The design, analysis, and performance of structural concrete slabs under punching shear loading conditions are topics that have been studied extensively over many decades and are well documented in the literature. However, the majority of the work reported in these areas is generally related to conventional concrete slabs subjected to highly idealized loading conditions. Structural engineers need to find new, innovative ways and methods to design new structures but also to strengthen existing infrastructure to ensure safety, resilience, and sustainability. These challenges can be addressed through the use of integrated systems and high-performance technologically advanced materials. We live in a new era of improved computational capabilities, advances in high-performance computing, numerical and experimental methods, and data-driven techniques, which give us broader access to larger and better data sets and analysis tools. These new advancements are essential to develop deeper insights into the structural behavior of concrete slabs under punching shear and to implement and analyze new materials and loading conditions. This Special Publication presents recent punching shear research and insights relating to topics that have historically received less attention in the literature and/or are absent from existing codified design procedures. Topics addressed include: the usage and impacts of alternative/modern construction materials (new concrete and concrete-like materials, nonmetallic reinforcement systems, and combinations thereof) on slab punching shear resistance, novel shear reinforcement or strengthening systems, the influence of highly irregular/nonuniform loading and support conditions on slab punching shear, impact loading, new design and analysis techniques, and the study of the punching shear behavior of footings. This Special Publication will be of interest to designers who are often faced with punching-related design requirements that fall outside of traditional research areas and existing code provisions, as well as for researchers who are performing research in related areas. Perspectives from a broad and international group of authors are included in this Special Publication, relating to a variety of punching-related problems that occur in research and practice. In particular, researchers from the United States, Canada, Ecuador, the Netherlands, Italy, Brazil, Israel, Portugal, Spain, the United Arab Emirates, and Germany contributed to the articles in this Special Publications. To exchange views on the new materials, tests, and analysis methods related to punching, Joint ASCE-ACI Committee 421, “Design of Reinforced Concrete Slabs;” Joint ASCE-ACI Committee 445, “Shear and Torsion;” and subcommittee ACI 445-C, “Punching Shear,” organized two sessions titled “Punching shear of concrete slabs: insights from new materials, tests, and analysis methods” at the ACI Spring Convention 2023 in San Francisco, CA. This Special Publication contains several technical papers from experts who presented their work at these sessions, in addition to papers submitted for publication only. Co-editors Dr. Katerina Genikomsou, Dr. Trevor Hrynyk, and Dr. Eva Lantsoght are grateful for the contributions of the authors and sincerely value the time and effort of the authors in preparing the papers in this volume, as well as of the reviewers of the manuscripts. Aikaterini Genikomsou, Trevor Hrynyk, and Eva Lantsoght Co-editors

This paper presents the application of a low-cost thick-shell nonlinear finite element analysis (NLFEA) procedure to estimate the punching shear resisting performance of reinforced concrete slab-column connections under variable connection shear stress conditions. Variation of connection stress conditions stems from columns with different cross section aspect ratios, different distributions of gravity loading conditions, and slabs constructed with significantly different planar reinforcement conditions in the orthogonal directions. In this regard, thirty-five isolated slab-column connection specimens presented in the literature were analyzed using a shell finite element-based analysis procedure and the results from these analyses were used to assess NLFEA model performance. All results were developed using a predefined set of material models and analysis parameters, defined on the basis of prior and unrelated validation studies, and were shown to provide good agreement with experimental findings without the need for calibration studies or the adoption of case-specific failure criteria. From the findings obtained, it was determined that the thick-shell NLFEA employed is suitable for estimating the punching shear response for slabs subjected to varied and highly non-uniform shear stresses within the connection regions and provided similar levels of precisions as that previously obtained for isolated slab-column connections constructed with idealized geometries and reinforcing conditions, subjected to idealized loading conditions.

While the punching shear behavior of centrically loaded footings has been investigated in the past, the influence of unbalanced moments has remained almost uninvestigated for footings. Nevertheless, unbalanced moments are also transferred into the column by shear stresses requiring consideration in punching shear design. Here, design approaches often use coefficients to increase the load on action side or to decrease the resistance. To fill the gap in test data necessary for validation of design approaches, tests of four centrically and fourteen eccentrically loaded footings without shear reinforcement were conducted. Here, innovative measurement techniques were used to determine the development of the compression ring at the column-footing connection. While the constriction of the concrete compression zone due to the multiaxial load transfer leads to the formation of a circumferential compression ring with multiaxial concrete strains for centrally loaded slabs, which enhances the punching shear resistance compared to one-way shear, this compression ring only develops to a reduced extent with increasing load eccentricity. Based on the test results, a new proposal for consideration of unbalanced moments is proposed and compared to existing design approaches according to ACI 318-19, Eurocode 2 and the stable version of new Eurocode 2.

Flat slabs with shear reinforcement not properly detailed and anchored as stated by ACI have been used in practice due to simplicity and the gained construction speed. This paper presents the results of 12 tests on slab-column connections with closed stirrups with anchorage variation and prefabricated truss bars as punching shear reinforcement. The behavior of the slabs, in terms of cracking pattern, displacements, and shear reinforcement strains, were analyzed, and ultimate loads were compared with estimations by ACI 318-19. Comparisons with the reference slabs without shear reinforcement showed that these two types of shear reinforcement effectively increased the load-carrying capacity of the tested slabs. For tests on slabs with closed stirrups, it was observed that if ACI detailing rules are followed, improvements in response and ductility of the slab-column connections should be expected. In the case of the slabs with prefabricated truss bars, it was observed that they were able to reach levels of punching shear resistance close to those of a reference slab with well-anchored stud rails. In both cases, further experimental research is needed. ACI 318-19 presented safe strength predictions for the different types of shear reinforcement tested, and in the case of the prefabricated truss bars, this was due to the conservative limitations imposed for calculating the crushing strength of the concrete strut close to the column.

Experimental tests have been performed on interior post-tensioned (PT) slab-column (SC) connections over the past several decades. This paper presents a comprehensive database of 92 such tests performed on interior PT SC connections without shear reinforcement under direct shear. The data was then analyzed to compare the accuracy of the punching shear provisions of ACI 318-19, Eurocode 2 (2004), and CSA A23-19. Several key parameters were evaluated for the PT SC specimens including the concrete compressive strength, specimen geometry, bonded flexural reinforcement ratio, and minimum area of bonded flexural reinforcement; and their influence on the two-way shear strength of these connections was studied. Recommendations are made for possible modifications to the provisions of ACI 318-19 including the limit on the value of the concrete compressive strength f_c^'. Areas for further study, including size effect and bonded flexural reinforcement requirements, are highlighted.