Report No.

FHWA-RD-79~138

FATIGUE OF CURVED STEEL BRIDGE ELEMENTS j

f

!

Design Recommendations for Fatigue of Curved Plate Girder and Box Girder Bridges April 1980 Final Report

FRITZ ENGINEERING·

LABORATORY LIBRARY

Girder I

Document is available to the public through the National Technical Information Service, Springfield, Virginia 22161

Prepared for FEDERAL HIGHWAY ADMINISTRATION Offices of Research & Development Structures & Applied Mechanics Division Washington, D.C. 20590

T echnicol ~eport Oocumentotion Poge 1. Report No.

2. Government Accession No.

3. Recipient's Cotolog No.

FH'NA- RD-79-138 ~~~~~~----------~----------------------47-n~~~--~-----------; .C. Title ond Subtitle 5. Report Dote

Anril 1980

FATIGUE OF CURVED STEEL BRIDGE ELEMENTS -

Design Recommendations for Fatigue of Curved Plate Girder and Box Girder Bridges

6. Performing Orgoni ~otion Code

1-.,,_...,_.._,_,__ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _---18. Performing 7

• Author's)

J. Hartley Daniels, John W. Fisher and B. T. Yer

9. Performing Orgonizotion Nome ond Add~eu

Report No.

Orgoni~otion

Fritz Engineering Lab Report No. 398.8 10. Work Unit No. (TRAIS)

35F2-052

Fritz Engineering Laboratory, Bldg. #13 Lehigh University Bethlehem, PA 18015

11. Contract or Gront No.

DOT-FH-11-8198

~--------------~~------------------------~ 12. Sponsoring Agency Nome ond Address U.S. Department of Transportation· Federal Highway Administration Washington, D.C. 20590

13. Type of Report one! Period Covered

Final Sept. 1974 - Sept. 1978 14 •. Sponsoring Agency Code

IS. Supplementary Notes

FHWA Contract Manager:

jerar Nishanian

(HRS-11)

16. Abstract

Research on the fatigue behavior of horizontally curved, steel bridge elements was conducted at Fritz Engineering Laboratory; Lehigh University, under the sponsorship of the Federal Highway Administration (FHWA) of the U.S. Department of Transportation. The ~ulti-phase investigation spanning nearly five years was performed in five Tasks: 1) analysis and design of five large scale horizontally curved steel twin plate girder assemblies and three large scale horizontally curved steel box girders, primarily for fatigue t~sting, 2) special analytical studies of the influences on fatigue of stress range gradient, heat curving, "oil canning" of webs and the spacing of internal diaphragms in curved box girders, 3) fatigue tests, to 2,000,000 cycles, of each of the above eight curved test girders, 4) ultimate strength tests of three of the curved plate ~irder assemblies and two of the curved box girders following the fatigue tests (compo~ite reinforced concrete slabs were added to two of the three curved plate girder assemlblies and to both curved box girders) and 5) development of design recommendations suit~ble for inclusion in the AASHTO bridge design Specifications. This is the ~ig~th and final report of the project and presents the results of Task b above. The entire project is described and the findings summarized which were presented in the previous project reports. The report concludes with suggested additions and modifications to the Tentative Design Specifications for Horizontally Curved Highway Bridges, prepared for the FHWA-DOT by CURT under Contract Number FH-11-7389, March 1975.

17. KeyWords

18. Oi stri bution Statement

Bridges (structures), design, fatigue, girder bridges, structural engineering, testing, torsion, welding 19. Security Clouif. (of this report)

Unclassified Form DOT F 1700.7 !B-721

Document is available to the public through the National Technical Information Service, Springfield, Virginia 22161

20. Security Clossif. (of this poge)

Unclassified

21. No. of Poges

.60

22. Price

ACKNOWLEDGMENTS '.The investigation reported herein was conducted at Fritz Engineering Laboratory, Lehigh University, Bethlehem,. Pennsylvania.

Dr. Lynn S.

