Beam to concrete-filled rectangular hollow section column joints using long bolts

peer reviewedThis paper presents a research on a specific type of unstiffened extended end-plate joint used to connect I-shaped beams to concrete-filled rectangular hollow section columns. The main idea is to use long bolts throughout the column to connect the beam end-plates, so avoiding intermediate connecting elements (e.g. a reverse U channel) or special bolts (e.g. blind bolts). However, the use of long bolts for beam-to-column connections is still rare in the construction and no design procedure exists in the Eurocodes; this justifies the pre-sent research. Firstly, a test program within a RFCS European project titled HSS-SERF “High Strength Steel in Seismic Resistant Building Frames”, 2009-2013 was performed. In this project, specimens subjected to sig-nificant bending moments (and shear) or to shear only was defined. Then, analytical developments based on the component approach and aimed at predicting the joint response have been carried out; their validity is demonstrated through comparisons with the tests. Finally, design guidelines have been provided

Fire performance of an unprotected composite beam behaviour with finite beam end restraints, rebar size and locations

The fire performance of steel connections is crucial to provide integrity and stability to floor systems. In full-scale fire tests, the steel frame systems experience large deflections and rotations, which in turn subject the connections to large axial forces and moments. The shear connections, which have limited rotational allowance due to a small gap distance between the beam and the supporting member, exhibit a semi-rigid behavior during fire. Further, the effect of the concrete slab is observed to be beneficial to the deflection behavior of the floor system in several experiments. In this study, the fire performance of a beam with a concrete slab is investigated with varying degrees of rotational rigidity and the tension capacity of the concrete slab with steel rebars. The thermo-mechanical analysis capability of Opensees is utilized

Numerical and Experimental Investigation of a Reference Aluminium Bolted Joint

In the herein presented paper the structural response of aluminium alloy bolted joints under tension is numerically and experimentally investigated. For the purpose of this research activity, the equivalent T-stub reference joint has been used and all special features of the employed structural aluminium have been incorporated into the mechanical model of the component. The proposed finite element model has been next calibrated with regard to test results obtained by an extensive laboratory programme. The aim of the aforementioned research effort was to contribute to the broadening of the knowledge on the behaviour of the aluminium bolted joints under tension by validating and calibrating the proposed numerical model comparing it with the results of a sequence of experimental tests. Certain important aspects of the numerical treatment of the problem, namely, strain-hardening and contact phenomena, along with comparisons to relevant experimental results, are included in the paper. In addition, both the codified failure mechanisms described in Eurocode 9 and the possible theoretical yield patterns have been verified, whereas in the meantime useful conclusions concerning the development of post-elastic failure zones on aluminium flanges of the T-stub have been reached

An investigation of the behavior of header end-plate connections under monotonic loading

In seismically active regions such as Turkey, the context of the nonlinearity provided by a building is based on the behaviors of structural components; beams, columns and their connections constituting the seismic force resisting system of the structure. Of these members, beam-to-column connections can play a considerably important role even if they have a capability of limited stiffness and flexural strength. Structural steel connections are mainly classified as a pinned or a moment connection. However, some beam-to-column connections having limited stiffness and flexural strength, which are called semi-rigid connections such as header end-plate connections designed so as to transmit only shear forces, can be characterized by moment-rotation relationship. This paper investigates the behavior of header end-plate connections using finite element (FE) modeling. The FE models include material, geometrical and contact nonlinearities. FE modeling technique was first verified through the test results of the experimental research performed by Aggarwal (1990). Then the effect of header end-plate thickness upon moment-rotation relationship was investigated. According to the analyses results, in addition to shear stresses, axial tensile stresses have been observed to occur in the bolts at the tension side and thickness of the header end-plate and beam web play a governing role in the development of initial rotational stiffness and the flexural strength of header end-plate connections

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

A probabilistic approach for a T-stub ultimate strength assessment using response-surface approximation

