coating is used extensively in sub-sea applications.

340 Stairs, Ladders, Walkways, Platforms, and Handrails

341 GeneralIt is important that individuals involved in layout or design of stairs, ladders, walk-ways, and platforms review the appropriate sections in the Safety in Designs Manual (SID) (Reference 15). The Safety in Designs Manual provides a summary reference of safety requirements and recommendations for Company facilities. New facilities or modifications must meet the safety requirements of the Safety in Designs Manual. Company standard drawings referenced herein conform to the requirements of the Safety in Designs Manual and have been checked thoroughly for compliance with the Occupational Safety and Health Act. Company standards are considered more complete than minimum legal requirements and, according to the Compliance Policy, must be followed. Engineering discretion may be used to comply with the Safety in Designs Manual or standard drawing contents, but devia-tions or omissions from established criteria are acceptable only when documented and specifically authorized by appropriate Engineering supervision or management.

Particular attention should be paid to required overhead and side design clearances, details of construction, and to the specific locations where each of the following safety features is required:

Railings Toeboards Hoop guards, ladder safety guards and drop bars Ladder cages Landing areas for stairs, ladders and stiles Intermediate landings for stairs and laddersJune 1997 300-32 Chevron Corporation

Civil and Structural Manual 300 Industrial StructuresCompliance with RegulationsThe contents of the Safety in Designs Manual are in compliance with OSHA requirements. The 1996 version was generated after extensive review of Federal and California OSHA standards, the Uniform Building Code, the Uniform Fire Code and National Fire Protection Association Standards.

There may be local requirements which exceed OSHA or are more restrictive and would therefore supersede the Safety in Designs Manual contents. Engineers, construction reps, or inspectors must be reminded of this fact and encouraged to discuss local requirements with knowledgeable local Company personnel.

Contract language should require compliance with current Company standards and applicable laws.

Existing facilities need not be modified if they meet legal requirements and adequate safety is provided.

Standard DrawingsWherever possible use the Companys standard drawings for stairs, ladders, and handrails. These drawings meet the requirements of the Safety in Designs Manual, are based on the design loads specified herein, and provide uniformity in designs. A list of standard drawings is in Section 382; the drawings are also included in the List of Standard Drawings and Forms.

Design UniformityIn all cases the design of walkways, ladders, and stairs should be uniform within any operating area. For additions or modifications to existing facilities, the require-ments of the Safety in Designs Manual should normally be followed. However, to achieve uniformity within a specific operating area it may be desirable at times to follow some existing practices. An example would be using tread run and riser heights to match existing stairs. If legal requirements are not met or adequate safety is not provided by following the existing practices in a given facility, then new or modified facilities should comply with the Safety in Designs Manual requirements.

342 Design LoadsThe Companys standard drawings and forms are based on the design loads given in this section. There is no need for detailed design unless anticipated loads and condi-tions differ from these standards.

StairsSuggested design load for stair stringers is 100 psf, but the load should not be less than a 1000 lb. concentrated load on the horizontal projected area of the stairs. Stair treads are normally selected from manufacturers standard sizes for a range of tread widths and spans. Manufacturers commonly use a 300-pound design load plus an additional 1/3 impact load for their calculation of recommended spans. This load is applied at the centerline of the span, and is distributed over the tread nosing and 4 bearing bars.Chevron Corporation 300-33 June 1997

300 Industrial Structures Civil and Structural ManualPlatforms/WalkwaysMinimum design load for walkways is 75 psf live load.

Minimum design loads for maintenance platforms should be 75 psf live load, or 2000-pound, concentrated load placed upon any space 2'-6" x 2'-6". However, such platforms should be designed for the maximum probable loads imposed by the intended use, for example, equipment loads which can be set down on platforms by fixed davits or monorails. Exchanger platforms should be designed to carry exchanger channel and shell covers, but not tube bundles.

Ladders. Designed for anticipated usage, but not less than a single concentrated load of 200 pounds. Companys Standard Drawing GF-M88575, Standard Ladders and Guards, has rungs, stringers, and support details that are adequate for loads far in excess of 200 pounds.

Railings. Anticipated loads but not less than 200 pounds at any point in any direc-tion on the top rail.

