Influence of the supplementary reinforcement on the shear strength of beams with prefabricated truss stirrups

Abstract

This paper presents the results of seven experimental tests in reinforced concrete wide beams, aiming to investigate their performance when subjected to shear, using prefabricated truss stirrups as shear reinforcement, as well as a supplementary reinforcement to control cracks by delamination. The main analysed variables were: position of the supplementary reinforcement, inclination of the shear reinforcement, and spacing between stirrups. Results showed that strength increments of up to 142% were obtained using the prefabricated truss stirrups. Furthermore, the experimental results were compared with the theoretical shear strength estimates of the tested beams, following the recommendations of NBR 6118 (2014), Eurocode 2 (2004), and ACI 318 (2014), in order to evaluate the safety level of these codes when designing concrete elements subjected to shear with the reinforcement used in this paper.

Shear in reinforced concrete beams with continuous internal transverse reinforcement

“…The beams with stirrups inclined to 60º, M-8-60 and M-4-60, presented greater strength capacity in comparison with the other tested beams, as observed by [4] in the tested beam with prefabricated truss stirrups inclined at 60º and with complementary reinforcement on both sides. The performance is due to the capacity of the inclined stirrups to allow a larger steel area in the cracks, ensuring greater strength to the beam.…”

“…The main variables analyzed were inclination of transverse reinforcement, diameter of the transverse steel bars and number of bars per layer, in such a way that these variations had the same transverse reinforcement ratio. In addition, reinforcement with internal anchoring had complementary reinforcement, to contribute to the anchoring and avoid delamination effect, with the same pieces used by [3], [4].…”

“…In addition, some research have pointed out that premature failures and delamination cracks were related to shear reinforcement with internal anchoring [6]- [8]. However, it is worth noting that, in some cases, it was possible to control the cracking by delamination in structures with internal shear reinforcement, through a COMPLEMENTARY REINFORCEMENT, as observed in the results of Pinto [4], in which the complementary reinforcement works as well as the transverse reinforcement, allowing the flow of forces and the functioning of the Mörsh truss, resulting in strengths equal to or greater than that of elements with closed stirrups and studs [3], [4], [10].…”

“…However, there may still be a conflict between the transverse and longitudinal reinforcement, since both types of reinforcement are external, that is, the ends need to be on the longitudinal bars. One of the alternatives to avoid the conflict between reinforcement is the use of shear reinforcement with internal anchoring, positioned between the tensile and compression bars, as discussed by [2]- [4]. Figure 2 shows the types of transverse reinforcement.…”

“…In this context, the use of transverse reinforcement with internal anchoring has been highlighted, with several articles about it being published [2]- [4], [6]- [13]. As the shear reinforcement with internal anchoring are positioned between the upper and lower bars of the flexural reinforcement, their positions can be independent, avoiding the conflict of bars.…”