| Recent years,the structural progressive collapse and disaster reinforcement technology have become one of the research concentrations in civil engineering.Implementing strengthening process on some import beams,columns,slabs,sub components,and some other regions of structures are capable of increasing the redundancy of structures,which is proved to be a method that could improve the progressive collapse resistance of structures,but relative studies are rarely conducted.In this paper,the influence of reinforced slabs on the space frame was experimentally investigated by using a new strengthening technology namely the strengthening technology of combined HPFL and steel.The research contents are shown as follows:1.The quasi-static progressive collapse tests including a RC space frames with slabs and a RC space frames reinforced with the strengthening technology of combined HPFL and steel were conducted by using the alternate path method.The mechanical features of slabs during the process of vertical progressive collapse of structures and the constitution of structures collapse resistance were studied by analyzing the resistance-unloading displacement curves,horizontal-unload displacement curves,strains of reinforcement in beam and slabs,and other data obtained by experimental program.The test results showed that:(1)The vertical progressive collapse resistance of RC frame structures consists of a process of transition from beam arch slab pressure-mechanism,through beam arch panel pull mechanism and beam cable slab pull-mechanism to slab pull mechanism.The mechanism of frame beams primarily provided the vertical resistance of structures,while pressure-mechanism lasted a short period.The pull-mechanism of slabs account for an increasingly proportion in the constitution of resistance,and the structural resistance including the pull-mechanism was greater than that provided only by beam cable mechanism.(2)the stiffness and the mechanical performance of slabs were improved by strengthening technology,therefore the pressure-mechanism was developed.Reinforced structure exhibited a faster increment in resistance,while the ultimate value of resistance lasted longer time,and the decrease of resistance assumed to be more moderate.The transmission path of the most unfavorable loads was improved by the reinforcement of slabs,thus the beam who was not adjacent to the failure columns possessed a much more severe torsional failure than beams in structures without strengthening.The reinforcement of slabs caused few influence on the horizontal displacement of the structure.2.The entire collapse processes of RC frame structures were simulated by using ABAQUS/explicit solver,in which the ductile damage fracture criterion of steel bars was introduced based on the elastoplastic theory.After verifying of the model rationality,the comparisons among simulations of frame with slabs,frame with strengthened slabs,and the only-frame were carried out,then,an analysis on influencing factors were actualized by finite element procedure.The results are as follows:(1)The proposed method for simulating the collapse of frames were verified by comparing the force-displacement curves,the propagation of cracks,and the harden-damage-fracture process of rebar,the numerical results showed a good agreement with the test results.(2)The slab provided a significant improvement on the progressive collapse resistance of frames,and the strengthening of slab made a further progress on resistance of frames.Meanwhile,the plastic hinge was observed at the base of column,the relatively weak section was shifted,so a suggestion that making an assurance on the mechanical form of columns was proposed.(3)As the border columns were deactivated,the mechanical features of structure in each stage were similar to the situation that the middle columns appeared to failure,but the resistance of structure in former state was significantly lower than that of structure in latter situation.Furthermore,the displacement corresponding to the maximum resistance was observed to be delayed as the border columns were deactivated.It suggests that the influence of border columns on structural progressive collapse resistance is less than that of middle columns.(4)The collapse resistance of structures was marginally affected by increasing the strength of grout.When the reinforcement ratio of steel strand was taken as twice and half of origin,the collapse resistance of structures turned to be the 1.3 times and 0.7 times of that of original structures,respectively.Therefore,it is inferred that the decrease in strength of grout and increase in reinforcement ratio of steel strand would provide a better effect.This paper systemically studied the progressive collapse resistance of space structures,by which the influence of the slab on structures with and without strengthening was quantified.The effectiveness of this strengthening technology was verified,and the mechanism of collapse was revealed,accordingly,a strengthening measurement and an indice were proposed.The research result achieved by this paper is of a great value to development of the existing code,promotion of the strengthening technology of combined HPFL and steel,and the guidance of the practical engineering. |
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