Keywords: composite bridge, orthotropic plate, experimental test, numerical analysis.

Nowadays the most modern and economical bridges are designed as composite structures with orthotropic plates. In a traditionally designed orthotropic bridge plates the trapezoidal, longitudinal stiffener is fully welded to the bottom flange of the main girder and it is partly welded to the web of the cross girder.

In bridge structures with orthotropic steel decks, it is a standard procedure to create a large U-shaped hole around the flange of the trapezoidal stiffeners in the web of the cross girders. In this way the trapezoidal stiffener can pass through the cross girders. Consequently, the cross girders have characteristic structural weaknesses as they have a significantly reduced web cross-sectional area. Under such conditions, the usual plate girder provisions that do not specify holes are used for the design of the cross girders with U-shaped stiffeners. The web sections of the cross girders are selected as compact sections. Furthermore, the reinforcement for the reduced web section of such cross girders are currently determined by empirical rules.

In Hungary a new type of connection between the longitudinal and transversal stiffeners has been developed considering economical, constructional and fabrication aspects of the composite bridge design. In the current design the longitudinal, the trapezoidal stiffener is fully cut around, therefore there is no connection between the longitudinal and the transversal stiffeners [1]. This solution helps in the fabrication and construction of composite bridges.

Nine welded, simply supported beams were tested with one concentrated load. The beams were classified as follows: type R (Rigid), type S (Standard) and type E (Economic). Each beam was assembled from steel plates.

The dimensions of the U-shaped holes around the trapezoidal stiffener were determined so they would permit the passage of U-shaped stiffeners with the standard size of 153/75x100mm. The depth of the slit is 20mm. The form of the U-shaped hole was kept as simple as possible.

The ultimate strength of test specimens with trapezoidal stiffeners was experimentally and numerically investigated. The specimens were constructed from three components, the stiffened plate, the trapezoidal stiffener and the cross girder.

In the experiments three arrangements were considered where the hole around the trapezoidal stiffener had three different shapes providing different connections between the trapezoidal stiffener and the web of the cross girder. Specifically when the components are fully welded to each other then the connection is rigid. When there is a hole in the web of the cross girder around the flange of the trapezoidal stiffener the connection is considered as standard. Finally when the trapezoidal stiffener is fully cut around in the web of the cross girder the connection is economical.

1

M. Ivanyi Jr., R. Bancila, "Ultimate Strength and Behaviour of a New Type of Orthotropic Plate" in "Proceedings of Steel-A New and Traditional Material for Building", (in press) Balkema Publishers Leiden, The Netherlands, 2006.

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