IBC-Structures definition-Pipe Truss

[maneesha0702]

I am designing a pipe truss. The person checking my calculations wants to check a loading combination of 0.6 DL+WL as per IBC. My question is does IBC apply to pipe truss. The checker thinks that pipe struss is a structure. There is no definition of structure in IBC. I feel that process industry practices(PIP) does not have this loading combination. The loading combination is only DL+WL as per PIP. Any comments pl.

 

[msquared48]

Why do you not think that a pipe truss is not a structure? The IBC pertains to all building structures and their components, trusses or otherwise. It also includes tanks, towers, and other non-building structures.

If the truss is not subject to wind forces, then the load combo does not apply. Otherwise, use it as suggested.

Mike McCann
MMC Engineering

 

[maneesha0702]

This pipe truss is for a process industry and that is why I feel that pip is applicable. I feel that in case of buildings the dead load may not be available where as for pipe truss those pipes are always available.

 

[JAE]

The 0.6D +/- W combination is really just a stability combination similar to using D +/- W with an overturning safety factor of 1.5. (1/0.6 = 1.67 which is close to 1.5)

If you have a pipe truss and it is exposed to wind, then as an engineer you would want to use at least a 1.5 SF against overturning in your design.

The original D+/-W combo that you cite still used a 1.5 SF. The 0.6D +/- W just codified it into a load combination.

 

[msquared48]

You saithat "I feel that in case of buildings the dead load may not be available where as for pipe truss those pipes are always available."

I guess I do not understand the difference here - dead load is always there - never, but never changes. It is the live load that varies, such as wind, earthquake, personnel, equipment, furniture, etc.

What are you getting at here?

Mike McCann
MMC Engineering

 

[JStephen]

While the IBC may cover various miscellaneous items, that doesn't always mean that IBC is required for those items. For example, I think Texas has a state-wide building code, but it is only applicable to commercial buildings, not to everything built.

 

[structuresguy]

I think he meant that there is an assumption that in buildings we overestimate the dead load that is actually on the structure. For some piece of industrial equipment, it would be easier to accurately estimate the dead load.

However, as JAE said, the 0.6DL is meant to provide a minimum safety factor without actually introducing safety factors into the equations.

 

[WillisV]

IMHO 0.6D+W is bogus for some conditions (like joist uplift). See my first post: thread507-202887

 

[maneesha0702]

Thanks to all of you for your responses. The other question I have is should I apply wind loads on both faces of the structure i.e the outside face of Left side and the inside face of right side if the wind is acting from left to right? When I am looking at Fig 6-21 of ASCE 7 NOTES 2 STATES that calculation of wind forces shall be based on the area of all exposed members projected on a plane normal to the wind direction.Any comments pl

 

[structuresguy]

Yes, for an open truss, you need to apply wind load to all surfaces that come in contact with the wind. So even if one member is directly in line with another in the direction of the wind, both members will get full wind load on them.

 

[maneesha0702]

Thanks for the information. Is it very specific in any code or is it engineering judgement.