CH 4 - Part III-Allowables Stress Design (ASD) Alternative

P1: MRM/SPH P2: MRM/UKS QC: MRM/UKS T1: MRMPB262A-03 PB262/Seismic.cls December 18, 2002 15:51 Char Count=

67PART III. ALLOWABLE STRESSDESIGN (ASD) ALTERNATIVE

As an alternative to the Load and Resistance Factor Design (LRFD) provisions for struc-tural steel design in Part I, the use of the Allowable Stress Design (ASD) provisionsin this Part is permitted. All requirements of Part I shall be met except as modified orsupplemented in this Part. When using this Part, the terms LRFD Specification,FR and PR in Part I shall be taken as ASD Specification, Type 1, and Type 3,respectively.

1. SCOPESubstitute the following for PART I Section 1 in its entirety:

These Provisions are intended for the design and construction of structural steelmembers and connections in the Seismic Force Resisting Systems in buildings forwhich the design forces resulting from earthquake motions have been determinedon the basis of various levels of energy dissipation in the inelastic range of response.These Provisions shall apply to buildings that are classified in the ApplicableBuilding Code as Seismic Design Category D (or equivalent) and higher or whenrequired by the Engineer of Record.These Provisions shall be applied in conjunction with the AISC Specification forStructural Steel BuildingsAllowable Stress Design and Plastic Design includingSupplement No. 1, hereinafter referred to as the ASD Specification. All membersand connections in the Seismic Force Resisting System shall be proportioned asrequired in the ASD Specification to resist the applicable load combinations andshall meet the requirements in these Provisions.Part III includes the Part I Glossary and Appendix S.

2. REFERENCED SPECIFICATIONS, CODES, AND STANDARDSSubstitute the following for the first two paragraphs of Part I Section 2:

The documents referenced in these Provisions shall include those listed in ASDSpecification Section A6 with the following additions and modifications:American Institute of Steel ConstructionSpecification for Structural Steel BuildingsAllowable Stress Design and PlasticDesign, June 1, 1989 including Supplement No. 1, December 17, 2001

Substitute the following for the last paragraph of Part I Section 2:Research Council on Structural ConnectionsSpecification for Structural Joints Using ASTM A325 or A490 Bolts, June 23, 2000,Appendix B

4. LOADS, LOAD COMBINATIONS, AND NOMINAL STRENGTHSSubstitute the following for Part I Section 4.2 in its entirety:

Seismic Provisions for Structural Steel Buildings, May 21, 2002American Institute of Steel Construction


68 PART III LOADS, LOAD COMBINATIONS, AND NOMINAL STRENGTHS [Sect. 4.

TABLE III-4-1Resistance Factors for ASDLimit State Resistance Factor

TensionYielding 0.90Rupture 0.75

Compression buckling 0.85Flexure

Yielding 0.90Rupture 0.75

ShearYielding 0.90Rupture 0.75

TorsionYielding 0.90Buckling 0.90

Complete-joint-penetration groove weldsTension or compression normal to effective area Base metal 0.90

Weld metal 0.90Shear on effective area Base metal 0.90

Weld metal 0.80Partial-joint-penetration groove welds

Compression normal to effective area Base metal 0.90Weld metal 0.90

Tension normal to effective area Base metal 0.90Weld metal 0.80

Shear parallel to axis of weld Weld metal 0.75Fillet welds

Shear on effective area Weld metal 0.75Plug or slot welds

Shear parallel to faying surface (on effective area) Weld metal 0.75Bolts

Tension rupture, shear rupture, combined tension and shear 0.75Slip resistance for bolts in standard holes,

oversized holes, and short-slotted holes 1.0Slip resistance for bolts in long-slotted holes

with the slot perpendicular to the direction of the slot 1.0Slip resistance for bolts in long-slotted holes with

the slot parallel to the direction of the slot 0.85Connecting elements

Tension yielding, shear yielding 0.90Bearing strength at bolt holes, tension rupture,

shear rupture, block shear rupture 0.75Contact bearing Bearing on steel 0.75

Bearing on concrete 0.60Flanges and webs with concentrated forces

Local flange bending, compression buckling of web 0.90Local web yielding 1.0Web crippling, Panel Zone web shear 0.75Sidesway web buckling 0.85

4.2. Nominal StrengthThe Nominal Strengths of members and connections shall be determined asfollows:Replace ASD Specification Section A5.2 with the following: The NominalStrength of structural steel members and connections for resisting seismic forces



Sect. 9.] PART III SPECIAL MOMENT FRAMES 69

acting alone or in combination with dead and live loads shall be determined bymultiplying 1.7 times the allowable stresses in Section D, E, F, G, H, J, and K.Amend the first paragraph of ASD Specification Section N1 by deleting or earth-quake and adding: The Nominal Strength of members and connections shallbe determined by the requirements contained herein. Except as modified in theseprovisions, all pertinent requirements of Chapters A through M shall govern.In ASD Specification Section H1 the definition of F e shall read as follows:

F e = 2 Es

(Klb/rb)2(4-1)

where:lb = the actual length in the plane of bending, in. (mm)rb = the corresponding radius of gyration, in. (mm)K = the effective length factor in the plane of bending

4.3. Design StrengthThe Design Strength of structural steel members and connections subjected toseismic forces in combination with other prescribed loads shall be determinedby converting allowable stresses into Nominal Strengths and multiplying suchNominal Strengths by the Resistance Factors given in Table III-4-1.

