Research On Progressive Collapse Resistance Of Structure Based On Alternative Path Method

Progressive collapse is defined as the spread of an initial failure from element toelement, eventually resulting in the collapse of an entire structure or adisproportionately large part of the structure. Several structural progressive collapsetook place in the last decades. As the initiating event is unknown, the purpose of thestudy is not to limit or eliminate the initial damage directly, and is to estimate whetherit will collapse after an initial damage and to improve progressive collapse resistanceof a structure.A regular concrete structure and an irregular concrete structure were designed,the dynamic effects of these models were discussed using alternate path method. Theprogressive collapse resistance of these models was discussed, and the differentmethods for resisting progressive collapse were provided. The detailed researchcontents and conclusions are as follows:1、The regular building was more likely to collapse after a column in the upperfloor removed than a column in the bottom floor removed. Progressive collapse fromthe top floor to the bottom floor occured after the corner column or the long edgecolumn in the upper floor removed. The structure did not collapse after a innercolumn or a short side column removed.2、 Nonlinear static analyses according to dynamic amplification factor inDoD2010can reflect dynamic response of structure just after column removal, but thedevelopment of damage and vertical displacement are ignored.3、X-type tie force method provided the alternative load path and reduce verticaldisplacement of joints soon after column removal, and prevented the damage of somecomponent. The ties along the floors in DoD2010were benefical to develop thetensioned membrane effect and were better than the ties along the beams in DoD2005.Tie force methods in DoD2005and DoD2010were invalid in restraining verticaldisplacement of joints soon after column removal, but can restain the development ofvertical displacement. The two methods were all beneficial for resisting progressivecollapse, but were not better than X-type tie force method.4、The irregular building with L-plan was more likely to collapse after a convexcorner column removed than a concave corner column removed. When a cornercolumn and a short-side column were removed, Beams, columns and floors above two columns collapse, and vertical displacement tended to accelerate more rapidly thancases after a column removed. Progressive collapse would occur from the sixth floorto the first floor. When two columns near the concave corner were removed, floorsabove two columns fall to the under floor, but the damage was not as serious as abovecase.5、Two retrofits were considered and their performances were compared with theoriginal L-plan structure. The analysis results showed that the steel braces in the roofwere effective in increasing the integrity of the structure and providing the alternativeload paths after the loss of the column. Reinforcement in all the beams and thecolumns were effective in increasing the structure strength and reducing progressivecollapse potential of the structure.