Beedle is the Director of Fritz Laboratory and Dr. David A. VanHorn is the Chairman of the Department of Civil Engineering. The work was a part of Fritz Laboratory Research Project 398, "Fatigue of Curved Steel Bridge Elements" sponsored by the Federal Highway Administration.(FHWA). of the United States Department of Transportation. The FHWA Project Manager is Mr. Jerar Nishanian.

The Advisory Panel

members are-Mr. A.·.p. Cole, Dr. Charles G. Culver, Mr. RichardS. Fountain, Mr. Gerald Fox, Dr. Theodore V. Galambos, Mr. Andrew Lally, Mr. Frank D. Sears, and Dr. Ivan M. Viest. The following members of the faculty and staff of Lehigh University made major contributions in the conduct of this work:

Dr. R. G. Slutter,

Dr. S. N. Iyengar, Dr. N. Zettlemoyer,· J·. M. Talhelm, D. duPlessis, Y. Erler, T. F. Cleary, R. Trevino, W. Herbein, R. P. Batcheler, M. Marzullo, J. Maurer, D. Abraham and T. A. Fisher. Ms. Shirley Matlock typed the manuscript. prepared by Mr. John Gera an9 his staff.

'

'

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ii

The figures were

TABLE OF CONTENTS

1.

2.

INTRODUCTION AND DESCRIPTION OF RESEARCH

1

1.1 1.2 1.3

1 2 3

REVIEW OF PROJECT TASKS 2.1 2.2 2.3 2.4 2.5

3.

Background Problem Stat~ment Objectives and Scope

5

Task 1 - Analysis and Design of Large Scale Plate Girder and Box Girder Test Assemblies Task 2 - Special Studies Task 3 - Fatigue Tests of Curved Plate Girder and Box Girder Test Assemblies Task 4 - Ultimate Load Tests of Curved Plate and Box Girder Assemblies Task 5 - Design Recommendations

5

11 18 20 20

FINDINGS

21

3.1

Analysis of Curved Plate and Box Girders

21

3.1.1

Design Recommendation

22

Fatigue Strength of Welded Details

23

3.2.1

29

3.2

3.3

3.4

3.5

3.6

Design Recommendation

Stress Concentration, Stress-Range Gradient and Principal Stress Effects on Fatigue Life

29

3.3.1 3.3.2 3.3.3 3.3.4

29 30 30 30

Stress Concentration Stress Range Gradient Principal Stress Effects Design Recommendation

Effect of Heat Curving on the Fatigue Strength of Plate Girders

30

3.4.1

31

Design Recommendation

Effect of Internal Diaphragms on the Fatigue Strength of Curved Box Girders

31

3.5 •. 1

31

Design Recommendation

Effect of Web Slenderness on Fatigue Strength

32

3.6.1

33

Design Recommendation iii

4.

PROPOSED SPECIFICATIONS AND COMMENTARY

41

5.

CONCLUSIONS AND RESEARCH NEEDS

45

6•

REFERENCES

48

APPENDIX A: APPENDIX B:

STATEMENT OF WORK LIST OF REPORTS PRODUCED UNDER DOT-FH-11-8198

iv

51 54

LIST OF ABBREVIATIONS AND SYMBOLS centerlin~

a

• diaphragm spacing, measured along

b£

• flange width (inches)

d

• transverse stiffener spacing (inches)

tf

• flange thickness (inches)

tw wi D w

• web thickness (inches) • initial out-of-flatness of web • web depth (inches)

F

= yield stress (psi)

y

(inches)

K

• stress intensity

R

• horizontal radius of curvature of test assembly (feet)

R

• horizontal radius of curvature of a plate girder (inches)

S

• stress range

r

I ,II o oa

welded detail types/subtypes for open section (plate girder)

• test assemblies

I

welded detail types/subtypes for closed section (box girder)

I

ca' cb

II ,etc. c

• test assemblies

v

U.S. Customary-SI Conversion Factors To convert

Multiply by

To

inches (in) inches (in) inches (in)

millimeters (mm) centimeters (em) meters (m)

25.40 2.540 0.0254

feet (ft) miles (miles) yards (yd)

meters (m) kilometers (km) meters (m)