343 Grating and Floor Plate Design and Selection

GratingSerrated steel grating should be used in the following situations:

For platforms where there is a need to see through, such as furnace firing platforms and plot limit block valve manifolds

For stair treads (with a distinctive, cast-abrasive, non-skid nosing) For platforms where operating conditions make steel plate with non-skid

coating ineffective, such as areas where liquid spillage is expected

In wet and cold climates where snow and ice commonly create walkway hazards

At one time, steel plate with non-skid coating was the recommended surface for platforms and walkways above 6 feet from grade. Currently, serrated steel grating is an acceptable option to steel plate. The disadvantages of grating include:

On elevated structures some individuals may find serrated steel grating stressful because of the see through aspect.

Small objects and tools can drop through to walkways or surfaces below. It is more difficult to work on, and is hard on the knees when kneeling.

Grating for coastal areas is normally ordered with galvanized coating. Galvanizing permits an extended period of use before first maintenance, as compared to painted grating. New galvanized grating is not normally painted. For inland areas (non-corrosive climates), grating which is painted instead of galvanized may be used if maintenance painting is not anticipated for five years. Maintenance painting of grating has proven to be time consuming and costly. Fertilizer plants and other June 1997 300-34 Chevron Corporation

Civil and Structural Manual 300 Industrial Structuresareas may warrant special coatings or the use of aluminum or fiberglass-reinforced plastic grating. Check with Fire Protection before specifying these materials. Coating or galvanizing should be done after fabrication and attachment of banding.

Acceptable manufacturers and types of bar grating for walkways are listed in Speci-fication CIV-EG-398. The type of grating acceptable to the Company is designated as W-19-4, a designation that is universally accepted by the bar grating manufac-turers. It has bearing bars on 1-3/16 inch centers, with cross bars at 4-inch centers, and is welded steel. Standards for grating are given in the Metal Bar Grating Manual published by National Association of Architectural Metal Manufacturers (NAAMM). Acceptable grating and serrated surfaces are illustrated in Figures 300-13 and 300-14.

Fig. 300-13 W-19-4 GratingChevron Corporation 300-35 June 1997

300 Industrial Structures Civil and Structural ManualExpanded metal gratings and mechanical locked gratings are not recommended. The only type of expanded metal grating that is acceptable to the Company is Grip Strut Safety Grating. Because of the higher cost over bar grating, Grip Strut is used only in special applications.

Grating used in areas exposed to weather should have bearing bars with 3/16 inch minimum thickness. Grating with 1/8 inch thick bearing bars may be used only in areas protected from weather or corrosion. For most installations, the preferred minimum bearing bar depth is 1-1/4 inch. Bearing bars with 1-inch depth should be limited to stair treads, and short spans, such as over trenches, not subject to vehicle loads.

Acceptable spans (the distance between supports in the direction bearing bars run) for grating are based on manufacturers safe load tables, and with a unit stress of 18,000 psi. Figure 300-15 provides recommended maximum spans, safe loads, and deflections for a range of spans and bearing bar sizes. Tables prepared by grating manufacturers are based on the NAAMM table. The tables are designed to provide safe live loads, and the weight of the grating does not have to be taken into account. Safe load tables are based on plain bearing bar grating, and an adjustment must be made for serrated grating to account for reduction in bar depth. This may be accom-plished by applying the reduction factors listed in Figure 300-16 to the tabulated safe loads.

Bearing Bar DirectionGrating is generally manufactured in panel sections 3 feet wide with lengths up to 24 feet. Bearing bars run the length of the panels. Layout and framing of walkways

Fig. 300-14 SerrationsJune 1997 300-36 Chevron Corporation

Civil and Structural Manual 300 Industrial StructuresFig. 300-15 Load TableSteel Grating Courtesy Gary GratingChevron Corporation 300-37 June 1997

300 Industrial Structures Civil and Structural Manualand platforms, and the specified direction of bearing bars, should take into account the orientation of the manufactured panels.

To a great extent it is a matter of personal preference as to the direction of run for the bearing bars. Primary considerations are to simplify fabrication, make economic use of material, and provide a consistent layout for a given area. The one exception is that at locations where there is a need to see through, the bearing bars should be oriented for maximum visibility.

It is good design practice in the selection of spans for deck grating to limit deflec-tions to 1/4 inch to avoid discomfort to pedestrians from too much flexing of the walking surface.

FasteningsNormal fastening of platform grating is with 3/16 inch fillet weld 1-1/2 inches long, spaced at intervals not exceeding 18 inches at edge supports, with a minimum of four welds per panel. Grating should be tack welded at 18 inch centers over interme-diate supports.

