Tests On Seismic Behavior Of Framed Columns Designed With Gravity Loads

The seismic fortification level in Chongqing is 6 degree according to the current Seismic Design Code of Buildings, GB50011-2001.But there are large amount of existing buildings that were designed only with gravity loads when the design code was not enforced. Besides, the Three Gorges Dam may induce earthquakes in the very near future; the buildings in this area may face with increasing seismic risk. Historical experiences of earthquake disasters in the areas with similar situations are not uncommon. Therefore, it is imperative to evaluate seismic behavior of such existing buildings.In this paper, comparative cyclic tests were carried out to investigate seismic behavior of framed reinforced concrete columns designed with gravity loads and/or designed with minimum reinforcement required by the seismic design code for the buildings in the area, where fortification level is 6 degree, and detailing is the third grade. The deformation capacity in particular, is evaluated in detail to show quantitatively the difference between. On this basis, retrofitting measures were proposed and tests were carried out.The following are main points of research and conclusions.(1) Cyclic loading tests of 6 RC framed columns taken from a six-story-three-bay frame, which were designed with gravity loads and seismic requirements of fortification level 6 degree, were carried out. The resulting difference show that earthquake-resistant capacity of the framed columns designed with gravity loads is terribly weak, both deformation and energy dissipation capacity are far behind the requirements of the seismic design code.(2) Two more framed columns designed with gravity loads were retrofitted using steel plate at the ends of the column. And cyclic tests were taken to evaluate their seismic behavior. Analysis of the experimental results shows that seismic behavior of these two columns has been improved significantly. Therefore, the retrofit scheme is very efficientShear equations from seismic design codes of GBJ10-89, GB50010-2002 and ACI318-99 were implemented to evaluate shear capacity of the framed column specimens in this paper. The analytical results show that the GBJ10-89 and GB50010-2002 codes may not be appropriate to estimate the shear capacity of framed columns designed with gravity loads or with minimum reinforcement...