AbstractThis paper presents experimental studies on the performance of planar moment steel frames with one column heated. The novelty of these tests is that the influences of key stages in the ...response of the heated column under gravity loading, including postbuckling and cooling phase after fire, on the progressive collapse resistance of steel frames were studied. Gas temperatures of the furnace, structural member temperatures, displacements, and strains in certain locations of the test frames were monitored during the tests. The test results show that steel columns with strong constraints from steel beams in a frame may fail in a quasi-static manner under fire, whereas those with weak constraints or large load ratios may fail with dynamic effects. In addition, the final equilibrium vertical displacement at the top of the column after sudden buckling can be even larger than the final displacement associated with gradual column removal. Moreover, in the cooling phase after fire further damage may occur to other members of the frame because of the thermal contraction of the heated column.
Many recent research studies focused on the development of innovative seismic resilient structures by chasing the objectives of minimising both seismic damage and repair time, hence allowing the ...definition of structures able to go back to the undamaged, fully functional condition, in a short time. In this context, the present study investigates an innovative type of self-centring damage-free steel column base (CB) connection and its beneficial effects when used within steel moment-resisting frames (MRFs). The proposed connection consists of a rocking column equipped with a combination of friction devices, providing energy dissipation capacity, and post-tensioned bars with disk springs, introducing restoring forces in the joint. Contrary to conventional steel CBs, the proposed connection exhibits moment–rotation behaviours that can be described by simple analytical equations, allowing the definition of an easy-to-apply design procedure. Numerical models of the connection, developed in OpenSees, are validated against experimental results and successively implemented within a four-storey case study steel MRF. Incremental Dynamic Analyses are performed to derive the samples of the demand for the engineering demand parameters of interest while accounting for the record-to-record variability. Fragility Curves show the effectiveness of the proposed solution in reducing the residual storey drifts and in protecting the first-storey columns from damage, hence providing significant advantages in terms of repairability, and hence resilience of the structure with a negligible increase on the overall cost. The results show that the damage-free behaviour of the CBs is a key requirement when self-centring of MRFs is a design objective.
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•Innovative type of self-centring damage-free steel column base connection.•Analytical Design procedure for moment-rotation response of the connection.•Validated OpenSees model of the column base against experimental results.•Incremental Dynamic Analyses and Fragility Curves.•Enhanced structural resilience through localised self-centring systems.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
•A 3D steel frame was analysed to study its resistance to fire-induced progressive collapse.•It is feasible to perform an explicit dynamic analysis for structures in fire by scaling a real fire time ...to seconds.•The uneven load transferring in the two planar direction plays a key role in the collapse modes.•The frame withstands the fire of single columns heated (load ratio of 0.25) but collapses for a higher load ratio of 0.5.•The frame collapses for a corner fire and long edge fire due to the uneven load redistribution.
This paper numerically investigates progressive collapse resistance of three-dimensional steel frames with reinforced concrete slabs exposed to localized fire using LS-DYNA. An explicit dynamic analysis is carried out and the real fire time is scaled down to save the computational cost. The prototype of the model is based on the eight-storey building in Cardington tests. The scenario of heating individual columns on the ground floor is first studied followed by a sever case of simultaneously heating four columns in one compartment. The collapse modes and load redistribution scheme of the frame subjected to different load ratios and fire locations are investigated. The modelling parameters such as mesh size, initial imperfection, timescale are first studied by validating against the fire test data. It is found that the mesh size has little influence on the responses of members at elevated temperature. The initial imperfection has significant effect on the load-bearing capacity of columns. The quasi-static behaviour of structures under a fire duration of hours can be simulated in a dynamic analysis by being scaled to seconds without causing oscillation of responses. The numerical results of the 3D frame show that the frame does not collapse in the case of single column heated for a fire design load (load ratio of 0.25 for columns). By increasing the load ratio to 0.5 as for the ambient design, progressive collapse occurs. For a fire of four columns heated, the frame collapses for the corner bay fire and long edge bay fire but withstands for the internal and short edge bay fires. The collapse modes are dominated by the uneven load redistribution in the two horizontal directions and the fire location, which cannot be simulated by a 2D model. The loads previously sustained by the buckled heated column are transferred more along the short span than the long span. The critical temperature of a column in a frame is significantly lower than that given in EC3, due to the fact that the translational and rotational restraint increase its load ratio and reduce its effective length, respectively. The critical temperature for the global collapse of the frame is about 50–100°C higher than that of individual heated columns.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
In this paper, two experiments were carried out to investigate the structural performance of the steel frame with CLT wall with damping system. In the first experiments, it was shown that sandwiching ...an aluminum-sprayed plate in bolt friction joints caused the slip of the joint and improved structural toughness. In the second experiments, by improving the details of the bolt joints and drift-pin joints, the initial stiffness was increased. Also, the damping effect was confirmed by comparing the energy absorption.
