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wood deck/pedestrian bridge

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We are designing three small pedestrian bridges/ boardwalk structures for a
local park, going over small canals. In the past I have used the local
building code provisions for the uniform live load for smaller boardwalk
structures, as well as some engineering judgement for point loads and
deflections. Local building code rules regarding handrail design were also
used. The designs came out fine and no construction or user complaints from
a serviceability standpoint (deflection/vibration/ bounciness).

However, on this project, I am rethinking my design loads after rereading
the local building code, as well as the larger scale of these bridges. From
the FBC, Chpt 16, the actual occupancy for use:

Balcony and decks (exterior) same as occupancy, but not less then 60 psf
On one and two family dwellings 40psf

Well, boardwalks and pedestrian bridges, etc., in a park are not attached to
a structure, these are nowhere near another structure. It seems like a
pedestrian bridge is outside of the intent of the building code load, given
for decks attached to structures or next to buildings. I suppose using 60
psf would be ok and reasonable, as the decks are 6ft wide. This means a 2ft
strip would accomodate about 4 people weighing 180lbs (not that likely). But
it could accomodate a class field trip, a party, who knows, so I feel better
using AASHTO guidelines for pedestrian bridges, for uniform live load=85psf,
and also for deflection > l/500. Since the local building code does not
really address this stuff, I think it it logical to cross compare with
another source. I doubt I will have to justify my design to a permitting
agency in detail, but I would like to use some nationally recongized
criteria.  Also, I was going to use handrail design, as well as sway/lateral
loading of the bridge, from the building code because they seem applicable
to this type of structure. This will govern over wind design because there
is not much for a lateral surface for wind.

Is their a problem mixing the two codes, using the building code for
handrail design, and sway design, and AASHTO for uniform live load and
deflection AASHTO? If anyone has the AASHTO handrail, and sway/lateral loads
handy for pedestrian bridges, or where I can download that info, that would
be appreciated.


Andrew D. Kester, EI
Structural Engineer
Bentley Architects & Engineers
665 W. Warren Ave.
Longwood, FL 32750

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