How to Apply Static seismic / Static acceleration loads

In this example we have a 20 ft. long run of 14”STD pipe full of liquid contents density 62.4 lbs/ft3 (SG 1.0), and 1” of insulation with a density of 14 lbs/ft3.

There are 2 ways to apply static acceleration loads (G) in CSiPlant, and either option will work. The first way is using the Define load pattern dialogue shown below left. Change Load Type to Earthquake as shown below even if the acceleration load is for transportation loading or other applications. Left click to highlight the Earthquake load pattern and click Modify Special Load button. Here we specify 1 G in the vertical Z direction. If we were applying lateral static seismic loads, we would type in a percentage of G in the X or Y direction. In this example, we will compare results between GR weight load and 1G vertical acceleration.

An alternative way to apply static acceleration loads is using the Define>Load case dialogue using nonlinear static case shown below right. Change load type to Acceleration, choose a direction, Z in this example, then type a scale factor depending on your current units. This example was in feet units, so typing 32.17 applies a 1 G load (32.17 ft/s^2). If instead we wanted to apply a .4G acceleration load, for example, we would have typed a scale factor of 12.868 (.4 X 32.17) if in feet units, or 3.92 scale factor for .4G if in meters. Acceleration loads using the static load case dialogue can be applied in translational and/or rotational directions for pitch, roll, and yaw rotations.

Here we compare anchor reactions in the vertical Z direction between ACCEL Z Load Case, ACCEL Z, and GR weight case. As expected, they are the same. The acceleration load defined in the load case dialogue using a scale factor is very slightly different due to round off. Had we input 32.17405 it would match exactly.

As you can see at the bottom of the output report, users have the option to display output results in any units that they choose.

When analyzing static acceleration loads (G) or dynamic loads, the Define>Mass Source dialogue can be quite important. The default shown below right is good for most piping-only analysis scenarios. However, if your model includes structural frame elements which are supporting heavy equipment loads, live loads, and cable trays, additional load patterns will likely need to be added to the Mass source. The “Element Self Mass” option is the same exact thing as a DEAD load pattern with selfweight multiplier of 1, so when that option is checkboxed, never include DEAD in the Load Patterns below as that will double-count selfweight mass.

ASCE 7 and other design standards require seismic loads to be analyzed with both piping and equipment empty of liquid contents, as well as analyze the scenario of piping and equipment full of liquid contents. In the scenario of empty liquid contents, the Fluid load pattern would have to be deleted from both the Mass source as well as deleted in the load case. CSiPlant enables users to define multiple different Mass sources in order to analyze these different scenarios all in the same analysis for side-by-side comparison of results.