For removable grating, such as for access to equipment, use galvanized steel saddle clips to fasten grating to support members as shown in Figure 300-17. Clips are normally secured using Nelson studs welded to the structural supports. Clips may also be secured with self-tapping screws, subject to approval by the operators. Using clips for securing grating is recommended only in locations where panels must be removable. The clips have a tendency to work loose, causing the grating to become uneven, and creating a tripping hazard.

Some installations have used Ram set studs for fastening clips. Experience has been mixed:

Sometimes they dont properly set. They easily break. They may locally overstress members.

Stair TreadsStairs serving platforms with grating walking surfaces should be furnished with treads fabricated from the same type grating as the platform. Typical bar size for treads with serrated bars is 1-inch x 3/16 inch, which is suitable for spans up to 2'-6". For stairs wider than 2'-6" the bar size must be increased to 1-1/4 inch or 1-1/2 inch. Each tread should be furnished with a distinctive, non-skid, cast

Fig. 300-16 Reduction Factors for Serrated Grating

Bar Depth (inches) Multiply by

1 0.82

1-1/4 0.86

1-1/2 0.88

1-3/4 0.90 June 1997 300-38 Chevron Corporation

Civil and Structural Manual 300 Industrial Structuresabrasive nosing, which provides protection against slipping. The edge of the plat-form at descending stairs should also be provided with cast abrasive nosing. Note that actual tread width must equal or exceed the specified tread run. Available stan-dard tread widths of 9-3/4 inches, 11 inches, or 12 inches are therefore required to conform with Companys stair requirements. Refer to stair tread illustration shown in Figure 300-18.

Stair treads are generally bolted to the stair stringers. This allows easy change out of damaged or corroded treads without hot work.

Fig. 300-17 Steel Saddle Clips Courtesy NAAMM

Fig. 300-18 Stair Tread DetailsChevron Corporation 300-39 June 1997

300 Industrial Structures Civil and Structural ManualBandingBanding is the welding of a flat bar to a side or end of a grating panel, or along the line of a cutout. The band does not extend above or below the bearing bars, except when it serves as a toe plate.

Load-Carrying Band. A band used in a cutout to transfer the load from unsup-ported bearing bars in the cutout to the supported bearing bars. The band should be welded to one side of each bearing bar with a 1/8 inch fillet weld.

Trim Band. A band which carries no load, but is used chiefly to improve appear-ance or eliminate a safety hazard. In this case, weld the band to every 4th or 5th bar. However, in locations where corrosion is a problem, for example coastal areas, it may be desirable to weld all bars to the band.

Steel Plate with Non-skid CoatingPlain steel plate with a non-skid coating is specified for platforms that do not require grating. Non-skid coatings contain small, hard grit particles that give an abrasive surface, and should be selected on the basis of severity of intended service. For guidelines on the selection of the appropriate coating refer to the Quick Refer-ence Guide in the Coatings Manual.

Checkered floor plate is not recommended for platforms and walkways, and its use as stair treads is not permitted. The disadvantages of checkered plates are poor non-skid qualities, difficulty in maintaining paint, and higher cost, which is more than for plain steel plate.

Steel plating for platforms is generally fastened to supporting members with inter-mittent fillet welding or plug welds at intervals not exceeding 18 inches. Where removable plates are required, plate should be fastened with 3/8-inch diameter cadmium plated steel flat head bolts which are countersunk at intervals not exceeding 18 inches. For some installations it may be necessary to specify complete seal welding to provide for liquid containment or because of environmental condi-tions. Continuous welding of steel plate should be made with 1/8 inch welds to minimize plate warpage.

Unless fluid containment is a requirement, a minimum of one 1/2 inch diameter drain hole is generally provided near the center of each panel of platform floor plate, to minimize collection of rainwater.

The thickness generally used for steel plate platform surfaces is 1/4 inch. A general rule of thumb in using this size plate is to limit the product of the width and length dimensions to around 24 square feet (example, 4 feet by 6 feet) when supported on four sides. Much larger plate support dimensions could be used that would adequately support a 40 psf live load; however, this would introduce excessive deflection or bounce in the deck when walked upon. Longer support spans also tend to accentuate ponding problems. For these reasons, the short span of the plate is generally limited to a maximum of 4 feet-0 inches with supports at about 6-foot spacing in the long span direction. For short spans, 3 feet-0 inches or less, the long span is not limited. Where joining of plates occurs between framing members, an June 1997 300-40 Chevron Corporation

Civil and Structural Manual 300 Industrial Structuresangle 1-1/2 by 1-1/2 by 1/4 inch should be used under the joint. Gaps between floor plates resting on a supporting member should be limited to about 1/4 inch.

