Table Of ContentINSTITUTION OF CIVIL ENGINEERS
Forensic engineering
The investigation of failures
Proceedings of the second international conference on forensic
engineering organized by the Institution of Civil Engineers and held
in London, UK, on 12-13 November 2001
Edited by B.S.Neale
ThomasTelford
Conference organized by Conference Office of the Institution of Civil Engineers on behalf of
the Structural and Building Board.
Technical Committee:
Brian Neale, Health & Safety Executive, UK (Chairman)
Gerlando Butera, Nabarro Nathanson
Dr W Gene Corley, Technical Council on Forensic Engineering, ASCE
Michael Neale, Neale ConsultingEngieners Ltd
Eamon O'Leary, Consultant
Professor Howard Wright, University of Strathclyde
International Scientific Committee ( * = invited)
Mr Mohammad Ayub, Occupational Safety & Health Administration, USA
Mr Kimball J Beasley, Wiss, Janney, Elstner Associates, Inc, USA
Dr Kenneth Carper, Washington Slate University, USA
Professor Kees D'Angremond, TUDelft, The Netherlands
Dr Milos Drdacky, Institute of Theoretical and Applied Mechanics, Academy of Sciences of the
Czech Republic
Professor Haig Gulvanessian, Building Research Establishment, UK
Dr Peter Ho, Incode Pty Ltd, Australia
Mr F S H Ng, Paul Y. - ITC Construction Holdings Ltd, Hong Kong, ROC
Dr I lias Ortega, Ortega & Kanoussi Technologies, Switzerland
Mr Vivian Ramsey*, Keating Chambers, UK
Professor Rob Shepherd, Earthquake Damage Analysis Corporation, USA
Professor Sam Thorburn, UK
Professor Iris Tommelein*, University of California at Berkeley, USA
Professor Jonathan Wood, Structural Studies & Design, UK
Co-sponsored by
The American Society of Civil Engineers Institution of Mechanical Engineers
Institution of Structural Engineers Health and Safety Executive, UK
Published by Thomas Telford Publishing, 1 Heron Quay, London E14 4JD. www.thomastelford.com
First published 2001
A catalogue record for this book is available from the British Library
ISBN: 0 7277 3094 0
© The authors and the Institution of Civil Engineers, unless otherwise stated, 2001
All rights, including translation, reserved. Except as permitted by the Copyright, Designs and Patents Act 1988, no
part of this publication may be reproduced, stored in a retrieval system or transmitted in any form or by any means,
electronic, mechanical, photocopying or otherwise, without the prior written permission of the Publishing Director,
Thomas Telford Publishing, Thomas Telford Ltd, 1 Heron Quay, London E14 4JD.
This book is published on the understanding that the authors are solely responsible for the statements made and
opinions expressed in it and that its publication does not necessarily imply that such statements and/or opinions are
or reflect the views or opinions of the publishers or the Institution of Civil Engineers or the organizers. While every
effort has been made to ensure that the statements made and the opinions expressed in this publication provide a
safe and accurate guide, no liability or responsibility can be accepted in this respect by the authors or publishers.
Printed and bound in Great Britain
Editor's preface
A warm welcome is extended to all delegates attending this Second International Conference
on Forensic Engineering organized by the Institution of Civil Engineers. Welcome also to
readers who were not able to attend. The international flavour of the conference extends from
Hong Kong to Mexico and the USA, and from South Africa to Holland and the UK.
For this year's conference, we welcome the American Society of Civil Engineers (ASCE) as
a co-sponsor, which joins in that role the UK-based, and internationally influential, Institution
of Structural Engineers, Institution of Mechanical Engineers and the Health and Safety
Executive.
The subject of this conference is the investigation of different types of failures of constructed
facilities and learning from investigations of failures. It is aimed at and those who may be
involved in some way, such as civil, structural, and mechanical engineers and architects. In
particular, it is aimed at investigators and those who may have some influence in preventing
failures in the future, both in the short term and also the medium and longer terms through
design, construction, operation, assessment and maintenance of facilities. It will also be of
interest to those who employ such professionals, including owners or occupiers of the
constructed environment, facilities managers and those in the legal professions.
