Several types of anchor are available t o transfer loads into structural concrete. They all utilize the concrete tensile strength. Many reinforced concrete structures are designed under the assumption that the concrete is cracked. Research shows that fasteners will attract cracks or even induce cracking. Therefore, the behavior of different types of fasteners in uncracked and cracked reinforced concrete has been studied extensively. Fasteners used in zones with potential concrete cracking must be suitable for this application. Suitable are cast-in-situ headed studs, post-installed anchors like undercut anchors and specially designed torque-controlled expansion anchors and adhesive anchors with follow-up expansion. They show a reduction of the concrete failure load of about 25-35% compared with uncracked concrete when located in o r close t o cracks with a width of 0.3-0.4 mm (0.0 I 24.0 I 6 in). This crack width can be expected in typical concrete members designed with ordinary crack control provisions. Based on comprehensive studies described in this article fastenings in uncracked and cracked concrete can be designed with sufficient accuracy. Progress in Structural Engineering and Materiais I998 Vol I(4): 392-403The demand for more flexibility in the planning, design and strengthening of concrete structures has resulted in an increased use of mechanical and chemical anchoring systems for structural applications.Most reinforced concrete (RC) members are designed under the assumption that the concrete is cracked under service load. It is known that the presence of cracks can substantially reduce the concrete capacity of fasteners[i*~. Some fasteners are not suitable for use in cracked concrete. Therefore, the design of anchors needs to consider the influence of cracks on the behavior of fasteners.This article describes the fastening systems available on the market and gives background information on the behavior and design of fasteners loaded in tension and shear and installed in cracked and non-cracked concrete. The state-of-the-art of fastenings is also described in ACI 355121 and Comite Euro-International du Beton (CEB)WI and by Eligehausen et al[r*i. Mechanical fastenings CAST-IN-SITU PARTSCast-in-situ elements are fastened to the formwork and cast into the concrete. They are available in a big variety of versions. A common example is a plate with welded-on headed studs (Fig. la). J-bolts are also often employed (Fig. lb). They are typically manufactured from smooth bars. The bolts are bent into a J-shape at one end and are threaded with coarse rolled threads. Channel bars (Fig. lc) comprise cold drawn or hot rolled U-shaped steel profiles with special anchoring elements. After removal of the formwork the attachment is fixed to the channel with special hammer-head or hook-head bolts. The anchoring elements such as T-shaped anchors or headed bolts are welded or forged to the back of the anchor channel. With all cast-in-place systems a tension load is transferred into the concrete by mechanical interlock. Abbre...

Aufgrund des hohen Vorfertigungsgrads gewinnen Elementplatten auch in Flachdecken zunehmend an Bedeutung. Wegen der hohen Querkraft‐ und Momentenbeanspruchung im Bereich des Decke‐Stütze‐Knotens ist dessen konstruktive Durchbildung von sicherheitsrelevanter Bedeutung. In der Praxis wird der Abstand der Elementplatten zur Stütze unterschiedlich ausgeführt. In Anlehnung an die in Zulassungen von verschiedenen Durchstanzbewehrungssystemen geforderte Mindestbreite der Fuge zwischen den Elementplatten von 4 cm wird auch der Abstand zwischen Elementplatte und Stützenanschnitt teilweise so groß gewählt. Eine solche Bauausführung hat den Vorteil, dass Abmessungs‐ und Lagetoleranzen ausgeglichen werden können. Nachteilig ist jedoch die zusätzlich erforderliche Abschalung der Fuge nach unten. Daher wird in der Praxis ein Heranführen der Elementplatte bis direkt an die Stütze bevorzugt.Anhand einer systematischen Versuchsserie mit speziellen Gitterträgern als Durchstanzbewehrung wurde zwischenzeitlich nachgewiesen, dass kleinere Abstände zwischen Elementplatte und Stütze die Durchstanztragfähigkeit nicht abmindern. Zur Bestätigung dieses Zusammenhangs auch für andere Durchstanzbewehrungssysteme wurden am Institut für Massivbau der RWTH Aachen zwei Durchstanzversuche mit Doppelkopfankern und speziellen Gitterträgern als Durchstanzbewehrung durchgeführt. Die Elementplatten wurden direkt bis an die Stützenkante geführt. Um Montageungenauigkeiten zu berücksichtigen, wurden die vorgefertigten Stützen zusätzlich zu hoch betoniert. Der Vergleich der Versuchsergebnisse mit denen jeweiliger Referenzversuche erlaubt Empfehlungen zur konstruktiven Durchbildung des Decke‐Stütze‐Knotens bei der Verwendung von Elementplatten in Flachdecken.Construction of slab‐column‐connections in semi‐precast flat slabsDue to the high degree of prefabrication, semi‐precast flat slabs are gaining importance. In this context, the construction of the slab‐column‐connection has a safety‐related significance. In daily engineering practice, the joint widths between semi‐precast slabs as well as the joint widths between semi‐precast slabs and the column's vicinity is constructed differently. The European Technical Approvals of different punching shear reinforcement systems limit the minimum joint width between semi‐precast elements to 4 cm. Following these provisions, the joint widths between semi‐precast slabs and the column's vicinity is constructed with 4 cm in some cases. An advantage of this approach is the possibility to adjust dimensional and positional tolerances at construction site. However, a disadvantage is the additional formwork for the joint from the soffit.A systematic test series with special lattice girders as punching shear reinforcement showed no reduction of the punching shear resistance for smaller joint widths between semi‐precast slabs and the column's vicinity. To confirm these test results, two punching shear tests with double headed studs and lattice girders as punching shear reinforcement were conducted at Institute of Structural Concrete (RWTH Aachen). In the tests, the influence of the joint width between semi‐precast slabs and the column's vicinity as well as the influence of column height tolerances were investigated. Based on the results of the tests, this article gives recommendations for the construction of slab‐column‐connections in semi‐precast flat slabs.

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