Shear strength of self-compacting concrete beams with small stirrups ratios

Abstract

In comparison with a vibrated concrete (VC) of the same strength class, self‐compacting concrete (SCC) typically has a lower coarse aggregate content and, possibly, a smaller maximum aggregate size. This may result in reduced aggregate interlock between the fracture surfaces of a SCC. Since aggregate interlock plays an important role in the shear strength of slender beams, SCC beams may have a shear strength lower than that of similar VC beams, but studies on that subject are still limited. This article summarizes an experimental programme that includes beams of high‐strength SCC and transverse reinforcement ratios around the minimum given by different codes – a case that had not been investigated so far. The shear strengths of those SCC beams are compared with those of VC beams with similar concrete compressive strength and small ratios of transverse reinforcement and also compared with beams calculated according to different code procedures.

Shear strength of slender SCC beams - possible differences from VC beams

“…From those beams, 54 of SCC and 11 of VC had h<300mm and 16 of SCC and 8 of VC had ρ>4%, values that do not correspond to real cases of beams and that lead to improved ultimate shear stress. Only 7 of the SCC beams had ρ w f yw close to the minimum recommended by codes of practice and high strength concrete, besides usual height value [12,15]. No beam had skin reinforcement.…”

“…Considering the shear database for VC beams without shear reinforcement of Reineck et al [23] and their SCC tested beams, Arezoumandi and Volz [20] concluded that there is no statistically significant difference between the ultimate normalized shear stress of VC and SCC beams. Resende, Shehata and Shehata [12] aimed to investigate the shear behaviour of high strength SCC beams and small amounts of shear reinforcement, case that had not been studied (only one beam with small value of ρ w f yw and f c ≈54MPa had been tested by Cuenca, Serna and Pelufo [15]). The six beams tested were produced with a SCC provided by a ready-mixed concrete supplier that had been used in a cast-in-place structure.…”

“…Two beams had the same ρ w f yw but different stirrups spacing and diameter and two had the same ρ w f yw and different ρ. Comparisons of the experimental shear strengths with calculated ones showed that the ACI 318:2014 [8] and the FIB MC 2010 [7] Level III of Approximation may lead to a non-conservative evaluation of the shear strength of SCC beams with small values of ρ w f yw , particularly if they also have smaller value of ρ. Resende, Shehata and Shehata [12] compared the ultimate shear stresses of the SCC beams with the ones of VC beams tested by Garcia [25]. This VC had a 90mm slump, the same type of coarse aggregate with d max =19mm used in the SCC and similar value of f c .…”

“…Comparison of the ultimate shear stresses of high strength SCC and VC beams with f c ≅ 70 MPa and small values of ρ w f yw [12] [7] consider only the web reinforcement contribution (V R = V s ), while the ABNT NBR 6118:2014 [22], ACI 318:2014 [8] and Level of Approximation III of FIB MC 2010 [7] consider the web concrete and steel contributions (V R = V c + V s ), where V s is based on a modified truss analogy. Table 2 gives the values of the angle between the concrete compression struts and the beam axis of the truss model (θ) and the equations of V c for the different calculation methods.…”

“…This paper analyses a database for beams tested by different authors who investigated the shear strength of SCC slender beams (shear span to effective depth ratio a/d ≥ 2.5) with no axial force. Some of those authors tested only SCC beams [10,11,12] while the others [13 -21], for the sake of comparison, tested SCC and VC beams and these VC beams are also included in the analysis. The shear strengths of SCC and VC beams are compared and the experimental shear strengths of the beams, V u , are compared with the ones calculated, V R , using the provisions of ABNT NBR 6118:2014 [22], ACI 318:2014 [8], EN 1992-1-1:2004 [23] and FIB MC 2010 [7].…”