Seismic Analysis Of Reinforced Concrete Frame Structure With Diagonal Struts

A type of reinforced concrete(RC)frame structure with diagonal struts was discussed.The performance of frame with diagonal struts is similar to the shearwall.so the diagonal struts enhance the frame approximately up to the frame-shear wall structure,which greatly improves the seismic performance of frame.The main investigation was carried out as following:(1)Taking 6-storey,2-span and 5 RC frames as the numerical models,17 frames with diagonal struts(different patterns,located at different storeys and spans)and 3 frames without diagonal strut were calculated by the general engineering design software PKPM,then the main indexes of structure were obtained under frequent earthquake.The calculation models meet the requirements of national codes,which is feasible in engineering,and is valuable with reference to engineering design.(2)The pushover and time-history analysis of 15 frames with diagonal struts were conducted by finite element software Midas-Gen,the capacity-demand curve and displacement-time curve of these 15 frames were obtained.The equivalent period,basement shear forces,maximum displacement,equivalent damping ratio and maximum inelastic storey drift ratios at performance point of these frames were summarized.(3)We found some defects of the Midas-Gen pushover calculation results.To overcome these defects,we wrote the static nonlinear ultimate analysis frame program(SNUAFP)by computer language Fortran90 and Matlab.The ultimate results of the frames were presented based on SNUAFP.The main research results are listed below:(1)On condition of approximate section size and steel area,the diagonal struts set in one frame-span enhance the original 6 grade of seismic intensity up to 7 grade of seismic intensity;the diagonal struts set in one frame-two span or set in two frame-one span enhance the original 6 grade of seismic intensity up to 7.5 grade of seismic intensity.(2)The plastic hinges are set automatically in commercial software(Midas-Gen)to describe the structural nonlinearity,but the calculation results are not reasonable.The method of plastic hinge's ultimate bending moment is put forward in our SNUAFP program.This ultimate bending moment is based on the stress-strain relationship of concrete and steel,element axial force and RC section property.When the total cross-section is cracked and steel bars are yielded,SNUAFP program "kills" the element automatically.The different frames are linked with rigid truss to simulate the rigid floor assumption.Therefore the setting of plastic hinge in our SNUAFP program is more reasonable.(3)When the stiffness of frame with diagonal strut is relatively weak,the diagonal strut set in middle and top storeys is unnecessary;when the stiffness of frame with diagonal strut is relatively strong,the diagonal strut set in top storey is unnecessary;when the stiffness of frame with diagonal strut is strong enough,the diagonal strut set in every storey is necessary to increase load carry capacity of structure.(4)The frame structures without the diagonal strut or with the diagonal strut are investigated respectively by design software PKPM,Pushover analysis,time-history analysis and our SNUAFP program.The calculation results are verified mutually,so seismic performance investigation is comprehensive.the conclusions own high reliability.