WHEEL LOADINGS ON WEB PANELS OF OVERHEAD CRANE BOX-GIRDERS AP Robertson ...

332 Pages·2015·54.55 MB·English

WHEEL LOADINGS ON WEB PANELS
OF OVERHEAD CRANE BOX-GIRDERS
A.P. Robertson
ABSTRACT
The bridge rail on an overhead crane torsion-box girder is
positioned directly above one of the web plates; this web is subjected
to wheel loadings from the lifting unit. The study concerns the load
carrying capacity of plate box-girder web panels subjected to an in­
plane wheel load at the panel midspan.
Investigations are made of the in-plane patch loading produced
on crane web panels by the distribution of a wheel load through an over-
lying rail and flange. Elastic buckling of a short-span model box-
girder web panel subjected to an in-plane wheel load is studied. A
computer analysis is presented to determine elastic buckling coefficients
for flat rectangular plates subjected to a uniform in-plane patch load
centrally disposed on one edge and supported by shear stresses on the
adjacent edges. Patch loads of various lengths are considered over a
range of plate aspect ratios for plates with various combinations of
simply supported and clamped edges. Some non-uniform patch loads mod­
elling approximately a distributed wheel load are also considered.
A plastic mechanism analysis originally presented by Roberts and
Rockey for predicting collapse loads of patch loaded plate girders is
studied and a modified form derived. Results are presented of a series
of collapse tests conducted on short-span model box-girders subjected to
a wheel load above one of the webs. The effect on the failure load of
rail size, web thickness, panel aspect ratio, and longitudinal web
^ stiffening is investigated. Several of the test web panels exhibited
snap buckling. From the results, a simple expression is developed for
predicting collapse loads of plate girders subjected to narrow patch
loads.
A series of recommendations are presented to aid structural
designers in taking account of patch loading on slender web panels.

