k.thiruththaninathan@yahoo.com

i am a Civil engineer.I am in need of guidance,Could Any one please help me in understanding the seismic load transfer in pipe sleepers. I was told that the total seismic load will be transferred to the anchor bays (axial stops) only, since seismic load is a incidental load and the intermediate supports will not play any role in resisting seismic load.

My Understanding is that, since the pipes are supported in intermediate sleepers between the anchor bays, there will be vertical load on those sleepers and when there is a vertical mass there will be a seismic component at that particular support. Hence the seismic load should be distributed among all the intermediate supports between the anchor bays.

Could anyone please tell me whether my understanding is correct, if not please guide me.

As a Civil Engineer, you must know that the horizontal acceleration is the main issue in seismic calculation. That's why you need "enough" Seismic Restraints on your piping as guides, axial stops and anchors. If your application has hot service lines, these restrains would restrict too much the thermal movement of pipes, overstressing them. This "conflict" can be solved by a mix of experience and calculations.

The first step is always understanding the basics.
You need a good start with a book about piping and supports, they are a lot on market.

You may have a look in B31E, Standard for the Seismic Design and Retrofit of Above-Ground Piping Systems, which establishes a method for the seismic design of above-ground piping systems in the scope of the ASME B31 Code for Pressure Piping. It is not a book, but I'm sure you can understand more than you know today.

Thank you for your suggestions

While analyzing for seismic loads, there are two options.
1. To ignore friction at all rest support, guides
2. To consider the frictional effects

In simple terms,

Usually w/o friction gives the highest anchor loads, since the resting support friction does not restrict the seismic displacements.

While analyzing with friction at support you may get a lower anchor loads since the friction at the rest support absorbs the seismic movement


In your case the option 1 would have been used to get the conservative seismic anchor loads.

The intermediate sleepers between the anchor bays may have only frictional component in lateral direction if you consider friction at resting supports.

There are recommendations/requirements to not consider the frictional effects in piping seismic calculation.

See for example ASCE 7, 15.5.2 Pipe Racks, 15.5.2.1 Design Basis:
"[...] See Section 13.6.3 for the design of piping
systems and their attachments. Friction resulting from
gravity loads shall not be considered to provide
resistance to seismic forces."

Best regards.