Pineda Project Thesis Final-Spring 2011

CALTRANS DIVISION OF EQUIPMENT MOBILE CRANE STABILIZATION DESIGN

Gabriel Pineda B.S., California State University, Sacramento, 2004

PROJECT

Submitted in partial satisfaction of the requirements for the degree of

MASTER OF SCIENCE

in

MECHANICAL ENGINEERING

at

CALIFORNIA STATE UNIVERSITY, SACRAMENTO

SPRING 2011

ii


A Project

by

Gabriel Pineda

Approved by: __________________________________, Committee Chair Dr. Kenneth S. Sprott ____________________________ Date

iii

Student: Gabriel Pineda

I certify that this student has met the requirements for format contained in the University format

manual, and that this project is suitable for shelving in the Library and credit is to be awarded for

the Project.

__________________________, Department Chair ________________ Susan L. Holl, Ph.D. Date Department of Mechanical Engineering

iv

Abstract

of


by

Gabriel Pineda When designing mobile equipment, workers safety is a paramount concern for Engineers at

Caltrans Division of Equipment. A hazardous condition occurred to a crane mounted

maintenance truck when it attempted to lift a load, lost stability and nearly overturned. It was

determined that the stabilization system in place was not sufficient to the size of the crane in use,

thus at full capacity would cause a tipping condition. To correct this stabilization issue, a pull out

type hydraulic outrigger was designed and built. Design criteria for the outrigger was for it to be

rugged for everyday use, structurally sound, safe to use, simple to implement in the field,

lightweight, and cost effective.

The hydraulic outriggers were designed using NX 6 and Solidworks software for three-

dimensional CAD modeling and detail drawings. A finite element analysis of the outriggers

structure was created using Solidworks simulation software, testing for deflection, stress, and

loading. A vehicle-tipping analysis was also completed to ensure the equipment would be stable

in a lift. Budget savings took into consideration labor costs, materials costs, design costs, and

future maintenance costs.

The results of the analysis show that by keeping the design simple and modifying the

existing hydraulic stabilization system to include a pullout type outrigger, we were able to design

a stabilization system that effectively corrects the dangerous tipping condition and is structurally

sound in a cost effective, safe, and easy to employ package.

_______________________, Committee Chair Dr. Kenneth S. Sprott _______________________ Date

v

ACKNOWLEDGMENTS

This project would not have been completed without the help and support of many people.

I would first like to thank Angela Wheeler from the California Department of Transportation,

Division of Equipment, for providing me guidance and support in the design of the stabilization

system. I would like to thank my advisor Dr. Kenneth S. Sprott for his guidance and

understanding on this project. Thanks are also extended to the many people at San Joaquin Delta

College for inspiring me to be sedulous in my studies with their many words of wisdom.

I would also like to give a special thanks to my friends and family for loving and

supporting me throughout my education. Especially my parents who without their endless

support emotionally and financially, I would have never been able to accomplish my goals. This

is ultimately for them; they have sacrificed many things in order to put four children through

college, a great accomplishment in its self.

