Retrofit of Seismic on Portion of Existing System?

3/14/2019

I have a healthcare building owner (five story building) who is doing a small remodel to about a third of a single floor. The existing sprinkler system is being modified (relocated and demo/new sprinklers) to accommodate the wall and ceiling changes.

The existing building is Seismic Design Category D, requiring seismic bracing, but the existing system has none. My recommendation to the owner (which aligns with their insurer's recommendation) is for retrofit of the whole floor if not the whole building.

The owner is looking to provide seismic bracing on only the system being modified.

Does this provide any benefit at all?

My concern is that without adequate bracing what is provided could possibly provide zero benefit or even make the system worse if part is fixed and another is not.

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2 Comments

Dan Wilder

3/14/2019 10:31:36 am

This goes beyond just adding bracing...are you providing clearances for ceiling/sprinkler penetrations, are flex couplings being utilized correctly, do you have the required clearances to/from structural members, do you have the correct clearances for pipe/non-frangible walls/floors, does the building have any seismic separations requiring the correct assembly, is the structure capable of the loads imposed by the sway bracing in the event of an earthquake? This also doesn't take into account anything on the building side that is out of our control like ceiling construction, column & floor support, foundation to name a few.

I'm going to equate this to providing support for a branch of a tree while you dig out the root ball....it's all going to fail without a complete approach to the entire structure. You are on the right path and this really needs to be an all or nothing approach or document exactly what you are providing with the concerns you have about the rest of the building.

PETE

3/14/2019 11:12:49 am

I'd like to echo DAN. I do most of my work in a seismic zone. I'd just say be careful what you are bidding. If there aren't clearances, you can provide flex couplings within so many inches of the penetrations(different for horizontal and vertical). Sprigs longer than 4 ft need restraint. Also, hangers should be retrofit with seismic restraint (tolco surge clips) if they are longer than 6", and all TBCs strapped (69R). Then you have to look at branch lines- 2 1/2" and over need lateral bracing if hangers are longer than 6", and if your zone of influence for the smallest incremental spacing for lateral bracing on the feed mains exceeds the max force values provided in 13 ch 9, you will need to longitudinally brace the branch lines fed by those mains to decrease the horizontal force in the zone of influence (this is rare and typically applies to long grids >150'). Last, he really needs to do the whole building, but I've had clients who want to break it up for budgeting reasons. It's really the client's choice. The idea behind seismic bracing is that the building is designed for seismic loads, and it will move in a seismic event. The sprinkler system is braced to the building and designed to move with the building without coming apart. With that in mind, bracing a single system would mean that system could be the only one that remains in service during a seismic event, assuming that a seismic event occurred during the interim time between retrofitting the single system and retrofitting the entire building.

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