M.P. Byfield

Murrah Building Collapse: Reassessment of the Transfer Girder

The bombing of the Alfred P. Murrah Federal Building caused a progressive collapse that consumed nearly one half of the building, killing 168 people. The use of a transfer girder along the front face of the building is often cited as the prime reason for the severity of the incident, although this paper provides evidence that suggests the transfer girder may not have been responsible. A method of predicting column failures due to blast is introduced and used to accurately predict the column failure pattern observed during the forensic investigation. The frame was adjusted with the transfer girder replaced with a conventional beam column arrangement. The failure pattern of the reconfigured building indicates that the extent of the collapse would be largely unchanged. This finding has important implications for the design of buildings that may be subjected to accidental or malicious damage. It is argued that the other buildings have demonstrated an ability to survive similar incidents and that the Murrah Building was vulnerable because it combined a glazed facade with open plan architecture, in addition to lacking alternative load paths capable of redistributing loads after multiple column failures

Building Robustness Research during World War II

This study reviews research carried out in the U.K. to understand and improve the robustness of buildings when subject to blast from high explosive bombs. The work concentrates on the performance of ordinary civilian buildings, with particular emphasis on multistory buildings framed in either reinforced concrete or structural steelwork. At that time, some of the data were used to enhance conventional building construction, principally on government buildings, and some were used to aid postwar hardened building construction. The two main U.K. researchers whose work is the basis of this paper (Professor Sir Dermot Christopherson and Professor Lord Baker) identified a number of building weaknesses that led to local or progressive collapse, including connections in steel-framed buildings, as well as detailing weaknesses in reinforced concrete constructions. This paper reviews these features, as well as those that added resilience to bomb damage, with particular emphasis to the use of masonry infill panels in ...

A Numerical Model for Predicting the Bending Strength of Larssen Steel Sheet Piles

Larssen piles are U-shaped in cross-section and are connected together by sliding joints to form quay walls, cofferdams and other types of retaining walls. Since the sliding joints are located along the centreline of the pile wall, slippage of one pile relative to another can lead to a 70% reduction in elastic bending strength. This slippage can be partially prevented by installing the piles in pairs, with the interlocks ‘crimped’ to prevent inter-pile movement. However, like non-crimped piles, the bending strength is difficult to predict since slip still can occur between the crimped pile pairs. This paper presents a numerical model for predicting the bending stresses and crimp forces in crimped pairs of Larssen piles. Tests are also reported on one-sixth scale pile walls constructed from extruded aluminium Larssen piles, with the results compared with those from the numerical model. Stress predictions from the numerical model are shown to be in close agreement with the experimental results, and can be used to economise on the crimping necessary to achieve the full composite bending strength.

Blast Modeling of Steel Frames with Simple Connections

AbstractThis paper is concerned with the problem that structural joints in whole-frame models cannot, at present, be replicated in sufficiently minute detail to realistically represent their behavior. It is well recognized that the structural joints represent the weakest link in building frames; therefore, frame models are potentially inaccurate in a critical area. The impact of this research is in the development of an accurate frame modeling approach that achieves a realistic treatment of joint response without significantly increasing the computational requirements. The method utilizes simplified connection models using rate-dependent nonlinear springs which, when assembled, allow a realistic representation of the connection behavior. The method is found to be capable of modeling strain-rate dependent material property effects with a high degree of accuracy and coping adequately with the force and rotation combinations which develop during blast response. Increased rotation rate, which occurs as a resp...

Analysis of reduced modulus action in U-section steel sheet piles

U-section steel sheet piles are commonly used for constructing retaining walls in marine environments and have been in widespread use throughout the world for most of the 20th century. Relatively recently, concern has been raised about the bending strength of this pile section, because U-section piles are connected together by interlocking joints located along the pile wall centreline. As the piles resist bending moments, inter-pile movement can significantly increase bending stresses. When this occurs, the wall is said to have exhibited reduced modulus action (RMA), reducing the bending strength and stiffness below the fully composite values normally assumed during design. In view of this concern, the recently introduced Eurocode 3: Part 5 has introduced strength reduction factors to account for the effect of RMA during design. The work presented herein has been carried out in order to provide more information as to the values that should be selected for these reduction factors. The work is based on the experimental testing of one-eighth-scale miniature piles.