Openings in PlatformsAttention must be given to openings through floorplate or grating required for piping, conduit, or equipment, to avoid the hazard of dropping tools or parts, or creating a tripping hazard. The following general guidelines apply. See the Safety in Designs Manual for specifics.

If possible, keep gaps between the floor surface and equipment or piping less than 1 inch. The larger the gap, the more likely a bolt or tool will fall through the gap.

Platforms on a horizontal vessel must be extended under the vessels curvature. If gap opening exceeds 1 inch, a toeboard must be provided.

Platforms on vertical vessels should not have a space exceeding 1 inch between platform and vessel or surface of insulation for an insulated vessel. If the gap opening exceeds 1 inch, a toeboard must be provided. If the gap is 3 inches or more, guard railing is also required.

Platforms bounded by vertical pipes should extend to the centerline of the pipes with cutouts around the pipes not exceeding 1 inch. If the spacing of the vertical pipes exceeds 9 inches, then a guard railing is required.

Floor plate openings. Openings should have maximum 1 inch clearance between floor plate and pipe, duct, or equipment. Circular openings 12 inches in diameter and larger, and rectangular openings 12 inches and larger in the smaller dimension should be banded with a toe plate if the opening between the plate and the pipe, duct or equipment exceeds 1 inch. A toe plate increases the maximum acceptable opening to 3 inches. If the gap is 3 inches or more, guard railing is also required.

Floor grating openings. Openings in grating with a maximum diameter or side dimension of 12 inches need not be banded, but should have a 1 inch maximum clearance from the equipment. Circular openings 12 inches in diam-eter and larger, and rectangular openings 12 inches and larger in the smaller dimension should be banded with bearing bars, and should have a maximum clearance between the equipment of 1 inch. A toe plate may be substituted for a bearing bar, in which case the acceptable clearance is increased to 3 inches. If the gap is 3 inches or more, guard railing is required.

All openings for pipe should be round.

StairsStair access and platforms are required for:

Points which require access for servicing or operating during each 8 hour shift Locations of mechanical equipment Location at which samples are to be takenChevron Corporation 300-41 June 1997

300 Industrial Structures Civil and Structural Manual Locations for servicing, maintaining, or operating equipment handling H2S Plot limit manifolds

Stair DesignThe exact number and locations of stairs will need to be reviewed and accepted by Operations and Safety. For platforms served by stairs, it is convenient to set the elevation above grade, or between platforms, at even multiples of 7-3/4 inches. This will facilitate the use of the Companys recommended standard riser and tread dimensions.

Riser = 7-3/4 inches

Tread = 9-3/4 inches

Where a stairway cannot meet the above requirements, the riser heights and tread run dimensions may be varied provided:

Tread run plus riser height dimension equals 17-1/2 inches.

Stair slope is between 30 degrees and 40 degrees.

All riser heights in any one structure or platform are the same.

To the greatest extent possible, all riser heights in a general area are the same.

For stairways starting at grade, where paving is concrete, the stair stringer should be bolted to the concrete. If necessary to maintain riser height, the paving at the bottom of the stair may be raised in height 2 inches to 3 inches and sloped gradu-ally (1:10 max) down to the adjoining paving. If the stair ends on asphaltic concrete, a concrete pad 2 feet-6 inches by 3 feet or larger, should be installed. If necessary, feather the paving up to meet the pad. For unpaved areas with gravel or crushed rock surface, a concrete pad with a minimum landing area of 2 feet-6 inches square or larger, should be provided. The height of this pad should be flush with the surrounding grade, or be set at 3 inches above grade. Refer to Figure 300-19.

The top flanges of the channel stair stringers at the base of the stair should be cut off at an angle of 45 degrees, ground smooth, and stringers cut off vertically to match front edge of first tread to avoid creating a tripping hazard.

Handrails and midrails should be provided on both sides of stairs serving walks or platforms requiring guardrails and midrails. Midrails should be omitted on the wall side of stairways adjoining walls.In spite of careful planning and effort, it is difficult to make stair stringers at the bottom of a flight of stairs terminate at the as built concrete slab elevation. The reasons for this include:

Frequently because of sloping slabs, the exact final grade elevation at the stair location is not known at the time the stair design is executed.

