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Re: wood deck/pedestrian bridge

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If you look at it from the perspective that you are using the more
permissive code (read "local building code") and then using more
conservative requirements for certain items (i.e., 85 psf for LL, L/500 for
deflection, etc.) then you really don't have a conflict.

However, I do think you are better off if you design everything according to
the AASHTO Pedestrian Bridge code, since you are designing pedestrian
bridges.  Check the AASHTO requirements for railing before you assume the
local code requirements are more restrictive.

M. David Finley, P.E.
2086 SW Main Boulevard - Suite 111
Lake City, FL  32025
386-752-6400

----- Original Message -----
From: "Andrew D. Kester" <andrew(--nospam--at)baeonline.com>
To: <seaint(--nospam--at)seaint.org>
Sent: Wednesday, March 26, 2003 8:11 AM
Subject: wood deck/pedestrian bridge


>
> 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.
>
>
> TIA
>
> Andrew D. Kester, EI
> Structural Engineer
> Bentley Architects & Engineers
> 665 W. Warren Ave.
> Longwood, FL 32750
> 1-407-331-6116
> andrew(--nospam--at)baeonline.com
> www.baeonline.com
>
>
>
>
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