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Project Title: Punching Shear Behaviour of Concrete Flat Slabs Reinforced with Basalt Fibre Reinforced Polymer (BFRP) Bars

  • Phd Student: Abdulhamid Ali Al Ajami
  • Supervisor: Dr Ashraf Ashour

Background

In recent years, civil engineers have raised concerns about the issue of durability of reinforced concrete structures. As a result, they have given increasing attention to advanced composite materials for reinforcing, strengthening, and rehabilitation of existing and new civil engineering construction, particularly with the use of FRP systems. The key advantages of composites over other traditional materials include low density, high specific strength, good corrosion resistance, improved thermal insulation and low thermal expansion.

The RC flat slab is one of the main structural elements, which is under intensive study to overcome uncertainty in punching shear prediction capacity, especially when FRP bars are used for reinforcing concrete structures instead of conventional steel structural bars. In this context, studies have been performed on the behaviour of punching shear capacity. However, further research is required to find more reliable and practical ways to predict punching shear capacity.

Aims

The main goal of the research detailed in this report is to use the test results of previous studies, including the latest work in the open literature, to produce a more accurate and reliable method for predicting RC slab punching shear capacity. The main objectives of the current research may be summarised as follows:

  • To develop a nonlinear ANN technique to predict the punching shear capacity of flat slabs reinforced with FRP.
  • To evaluate the accuracy of the equations in the design codes, namely CSA S806 (2012), ACI 440 (2006), and BS 8110 (1997), for punching shear strength of FRP two-way flat slabs.
  • To investigate the effect of different column shapes on punching shear.
  • To develop an analytical solution, based on the deformability concept, to predict punching shear strength.
  • To investigate BFRP reinforcement in the punching shear capacity of two-way flat slabs, where experimental results are assessed for accuracy.

Research Significance

One of the main objectives in this research is to compare slabs reinforced by BFRP bars with slabs reinforced by GFRP bars, which are of the same real dimensions as those used in field studies, such as by Benmokrane et al. 2012 and Mohamed Ashour, 2013. On the other hand, it presents experimental results on the effects of FRP flexure on punching-shear capacity of flat slabs. The accuracy of current equations in the FRP design codes and guidelines, CSA S806 (2012), ACI 440 (2006) and BS 8110 (1997), and other design approaches from the literature are assessed. This research also develops a new database of results from concentric punching shear tests of BFRP two-way slabs. Hence, this work aims to provide useful information to researchers and practising engineers. While, FRP bar properties were improved commercially, a review study of punching shear behaviour is required. Moreover, compared with Steel Reinforced Concrete (SRC), the combination of the matrix phase with a reinforcing phase produces a new material system which needs further experimental study to be properly understood.

Methodology

The experimental works and analytical studies are conducted according to the objectives of this research. The experimental work comprises three parts which include construction and testing of twelve full-scale interior slab-column connections reinforced with BFRP bars and steel respectively. In Part 1, four slab-column connection specimens reinforced by BFRP bars were tested, in Part 2 four GFRP reinforced specimens were used, and Part 3 involved two steel reinforced specimens. In terms of dimensions each specimen was 2200 mm long in both directions, with a central column stub extending 400 mm beyond the top and bottom surfaces of the slabs. A simple support was employed along all four edges. A concentric load was then applied to the slab through the column stub from the top. The experimental programme plan of investigation includes the following parameters: (i) flexural reinforcement ratio (ranging from 0.34% to 1.66%) and type (steel, BFRP and GFRP); (ii) steel, BFRP and GFRP compression reinforcement; (iii) slab thickness (200 mm); (iv) column shape (200 x 200 mm  square and 340 mm cylinder diameter); (v) normal concrete strength.

Reference

ACI 440 Committee, 2006. Guide for the Design and Construction of Concrete Reinforcement with FRP Bars (ACI 440. 1R-06). American Concrete Institute, Farmington Hills, Mich. 44p.

Banthia, N., Al-Asaly, M., and Ma, S. 1995. Behaviour of Concrete Slabs Reinforced with Fibre-reinforced Plastic Grid. Journal Materials in Civil Engineering, 7(4): 252-257. doi:10.1061/(ASCE)0899-1561(1995)7:4(252).

Benmokrane, B., Ahmed, E., Dulude, C., and Boucher, E. 2012. Design, construction, and monitoring of the first worldwide two way flat slab parking garage reinforced with GFRP bars. In Proceedings of the 6th International Conference on FRP Composites in Civil Engineering. Rome, Italy, 13-15 June. 8 p.

Canadian Standards Association (CSA). 2012. Design and construction of building structures with fibre reinforced polymers (CAN/CSA S806-12). Rexdale, Ont., Cnada.

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