The conference is being held just two months after the attacks in the USA on the Pentagon in
Washington DC, and the World Trade Center in New York which resulted in the subsequent
progressive collapse of the twin towers. It is a time when the events are still very much in
people's minds. It is a time also when the strengths and safety of buildings have come into
focus, with much public discussion. Professional engineers in particular are making informed
contributions to that debate. Structural safety is a focus of this conference, and many papers
discuss levels of safety in a variety of contexts.
The papers in this volume cover a variety of subjects, such as: case studies of failures,
ranging from catastrophic to serviceability failures, including mechanical engineering,
structural engineering (both macro and micro) and geotechnical engineering; failures in a
variety of structures (such as different types of buildings and bridges); failures in a variety of
materials (such as steel, concrete, timber and masonry); claddings and fixings; failures due to
a variety of initiators (including climatic and impact); investigation techniques and tools;
presentation of evidence, for example for insurance, civil and criminal purposes;
responsibility and culpability for failures; learning from failures; acceptable factors of safety,
and the role of codes, including a new parallel development in both Europe and the USA.
A subject close to forensic practitioners, of whatever discipline, is the need to be seen as
credible and professional, with their opinions and outputs taken as sound, appropriate and
reliable. The introduction to the conference, through the Keynote Address (not included in
these proceedings), considers the need for "convincing credibility" and includes descriptions
of the background to and operation of the Council for the Registration of Forensic
Practitioners (CRFP). This is a relatively new body, based in the UK, which is creating a
register of practitioners, who will have to undergo scrutiny with respect to their credibility as
experts before being allowed onto it. The aim is to help both forensic practitioners and those
who employ them. Initially, the CRFP will be involved with forensic scientists.
This 2001 conference is building on the success of the first conference, held on 28-29
September 1998, by recognizing the widening interest in the topic. Thus the broader
sponsorship has been complemented by a call for papers, rather than by inviting papers,
hence each paper has been subject to a review process.
As Chairman of the conference organising committee, I should like to thank all the speakers
and delegates, the co-sponsors, the Institution of Civil Engineers conference office (and in
particular Barbara O'Donoghue and Penny Ryan) for their work with this conference,
Thomas Telford Publishing and also Gerlando Butera, Dr Gene Corley, Eamon O'Leary,
Michael Neale and Professor Howard Wright for their work on the Organizing Committee.
