Assessing the Stringer-Panel Method as an Alternative Design Approach for Deep Beams A Comparative Study with the Strut-and-Tie Method

Abstract

The design of discontinuity regions (D-regions) in reinforced concrete structures presents a challenge due to non-linear stress distributions, which make traditional beam theory insufficient. Two analytical methods for the design of such regions are the Strut-and-Tie Method (STM) and the Stringer-Panel Method (SPM). STM, which is widely used and recommended in most design codes, is suitable for ultimate limit state design but lacks compatibility considerations necessary for serviceability limit state analysis. In contrast, SPM offers the possibility of integrating compatibility conditions and offers potential for both ULS and SLS applications, although it remains less familiar to practising engineers. This study investigated and compared STM and SPM through parametric analyses on deep beams with varying span-to-depth ratios and varying sizes of a central opening. Re inforcement layouts were designed according to both STM and SPM, and the performance was assessed through analytical calculations and validated via non-linear finite element analysis (FEA) using DIANA. The results from the FEA for STM and SPM were com pared to each other, as well as to the analytical calculations. Key parameters evaluated included reinforcement quantity, failure load, crack width, deflection, and reinforcement stress distribution. The results showed that both methods produce comparable reinforcement quantities and ultimate capacities, with no consistent trend favouring one method over the other. SPM demonstrated better adaptability to geometric variations and allowed direct calculation of deflections, making it more suitable for automation and preliminary design stages. How ever, limitations in post-cracking predictions highlight the need for stiffness reduction factors to improve the accuracy of SPM in the non-linear range. It was concluded that SPM is a fully viable alternative to STM for designing D-regions in concrete beams, particularly when serviceability considerations and automation potential are prioritised. Although neither method proved universally superior, the structured ap proach of SPM suggested valuable opportunities for broader adoption in structural design practice.