The main goal of the study is to examine and demonstrate the application of a developed probabilistic framework to the analysis of a chosen general type of steel connection component in order to obtain the basic characteristics of its mechanical behaviour with regard to the chosen type of the input geometry and material properties. Accordingly, as a typical representative of the component method proposed by the Eurocode the equivalent T-stub was chosen as a subject of the study. This type of structural element has the capability to address the behaviour of several parts of the connection: column flange in bending, end plate in bending and flange cleat in bending. A method is proposed to determine the probability density function of the ultimate strength using a response-surface approach coupled with FEM applied to a stochastic structural model. The results of a study were processed by means of sensitivity analysis to determine the importance level of the input variables

Assessment of retrofit measures to prevent progressive collapse in steel structures

Man-made hazards, such as fires, explosions, or impacts, may have severe social and economic consequences and, therefore, should be carefully considered during the design of new, as well as, during the retrofitting of existing structures. Among others, these events could induce the progressive collapse of structures, in which the localised failure spreads from the single affected structural component to other parts of the structure. It is important to highlight that most existing structures worldwide have been designed before the introduction of design rules against progressive collapse. Therefore, it is nowadays of paramount importance to identify effective retrofit measures to renovate existing structures and return safer buildings to the community, including explicit design considerations against progressive collapse. The present paper investigates the effectiveness of three different retrofit measures, namely roof-truss, bracing, and cable systems, conceived to increase the structural robustness and hence mitigate the progressive collapse risk in steel structures. A case study steel moment resisting frame (MRF) was studied by performing non-linear static analyses in OpenSees and investigating its response before and after retrofitting. The progressive collapse was simulated by considering central column loss scenarios, and the ability to prevent the spread of failures of the original and retrofitted structures was examined. The present study sheds some light on the effectiveness and limitations of the considered retrofit measures in improving the overall robustness of the frame. The results show that, after the column removal, the original configuration of the selected MRF fails due to column buckling. Therefore, only the roof-truss and bracings strategies effectively improve the frame’s robustness and allow the creation of alternative load paths. Additionally, some critical aspects to be carefully considered in the design of the retrofit measures are indicated

An experimental study of composite effect on the behaviour of beam-column joints subjected to impact load

[EN] This paper presents an experimental study on structural behaviour of composite beam-column joints under a middle column removal scenario. Specimens were subjected to impact loads from an MTS drop-weight testing machine. Two joints with welded unreinforced beam flange and bolted web connections were designed per AISC 360-10. One of the beam-column joints had a thicker composite slab. The joints were restrained by pinned supports at two beam ends, which were connected to rigid A-frames to represent boundary conditions from adjacent structures. Test results indicated that the composite slab significantly affected the impact force due to an increase of inertia. However, other structural responses (especially displacement of the middle column) decreased due to increase of stiffness contributed by the thicker composite slab. The finding was that increasing thickness of composite slab can increase the resistance of composite joint significantly due to increased composite effect. More experimental studies were conducted to investigate other types of joints.Chen, K.; Tan, KH. (2018). An experimental study of composite effect on the behaviour of beam-column joints subjected to impact load. En Proceedings of the 12th International Conference on Advances in Steel-Concrete Composite Structures. ASCCS 2018. Editorial Universitat Politècnica de València. 905-912. https://doi.org/10.4995/ASCCS2018.2018.6952OCS90591

Dynamic Increase Factors for progressive collapse anaylsis of steel structures accounting for column buckling

Man-made hazards, such as fire, explosions, or impacts, may induce the progressive collapse of structures, in which the localised failure spreads from the single affected structural component to other parts of the structure. A typical approach to model progressive collapse consists in performing static column removal analyses considering a Dynamic Increase Factor (DIF), whose determination becomes paramount to account for the dynamic effects related to a sudden column loss scenario. Current recommendations on the definition of such factor mainly consider a beam-type collapse in non-linear analyses, though different mechanisms, e.g., column buckling, may govern progressive collapse events. This paper presents the determination of the DIFs through a numerical procedure for five steel structures with an increasing number of storeys. Both global and local imperfections are modeled to account for the geometric non-linearities of the structure and column buckling. DIF values are obtained considering two different Engineering Demand Parameters (EDPs), suited for describing beam-type and column-type mechanisms respectively. The evaluated DIFs are compared with the values recommended in the current UFC design prescriptions for progressive collapse, and considerations on the choice of the appropriate DIF values are provided