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.

An interim report reviewing several insights that have been gained in our ongoing research on punching shear capacity of RC flat slabs subjected to impact loads is presented. A typical RC building with flat slabs that is designed according to current standards is discussed. A collapse scenario of a top slab with failed connections is considered and its impact with a slab underneath is analyzed. The suitability of standards’ design criteria to provide safe design against punching shear is evaluated.

It was found that larger span slabs undergo heavier damage, therefore we focus on shorter span slabs to examine the lower bound damage. Falling from a floor height causes complete failure of the impacted slab-column connection. The slab around the column is severely damaged and the bending and shear reinforcement is ruptured. Rebars’ yield occurs within milliseconds from impact, while the impacted slab hardly starts its downward displacement. A major part of the impacted slab moves uniformly with severe damage concentration at the slab-column connection region.

The complex impact response of the slabs is analyzed, and new insights are gained. It demonstrates that the cur-rent static-loading based design standards cannot provide resilience to flat slab connections under impact load-ing and therefore cannot prevent a progressive collapse scenario.

Columns supporting reinforced concrete two-way slabs often have non-circular or non-square cross-sections. The punching shear design of alternative column geometries is addressed in ACI 318-19, although the basis for these provisions is unclear as experimental tests of irregular column geometries are limited. In particular, the punching shear behaviour of special-shaped slab-column connections, such as L-shaped connections, has received limited interest. In this paper, nonlinear finite element analysis (FEA) is used to study the influence of column geometry, column location with respect to the slab centroid and the presence of slab openings on the punching shear behaviour of interior L-shaped slab-column connections subjected to gravity loading. The FEA suggests that the diagonal portion of the critical perimeter between the column flanges assumed in ACI 318-19 is ineffective in transferring load between the slab and the column. The FEA also suggests that ideally slab openings around interior L-shaped slab-column connections should be located between the two column flanges of each connection. Locating the openings in this area minimizes their negative impact on punching capacity and is beneficial from an architectural perspective, as the openings and services can be hidden from view. The punching capacities predicted by the FEA, the ACI 318-19 concentric punching shear provisions and the eccentric shear stress model outlined in ACI 421.1R-20 are also compared.

A large number of bridges in the Netherlands have transversely post tensioned deck slabs cast in-situ between flanges of precast girders and were found to be critical in shear when evaluated by Eurocode 2. To investigate the bearing (punching shear) capacity of such bridges, a 1:2 scale bridge model was constructed in the laboratory and static tests were performed by varying the transverse prestressing level (TPL). A 3D solid, 1:2 scale model of the real bridge, similar to the experimental model, was developed in the finite element software DIANA and several nonlinear analyses were carried out. It was observed that the experimental and numerical ultimate load carrying capacity was much higher than predicted by the governing codes due to lack of consideration of compressive membrane action (CMA). In order to incorporate CMA in the Model Code 2010 (fib 2012) punching shear provisions for prestressed slabs, numerical and theoretical approaches were combined. As a result, sufficient factor of safety was observed when the real bridge design capacity was compared with the design wheel load of Eurocode 1. It was concluded that the existing bridges still had sufficient residual bearing capacity with no problems of serviceability and structural safety.

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.