Working to normal construction tolerances contributes to dimensional prob-lems in final fit-up of stairs.June 1997 300-42 Chevron Corporation

Civil and Structural Manual 300 Industrial StructuresFig. 300-19 Stair LandingsChevron Corporation 300-43 June 1997

300 Industrial Structures Civil and Structural Manual Slabs adjacent to pile-supported foundations may settle with respect to the structure. This can be a continuing problem during the life of the installation. If this problem is expected to occur, it may be desirable to support the bottom of the stair off the foundation, or a pile-supported landing pad might be consid-ered.

The normal remedy for correcting elevations at the bottom of stairs is to build up the slab, and to slope up the paving around it as illustrated in the Safety in Designs Manual. The 2 feet-6 inches by 2 feet-6 inches minimum flat landing area dimen-sion must be maintained.

344 Ladders, Cages, and GuardsPlatforms for which ladder access must be provided include:

Locations which require access for operating equipment such as valves and motors, when access is required less frequently than once per 8-hour shift.

Locations requiring access for maintenance only of appurtenances such as manholes, column or vessel nozzle flanges, relief valves, removable heads or covers, for example. Platforms need not be provided for services less than 15 feet above grade when access is required only for maintenance, if they can be reached from temporary tubular scaffolding without interfering with operating or emergency access to equipment.

For platforms served by ladders it is generally desirable to set the elevation above grade, or between platforms at even multiples of 1 foot-0 inches.

Inclined ladders are undesirable. If used, because clearance problems require the ladder to be sloped, the incline forward shall not be greater than 15 degrees from the vertical.

Side access ladders are preferred to front access ladders, as entry at the top of the ladder is easier and safer.

Ladders should be arranged so the user faces toward equipment or structures rather than facing open space.

Ladder rungs must be positioned so that the centerline of the rung at the top plat-form is at the same elevation as the top of the platform walking surface. Where more than one platform is served by a ladder, intermediate platforms should be located so that the top of each platform lines up with the centerline of a ladder rung. The spacing between ladder rungs should be maintained at 12 inches and the bottom rung should be 6 inches to 18 inches above the platform or finished pave-ment.

The space around a ladder that must be kept free from obstructions is the same as the space required for a standard ladder cage, whether a ladder cage is provided or not. The minimum clearance behind ladders is 7 inches measured from the center-line of the ladder. Common problems are conduits, stiffening rings, foundations, field routed small piping, or insulation that reduce the 7 inch clearance. Minimum June 1997 300-44 Chevron Corporation

Civil and Structural Manual 300 Industrial Structuresside clearance is 15 inches from centerline of ladder with minimum 30 inches clear-ance in front of ladder. This 30 inch by 30 inch clearance envelope includes the bottom landing area of the ladder and extends upward for the full length. Ladder stringers and rungs must be kept free of attachments other than those required to support the ladder.

Ladders which could be climbed inadvertently on the back side must have a barrier installed per Drawing GF-M88575. The maximum vertical run of ladder must be 30 feet.

Ladders attached to equipment subject to thermal expansion must be provided with slotted support clips at the ladder feet.

Cages must be provided on all ladders serving platforms 20 feet or higher above grade.

Drop bars must be provided on all ladders serving platforms which are 2 feet-6 inches or higher above grade.

Hoop guards must be provided on all ladders serving platforms 10 feet or higher above grade.

350 Guyed StacksThis subsection discusses the use, design, and installation of guys for stack support. Discussion of other structural topics, such as vortex shedding, foundations, or deadmen, is not included.

351 Use and LayoutGuys are required to provide structural stability for furnace stacks and flare stacks that cannot be designed as self-supporting. Layout of guys is dependent on space availability, height of stack, number of guys required, obstructions, clearances over roads, and layout of roads and other facilities in the area.

The primary objective must be to provide: A safe design for structural support of the stack under all conditions

Physical protection of the guys themselves from moving vehicles or construc-tion equipment

Except where there is no alternative, guys should be oriented to avoid crossing roads. Where guys cross roads, the minimum clearances given in the Safety in Designs Manual (Reference [15]) should be maintained.Deadmen should be located as far from roads as possible, but a minimum of 25 feet outside of road shoulder is recommended. If guys and deadmen could be exposed to vehicle damage, or if there is a hazard to personnel, suitable guy protectors should be provided.Chevron Corporation 300-45 June 1997

300 Industrial Structures Civil and Structural ManualThe most efficient angle of inclination from the horizontal for guys is 45 degrees. In practice this is not always possible due to layout requirements, and frequently guys attached at multi-levels to the stack will be anchored at the same deadman.

Guys with angles of inclination less than 30 degrees are not as efficient because the corresponding sags and cable elongation are greater than for guys with steeper incli-nation. Th