Civil Engineering Reference
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(i) steel fatigue design,
(ii) concrete fatigue design and
(iii) securing of a rigid shear joint.
Here, the interaction between the fatigue behavior of different components has to be
considered (“Fig. 12”): e. g. degradation of the concrete dowel leads to decrease of the shear
connection. This affects the stress distribution over the cross section and therefore the steel
fatigue design.
Figure 12:
Schematic illustration of the interaction of the fatigue verifications
(i) Steel fatigue
The steel fatigue design is based on the geometric stress approach. The stress amplitude at
the hot spot is determined for the fatigue load model and compared with the material fatigue
strength. The fatigue strength (resistance) is described by the fatigue strength curve of detail
category 125 (machine gas cut edges having shallow and regular drag lines) or of detail cat-
egory 140 (machine gas cut edges with subsequent dressing) in accordance with EN 199419.
The geometric stress amplitude (action) is the sum of stresses due to longitudinal shear forces
(local effects) and bending of the composite beam (global effects). Both parts are ampli-
fied by stress concentration factors depending on the geometry of the composite dowel. The
nominal stresses are defined as longitudinal shear stress (local) and normal stress (global) at
the dowel base.
(9)
with
(10)
The stress concentration factors
kf,L
(local) and
kf,G
(global) for the clothoid and puzzle
shape are determined by finite element analysis and verified by strain measurements in cyclic
push out and beam tests [15] (“Fig. 13”). The stress concentration factors are applicable for
steel sections with a lower flange and concrete strength C20/25 and higher. To exclude low
cycle fatigue, the geometric stress amplitude is limited to 2 ∙
fy
and the upper geometric stress
is limited to 1.3 ∙
fy
.
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