•The energy dissipation of the RCED-BF was almost determined by the RCED brace.•The stiffness of the RCED-BF was dominated by the RCED brace.•With the increase of the maximum structural response, the ...energy dissipation coefficient would decrease continuously.•A value of 1.2 could be taken as the re-centering resistance coefficient.
Traditional steel frames will experience large residual drifts under strong earthquakes. An innovative re-centering energy dissipative (RCED) brace was developed, which was able to pull steel frames back to their initial positions after an earthquake and dissipate energy by a friction damper device. In order to study the re-centering and energy dissipation capacities of RCED braced frame (RCED-BF), a prefabricated steel frame (PSF) and three RCED-BFs were designed and tested. The results show that the RCED-BF almost dissipated all the energy by the RCED brace. The diameter of high-strength bolts affected the energy dissipation capacity of RCED-BF significantly, while that of tendons did not. The maximum theoretical value of the energy dissipation coefficient of RCED-BF was 4, which decreased continuously with the increase of the maximum lateral deformation of RCED-BF. The stiffness of the PSF was fairly small and therefore the stiffness of RCED-BF was dominated by RCED brace. A value of 1.2 could be taken as the re-centering resistance coefficient of the RCED-BF.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
AbstractAs demonstrated by terrorist attacks against the Murrah Building in Oklahoma City and a U.S. Embassy building in Nairobi, Kenya, some structures may be vulnerable to progressive collapse. ...Previous computational studies have shown that floor systems play a key role in redistributing loads during progressive collapse events, but only a few experimental studies support these results. The aim of the current research is to experimentally characterize the behavior of steel-concrete composite floor slabs under column loss scenarios. Two large-scale tests on isolated sections of a steel-framed building were conducted until complete collapse. The two specimens were designed and detailed according to commonly used practices found in buildings in the United States. No special provisions to mitigate progressive collapse were included in the design. The first specimen was an interior 2-×2-bay section, and the second specimen was an exterior 2-×1-bay section. Both specimens were tested under a center column loss scenario. The column was statically removed while the floor slab was uniformly loaded under service load conditions. Because both specimens survived the column removal stage, the slab was subsequently loaded with a uniformly distributed load until total collapse was achieved. Observations from the test program indicate the potential for significant capacity of composite floor systems following column loss.
Most of the approaches to the progressive collapse analysis of steel frames have focused so far on computational methods which try to capture the solution of the system responding to localized ...damage. For the case of progressive collapse, damage is included in the model through the removal of a key element of the structure. The computational difficulty of these approaches, however, makes it very hard for practicing engineers to perform these analyses. For that reason, it is very important for the engineering community to develop simple and reliable analytical tools which could provide useful information on the response of a structure to a column loss. This paper applies a threat-independent analytical method regarding the corner column loss case, which has been presented by the author in previous papers to a wide range of symmetric and non-symmetric steel moment-resisting (sway) frames. The analytical and simple method can indicate the collapse mechanism of a steel frame for the case of a corner column loss through the development of critical ductility curves. The impact of the number of floors, the column removal location, the vertical irregularity and the design of the frames is also studied.
•Progressive collapse modes of steel frames for corner column removal•Column buckling and yielding‐type initiated progressive collapse•Analytical method for the vulnerability assessment of damaged systems•Sensitivity analysis of regular and vertically irregular steel frames•Threat‐independent analytical method for progressive collapse of steel frames
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•Analysis of load redistributions in a structure when a localized fire affects a column.•Tension builds up in the fire-exposed column due to heating-cooling sequence.•This overloads the adjacent ...columns potentially leading to progressive collapse.•The behavior is observed on a twenty-story steel frame building under localized fire.•Fire loading cannot be addressed by an event-independent column loss approach.
In progressive collapse analysis, event-independent column loss is commonly used as a design scenario. Yet this scenario does not account for the fire-induced thermal forces that develop in case of a fire. The thermal forces may cause detrimental load redistributions in the structure, notably during the cooling phase. However, as the response of entire structures during the full course of fires until burnout has received little attention, these effects are not well established. The objective of this paper is to analyze the mechanisms of load redistribution in a structural system comprising a column subjected to localized fire, with a focus on the effects of the cooling phase. Numerical simulations by nonlinear finite element method are used, after validation against experimental data. The observed mechanisms result in tension building up in the fire-exposed column and overloading the adjacent columns in compression. Consequently, the damaged vertical member redistributes a force that is larger than the force initially carried. This can lead to failure of vertical members not directly affected by the fire and trigger a progressive collapse. These mechanisms are parametrically studied on a simple system composed of a column and a linear spring. Major parameters influencing the residual tensile force in the fire-exposed column are the maximum reached temperature and the relative stiffness of the remainder of the structure. The analysis of a twenty-story steel frame building under localized fire attacking one ground level perimeter column confirms the development of these mechanisms in a real design. The results have important implications as they question the validity of an event-independent design scenario for capturing the influence of column failure due to fire loading.