vi

TABLE OF CONTENTS Page

Acknowledgments....v

List of Tables ..viii

List of Figures..ix

Chapter

1. INTRODUCTION......1

Problem Description....1

Significance of Problem......5

Scope of Study........6

Organization of Project.......6

2. LITERATURE SURVEY......8

Overview.8

Injury Statistics8

Design and Safety Standards...9

Mobile Crane Design..10

3. DESIGN OF OUTRIGGER STABILIZATION SYSTEM..16

Engineering Requirements..16

Static Stability Requirements..17

Outrigger Retrofit Design Considerations ...19

Telescoping Pull-out Assembly ..20

Loads ..22

vii

Mounting Tube.......23

Extension Tube...25

Final Assembly...27

4. TESTING.......30

Static Stability Calculation.30

Finite Element Analysis.....32

Prototype Trial....35

5. RESULTS......37

Stabilization System safety.....37

Structural Integrity .....37

Certification....38

6. CONCLUSIONS...39

Significance of Results...39

Goals Realized....39

Future Process and Design Considerations.....40

Appendix A. Three Dimensional CAD Models.....43

Appendix B. Failed Stabilization Test Pictures..47

Appendix C. Installation Figures49

Appendix D. Final Pictures....53

Work Cited .....54

viii

LIST OF TABLES Page

1. Table 1 Safety Factor Comparison..14

2. Table 2 Soil Carrying Capacity............................15

3. Table 3 Maximum Capacity Chart Venturo ET18KX Telescopic Crane ....51

ix

LIST OF FIGURES Page

1. Figure 1 Sign Truck....2

2. Figure 2 Sign Truck Stability Diagram..3

3. Figure 3 Failed Stability Calculation , Stability Factor 1.12..4

4. Figure 4 Commercial Truck-Mounted Crane - Telescoping Boom .11

5. Figure 5 General Stability Area for Corner Mounted Crane.....13

6. Figure 6 Ideal Stability Calculation, Stability Factor 1.4..18

7. Figure 7 Ineffective Outrigger Stabilization System .. 19

8. Figure 8 Allowed Design Envelope.. .. 21

9. Figure 9 Mount Tube ....23

10. Figure 10 Mount Tube Retaining/Side Plates.... 24

11. Figure 11 Mounting Bracket...... 25

12. Figure 12 Tube with Jack Mount ...... 27

13. Figure 13 Extension Tube Assembly Retaining/Slide .. 27

14. Figure 14 Complete Assembly Pull-Out Outrigger ... 28

15. Figure 15 Assembly.... 28

16. Figure 16 Front View Assembly .... 29

17. Figure 17 Top View Assembly ...... 29

18. Figure 18 Final Design Stability Calculation, Stability Factor = 1.67 ... 31

19. Figure 19 Second Order Tetrahedral Mesh of Extension Tube .. 32

20. Figure 20 Extension Tube von mises stress distribution..... 33

21. Figure 21 Second Order Tetrahedral mesh of Assembly ... 34

22. Figure 22 Outrigger Assembly von Mises stress distribution .... 35

x

23. Figure 23 Extension Tube Assembly...... 43

24. Figure 24 Sign Truck Body..... 43

25. Figure 25 Rear Profile..... 44

26. Figure 26 Drivers Side Profile, Left Side Outrigger not shown .... 44

27. Figure 27 Passenger Side Profile.... 45

28. Figure 28 Max Tipping Angle of Crane...... 45

29. Figure 29 Underside Profile.... 46

30. Figure 30 Failed Stabilization Configuration ..... 47

31. Figure 31 Tipping Condition Lifting 1691 lb load at 117.75 for center of crane.. 47

32. Figure 32 Driver Side Outrigger Lifting During Test. 48

33. Figure 33 Venturo Flatbed Recommended reinforcement for ET18KX..... 50

34. Figure 34 Caltrans Crane Rienforcement Drawing E2-D208-04.... 52

35. Figure 35 Final Sign Truck Drivers Side.... 53

36. Figure 36 Final Sign Truck Passenger Side.... 53

1

Chapter 1

INTRODUCTION

California Department of Transportation also known as Caltrans is a government

department that has been serving the people of California for over 100 years. With their mission

statement to improve mobility across California, it is Caltrans task to build and maintain the

state highway system and various public transportation systems throughout California. One of

the many goals of Caltrans is to be the safest transportation system in the nation for users and

workers.

Among the many departments within Caltrans is the Division of Equipment, whose job it is

to purchase, design, fabricate, and repair over 13,000 pieces of mobile equipment within the

Caltrans fleet1. The equipment ranges from the specialized snow moving equipment, passenger

vehicle boat ferrys, and lane barrier moving machines, to the numerous highway maintenance

vehicles; bridge trucks, cone trucks, litter pickups, 4-yard dump trucks, and highway marking

vehicles to name a few.

Problem Description

Caltrans, Division of Equipment designs and builds specialized trucks to meet the needs of

California on the roads and highways. One truck in particular is designed to be capable of

installing, replacing and removing road signs also known as the Sign Truck as shown in figure 1.

This is done by use of a truck mounted mobile crane capable of a 1125lb load at 16 feet from the

center of the crane.

2

Figure 1 Sign Truck

While in the certification process, the Sign Truck began to tip, thus failing certification.

The cause of the instability was determined to be the failure of the stabilization system to counter

the force of the lifting load. Figure 2 below displays a stability diagram of the Sign Truck. In

Figure 2, the tipping line represents the fulcrum drawn from the front axle center of mass to the

rear outrigger. The risk of overturning is greatest when the crane boom is at a right angle to this

line.

3

Figure 2 Sign Truck Stability Diagram

4

Figure 3 shows the failed geometry results based on the stability diagram of figure 2. The results

of the Stabilization Moment (MS) and Tilting moments (MT) are used to find the safety factor

against overturning (MS/MT). The factor of safety against overturning is required to be greater

than or equal to 1.17 as ASME standard8 or 1.4 for severe operation4.

Failed Stability Calculation for Rear Mounted Crane

Input Weight

(lbs)

Rear Axle Weight PR = 6200

Stabilizing Moment (MS):

Crane Pedestal G1 = 197

Crane Weight G2 = 1050

Ms = 19228.13 ft-lbs

Crane Load PL = 1125

Tilting Moment (MT):

Input Distance

(in)

MT = 17157.49 ft-lbs

Outrigger Distance from Center Line of Truck

X = 45.7

Safety Factor Against Overturning: F.Axle to R.Axle A = 165

MS / MT = 1.12

R.Axle to Outrigger B = 23.875

=> 1.40

Outrigger to Crane C = 11.25

Rear Mounted Crane Standard

Center line to Crane F = 37

Extension outside of body

Crane Maximum Reach L = 192

-2.3 inches

Center Gravity of Crane H2 = 20

Calculated

Pedestal to Tipping Line LC =

8.99

Crane load to Tipping Line a =

183.01

Rear Axle to Tipping line LR =

38.80

Tipping Line Angle w = 13.60

Figure 3 Failed Stability Calculation, Stability Factor 1.12

5

The results shown in figure 3 and indicate a stability factor of 1.12, which does not comply with

standards and confirms the mode of failure to be the stabilization system as there is no margin of

safety for shock conditions. Nine vehicles in total were outfitted with the failing outrigger/crane

configuration.

In order to correct, all nine vehicles will need to be retrofit with a new stabilization system.

The new system includes outriggers that extend further away from the body, thus moving the

tipping line out and stabilizing the unit. The new outrigger will be engineered to counter the

tipping reaction of the vehicle and the stresses involved during a lift, all within the space

available.

Significance of Problem

In the past, the Sign Truck may have been designed for a smaller crane and for this reason

the outriggers were set at a fixed position along the side of the trucks body. This was sufficient to

counteract the tipping force with a lower capacity crane. However, the current configuration of

the vehicles are outfitted with a larger 18,000 ft lbs moment rated crane, making it necessary to

correct the stabilization system to resist the new tipping force created. Tipping is a very serious

issue, causing a danger to workers safety. The Sign Trucks must be safe to operate and pass

certification before Caltrans workers can use them. There are many safety standards that must be

met in order for a crane to pass certification. The most critical standards for mobile cranes are

federal OSHA 1910.180 and ANSI B-30.5, which must be followed to insure workers safety.

