Structures

Role of Force Resultant Interaction on Ultra-High Performance Concrete

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Abstract

With considerably high strength and high ductility due to the fiber bridging effect, ultra-high performance concrete (UHPC) beams can be designed without shear reinforcement. This could make UHPC beams shear critical members when high-strength flexural reinforcement is used. Classical uniaxial moment-curvature analysis would overestimate stiffness and capacity of the elements in the case of shear critical behavior. Stiffness reduction is often introduced by adding shear deformations, while beam capacity is reduced through the introduction of new shear strength design formulas or based on uniaxial normal stress level. However, this adjustment does not precisely explain the underlying causes of shear failure of the UHPC beams. The purpose of this research is to quantify the force resultant interaction of UHPC flexural members as well as their failure modes by using available biaxial stress state analysis approaches such as modified compression field theory (MCFT) and the finite element method. The load-displacement results are compared with moment-curvature analysis. Various experimental specimens were tested to validate the analytical results including unreinforced UHPC prisms, UHPC prisms reinforced with ASTM Grade 60, and UHPC prisms reinforced with high strength steel (HSS). Flexural failure was observed on unreinforced UHPC and UHPC-Grade 60 steel reinforced specimens, where the crack opening gradually widened at the bottom layer of the concrete below the loading position. On the other hand, UHPC-HSS specimens largely failed in shear from a diagonal tension crack and crushing of concrete top layer. The accuracy as well as the limitations of the analysis methods used are identified and discussed based on experimental test results.

Keywords: high strength steel rebar, moment-curvature analysis, modified compression field theory, flexural test

How to Cite:

Chan, T., Mackie, K. R. & Xia, J., (2016) “Role of Force Resultant Interaction on Ultra-High Performance Concrete”, International Interactive Symposium on Ultra-High Performance Concrete 1(1). doi: https://doi.org/10.21838/uhpc.2016.61