CAMBER
Camber, as it relates to these kinds of bridges, causes considerable confusion. In this instance, camber is defined as rise at bridge center / bridge length = camber %. The following points should help:
The arch of a truss or girder bridge is not structural. You may specify the bridge with any amount of arch desired, or none at all.
A flat bridge would be specified as “dead load” camber. This indicates to Excel to put enough camber in the members to offset the bridge’s own dead load and a bit extra to offset any creep over time.
In the pre-fabricated bridge industry, positive camber is usually expressed as the percentage of the bridges length that produces “X” rise at the center of the span. This percent is not the deck slope or pitch. Example: A 100′ bridge with “1%” camber will have 1′ of rise at center, but about a 4% slope at the ends. Camber is applied as approximately a radius in the bridge members.
Sometimes for aesthetic or clearance reasons, more camber is desired. If ADA is not required, or if an “alternate route” is available to the impaired, 2.5% camber is most often specified. For foot traffic, some architects & engineers contend that camber over 3-5% would be too likely to cause slip and fall problems.
In multiple span bridges, whether continuous or separate simple spans, camber should be expressed as a percentage of the total bridge length. This way Excel’s engineers will be responsible to properly camber each bridge section so it appears as one smooth continuous arch.
If a highly arched appearance is desired, Excel can employ a number of methods to give this aesthetic, depending on the bridge size and the budget.
