A relatively easy way to double check is to calculate the reactions of the girder using the
supported load area.
Review the diagram above. Each of the colored squares represents 1 square foot. We know
that half of the 10' span will be supported by the girder. In addition half of the 2' distance
between the girder and the adjacent truss will be supported by the girder. Looking closer, we
see that half of the load supported by the girder is distributed to each bearing (the reactions).
Using the formula below, we can calculate the girder reactions.
Total Area = 120 ft²
Total PSF = 40
The result will be close but also conservative because we did not deduct the width of the
bearings.