6

In a National Institute for Occupational Safety and Health (NIOSH) Publication in 2006, it

was reported that one crane tips over every 10,000 hours of crane use in the United States. 80% of

these accidents are attributed to exceeding the crane capacity. More than half of these accidents

were a result of swinging the boom or not fully extending the outriggers2. Operator error is

difficult to correct because it is human nature to make mistakes, however engineering a system

that eliminates some of that possible error is a safer and more reliable way to get the job done.

Scope of Study

After examining the problem, it was determined that the truck was tipping because the

crane position relative to the outrigger on the passenger side of the vehicle was too short for the

capacity of the crane. This project is geared toward the research, design, and testing of a new

pull-out type outrigger that exceeds the current industry safety standards for tipping and structural

stability. The final product will be designed for maximum manufacturability and cost. The

project will be fully designed using three dimensional CAD, and FEA software packages.

Prototype outriggers will be built and tested in the Caltrans, Division of Equipment Headquarters

shop.

Organization of Project

The following chapter is composed of a literature survey of mobile crane design, injury statistics,

and industry standards for design. Chapter 3 deals with the design of the outrigger stabilization

system including the use of three dimensional CAD software. Design requirements and

7

considerations are also discussed. Testing for structural integrity, as well as prototype testing is

included in chapter 4. Finite Element Analysis software is also used to analyze the structure.

Chapter 5 shows the results found from the various tests performed. The significance of the

results along with goals realized and Caltrans future design considerations are expressed in the

final chapter.

8

Chapter 2

LITERATURE SURVEY

Overview

An incredible variety of cranes have been designed since the introduction of high-strength

steels in the 1950s. The proliferation of cranes in construction is impressive, with approximately

125,000 cranes operating among all sectors of the United States construction industry alone6.

When it comes to cranes there are two basic forms, the mobile crane and the tower crane. The

mobile crane is the focus of this survey.

Injury Statistics

Mobile crane incidents can cause massive production delays, devastating property

damage, and loss of life. Estimates suggest that cranes are involved in up to one-third of all

construction and maintenance fatalities6. To add to this research by the Journal of Construction

and Management, it was found that mobile cranes represented over 88% of the fatal accidents

investigated. This is a significant amount for one crane type. The contributing factors leading to

fatalities caused by crane tip over were overload, loss of center of gravity control, outrigger

failure, high winds, side pull, and improper maintenance11. The research shows that most

accidents involving mobile cranes are due to carelessness or inattention of the operators or people

around them. By incorporating electronic safety measures and engineering out some factors that

attribute to this carelessness or inattention, many of these types of accidents may be reduced.

Many in the industry are attempting to improve conditions in the work force so that working and

operating around a crane becomes much safer. Currently legislation has targeted the employers

9

as well as operators of mobile cranes. Requiring certification and training, where in the past it

was not required for most small cranes. As well as increasing inspections of mobile cranes and

construction sites.

Design and Safety Standards

With the recent acceptance of very high-strength steels and the increasing needs at

construction sites, cranes have experienced a remarkable growth in lift capacity and boom

lengths. With this growth have come situations where the old stability margins might not provide

adequate reliability5. With new technology, cranes have evolved to be safer and more reliable

than they ever have been in the past. For instance, mobile crane technology now has the

capability to have electronic monitors to check load sensors, dynamometers, pressure sensors, and

a myriad of other electronic safety devices. However even with the new devices for safety it is

still up to the engineers and operators to be knowledgeable and cognizant of what they are doing.

Leading the push for safety standards is the American Society of Mechanical Engineers otherwise

known as ASME. ASME provides the standard for Mobile and Locomotive Cranes known as

B30.5. B30.5 contains provisions that apply to the construction, installation, operation,

inspection testing, maintenance, and use of cranes and other lifting and material handling related

equipment9. Other sets of standards that are applicable are the Occupation Safety and Health

Administration (OSHA), with Title 29, 1910.180 also, Local California Cal/OSHA, Title 8

standards. OSHA and Cal/OSHA standards mirror or reference many of the ASME B30.5

standards. The Society of Automotive Engineers (SAE) also has various standards for mobile

10

cranes as they relate to commercial vehicles. The Internationally Organization for

Standardization (ISO), also publishes a set of standards for the mobile carne industry.

Mobile Crane Design

Mobile cranes are comprised of hoisting machinery combined with both a base carrier and

a revolving superstructure. These cranes, can be either mounted directly onto wheels or truck

mounted, usually stand on four outriggers that are located at the corners of the lower base carrier.

The outriggers extend laterally and bear on the ground during hoisting operations to keep the

crane horizontal8. Mobile cranes exist in many forms, from locomotive cranes to crawler type

cranes; the emphasis of this report is on the Commercial Truck-Mounted Crane.

The American Society of Engineers defines a commercial truck-mounted crane as: A crane

consisting of a rotating superstructure (center post or turntable), boom, operating machinery, and

one or more operators stations mounted on a frame attached to a commercial truck chassis,

usually retaining a payload hauling capability whose power source usually powers the crane. Its

function is to lift, lower, and swing loads at various radii9, as shown in figure 4.

11

Figure 4 Commercial Truck-Mounted Crane Telescoping Boom9

For this study, we explore the mechanics of a Commercial Truck-Mounted Crane where the crane

is placed in the rear of the vehicle.

