This article explains the camber values in RDSO standard drawings for open web girders, detailing how these values are determined under different loading conditions and their significance in ensuring structural integrity.
In the construction and engineering of open web girders, understanding camber values is crucial for ensuring structural integrity and performance. This article delves into the camber values provided in the RDSO (Research Designs and Standards Organization) standard drawings for open web girders, explaining their significance and how they are interpreted.
Camber refers to the intentional upward curvature of a beam or girder. This curvature is designed to counteract deflection that occurs when loads are applied. In the context of RDSO standard drawings, camber values are specified to ensure that girders maintain their structural shape under various loading conditions.
In all RDSO standard open web girder drawings, a camber table is included. This table displays camber values under different conditions:
The camber values provided up to the mid-panel point cover half of the girder. Due to the symmetrical nature of the girder arrangement, the remaining camber values can be derived from these initial values.
The camber value labeled as A represents the camber required to mitigate deflection caused by various loads:
This value is termed "camber on jack" because it indicates the amount by which the panel points will be raised during trial assembly when the girder is supported on jacks. At this stage, no load has been transferred to the girder, and it is resting solely on the jacks.
Once the jacks are removed, the dead load is transferred to the girder, which results in some deflection. The camber value labeled B reflects the remaining camber after this transfer, accounting for:
At this point, the girder is dismantled and transported to the site, where additional loads such as track guard rails and checkered plates are laid over it, contributing to the superimposed dead load.
The final camber value, labeled C, is known as the residual camber. This value represents the actual camber after the final erection of the girder at the site, ready to receive live loads. Residual camber is a critical parameter that indicates the health of the girder. Ideally, when the live load for which the girder was designed is applied at design speed, the girder should assume a nominal shape, meaning the bottom chord should become horizontal.
In the camber table, the value of C at midspan (L5) is noted as 6.544 mm, which corresponds to the deflection observed during load testing under design conditions.
Understanding the camber values in RDSO standard drawings for open web girders is essential for engineers and construction professionals. These values not only guide the assembly and erection of girders but also play a vital role in ensuring their structural integrity under various loading conditions.
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