A NEW APPROACH FOR NONLINEAR ANALYSIS OF REINFORCED CONCRETE STRUCTURES USING LATTICE ELEMENT METHOD

Abstract

Fracture processes due to mechanical loading are a major cause of damage in concrete structures. An adequate comprehension of these processes is important not only for ensuring safety of construction but also for optimizing the material behavior, which would fulfill beneficial economical effects. Apparently, crack formation and propagation in concrete are affected by its highly disordered structure. Therefore, this structure should be taken into account while modeling the material behavior. At present fracture is modeled at different level of observation, ranging from the macroscopic level, where material is considered homogenous and nonlinear -constitutive relations are used, to meso, micro, or even to atomic or sub-atomic scale. Lattice element method (LEM) is considered a pioneer approach in studying the behavior of concrete at different level of observation. The main objective of the current thesis is to introduce the LEM as a numerical modeling tool for studying the behavior of reinforced concrete structures on the macro level of observation. The LEM divides the analyzed medium into a net of 2-dimesion frame elements. These elements are connected by nodes each of which has three degrees of freedom. The reinforcement is modeled as continuous elements adjacent to the concrete elements. The failure of elements is reached when the calculated principal stresses of the elements exceed the cracking strength of the material. A computer program utilizing the LEM was developed to apply the method for different structural elements. The method is well verified in the linear analysis conditions to check the accuracy of calculated displacements and internal stresses. The results showed high accuracy if elements of small size are used. The study showed that increasing the number of elements improves very much the accuracy but increases the time required for solution. On the other hand, the regular square without diagonal elements mesh shape has been proved to be very adequate for the method compared with the regular square with diagonal elements. After verifying the results in case of elastic-loading condition, nonlinear material models are adopted in the program to follow the structural behavior under monotonic loading condition till the start of collapse. The material models that were adopted are; concrete compression, tension, and shear models, and steel compression and tension models. The simulation results are compared with the results obtained by several