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Simplified calculation model of bearing capacity of wall structure.
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•The steel frame fabricated with CFS composite wall structure was proposed in this paper.•Cyclic loading tests of ...five full-scale specimens were conducted.•A simplified superposition method was used to evaluate the bearing capacity of the proposed wall structures.
In this study, a novel hybrid wall structure of a hot-rolled steel frame fabricated with a cold-formed steel (CFS) composite wall is proposed. Ceramsite concrete is lightweight concrete that is used in CFS composite walls. The seismic performances, including the failure mode, hysteretic behavior, shear capacity, stiffness, ductility, and energy dissipation performance, of four specimens of steel frame fabricated with CFS composite wall and one specimen of conventional CFS composite wall were evaluated under low-cyclic loading. The experimental results showed that the collaborative working performance of the steel frame and infilled CFS composite wall was optimum, and the proposed fabricated wall structure had a significant effect on the bearing capacity, stiffness, and energy dissipation capacity. The infilled CFS composite walls were damaged earlier than the steel frames. The damage was primarily characterized by the compressive failure at the corners of fillers, loss of diaphragm effect, screw connection failure, and bond-slip failure between the CFS framing and fillers. However, the steel frames exhibited no obvious damage, which effectively restrained the infilled CFS composite walls and prevented them from severe collapse. In addition, enhancing the strength of the fillers and increasing the section area of the studs improved the bearing capacity of the structure; however, they were detrimental to the ductility. Wall opening reduced the bearing capacity and initial stiffness of the structure; however, it improved the ductility. Furthermore, a superposition method was used to calculate the bearing capacity of the proposed structure. The calculated results showed a superior accuracy in comparison with the experimental results.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
•The proposed method assesses storey stability of frames with axially deforming beams.•The equivalent springs concept is used to model the lateral stiffness of frame members.•The effect of axial beam ...deformations can significantly affect critical loads.•The local stiffness reduction factor predicts the effect of axial beam deformations.
If the beams in a structural frame are not connected to slabs or other rigid diaphragms, the beams will axially deform when the frame is subjected to lateral loads, reducing the critical loads and increasing local deflections in the structure. The consideration of beam axial deformations always reduces the lateral stiffness of the frame, but has so far been neglected in storey-based stability methods. The lateral stiffness of a semi-braced (tension-only), semi-rigidly connected steel frame accounting for the axial deformations in its connecting beams is derived in this paper. The equations also apply to unbraced frames and/or idealized connections, which are commonly encountered or assumed in practice. It is demonstrated that the effect of beam axial deformation on the lateral stiffness of the frame can conveniently be accounted for using the concept of equivalent series and parallel springs. A lateral stiffness reduction factor is also introduced to predict the effects of beam axial deformations. The theoretical accuracy of the proposed method is verified via finite element analysis and the method is demonstrated via numerical examples. The effect of beam axial deformations on the critical gravity loads of frames was found to be significant in some cases, especially when the ratio of beam axial stiffness to column lateral stiffness is small – that is, within the order of 102. However, axial beam deformations have negligible effects on the critical gravity loads if the ratio is sufficiently large or where rotational buckling governs the failure mode, within the order of 103 or above.
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In this research, the seismic performance of a half-scaled three-storey high strength steel frame with curved knee braces (HSSF-CKB) under extreme earthquakes was investigated through shaking table ...tests. The test results demonstrated that the test structure maintained an encouraging recentring capacity under extreme earthquakes. By replacing the damaged curved knee braces, the structural stiffness was recovered to a certain extent. The failure mode of the test structure was governed by fracture of high strength steel beams, buckling of curved knee braces, and concrete crushing. Furthermore, a previously proposed analytical model for HSSF-CKBs was further validated by the test data.
•A half-scaled, three-storey HSSF-CKB was subjected to simulated extreme earthquakes.•Encouraging recentring capacity of the test structure was observed.•Structural repair was achieved through CKB replacement.•The failure mode of the test structure was identified.•A previously proposed analytical model was further validated.
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This paper presents an accurate and efficient numerical procedure for evaluating the system reliability of steel frames with semi-rigid connections. The ultimate strength and behaviour of the frame ...were predicted using a refined plastic hinge model due to its computational efficiency, whilst the nonlinear behaviour of semi-rigid connections was captured using a three-parameter power model. The statistical properties for the three parameter power model were obtained based on available experimental results. The sensitivity of reliability to the model error was also studied. Monte Carlo simulation was used to estimate the probability of failure and the reliability index of a system. Two example frames subjected to combined gravity and wind loads were examined and their system reliability indices for both strength and serviceability limit states were evaluated based on the randomness in loadings, material and geometric properties and semi-rigid connections. The results indicate that the frame reliability is strongly affected by semi-rigid connections.
•An efficient procedure was proposed for reliability analysis of semi-rigid frames.•The statistical properties of the connection model were obtained.•The reliability sensitivity to the model error was also investigated.•The frame reliability is strongly affected by semi-rigid connections.
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