Assessment of shear capacity methods of steel fiber reinforced concrete beams using full scale prestressed bridge beams
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Steel fiber addition in concrete is widely known to increase the non-flexural performance of concrete structures such as shear capacity. Design guides such as fib Model Code (2010) have recognised this effect and that these guidelines may become widely accepted. The current design guides are based on laboratory scale tests which may be compromised by the scale effects. This paper reports the results of full sized precast prestressed bridge beams that were fabricated and tested to shear failure. Two beams had steel fiber and two beams were plain concrete. None of the beams had any vertical shear reinforcements. The addition of steel fiber at the dosage of 60 kg per cubic metre resulted in more than twice the shear capacity as compared to the beams without steel fibers. The results of the fiber reinforced beams were compared with the calculated shear capacity of the fib Model Code (2010) and plastic design method. This paper presents a method to include prestress in previously developed plastic design method. The model code method predicted an increase of shear capacity of 22 % as compared to the experimental results of 112 % increase due to steel fiber addition. This demonstrates that the model code is not effective in taking into consideration of the contributions by steel fibers. The plastic design approach predicted an increase of shear capacity of 122 % which is close to the experimental values. Based on this full scale tests, the plastic design approach appears to be more suitable for estimation of shear capacity enhancement when steel fibers are used.
KeywordsSteel fibers Concrete Shear Prestressed Plastic method fib Model Code
The authors are grateful to Professors Linh Hoang and M.P. Nielsen from the Technical University of Denmark for hosting the first author of this paper as a visitor and the valuable discussions and clarifying the issues on Plastic Design approach. The authors are also grateful to Professor Stephen Foster for the discussions and introduction to the Variable Engagement Model.
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