Seismic Effect Analysis And Performance Evaluation Of Plate Stairs In RC Frame Structure

Stairs are main vertical transportation channel in normal use of building.They are also important or the only escape route in the earthquake,fire or other natural disasters.However,reinforced concrete(RC)plate stairs were subjected to various types of damage in 2008 Wenchuan earthquake.The damage of stairs was more serious than the main frame structure and the stairs could not play their proper roles.Thereafter,many researchers began to study seismic behavior of RC stairs and to improve designs for the new buildings plate stairs.However,seismic performance evaluation and effective seismic retrofit for plate stairs in existing reinforced concrete frame structure have not been found.Seismic influence factors and seismic performance evaluation method of in reinforced concrete frame structure was systematically studied in this paper.The main work is as follows:(1)Failure modes of plate stairs was summarized according to previous investigation reports of seismic damage.Moreover,mechanisms of seismic damage to plate stairs were analyzed based on traditional design for stairs.(2)A stairwell structure numerical model with plate stairs was established using the finite element software,OpenSees.The corrected Kent-Park concrete and the Menegotto-Pinto rebar constitutive models are adopted.A multi-layer shell element is used to simulate plate stairs.The numerical model was validated by comparison between the analytical and the experimental results.(3)Influence of stair plate thickness,arrangement of reinforcement,slope and stair steps on the behavior of stair plate in tension and compression was investigated according to previous experimental research and the established numerical model of the stairwell.Effects of staircase components,stair plate thickness,rebar of stair slabs and span of stair on staircase were analyzed.The advantages and disadvantages of the two stair seismic designs proposed were compared.(4)The quantified indicators for seismic performance level of plate stairs were determined according to statistics of experimental phenomena and results of plate stairs.A relationship between story drift angle of frame structure and the quantified indicators of axial tensile rate of plate stairs was deduced.Finally,we put forward seismic performance evaluation methods and procedures for existing frame structures and plate stairs were interpreted by taking a five story frame structure as an example.(5)A new seismic retrofit measure and the corresponding construction technology for the existing reinforced concrete plate stairs were proposed.