Tiejiong Lou

Flexural Response of Continuous Concrete Beams Prestressed with External Tendons

This article presents the results of a numerical investigation of the flexural behavior of continuous externally prestressed concrete beams. Aspects of behavior studied include the increase in stress in external tendons, moment redistribution in the postelastic range, and secondary moments as a result of prestressing. A finite-element model for the full-range analysis of continuous externally prestressed concrete beams is introduced. The model predictions agree well with the experimental results. The analysis shows that the ultimate stress increase in external tendons of continuous beams is dependent on both the number and rotation of plastic hinges that can be developed at failure load. The degree of moment redistribution is significantly influenced by the nonprestressed tension steel and the pattern of loading. An approach based on the linear transformation concept is designed to examine the secondary moments over the entire loading up to the ultimate. The results indicate that the secondary moments increase linearly with the prestressing force and can be conveniently calculated by an elastic analysis.

Effects of Ordinary Tension Reinforcement on the Response of Beams with Unbonded Tendons

This paper describes an analytical investigation of the flexural response of unbonded prestressed beams and the ultimate stress increase in unbonded tendons, with particular emphasis on the effects of bonded ordinary tension reinforcement. A numerical model, based on the finite element method incorporating an arc-length solution technique, is developed to predict the entire nonlinear response of concrete beams prestressed with unbonded tendons. The reliability of the proposed analysis is verified by comparing the analytical predictions with the experimental results. Two parameters relating to bonded ordinary tension reinforcement are analytically investigated. The analytical results show that an unbonded prestressed concrete beam without any ordinary tension reinforcement exhibits very poor behaviour. However, with the minimum amount of ordinary tension reinforcement provided, the flexural behaviour of the beam is greatly improved. The variable yield strength of ordinary reinforcement in combined reinforcing index is inappropriate in its current form since the calculated prediction is inconsistent with the actual trend of the variation of ultimate stress increase in tendons.

Interaction between Time-Dependent and Second-Order Effects of Externally Posttensioned Members

AbstractFor external tendon members subjected to sustained loads, the time-dependent effects resulting from concrete creep, shrinkage, and tendon relaxation would interact with the second-order effects resulting from the change in tendon eccentricities with the development of time-dependent deformations. This interaction should be adequately considered in a time-dependent analysis of this type of member. This paper presents a numerical model developed to predict the long-term behavior of externally prestressed concrete members at service conditions, taking into account the interaction between time-dependent and second-order effects. The proposed method of analysis is verified with the available experimental results. The time-dependent behavior of externally prestressed concrete members is evaluated, focusing on the effect of deviators and nonprestressed steel. The results demonstrate that the second-order effects result in significant changes in long-term responses other than the prestress loss. The effec...

Influence of Span-Depth Ratio on Behavior of Externally Prestressed Concrete Beams

This paper describes a numerical study on the flexural behavior of concrete beams prestressed with external tendons, focusing on the effect of the span-depth ratio on the response characteristics and the ultimate stress in tendons and ductility behavior. A nonlinear model, calibrated by the available experimental results of externally prestressed specimens, is used for the parametric evaluation. The results show that the second-order effects of externally prestressed beams with two deviators at third points become increasingly important with the increase of the span-depth ratio and that, due to these effects, a higher span-depth ratio registers a lower ultimate moment capacity. The effect of the span-depth ratio on the ultimate tendon stress is dependent on the type of loading for internal unbonded tendons and on the configuration of deviators for external tendons. The analysis also indicates that, irrespective of second-order effects, the span-depth ratio has an insignificant effect on the ductility of beams, and center-point loading mobilizes higher deflection ductility than third-point or uniform loading.