In most cases commercial truck mounted cranes use a telescopic type crane, which is the

case for this investigation. The telescopic crane gets its designation from the style of boom which

consists of several nested closed-tube sections that are extended or retracted by a hydraulic

cylinder; boom angles are controlled using one or more hydraulic cylinders located between the

boom base and the crane turntable6. Mobile boom cranes can vary in lifting capacity from 1 to 6

tons for commercial truck mounted cranes and up to 1000 tons for the very large specialized

crane mounted truck systems. Commercial truck mounted cranes usually have booms that can

extend up to 25 feet, however specialized crane mounted truck system can extend to lengths of up

to an amazing 600 ft.

12

The first aspect in the design of a truck mounted crane system is to determine if the body

will support the loads involved with lifting. Most manufactures will have a recommended

practice for reinforcement depending on the size or type of crane and body type. In this case, a

flatbed body is utilized. The manufactures recommended body reinforcement is shown in figure

33 of appendix C. The main support structure is made of two MC 4 x 13.8 lbs. /ft. ship channels

and a boxed steel mounting plate for the crane. The truck body used for this survey employed

the recommended design as shown in figure 34 appendix C, which illustrates the build drawing

used for the sign truck body.

The next important feature of a truck-mounted crane is stability. It is necessary to check

the trucks stability against overturning to ensure the safety of the workers. Figure 5 shows the

general stability area of a rear corner mounted crane truck. The figure shows the areas at which

the crane is most adept and least likely to lose stability.

13

Figure 5 - General Stability Area for Corner Mounted Crane4

The stability system in a truck-mounted crane mainly consists of two or four outriggers.

There are many outrigger styles but the basic purpose is to level and move the tipping fulcrum of

14

the vehicle to the point at which there is a safe stability factor from overturning at maximum load.

Stability Factor is the ratio of tipping load to the rated load. Stability factors vary from one

standard to the next as shown in table 1.

USAa United Kingdomb Australiac ISOd Japane

1.17(=1/0.85) 1.25 1.33(=1/0.75) 1.25 1.27

Comparison of Safety Factors for Hook Load in the Stability of Mobile Cranes Supported by outriggers

aU.S. Department of Labor,OSHA, 2011

bBritish Standards Institution, 1991.cStandards Association of Australia, 1995.dInternational Organization for Standardization, 1991.eLabour Standard Bureau, Ministry of Labour, Japan, 1978.

aAmerican Society Of Engineers, ASME B30.5-2007

Table 1 Safety Factor Comparison8

Table 1 shows the various stability factors that were established on the assumptions of a level

machine, on firm supports in calm air and in the absence of dynamic effects. For this reason, it is

not entirely correct to use these factors as a working stability factor. Dynamic effects of a

bouncing weight or swinging load can possibly cause an upset condition if the vehicle is already

on the ragged edge of the stability factor. For this study, the stability factor that is used is 1.4

based on the Utility Vehicle Design Hand Book released by the Society of Automotive Engineers

(SAE)4. The Handbook recommends a stability factor of 1.4 for severe operation conditions, 1.2

for normal operations and 1.1 for gentle operations. Severe operation takes into account shock

loads and other dynamic effects and increases the safety factor accordingly. In the interest of

15

safety for the Caltrans workers and operators, a stability factor of 1.4 or above will be the

standard for crane-mounted vehicles.

Another concern involving the stability of the crane is the ground bearing pressure of the

outrigger pads. The pad is the area underneath the outrigger leg that distributes the load of the

crane to the ground. Soil bearing pressure refers to the ability of soil to support load applied to

the ground. Table 2 below indicates estimated bearing capacities of different soil types for

buildings and cranes. Mobile crane operators need to be cognizant of the type of soil they are

operating on and apply cribbing when required underneath outrigger jacks to spread the load over

a larger surface area. Engineers must also be aware of soil conditions that the crane may

encounter when designing the outrigger pads and cribbing structure.

Table 2 Soil Carrying Capacity5

16

Chapter 3

DESIGN OF OUTRIGGER STABILIZATION SYSTEM

Engineering Requirements

The basic requirements that the stabilization system must have are the following:

- The system will need to be made of materials that can be easily purchased and machined

o Common Sizes of Structural Steel tube, angle and plate

- Size constraints limit design to be under the truck frame

o Conceivably a telescoping or swing out outrigger extension.

- Cost of materials and build should be minimal

o Simple design that can be made in Caltrans HQ Shop with the equipment that is

available.

o Will need to reuse as much of the existing system as possible.

- Durable

o Able to withstand the punishment of daily use and environment

- Easy to use

o The outrigger must be easily stored for driving

o Not too heavy for a Caltrans worker to set up

o Operation must be simple

- Designed to current safety and industry standards

o ASME B30.5, OSHA 1910.180, Cal/OSHA Title 29, and SAE.

o Federal Motor Vehicle Safety Standards (FMVSS)

17

Static Stability Requirements

After analyzing these requirements, the first concern was to determine how far the

outriggers needed to extend in order to achieve ideal stability by current standards. In figure 6 the

cranes maximum capacity (PL), vehicles rear axle weight (PR), mounting pedestal (G1) and crane

weight (G2) are used for the stability calculation to determine the distance (X) the outrigger must

extend to meet current stability regulations with a safety factor of 1.4. Microsoft Excel was used

to create a calculation spreadsheet in order to input and process data. Results from Figure 6

indicate that the ideal tipping angle would be 15.81 degrees. From this angle, it was calculated

that an outrigger that extends 53.5 inches from the center of the truck body would accomplish a

safety factor of 1.4 for stability. The design goal was to design an outrigger extension that meets

the length of 53.5 inches from the center of the truck or extend beyond thus increasing the

stability factor.