0.305 1.61 0.91

square inches (sq in) square feet (sq ft) square yards (sq yd) acres (acre) square miles (sq miles)

square square square square square

cubic inches (cu in) cubic feet (cu ft) cubic yards (cu yd)

cubic centimeters cubic meters (m3 ) cubic meters (m3 )

pounds (lb) · tons (ton)

centimeters (cm2 ) meters (m2 ) meters (m2 ) meters (m2 ) kilometers (km2 ) (c~)

16.4 0.028 0.;765 0.453 907.2

kilograms (kg) kilograms (kg)

4.45 9.81

one pound force (lbf) one kilogram force (kgf)

newtons (N) newtons (N)

pounds per square foot (psf)

newtons per square meter (N/m2 ) kilonewtons per square meter (kN/m2 )

pounds per square inch (psi)

6.45 0.093 0.836 4047 2.59

gallons (gal) acre-feet (acre-ft)

cubic meters (m3 cubic meters (m3

gallons per minute (gal/min)

cubic meters per minute

newtons per square meter (N/m2 )

pascals (Pa)

vi

47.9 6.9 0.0038 1233

) )

(m3

/min)

.0.0038 1.00

1. 1.1

INTRODUCTION AND DESCRIPTION OF RESEARCH

Background In 1969 the Federal Highway Administration (FHWA) of the U.S.

Department of Transportation (U.S. DOT), with the sponsorship of 25 participating state transportation departments, commenced a large research investigation of horizontally curved plate and box girder bridges.

The

investigatio·n was conducted by four universities (Carnegie-Mellon, Pennsylvania, Rhode Island, and Syracuse) and was commonly referred to as the CURT (f_onsortium of :Q.niversity g_esearch _1eams) Project.

The investigation

was directed ·towards the development of specific horizontally curved steel girder design guidelines for possible inclusion in the AASHTO bridge design specifications. The tentative specifications (l, 2 ) resulting from the CURT investigation incorporate their findings as well as input from other simultaneous efforts such as from the University of Maryland. included an extensive literature survey. therefore been taken into account.

The CURT project also

Prior curved girder work has

However, the tentative specifications

do not suggest provisions related to fatigue.

The CURT program concluded

:':0,.

with a recommendation that future research investigate the fatigue behavior of horizontally curved steel bridges. While the CURT investigation was in progress, considerable work was underway at Lehigh University in the area of straight girder fatigue.

Two

reports were produced which clarified the understanding of the fatigue per4 formance of steel bridge members. ( 3 • ) The findings of this research resulted in a major revision of fatigue design rules in 1974 and is now incorporated in the fatigue provisions of the Twelfth Edition (1977) of the AASHTO Standara2Specifications for Highway Bridges. ( 5 ) Two other reports provide condensed commentary and guidance related to the application of the new pro6 visions. ( ,7) However, since no horizontally curved girders were analyzed

f

or tested.,

d~rect

was not assured.

r

applicability of the new specifications to these members Furthermore, no previous fatigue research on horizontally

curved girders can be found in the literature.

1

In 1973 the FHWA sponsored a research investigation at Lehigh University entitled "Fatigue of Curved Steel Bridge Elements".

This is a

multi-task analytical and experimental investigation into the fatigue behavior of horizontally curved steel plate and box girders for highway bridges.

The investigation was completed in 1978.

are shown in Appendix A. is given in Appendix B. 1.2

The five project tasks

A list of all reports produced in this project This is the final report of the project.

Problem Statement Concern has been expressed that the extensive lateral bracing

required in horizontally curved steel plate girder bridges, coupled with the unequal deflections of adjacent girders and the attendant complicated state of stress may lead to welded details which are sensitive to repetitive loads.

Similarly, the internal bracing and stiffening required of hori-

zontally curved steel box girders which are subjected to torsional, lateral and longitudinal forces may also produce welded details sensitive to repetitive loads. Real fatigue problems have been encountered in straight girder bridges.

Fatigue cracks have occurred primarily at cover plate ends as a

result of extreme volumes of traffic and lower than estimated fatigue resistance, as well as at stiffeners; braces and other attachments, primarily as a result of displacement-induced stresses.

