Field measurements at a composite bridge with composite dowels as shear connectors - Economical Bridge Solutions based on Innovative Composite Dowels and Integrated Abutments - page 76

Stresses due to global bending of the composite girder and stresses caused by local
bending of the steel dowel superimpose within the region of the socalled hot-spot at the foot
of the dowel (“Fig. 22”, “Fig. 19”). Furthermore the stresses are increased due to geometric
notch effects. Close to the bridge's bearings (axis 20 and axis 30) normal stresses due to local
bending of the steels dowels, caused by shear forces to be distributed by the dowels, predomi-
nate. In mid-field, global bending still governs the stress state. However, as the stresssums of
global and local stress have to be taken into account, the hotspots both at midfield as well as
at the bearings have to be investigated to find the critical crosssection. In the case given here,
the critical stresses can be found close to the bearings.

Figure 22: Measured strains / stresses within the region of the hot-spot, lower external

reinforcement, compared to calculated values for condition I (left) and condi-
tion II (right)

The results presented here show, that the maximum tension stress of about 2 kN/cm 2
can be measured in mid-field in the region of the lower flanges. Therefore the stresses in
this region (strain gauge S45 and strain gauge S46) induced by the test train (100 km/h) are
compared to those caused by the scheduled regional train RE 3343 (120 km/h). The cross-
ings lasted about 1 s (BR 132) and about 2 s (RE 3343) respectively (“Fig. 23”). The bogies
are visible in both plots, whereas the two central bogies of BR 132 merge due to the short
distance between them (comp. “Fig. 6”). Furthermore the stresses caused by the regional
train prove to be clearly smaller (about 0,87 kN/cm 2 ) than the ones caused by the test train
(“Fig. 23”, left).