This paper reports two new tests conducted to augment available data highlighting the structural performance of multistory steel frames under progressive collapse. The investigated steel frames had different geometrie...This paper reports two new tests conducted to augment available data highlighting the structural performance of multistory steel frames under progressive collapse. The investigated steel frames had different geometries, different boundary conditions, different collapse mechanisms, different damping ratios and different connections. Overall, the paper addresses how multistory frames would behave when subjected to local damage or loss of a main structural carrying element. The obtained results can form a data base for nonlinear finite element models. The deformations of the investigated steel frames and failure modes under progressive collapse were predicted from the finite element analysis, with detailed discussions presented.展开更多
This paper investigates the behavior of steel frames under progressive collapse using the finite element method. Non-linear finite element models have been developed and verified against existing data reported in the ...This paper investigates the behavior of steel frames under progressive collapse using the finite element method. Non-linear finite element models have been developed and verified against existing data reported in the literature as well as against tests conducted by the authors. The nonlinear material properties of steel and nonlinear geometry were considered in the finite element models. The validated models were used to perform extensive parametric studies investigating different parameters affecting the behavior of steel frames under progressive collapse. The investigated parameters are comprised of different geometries, different number of stories and different dynamic conditions. The force redistribution and failure modes were evaluated from the finite element analyses, with detailed discussions presented.展开更多
The progressive collapse of steel frame structures under the blast load was investigated using LS-DYNA. The multi-material Eulerian and Lagrangian coupling algorithm was adopted. A flu-id-structure coupling finite ele...The progressive collapse of steel frame structures under the blast load was investigated using LS-DYNA. The multi-material Eulerian and Lagrangian coupling algorithm was adopted. A flu-id-structure coupling finite element model was established which consists of Lagrange element for simulating steel frame structures and concrete ground, multiple ALE element for simulating air and TNT explosive material. Numerical simulations of the blast pressure wave propagation, struc-tural dynamic responses and deformation, and progressive collapse of a five-story steel frame structure in the event of an explosion near above ground were performed. The numerical analysis showed that the Lagrangian and Eulerian coupling algorithm gave good simulations of the shock wave propagation in the mediums and blast load effects on the structure. The columns subjected to blast load may collapse by shear yielding rather than by flexural deformation. The columns and joints of steel beam to column in the front steel frame structure generated enormous plastic defor-mation subjected to intensive blast waves, and columns lost carrying capacity, subsequently lead-ing to the collapse of the whole structure. The approach coupling influence between struc-tural deformation and fluid load well simulated the progressive collapse process of structures, and provided an effective tool for analyzing the collapse mechanism of the steel frame structure under blast load.展开更多
This paper presented a methodology for the analysis and design of steel connections under a double-span connection within the context of preventing progressive collapse. First, various connection models were described...This paper presented a methodology for the analysis and design of steel connections under a double-span connection within the context of preventing progressive collapse. First, various connection models were described and their pros and cons were provided. Then, the load-displacement characteristics of a component-based spring model were described. Thirdly, an experi-mental study on the behaviors of shear tab connections under tension was presented. The main sources of the deformation capacity of the shear tab connections were identified. Finally, a design example of a shear tab connection was provided to illustrate the methodology.展开更多
In this paper,we propose a probabilistic method for analysing the collapse time of steel frame structures in a fire.The method considers the uncertainty of influencing factors.Tornado diagrams are used for sensitivity...In this paper,we propose a probabilistic method for analysing the collapse time of steel frame structures in a fire.The method considers the uncertainty of influencing factors.Tornado diagrams are used for sensitivity analysis of random variables.Structural analysis samples are selected by Monte Carlo method,and the collapse times of different structural samples are calculated by fire time history analysis.A collapse time fragility curve is fitted according to the calculated collapse times of the samples.A reliability index of the collapse time is used as a quantitative standard to evaluate the collapse performance of a steel frame in a fire.Finally,this method is applied to analyse the collapse time fragility of an eight-storey 3 D steel frame structure under different compartment fire scenarios and fire protection levels.According to the collapse time fragility curve,the effects of the different fire scenarios and protection levels on the collapse resistance of the structure under fire are evaluated.展开更多