18

Ideal Stability Calculation for Rear Mounted Crane

Input Weight

(lbs)




If G2 lies inside of tipping line Crane Weight G2 = 1050

Ms = 23143.97 ft-lbs



Input Distance

(in)

MT = 16493.88 ft-lbs


X = 53.5

Safety Factor Against Overturning:

F.Axle to R.Axle A = 165

MS / MT = 1.40


=> 1.40




Extension outside of body Crane Maximum Reach L = 192

5.5 inches

Center Gravity of Crane H2 =

20

Calculated


16.07


175.93


44.95


Figure 6 - Ideal Stability Calculation, Stability Factor 1.4

19

Outrigger Retrofit Design Considerations

The current failed stabilization system is made up of two solid mounted hydraulic jacks

with hydraulic drivelines, and safety limit switches. Two square tube members bolted to the

truck frame and body as shown in figure 7 are used to brace each jack.

Figure 7 Ineffective Outrigger Stabilization System

After analyzing the current unsuccessful outrigger system, it was determined that several

components could be salvageable in the interest of saving expenses. Reusing the current

hydraulic jack assembly would save time and costs. Ordering a new jack would take anywhere

from four to five weeks and delay the manufacture as well as adding cost. The current jacklegs

were in good condition and would need minimal adjustments to retrofit to the new design. The

20

safety limit switch is a safety device that signals the operator that the outrigger is so the will not

drive off with an outrigger still deployed. This safety device was also in good condition and

could be easily transferred to the new design. The jack includes hydraulic hoses to extend down

and retract the outrigger pads. These hydraulic lines were not able to be reused because they

were not long enough to extend beyond the truck body. To determine if the jack pad should be

reused the ground bearing pressure would need to be calculated. The Jack pad on the assembly

had a surface area of 64 inches square. With an estimated maximum load of 7000 lbs force acting

on the outrigger, the bearing pressure on the ground would be 109 psi or 7.8 tone/ft2. According

to Table 2, this pad would be sufficient for compact gravel or road surface however blocking

would be needed for loose or firm gravel. This would not be a problem, as distributing the load

or blocking is a required practice for most outrigger pads. Blocking is an extra pad that

distributes the load over a larger area.

Telescoping Pull-out Assembly

One of the engineering requirements specifies a size limitation. This limitation was placed

because the current body would undertake a significant rebuild if a traditional style outrigger

cross tube were to be mounted across the rear of the truck or under the frame. A system that

would bolt in and utilize current parts would be far more desirable in saving cost, time and

labor. It is for this reason the stabilization needed to be contained within the truck frame rail and

outside of the body. Figure 8 shows the area of which the new stabilization needed to be

contained.

21

Figure 8 Allowed Design Envelope

In order to fit within the design envelope a swing out type outrigger and telescopic type

outrigger system were investigated. An arm extension of 8 to 12 inches was required to pivot out

from the body in order for the swing out type outrigger system to work. Several objects that were

obstructive to this design were the tool circuit hydraulic lines, hydraulic valve, the hydraulic oil

filter and the rear wheel. In order to use the swing out style these object would need relocation.

Ultimately, the telescopic type outrigger system provided the best option because the

extension arm would fit within the given space without the need to modify the filter or tool circuit

location. The two MC 4 x 13.8 lbs. /ft. ship channels used for body reinforcement provided the

ideal location to mount the outrigger. The limiting length of the pull out was determined by the

distance allowed from the truck frame to the outside edge of the body. With this length, a pull

out of 12.5 inches to the center of the outrigger jack could be accomplished. Based on this

22

distance, it was calculated that the factor of safety against overturning would be 1.67 as shown in

figure 18 on page 31.

Loads

To begin the design of the outriggers the engineering stresses of the structure were

calculated based on the worst-case scenario of outriggers supporting the entire weight of the truck

and payload, plus the weight of the crane and cranes maximum load. As the leverage increases,

outrigger pressure increases nearest the load. This worst case scenario is calculated at the static

moment of least stability where the lifting load is furthest away. Using the stability diagram in

figure 2 of page 3, the maximum bearing load (BL) on the inside outrigger pad is calculated. The

moment equation is based point S, which is the drivers side outrigger point of contact with the

ground.

(1)

(2)

Solving for BL where W is the distance of the driver side outrigger to the centerline of the truck

which is 48 inches, and TL is the vehicles maximum payload of 3500 lbs, we get BL = 8334 lbs.

This will be the load used in calculating structural integrity for all components of the stability

system. By SAE standard J1063 and B30.5 instruction for design of a prototype outrigger

23

structure the minimum strength margins for yielding in uniform rated loads will be 1.5 or above,

and for stress concentration areas surrounded by considerable low stress will be 1.1 or above.

Mounting Tube

To begin the design of the telescopic outrigger a mounting base was needed. The

Mounting Tube would be made of standard 5 x 5 x x 20 inch long structural steel square

tubing. This was selected because of the availability in house and structural strength of the

member. The mounting tube would need to be able to withstand a moment load of up 18000 ft

lbs and the rear axle weight of the truck plus cargo payload.

Figure 9 Mount Tube

24

Another key element was the reinforcement of the leading edge on the mount tube. This

was added because the concentrated load of the cantilevered extension tube was too great for the

tube alone. A 5 x 5 x x 2 inch long tube was welded to the end. This increased the cross

sectional area and reduced the stress. For the assembly four plates made of 4130 were attached

with -20 flat head screws to retain the extension tube and provide a hard slide plate for the

extension tube to slide against as shown in figure 10.

