Determine The Reasonable Structure, The Modal Number. Vibration Mode Decomposition Method

It's necessary to decide the reasonable mode number when we are analyze earthquake action in construction design. There are some advice and computation methods on reasonable mode number in some internal and external books, but these methods have no sufficiency testimonies, so it's to important that how to decide the reasonable mode number in more rational method.At first this paper brings forward that it ought to decide the reasonable mode number according to definite base related to the advice of ((code for seismic design of building)} (GB50011?001) which computes 9 ~ 15 modes when we design buildings constructions calculating torsion. So firstly this paper probes into the settling method of the construction vibration system characteristic problems, thus establishes theoretical base of the later expatiation.In the following the paper expounds the earthquake response spectrum^ the response spectrum curve and the most important portion------the meaning and the usage of design earthquake response spectrumetc. The chapter 4 enters this paper's core in due form------the decision ofreasonable mode number in mode-superposition method. The method gets from mode-superposition method on earthquake response analysis. It puts forward a method of deciding the reasonable mode number by controlling eigen parameter when we design buildings. The method of controlling eigen parameter can be classified into two methods: controlling effective eigen parameter and controlling mass center eigen parameter. The paper precisely proves these methods, and the feasibility and the veracity of these methods are demonstrated. It point out that controlling mass center eigen parameter more rational because it control the eigen parameter of every story and every direction. In this chapter the realizing way of these methods is pointed out. At the same time, the paper still demonstrates the method of deciding mode-number by effective mass, and compares these methods.How to realize the method of deciding reasonable mode-number by controlling eigen parameter ? The chapter 5 has the result. This portion clearly clarifies the relation of effective mass and earthquake force and the relation of eigen parameter and displacement N earthquake force, so the comparison of two methods can go on more successfully. Simultaneously a lot of examples are done with and analyzed in order to decide the coefficient.Chapter 6------the conclusion comes from the demonstrations above.It points that the method of deciding reasonable mode-number by controlling mass center accumulative eigen parameter is based on eigenvalue and is rational while the method of deciding mode-number by effective mass is found on the mass although both are the methods of deciding mode-number. Relatively, the former controlls the eigen parameter of every direction of every story; the later controls the total mass of the construction .