ASCE building or non building similar to a building 2

[irishengdave]

We are designing a 9 storey steel industrial building supporting mechanical equipment. There is a designated area where 5/6 people work 5 days over 40 hrs per week. The building is cladded.

What category does it fit into, building or non building similar to a building? Problem is, if we design it as a building it becomes a special concentric ally braced steel frame which we are trying to avoid.

 

[amec2004]

In terms of seismic design, it's a building.

The key point for judgment is if there is significant "storey" level in the structure with floors such as composite floor or hor braced diaphragm making this structure behave in a "storey" wise mode shape.

The weight of mechanical equipment should not exceed 25% of combined (structure + equipment) weight. If it is more than 25%, it shall be classified as nonbuilding structure supported by other structure and the mechanical equipment, one of the example is vertical vessel, shall participate in the seismic analysis which will impact the combined structure's dynamic characteristics.

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[irishengdave]

Chapter 11 of asce defines a building as an enclosed structure whose intended use is to provide shelter for human occupants.

It is difficult to categories this structure. It's primary use is to support large pieces of mech equipment. A tiny part of it only provides shelter for humans.

It seems like overkill to put in the building category. The seismic design requirements are much more stringent.

 

[irishengdave]

Amec, your key point for judgement can put it in both categories. I will need to read the code regarding your point about the weight of equipment.

 

[hokie66]

I don't know the 'code' answer to your question, but why would you design an industrial structure to a less robust standard than a commercial structure? In my experience, industrial structures are ALWAYS more robust.

 

[SAIL3]

IMO, non-building similar to buildings....there will always be a minimal number of workers in these facilites..for tie-dn of equipment for seismic loads, I would use the component section...

 

[amec2004]

My reply as the followings

>>pieces of mech equipment. A tiny part of it only provides shelter for humans

In terms of seismic design, there is no big difference between equipment and human except one thing, the load importance factor Ie in Canadian NBCC 2005 code or something like increasing occupant category in ASCE. For post-disaster structures like power station or hospital you have to apply a higher importance factor to increase the seismic load. Other than that, the analysis treats both human and equipment as mass in the analysis. To achieve an accurate seismic analysis, the following things matter

1. What is the mass participating in the dynamic analysis and base shear distribution. Both human and equipment are mass. For equipment mass you shall count operating weight. For occupant live load you cannot count the full load, like carpark structure you cannot take the load of every storey fully parked as mass, for roof snow load you can only count 25% as mass etc

2. How to get the accurate period Ta for analysis
This comes to the building structure and non building structure like vertical vessel. It’s important to workout the accurate period to get the right seismic response from design spectral curve

3. How to distribute the base shear to each level or lumped mass node

Why and how ASCE classifies the structure is based on the facts that make above 3 items analyzed correctly.

Most of petrochemical facilities can be classified as the following categories:

1. Building Structure
2. Nonbuilding Structure Similar to Building
3. Nonbuilding Structure Not Similar to Building
4. Nonbuilding Structure (Less Than 25% Comb Wt) Supported by Other Structure
5. Nonbuilding Structure (More Than 25% Comb Wt) Supported by Other Structure

>>I would use the component section...

There are two parts of seismic analysis: Global and Local.
For global you have to count the equipment mass in each level’s lumped mass and work out the Ta, get the base shear, and distribute the base shear to each storey (lumped mass node)
For local part is what you talking about component section, an equipment sitting on lower floor and roof floor get different seismic response.

You have to check both Global and Local.

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[Ron]

It's a building. Further, the use might change as companies change. Don't limit the downstream use of a large, expensive structure.

 

[SAIL3]

My understanding of the reason for having those two different catagories in the Code was due to their intended use with the main difference being that the main use for buildings were intended for human occupation wheather public or private...I could certainly be mistaken in this...Ron mentioned a good point about the possibility of this industrial bldg being converted in the future for human occupation which happens frequently and based on that it would seem like sound engineering judgement to incorporate this into the design now....the more I think about it, the less sense it makes as the response of a structure to design loading is not influenced by it's current use......waffle, waffle...

 

[irishengdave]

I think it should be categorized as a building and designed as a special braced frame. I think it is probably not relevant how many people occupy the building. I was just wondering if there was something more explicit contained in the codes which would clearly put it in the other category. But that is a good point about its future usage.