question for any civil engineers/bridge builders?

[BDG]

Sorry to ask this on the board but someone may know the answer.

I come through roadworks on the M60 where they are building several new bridges.

Why do you have the not inconsiderable bulk of a bridge span supported by a small contact patch between the span and the actual upright support of the bridge. The contact patch appears to be about 10% of the top of the upright.

Surely this must concentrate the load on a small area rather than spread the load.

I hope that makes sense from the description.

???:puzzled:

[moto748]

Because the bridge is designed to have a virtual "knife-edge" support. Hence it is "pin-jointed" (if it's an end span).

This means that no unwanted bending forces are transmitted to the supports, or the bridge itself. The bridge is free to "rock" a little at the support.

[rockhopper]

good answer!

[BDG]

Thank You Moto748.

I will file that gem of information away and in 10 years time at some diner party when someone else asks i'll sound really clever, even though i'm not:D