An improvement to the direct stiffness calculation(DSC) method for bending-type frame structures was proposed here,it could be used to conduct damage assessment.The corresponding system identification toolbox in the platform of OpenSees was expected to be used in engineering.The proposed improvement was simple,but apparently quite effective,the modification of the DSC method for damage detection and the system identification toolbox were applicable to practical bending-type frame structures.Aiming at the benchmark test of a 12-story reinforced concrete frame model performed on a shaking table in Tongji University,a simulation model for this benchmark test under excitation of several seismic waves was evaluated to verify the modified DSC technique and the system identification toolbox.The results showed that the preliminary assessment using the improved direct stiffness method and the corresponding system identification toolbox is feasible and efficient for damage detection of bending-type structures.

Abstract:The numerical simulations for the benchmark test of a 12-story reinforced concrete frame model carried out in Tongji University in 2003 were conducted in consideration of cumulative effect caused by series of earthquake events in platform of OpenSees. Meanwhile the damage status of the model was evaluated by using the System Identification toolbox of OpenSees formed by the principle of the improved direct stiffness method. Through comparison with the damaging description in several cases during the test, it is demonstrated that the preliminary assessment by using the System Identification Toolbox to conduct damage detection of 3-D frame structures in different direction are feasible and effective.

An improvement to the Direct Stiffness Calculation (DSC) method and corresponding new damage index, Stiffness Variation Index (SVI), is proposed in this paper. SVI is a parameter related to modal curvature and bending moment calculated, respectively, by central difference scheme to displacement and integral method to load. The proposed improvement makes the DSC technique applicable to damage detection of practical bending-type structures. Research on the effect of measurement errors was performed through numerical simulation. Moreover, a continuous steel beam was tested to verify the modified DSC technique in the condition of concentrated damages. The limitation of measurement points and number of modes are discussed. The results show that the improved direct stiffness method is feasible and efficient in the damage detection of bending-type structures.