Enhancing Punching Strength and Deformation Capacity of Flat Slabs

Abstract

Punching reinforcement systems have significantly developed in recent years as they allow enhancing the punching resistance of slab-column connections as well as their deformation capacity. These systems, with varying geometry and layout, normally consist of vertical or inclined shear reinforcement with both ends anchored on the compression and tension side of the slab. For very high levels of load, when even common punching reinforcement systems cannot safely ensure the transfer of loads, steel shear heads are usually embedded in the slab to enhance the resistance of the connection. Yet, shear heads might be expensive and difficult to place in construction sites. Following the principle of the dowel action of the compression reinforcement, this paper introduces a novel system to efficiently reinforce slabs against punching shear by using large-diameter double-headed studs acting as shear dowels. This system enhances the performance of shear-reinforced slabs with respect to conventional solutions and might be an efficient alternative to shear heads for a large number of practical situations. The system is validated by means of a specific experimental program including 11 axisymmetric punching tests on interior slab-column connections. The results demonstrate not only the increase of the punching strength but also the deformation capacity of the connection. It is also shown that the system can be consistently designed accounting for the doweling forces by making use of the theoretical frame of the Critical Shear Crack Theory (CSCT), allowing to understand the activation of the shear dowels on the basis of the deformation of the member.

Doppelkopfanker als Querkraft‐ und Durchstanzbewehrung – Aktueller Stand und Ausblick

“…Die horizontalen Ankerstäbe werden parallel zur Plattenebene in der Druckzone angeordnet und wirken als zusätzliche Schubdübel (Versuchsergebnisse siehe z. B. Cantone et al [15]). Ein zugelassenes Beispiel für eine derartige Systemerweiterung ist in Bild 2 dargestellt.…”

Mechanical modeling of dowel action and the influence of small amounts of shear reinforcement on the shear‐transfer actions in RC beams

“…The position of points A and B can, therefore, be determined from the plastic solution at the initiation of pure dowel action by a rotational and horizontal equilibrium, similar to other approaches. 26,[49][50][51] However, it should be noted that for small angles of the shear crack at the intersection with the dowel, the position of the endpoints potentially could be influenced by a breakout failure of the concrete (see, for example, Cantone et al 52 ). Figure 12a shows the forces acting on the dowel in the plastic state at the initiation of pure dowel action for a beam with shear reinforcement.…”

Optimization of a flat slab with different type of punching reinforcement

“…200 mm) according to Table 1. The structural performance of this system has been assessed by extensive research [10], which allowed developing the following design recommendations [15].…”

“…Several theoretical and experimental researches have been conducted to consider types of the punching reinforcement, particularly in [3][4][5][6], as well as study on influence of column size and slab slenderness [7,8]. Punching capacity is often one of the key parameter for design of a reinforced concrete slab thickness in buildings [9,10]. Location of columns supporting a flat slab, especially at the edge and corner positions may resist the sheer stresses caused by bending moments and transverse loads.…”