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It is necessary to use large-diameter (0.7 and 0.85 in. [17.8 and 21.6 mm]) strands in unbonded post-tensioned structures to address the question on flexural response, particularly regarding its strength. A series of experiments were conducted to investigate the ultimate stress of the large-diameter strands as unbonded tendons in simply supported members. Two crucial factors—prestressing reinforcement index and global reinforcement index—are obtained from the cross-sectional equilibrium equation and test data of the present and already-existing experiments. Both crucial factors are used to derive equations to predict the increase in stress and ultimate stress of large and normal diameter strands. Evidences support the behavior and demonstrate the feasibility of large-diameter strands for PT structure in terms of static loading. [ABSTRACT FROM AUTHOR]

The behavior of rubber layers under pure compression has been investigated to considerable extent in the literature. The most widely used approach is the so-called pressure solution , which is based on several assumptions, most notably that the stress state is dominated by the hydrostatic pressure. Other approaches have also been considered, but for nearly incompressible material and thin layers their predictions are very similar to those of the pressure solution. Nearly all past studies on the subject have focused on rubber layers that are bonded to either rigid or flexible supports (or reinforcement). Unreinforced (i.e., single layer) rubber pads are often installed as unbonded, i.e., without steel end plates connecting them to their top and bottom supports. In an unbonded application, rubber pads rely solely on friction to develop shear resistance along the contact interfaces. This shear resistance is necessary to provide the pad with an adequately large vertical stiffness. The effect of the frictional restraint along the top and bottom contact surfaces and the influence of partial slip have received very little attention in the literature. In this paper, we present a theoretical analysis for the behavior of an unbonded rubber layer, including the effects of the elastomer’s bulk compressibility and the contact slip at the supports. Results of a finite element analysis are also presented and shown to be in good agreement with the results of the theoretical analysis. [ABSTRACT FROM AUTHOR]

A full-scale experimental study was undertaken to observe and assess the behavior of continuous concrete beams with external prestressed bars. Three beams--a control beam and two comparable beams strengthened using external prestressed bars--were tested in two-point loading of the interior span of three continuous spans. The diameters of the external prestressed bars were 18 and 22 mm (0.71 and 0.87 in.), respectively. For the strengthened beams, V-shaped profiles were used with a deviator located at the middle bottom of the interior span, and the effective prestress was 45% of the yield strength of the external steel bars. Test results indicate that the external prestressing increased the load-carrying capacity by about 25% and the flexural stiffness by about l5%. An analytical model developed by the authors was applied that uses the beam collapse mechanism, plastic hinge length, and deformation of external bars depending on the beam deformation at the deviator point. Predictions of the nominal strength and the corresponding external bar stress compared closely to the test results. [ABSTRACT FROM AUTHOR]

The objective of this paper is to study the influence of thickness of individual elastomer layers (first shape factor) on the vertical and horizontal responses of fiber reinforced elastomeric bearings that are not bonded or mechanically fastened to their top and bottom supports. By definition, the first shape factor, S1, is the ratio of the plan area to the perimeter stress-free area of a single elastomer layer within the bearing. Results of a comprehensive 2D-finite element study on a large group of bearings with different shape factors of 10, 15, 20, 30, and 40 suggest that the shape factor S1 is a critical parameter in controlling both the vertical compression modulus of the bearing and the level of stress in the fiber-reinforcing layers. Furthermore, the secant horizontal stiffness and the stress demand in the bearing elastomer material are to a limited extent influenced by the parameter S1. [ABSTRACT FROM AUTHOR]

This paper reports on the experimentally observed response of five large-scale, isolated, multi-story, unbonded post-tensioned (UPT), precast concrete walls with horizontal joints under combined gravity and lateral loading. Test results show that the limit states that characterize the lateral load response of the walls occur as anticipated. The results demonstrate that the response of UPT precast concrete walls can be controlled by adjusting parameters such as the total area of post-tensioning (PT) steel and the level of prestressing. In addition, the results show that these walls can undergo significant nonlinear lateral drifts without significant damage while maintaining their self-centering characteristics, eliminating residual lateral drift. [ABSTRACT FROM AUTHOR]

Shake table testing and an analytical study were conducted to investigate the seismic performance of unbonded prestressed hollow concrete columns constructed with precast segments. A prototype column was designed based on the current bridge specifications by AASHTO. A one-fourth-scale model column was constructed by match casting. Shake table testing that consisted of 15 runs based on the 1995 Hyogo-Ken Nanbu (Kobe) Earthquake was conducted. The specimen performed very well with essentially no residual displacement and only limited concrete spalling at the base. A parametric study was conducted using a nonlinear twodimensional finite element pushover analysis. An equation to estimate the strain in the prestressing strands was proposed. A simplified method to calculate the load-displacement relationship showed good correlation with the pushover analysis results. Unbonded prestress columns can be designed to provide excellent drift capacity with limited permanent displacements. [ABSTRACT FROM AUTHOR]

This study presents the development of an analysis method to predict the moments at first yielding and at ultimate strength of reinforced concrete beams strengthened using a V-shaped posttensioning steel rod system. The analysis requires determination of a total elongation of the external posttensioning rods, which is interdependent upon the neutral axis depth, deflection, and strains and stresses in beam components at both internal steel yielding and ultimate strength stages. The iteration algorithm was computationally programmed. The test results from a total of 14 full-scale beams were used to verify the analysis method that predicts the yield moment, moment capacity, and corresponding unbonded steel rod stresses. Finally, a flexural design method is developed for reinforced concrete beams externally posttensioned using a V-shaped steel rod system. [ABSTRACT FROM AUTHOR]