AbstractShake-table tests, subjected to mainshock–aftershock sequences, were conducted on a 1/3-scaled 3-story steel frame equipped with self-centering viscous-hysteretic devices (SC-VHDs) and its ...primary frame to investigate the effect of the aftershock on seismic performance. It was found that the SC-VHD can effectively reduce 30%–50% of the peak drift and 50%–80% of the residual drift, respectively. Additionally, the peak and residual drifts of the 3-story primary frame under the mainshock–aftershock sequences were more than those under the mainshock-only sequences, while the peak and residual drifts of the 3-story SC-VHD frame under the mainshock-only and mainshock–aftershock sequences were basically the same. A numerical simulation method for the SC-VHD frame was further developed and validated, based on which 6-, 9-, and 12-story SC-VHD frames were analyzed to investigate the seismic performance of medium- high-rise SC-VHD frames. Both shake-table tests and numerical analysis indicate that the peak and residual drifts of the 3-, 6-, 9-, and 12-story SC-VHD frames can meet the design objective under the mainshock–aftershock sequences.
Under severe earthquakes, a significant number of unexpected plastic hinges and brittle failure were found in conventional rigid beam to column welded connections of steel frames. To improve the ...seismic performance of steel frames, an innovative prefabricated self-centering beam to column (SCBC) connection was proposed and experimentally validated in this paper. The SCBC connection consisted of disc springs at the bottom flange of beam and a rotation friction hinge (RFH) at the beam end. The bottom disc springs could not contact with slab systems and provided restoring moment, whereas the RFH was designed to dissipate seismic energy. Firstly, its configuration form and design methodology were introduced. Then cyclic tests of a 1/4 scale SCBC connection specimen was carried out and the responses of the SCBC connection was compared to that of the RFH. Finally, the restoring force model of the SCBC connection was established through theoretical analysis. The experimental and analytical results demonstrated full flag-shaped hysteretic curves of the SCBC connection under cyclic loadings, verifying the desirable energy dissipation capacity and reliable self-centering capability of the SCBC connection. The calculation results based on the restoring force model were in good agreement with the test results, showing that the proposed restoring force model could reasonably predict the hysteretic behavior of the SCBC connection.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
•A seismic life-cycle cost (SLCC) analysis framework is proposed.•Cost-based fragility analysis is used instead of the performance-based one.•SLCC assesses costs over lifetime considering the ...equipped time of SPW.•A method is proposed to simplify the computing works of SLCC.
The steel panel wall (SPW) has been proposed for strengthening mid-rise and high-rise steel frame buildings. Compared with the steel plate shear wall (SPSW), the SPW is connected to the beam with only high-strength bolts to avoid high flexural and axial demands in the boundary columns due to tension field action. The bolt-connected SPW can be easily installed and disassembled and can be used in seismic retrofit or repair. The SPW can be freely placed into the steel frame to support architectural demands. In evaluating the SPW for reducing the damage cost of steel frame buildings, the life-cycle cost analysis (LCCA) approach is used to assess the final cost of the structure over the lifetime considering both increased initial cost and reduced damage/repair cost. In this paper, a seismic life-cycle cost (SLCC) assessment method is proposed for steel frames equipped with steel panel wall (SPWF) structures. Cost-based seismic fragility analysis is presented in this method to consider the uncertainty between failure probability and damage cost, and various types of uncertainty are included. Numerical investigations are performed to examine the efficiency and feasibility of the proposed method. Finally, a preliminary method is presented for simplification of the relationship between the SLCC and structural parameter, and the aim of the method is the use of a simple function instead of complicated and large computing tasks. This idea offers a new method for future engineering practice and structural optimization.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
A steel frame building was tested by physically removing four first story columns from one of the perimeter frames prior to building's scheduled demolition. The purpose of the field experiment was to ...simulate sudden column loss in buildings that may cause progressive collapse. Another objective was to investigate the load redistribution within the building after each column removal. The measured experimental data and observed performance of the building was valuable because it is very difficult and cost-prohibitive to build and test three-dimensional full-scale building specimens in the laboratory. Generally, the design code requirements prescribe simplified analysis procedures involving instantaneous removal of certain critical columns in a building. Design methodologies and simplified analysis procedures recommended in the design guidelines were also evaluated using the experimental data. In this study, two and three-dimensional models of the building were developed and analyzed to simulate the progressive collapse response. The effectiveness of the analysis procedures was evaluated by comparing with the experimental data.
