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.

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.

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.

One-way slabs under concentrated loads may fail by one-way shear, punching, flexure or a mixed-mode be-tween them. This study examines the benefits of using Linear Elastic Finite Element Analyses (LEFEA) combined with analytical expressions to predict the shear and punching capacities of such slabs. Besides, the determination of the most critical shear failure mechanism is also addressed. A simplified approach is proposed to predict the shear and punching capacity without numerical models. Forty-eight tests of simply supported slabs under concentrated loads were evaluated. The LEFEA was conducted with ABAQUS. The analytical expressions are based on the Critical Shear Crack Theory (CSCT). The coupling of the CSCT-expressions with the LEFEA accurately predicts the governing shear failure mechanism and the shear capacity of most test results. In this study, it was also found that the punching capacity predictions may be improved by considering the influence of the slab width and load size on the governing failure mechanism. A similar level of precision was achieved using only analytical expressions when properly calibrated. Therefore, the CSCT expressions can be used at different stages of design and assessment of existing structures according to the Level of Approximation required.

In design, the sectional depth of reinforced concrete spread footings is usually governed by design code provisions for punching shear, which are derived primarily from experiments on slab-column connections. Previous experiments have shown that the punching behavior of concentrically loaded spread footings differs from that of slab-column connections. This paper describes punching of a concentrically loaded spread footing by combining conventional strut and tie modeling with the concept of an arch strip, part of the Strip Model. By itself, the Strip Model describes the behavior of slab-column connections under a variety of loading conditions. For spread footings, Strip Model concepts need to be combined with conventional strut and tie modeling to adequately describe load transfer in a concentrically loaded spread footing. Two methods are explored, each producing closed-form expressions for the footing capacity that agree well with experimental results (112 tests from the literature). The analyses make it possible to estimate the fraction of footing load that is carried by conventional strut and tie behavior. The experimental results are also compared to punching shear capacities in accordance with ACI 318-19. The Strip Model produces results with roughly the same average test-to-predicted ratio (in the order of 1.3) as ACI 318-19 but with a lower coefficient of variation (10.3% compared to 15.8%). This work shows how a lower-bound plasticity-based model can be used for the practical case of determining the capacity of reinforced concrete spread footings failing in punching shear.