Investigation Of Energy Balance Based Nonlinear Static Procedure And Damage-Reduction Design Spectra For Building Structures

Recently severe earthquakes hit the world frequently, which have caused significant engineering structure damage, calsualities and economic loss. As the level of urbanization increasingly improving in China, a great number of tall buildings have been built at most of large-and medium-sized cities, and some of them belong to earthquake-prone regions. Currently, it is still socially and economically worthwhile to improve the seismic capacity of engineering structures due to the unpredictable earthquake. Based on the key project "Investigation on the dynamic failure modes and damage-resistant/reduction optimum design for the super-high-rise buildings under the hazards (90815023)" in the major project "Damage evolution of civil infrastructure under strong earthquake and wind" funded by National Natural Science Foundation of China, this paper primarily focuses on the study of the simplified nonlinear analysis procedures, life-cycle cost optimum design and damage-reduction design for buildings under the earthquakes, which may provide the theoretic and methodological insights on seismic design for tall buildings.Firstly, the philosophy of seismic design for engineering structures, and the recent development of nonlinear static procedures (NSP), life-cycle cost oriented optimum design and structural damage-reduction design are briefly reviewed. The basis of the seismic analysis for buildings is systematically summarized, where the motion equations of the buildings under earthquakes, elastic modal time history and response spectrum analysis methods, nonlinear static procedures are covered. And the four classic nonlinear static methods are focused, including the equivalent linearization method, displacement coefficient method, N2method and modal pushover procedure.A great challenge to performance-based seismic design is to develop an effective and feasible procedure for analyzing and evaluating the seismic demands. Currently, nonlinear static procedure or pushover analysis is accepted by more and more guideline documents and codes, and being viewed as the standard practice. In order to avoid the reversal of the traditional pushover curve, the energy balance based multimode pushover analysis method is developed herein, which can capture the higher mode effects well. Compatiable with the capacity spectrum method, the proposed method has incorporated the concept of modal energy capacity and demand, and retained attractiveness with invariant force distribution. The planar structures under near fault ground motions are utilised to numerically evaluate the proposed approach effectively, and the energy demands of the higher mode are assumed to be elastic, which the proposed method can predict the seismic demands well.Then the applicability of the proposed method for one-way asymmetric-plan buildings, including Torsionally-stiff (TS), Torsionally-similarly-stiff (TSS), Torsionally-flexible (TF) structural systems, are investigated in this paper. It is shown that the proposed method estimates the seismic responses well for TS and TF systems with elastic modes weak-coupled, while underestimates the seismic demands greatly for TSS system with elastic modes strong-coupled. Additionally, the accuracy of the proposed method decreases as the intensity of the ground motion increases. In essence, the proposed method is an extended version of response spetrum analysis method in the inelastic range.Besides, the life-cycle cost oriented structural optimization design using the modified modal pushover analysis procedure has been carried out. The damage loss is estimated through the fuzzy-decision technique, and the adopted modified modal pushover method can capture the higher mode effects effectively. It is to be mentioned that the design spectrum based practical modal pushover procedure is utilized as the seismic analysis considering the seismic design displacement demands easily in the process of the optimization. The proposed optimization problem is solved by the adaptive simulated annealing algorithm, in which not only have the cost-effective optimum design achieved, but it is found that the stuctural robustness of the optimum design has been improved greatly as well.Finally, the building systems with metallic structural fuses are investigetd in detail. In the damage-reduction design the entire structural system is conceptually divided into two parts:the main functional struture and the damage-reduction element (or structural fuse). Under the strong earthquake the damage-reduction elements are damaged through dissipating the energy or even completely sacrificed to protect the main functional structure. The damage-redution spectrum has been formulated through the ductility equation of the trilinear single degree of freedom (SDOF) system, and parameterally studied, in which the effective parameter sets satisfying the structural fuse concept are obtained. Then the period constraint condition and the equations of demanded yield forces are formulated, the force-based design and retrofit procedures are given respectively, and a design example is utilized to show the effectiveness of the proposed procedures.