Experimental Research And Analysis On Seismic Performance Of Precast Concrete Bottom Column

Pre-fabricated concrete structure is one of the main systems for the development of residential industrialization, as it can promote the level of housing industrialization and construction mechanization, reduce energy consumption and conserve resources, and achieve green construction as well as sustainable development of building industry.The seismic performances of prefabricated concrete structure depend on the corresponding behaviour of the structural members as well as their connections. The bottom column of prefabricated reinforced concrete frame is regarded as the primary vertical load-bearing member and the member for resisting lateral force. It has been known that the seismic performance of the bottom column and its connection plays a significant role on that of the whole frame structure. However, the experimental research concerning the bottom column is limited. To this end, this research focuses on examining the seismic behavior of prefabricated bottom column and its connections in frame structures through the following investigation.(1) In order to obtain the minimum anchorage length of reinforcing bar in corrugated metal tube within a high-strength cast-able, a pull-out experiment on a total of 48 specimens in 16 groups is carried out. The main study emphasizes on the influence of the diameter of corrugated metal tube D, the bar diameter d, the ratio of corrugated metal tube diameter D and bar diameter d(D/d), anchorage length of reinforcing bar la and other factors on the performance of the anchor. The relationship curve of tensile load-bond slip is obtained, and the effect of la and D/d on average stress of reinforcing bar, as well as the influence of product of la and D/d on the ultimate tensile strength of reinforcing bar is investigated.(2) Based on the commonly used pulp anchored and plug-in methods for column-to-column connections in "monolithic reinforced concrete frame assembly and connecting node design rules" of CECS43:92, the pulp sleeve anchor bar connection method for the implementation of column-base connection proposed by domestic and foreign scholars is firstly improved. The main process of the improved connection method included:(i) Making concrete foundation and curing, embedding corrugated metal casing in the position of longitudinal reinforcement simultaneously,(ii) Precasting reinforced concrete column and curing with the longitudinal reinforcement extending to the bottom of the column,(iii) Pouring the high strength cast-able in the inner sleeve of embedded corrugated metal casing,(iv) Installing the precast reinforced concrete column and making sure that the column longitudinal reinforcement is inserted into the corrugated metal tube in order to complete the connection between the bottom column and its foundation. To verify the reliability of the connecting method, seismic performance of precast concrete long columns and short columns, as well as the overall cast-in-place concrete long columns and short columns are tested individually through the comparative experimental research.(3) To study the seismic performance of precast reinforced concrete long columns made by the above method, the seismic test on eight precast concrete and one monolithic cast-in-place concrete long columns under low reversed cyclic horizontal loads are carried out. Effect of the axial pressure ratios, production methods, stirrup strength grade, longitudinal steel bar in the range of 5 times of longitudinal reinforcement diameter, and concrete bonding status on seismic performance of precast reinforced concrete columns is studied. The failure pattern of the long columns, the horizontal force- lateral displacement hysteresis curves, the characteristics of the skeleton curve, ductility index, stiffness degradation, strength degradation and ultimate bearing capacity of the long column specimens are recorded and discussed. The energy dissipation capacity of the long columns is also presented and compared.(4)To study the seismic performance of the precast reinforced concrete short column constructed by the aforementioned method, four prefabricated reinforced concrete and two overall in-situ reinforced concrete short columns are tested under the low cyclic reciprocating horizontal loads. The parametric study on the axial compression ratio, production method, longitudinal reinforcements in the range of 5 times of its diameter and concrete bonding conditions are carried out for seismic performance of precast reinforced concrete short columns. The failure modes, horizontal force-lateral displacement hysteresis curve, the characteristics of skeleton curve, ductility index, stiffness degradation and strength degradation characteristics, as well as ultimate bearing capacity and crack resistance of each short column specimens are all recorded and presented. Finally, using the finite element software of USC-RC and ABAQUS, the concrete short columns with different axial compression ratios, longitudinal reinforcement ratio, steel and concrete strength are investigated. The characteristics of the skeleton curves and the ultimate bearing capacity of reinforced concrete short columns were obtained.Furthermore, based on the above results, the following conclusions are drawn:(1) It is shown that the required anchorage length of reinforcing bar in corrugated metal tube within a high-strength cast-able was far less than that stated in Code for design of concrete structures(GB50010-2010). Accordingly, some recommendations are proposed as follows:(i) The diameter of corrugated tube D should be taken as 2 to 3 times of the bar diameter d.(ii) When D/d is 2, the required minimum anchorage length of reinforcing bar la was suggested to be taken as 15 d.(iii) When D/d is 3, the minimum anchorage length la should be taken as 10 d.(iv) When D/d is an intermediate value, linear interpolation between 15 d and 10 d can be taken for the minimum anchorage length.(2) The improved pulp sleeve anchor bar connection method provided a reliable implementation for column-base connection. Moreover, it is found that the seismic performance of precast reinforced concrete long columns made by the above method was better than that of monolithic cast-in-place reinforced concrete member. This improved method can be employed in pre-fabricated concrete structures.(3) The setup of plastic zones at the base of the reinforced concrete long columns made no obvious reduction of their lateral capacity, but significantly increased their ductility and energy dissipation capacity. It is proved that this design method can be used for reinforced concrete frame columns under seismic requirements. However, when the plastic zones were applied at the base of the reinforced concrete short columns, their lateral capacity decreased dramatically, but the increase of their ductility and energy dissipation capacity was limited. Thus, it is not recommended to set up the plastic zone at the base of RC short column.