Such problems can be

avoided in straight girder design by adherence to the new fatigue provisions of the bridge design specifications. ( 5 ) There is concern that more fatigue problems may exist in curved

gi~der

bridges because bracing members and

connections, for example, carry forces which are more complex than the nominal forces in straight girders. Concern has also been expressed about the fatigue problems associated with "oil canning" of curved thin web plates with stiffeners.

Oil canning is

a term used to mean the lateral displacement of the web plate of a plate or box girder, straight or horizontally curved, under cyclic loads.

Existing

web slenderness (depth-thickness ratio) requirements for straight girders are based on buckling and fatigue considerations. ( 5 ) Prior fatigue tests 2

indicated that for straight girders the web bending stresses due to initial imperfections in the web panel did not cause fatigue problems as long as the web was within the specified slenderness limit. (B)

Due to curvature

effects, the web of a curved girder which is subjected to bending tends to deform outward in the compression region and to flatten out in the tension reg i on. (9,10,11) These.deformations pro d uce we b b end ing stresses whi c h are of concern.

By using a simple physical model to account for the shell

action at a curved panel, an expression was developed for the web slenderness However, no

ratio required to limit these web bending stresses

experimental results on the fatigue behavior of curved panels were available to substantiate this expression.

Testing and examination of curved girders

with respect to this aspect have been completed and the results summarized herein. Questions have also been raised regarding the influences of three other factors on the fatigue behavior of curved plate and box girder bridges.

These are (1) stress range gradients across the flanges of plate

girders, (2) residual stresses due to heat curving plate girders and (3) spacing of internal diaphragms in curved box girders.

These factors were

examined analytically and the results are summarized herein. 1.3

Objectives and Scope The objectives of this investigation are:

(1) to examine the

fatigue behavior of horizontally curved steel plate and box girder highway bridges, (2) to develop fatigue design guides in the form of simplified equations, charts or specification provisions suitable for inclusion in the AASHTO bridge specifications, and (3) to investigate the ultimate strength behavior of curved steel plate and box girder highway bridges. Before the second objective is carried out it is intended that the fatigue behavior of curved girders be compared with straight girder performance to determine if in fact revisions to the AASHTO specifications are necessary. It has long been recognized that fatigue problems ln steel bridges are most probable at details associated with bolted and welded connections in tensile stress range regions.

Straight girder research has shown that

welded details are more fatigue sensitive than bolted details.

Modern

bridge structures utilize welded connections extensively in the construction of main members and for securing attachments such as stiffeners and 3

gusset plates.

Therefore, the investigation is centered· on the effect of

welded details on curved girder fatigue strength.·

The investigation also

examines other areas of concern such as the "oil canning" effect.· The work is broken down into five tasks as shown in· Appendix A. In Task 1 the analysis and design of large scale horizontally curved plate and box girder test assemblies are performed, inciuding br:idg~ Cl_assifica~.. tion and selection of welded details for study.

Task 2 concerns special

studies on stress range gradients, heat curving residual stresses, web slenderness ratios and diaphragm

spacing as related to fatigue performance.

Fatigue tests of the large scale test assemblies are performed 'iri Ta-sk ···3: Ultimate strength tests of three curved plate girder as.sembi"ies arid two curved box girders are performed in Task 4.

Comp-osite reinforced' concrete

slabs were added to two of the three curved plate girder assemblies and to both curved box girders.

Design recommendations for fatigue of- curved .

plate and box girder highway bridges are prepared as Task -5 based onc'the work of Tasks 1, 2 and 3.

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4

2.

REVIEW OF PROJECT TASKS

The following is a review of project Tasks 1, 2, 3 and 4 (Appendix A).

This report constitutes the work done in Task 5.

The project

findings are reported in Chapter 3.

2.1

Task 1 - Analysis and Design of Large Scale Plate Girder and Box Girder Test AssembliesC13) The experimental phase of the fatigue investigation (Task 3) required

large scale test girders.

