Design of composite dowels as shear connectors according to the German technical approval - Economical Bridge Solutions based on Innovative Composite Dowels and Integrated Abutments - page 47

[10] [14] and by HOCHTIEF [9]. They led to a further development of the pry-out model and
new models for steel failure. Seidl [16] developed design models for distance effects on con-
crete pry-out and vertical splitting of composite dowels in concrete tee-beams. The beginning
of the clothoid strip - an optimization for fatigue loading - can be found in [4], [5]. This strip
was finally used for the prefabricated composite bridge type VFT-Rail ® , which was approved
by the German railway authority (EBA) [7].

Figure 3: Bridges with composite dowels: road bridge in Pöcking (left) and Simmerbach

(right) (photos: SSF Ingenieure AG, Munich)

2. Scope of the general technical approval

The new German general technical approval Z-26.4-56 [3] regulates composite dowels in
clothoid (CL) and puzzle (PZ) strip (“Fig. 4”). The geometry can be scaled in dependence
of the distance of the openings e x between 150 ≤ e x ≤ 500 mm (notations see “Fig. 5”). The
lower bound ensures a sufficient shear area for a ductile failure mode in the failure mode
concrete shearing. The upper bound limits the maximum distance between composite dowels
to prevent an unacceptable curtailment of the dowel capacity. The plate thickness can be
varied between 6 ≤ t w ≤ 60 mm with a ratio of thickness to height between 0.08 ≤ t w / h D ≤ 0.5.
However, in the design formulas a thickness of up to 40 mm only is allowed to be considered.
The minimum perpendicular distance of two steel plates is defined as 120 mm to ensure a
sufficient installation of the reinforcement in between. For composite dowels structural steel
in grade S235, S355 and S460 acc. to EN 10025 can be applied.
A minimum distance of 20 mm between concrete surface and top edge, respectively
base, of the composite dowel has to be kept (“Fig. 5”). The distance from the opening to the
concrete edge has to be in longitudinal direction more than 2.5 times the concrete pry-out
cone h po and in perpendicular direction more than 5.0 times of h po . This ensures the full de-
velopment of the concrete pry-out cone, if pry-out failure occurs. The minimum distance in
perpendicular direction can be neglected, if in beam type sections the concrete reaches to the
steel flange and confinement stirrups are installed (see below). This prevents pry-out at the
lower concrete surface. A minimum width of beam type sections of 250 mm is required. For
the composite section, concrete strengthC20/25 to C60/75 can be chosen (equal to the range
given in EN 199411).
Composite dowels can be used under sagging and hogging moment for static as well as
fatigue loading. However, structural members with centric tension forces perpendicular to