عبدالامام كريم مهدي أبوصيبع

ABSTRACT: Post-tensioning techniques have become very popular and a primary method in long spans continuous bridges and other structures due to their excellent performance in controlling cracking and excessive deflection. Moreover, the use of continuous prestressed concrete beams leads to shallower cross-sections, requires less maintenance cost, and enhances the durability of concrete in the negative moment region. Since using post-tensioned unbonded tendon requires particular analysis methods to predict the stress in the unbonded tendon because of the bond lack between the tendon and the adjacent concrete, thus this research presents an analytical approach to estimate the stress in the tendon and provide full-range of load versus deformation at different location of the span length at various load levels. The model used a trussed-beam system in additional to moment and force equilibrium equations to find the unknowns which include the stress in the unbonded tendon, deflection, and neutral axis depth. The analytical part included analyzing and estimating the stress in the unbonded tendon for beams subjected to a third-point and single-point load. The proposed approach was validated with results from the performed beam tests in addition to test data in the literature. The experimental part included 20-ft long continuous High Strength Concrete (HSC) beams post-tensioned internally with bonded and unbonded tendons. The experimental approach included casting, instrumenting, and load testing of 8 continuous span beams at various levels of prestressing and combination of tendons. Various design parameters such as the area of non-prestressed steel in tension at the maximum positive and negative moment locations and effective prestress in the bonded, and unbonded tendons are considered. Both models show a good correlation between predicted and experimental results. Furthermore, the effect of different design parameters on the flexural response was investigated. This study demonstrates that some design parameters have a significant influence on the results while the impact of other variables can be ignored.

ABSTRACT In this investigation, an analysis is presented for estimating the in-plane large displacement elastic stability behavior of rigidly jointed statically indeterminate steel frames and trusses consisting of members with rigid gusset plates subjected to proportional increasing loads. The analysis adopts the beam-column approach and models the structure's members as beam-column elements. The formulation of the beam-column element, is based on Eulerian approach, allowing for the influence of the axial force on bending stiffness. Also, changes in member chord length due to axial deformation and flexural bowing are taken into account. The stability and bowing functions with gusset plates and including shear effect for prismatic and non-prismatic members have been derived in this study and compared with the other researchers. The formulation of the modified tangent stiffness matrices (TSM) in local and global coordinates for prismatic and non-prismatic members, which takes into account the effect of geometrical nonlinearity, the effect of the presence of the gusset plates and the shear effect have been presented. These matrices take the form of the classical tangent stiffness matrix in case of absence of end member's gusset plates (i. e., g1=g2=0) which has been already clarified in the study. In addition, a special procedure used in the calculation of axial force has been presented with a modified axial deformation formula for members with gusset plates, this formula takes the form of the classical formula in case of absence of gusset plates which has been already clarified in the study also. The present study helps to analyze structures consisting of members with gusset plates and by including shear effect by treating each member as a single member, then the results of analysis are compared with exact solution by considering each member to be consisting of three elements, one of inner part with classical properties of the member and two terminal parts with infinite rigidity. So, a multi-purpose computer program (NAGMSHE) has been coded in Quick Basic (version 4.5) language for carrying out the proposed analysis. In order to verify the effectiveness of the new modified tangent stiffness matrix and the modified axial deformation formulation, some case studies reported by previous researchers are utilized for analogies presented in the current study. As a result of this investigation, several important conclusions are drawn, which assure the necessity of including the influencing parameters in the analysis of the large displacement elastic behavior of structures, the effect of gusset plates ranging from (6.3-22.3%) for the critical load in structures. In addition, it is concluded that the new modified Tangent Stiffness Matrix and all other modified proposed formulas developed for the first time, represent a good tool with which the large displacement elastic behavior of steel structures with gusseted members can be well estimated.