NONLINEAR BEHAVIOR OF PARTIALLY PRESTRESSED CONCRETE MEMBERS

The object of this research is to study the effects of nonlinear behavior of partially prestressed concrete members. Of particular interest are the analytical models used to develop computer and manual methods for predicting deflections. This dissertation reviews the following sources of nonlinearity. The first of these sources is that caused by material properties, such as creep and shrinkage of concrete, and relaxation of prestressing steel. The second source is due to cracking of concrete under loading. A review of the current analytical methods is presented. This review shows that the use of the linear law of creep and age-adjusted modulus of elasticity produces an accurate model of nonlinearity due to material properties. For cracking conditions, the model may be further developed by modification of the member rigidity. A computer model and a manual method are developed using the above mentioned theories. The computer model is verified against test data. The accuracy of the manual method is substantiated by comparison of its results with those obtained by the computer model. A discussion of the causes of tension stiffening is presented. The empirical approach for consideration of tension stiffening in conventionally reinforced members is reviewed. An extension of the empirical method for application to prestressed members is proposed. A comparison of the empirical methods and results from computer predictions is accomplished. The two methods proposed here are offered as engineering design aids. The computer method is suited for statically indeterminate, multilayered prestressed concrete beams and frames. It requires a significant amount of computer memory and execution time due to the complexities of material and geometric nonlinearities. The manual method is intended as a powerful means of approximately calculating immediate and long-term deflections of simply supported noncomposite beams. The manual method empirically accounts for tension stiffening