Governing failure criterion of short-span hybrid FRP-UHPC beams

Significance 

Structural engineering is one of the rapidly developing fields over the past few years. Taking advantage of the advancement in the technology, more quality, and complex structural components are being built, thus creating demand for high and efficient construction and building materials. Ultra-High Performance Concrete (UHPC) is a good example of such new materials. It is formed from cured concrete and steel or organic fibers. Therefore, it possesses better qualities for strength, ductility, weight and environmental impact as compared to other materials such as mild steel. On the other hand, fiber reinforced polymers (FRP), which also comprises of a family of new materials are made by combining thin fibers with their appropriate matrices for holding the fibers together. They too exhibit good properties as far as strength and lightweight are concerned.

Various materials are susceptible to various modes of failures. Therefore, optimizing materials will ensure that materials are used depending on their performance under different loading conditions. A section of UHPC flange and glass fiber reinforced polymers (GFRP) have only been studied for flexural behavior without considering the shear behavior. Hence, it has been challenging to predict the failures of such sections due to high shear stress from their flexural failures. This is because of the high strength property exhibited by the sections as well as the changing failure mode under investigation from study to study. It, therefore, require a comprehensive study of the sheer performance of the hybrid section of the UHPC and GFRP materials.

A team of researchers at the University of Calgary in Canada: Ph.D. candidate Mina Iskander, Professor Raafat El-Hacha, and Dr. Nigel Shrive conducted an experimental shear performance investigation of a hybrid section constructed from ultra-high performance concrete flange with a glass fiber reinforced polymer. The bottom part of the section was built from either a carbon or steel fiber reinforced polymer. They tested seven specimens and induced shear failure by applying a point load of 280mm from one support to another support over a span of 1120 mm. They then investigated the type of the reinforcement used for the bottom section and the effect of the flange dimensions which formed part of the two most significant parameters. Lastly, simple finite element analysis was used to interpret the cost of failure in the system. Their research work is published in the journal, Composite Structures.

The authors observed a consistent shear stress failure behavior irrespective of the varying parameters since all the seven specimens tested failed similarly. Additionally, they found out that failure started by crack propagation of the GRFP box section at the corners then followed by cracking of the UHPC flange.

The calculated shear stresses at the point of failure revealed that the observed mode of failure was not only as a result of the high shear stress but may also include other factors, especially at the corners. The failures at the corners of the section could be minimized by application of a proper reinforcing system. However, the type of material for the bottom section, that is, either CFRP or SFRP had an almost negligible effect on the shear resistance of the sections.

Reference

Iskander, M., El-Hacha, R., & Shrive, N. (2018). Governing failure criterion of short-span hybrid FRP-UHPC beams subjected to high shear forces.  Composite Structures, 185, 123-131. .

Go To Composite Structures

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