•A steel frame building was tested by physically removing four first story columns.•2-D and 3-D models of the building were analyzed.•Calculated demand-to-capacity ratios exceeded the specified limits.•Although analytically collapse was predicted, test building did not collapse.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
•We have proposed a spatial prefabricated self-centering steel frame (PSCF).•The spatial PSCF has avoided on-site aerial tension of steel strands.•A new floor slab is developed to accommodate the ...frame expansion.•Web friction devices are installed to dissipate energy and protect main structure.•Design targets of the PSCF have been proposed to conduct performance-based design.
The structural system of prefabricated self-centering steel frame (PSCF) was proposed previously by the author. Experimental studies focusing on PSCF connections, plane frame, overall structures as well as the numerical simulations were conducted. Compared with the self-centering steel frame (SCF), the PSCF has avoided the on-site aerial tension of steel strands and simultaneously achieves similar seismic performance as well as self-centering capacity. While the self-centering function of both PSCF and SCF may be restrained by conventional floor systems. Based on this thesis, a spatial PSCF with a new type of floor system containing sliding secondary beams was proposed in this paper to enable the frame expansion, and pseudo-dynamic and quasi-static tests toward it were conducted. The test results indicated that the proposed new floor system was reliable and feasible in accommodating the frame expansion. Meanwhile, the spatial PSCF with the new floor system has a favorable self-centering capacity, reliable gap-opening mechanism, superior seismic performance and enough redundancy to withstand multiple aftershocks.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
•Six full-scale single-bay two-story ordinary and high strength steel (HSS) frames were tested under cyclic loading.•Cover-plate reinforced connections were employed in all the frames to improve ...their performance.•Global responses including observations, hysteresis and backbone curves, deformation and energy dissipation were presented.•The frames using compact or noncompact HSS columns accommodated an overall drift ratio of 4%.•The frame using slender HSS columns experienced about 50% deterioration in lateral strength at 3% overall drift ratio.
Cyclic tests were performed on six full-scale single-bay two-story frames, including one frame using Q345 (fy=345MPa) ordinary strength steels, and another five frames using Q460 (fy=460MPa) high strength steels or Q890 (fy=890MPa) ultra-high strength steels in only columns or both beams and columns. The frames were designed to provide strength and ductility for earthquake resistance with energy dissipation located at member ends by flexural yielding, and panel zones by shear yielding. Cover-plate reinforced connections were specified to relocate the plastic hinge beyond the nose of cover plates and away from the face of column to improve connection performance. As the first of two companion papers on this experimental study, this paper presents detailed procedures to design the specimens, and then provides the outline of test program including test setup, loading protocol and instrumentation. After that, global responses in experimental results, including test observations of each specimen throughout the test and their hysteresis and backbone curves, deformation and energy dissipation in each half-cycle and in total, were described. The results evidenced that satisfactory seismic behavior was identified by using high strength steel columns with compact or noncompact sections in frames, and the maximum overall drift ratio reached 4.0%. Even the frame with ultra-high strength steel columns with slender sections accommodated an overall drift ratio of 3.0%. No soft-story mechanism occurred in all the frames. Local responses in beams, columns and connections, especially in panel zones, will be examined in the second companion paper.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
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