Slenderness effects in prestressed concrete columns.

Abstract

The main goal of this research was to develop a rational methodology to account for material and geometric nonlinearities and the effect of sustained loads due to creep and shrinkage in prestressed concrete columns and bearing walls with rectangular or flanged shapes. This goal was accomplished through the following objectives: (1) developing an analytical model utilizing the nonlinear analysis of the finite element concept, (2) verifying the accuracy of the model by comparing predicted results with the available experimental results, (3) running parametric study to evaluate the effect of various variables on ultimate load and effective EI, and (4) developing design procedures. The analytical model was implemented in a general computer program in Fortran-77 language. The program was used to predict the load-deflection curves and the ultimate loads of one hundred-forty three tested prestressed concrete columns and walls from three independent investigations. Good agreement is observed between the analytically obtained results and the test results. The investigated parameters were the slenderness ratio, the concrete strength, the area of steel, the depth of steel, the effective prestress, the ratio of sustained load and the eccentricity of the load. Various conclusions about the effect of these variables were drawn. Finally, an alternative method for calculating the effective EI was proposed and verified by comparing it to analytical and experimental data. The main conclusions of this study were: (1) the finite element model developed in this study provides an accurate prediction of experimental results of prestressed concrete columns, (2) the effective EI is significantly affected by numerous variables such as eccentricity of the load, percentage of steel, and other component materials, and (3) the proposed design methodology simulates actual behavior of PC columns much better than the current ACI-Code and PCI recommended procedures.