PROPOSAL OF HYSTERESIS MODEL OF TIMBER SHEAR WALLS CONSIDERING FATIGUE BEHAVIOR AND APPLICATION TO EQUIVALENT LINEARIZATION TECHNIQUE

Study on fatigue behavior of timber structures subjected to repeated earthquake motions: Part 2

Abstract

 Mechanical performance of timber shear walls is clearly related to the loading protocol because the components indicate fatigue phenomenon. Several hysteresis models of timber structures for time history analysis have proposed, and some of them took the strength deterioration due to fatigue behavior into account. In this paper, a new hysteresis model considering fatigue behavior is developed. The key idea is to express the effect of fatigue behavior by downward modification of the envelope curve. In addition, equivalent linearization technique considering performance deterioration is discussed. The authors have reported that maximum earthquake response is not always controlled by response spectrum and the input energy is likely to be the additional parameter.

 Chapter 2 introduces the algorithm of proposed hysteresis model. The rule to consider the fatigue behavior mainly follows the method the authors have proposed, but some improvements are made. Chapter 3 and chapter 4 introduce comparison between analytical results by the proposed model and experimental results of static random loading test and shaking table test, respectively. Chapter 5 introduces application of the fatigue evaluation to equivalent linearization technique. Chapter 6 concludes this paper. The followings are findings of this research.

 1) Hysteresis model considering strength deterioration due to the fatigue behavior was proposed. The key ideas are to express the strength deterioration by downward modification of envelope curve and to take the effect of interaction between positive/negative damages of plywood type walls into account.

 2) The proposed model could simulate experimental results of static random loading test and shaking table test.

 3) It was found that deterioration of equivalent stiffness K_eq and equivalent damping ratio h_eq could be related to accumulated responses(f(Δ, n) and Δ_n/Δ) up to the maximum response. Evaluation method of K_eq and h_eq considering the deterioration by energy spectrum were proposed.

 4) Based on the above method, equivalent linearization technique considering deterioration during earthquake response was proposed. Since lower limits of equivalent stiffness and equivalent damping ratio which were associated with deterioration were estimated, the proposed method could conservatively predict results of time history analysis.

 Although response spectrum method is originally to predict maximum earthquake response, input intensity which causes ultimate deformation is predicted. In order to extend the method to arbitrary deformation level, additional study is required, and it will be presented in the next paper.