For designing a pipe support (random on platform or additional field support) structural engineer requests for LOADS for the piping system.Its the responsibility of the piping designer to provide with the loads unless there is a provision in the project guidelines that loads will be calculated by the structural engineer himself.
In general there are two ways that are usually followed to determine the loads.
FOR VERTICAL LOADS
Methods of calculating piping loads fall into two categories:
Category A - Precise calculation.
Category B - Quick calculation.
Both work but Category B is a more conservative approach in load determination.
With Category A:
The load imposed upon the support is 50% of the horizontal run upstream of the calculated support point and the next support and 50% of the horizontal run downstream of the calculated support point.
If there is a vertical run in the configuration, the support nearest the vertical part will receive 100% of the vertical load plus the horizontal components as above.
Another train of thought regarding the vertical component is that it could also be treated as you would treat a horizontal run with a valve in it - this is a concentrated load calculation. See the next paragraph for an explanation of concentrated load calculation.
A concentrated load is one that is defined as uneven loading between two support points. For example, if you have a valve in the exact center of a horizontal run - the supports for that portion will each receive 50% of the total weight of the valve and flanges. If the same valve in the same run is located such that it is 1/4 of the run from one of the supports, then a calculation is necessary. The result is that the support nearest the valve will receive 75% of the total valve weight and the support further away will receive only 25% of the total weight of the valve and flanges, in other words, the loads are proportional depending on the valve placement. This could be applied to vertical pipe load calculation - the vertical configuration would have the same effect as a valve & flanges.
At times, based on information that is not "firm" or the lack of certainty/confidence regarding the individual or state of the design doing the calculation for Category A, it may be desirable to add a contingency load, or, "bump" the final calculated load. There is no rule established for this. Some designers "bump" the load by 5% or 10% to provide a sense of confidence in their work - no one wants a support to fail because he/she has established a load that is too light and have the support fail when it realizes the "real" load.
I have also seen a designer "bump" the calculated load by 10%, then his supervisor "bumps" it 10%, then structural engineering "bumps" it yet another 10 %. You then have a load equal to 133.1% of the precisely calculated load. Your support will definitely not fail.
With Category B:
This is a "shortcut" calculation. All the designer needs to do to calculate the load is add the following:
Weight of the pipe using the length of the maximum pipe span (100%) + weight of water for the same length of pipe.
This quick calculation method gives loads ranging (approximately) from 100% to 135% of the precisely calculated load (for pipe filled with water only - valves are used in this example). Again, your support will definitely not fail.
There are no factors for concentrated load because 100% of the valve weight and flange weight would be used in the equation.
In doing this "shortcut," a very conservative load is determined.
In both categories it is necessary to add the weight of pipe insulation, valves, flanges & bolts - see Charts available with the design guide for these weights.
FOR HORIZONTAL LOADS
If it is known there are horizontal loads (anchors and directional anchors) and there is no pipe stress input (the line did not go to stress or did not qualify for stress analysis) - the horizontal load can be submitted to structural engineering determined by multiplying the vertical load by .30 - this is a conservative approach.