Evaluierung der zentrischen Resttragfähigkeit von randnahen Verbundankern nach erfolgtem Betonkantenbruch

Abstract

Das dem derzeitigen Stand der Technik entsprechende Bemessungskonzept für Verankerungen führt bei randnahen Mehrfachbefestigungen unter Querbelastung und in weiterer Folge auch bei einer kombinierten Beanspruchung zu teilweise konservativen Ergebnissen. Aus bereits durchgeführten Untersuchungen zur Verbesserung des vorhandenen Bemessungskonzepts für randnahe Mehrfachbefestigungen unter Schrägzugbelastung geht hervor, dass solche Verankerungen nach dem Versagen der ersten Ankerreihe durch Betonkantenbruch noch Resthaltekräfte aufweisen, weshalb eine Berücksichtigung dieser zur Steigerung der Effizienz der Bemessung beitragen kann. Da die quantitative Beschaffenheit dieser Resttragfähigkeit jedoch noch weitgehend unerforscht ist, wird in diesem Beitrag auf Basis experimenteller Untersuchungen aufgezeigt, in welcher Größenordnung sich diese Resthaltekräfte bewegen. Hierzu wird eine randnahe Einzelbefestigung des Verbunddübeltyps zunächst unter reiner Querlast in Richtung des freien Bauteilrandes bis zum Eintritt des Betonkantenbruchs belastet und anschließend die zentrische Resttragfähigkeit bestimmt. Evaluation of the residual capacity in tension on bonded anchors close to the edge after concrete edge failure The state of the art design concept for anchorages in concrete leads to partly conservative results especially for fastenings close to the edge under shear load or subsequently under inclined load. Former investigations concerning the improvement of the actual design concept for anchorages close to the edge under inclined load show that such fastening situations have a residual capacity, although the first anchor row has already failed under shear load due to concrete edge failure. Therefore, the provision of this residual capacity can increase the performance of the design concept. Due to the lack in the quantitative range of the residual capacity, the scale of these forces was identified based on experimental tests within this article. Hence single bonded anchors close to the edge are loaded in a first step with a shear load towards the free edge until the concrete edge fails and afterwards the centric residual capacity is determined.

Extended concrete capacity design method for anchors close to non‐rectangular edges

“…To calculate the mean resistance value of a single anchor according to Appl 37 in plain uncracked concrete without edge influence, Equation (2) in principle can be used for both mechanical and bonded anchor types. In case of boundary influence, besides the concrete breakout adjustment due to the edge and anchor group boundary conditions described by the CCD method, further investigations due to atypical boundaries are proposed in terms of the tributary volume approach for rectangular edges by Bokor et al, [38][39][40] while the residual resistance of anchors near damaged edges is investigated experimentally by Stierschneider et al 41 Of interest is also the finding in the tests by Obayes et al, 42 that surface voids near the anchor did not seem to influence the concrete cone formation and the respective strength as the cone failure planes envelop these voids.…”

“…To calculate the mean resistance value of a single anchor according to Appl 37 in plain uncracked concrete without edge influence, Equation () in principle can be used for both mechanical and bonded anchor types. In case of boundary influence, besides the concrete breakout adjustment due to the edge and anchor group boundary conditions described by the CCD method, further investigations due to atypical boundaries are proposed in terms of the tributary volume approach for rectangular edges by Bokor et al, 38–40 while the residual resistance of anchors near damaged edges is investigated experimentally by Stierschneider et al 41 Of interest is also the finding in the tests by Obayes et al, 42 that surface voids near the anchor did not seem to influence the concrete cone formation and the respective strength as the cone failure planes envelop these voids. where is a factor depending on the specific fastening product used and on whether the application is in cracked or uncracked concrete, typically derived from testing, is equal to the value of 1.0 for an undisturbed uniaxial compression stress state (this occurs for equal to approximately 5 anchor diameters), is equal to the value of 0.8 for anchors within compression zones with cracks developing parallel to the compression direction (this occurs for greater than 5 anchor diameters), f cc is the mean compressive strength measured at 200 mm concrete cube specimens, and it is equal to 0.8 f cc,150 for 150 mm cube specimens.…”