Crack propagation and residual load‐bearing behavior of composite dowels – effects on the global behavior of composite girders under cyclic loading

Abstract

Fatigue of a composite girder according to Eurocode 4 is carried out on the decisive shear connector. It is not taken into account that the composite girder is an internally highly statically indeterminate system in which the failure of a dowel does not necessarily lead to the failure of the girder. This applies in particular to composite dowels which are characterised by a crack propagation phase with a high residual load‐bearing capacity of a damaged dowel. In own small part and girder tests as well as numerical studies, numerous positive load‐bearing effects could be identified in composite girders with composite dowels, which increase the lifetime of the girder. In case of an initial crack in a steel dowel, followed by crack propagation, the stiffness degradation of the damaged connector leads to a redistribution of forces. The lifetime of a girder is limited by the residual capacity of the composite joint or by a global failure with increasing partial connection. A global safety concept for composite girders taking into account the crack development and residual strength of the dowels as well as the redistribution of forces within the composite joint holds an enormous economic potential. This article shows how these effects can be taken into account.

Probabilistic Design of Composite Girders Considering the Degradation of the Shear Connection and the Redistribution of Forces

“…Using cyclic stresses, cyclic stress intensity factors can also be determined, Figure 4 c). Equations ( 4) and (5) were derived in [12,13] for composite dowels based on numerical parameter studies [14,15], where nominal stresses were replaced by shear stresses, considering the amplitude of dowel forces ΔP, the dowel spacing ex, the web thickness tw and one function Y both for crack and component geometry. Possible values for Ym and Yb are given in chapter 3.…”

Fatigue behaviour of composite girders with composite dowels assuming randomly distributed input parameters

“…The simulation was then repeated for different crack lengths using the red crack path of Fig. 3a [12]. Fig.…”

“…The phase of crack propagation in the steel teeth of composite dowels was evaluated in a recent research project [10][11][12]16]. Using well-known approaches from linear elastic fracture mechanics, experimental tests and numerical parametrical studies, a concept for calculating rates of crack propagation was developed, see Fig.…”

“…Crack gauges were fitted in front of the notch to measure the first 5 mm of crack propagation. Further information about testing and validation can be found in [12].…”

“…1b, 1c). Assuming randomly distributed values for the number of load cycles N crack until crack initiation, there will be cracked dowels with a redistribution of shear forces to adjacent uncracked dowels [10][11][12]. Other input parameters can also…”