Behavior, design and testing of anchors in cracked concrete

Reinforced concrete structures will generally be cracked under service load due to tensile stresses caused by loads or by the restraint of imposed deformations. Therefore, in general, the design of anchors should be based on the assumption that the concrete is cracked

Reibschlüssige Dübelverbindungen im Stahlbetonbau

In den letzten Jahren hat im Stahlbetonbau die Befestigungstechnik mit reibschlüssigen Dübelverbindungen (Metallspreizdübeln) zunehmend an Bedeutung gewonnen. Allerdings existiert bisher keine allgemein anerkannte Theorie zur Bemessung dieser Befestigungen. Daher wird das Tragverhalten von Metallspreizdübeln im ungerissenen und gerissenen Beton erläutert, und es werden zulässige Anwendungsbedingungen für Dübelverbindungen abgeleitet

Behaviour of fasteners under monotonic or cyclic shear displacements

An experimental program was carried out to investigate the behaviour of metallic fasteners (undercut, torque controlled expansion and chemical anchors) embedded in cracked concrete and subjected to shear displacements, under shear displacements is similar. Fasteners situated close to an edge and loaded towards the edge exhibit brittle concrete failure. Cyclic loadings are possible only for displacements which are much lower than the values corresponding to the monotonic peak load. Fastenings away from an edge will cause steel failure with large displacements. During cyclic loading, a severe force-response degradation was observed. Empirical formulae are proposed to predict the strength of anchors, as well as strength degradation during cyclic loading

The rotation capacity of plastic hinges in reinforced concrete beams and slabs

A mathematical model for calculating the rotation capacity of plastic hinges in reinforced concrete beams and slabs is presented. The model is based on the integration of the section curvature along the beam, taking into account the contribution of concrete between cracks (tension stiffening) and the shifting of the tensile force by shear cracks. The material behavior of reinforcing bars, concrete and bond is described as realistically as possible. The analytically predicted rotation capacities of about 70 beams compare favourably with the experimental results. The parameter studies demonstrate that the plastic rotation capacity of hinges given by the CEB-FIP Model Code is unconservative for cold worked deformed reinforcing bars with a low ratio tensile strength to yield stress and a low value of the uniform elongation

Anchorage to concrete

Summarizing it can be said that material models based on plasticity and stress-strain relationships together with stress criteria indicating failure do not catch all aspects of anchor behavior as observed in experiments. Furthermore the predicted failure load depends on the element size and number of load steps. A better explanation of anchorage behavior can be expected by means of fracture mechanics

