Influence of Transverse Steel and Casting Direction on Shear Response and Ductility of Reinforced Ultra-High Performance Concrete Beams

Authors: Timothy E. Frank, Peter J. Amaddio, Elizabeth D. Decko, Alexis M. Tri, Darcy A. Farrell, Cole M. Landes

Abstract:

Ultra-high performance concrete (UHPC) is a class of cementitious composites with a relatively large percentage of cement generating high compressive strength. Additionally, UHPC contains disbursed fibers, which control crack width, carry the tensile load across narrow cracks, and limit spalling. These characteristics lend themselves to a wide range of structural applications when UHPC members are reinforced with longitudinal steel. Efficient use of fibers and longitudinal steel is required to keep lifecycle cost competitive in reinforced UHPC members; this requires full utilization of both the compressive and tensile qualities of the reinforced cementitious composite. The objective of this study is to investigate the shear response of steel-reinforced UHPC beams to guide design decisions that keep initial costs reasonable, limit serviceability crack widths, and ensure a ductile structural response and failure path. Five small-scale, reinforced UHPC beams were experimentally tested. Longitudinal steel, transverse steel, and casting direction were varied. Results indicate that an increase in transverse steel in short-spanned reinforced UHPC beams provided additional shear capacity and increased the peak load achieved. Beams with very large longitudinal steel reinforcement ratios did not achieve yield and fully utilized the tension properties of the longitudinal steel. Casting the UHPC beams from the end or from the middle affected load-carrying capacity and ductility, but image analysis determined that the fiber orientation was not significantly different. It is believed that the presence of transverse and longitudinal steel reinforcement minimized the effect of different UHPC casting directions. Results support recent recommendations in the literature suggesting that a 1% fiber volume fraction is sufficient within UHPC to prevent spalling and provide compressive fracture toughness under extreme loading conditions.

Keywords: Fiber orientation, reinforced ultra-high performance concrete beams, shear, transverse steel.

References:

[1] M. Bermudez, K.-W. Wen, and C.-C. Hung. “A Comparative Study on the Shear Behavior of UHPC Beams with Macro Hooked-End Steel Fibers and PVA Fibers,” Materials 15, no. 4, February 16, 2022, 1485.
[2] M. Pourbaba, H. Sadaghian, and A. Mirmiran. “A comparative study of flexural and shear behavior of ultra-high-performance fiber-reinforced concrete beams,” Advances in Structural Engineering 22, no. 7, May 2019, pp. 1727-1738.
[3] V. Kodur. “Analysis of Flexural and Shear Resistance of Ultra High Performance Fiber Reinforced Concrete Beams without Stirrups.” Engineering Structures 174, 2018, pp. 873-884.
[4] Y. Shao and S. L. Billington. “Utilizing Full UHPC Compressive Strength in Steel Reinforced UHPC Beams,” Second International Interactive Symposium on UHPC. Iowa State University Digital Press, 2019.
[5] O. Wang, H.-L. Song, C.-L. Lu, and L.-Z. Jin. “Shear Performance of Reinforced Ultra-High Performance Concrete Rectangular Section Beams.” Structures 27, October 2020, pp. 1184-1194.
[6] F. Baby, et al. “Shear Resistance of Ultra High Performance Fibre-Reinforced Concrete I-Beams.” Fract. Mech. Concr. Concr. Struct.—High Perform. Fiber Reinf. Concr. Spec. Load. Struct. Appl, 2010, pp.1411-1417.
[7] S. Gomaa, T. Bhaduri, and M. Alnaggar. “Coupled Experimental and Computational Investigation of the Interplay between Discrete and Continuous Reinforcement in Ultrahigh Performance Concrete Beams. I: Experimental Testing,” Journal of Engineering Mechanics 147, no. 9, September 2021.
[8] Y. Shao, and S. L. Billington. “Impact of UHPC Tensile Behavior on Steel Reinforced UHPC Flexural Behavior” Journal of Structural Engineering 148, no. 1, January 2022, 04021244.
[9] S.-T. Kang and J.-K. Kim. “Investigation on the Flexural Behavior of UHPCC Considering the Effect of Fiber Orientation Distribution,” Construction and Building Materials 28, no. 1, March 2012, pp. 57-65.
[10] D.-Y. Yoo, S.-T. Kang, and Y.-S. Yoon. “Effect of Fiber Length and Placement Method on Flexural Behavior, Tension-Softening Curve, and Fiber Distribution Characteristics of UHPFRC,” Construction and Building Materials 64, August 2014, pp. 67-81.
[11] B. Graybeal, I. De la Varga, and L. F. M. Duque. "Fiber reinforcement influence on the tensile response of UHPFRC," First International Interactive Symposium on UHPC. Iowa State University Digital Press, 2016.
[12] B. Zhou and Y. Uchida. “Influence of flowability, casting time and formwork geometry on fiber orientation and mechanical properties of UHPFRC,” Cement and Concrete Research 95, May 2017, pp. 164-177.
[13] Standard Practice for Fabricating and Testing Specimens of Ultra-High Performance Concrete, ASTM C1856, ASTM International, Volume 04.02, West Conshohocken, PA, 2017.
[14] Building Code Requirements for Structural Concrete, ACI 318-19, American Concrete Institute, Farmington Hills, MI, 2019.
[15] S. Gomaa, and M. Alnaggar. "Transitioning from shear to flexural failure of UHPC beams by varying fiber content," Second International Interactive Symposium on UHPC. Iowa State University Digital Press, 2019.