Looking for bridge design to BS 5400? BS 5400 is consists of several parts that included all the information to be followed when a bridge is designed. Specification of bridges, loads and other relevant information can be found in the code.
Generally, the main task of a concrete bridge is the designing of the precast beams. Depending on the method of stress is applied on the beam, precast beams are categorized as post-tension beams and pretension beams.
Firstly, the beam is designed for the transfer stage and service stage. Depending on the loading of the bridge and weight of the beams, pre-stress/post tension forces are selected in either method. Ultimate bending moment and shear capacity are found finally.
The following sketches indicate the methods of calculating the stresses at the transfer stage and service stage. Sign convention: Tension Positive; Compression Negative
From the above equations, four equations can be derived for finding the pre-stress force and eccentricity(where to place tendons) by drawings the graphs of “e” Vs 1/Pe. At the initial stage, pre-stressing losses are assumed around 15% and later it will be verified.
When the eccentricity and the effective prestressing force are known, the ultimate bending moment can be calculated from the first principles (strain compatibility method, etc.) or from the equations given in the code. Shear design can also be done using the equations given in the code for crack and un-cracked sections.
The design of the post-tensioned beam for ultimate limit states is discussed in the article Bridge Beam. It could be useful to know the method of calculating the ultimate moment capacity of the beam.
The article prestressed composite beams design also cold also referred for more information on technical explanations and worked example.