Figure 10 Mount Tube Retaining/Slide Plates

The next feature of the assembly is the mounting angles. The angles (shown in figure 11)

were necessary because mounting tube could not be mounted underneath the body reinforcement

Channel. Each Angle mount was reinforced with two inch plates. A four bolt pattern was used

to attach four - 13 hex head bolts to the body reinforcement channel.

25

Figure 11 Mounting Bracket

Extension Tube

The design of the telescoping extension tube required a structural steel component to fit

within the dimensions of 5 x 5 x x 20 inch Mounting Tube. The member needed to be able to

withstand a force of approximately of 8334 lbs at the jack attachment. To begin, a structural steel

tube was assessed with varying thicknesses in order to choose the structure that was best

structurally and kept the weight manageable for a pull out. Treated as a simple cantilevered beam,

the applied bending moment was calculated to be 150,012 ft lbs. To calculate the bending stress

(max) the following equation was used:

(3)

26

Where M is the bending moment, Y is the distance from the neutral plane and I is the

moment of inertia. From the Ryerson Steel structural beam handbook the moment of inertia of a

4 x 4 steel beam of 3/8 wall has a moment of inertia of 10.7 and a distance of 2 from the neutral

plane. This gives a bending stress of 28039 psi. The structural steel was made to meet ASTM

A500 Grade B which has a yield stress of 46000 psi. This would give the extension beam a

safety factor of approximately 1.64 from yield. Another important factor in tube selection is the

deflection in the beam, if the beam deflects too much it is a sign that failure can occur. The

deflection was analysed using the deflection equation for cantilevered beams:

(4)

Where W is the bearing load, L is the length to the max bending stress, E is the elastic modulus of

the material (E = 29 x 106) and I is moment of inertia. The deflection for the extension beam is

0.0195 inches, which is minimal.

A mounting plate for the outrigger jack (as shown in figure 13) was welded on and six -

13 bolt clearance holes were used for attachment. To retain the extension tube so that it stops

before pulling out, four 4130 steel plates were attached to the end once assembled as shown in

figure 13. Figure 12 also shows a 13/32 diameter hole carefully positioned in the center of the

beam so that it would not affect the bending stress. The hole is used to allow a 3/8 inch diameter

pin to lock the outrigger in the out position so that it would not slip during a lift.

27

Figure 12 Extension Tube with Jack Mount

Figure 13 - Extension Tube Assembly Retaining/Slide Plates

Final Assembly

Figure 15 shows the completed assembly of the pull-out style outrigger. The design is

simple and allows for easy bolt in underneath the truck body.

28

Figure 14 Complete Assembly Pull-Out Outrigger

To accommodate the outrigger jack, the side of the truck frame is sectioned out as shown in

figure 15. Another feature added was a handle to the outrigger jack to make it easier to pull out.

Figure 15 - Assembly

29

Figure 16 Front View Assembly

Figure 17 Top View Assembly

30

Chapter 4

TESTING

Static Stability Calculation

Based on figure 2, the following equations were used to solve for the safety factor against overturning:

Stabilization Moment: MS = (PR x LR)+(G1 x LC)+(G2 x (LC-H2)) (5)

Tilting Moment: MT = PL x a (6)

Where,

LC = ((A+B+C)*(sin(w)) (F/cos(w)) (7)

LR = (sin(w))*A (8)

a = L - LC (9)

w = Tan-1(X/(A+B)) (10)

These equations were entered into a spreadsheet to evaluate several conditions, including mode of failure (figure 3), ideal stability dimensions (figure 6), and final stability verification (figure 18).

31

Final Design Stability Calculation for Rear Mounted Crane

Input Weight

(lbs)




Crane Weight G2 = 1050

Ms = 26542.46 ft-lbs



Input Distance

(in)

MT = 15922.38 ft-lbs


X = 60.5

Safety Factor Against Overturning: F.Axle to R.Axle A = 165

MS / MT = 1.67


=> 1.40




Extension outside of body

Crane Maximum Reach L =

192

12.5 inches

Center Gravity of Crane H2 =

20

Calculated


22.16


169.84


50.30


Figure 18 Final Design Stability Calculation, Stability Factor = 1.67

32

Finite Element Analysis

Finite element analysis, also known as FEA, is a numerical method used for solving field

problems described by a set of partial differential equations12. In this case it will be used for

solving partial differential equations to predict the outcome of materials and structure in response

to force. The output of the partial differential equations will be the stress, strain, and deflection of

the given part. Because the number of simultaneous equations can get very large during an

analysis, computer software is used. FEA software is a very powerful analysis tool for design

engineers to realize the nature of their designs. For this study, Solidworks Simulation was used to

analyze and optimize the design.

The first step in a model is to apply the loading conditions and constrains. The extension

tube was given a cantilevered load of 8334 lbs to mimic the maximum loading condition, and

constrained 16 inches at the end of the tube. Next, a mesh is created using second order

tetrahedral elements because they offer more accurate results for solid meshing.

Figure 19 - Second Order Tetrahedral Mesh of Extension Tube

33

The results for the extension tube indicated a von Mises stress of 28,917 psi at the constrained

end that simulates the Mounting Tube face location. The maximum deflection was found to be

0.044 inches. The maximum stress was below the max yield of 46,000 psi for the structural steel

tube. The factor of safety for this load case was 1.6.

Figure 20 Extension Tube von Mises stress distribution

The second component analyzed for stress distribution under loading was the mounting

tube. The mounting tube was given a simulated cantilevered load of 8334 lbs to mimic the

maximum loading condition and was constrained by the eight mounting bolt holes. The assembly

model was then meshed using second order tetrahedral elements, as shown in figure 21.