7. CONNECTIONS, JOINTS, AND FASTENERS7.2. Bolted JointsSubstitute the following for Part I Section 7.2 fourth paragraph in its entirety:

The design resistance to shear and combined tension and shear of bolted jointsshall be determined in accordance with the ASD Specification Sections J3.5 andJ3.7, except that the allowable bearing stress at bolt holes Fp shall not be takengreater than 1.2Fu .

9. SPECIAL MOMENT FRAMES9.3. Panel Zone of Beam-to-Column Connections

(beam web parallel to column web)Substitute the following for Part I Section 9.3a in its entirety:

The required thickness of the panel zone shall be determined in accordance withthe method used in proportioning the panel zone of the tested connection. As aminimum, the required shear strength Ru of the panel zone shall be determined fromthe summation of the moments at the column faces as determined by projectingthe expected moments at the plastic hinge points to the column faces. The designshear strength v Rv of the panel zone shall be determined using v = 1.0.



70 PART III SPECIAL TRUSS MOMENT FRAMES [Sect. 12.

When Pu 0.75Py ,

Rv = 0.6Fydctp[

1 + 3bcf t2c f

dbdctp

](9-1)

When Pu > 0.75Py ,

Rv = 0.6Fydctp[

1 + 3bcf t2c f

dbdctp

] [1.9 1.2Pu

Py

]. (9-1a)

where:tp = total thickness of Panel Zone including doubler plate(s), in. (mm)dc = overall column depth, in. (mm)

bcf = width of the column flange, in. (mm)tc f = thickness of the column flange, in. (mm)db = overall beam depth, in. (mm)Fy = specified minimum yield strength of the Panel Zone steel, ksi (MPa)

9.7. Beam-to-Column Connection RestraintSubstitute the following for Part I Section 9.7b(1) in its entirety:

The required column strength shall be determined from the ASD load combinationsstipulated in the Applicable Building Code, except that E shall be taken as the lesserof:

(a) The Amplified Seismic Load(b) 125 percent of the frame Design Strength based upon either the beam design

flexural strength or Panel Zone design shear strength

12. SPECIAL TRUSS MOMENT FRAMES12.4. Nominal Strength of Non-special Segment MembersSubstitute the following for the first sentence in Part I Section 12.4:

Members and connections of STMF, except those in the special segment definedin Section 12.2, shall have a Design Strength to resist ASD load combinations asstipulated by the Applicable Building Code replacing the earthquake load termE with the lateral loads necessary to develop the expected vertical nominal shearstrength in the special segment Vne given as: [balance to remain unchanged]

12.6. Lateral BracingSubstitute the following for the first sentence in Part I Section 12.6:

The top and bottom chords of the trusses shall be laterally braced at the ends of thespecial segment, and at intervals not to exceed Lc according to ASD SpecificationSection F1, along the entire length of the truss.



Sect. 14.] PART III ORDINARY CONCENTRICALLY BRACED FRAMES (OCBF) 71

13. SPECIAL CONCENTRICALLY BRACED FRAMES (SCBF)Substitute the following for Part I Section 13.4a(2) in its entirety:

(2) A beam that is intersected by braces shall be designed to support the effectsof all tributary dead and live loads assuming that the bracing is not present.

Substitute the following for Part I Section 13.4a(3) in its entirety:(3) A beam that is intersected by braces shall be designed to resist the effects

of ASD load combinations as stipulated by the Applicable Building Code,except that a load Qb shall be substituted for the term E . Qb is the maximumunbalanced vertical load effect applied to the beam by the braces. This loadeffect shall be calculated using a minimum of Py for the brace in tension anda maximum of 0.3 times c Pn for the brace in compression.

14. ORDINARY CONCENTRICALLY BRACED FRAMES (OCBF)Substitute the following for Part I Section 14.2 in its entirety:

14.2. StrengthThe Required Strength of the members and connections, other than brace connec-tions, in OCBF shall be determined using the ASD load combinations stipulatedby the Applicable Building Code except E shall be taken as the Amplified SeismicLoad. The Design Strength of brace connections shall equal or exceed the expectedtensile strength of the brace, determined as Ry Fy Ag . Braces with Kl/r greater than4.23

Es/Fy shall not be used in V or inverted-V configurations.



72


Documents

CH 4 - Part III-Allowables Stress Design (ASD) Alternative