A unifying strut-and-tie model for conventionally reinforced link beams

Abstract

Reinforced concrete link or coupling beams are usually cast integral with wall piers to help them act as a unit to resist lateral loads. The use of deep beam design in ACI 318-19 provisions leads to conservative shear designs for link beams which do not follow Euler-Bernoulli beams. Instead, strut-and-tie systems are used. The paper demonstrates the modeling of such beams using strut-and-tie provisions of ACI 318-19 Ch. 23. Alternatively, to using a time-consuming trial-and-error process, a unified general multi-panel strut-and-tie model is proposed, and simple design equations are developed to directly design conventionally reinforced link beams subjected to high shear force demand. As link beams have often a small span-to-depth ratio, the first one- and two-panel strut-and-tie models are considered basic and common. The one-panel model consists of a direct inclined compression concrete strut with horizontal tension ties in addition to the required crack-control web reinforcement and is used wherever the strut-tie angle is greater than the ACI minimum of 25 degrees; one vertical-to-two horizontal. The two-panel model is used when the beam span is too long to use the one-panel model and consists of one vertical tension tie and two steep inclined compression concrete struts. Worked design examples have been presented to justify and demonstrate the ease of implementation of the considered first two simple and direct models of the proposed unified general multi-panel strut-and-tie model. The predictions of the two basic models have been compared with five sample calculations and the comparison shows a good agreement.