Five plate girder assemblies and three box gir-

der assemblies were designed and fabricated to investigate the fatigue behavior of typical welded details usually found in curved girders and to study the effect of web slenderness "oil canning" on the fatigue of curved girder webs. In order to provide full scale welded details with realistic residual stress fields and stress range gradients in the vicinity of the welded details, as well as reasonable flange and web dimensions, large scale test girders were required.

Examples of the test girders are shown in Figs. 1

through 4. The test girders were analyzed using available computer programs and designed in accordance with the 1973 AASHTO Specifications and 1974 Interim, including the modifications suggested in the CURT tentative design specifications. (l, 2 ) Three major constraints governed the design of the plate girder assemblies and box girders for testing.

First, it is desirable for all

welded details on a given test girder to fail in fatigue at approximately the same cycle life in order to reduce testing time and the problems associated with fatigue crack repair.

The test girders were designed to a fati-

gue life of two million cycles for all details tested.

The required stress

ranges were estimated using the AASHTO fatigue provisions.

The allowable

stress ranges specified by AASHTO represent the 95% confidence limit for 95% survival.

Therefore, to ensure the formation of visible fatigue cracks

and to allow for a small margin of error in the analysis the design stress ranges were selected approximately 2 ksi higher in the flanges and 1 ksi higher in the webs than the allowable stress ranges specified by AASHTO. 5

Jack Loco t ionLoad Position 2

2

9

Girder

1

tf

Dw

tw

Dw/tw

8"

1/2

58

3/8

155

3/4

58

5/16

186

10

2 bf

bf

= flange

width

flange thickness Fig. 1

Dw

= web

depth

t

= web

thickness

w

Plate Girder Test Assembly 2 - Cross Section Dimensions and Locations of Group 1 Details on Tension Flanges

6

10

11

• •

~----------~--------~

• •

•

4•-10

11 3/all

1 ..

Fig. 2

Girder I

Girder 2

51-011

Plate Girder Test Assembly 2 - Cross Section at Interior Diaphragms

7

Web-Diaphragm Joints { typ) Outer Web

Inner Web

Radius= 120' Span= 36'

Load Positioned Over Joints 3

¢7

I l

l

J Fig. 3

Schematic Plan View of Typical Box Girder Test Assembly

I

l

8

12

11

36"

6"x 2" (typ.)

•1 ~ 3

11

X 3 X 3te" 11

36" '.:,.- ..

9"

'.

Fig. 4

Box Girder Test Assembly 1 - Cross Section at Interior Diaphragms

9

( fyp)

Second, the span length, centerline radius, and number of plate girders in each plate girder assembly and the cross section dimensions of the box girders are limited by the dimensions of the dynamic test bed in Fritz Engineering Laboratory and the method of loading. Third, the maximum loading which can be applied to the test girders is limited by the maximum dynamic load capacity of the available pulsating jacks.

Amsler pulsators and hydraulic jacks having 110 kip dynamic capa-

city and a maximum usable stroke of 0.35 inches were used. Execution of Task 1 was carried out in light of these constraints through the following procedure: 1.

An examination of the

ch~racteristics

of existing curved girder

bridges and a classification of welded details was performed._ 2.

A preliminary design of the test assemblies was performed. a) Preliminary design of the plate girder test assemblies was achieved using the ·V-load method. (l 4 ) b) Preliminary design of the box girders was accomplished by assuming that the assemblies were straight, and carrying out a simple structural analysis.

3.

Following the preliminary designs, the test girders were analyzed

using the most recently available cumputer programs.

Two different programs

were used to analyze each plate girder test assembly and another two were used to analyze each box girder.

Thus, a check on the accuracy of the stress

range and deflection conditions as required by the first and third design constraints was provided. a) The plate girder test assemblies were analyzed using the Syracuse(l 5 ) and CURVBRG(l 6 ) computer programs. Reasonable agreement between the results of both programs was obtained. b) The box girder test assemblies were analyzed using the SAP IV(l?) and CURDI(lS) computer programs.

Reasonable agree-

ment between the results of these programs was also obtained. 4.

Revised preliminary designs were prepared as required by the re-

sults of the computer analyses. 5. Step 3.

The revised preliminary designs were analyzed as outlined in Several cycles of design (Step 4) and analysis (Step 5) were

required to satisfy the above design constraints. 10

6.

