FG Bautechnikgeschichte
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(2016)
Bridge bearings made of iron or steel, first used in early railroad bridges about 150 years ago, are relatively small
structural components that support the loads of bridge superstructures. Fixed bearings directly transfer forces from a bridges superstructure to its substructure. Movable bearings, such as sliding bearing plates, rollers and rockers, accommodate the thermal expansion of the superstructure without transferring it to the substructure. Rocker bearings tilt to accommodate thermal movement, theoretically without imposing stresses on the substructure. This paper concerns rocker bearings which are non-redundant components and have two states: stable and toppled over. When these bearings topple over, no alternate load paths exist, which results in a failed superstructure. As such, rocker bearings are critical bridge components. An overview is given of the history of use and failures of rocker bearings from nineteenth-century railroad bridges to US highway bridges with tall and slender rocker bearings that date from the late 1950s.
During the Late Period in Egypt (664–332 BC), a new type of temple enclosure wall occurs throughout the country that is unprecedented in size and form. In past research, the form of these wave-shaped walls has been interpreted both technically and symbolically. However, a homogeneous concept in the evaluation of this novel construction technique is still absent.
In the context of the ongoing efforts to maintain historic bridges still in use the corresponding bearings made from historic iron or steel have re-entered the perception of engineers. For the structural assessment of the bearings it is essential to find a procedure that allows for identifiying the material properties, while being minimally invasive at the same time. However, in particular the investigation of cast steel, which had become the material most widely employed for bearings by the end of the 19th century, has been largely neglected in technical literature until now. The paper presents results of hardness measurements to determine the tensile strength of bridge bearings made from cast steel. The emphasis was on finding the appropriate measurement method and to define requirements with regard to an adequate surface preparation. The tests showed that hardness measurements with the Leeb-method yield very good results for assessing the tensile strength of historic bearings material. The investigations were part of a research project performed at BTU Brandenburgische Technische Universität in co-operation with BAM Federal Institute for Materials Research and Testing in Berlin and were funded by the DFG German Research Foundation. The tests to evaluate the potential of hardness measurements were carried out at and supported by the BLOCK Materialprüfungsgesellschaft mbH Berlin.