This study presents the investigation of the approach which was presented by Thaer M.Saeed Alrudaini to provide the alternate load path to redistribute residual loads and preventing from the potential progressive coll...This study presents the investigation of the approach which was presented by Thaer M.Saeed Alrudaini to provide the alternate load path to redistribute residual loads and preventing from the potential progressive collapse of RC buildings.It was proposed to transfer the residual loads upwards above the failed column of RC buildings by vertical cables hanged at the top to a hat steel braced frame seated on top of the building which in turn redistributes the residual loads to the adjacent columns.In this study a ten-storey regular structural building has been considered to investigate progressive collapse potential.Structural design is based on ACI 318-08 concrete building code for special RC frames and the nonlinear dynamic analysis is carried out using SAP2000 software,following UFC4-023-03 document.Nine independent failure scenarios are adopted in the investigation,including six external removal cases in different floors and three removal cases in the first floor.A new detail is proposed by using barrel and wedge to improve residual forces transfer to the cables after removal of the columns.Simulation results show that progressive collapse of building that resulted from potential failure of columns located in floors can be efficiently resisted by using this method.展开更多
This study investigates the efficiency of two types of rehabilitation methods based on economic justification that can lead to logical decision making between the retrofitting schemes. Among various rehabilitation met...This study investigates the efficiency of two types of rehabilitation methods based on economic justification that can lead to logical decision making between the retrofitting schemes. Among various rehabilitation methods, concentric chevron bracing（CCB） and cylindrical friction damper（CFD） were selected. The performance assessment procedure of the frames is divided into two distinct phases. First, the limit state probabilities of the structures before and after rehabilitation are investigated. In the second phase, the seismic risk of structures in terms of life safety and financial losses（decision variables） using the recently published FEMA P58 methodology is evaluated. The results show that the proposed retrofitting methods improve the serviceability and life safety performance levels of steel and RC structures at different rates when subjected to earthquake loads. Moreover, these procedures reveal that financial losses are greatly decreased, and were more tangible by the application of CFD rather than using CCB. Although using both retrofitting methods reduced damage state probabilities, incorporation of a site-specific seismic hazard curve to evaluate mean annual occurrence frequency at the collapse prevention limit state caused unexpected results to be obtained. Contrary to CFD, the collapse probability of the structures retrofitted with CCB increased when compared with the primary structures.展开更多
A satisfactory ductile performance of moment-resisting reinforced concrete concentric braced frame structures (RC-MRCBFs) is not warranted by only following the provisions proposed in Mexico’s Federal District Code (...A satisfactory ductile performance of moment-resisting reinforced concrete concentric braced frame structures (RC-MRCBFs) is not warranted by only following the provisions proposed in Mexico’s Federal District Code (MFDC-04). The nonlinear behavior of low to medium rise ductile RC-MRCBFs using steel X-bracing susceptible to buckling is evaluated in this study. The height of the studied structures ranges from 4 to 20 stories and they were located for design in the lakebed zone of Mexico City. The design of RC-MRCBFs was carried out considering variable contribution of the two main lines of defense of the dual system (RC columns and steel braces). In order to observe the principal elements responsible for dissipating the earthquake input energy, yielding mappings for diff erent load-steps were obtained using both nonlinear static and dynamic analyses. Some design parameters currently proposed in MFDC-04 as global ductility capacities, overstrength reduction factors and story drifts corresponding to diff erent limit states were assessed as a function of both the considered shear strength and slenderness ratios for the studied RC-MRCBFs using pushover analyses. Additionally, envelopes of response maxima of dynamic parameters were obtained from the story and global hysteresis curves. Finally, a brief discussion regarding residual drifts, residual drift ratios, mappings of residual deformations in steel braces and residual rotations in RC beams and columns is presented. From the analysis of the obtained results, it is concluded that when a suitable design criterion is considered, good structural behavior of RC-MRCBFs with steel-X bracing can be obtained. It is also observed that the shear strength balance has an impact in the height-wise distribution of residual drifts, and an important “shake-down” eff ect is obtained for all cases. There is a need to improve design parameters currently proposed in MFDC to promote an adequate seismic performance of RC-MRCBFs.展开更多
文摘This paper reports two new tests conducted to augment available data highlighting the structural performance of multistory steel frames under progressive collapse. The investigated steel frames had different geometries, different boundary conditions, different collapse mechanisms, different damping ratios and different connections. Overall, the paper addresses how multistory frames would behave when subjected to local damage or loss of a main structural carrying element. The obtained results can form a data base for nonlinear finite element models. The deformations of the investigated steel frames and failure modes under progressive collapse were predicted from the finite element analysis, with detailed discussions presented.
