Field measurements at a composite bridge with composite dowels as shear connectors - Economical Bridge Solutions based on Innovative Composite Dowels and Integrated Abutments - page 64

Figure 6: Railcar class DBAG 612, 2'B'+B'2'

3. Rail support points

The forces acting on the rail support points as well as the stresses in the rails at both ends of
the superstructure were determined during the design process by means of a structural analy-
sis (section 3.1). These calculations were based on national railway codes “Ril 804 Module
5404” [9] and “Ril 804 Module 5405” [10] which were not compulsory.

3.1 Determination of design values

The theoretic values of rail stresses and forces acting on the single rail support points were
determined by means of a framework model. This model consisted of the superstructure
(layer 1) and the two single rails (layer 2). These rails were continuing with a length of L D =
0.5 ⋅ L T + 40 m = 46.58 m according to DIN Fachbericht 101, annex K.3.4 (4) [11] adjacent
to the superstructure in both directions.
The rails were coupled to the superstructure by horizontal and vertical springs, repre-
senting the rail support points (“Fig. 4”). The vertical spring stiffness of the rail support point
was governed by the properties of the elastomer bearing (“Fig. 7”), whereas the stiffness
(22.5 kN/mm = 22,500 kN/m) was determined in advance by TU Munich (internal research
report N° 1689a) for design purpose.
The horizontal creep resistance for the horizontal coupling springs was determined ac-
cording to DIN Fachbericht 101, figure K.3 [11], as the rails are fixed directly to the super-
structure. For the load case “temperature difference” the values for an unloaded track (c =
18,000 kN/m per single rail, yield value F = 9.0 kN/m) were used. For the load case “braking”
the corresponding values for a loaded track (c = 36,000 kN/m per single rail, yield value F =
18.0 kN/m) were considered.
In the region of backfill the vertical spring stiffness was calculated by combining the
spring stiffness of the rail support point and the spring stiffness of the elastic bedding (sleep-
ers on ballast bed). For that case, a value of 0.10 N/mm 2 was chosen according to [12], which
resulted in a total spring stiffness of 14,300 kN/m for each single vertical spring.
Using the design rules provided by [11], forces acting on the rail supports and stresses
in the structure were calculated. These values were compared to the insitu measurements as
shown in chapter 3.2.2.
The maximum stresses in the rail track at the abutments due to horizontal forces were
determined to be 37.1 N/mm 2 . This value by far did not exceed the limiting value of 92 N/
mm 2 as given by DIN FB 101, annex K.3.6 [11].
The maximum stresses in the rails due to bending summed up to 170.6 N/mm 2 .
Forces acting on rail support points due to temperature loading were:

max F Z = 16.40 kN (at 1 st rail support point on superstructure due to temperature in-
duced vaulting);