Analysis Of The Interaction Between Precast Stair And Frame Structure Under Earthquake Action

To study the influence of precast stair on cast-in-place frame structure under earthquake action, th ree concrete fra me structures with monolithic cast-in-s ite stairs, prefabricated stairs of separated connection and without stairs, respectively, were designed. PKPM and SAP2000 software were used to ca rry out the modal analysis and the response spectrum analysis of th e three schemes, and the vib ration characteristics and seis mic response parameters were compared and analyzed.The main contents and conclusions, suggestions are as follows:(1) Analysis of interaction between stairs and frame structure.Modal analysis and response spectrum analysis of the three schemes were carried out to achieve the natura l period, vibration characteristic s, seismic response param eters, displacement and base shear under horizontal ea rthquake. It turns out that the vibration characteristics stay the same while the natural periods of the struct ures change obviously. The stiffness of fram e structure is enhanced obviously by cast-in-s ite stairs, with the lateral displacement decreases and the base shear increases. The contribution of precast stair to the frame structure is smaller in comparison.(2) Impact of stairs on adjacent members.Mechanical analysis of stair plates, ladder pos ts, and landing beam s under horizontal earthquake action shows that: the effect of cast-i n-place stair on adjacent frame column is very significant, especially on the bottom floor. The magnitude of the difference is over 30%. Members next to the staircase in model of frame structure with precast stair have a smaller stress compare to model with cast-in-place stair.(3) Stress distribution of the stairs was analyzed under horizontal earthquake action.The analysis results show that ladder co lumn axial force and shear force changed little, and bending moment in the column end increase significantly; Ladder beam bending moment and shear force focused on cross neutralization support position, at the same time has a large axial force, shear dam age to the platform beam effect is outstand ing. Stress concentration occurs on area of the platform boards around stair shaft, the beams on both sides of gang-boards, and four angular points of gang-boards in different direction under horizontal earthquake action.(4) Conclusions and suggestions: the stiffn ess of frame structure is enhanced obviously by cast-in-site stairs which changes the mechanical behaviors of some members, therefore, the effect of s tairs on frame structure should be allowed for when conducting seismic design. Precast stairs have a m ore reasonable seismic behavior than cast-in-site stairs and have a relative smaller impact on frame structure.