AR
The Construction Industry Research and Information Association (CIRA) in conjunction with The Cement and Concrete Association carried out a five year research programme to evaluate the various methods available for the design of bridge decks (Pennells, 1978). The Research programme yielded the following.
The four analytical tools deemed to be appropriate analytical tools in a given circumstances.
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The load distribution method
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Grillage analysis
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The finite strip method
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Finite-plate elements
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Upon reveiw of discussion it was decided that, a line-beam analysis would produce adequately reasonable results. The simplifying assumption that a bridge can be reduced to the analysis of a simple beam is a significant stretch from reality, but the use of this methodology has proven to be effective in the design of bridges for many years
Due to the simplistic nature of a line beam, it is possible to employ the use of and influence line diagram to determine the critical locations to place moving point loads in order to calculate the most adverse effects. The image above shows the location to place a point load in order to create the largest bending moment in span 1 of a 3 span beam.
A grillage analysis is the most widely used method of analysing bridge decks. It is believed that the system of interconnecting beams forming a grillage, gives a pictorial analogy of the structure that is easy to comprehend.There are no restrictions to support conditions; the cross-section need not be constant. Skew decks can be modelled provided a grillage can be generated that is a representation of the bridge deck.
this analytical method is reputed to be very versatile, and is capable of representing complex structures acting in a complicated manner. It should be noted that the versatility of this method leads to the use of complex computer programmes that do not behave as anticipated. As a result of this methods complexities it is not recommended for design engineers that are not well versed in computer lore or the mathematics in the behaviour of plates.
Due to the simplistic nature of a line beam, it is possible to employ the use of and influence line diagram to determine the critical locations to place moving point loads in order to calculate the most adverse effects. The image above shows the location to place a point load in order to create the largest bending moment in span 1 of a 3 span beam.