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CURATOR
A pinboard by
PRASHANT MOTWANI

RESEARCH SCHOLAR, INDIAN INSTITUTE OF TECHNOLOGY

PINBOARD SUMMARY

Investigating use of compiste strands in place of Steel strands in Prestressed Concrete application

The transfer of prestress force from prestressing strands to the surrounding concrete is dependent on the bond between the two materials. It is essential to understand the actual bond stress distribution along the transfer length to determine the transfer zone in pretensioned concrete. The first part of this study examine the effects of excessive slip on steel strand transfer length and moment envelop of pretensioned bridge girders. For this, a 3-D nonlinear Finite Element Model has been developed to simulate the transfer of prestress force from steel strands to concrete in pretensioned bridge girders. Overall slips of the steel strands over the transfer length were calculated from the Finite Element Model using a theoretical relationship proposed by previous researchers. Results obtained from the Finite Element analysis showed that the transfer length in the girders increases substantially due to the slippage of the strands. Investigation of the flexural behaviour of the bridge girder with varying strand surface conditions showed that the moment capacity of the girder with significant strand slips is reduced in the development region. It can thus be concluded that, strand slipping measurement should be added to the quality control procedures for pretensioned members. Steel strands are susceptible to corrosion and show very high prestress loss. A potentially alternative to prestressed Steel strands, would be Carbon Fiber Reinforced Polymer (CFRP) Strands and Aramid Fiber Reinforced Polymer (AFRP) Strands. Composite rods manufactured from artificial polymer materials such as Glass, Aramid and Carbon fibres can be adopted as strands for prestressing of concrete members. The use of composite materials like Fibre Reinforced Polymer (FRP) strands is evolving and is currently shifting from theoretical investigations into prototype installation. In the second part of this study, a 3-D linear Finite Element Model has been developed to simulate the transfer of prestress force from Steel, Carbon and Aramid fibre strands to concrete in a pretension member. The Finite Element Model has been validated using experimental studies. Overall slip of steel and FRP strands were calculated from the Finite Element Model using a theoretical relationship proposed by previous researchers and the end slips were directly measured from the Finite Element Model.

4 ITEMS PINNED

Strand bond stress–slip relationship for prestressed concrete members at prestress release

Abstract: The transfer of prestress force from prestressing strands to the surrounding concrete is dependent on the bond between the two materials. Understanding the actual bond stress distribution along the transfer length results in optimized design of the transfer zone of prestressed concrete members. Equations of estimating the transfer length in ACI 318 code and AASHTO LRFD bridge design specifications simply take into account the effect of the strand diameter only. The objective of this study is to provide a generalized procedure for determining the bond stress–slip relationship accurately by incorporating the effects of additional parameters, such as concrete compressive strength at prestress release, center-to-center strand spacing, and concrete bottom cover. First, the bond stress distribution along the transfer length of a prestressed concrete member is formulated based on longitudinal slip–strain compatibility, force equilibrium and invariable bond stress–slip relationship along the transfer length. Second, a generalized Inverse Problem-Solving approach is introduced to determine best parameter coefficients through minimizing the discrepancy between the calculated and measured results. Two types of measurements (i.e., transfer length and end slip) reported in the literature are utilized to demonstrate the proposed approach. Predicted transfer length and end slip values using the calibrated bond stress–slip relationship show better agreement with the test data compared to those predicted by ACI 318 code and AASHTO LRFD bridge design specifications. Third, a computational procedure is developed and an example is presented to assist engineers using the developed formulae for determining the bond stress distribution along the transfer length of prestressed concrete members.

Pub.: 30 Jan '15, Pinned: 27 Jul '17