Research On The Seismic Damage Analysis And Strengthening Method&Improvement Measure Of Staircase In R.C. Frame Structure

Several earthquakes both in China and abroad had caused large numbers of cast-in-place reinforced concrete staircase seriously damaged, which cut off the evacuation passage, the repair and strengthening of damaged staircases are dif-ficult as well. Before new code is published in2010, the design of the staircase components are considered as cant beams which only bear the vertical loads, but its contributions of the lateral stiffness and seismic action to the main body structure are ignored, therefor, the cause and the process of seismic damage of staircase are worthy for further study to find new ways to relive or avoid the damage in the further design and construction. The following researches started by slab staircase in reinforced concrete frame structure are discussed in this pa-per:(1) Summarization of seismic damages and the failure mechanism of rein-forced concrete staircase. By collecting the earthquake damage features of cast-in-place reinforced concrete staircases in reinforced concrete structures both in China and abroad, the seismic situations and basic law are summarized, the failure mechanism of staircase participated in the working of building structure is studied by theory analysis.(2) Experimental and research on the seismic damage of staircase in available R.C. frame structure. A regular reinforced concrete frame structure is designed by the traditional method. A1/3scaled one-storey reinforced concrete frame structure model with staircase selected form the first floor is constructed, ex-periment under slow frequency cyclic horizontal loading is carried out, the fail-ure mechanism of the model is summarized by the phenomena of test, the stair-case provided obvious supporting force during the whole elasto-plastic defor-mation, its lateral stiffness must not be disregarded. The result of the experiment proves the theory analysis.(3) Experimental and research on the strengthening method of staircase in seismic damaged or existing R.C. Frame Structure. Base on the theory analysis, the methods to strengthen the rigidity of the staircase, such as, add new shear wall or wing wall, set supports, are proposed. After the seismic strengthening measure is taken to the damaged model, a repeated low cycle loading test is carried out, the result of the experiment proves that the earthquake resistant be- havior of staircase is improved remarkable, the reinforcement method has good effect which can provide a basis for the strengthening for the seismic damaged and existing buildings.(4) Experiment and research on the improvement measure of staircase in new R.C. frame structure. A experiment of the improved staircase model using slip-ping-foot measure under slow frequency cyclic horizontal loading is carried out, it verified the validity and rationality of this method, and proved that it can ob-viously reduce the influence to the lateral stiffness of whole structure after the measure was taken, avoid to be a "K" type support as well, which makes structural calculation and analysis simple and easy. At last, several improvement measures of slab stair both in China and abroad are reviewed, such a study can provide reference for the design of the staircase in new buildings.(5) Based on the comparison of the experimenting phenomena and datum of the three tests, the differences of the damage phenomena, earthquake resistant behavior and design concept of the three models are summarized. Finite-element analyses by the software named MSC.Marc are done, the results show the effec-tiveness of tests.In the end, the issue for the further study according to this research is raised.