| Over the past few decades,the industrialization of new building technologies based on prefabricated reinforced concrete(PC)structures has become a strategic subject due to its advantages of less manual labor,improved standardization and quality control,reduced environmental impact,high construction efficiency,and good economic performance.However,the seismic performance and integrity of a PC structure are essentially governed by the properties of the connections between various prefabricated units.The damage and collapse of PC buildings caused by the failure of prefabricated units' connections have been reported in many experimental studies and field observations after the earthquake.Meanwhile,the assembly construction of the prefabricated unites connections in site is complex,and this further resulted in the current practice of using heavily-distributed reinforcing bars,setting temporary supports,and casting concrete.A novel prefabricated reinforced concrete(PC)self-sustaining moment-resisting frame was developed to solve these problems discussed above.The proposed PC frame was composed of PC multi-story columns with corbels,PC beams with U-shell at beam ends,and precastprestressed hollow-core slabs,et al.Hence,no temporary supports were required for the precast beams and slabs during the assembly construction process in site.To investigate the seismic performance of the proposed PC frame,thirteen large-scale connections of prefabricated components were designed and tested under quasi-static cyclic loading to study the seismic performance of these PC connections.The types of these test specimens included: PC columnto-foundation connections,PC self-sustaining cruciform beam-column connections,and two kinds of PC self-sustaining exterior beam-column connections.In detail,this research included contents as follows:(1)The large-diameter high-strength reinforcing bars were adopted in the precast column as longitudinal reinforcement for convenient assembly construction in site.In the two prefabricated assemblies,the columns were connected to the foundation using grouted sleeves(PC-S)and grouted corrugated ducts(PC-C),respectively.The test results showed that both types of connections exhibited similar strength but reduced energy dissipation capacities,and different failure patterns as compared to the cast-in-place specimen.In specimen PC-S,buckling of the longitudinal bars and rupture of stirrups at the top of the grouted sleeves were observed,and this led to lower ductility with an ultimate lateral drift ratio of 4.5%.In specimen PC-C,a more pronounced pinching behavior was observed after a lateral drift ratio of 2%,and this was due to the significant bond-slip of longitudinal bars in the overlap region.(2)To investigate the seismic performance of the proposed beam-column connection,five large-scale PC self-sustaining cruciform beam-column connections specimens and one conventional RC connection as reference were designed and tested.The test parameters included the length and area of the flexural reinforcing bars placed at the bottom of PC U-shells,and the anchorage measures(stirrups)inside the PC U-shell.The test results showed that the use of longer flexural reinforcing bars had little influence on the load-carrying capacity,but contributed to the initial stiffness and energy dissipation capacity.The load-carrying capacity increased by 24% when the area of flexural reinforcing bars increased by 50% in the U-shell region.The incorporation of stirrups in the overlapping region of beam flexural reinforcing bars and longitudinal rebars improved their bond-slip behavior,resulting in the energy dissipation capacity of the PC beam-column connections improved by 16.5%.(3)Anchorage steel plates were used for longitudinal reinforcement and flexural reinforcing bars inside the PC U-shell in the two kinds of PC self-sustaining exterior beamcolumn connections due to the congestion of the reinforcing bars at the connection zone.The test results showed that the load-carrying capacity of PC self-sustaining exterior beam-column connections was lower than RC connections.Compared with the RC connection,the loadcarrying capacity of the PC exterior beam-column connection in the middle story was reduced by 24.5% and 16.8% in the positive and negative direction,respectively.The load-carrying capacity of the PC exterior beam-column connection in the top story was reduced by 21.7% and13.9% in the positive and negative direction,respectively.The deformation capacity and ductility of the PC self-sustaining exterior beam-column connections were much weaker than RC connections.The ductility ratio of the PC exterior beam-column connection in the top story was 1.93,meanwhile,the ductility ratio of RC connection was 2.41.In the early stage,the energy dissipation capacity of the PC exterior beam-column connection was superior to the RC connection,however,their cumulative energy dissipation capacity was insufficient.Different plastic hinge mechanisms at the column bases and length of plastic hinges were proposed for the PC column-to-foundation connections.The distributions the reinforcement strains measured from the tests(including longitudinal reinforcement,stirrups,grouted sleeves,and spiral stirrups et al.)provided detailed information in support of the identification of the different plastic hinge mechanisms.Combined with the cracking patterns and failure modes,the mechanical mechanism and deformation distribution of the two PC column-to-foundation connections were investigated.The plastic hinge lengths of RC specimen,PC column-tofoundation connection with grouted sleeves,and PC column-to-foundation connection with grouted corrugated ducts were 450 mm,750 mm,and 250 mm,respectively.Further improvements in the two types of prefabricated column-to-foundation connections were recommended.The mechanical model and load-carrying capacity calculation method of the proposed PC self-sustaining beam-column connections were proposed.This mechanical model could describe the failure pattern and accord with the mechanical mechanism of the test specimens.The comparison between the calculation and test results showed that the theoretical calculated load-carrying capacity was reduced by 10%-12% for different PC self-sustaining cruciform beam-column connections.That was attributed to the exclusion of the contribution of the corbel for the negative moment-carrying capacity.When calculating the load-carrying capacity of PC self-sustaining exterior beam-column connections,the tension stress of flexural reinforcing bars placed inside PC U-shells and longitudinal reinforcement of PC beams should be decreased by10%.The theoretical calculated moment-carrying capacities of PC exterior beam-column connections were less than the test results by 6.6% and 14.6% in positive and negative directions,respectively.Overall,the theoretical calculations were reasonable and conservative.Based on the test results,numerical simulation at the node level was carried out.Two kinds of models were developed by using Open Sees software with the zero-length element and beamcolumn joint element,respectively.The feasibility and reasonability of both modeling methods were verified by fitting and analyzing with test data.The finite element models of five-story and three-span RC frame and PC self-sustaining moment-resisting frame structures were established.The maximum inter-story lateral drift ratio was chosen as the evaluation index of post-seismic performance,and the post-seismic results of the two structures under the action of small,moderate,and high earthquakes were compared to analyze the different trends and postseismic performance.The results of the finite element analysis indicated that the PC selfsustaining moment-resisting frame met the requirements of seismic codes,but its seismic performance was slightly weaker than the RC frame.The seismic performance of connections of prefabricated components and precast reinforced concrete moment-resisting frames were investigated in detail and deeply through experimental research and theoretical analysis.The seismic behavior of the PC self-sustaining frame was fully estimated and increased its application in moderate-and high-seismic regions. |
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