Final designs of each of the test girders were made and included

complete designs of the_ required diaphragms, transverse stiffeners, bearing stiffeners, etc. and preparation of design drawings for fabrication.

Fabri-

cation contracts were let on the basis of competitive bids. Each of the five plate girder asl).emblies. had a centerline span length of 40 feet and a centerline radius of 120 fe.et? and were loaded at the quarter points either directly over the inner girder or at the test assembly centerline. The applied load range was from 5 kips to 105 kips and the maximum deflection under the load was approximately 0. 35 inches.

The dimension· of· the girde.rs

are summarized in Table 1. Each of the three box girders. has. a centerline span length of 36 feet and a centerline radius of 120 feet, and are loaded at the quarter points directly over th_e inner web,

The applied load range and

deflection conditions are similar to those for the plate girder assemb.lies. The work of Task 1 also included the selection-of typical welded details which are fabricated into the test girders..

Tables 2 and 3 sh.ow

the welded details selected for the plate girder assemblies and b.ox girders (13) .

The detail type is given by the Roman numerals and suBs-cripts,

The

AASHTO fatigue category and allowable stress range for 2,000,000 cycles of load application is also shown for each detail. Some of the results of the Task 1 studies. will be summarized in Chapter 3 on the findings of this project. 2.2

Task 2 - Special Studies The special studies contemplated at the start of the project are

l~st~d

..

in Appendix A.

As the project progressed, it became necessary to

enlarge the scope of the special studies. was performed outside the project.

Some of this additional work

The findings from all the special

studies are reported in Chapter 3. The significance of a fatigue crack growing across the width of a flange in the presence of a stress range gradient was studied. 11

The

TABLE 1 PLATE GIRDER ASSEMBLY AND BOX GIRDER GEOMETRIES

Type

Assembly

Girder

No.

Plate Girder Assembly

No.

bf (in)

tf (in)

D w (in)

1

1 2

12 12

1 1

54 54

3/8 9/32

2

1 2

8 10

1/2 3/4

58 58

3/8 5/16

3

1 2

8 10

1/2 3/4

58 58

3/8 . 3/8

4

1 2

8 12

1/2 1

52 52

3/8 3/8

5

1 2

8 12

1/2 1

52 52

3/8 3/8

tf (in)

D w (in)

.w (in)

b (a) f (in)

Girder Type

·Box Girder

Web

No.

w (in)

t

1

inner web outer web

36 36

3/8 3/8

36 36

3/8 3/8

2

inner web outer web

36 36

3/8 3/8

36 36

3/8 3/8

3

inner web outer web

36 36

3/8 3/8

36 36

3/8 3/8

(a)Bottom flange width

~-:::_~-

CENTERLINE DATA Type

Radius (ft)

Span (ft)

Plate Girder Assembly

120

40

Box Girder

120

36

12

T

t

TABLE 2

SUMMARY OF WELDED DETAILS FOR PLATE GIRDER TEST ASSEMBLIES

Zo

,. .AL

TS

w-

,

\_F IIo

W F TS GP •

'I

--, _,L_

-

Web Flange Transverse Stiffener Gusset Plate Predicted Crack Location

TS

w-

F

16 II

16"

I

..

J

GP

II )

I

-TS GP

16 I

' '

v

GP

),

'

I(

IJ

11

-

~w F

F

16"

JLob

-

WJ 1.1

F

(

~

J ~

GP

"'

GP

vw.l

16

~

--

-·TS

w_/

-

I

16 II

I

F

I

11

z.rrJ.r-~~.r....r...:.

GP

13

if )

......_

TABLE 3

SUMMARY OF WELDED DETAILS FOR BOX GIRDER TEST ASSEMBLIES

c

I co

13

,

~

c

Icb

TS

w-

13

,"

w-

TS I I I I

TS

I

v

F_/

F_/

c

IIc

13

~

r

TS

wI

.~

F_/ C-D

mea

13-10

E 8

mcb {TS.

{TS ~

I

LS

LS

)

~

I

v

'--For W

c

)

13

'