Shaking Table Experimental Study On Seismic Strengthened Brick Masonry Structures

It was shown by the previous seismic damages, that masonry structureswithout seismic fortification or being designed by the earlier seismic code wereseverely damaged in our country, with serious casualties and property loss. Inthis paper, with brick masonry as the research object, the validity of structurestrengthened with external steel reinforcement mesh mortar layer was testified.The discriminate method of seismic damage states was given. The references forseismic appraisal and strengthening of brick masonry structure especially foraged ones was provided, which had significant value for disaster prevention andmitigation of the enormous amount of buildings from urban and rural areas.The1:4scale model for shaking table test was designed as a typicalthree-storey-office building in1970’s as a prototype with references to theearlier seismic code, and strengthened with external steel reinforcement meshmortar layer. The first and second storey was strengthened and the third storeywas untouched as comparison. The key techniques of the process of modelingwere discussed, especially the determination of brick dimension and theco-working of the three different kinds of material, i.e. reinforcement mesh,mortar layer and brick wall. The selection of model material, the determinationof similitude relationship, the construction methods of details of seismicmeasure and reinforcement layer were presented. The realizing way of structuralmembers and the details of seismic measures were described in detail. Thescheme of shaking table test was determined, including simulation of wallvertical compressive stress, the artificial mass, the distribution of test instrumentand strain gauge, the selection of ground motions and the testing conditions.The shaking table test was completed and the experimental phenomena anddate was analyzed. There were three stages in the experiment, namely seismiccapability stage, damage mode stage and collapse stage. By comparing theresearch on strengthened storeys and unstrengthened storey, the whole structurestrengthened and unstrengthened, local positions with and without details ofseismic measure, the distribution of the major cracks in the wall, and the effectson local positions of seismic measure were analyzed. It was shown by testresults that by using external steel reinforcement mesh mortar layer, the seismicability of strengthened structure was improved significantly. The seismic abilityof strengthened storeys could meet the seismic fortification requirement of IXdegree which is＂repairable under fortification earthquake＂and＂no collapsing under rarely earthquake＂while the whole structure with unstrengthened storeycould meet the seismic fortification requirement of VIII degree, which meansthe seismic intensity increased by one degree at least. The weak position ofstoreys strengthened and unstrenghened were different and the damage mode ofstructure could be changed by reinforced layer. The dissipation ability and safetyof strenghened structure performs better than the unstrenghened ones. Thereinforcement layer and the brick wall worked together well when subjected toearthquake. The ability of collapse resistance performed well with the measuresof the details of seismic measures, such as reinforcement strengthen band, ringbeam and tie bar in brick wall. By analyzing the experimental data ofacceleration, displacement and strain, the acceleration amplification factor andinter-storey displacement suddenly changed in unstrengthened third storey. Thedistribution of earthquake load on lateral members was similar to the trends ofcalculation. The lateral displacement curves of the whole strenghened structurewere bending type.Then the discriminate method of damage state was studied, includingseismic ability and damage mode. Two concepts were discussed, namely indexof compound seismic capability in＂standard for seismic appraisal of building＂and coefficient of seismic capability in method of Yang Yucheng. By introducingthe method of Yang into standard for seismic appraisal with the simple type ofthe standard, three-leveled seismic ability discriminate method was provided,and formulations based on design parameters of ground motion were given.Based on the experimental results of brick masonry walls, after the occurrenceconditions of different damage modes were discussed, the practical discriminatemethod of the damage mode was given. Three examples were analyzed by usingthe discriminate method given in this paper. Those results were compared withreal seismic disaster phenomena. The feasibility of the method was verified.