Multi-Scale Analysis Method Of Force Flow Transfer And Crack Propagation In Concrete Structures

Multi-scale analysis is the process that different scale elements or principles are adopted in different parts of the model according to actual needs. In civil engineering field, multi-scale problems can be divided into two kinds in accordance with research purpose, namely, structure multiscale and material multiscale. There are mainly two research points in the paper based on the multiscale idea:configuration of strut-and-tie models (STM) and crack propagation in concrete structures. And the advantages of the multiscale method are certified by means of theoretical derivation, numerical simulation and experiments in the lab. Moreover, the two research points are combined organically to guide reinforcement design of disturbed regions in concrete structures. Main research contents are as follows:(1) Bidirectional topology optimization programs are developed based on the evolutionary structural optimal method (ESO). The function of the programs are to find the optimal load-transfer configuration and then confirm the STM of the structure. Due to incompetence of traditional finite element models and optimization methods, a new region-dividing ESO method is proposed based on the multiscale analysis. On this basis, load-transfer laws and STMs of some regions are studied, such as, anchorage zones, box girders.(2) A program for generating three-phase composite material models of meso-scale concrete is developed based on Monte Carlo stochastic theory and non-uniform characteristics of concrete. In consideration of non-uniform characteristics of each phase itself, the Weibull distribution function is introduced to describe the mechanical parameters of each phase, furthermore, the defect of traditional Weibull distribution function is improved. In the respect of crack propagation simulation, a new practical method for simulating crack path is put forward and corresponding concrete fracture algorithm is compiled.(3) Depending on the practical engineering, crack propagation experiments of concrete structures under direct and indirect loads are conducted. On the basis of crack propagation procedure under direct loads, a complete set of codes are compiled for the simulation of concrete fracture under temperature-humidity coupling loads. Then the algorithm is used to simulate the test process. A series of beneficial conclusions are obtained by comparing numerical results and experiment data.(4) There exist some organic connections between the STM idea and fracture propagation theory. In the paper, combined application of the STM design method and crack propagation technology is executed. The ideal STM confirmed by multiscale optimization method can be simplified in virtue of crack position and distribution obtained by crack simulation technology. The reinforcement design can be executed referring to ACI-318 specification after internal forces of struts and ties are obtained.(5) Based on the finite element analysis software ANSYS, a piece of software is developed to simulate the fracture process of meso-scale concrete structures by using APDL language and Tcl/Tk language. The software is embedded in ANSYS in the way of seamless connection. At last, practicability of the software is tested and certified by an application example.