Rolled Beam In-Concrete Bridges can be usually manufactured with a high slenderness L/h of from 25 to 30 and are still characterized by a relatively high stiffness. The higher stiffness results in less deformation. Compared to the usual composite steel , there are only cracked cross-sections in frame bridges. In the case of simply supported beams, the concrete cross-section cracks at the bottom of the field region, whereas in the case of frame and multi-span bridge structures the concrete cross-section also cracks at the top of the support area.

The behavior of casted steel girders depends strongly on this crack formation. This special feature requires special requirements for all verifications. Analogous to composite steel, the basic calculation is based on the total cross-section method. The reduction numbers can be calculated either according to DS 804 Annex 8, DIN EN 1992-1-1, or the E_c(t)-method. In the non-cracked area, the composite section is transformed into an equivalent steel section, while in the cracked area the section values are determined by the position of the plastic zero lines. The tensile stressed part of the load-bearing section is usually neglected.

The Engineering office of Stefan Kleffel in Rippershausen-Solz in Thuringia has currently carried out the structural analysis for an skewed Rolled Beam In-Concrete overpass bridge for the river Hasel in Dillstädt/Schwarza with a span of 12,40 meters and a variable width of 6,50 to 9,13 m meters. The superstructure of C35/45 consists of nine steel Girders set in concrete, each with a HEM 400 profile and the material S355. The longitudinal girders are fixed into an end transverse beam, which in turn are supported on deep-founded bored piles. A local traffic load of category 4 was assumed as a traffic load.

„With this assignment from the public administration sectors we have designed meanwhile the third Rolled Beam In-Concrete Bridge“, reported specialist Engineer Stefan Kleffel. „From the beginning, the structure was intended to be this type of bridge. Otherwise we wouldn´t be able to realize this structure with such a small cross-sectional height in comparison with any other construction, which was required by the underflowed River. The high flowing potential of the river made it particularly difficult to construct supporting scaffolding, which meant that a reinforced concrete bridge had to be ruled out in principle. With an optional prestressed concrete bridge, we would not have been able to meet the budget of the commissioning municipality,“ the expert continues.