34

Figure 21 Second Order Tetrahedral Mesh of Assembly

The results of the maximum von Mises stress analyss indicated a stress of of 43,272 psi and

a maximum deflection of .018 inches. The maximum stress of the assembly is located at the

connection point between the Angle bracket and the top of the mounting tube. These results

however were not used in the strength determination because the point load would increase no

matter how refined the mesh became. This is a common occurrence for FEA models and is

known as elasticity theory where sharp re-entrant corners are infinate. In some cases the stress

anomolies can be repaired with simplifying the model or adding fillets to edges, however in this

instance the geometry proved to be to beyond my experties and must be studied at a futer time in

more depth.

35

Figure 22 Outrigger assembly von Mises stress distribution

Prototype Trial

In addition to a stabilization calculation of the failed outriggers shown in figure 3, a live

test was performed to verify the tipping condition. Figure 31 in appendix B, shows the load in a

tipping condition when attempting to lift 1691 lbs at 117.75 inches from the center of the crane.

The crane should have been capable of a load of 1800 lbs at 120 inches. This was below the

manufactures maximum capacity. Figure 32, in Appendix B, shows the left outrigger lifting

from the ground indicating the beginning of a tipping condition.

After manufacture, the prototype telescoping outrigger was tested for stability as well. The

test procedure consisted of a 1,691 lb. test load at various radius and angles of lift. The procedure

began with a test load of 1,691 lb. at 108 inches from the truck. This load was then pivoted

around the vehicle to check for any areas of instability. At the same time the structure was

36

visually examined to make sure there were no signs of possible failure. The consecutive lifts

were made at 6 intervals away from the truck and rotated around the full motion of the crane.

The full capacity of the crane was reached at 128.5 inches from the vehicle which is in line with

the rated capacity of 1,680 lbs at 128 inches from the center of the crane. The crane is designed

to shut all functions that extend the radius of the crane out if the working load exceeds the rated

load. This occurred at 128.5 inches from the center of the crane. The crane showed no signs of

instability or structural damage.

37

Chapter 5

RESULTS

Stabilization System Safety

A stability factor of 1.67 was achieved which was greater than the standards of crane

safety of 1.14. With a foot print of 64 in2 the outrigger pad has a bearing load of 130 psi or 9.37

ton/ft2, which was acceptable for most soil conditions, however a block pad or cribbing

underneath the outrigger pad of approximately 144 in2 or greater is recommended.

Structural Integrity

The vehicles may never see a maximum capacity lift or have the truck loaded to maximum

capacity, however the outrigger was designed based on the worst case possible. The worst-case

event delivered a structural safety factor of 1.6, for the extension tube and was verified with FEA

models. This was in agreement with the minimum strength margins set by SAE for prototype

outrigger testing. The mounting tube FEA model had mixed results with spikes near and above

the yield strength of the material. One possible reason for the divergent stress results could be the

theory of elasticity, were the stress in sharp re-entrant corners is infinite. The more refined the

mesh elements became, the larger the stress developed. Rounding sharp edges in the model, and

simplifying the geometry to alleviate this issue helped with some sharp edges, but for some there

was no remedy. After comparing several results it was determined, the max von Mises stress

could not be used for these models as they varied widely from 20,000 to 200,000 psi, however,

displacements of consecutive models did converge around to 0.018 inches, which was helpful in

understanding the rigidity of the structure. Based on the FEA analysis of the edge stress

38

concentrations it is safe to allow the irregularities in the edges of the parts because the

surrounding areas had high factors of safety relative to the inconsistencies.

Certification

A licensed mobile crane certifier does the certification of every truck-mounted crane that

leaves the Caltrans yard. A certification certificate is given if the vehicle passes a battery of tests

and visual checks. Once the new stabilization system was complete and tested, the certification

process was initiated.

During the final certification, it was noticed that the licensed mobile crane certifier was not

correctly testing the unit. While setting the outriggers up for the certification lift, the certifier

failed to extend the outrigger far enough down into the ground to properly unload the spring

weight of the rear end. This misstep could have potentially caused a tipping failure by not

distributing the weight into the outriggers and moving the tipping line of the truck in an

unpredictable manner. This demonstrates how easy it is for human error to occur. Once

corrected the test continued and the new stabilization system passed certification.

39

Chapter 6

CONCLUSIONS

Significance of Results

The new stabilization system will provide safety and stability to the Sign Truck and allow

the vehicles to be utilized in the field for many years to come. The system was designed to be

easily mounted and contained underneath the body of the vehicle whereas typical systems are

mounted to the rear bumper. This allowed for ease in manufacturing and time savings. Many of

the concepts and design elements will help in evaluating and designing future mobile truck

mounted cranes within Caltrans Division of Equipment.

Goals Realized

- Tipping condition was eliminated by use of a pull-out type outrigger allowing the Sign

Truck to be used safely in the field. The new system extends a total of 14.5 inches from

the side of the truck, and achieved a factor of safety of 1.67 against overturning.

- Stabilization system was structurally sound and rugged for everyday use.

- Compact unit that is contained underneath the body.

- Safety systems that were implemented were; an operator warning if the outriggers are not

stored correctly, an emergency stop switch, a lift warning rear mounted horn, also

signage was use to warn of possible pinch or crush points.

- Simple to implement outrigger, where the operator only needs to grab the pull handle to

extend the telescopic outrigger out, lock the outrigger in place with a pin, and use the

hydraulic lever to extend each of the outrigger pads to the floor.

