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Bridge Engineering

In grillage analysis of skew bridge, should a skew mesh be adopted or the transverse members are set orthogonal to the main members?

For skew deck, the transverse members are set orthogonal to the main members to find out the correct moment and deflections. Skew decks develop twisting moments which is more severe for higher skew angles.

The most economical way of designing reinforcing steel is to place the reinforcement along the direction of principal moment.

Are knife edge loads the representation of wheel axles?

In BS5400 the traffic loads for HA loading are given by the uniformly distributed loads along the loaded length and a knife edge load.


What is the exact coverage of HA loading?

Type HA loads first appeared in 1945 and the concept of HB load was introduced in BS 153 in 1954. Type HA loads is the normal loading for United Kingdom and covers vehicles up to 44 ton. HA loads are represented by a uniformly distributed load with a knife edge load. HA loads have covered the following situations:

(i) More than one vehicle occupying the width of a lane;


Which type of multiple-cell box girder is better, cells connected by top flanges or cells connected both by top and bottom flanges?

When the depth of a box girder bridge exceeds 1/6 or 1/5 of the bridge width, it is recommended to be designed as a single cell box girder bridge.

However, if the bridge depth is smaller than 1/6 of the bridge width, then a twin-cell or multiple cell is a better choice . However, even for wider bridges with small depths, the number of cells should be minimized because there is not much improvement in transverse load distribution when the number of cells of box girder is increased to three or more.


What is sucker deck principle for variable depth bridge decks?

For a variable depth bridge deck, the depth of continuous multi-span bridge deck is increased in pier supports and this absorbs sagging moments in the mid-span with the consequent increase in hogging moments in pier supports. As a result, the mid-span depth can be significantly reduced due to the reduction in sagging moment. In essence, this sucker deck principle is applied in locations where headroom requirement is of great concern.