This paper presents an experimental investigation into end-plate beam column connections for buildings. The work demonstrates that a fourfold 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. (C) 2017 American Society of Civil Engineers.

History has demonstrated that buildings designed to conventional design codes can lack the robustness necessary to withstand localised damage, partial or even complete collapse. This variable performance has led governmental organisations to seek ways of ensuring all buildings of significant size possess a minimum level of robustness. The research community has responded by advancing understanding of how structures behave when subjected to localised damage. Regulations and design recommendations have been developed to help ensure more consistent resilience in all framed buildings of significant size, and rigorous design approaches have been specified for buildings deemed potentially vulnerable to extreme loading events. This paper summarises some of the more important progressive collapse events, to identify key attributes that lead to vulnerability to collapse. Current procedures and guidelines for ensuring a minimum level of performance are reviewed and modelling methods for structures subjected to localised damage are described. These include increasingly sophisticated progressive collapse analysis procedures, including linear static and non-linear static analysis, as well as non-linear static pushover and linear dynamic methods. Finally, fully non-linear dynamic methods are considered. Building connections potentially represent the most vulnerable structural elements in steel-framed buildings; their failure can lead to progressive collapses. Steel connections also present difficulties with respect to frame modelling and this paper highlights benefits and drawbacks of some modelling procedures with respect to their treatment of connections.

This paper is concerned with determining the minimum stand-off distance required to prevent column failures in reinforced concrete framed buildings. This is of interest because column failures can initiate progressive collapse, resulting in mass casualties. A technique is developed to determine the critical range at which failure will occur for a given weight of explosives and thus provide a safe scaled distance. The method is used to carry out a parametric study of a range of reinforced concrete columns of variable dimensions and strengths. The corresponding data were used to predict safe scaled distances for columns (with and without clearing). These values can be used to estimate the minimum stand- off distance required to prevent progressive collapses of buildings that may be subjected to deliberate blast loading.

j1 Michael Byfield Beng, PhD, MIStructE, MICE, CEng School of Civil Engineering and the Environment, University of Southampton, UK j2 Wjesundara Mudalige BEng School of Civil Engineering and the Environment, University of Southampton, UK j3 Colin Morison BSc, MSc, PhD, RSES, CEng, MICE Security and Explosion Effects Division, TPS Consult, Croydon, UK j4 Euan Stoddart BEng, PhD School of Civil Engineering and the Environment, University of Southampton, UK

This 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 response to blast loading, is shown to modify the rotational stiffness in joints which can in turn lead to increased dynamic shear forces. Structural models which oversimplify joint stiffness and which ignore strain-rate effects are shown to lead to potentially unsafe solutions.

This paper introduces the use of rate dependent springs to component-based joint models. This allows strain rate hardening as well as strain rate induced reductions in ductility to be included in component spring models for inclusion in non-linear dynamic analysis. Experimental tests of fin-plate connections are carried out under static and dynamic conditions with loading time as low as 32 ms to failure. The joints were tested under the combined effects of tensile load and rotation in order to simulate the complex conditions experienced by joints during catenary action. The strain rate modifications to the component models of the joint were observed to be able to accurately model strain rate induced hardening, as well as reductions in failure rotation which occur in joints under dynamic conditions.The rate dependent component models were subsequently incorporated directly into sub-frame models to simulate catenary action developed due to the loss of support to a column. The individual failure criteria of the joint components provide for an accurate simulation of the progressive fracture of joints during collapse. The results are compared with the conventional approach in which joints are modelled using axial and rotational springs. The comparison reveals that, for the scenario investigated, the conventional method leads to a 20% overestimation of load capacity, due to the lack of inclusion of dynamic material property effects and moment capacity reductions resulting from prying action and catenary action axial forces. Thus the approach goes some way to developing a more realistic approximation of moment-tension-rotation response through to fracture of joints in whole frame progressive collapse computer simulations. (C) 2012 Elsevier Ltd. All rights reserved.

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 attributable 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. DOI: 10.1061/(ASCE)CF.1943-5509.0000227. (C) 2012 American Society of Civil Engineers.

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.

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 framed buildings. Much of the information on building performance is relevant to today's engineers engaged in the design of buildings to survive blast from terrorist attacks involving a vehicle-borne improvised explosive device.

This paper examines the redistribution of loads following removal of support to columns in multistorey buildings. The common types of alternative load path are discussed, including arching action, double span beam action, catenary actions in the floor system, and alternative load paths through out-rigger trusses installed in higher floors. The tying force method relies on catenary action to redistribute loads in the event of loss of support at lower level. The mechanics of this mechanism are investigated by way of a case study of a steel framed building. The structure comprises composite metal decking floor slabs and composite beams with flexible end-plate connections. The rotation capacity of the connections is determined using the component method and the tying capacity of the connections is determined using a standardised industry design approach. The factor of safety against (progressive) collapse is estimated at between 0.08 and 0.19, depending on the assumptions made concerning slab strength and the dynamic amplification of loads. This study would indicate that the tying force method may not be able to successfully redistribute loads following loss of support to single columns.

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.

This special issue of the highly respected Civil Engineering journal from the Proceedings of the Institution of Civil Engineers looks to study and learn from the catastrophes, collapses and failures that fascinate and horrify the civil engineering community.