Research On Overstrength Factors Of Reinforced-Concrete Frame Structures

The basic concept and the current research results of RC frame structure overstrength were simply introduced. The basic method and calculating process of overstrength factors, as well as various factors which bring about overstrength were emphasised. Based on existing study, this paper have mainly resolved the determination of overstrength factors. At the same time, the factors producing overstrength were also analysed to make the calculating factors in reason. The main work of this paper is as follow:(1) Determining the overstrength factors of RC structure. Firstly, according to the each adjustment coefficient in the expression for members cross-section seismic bearing capacity, the overstrength factors of RC structure were estimated. Then, the calculating method for characteristic value of horizontal seismic force based on current code, as well as the simplified plastic hinge method at the bottom of the column to calculate the characteristic value of bearing capacity of a story were introduced. Finally, the characteristic value of horizontal earthquake force were calculated for a 8-stories frame structure which are designed strictly according to Chinese seismic code. The bearing capacity of the structure were accounted by simplified plastic hinge method at the bottom of the column, and the overstrength factors of the RC structure were determined. Moreover, the pushover analysis were executed by ETABS software.(2) Factors analysising to bring on the overstrength. For 14 model of RC frame structures which are designed strictly according to Chinese seismic code, the effects of level number, story height, seismic fortification intensity, unilateral renforcement ratio, material hardening and redistribution of internal forces on frames construction overstrength were analyzed.By the researches above, the main conclusions can be obtained as follows: (1) the minimum overstrength coefficient of estimate is achieved to be 2; (2) As level number is increased, the overstrength factor is gradually increased; (3) As the story height is increased, the overstrength factor is gradually decreased; (4) As the seismic fortificationis intensity is increased, the overstrength factor is gradually decreased; (5) There is no direct relationship between the overstrength factor and unilateral renforcement ratio; (6) The overstrength factor is increased for material strength and redistribution of internal forces.