Superimposed dead load and superimposed live load are still computed manually,
the same way as the 19th century designer. Self-weight may be computed manually, or
may be determined by software. The
AASHTO Guide Specifications for the Design of
Pedestrian Bridges (AASHTO, 1997) prescribes the live load value. It may vary
between 3.11 kPa to 4.07 kPa (65 psf to 85 psf), depending on the area of the walkway.
The late 19th century and early 20th century designer selected design wind loads on a
case-by-case basis, which varied typically from 1.44 kPa to 2.39 kPa (30 psf to 50 psf)
applied to the projected area of the components (Smith 1881, Waddell 1898, and Cooper
1905). Today’s AASHTO
Guide Specifications for the Design of Pedestrian Bridges
mandates 3.59 kPa (75 psf) applied to the same area.