WHEEL LOADINGS ON WEB PANELS
OF OVERHEAD CRANE BOX-GIRDERS
by
Adam Patrick Robertson
A thesis submitted to the University of Leicester
for the degree of Doctor of Philosophy
FEBRUARY
1983
ProQuest Number: U336380
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ACKNOWLEDGEMENTS
The author wishes to express his sincere thanks to all those who
have contributed towards the work of this thesis in any way, large
or small.
The author is particularly indebted to Dr. B. Hayman for his super­
vision of the work; his comments, suggestions and encouragement have
been an invaluable contribution. Special thanks also go to Mr. C.
Morrison, Experimental Officer, Leicester University Engineering Depart­
ment, for his assistance with the experimental work, and to the
Technician Staff of the same Department.
The assistance, financial and practical, provided by Herbert Morris Ltd.,
Loughborough, Leicestershire, is gratefully acknowledged. Without their
co-operation, construction of a test frame and test specimens essential
to the work might not have been possible. Thanks are extended parti­
cularly to Mr. R. Widdowson and Dr. H. Jack for supporting the work
programme; to Mr. C. Grimley and Mr. A. Roper for technical advice; and
to Mr. T. Pawley for arranging and administering the collaborative work
on the part of the fipm.
The author is very grateful to Helen Townsend for her excellent work in
typing the majority of a difficult manuscript in limited time; to Paul
Smith for his careful photography work; and to Doug Pratt, Noreen
Berridge and Joyce Meredith for assistance with the figures.
Funding of this CASE Project by The Science and Engineering Research
Council is gratefully acknowledged.
11
SUMMARY
In torsion-box design of twin girder overhead cranes, the bridge rail
on which the lifting unit runs is positioned eccentrically on the girder,
directly above one of the web plates. This web is subjected to in-plane
patch loading produced by the spread of a wheel load through the overlying
rail and flange. This study concerns the load carrying capacity of plate
box-girder web panels subjected to a wheel load at the midspan of the
panel.
Distribution of a wheel load through a rail and flange is investigated
from recordings made of in-plane vertical stress distribution profiles
along the upper edge of a web panel of a short-span model box-girder.
The girder was loaded through various interfaces above the web by a wheel
load. A simple method is proposed for relating a distributed wheel load
to an equivalent uniform patch load. Methods for estimating distributed
wheel loading lengths are investigated. It is shown that crane web
panels are generally subjected to patch loads of short length, occupying
less than one-quarter of the panel length.
A computer analysis is presented to determine elastic buckling coeffic­
ients for flat rectangular plates subjected to a uniform in-plane patch
load centrally disposed on one edge and supported by shear stresses on
the adjacent edges. Patch loads of various lengths are considered over
a range of plate aspect ratios for plates with various combinations of
simply supported and clamped edges. Also considered are some non-
uniformly distributed patch loads modelling approximately a distributed
wheel load. For the large majority of geometries considered, it is
the support condition along the loaded edge which has greatest influence
Ill
on the buckling load. Correlation with buckling loads estimated from
experimental measurements on a model crane girder web panel indicated
that an assumption of simply supported panel edges is over-conservative
and that it is probably more representative to consider the edges attached
to the flanges as clamped.
Ultimate load carrying capacity is considered. A plastic mechanism
analysis originally presented by Roberts and Rockey is studied and a
modified form derived which reveals the transition region from collapse
initiated by direct web yielding for girders with stocky webs to failure
by a mechanism of out-of-plane web deformation for girders with slender
webs. Certain approximations in the original analysis are shown to
involve the omission of terms which can contribute significantly to the
plastic work expression. Inclusion of these terms, however, whilst
offering potential refinement, increases considerably the complexity of
the analysis.
Results are presented of a series of collapse tests conducted on short-
span model box-girders subjected to a wheel load above one of the webs.
The effect on the failure load of rail size, web thickness, panel aspect
ratio, and longitudinal web stiffening is investigated. Snap buckling
was exhibited by several of the test web panels. From the results, a
simple expression is developed for predicting collapse loads of plate
girders subjected to narrow patch loads.
The main findings of the work are used as ab asis for a series of
recommendations to aid the structural designer in taking account of patch
loading on slender web panels.
IV
CONTENTS
Page
Acknowledgement s i
Summary ii
Notation viii
CHAPTER 1 DISCUSSION OF THE PROBLEM
1
1.1 Introduction
1
1.2 Electric Overhead Travelling Cranes
1.3 Crane Box-Girders 3
4
1.4 Wheel Loads
1.5 Current Design of Crane Bridge Girders 7
1.5.1 Design Codes 7
8
1.5.2 Bearing Stresses from Wheel Loads
10
1.5.3 Web Panel Buckling
12
1.6 The Present Investigation
1.7 Terminology 13
CHAPTER 2 PATCH LOADS ON CRANE WEB PANELS
16
2.1 Introduction
21
2.2 Previous Work
2.3 Experimental Investigation of Patch Loads 27
2.3.1 The Test Equipment 27
2.3.2 The Test Procedure 32
2.3.3 Results 33
2.3.4 Discussion 35
40
2.4 Estimation of Equivalent Patch Load
2.5 Web Panel Buckling Under Patch Loading 49
2.6 Experimental Investigation of Panel Buckling 55
V
Page
2.6.1 Southwell Plots 55
2.6.2 Buckling Profiles 66
2.7 Conclusions 68
CHAPTER 3 ELASTIC BUCKLING ANALYSIS FOR PATCH LOADED PLATES
3.1 Introduction 70
3.2 Origin of the Method 72
3.3 Method of Analysis 73
3.3.1 General Description 73
3.3.2 Functions Employed 79
3.3.3 Computational Developments 84
3.3.4 Convergence and Accuracy 85
3.4 Results and Analysis of Results 89
3.5 Non-Uniform Patch Loading 109
3.6 Conclusions 113
CHAPTER 4 COLLAPSE LOAD ANALYSIS
4.1 Introduction 115
4.2 Mechanism Analysis by Roberts and Rockey 119
4.2.1 Slender Webs 119
4.2.2 Stocky Webs 123
4.2.3 Comments 123
4.3 The New Mechanism Solution 127
4.3.1 Basic Hinge Kinematics 127
4.3.2 The Mechanism 129
4.3.3 Plastic Work 131
4.3.4 Computation of Solution 135
4.4 Collapse Load Curves from New Solution 135
4.5 Comparison of the Two Analyses 151
4.6 Web Deformation at Collapse 158