Brian S. Neale
uiLa.il o. i\ecut
Health and Safety Executive
Chairman of the Conference Organizing Committee
Contents
1 Effects of structural integrity on damage from the Oklahoma City,
USA, bombing
W.G. Corley, R.G. Smith and L. J. Colamsso 1
2 Ladbroke Grove crashworthiness accident investigation
A.P. Bright, N. Kirk, S. Manteghi and P.J. Murrell 13
3 A staged forensic approach to resolve geotechnical engineering claims
R.P. Thompson 21
4 Investigation of failures of marble facades on buildings
I.R. Chin 29
5 Material evidence: the forensic investigation of construction and other
geomaterials for civil and criminal cases
I. Sims 39
6 The assessment of mechanical failures
M.J. Neale 51
7 Structural failure and assessment of a department store
M. Holicky 55
8 Forensic evaluation of concrete industrial slabs-on-grade
S.M. Tarr and W.G. Corley 65
9 Failure prevention in the construction project
I. Ortega 75
10 Mitigation of failures due to inappropriate loading during construction
- a European code
B.S. Neale 83
11 Development of the ASCE 37 Construction Loads Standard to mitigate
construction failures
J.F. Duntemann and R.T. Ratay 93
12 Case study: design, construction and serviceability issues for a precast
concrete facade subject to hurricane-force wind loads
M.K. Schmidt and I.R. Chin 101
13 The application of logic to evidence
J. McCullough 109
14 Technically yes, but... Forensic engineering and insurance
R. Radevsky 119
15 Who pays?: Culpability of experts for building failures in Singapore
A.M. Netto and A. Christudason 127
16 A selection of forensic engineering cases
D. Wassermann 133
17 Post-mortem seismic evaluation of an office building
R. Shepherd 141
18 Imminent collapse of wood structures affected by decay
K.B. Simons 149
19 Investigation into the collapse of Injaka Bridge, South Africa
F. Rowley 159
20 Architects: What can they learn from forensic engineers?
K.L. Carper 169
21 Learning from failures - experience, achievements and prospects
M. Drdacky 175
22 Advanced method to control the safety factor of a civil structure after
a collision
A. deBoer 185
23 Collapse: the erosion of factors of safety to 0.999
J.G.M. Wood 195
24 A knowledge based survey of buildings for structural reliability
evaluations
R.E. Gori 203
25 Investigation and repair of an improperly constructed masonry
barrier wall system
T.M. Krauth, W.T. Ruth and D.W. Vannoy 213
Poster Paper: Assessing building wall system failures
K.J. Beasley and D.R. Stieve 221
Effects of structural integrity on damage from the
Oklahoma City, USA bombing
DR. W. GENE CORLEY, Senior Vice President
Construction Technology Laboratories, Inc., Skokie, Illinois, USA
ROBERT G. SMITH, Technical Consultant
Erico, Inc., Solon, Ohio, USA
LOUIS J. COLARUSSO, Senior Development Engineer
Erico, Inc., Solon, Ohio, USA
ABSTRACT
Starting in 1989 (Ref. 1), the ACI Building Code began requiring integrity reinforcement
at the perimeters of all buildings and at all slab column intersections. The Commentary to
Section 7.13 states that the purpose of this reinforcement is
"to improve the redundancy and ductility in structures so
that damage to major element be confined to a
relatively small area and the structure will....maintain
overall stability."
This paper reviews requirements for structural integrity reinforcement after 1989,
describes a case study of blast-damage to the Murrah Federal Building in Oklahoma City,
and shows how the use of full capacity butt splices could have greatly reduced the
casualties in that blast.
INTRODUCTION
Required Integrity Reinforcement
Since 1989, requirements for structural integrity reinforcement have been listed in Section
7.13 of the ACI Building Code (Ref. 1). In general, Section 7.13 requires one-sixth to one-
quarter of the reinforcement in perimeter beams to be continuous about the building. In
addition, Section 13.4.8.5 requires two bottom bars in each direction be carried through
columns continuously or anchored within the columns.
The purpose of integrity reinforcement for both spandrel beams and slab column
intersections, is to provide a small capacity, even after failure of a column or slab at any
one location.
In Chapter 21, toughness is required throughout the structure for seismic resistance, to
obtain required toughness, Section R21.3.2 states the following:
"Lap splices are prohibited at regions where flexural
yielding is anticipated because splices are not reliable
under cyclic loading into the inelastic range."
Oklahoma City Bombing
In 1995, the Murrah Federal Office Building in Oklahoma City was heavily damaged by a
terrorist bomb blast (Ref. 2). A forensic investigation of damage to the Murrah Building
disclosed that failure occurred in three columns supporting a transfer girder on the north
Forensic engineering: the investigation of failures. Thomas Telford, London, 2001.
2 FORENSIC ENGINEERING: INVESTIGATION OF FAILURES
side of the building. One of these columns was destroyed by brisance or shattering while
the adjacent two failed in shear. After losing support from the three columns,
approximately 50 percent of the floor area of the building collapsed, producing a large
number of casualties. Details of the forensic investigation are reported in Ref 2.
A photo of the Murrah Building prior to the terrorist attack is shown in Fig. 1. The
transfer girder supported on four intermediate columns can be seen just below the glass
curtain wall.
Fig. 2 shows a drawing of the building north elevation with the explosive-laden truck
parked in the street beside it. Also shown in the figure is the resulting crater. Fig. 3 shows
a plan view of the crater and location of the column nearest the truck. As reported in Ref.
2, a bomb having an explosive power equal to approximately 4,000 lbs. of trinitrotoluene
(TNT) was detonated in the truck.
Analysis of damage in the field and calculation of effects of the explosion determined that
the nearest column, G20 as identified in Fig. 4, would have been destroyed by brisance or
shattering. Approximately 40 ft each side of the column that was destroyed, adjacent
columns were found to have exceed their shear strength, but been approximately at their
flexural capacity. As a result, the adjacent columns failed in shear, thereby leaving the
spandrel beam without support for distance of approximately 160 ft.
As indicated in Fig. 5, three of the transfer girder top bars were continuous but none of the
bottom bars were. A similar pattern was present in spandrel girders above the third floor
as shown in Fig. 5. Consequently, there was no effective integrity reinforcement in this
building. It must be noted that at the time the building was built, no integrity
reinforcement was required. Analyses show that this building met or exceeded code
requirements in every way that was checked.
