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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.
For public use, in order to meet ADA, the general practice is to specify the camber at 1.2% of the length, or "maximum slope per ADA 5%" can be specified, which amounts to the same thing.
To maximize the pleasant arched look and still meet ADA, call out "2% camber" or "maximum slope per ADA 8.3%." ADA then requires toe plates and pipe ADA hand rails be added. ADA only allows the 8.3% slope continuously for 30', so on the longer spans this specification will not meet ADA.
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. Please call to discuss.
Learn more about common pitfalls
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