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Re: wood deck/pedestrian bridge

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Andrew,

Code provisions 3552845237549374.3473 of the 2000 IBC strictly prohibits
the use of any other code with the 2000 IBC code since that may mean the
some revenue may be going to some other code development group.





Of course, I am just kidding.  The real answer would depend.  Basically,
keep in mind that a code is only a set of minimum requirements.  There is
nothing is any code that says that you cannot use more severe
requirements.  Thus, if you apply provisions to two codes, as long as you
are selecting the more severe provisions from either of the two codes,
then you are technically meeting the provisions of both codes.

The first question is: what code is required by the governing
jurisdiction?  Since it is the governing jurisdiction (and there maybe
more than one) that determines what code buildings/structures must comply
with, you need to get from them any requirements.  Once you get which code
to use, then as long as you meet all the requirements of that code, you
are fine from a legal compliance point of view with the government.  It
then becomes a matter of do you want to use additional requirements that
are more severe than the code requirements that make you as the engineer
on the project more comfortable with the potential behaviour of the
structure.  This include doing something "more" than the code that must be
used requires due to a belief on your part that it does not adequately
adddress your situation, which may leave the users/public exposed to some
unacceptable risk or some unacceptable serviceability issue (i.e. too much
bounce in the structure, etc).

HTH,

Scott
Ypsilanti, MI


On Wed, 26 Mar 2003, Andrew D. Kester wrote:

>
> 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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