40

- Overall, the telescopic outrigger assembly weighs 80 lbs. The pull out arm weighs 35 lbs,

which is within the realm for any operator to use.

- Because various parts were reused from the last stability system and stock build materials

were used for the structure, costs were able to stay within $300 for parts and $600 for

labor per vehicle.

Future Process and Design Considerations

To avoid similar problems in the future, stabilization studies must be made for every

mobile crane over 2000 lbs in capacity. This would allow design engineers to adjust stabilization

systems prior to a truck build. In addition, it would be advantages to create a pilot or test vehicle

prior to completing an entire run of vehicles. In this case it could have saved design and labor

time had the problem been caught early on.

Designing outriggers is a time consuming process. In the future where possible, I would

advise to use the crane manufacturers pre-engineered outriggers. On future sign trucks, the body

may need a redesign for use with manufacturers full stabilizer system. Current utility bodies

include a bumper step with outrigger included that mount directly to the rear frame and crane

support. The Sign Truck can benefit from this type of set up.

Even with proper training, human error still exists. As demonstrated by the incorrect use of

the outriggers by the crane certifier. Perhaps, prominent signage for proper crane use will be in

future builds. Another possibility could be a limit sensor that makes certain the weight of the

truck is unloaded from the rear leaf springs before the crane is allowed electrical power. Another

would be outrigger load sensors so the operator would know if the rear truck springs are unloaded

and if there is potential for soil overloading. Most cranes at present come from the manufactures

41

with many safety features like capacity overload sensors and load blocks, it may be possible to

have manufactures add in more safety features as costs of electronics become more affordable.

The next step is to have a field review of the stabilization setup with the end users and get

feedback based on the Sign Truck performance also to inspect for and damage or signs of

structural issues like chipping paint. Based on that feedback the stabilization system on Sign

Trucks and future mobile crane vehicle design will continuously improve.

42

APPENDICES

43

APPENDIX A

Three Dimensional CAD Models

Figure 23 Extension Tube Assembly

Figure 24 Sign Truck Body

44

Figure 25 - Rear Profile

Figure 26 Drivers Side Profile, Left Side Outrigger not shown

45

Figure 27 Passenger Side Profile

Figure 28 Max Tipping Angle of Crane

46

Figure 29 - Underside Profile

47

APPENDIX B

Failed Stabilization Test Pictures

Figure 30 Failed Stabilization Configuration

Figure 31 Tipping Condition Lifting 1691 lb load at 117.75 for center of crane.

48

Figure 32 Driver Side Outrigger Lifting During Test

49

APPENDIX C

Installation Figures

50

Figure 33 Venturo Flatbed recommended reinforcement for ET18KX10

51

Table 3: Maximum Capacity Chart - Venturo ET18KX Telescopic Crane10

52

Figure 34 - Caltrans Crane Reinforcement Drawing E2-D208-04

53

APPENDIX D

Final Pictures

Figure 35 Final Sign Truck Diver Side

Figure 36 Final Sign Truck Passenger Side

54

WORK CITED

1. California Department of Transportation

2. National Institute for Occupational Safety and Health (NIOSH).

. 2011. 7 April 2011

.

Preventing Worker

Injuries and Deaths from Mobile Crane Tip-Over, Boom Collapse, and Uncontrolled

Hoisted Loads.

3.

2006-142. 9 April 2011 < http://www.cdc.gov/niosh/docs/2006-

142/pdfs/2006-142.pdf>

Venturo

4. Hoelzle, John F., Amrhyn O.C., and McAlexander Gary A.

. 2011. 15 April 2011

Utility Vehicle Design

Handbook

5. Shapiro, Lawrence K and Jay P.

. Warrendale, PA, 1991

Cranes and Derricks, 4th edition

6. Neitzel, Richard L., Seixas Noah S., and Ren Kyle k.

. Lynbrook, New

York, 2011

A Review of Crane Safety in the

Construction Industy

7. IMT

. Applied Occupation and Environmental Hygiene Volume 16(12):

1106-117, 2001

Crane Installation Manual

8. Tamate, Satoshi., Suemasa, Naoaki.,and Katada, Toshiyuki.

99901230: 20070220, 2011

Analysis of Instability in

mobile Cranes due to Ground Penetration by Outriggers.

9. American Society of Mechanical Engineers.

Journal of Construction

Engineering And Manangement ASCE, June 2005

ASME B30.5-2007 Mobile and

Locomotive Cranes

10. Venturo

. New York, March 7, 2008

Crane Instruction Manual. ET18KX 21300, 7-29-03

55

11. Beavers, J.E., Moore, J.R., Rinehar R., and Schriver R. Crane-Related Fatalities in the

construction Industry. Journal of Construction Engineering and Management

12. Kurowski, Paul.

ASCE,

2006

Engineering Analysis with Solidworks Simulation 2010

. Mission KC

2010

CALTRANS DIVISION OF EQUIPMENT MOBILE CRANE STABILIZATION DESIGNCALTRANS DIVISION OF EQUIPMENT MOBILE CRANE STABILIZATION DESIGNAbstractACKNOWLEDGMENTSTABLE OF CONTENTSLIST OF TABLESLIST OF FIGURESChapter 1INTRODUCTION

Chapter 2Chapter 3Chapter 4Chapter 5Chapter 6APPENDIX AThree Dimensional CAD ModelsAPPENDIX BFailed Stabilization Test PicturesAPPENDIX CInstallation FiguresAPPENDIX DFinal Pictures

Documents

Pineda Project Thesis Final-Spring 2011