Effect of shear span-to-effective depth ratio on shear strength of conventional and lightweight reinforced concrete beams

Abstract

Shear span-to-effective depth (a/d) ratio plays a critical role in the behavior of reinforced concrete beams, and quantifying the shear strength of concrete remains an intricate problem. Lightweight aggregate concrete (LWC) made with sintered fly ash aggregates, has weaker mechanical properties causing the shear failure plane to pass through both the aggregates and cement matrix necessitating the comparison with conventional concrete. So, this paper investigates the effect of shear span-to-effective depth (a/d) ratio on shear behavior of M40 grade concrete made with sintered fly ash aggregates and normal weight aggregates. Eight beams of size 200×300×2200 mm were tested under four-point loading by varying the a/d ratio from 1 to 2 to investigate the shear behavior. LWC exhibited shear capacity, approximately 7-13% lower than that of conventional concrete over the a/d ratio 1 to 2. Research findings confirm that the shear strength decreases as the shear span-to-effective depth ratio increases in both conventional and lightweight concrete. When the a/d ratio increased from 1 to 1.5, the shear strength of concrete decreased by over 35%, while a further increase from 1.5 to 2 resulted in a reduction of more than 15%, indicating a nonlinear decline in performance. To address the non‑linear relationship caused by the a/d ratio and lightweight aggregate effect, a modified ACI equation for predicting the shear capacity was proposed and validated using experimental results and existing literature models.