Progressive collapse: the case of composite steel-concrete frames

Residual strength and alternate load paths are two fundamental design strategies to ensure adequate resistance against progressive collapse of structures. This paper presents an experimental study carried out on two full-scale steel and concrete composite frames to investigate their structural behaviour in case of a column collapse. The study focusses on the redundancy of the structure as provided by the beam-slab floor system as well as by the ductile beam-to-column joints. The specimens were ground floor sub-frames ‘extracted’ from two reference buildings designed in accordance to the Eurocodes. The frames have the same overall dimensions, but a different, symmetric and asymmetric, configuration of the column layout. In both tests, the collapse of an internal column was simulated. The paper presents the main features of the frames and the principal outcomes of the test on the symmetric frame

Steel-concrete frames under the column loss scenario: An experimental study

Accidental events, such as impact loading or explosions, are rare events with a very low probability of occurrence. However, their effects often lead to very high human losses and economic consequences. An adequate design against these events should reduce the risk for the life of the occupancy, minimize the damage extension and enable a quick rebuilding and reuse. A structure fulfilling these requirements is ‘robust’. Different strategies can be pursued for accidental events, and among them, methods based on the residual strength or the alternate load path are frequently adopted because applicable to a vast range of structures. Adequate design strategies based on them require an in-deep knowledge of load transfer mechanisms from the damaged to the undamaged part of the structure. As to the frames, the important role of joint ductility was pointed out in recent studies. Besides, the flooring systems substantially affect the spread of the damage, but the research on this subject is still very limited. The present study focuses on steel-concrete composite frames under the column loss scenario. It aims to better understand the influence of both frame continuity and floor systems in the development of 3D membrane action. Two geometrically different 3D steel-concrete composite full-scale substructures were extracted from reference buildings and tested simulating the column collapse scenario. This paper illustrates the preparatory studies, the main features of the specimens and the outcomes of the first test. The test provided an insight in the need for an enhanced design of joints and pointed out the key features of the response of the floor system

Long-term behaviour of composite steel-concrete structures: an overview of the state of the art

This paper presents the current state of the art on the modelling and experimental work dealing with the long-term behaviour of composite steel-concrete structures and how this affects the response at service and ultimate conditions. The structural elements considered include columns, slabs and beams. In the latter case, only H-shaped or box steel sections with a solid and composite slabs have been considered. In the initial part of the paper considerations on the time-dependent behaviour of the concrete are provided for each structural element to account for the different drying conditions which, for example, occur in the presence of the hollow sections in columns and of the steel deck in floor systems. When presenting previous work on the long-term response of composite columns particular attention is placed on the influence of time effects on the ultimate response, considerations on confinement at service conditions and creep buckling. Only brief considerations are provided for the long-term response of composite slabs because of the very limited work carried out in this area. Despite this, recent research dealing with the development of shrinkage gradients through the thickness of slabs cast on profiled sheeting is provided. Considerations on the work carried out to date on composite beams are presented with particular focus given to design related issues, such as the determination of the concrete slab effective widths, shear-lag effects, influence of time effects on the ultimate response, prestressing and buckling. The paper concludes with recommendations for future research work to be carried out in this area

Design considerations on the long-term behaviour of composite steel-concrete bridges

This paper deals with the service behaviour of composite steel-concrete bridges, with particular attention devoted to how this is influenced by the time-dependent behaviour of the concrete, such as creep and shrinkage. The paper outlines some of the main aspects which need to be addressed in their service design, which include the evaluation of the influence of creep and shrinkage on the stress state and deformations in-duced in the concrete slab and steel girder, and how these vary with time when the composite bridge is sub-jected to external static loads, geometrical actions and shrinkage effects. Other significant design considera-tions considered focus on how shear-lag effects, the shear deformability of the steel girder and different casting sequences specified during construction affect the deformations and stress distributions of a composite steel-concrete bridge over time

An experimental evaluation of the performance of a smart-beam system.

A research effort has been launched at the University of Trento, aimed at developing an innovative distributed construction system based on smart prefabricated concrete elements allowing for real-time condition assessment of civil infrastructures. So far, two reduced-scale prototypes have been produced, each consisting of a 0.2×0.3×5.6 m RC beam specifically designed for permanent instrumentation with 8 long-gauge Fiber Optics Sensors (FOS) at the lower edge. The sensors employed are FBG-based and can measure finite displacements both in statics and dynamics. The acquisition module uses a single commercial interrogation unit and a software-controlled optical switch, allowing acquisition of dynamic multi-channel signals from FBG-FOS, with a sample frequency of 625 Hz per channel. The performance of the system is undergoing validation in the laboratory. The scope of the experiment is to correlate changes in the dynamic response of the beams with different damage scenarios, using a direct modal strain approach. Each specimen is dynamically characterized in the undamaged state and in different condition states, simulating different cracking levels. The location and the extent of damage are evaluated through the calculation of damage indices which take into account changes in frequency and in strain-mode-shapes. This paper is a detailed description of the experimental work conducted on one of these prototypes and shows how the damage distribution detected by the system is fully compatible with the damage extent appraised by inspection

Considerations on the long-term behaviour of composite steel-concrete bridges

This paper deals with the service behaviour of composite steel-concrete bridges, with particular attention devoted to how this is influenced by the time-dependent behaviour of the concrete, such as creep and shrinkage. The paper outlines some of the main aspects which need to be addressed in service design, which include the evaluation of the influence of creep and shrinkage on the stress state and deformations induced in the concrete slab and steel girder, and how these vary with time when the composite bridge is subjected to external static loads, geometrical actions and shrinkage effects. Considerations are also provided on howshear-lag effects, the shear deformability of the steel girder and different casting sequences specified during construction affect the deformations and stress distributions of a composite steel-concrete bridge over time