Off-campus UMass Amherst users: To download dissertations, please use the following link to log into our proxy server with your UMass Amherst user name and password.
Non-UMass Amherst users, please click the view more button below to purchase a copy of this dissertation from Proquest.
(Some titles may also be available free of charge in our Open Access Dissertation Collection, so please check there first.)
Nonlinear behavior of frames with flexible joints
Abstract
The purpose of this research is to carry out geometric and material nonlinear analyses of planar frames with rigid, hinged, and flexible joints. The stiffness matrices of elements with various boundary conditions are derived using the energy method. The elements are subjected to both axial load and bending and their stiffness matrices are functions of the axial load. Each member is idealized by a series of finite elements. Structure deformations, reactions, and internal member forces are obtained through the matrix stiffness method of analysis. The research consists of three main parts. The first deals with geometric nonlinear analysis of frames. P $-$ $\Delta$ effects are taken into account in the analysis since equilibrium equations are based on deformed geometry. An evaluation of the number of finite elements used in frame analysis and the influence of flexible bays on rigid bays are also included. Two methods of analysis, the second-order incremental and the direct methods, are presented. In the second part of the investigation inelastic stresses are also included and a frame is analyzed up to the collapse load. The load increases monotonically, the material is elastic-perfectly plastic and the plastic hinges form only at element endpoints. Reduction of plastic moments due to axial loads is also included. Three methods of analysis--two incremental and one simplified nonincremental--are discussed here. In the first the well known slope-deflection equations are employed. The real values of the stiffness coefficients are considered. The second method is again incremental and uses member tangent stiffness matrices. The third is a simplified method and essentially uses the direct rather than the incremental procedure between two successive plastic hinges. The inclusion of the nonlinear behavior of flexible joints in a second-order inelastic analysis is studied in the third part of the thesis. The nonlinear behavior of seven types of connections are described by nonlinear parametric functions found in the literature. These functions are replaced here by piece wise linear functions. Two methods are presented that use secant stiffness matrices within a load step. The first is a linear incremental method that does not iterate within a load step and assumes the stiffness coefficients for the flexible joints already existing at the beginning of the load step. By comparison, the second method is incremental nonlinear and performs iterations within a load step in order to calculate the correct stiffness coefficients of the flexible joints.
Subject Area
Civil engineering|Engineering|Aerospace engineering
Recommended Citation
Delis, Efthymios A, "Nonlinear behavior of frames with flexible joints" (1991). Doctoral Dissertations Available from Proquest. AAI9207384.
https://scholarworks.umass.edu/dissertations/AAI9207384