Collapsing process simulations of timber structures under dynamic loading II: simplification and quantification of the calculating method
In a previous paper we presented the efficacy of the extended distinct element method (EDEM) on the collapsing process simulation of timber-frame structures. The results obtained were qualitative, and the need for quantitative simulation was pointed out. In this report, we improved our simulating programs with the aim of establishing a quantitative simulation by EDEM. For this purpose, the parameters of the frame members (beam or column) were determined by comparing the simulated results of four-point bending tests with experimental results. Other parameters of plywood and joint members were determined by simulations of two rail shear and slip tests of joint parts, respectively. Using these parameters we made simulations of the collapsing process of an actual-size plywood-sheathed wall and at the same time carried out the experiments under similar conditions. Simulated load–displacement curves of the plywood-sheathed wall were similar to those obtained in the experiments, and the sequence of failure at nailed joints of the simulation model gave good agreement with that of the experimental collapsing processes. Using these processes, we believe that we established a basic quantitative simulation method to test the collapsing process of timber-frame structures.
Seismic performance of post and beam timber buildings I: model development and verification
This paper presents a structural model called “PB3D” to perform nonlinear time history analyses of post and beam timber buildings under seismic loads. The model treats the three-dimensional structure as an assembly of roof/floor diaphragms and wall subsystems. The roof/floor diaphragms are modeled by beam elements and diagonal brace elements in order to take into account the in-plane stiffness. The wall system consists of vertical beam elements, for wall posts, as well as nonlinear shear springs to consider the contribution of diagonal wall bracing members or sheathing panels. The hysteretic characteristics of the shear springs are represented by a simplified, mechanics-based model named a “pseudo-nail”. Standard finite element procedure is used to construct the system’s equation of motion, which is solved by Newmark’s integration. The model was verified against shake test results of a three-story post and beam building subjected to strong ground motions scaled to the 1995 Kobe earthquake. Model predictions agreed very well with the test results in terms of base shear forces and inter-story drift responses. This model provides a robust and efficient tool to study the seismic behavior of post and beam timber buildings.
FRACTURE ANALYSES OF CONCRETE STRUCTURES BY THE MODIFIED DISTINCT ELEMENT METHOD
A new method for analyzing the fracture of concrete structures is proposed in which concrete is considered a granular assembly. Because concrete is a complex, extremely heterogeneous material, it is difficult to analyze it's failure properties by the Finite Element Method (FEM) in which concrete is considered a homogeneous, continuous medium. We have developed a Modified Distinct Element Method (MDEM) that can be applied to the problems of fracture of concrete structures. In the MDEM the respective major constituents of concrete, gravel and mortar, are represented as circular particle elements and nonlinear springs, called pore-springs. We have used the MDEM to simulate the dynamic fracture behavior of concrete structures. The numerical results obtained are in good agreement with the seismic damage recorded during past earthquakes.