Citation :

Enow Ano Affuembey, Naftary GATHIMBA, John Nyiro Mwero, "Effect of Void Depth on Flexural Strength, Ductility, and Strain Response of Hollow-Core RC Beams with Tension-Zone uPVC Conduits," International Journal of Civil Engineering, vol. 13, no. 8, pp. 137-151, 2026. Crossref, https://doi.org/10.14445/23488352/IJCE-V13I8P108

Abstract

Longitudinal voids formed by embedded conduits lessen the self-weight and material use of reinforced concrete beams. However, most publications regard the void as a passive cavity and ignore the contribution of the retained, bonded conduit. This paper investigates the relation of the void depth to the flexural response and ductility of hollow-core reinforced concrete beams with sand-coated unplasticized polyvinyl chloride conduits. The beams (150 × 250 × 1200 mm) were organized in five groups and subjected to a four-point bending test with a shear span-to-effective-depth ratio of a/d = 2.10. Pipe-in beams, which retained the sand-coated conduit at 0.29h and 0.42h from the soffit, and without pipe beams, which were voided at the same distances from the soffit, were also constructed. Pushout bond test provided a mean interfacial bond stress of 2.333 MPa, with a mean bond capacity of 14.66 kN, which exceeded the tensile capacity of the conduits, providing evidence that the sand-coated interfaces of the tested conduits achieved bond and fully tensioned the conduits before yielding of the conduits. The 0.29 h PI beam had the highest mean moment capacity at Mu = 26.197 kN·m (+11.85% over control). Pipe-wall strain gauges recorded εpvc = 0.01443 (above the uPVC yield strain of 0.01145). The 0.29 h WO beam had (μ = 10.74) and (Eabs = 2569.95 kN·mm) and achieved the highest ductility index and energy absorption while maintaining moment capacity within 3.03% of the control. The 0.42h PI beam had the lowest ductility (μ = 3.77) and energy absorption (975.80 kN·mm). ACI 318-19 nominal predictions underestimated absolute capacity across all groups but correctly reproduced the relative performance ranking. The findings indicate that void depth relative to the neutral axis, rather than void area alone, is the governing parameter in the load-ductility response of hollow-core RC beams with tension-zone uPVC conduits.

Keywords

Hollow-core RC beam, uPVC conduit, Void depth, Flexural ductility, Energy absorption, Composite bond.

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