文摘This paper investigates the behavior of steel frames under progressive collapse using the finite element method. Non-linear finite element models have been developed and verified against existing data reported in the literature as well as against tests conducted by the authors. The nonlinear material properties of steel and nonlinear geometry were considered in the finite element models. The validated models were used to perform extensive parametric studies investigating different parameters affecting the behavior of steel frames under progressive collapse. The investigated parameters are comprised of different geometries, different number of stories and different dynamic conditions. The force redistribution and failure modes were evaluated from the finite element analyses, with detailed discussions presented.
基金Supported by National Natural Science Foundation of China(No.50608026)
文摘The progressive collapse of steel frame structures under the blast load was investigated using LS-DYNA. The multi-material Eulerian and Lagrangian coupling algorithm was adopted. A flu-id-structure coupling finite element model was established which consists of Lagrange element for simulating steel frame structures and concrete ground, multiple ALE element for simulating air and TNT explosive material. Numerical simulations of the blast pressure wave propagation, struc-tural dynamic responses and deformation, and progressive collapse of a five-story steel frame structure in the event of an explosion near above ground were performed. The numerical analysis showed that the Lagrangian and Eulerian coupling algorithm gave good simulations of the shock wave propagation in the mediums and blast load effects on the structure. The columns subjected to blast load may collapse by shear yielding rather than by flexural deformation. The columns and joints of steel beam to column in the front steel frame structure generated enormous plastic defor-mation subjected to intensive blast waves, and columns lost carrying capacity, subsequently lead-ing to the collapse of the whole structure. The approach coupling influence between struc-tural deformation and fluid load well simulated the progressive collapse process of structures, and provided an effective tool for analyzing the collapse mechanism of the steel frame structure under blast load.
文摘This paper presented a methodology for the analysis and design of steel connections under a double-span connection within the context of preventing progressive collapse. First, various connection models were described and their pros and cons were provided. Then, the load-displacement characteristics of a component-based spring model were described. Thirdly, an experi-mental study on the behaviors of shear tab connections under tension was presented. The main sources of the deformation capacity of the shear tab connections were identified. Finally, a design example of a shear tab connection was provided to illustrate the methodology.
基金Project supported by the National Natural Science Foundation of China (No. 51678358)。
文摘In this paper,we propose a probabilistic method for analysing the collapse time of steel frame structures in a fire.The method considers the uncertainty of influencing factors.Tornado diagrams are used for sensitivity analysis of random variables.Structural analysis samples are selected by Monte Carlo method,and the collapse times of different structural samples are calculated by fire time history analysis.A collapse time fragility curve is fitted according to the calculated collapse times of the samples.A reliability index of the collapse time is used as a quantitative standard to evaluate the collapse performance of a steel frame in a fire.Finally,this method is applied to analyse the collapse time fragility of an eight-storey 3 D steel frame structure under different compartment fire scenarios and fire protection levels.According to the collapse time fragility curve,the effects of the different fire scenarios and protection levels on the collapse resistance of the structure under fire are evaluated.
