| Owing to the high degree of industrialization,convenient construction and environment protection,prefabricated reinforced concrete(PC)structures have been gradually applied and promoted in actual projects.In addition,various PC connections have been proposed.The existing fabricated structures are mainly "equivalent cast-in-situ" fabricated structures,which do not give full play to the advantages of seismic performance of fabricated structures.Generally,the concept of “strong-column and weak-beam” is the main principle in structural design.Nevertheless,when PC structures are subjected to earthquakes,the bending moment of the connection becomes uncontrollable,due to the increase in the beam overstrength moment and corresponding column moment demand.This leads to the damage of the joint area and column.In other words,the structures will present disadvantageous damage to the strongcolumn and weak-beam system.It even affects the two design criteria of "strong connection and weak member" and "strong shear and weak bending".Therefore,it is necessary to propose a single-yielding precast concrete(SYPC)beam-to-column connection with a direct force transmission path,simple and efficient construction,easy to repair after earthquake,and with controllable flexural bearing capacity.This is in line with the development trend of building industrialization,and is conducive to the realization of the “strong-column and weak-beam”structural design concept.This dissertation focuses on the seismic evaluation and further improvement of the SYPC beam-to-column connection through means of theoretical derivation,experimental analysis and numerical simulation.Finally,an elastic displacement spectrumbased design method for SYPC frame was proposed.The detailed research results are listed as follows:(1)The concept and construction of the SYPC beam-to-column connection was proposed.Firstly,the flange effect of the slab was studied,and the adverse impact of the slab contribution on the realization of the design principle of "strong column and weak beam" was analyzed.In order to effectively realize the "strong column and weak beam","strong shear capacity and weak bending capacity",and "strong connection and weak member" design principle,a SYPC beam-to-column connection with controllable bending moment at the beam end was proposed.The construction and stress mechanism of SYPC beam-to-column connection was studied.At the same time,the design concept of adding vertical slot and adding the strength of top longitudinal reinforcements was proposed,which can induce the replaceable energy dissipation connector(REDC)at the bottom of the connection to yield first under negative bending moment,so as to realize that the bending moment of the beam end was completely controlled by the REDC at the bottom of the connection.The single-yielding mechanism,controllable bending moment,shear transfer mechanism and anchorage characteristics of reinforcement in columns were studied,and the semi-rigid characteristics of SYPC beam-to-column connections are studied.Finally,the advantages of SYPC beam-to-column connections were summarized.(2)A preliminary experimental study and theoretical analysis of the SYPC beam-tocolumn connection was carried out.The flexural capacity and single-yielding mechanism of SYPC beam-to-column connection was studied.Based on the proposed SYPC beam-to-column connection,three low-cycle pseudo-static tests were carried out by replacing three REDCs with different parameters on a full-scale specimen,and the seismic performance of SYPC beam-tocolumn connection was studied.The energy dissipation capacity provided by the REDC at the bottom of the SYPC connection,and the repairability of the SYPC connection after earthquake were evaluated.Combined with the test results and the section analysis results of SYPC beamto-column connections,the influence of the concrete in the middle compression zone on the strain of the top longitudinal reinforcement and additional bending moment of the SYPC beamto-column connections was explored.On this basis,three finite element models were established to further analyze how to reduce the additional bending moment of the connection and keep the top longitudinal reinforcements always in the elastic range.Finally,relevant design suggestions and formulas were put forward for the performance objectives of controllable flexural bearing capacity and single-yielding mechanism.(3)Further experimental research was carried out for SYPC beam-to-column connection.In order to realize the convenience of prefabrication and keep the top longitudinal reinforcements always elastic,the SYPC beam-to-column connection was further improved.The main improvements consist of increaseing the vertical slot height and the introducing of two side shear transfer components.Five low-cycle quasi-static loading tests were conducted respectively on the single full-scaled specimen of the SYPC beam-to-column exterior connection and interior connection using five REDCs with different sizes.The hysteresis characteristics,failure mode and damage state of the improved SYPC connection were studied.The bearing capacity,energy dissipation and stiffness of the SYPC connection were analyzed,and the height of the neutral axis,the elongation of the beam and the strain of the REDC at the bottom of the connection were discussed.It was verified that the SYPC connection has the characteristics of single-yielding mechanism and easy to repair after earthquakes,and the controllable bending moment was realized.The adverse effect of beam elongation effect on the realization of the principle of "strong-column and weak-beam" in the process of frame lateral deformation was deeply studied,and it was pointed out that the connection constructed by SYPC has less beam elongation effect,which is conducive to the realization of the principle of "strong column and weak beam".(4)Regarding the analysis of seismic performance parameters of SYPC frame,the finite element model of SYPC beam-to-column connection was established and verified based on the test results.By changing many parameters of SYPC beam-to-column connection,the parametric analysis based on low-cycle quasi-static was carried out,the influence of various parameters on the seismic performance of SYPC connections was studied.Secondly,by changing the length of REDC core plate,the parametric analysis of SYPC frame based on dynamic time history analysis was carried out.An 8-degree area was selected and a six-story SYPC frame was modelled in Open Sees where a parametric analysis of its seismic performance under small and large earthquakes was conducted.The inter story drift and inter story deformation mode of SYPC frame were investigated as well as the influence of the REDC core plate length on the stiffness of the SYPC frame.(5)The direct seismic design method of SYPC frame based on the elastic displacement spectrum was proposed.Combined with the limit value of structural inter story drift under earthquake performance objectives specified in Code for seismic design of building in China,the most stringent level was directly determined according to the the equal displacement rule for performance-based design,so as to avoid three times of design to meet the performance requirements of different levels.Using the advantage that the equal displacement rule can quickly and accurately determine the elastic-plastic required displacement of the structure under earthquake,an elastic displacement spectrum-based design approach for SYPC frame was proposed.The stiffness reduction coefficient of the structure was determined by the stiffness ratio and period ratio of the designed structure,and then the joint constraint coefficient satisfying the target displacement was determined by the relationship between the lateral stiffness ratio and the joint constraint coefficient.The design method focuses on the length and cross-sectional area of REDC,which can meet the requirements of keeping elasticity of the structure under minor earthquakes(corresponding to 63% probabilities of exceedance in 50years)and concentrated damage under medium earthquakes(corresponding to 10%probabilities of exceedance in 50 years)and severe earthquakes(corresponding to 2%probabilities of exceedance in 50 years).In addition,the demand of low-cycle fatigue life of REDC was considered to meet the demand of structural ductility.At the same time,the stiffness characteristics of the structure were reviewed to meet the demand of frame deformation mechanism.The results of nonlinear time history analysis of the example structures indicate that the structure designed by the design method meet the limit value of the target inter story drift corresponding to the preset performance target under the three earthquake performance objectives,which verifies the accuracy and effectiveness of the proposed design method. |
PDF Full Text Request