Composite connections at perimeter locations in unpropped composite floors

Of all new multi-storey buildings in the UK, approximately 40% use composite floor construction. This type of construction is structurally efficient because it exploits the tensile resistance of the steel beams and the compressive resistance of the concrete slabs. This composite action allows shallower steel beams to be used because of the increased flexural strength and stiffness. Research has shown that more savings, approximately 25% on weight or depth of individual beams, can be achieved if composite connections are adopted. With such connections, increased, moment of resistance can be achieved by introducing dedicated slab reinforcement, which acts like an additional row of bolts in an extended end plate. However, the use of composite connections is not widespread. This is due in part to two problems addressed herein. Firstly, the existing composite connections design and detailing rules can currently only be used with beams that are propped during construction, whereas unpropped construction is generally a preferred and more economic construction method. For applications where it is important to minimise beam depth, even if this is at the expense of heavier perimeter columns, practical details are also required for single sided moment resisting connections. In order to investigate these problems, a test was carried out at the Building Research Establishment, UK, on a full-scale unpropped sub-frame that incorporated a novel exterior column connection. The results of this test, with an emphasis on the exterior column connection, are presented in this paper.

Calibration of design procedures for steel plate girder design

Test data for plate girders failing in shear have been used as the basis for a calibration of the two design procedures given in Eurocode 3 (EC3). The shear buckling resistances predicted by the simple post-critical and tension field methods were used in a modification of the Annex Z method for determining the numerical values of partial safety factors on resistance to achieve the target reliability of the Code. The analyses demonstrated that plate girder design falls well short of the recommended target reliability and an adjustment to the design methods is therefore proposed.

Robustness of Beam-to-Column End-Plate Moment Connections with Stainless Steel Bolts Subjected to High Rates of Loading

This paper presents an experimental investigation into end-plate beam column connections for buildings. The work demonstrates that a four-fold increase in the energy absorbed to failure can be achieved by replacing carbon steel bolts with their stainless steel counterparts. Experimental tests were carried out under load control and these provided the opportunity to observe the time required for connection fracture. Under quasi-static loading, connections tested with stainless steel bolts showed clearly visible signs of distress prior to failure; whereas the carbon-steel bolted equivalents provided no warning of failure prior to brittle fracture. Experimental tests were carried out on bolts and these showed strain rate induced strength enhancements. End-plate connections were also tested under high strain rates. Loading rate was not observed to significantly affect the performance of stainless steel bolted connections. However, carbon-steel bolted connections were observed to weaken under high strain rates, therefore dynamically increased material properties did not always translate into increase connection strength. The design strengths predicted using Eurocode 3 were found to be in good agreement with the experimentally observed values under quasi-static loading for both bolt types. Under high-strain rate conditions the Eurocode 3 method was also found to provide a good prediction for stainless steel bolted connections; but was found to over predict for carbon-steel connections. The simple modification of replacing carbon-steel bolts with their stainless steel equivalents is shown to be an effective way of improving the performance of industry standard connections. This modification is of relevance to the design of buildings and other structures in which the ductility is of high importance, for example in structures which may need to resist transient loads from blast or impact.

Load Redistribution Using Compressive Membrane Action in Reinforced Concrete Buildings

The primary function of any designed structure is to be able to support pre-determined static loads which allow the building to be occupied for its intended use. In the design process the unlikely event that the building is damaged must be considered. Often the focus is directed to the loss of primary loading elements that are fundamental to the integrity of the structure. The damage that is caused as a consequence may propagate causing collapse of surrounding elements culminating with the loss of an extensive proportion of the floor area. To prevent collapse inherent alternative load paths can be utilised. Both the elastic and plastic approved methods for the design of reinforced concrete in modern codes of practice neglect the effect of membrane forces. It has been recognised for some time that the omission of compressive membrane action (CMA), also described as ‘arching action’, can lead to a significant underestimation of load capacity. Previous studies which have attempted to determine if CMA is capable of supporting damaged columns under accidental loading conditions have not had supporting experimental testing of slabs at appropriate span to depth ratios. This paper presents an experimental program conducted on laterally restrained slab strips at approximately half scale. Combined with an analytical study, the extent to which CMA can be used as an effective robustness tool has been assessed.

Reduced Modulus Action in U-Section Steel Sheet Pile Retaining Walls

U-section steel sheet piles are used for constructing retaining walls and they are connected together to form continuous walls using sliding joints located along their centerlines. Interpile movement along these joints can, in theory, reduce strength by 55% and stiffness by 70%, in comparison with the performance of piles in which no slip occurs (full composite action). This problem of interlock slippage is known as reduced modulus action (RMA). Despite the potential for this problem, it is common practice in many countries to ignore RMA in design, although the exact conditions governing when it becomes a design issue are not fully understood. This paper presents results from an investigation into this problem using experimental tests carried out using miniature piles. Unlike previous studies these tests were carried out using a similar load arrangement to that found in practice. The investigation indicates that the loading configuration affects the development of RMA and that friction between pile interlocks has the potential to mitigate much of the effect of RMA. A numerical model simulating the tests was developed and it has been used to model full-scale piles. The study indicates that many commonly occurring forms of steel sheet pile walls are unlikely to exhibit significant problems from RMA and this is relevant to pile design using Eurocode 3: Part 5.