Ref. 2 indicated that shear failures of two of the three columns could have been prevented
if only a small amount of hoop steel had been provided. It is also possible that the column
nearest the bomb could have been saved if full confinement reinforcement had been
provided. However, for purposes of this discussion, it will be assumed that the column
nearest the truck would be destroyed by brisance.
In Ref. 2, an analysis is made with one column removed. The three mechanisms that could
develop after removal of one column are shown in Fig. 6. Calculations indicate that
Mechanism 2 results in a capacity of approximately 60 to 70 lbs. per sq ft floor above the
spandrel beam. This is significantly less that the approximately 110 lbs. per sq ft of self-
weight plus live load that existed in the building. Consequently, removal of any one
column supporting the as-built transfer girder would cause failure of all of the floors above
over a length of about 80 ft.
FULL CAPACITY MECHANICAL BUTT SPLICES
Reduction in Loss
In the 1999 ACI Code, (Ref.3) full capacity mechanical butt splices were recognized for
the first time. Classified as Type 2 mechanical splices in Section 21.2.6.1(b), they are
required to "develop the specified tensile strength of the spliced bar." ACI 318-99 permits
use of Type 2 splices at any location, including hinging regions. Consequently, Type 2 full
capacity mechanical butt splices can be used to connect integrity reinforcement and
improve the blast and/or seismic resistance of concrete structures.
If integrity reinforcement in the spandrel beams of the Murrah Building was maximized by
making all of the bars continuous with full capacity mechanical butt splices, significant
increase in the capacity of Mechanism 2 of Fig. 6 would be realized. Using Mechanism 2
PAPER 1: CORLEY, SMITH AND COLARUSSO 3
with 100 percent of the bars spliced with full capacity mechanical butt splices, calculated
capacity of the building would be at least 140 lbs. per sq ft. Unit weight of the building,
including some live load, is approximately 110 lbs. per sq ft. Consequently, even if one
column had been removed the building would not have collapsed.
Although collapse of the building frame would have a high probability of being prevented
by making all of the reinforcement in spandrels continuous, several of the floors would be
destroyed as a result of brisance. Consequently, the reduction in catastrophic damage to
the building would not be 100 percent, but is estimated to be approximately 80 percent.
As indicated in Ref. 2, almost all of the casualties were the result of building collapse, not
air blast. Consequently, if building collapse is reduced by 80 percent, casualties would be
reduced by a similar amount.
Cost Analysis
To determine what the additional cost might be if full capacity mechanical butt splices had
been used in the Murrah Building, a review of cost studies done by Cagley and Associates
and reported in Ref. 4 was made. Fig. 7, courtesy of ERICO, shows their full capacity butt
splices being installed on bars approximately the size of those used in the Murrah
Building. Fig. 8 shows a close-up of an ERICO full capacity butt splice. As can be seen,
these splices are relatively small in size and not very difficult to install.
Cost analyses done by Cagley and Associates (Ref. 4) show that the increased cost of
mechanical butt splices over lap splices in a 12-story parking deck was less than 'A of 1
percent of the cost of the building. In an office structure, such as the Murrah Federal
Building, the cost of mechanical splices would be even a smaller percentage of the total
cost. Considering that use of full capacity butt splices could be limited to only that portion
of the building exposed to the street where the bomb was detonated, estimated total cost
differences are approximately 1/8 of the total cost of the building. This cost difference is
insignificant.
SUMMARY
This paper discusses the potential for using mechanical full capacity butt splices to
increase blast and earthquake resistance of buildings. The need for integrity reinforcement
to reduce damage in a building when unanticipated intense loads destroy a single element
is discussed. A prohibition against lap splices in hinging regions of buildings designed to
resist earthquakes is noted.
Terrorist bombing of the Murrah Federal Building in Oklahoma City is used as a case
study. It is shown that without integrity reinforcement, strengthening of columns could
only reduce damage by about 50 percent. However, if full capacity mechanical butt splices
had been used to make all of the spandrel beam reinforcement continuous, collapse of the
building would have been reduced by an estimated 80 percent with a similar reduction in
casualties. The estimated additional cost to provide this continuous reinforcement is
approximately 1/8 of 1 percent, much less than the variation in estimating the cost to
construct the building.
4 FORENSIC ENGINEERING: INVESTIGATION OF FAILURES
Fig. 1 Murrah Building Prior to Blast.
