Recommended Load Cases for Hanger Selection - CAESAR II - Help

CAESAR II Users Guide

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CAESAR II
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CAESAR II Version
13

CAESAR II must analyze two additional load cases to get the data required to select a variable support, if you want to let the software design spring hangers. The two basic requirements for sizing hangers are the deadweight carried by the hanger, which is hanger hot load, and the range of vertical travel to be accommodated.

The first load case, traditionally called restrained weight, consists of only deadweight (W). For this analysis, CAESAR II includes a rigid restraint in the vertical direction at every location where a hanger is to be sized. The load on the restraint from this analysis is the deadweight that must be carried by the support in the hot condition.

For the second load case, the hanger is replaced with an upward force equal to the calculated hot load, and an operating load case is run. This load case, traditionally called free thermal, includes the deadweight and thermal effects, the first pressure set if defined, and any displacements, W+D1+T1+P1. The vertical displacements of the hanger locations, along with the previously calculated deadweights, are then passed on to the hanger selection routine. After the hangers are sized, the added forces are removed and replaced with the selected supports along with their pre-loads cold loads designated by load component, H. Load component H can appear in the load cases for hanger design if you have predefined any springs. In this case, it would represent the pre-defined operating loads.

CAESAR II then continues with the load case recommendations as defined above. A typical set of recommended load cases for a single operating load case spring hanger design is as follows:

Case 1

W

Weight for hanger loads

Case 2

W+D1+T1+P1

Operating for hanger travel

Case 3

W+D1+T1+P1+H (OPE)

Operating, hangers included

Case 4

W+P1+H (SUS)

Sustained load case

Case 5

L3-L4 (EXP)

Expansion load case

These hanger sizing load Cases 1 and 2 generally supply no information to the output reports other than the data found in the hanger tables. Cases 3, 4, and 5 match the recommended load cases for a standard analysis with one thermal and one pressure defined. The displacement combination numbers in Case 5 have changed to reflect the new order. If multiple temperatures and pressures existed in the input, they too would appear in this set after the second spring hanger design load case.

Two other hanger design criteria also affect the recommended load cases. If the actual cold loads for selected springs are to be calculated, one additional load case, WNC+H, would appear before Case 3. If the hanger design criteria of the piping system are set so that the proposed springs must accommodate more than one operating condition, other load cases must appear before Case 3 above. You must perform an extra hanger design operating load case for each additional operating load case used to design springs. See Load Cases with Hanger Design for more information on these options.