文摘This study presents the investigation of the approach which was presented by Thaer M.Saeed Alrudaini to provide the alternate load path to redistribute residual loads and preventing from the potential progressive collapse of RC buildings.It was proposed to transfer the residual loads upwards above the failed column of RC buildings by vertical cables hanged at the top to a hat steel braced frame seated on top of the building which in turn redistributes the residual loads to the adjacent columns.In this study a ten-storey regular structural building has been considered to investigate progressive collapse potential.Structural design is based on ACI 318-08 concrete building code for special RC frames and the nonlinear dynamic analysis is carried out using SAP2000 software,following UFC4-023-03 document.Nine independent failure scenarios are adopted in the investigation,including six external removal cases in different floors and three removal cases in the first floor.A new detail is proposed by using barrel and wedge to improve residual forces transfer to the cables after removal of the columns.Simulation results show that progressive collapse of building that resulted from potential failure of columns located in floors can be efficiently resisted by using this method.
文摘This study investigates the efficiency of two types of rehabilitation methods based on economic justification that can lead to logical decision making between the retrofitting schemes. Among various rehabilitation methods, concentric chevron bracing（CCB） and cylindrical friction damper（CFD） were selected. The performance assessment procedure of the frames is divided into two distinct phases. First, the limit state probabilities of the structures before and after rehabilitation are investigated. In the second phase, the seismic risk of structures in terms of life safety and financial losses（decision variables） using the recently published FEMA P58 methodology is evaluated. The results show that the proposed retrofitting methods improve the serviceability and life safety performance levels of steel and RC structures at different rates when subjected to earthquake loads. Moreover, these procedures reveal that financial losses are greatly decreased, and were more tangible by the application of CFD rather than using CCB. Although using both retrofitting methods reduced damage state probabilities, incorporation of a site-specific seismic hazard curve to evaluate mean annual occurrence frequency at the collapse prevention limit state caused unexpected results to be obtained. Contrary to CFD, the collapse probability of the structures retrofitted with CCB increased when compared with the primary structures.
基金National Science and Technology Council of Mexico (Conacyt)
文摘A satisfactory ductile performance of moment-resisting reinforced concrete concentric braced frame structures (RC-MRCBFs) is not warranted by only following the provisions proposed in Mexico’s Federal District Code (MFDC-04). The nonlinear behavior of low to medium rise ductile RC-MRCBFs using steel X-bracing susceptible to buckling is evaluated in this study. The height of the studied structures ranges from 4 to 20 stories and they were located for design in the lakebed zone of Mexico City. The design of RC-MRCBFs was carried out considering variable contribution of the two main lines of defense of the dual system (RC columns and steel braces). In order to observe the principal elements responsible for dissipating the earthquake input energy, yielding mappings for diff erent load-steps were obtained using both nonlinear static and dynamic analyses. Some design parameters currently proposed in MFDC-04 as global ductility capacities, overstrength reduction factors and story drifts corresponding to diff erent limit states were assessed as a function of both the considered shear strength and slenderness ratios for the studied RC-MRCBFs using pushover analyses. Additionally, envelopes of response maxima of dynamic parameters were obtained from the story and global hysteresis curves. Finally, a brief discussion regarding residual drifts, residual drift ratios, mappings of residual deformations in steel braces and residual rotations in RC beams and columns is presented. From the analysis of the obtained results, it is concluded that when a suitable design criterion is considered, good structural behavior of RC-MRCBFs with steel-X bracing can be obtained. It is also observed that the shear strength balance has an impact in the height-wise distribution of residual drifts, and an important “shake-down” eff ect is obtained for all cases. There is a need to improve design parameters currently proposed in MFDC to promote an adequate seismic performance of RC-MRCBFs.
