Seismic Performance Design Of RC Frame Structure Considering The Effect Of Cast-in-place Floor Slab

The performance-based seismic design is a completely new idea of seismic design appeared in 1990s,which requires the structures suffering from earthquake to meet the designed performance goals.Researches on historical earthquake damage indicate that cast-in-place floor slabs is the main reason for the RC frame structure to form the failure mode of "strong beam weak column",by which the flexural capacity of the frame increases,and the seismic performance of the structure enhances.On the basis of previous researches,the main contents are as follows:(1)Based on the Code for Seismic Design of Buildings(GB50011-2010)and domestic and foreign scholars' investigations on the seismic performance index quantification and the performance objectives of RC frame structure,the inter-story drift angle was selected as the structural performance indicator and was then quantified.(2)A three-layer 3×3 bay RC frame structure was designed with PKPM,and three models were established using the FEM software of ABAQUS,which contained a bare frame structure model,a 3D RC frame structure with floor slabs(with slab rebar)model and a RC frame structure with floor slabs(without slab rebar)model.By comparing the structural performance points,the inter-story drift angles,the stress of beam and column reinforcement and the actual internal force of beam and column of the previous three models,the influence of cast-in-place floor slabs on the seismic performance of RC frame structures was analyzed.The results showed that the structural base shear force was increased due to the cast-in-place floor slabs,and the overall deformation of the structure was also reduced.The reinforcement effects on the beam end bending capacity and axial force could not be ignored,and the actual bending moment of the column end was significantly greater than that of the empty frame.The structure was less prone to form the "strong column weak beam" failure mode,and weakened the seismic performance.(3)The effects of cast-in-place floor slabs on the actual forces of frame beams and columns were considered to adjust the reinforcement plan for the model calculated according to the current design method:1)Alter the column end bending moment increase coefficient to 1.5.2)Alter the column end bending moment increase coefficient to 1.5 and take the strengthening effects on negative bending moment and axial force of cast-in-place floor slabs into account simultaneously.ABAQUS was applied to establish the models corresponding to the two reinforcement plans,and the difference in seismic performance of the three models and achievement of each model's performance target level were then analyzed.The comparison results showed that the reinforcement plan which had considered the influence of cast-in-place floor slabs on the beam end and altered the column end bending moment increase coefficient,was more conducive to form the "strong column weak beam" failure mode and could improve the structural seismic performance.Compared with the existing seismic design method,the reinforcement plan could achieve higher performance goals and be more economical.It is suggested that consideration should be given to the enhancement of the bending moment and axial force of the beam end in the effective flange area of the cast-in-place floor slabs in the process of structural design.(4)A seismic performance design example of a four-story RC frame structure was conducted,and the reinforcement plan considering the strengthening effects on negative bending moment and axial force of cast-in-place floor slabs and altering bending moment increase coefficient was applied.The calculation result showed that the structure could meet the performance target requirement,and the feasibility of the reinforcement plan was verified.