Strengthening precast-prestressed hollow core slabs to resist negative moments using carbon fibre reinforced polymer strips: an experimental investigation and a critical review of Canadian Standards Association S806-02

Abstract

Behaviour of precast-prestressed hollow core slabs has been extensively studied when these slabs are subjected to positive bending moments, a practical application typical of hollow core slabs. However, in many projects it may be required to have an overhanging part of the roof to act as a cantilever. In doing so, and using precast-prestressed hollow core slabs, the slabs would be subjected to negative moments, atypical for hollow core slabs. In this paper, the behaviour of precast-prestressed hollow core slabs is experimentally investigated when they are subjected to negative bending moments. A proposed strengthening detail to increase the negative moment resistance of hollow core slabs using bonded carbon fibre reinforced polymer (CFRP) strips is presented. The CFRP strips were bonded to the top side of full-scale precast-prestressed hollow core slabs in the negative moment zone in different configurations. In two of the tested slabs the bond between the prestressing strands and the concrete was initially broken (during casting of the slabs) in the negative moment zone. The slabs with the bonded CFRP strips were tested to failure and the load–deflection behaviour was recorded. The results of the tests are presented and the strength enhancement of the hollow core slabs using the proposed technique is reported. The increase in the negative moment resistance of the CFRP-bonded hollow core slabs experimentally determined is also compared with the CSA-S806-02 prediction for the moment resistance of concrete elements with bonded CFRP strips.Key words: carbon fibre reinforced polymer (CFRP) strips, hollow core slab, flexure strengthening, prestressed concrete, precast slabs, prestressing strands.

A State-of-the-Art Review on Debonding Failures of FRP Laminates Externally Adhered to Concrete

“…Bakay et al (2009) gathered current analytical models for predicting the strength of RC beams reinforced with FRP and applied them to an experimental program. These methods included Canadian standard CSA (2002) from ISIS Canada, the simplified shear method (CSA 2002), shear friction, the Blaschko et al (1998) model, the Plevris et al (1995) model, andthe Hosny et al (2006) model. The ISIS guidelines do not provide information on how to predict shear capacity of beams with only soffit bonded CFRP.…”

“…The Plevris et al (1995) method postulates failure is directly proportional to the shear modulus and the areas of steel and FRP reinforcement. The Hosny et al (2006) method was adopted from Chen and Teng (2001) and slightly altered some of the constraints. The Plevris et al (1995) method grossly overestimated strengths, while the Hosny et al (2006) method delivered results that reasonably agreed with the test data while maintaining some conservatism.…”

“…The Hosny et al (2006) method was adopted from Chen and Teng (2001) and slightly altered some of the constraints. The Plevris et al (1995) method grossly overestimated strengths, while the Hosny et al (2006) method delivered results that reasonably agreed with the test data while maintaining some conservatism. The comparison of these models can be seen in Fig.…”

Reply to Discussion by S. Chen on "Strengthening precast-prestressed hollow core slabs to resist negative moments using carbon fibre reinforced polymer strips: an experimental investigation and a critical review of Canadian Standards Association 806-02"

“…The proposed approach in our work that implements a new debonding model (Teng et al 2002) into the current design procedures improves the current practice and gets the experimental results closer to predictions of codes of practice such as Canadian Standards Association (CSA) standard CSA-S806-02 (CSA 2002, Hosny et al 2006a) and American Concrete Institute (ACI) standard ACI 440. 2R-02 (ACI 2002, Hosny et al 2006b).…”

“…2R-02 (ACI 2002, Hosny et al 2006b). However, and despite this improvement, we still consider that our proposed method does not show a perfect agreement with the experimental results and still needs further fine tuning to its parameters as mentioned in Hosny et al (2006a). Currently, an experimental and numerical investigation is on-going to achieve this goal.…”