• International Journal of Concrete Structures and Materials
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• 제11권1호
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• pp.1-16
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• 2017

The compression or tension-controlled failure mode of concrete beams prestressed with unbonded FRP tendons is governed by the relative amount of prestressing tendon to the balanced one. Explicit assessment to determine the balanced reinforcement ratio of a beam with unbonded tendons (${\rho}^U_{pfb}$) is difficult because it requires a priori knowledge of the deformed beam geometry in order to evaluate the unbonded tendon strain. In this study, a theoretical evaluation of ${\rho}^U_{pfb}$ is presented based on a concept of three equivalent rectangular curvature blocks for simply supported concrete beams internally prestressed with unbonded carbon-fiber-reinforced polymer (CFRP) tendons. The equivalent curvature blocks were iteratively refined to closely simulate beam rotations at the supports, mid-span beam deflection, and member-dependent strain of the unbonded tendon at the ultimate state. The model was verified by comparing its predictions with the test results. Parametric studies were performed to examine the effects of various parameters on ${\rho}^U_{pfb}$.

• Steel and Composite Structures
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• 제26권2호
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• pp.213-226
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• 2018

This paper focuses on the seismic protection of slender old masonry structures by the implementation of prestressing devices at key locations. The devices are vertically and externally located inside the towers in order to be reversible and calibrated. An extensive parametric study on a selected slender tower is carried out based on more than 100 nonlinear static simulations aimed at investigating the impact of different parameters on the seismic performance: (i) different prestressing levels; (ii) shape memory alloy superelasticity and (iii) changes in prestressing-forces in all the stages of the analysis until failure and masonry toe crushing. The tendon materials under analysis are conventional prestressing steel, fiber-reinforced polymers of different fibers and shape memory alloys. The parametric study serves to select the most suitable prestressing device and optimal prestressing level able to dissipate more earthquake energy. The seismic energy dissipation is evaluated by comparing the structural capacity curves in original state and retrofitted.