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Re: Tubular Steel Bridge Review

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Tom,
It's a pipe rack or pipe bridge but has a walkway.
The water depth in offshore is around 5.0m.
The contractor is planning to use single driven pile at onshore and offshore for supporting the bridge.
Sufficient  plan bracings are provided in both top and bottom framing (The bridge cross section dimensions are 3.5m (12ft) high by 2.5m (8ft) wide. But no sway/knee braces are provided in cross section.
regards
Ashraf

 
On 08/04/2009, Tom.Hunt(--nospam--at)fluor.com <Tom.Hunt(--nospam--at)fluor.com> wrote:

Ashraf,

I assume you are describing a "pipe bridge" as opposed to a vehicular bridge with pipes.  If this is your case, then the design would likely be governed by the IBC with it's reference codes to ASCE  and AISC.  The load combinations would primarily come from the IBC, the loadings (i.e. LL, Wind, Seismic, etc.) would primarily come from ASCE 7, and the basic steel design would come from AISC 360 plus AISC 341 for seismic.  For horizontal and vertical deflection limitations you should first get with the pipe stress engineer as this will probably govern over anything from the IBC or AISC.  For the individual structural steel members if they are not governed by stress or overall deflection requirements then they are likely to be limited by either AISC kl/r or b/t ratios.  If the offshore portion is in deep water then it may be better to have the fixed end onshore where it is easier to install a substantial footing at or near grade.  For this span you should definitely have horizontal bracing for both the top and bottom chords to cut down on the unbraced lengths.

Regards,

Thomas Hunt, S.E.
Fluor




Ashraf Manjappara <ashraf.manjappara(--nospam--at)gmail.com>
04/08/2009 09:18 AM
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Tubular Steel Bridge Review





Hello,
I am reviewing the design of a simply supported rectangular welded tubular truss bridge of 48.0m to support crude oil pipes. The bridge is supported by two single piled supports one is in offshore (sliding) and one in onshore (pinned) . The major concern is the top chord in which they used 10.75" dia tubulars. I am worried about the global buckling of the top framing in the horizontal plane. We are mainly following American standards such as API RP 2A, AISC etc.
 I would like to get some feed back on the follwoing issues.
1. Is there any limit on the Span/tubular dia limit on Bridges?
2. Is there any minimum size to be used in Tubular bridges for chords/braces?
3. How can I disinguish between major and minor brace?.
4. The design shows 30cm lateral deflection for the offshore support frame. What is the limit on the allowable deflections?.
5. What are the major things to be looked when reviewing tubular bridges design?.
6. Which is the preferred location for pinned end (whether onshore support or offshore support) ?.
7. What is the effective length to be considered for top chord (compression) if there is no knee/sway bracing in the cross sections ?. Sufficient braces are provided in between the top chords and bottom chords. But knee braces in cross section is provided only at the ends.
Thanks in advance,
regards
Ashraf
 
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