Übergreifungsstöße von Rippenstäben unter schwellender Belastung

Es wird über vom Deutschen Ausschuß für Stahlbeton finanzierte Versuche an Balken und Platten mit durch Übergreifung in einem Schnitt gestoßener Bewehrung berichtet. Diese sollten zur Ermittlung der Verbundspannungen und des zulässigen Anteils der gestoßenen Stäbe am Gesamtquerschnitt der Bewehrung in einem Schnitt für Rippenstäbe aus BSt 42/50 R bei nicht ruhender Belastung dienen. Die Versuche werden beschrieben und die Ergebnisse ausführlich erläutert. Es zeigte sich, daß die in DIN 1045 vorgesehene Abminderung der zulässsigen Verbundspannungen bei nicht ruhender Belastung nicht erforderlich ist. Die Norm wurde zwischenzeitlich entsprechend ergänzt. Weiterhin können bei einlagiger Bewehrung auch bei dicken Stäben (de≤28 mm) Vorstösse mit den in DIN 1045 geforderten Übergreifungslängen ausgeführt werden; für dünne Stäbe (de≤14mmm) sind kürzere Übergreifungslängen möglich. Die in DIN 1O45 enthaltene günstige Beurteilung von Stößen, die um die halbe Übergreifungslänge gegeneinander versetzt sind, gegenüber Vollstössen ist bei konstanter Balkenbreite allerdings nicht berechtigt. Weiterhin ist es erforderlich, die in DIN 1045 angegebenen Hakenabzugswerte deutlich zu reduzieren. Außerdem erscheint es notwendig, die Ausbildung der Querbewehrung insbesondere bei > 50%-Stößen dicker Stäbe in engen Abständen strenger als bisher zu regeln.A report is given about tests financed. by the Deutscher Ausschuß für Stahlbeton on beams and slabs 'with lap splices of the reinforcement by which the permissible bond stresses and the permissible portion of spliced bars of the total section of a reinforcement should be determined for ribbed bars BSt 42/50 R at cycling load. The tests were described and the results interpreted in detail. lt is shown that the reduction of the permissible bond stresses at cycling load demanded by DIN 1045 is not necessary. In the mean time the code was changed in this sense. Furthermore it is possible to execute even with thick bars (de≤28 mm)100%-splices in one layer with the overlapping length demanded by DIN 1045 ; for thin bars (de≤14mmm) shorter overlapping lenths are possible. According to DIN 1045 splices staggeredby half of the overlapping lengthin comparison to 100%-splices are more favorable.Tjis is not justified for beams with a constant width. Furthermore it is necessary to reduce considerably the reduction values for hooks given by DIN 1045. Besides of that, it seems to be necessary to regulate more firmly than until especially for > 50 %-splices of thick bars situated close to eachother

A fracture mechanics based description of the pull-out behavior of headed studs embedded in concrete

According to the experiments the behavior of headed studs embedded in a large concrete block and loaded in tension with the support reactions relatively far away from the anchor is controlled by stable growth of the circumferential failure crack up to maximum load. Just before reaching maximum load the area of cracked concrete is only some 25% to 30% of the whole surface of the fracture cone, which is mainly formed in the descending part of the large embedment depth loaddisplacement curve the load transferred in the cracked area is relatively small compared to the total load

The rotation capacity of plastic hinges in reinforced concrete beams and slabs

A mathematical model for calculating the rotation capacity of plastic hinges in reinforced concrete beams and slabs is presented. The model is based on the integration of the section curvature along the beam, taking into account the contribution of concrete between cracks (tension stiffening) and the shifting of the tensile force by shear cracks. The material behavior of reinforcing bars, concrete and bond is described as realistically as possible. The analytically predicted rotation capacities of about 70 beams compare favourably with the experimental results. The parameter studies demonstrate that the plastic rotation capacity of hinges given by the CEB-FIP Model Code is unconservative for cold worked yield stress and a low value of the uniform elongation

Size effect in concrete structures

The size effect for notched-tension specimens, three-point bend specimens, pull-out headed anchor specimens and beams loaded in torsion are calculated using a 2D and 3D finite element program. The program is based on the nonlocal microplane model. The calculated failure loads are compared with previously obtained experimental results. Test results and calculated data are compared with the recently proposed size effect law. Results of tests and analysis exhibit significant size effect that should be taken into account in design practice. It is demonstrated that the nonlocal microplane model used in a 2D and 3D finite element code can correctly predict failure loads for similar specimens of different sizes

Befestigungstechnik im Bauwesen - bewährte Verfahren und neue Entwicklungen

Die Befestigungstechnik leistet einen selbstverständlichen und unentbehrlichen Beitrag zum wirtschaftlichen Bauen. Eine Vielzahl von Befestigungssystemen gewährleisten - bei sachgemäßer Anwendung - die sichere Einleitung auch hoher Lasten in Beton und Mauerwerk. Aufgabe des Anwenders ist es, das für den jeweiligen Ankergrund und Verwendungszweck optimale Befestigungselement aus dem breiten Angebot auszuwählen und zu montieren. Trotz der Informationsfülle von Firmenunterlagen und Zulassungsbescheiden ist ein Wissensdefizit über Funktionsprinzipien, Anwendungsbedingungen und -bereiche sowie richtige Montage festzustellen