Example: Multiple Load Case Spring/Hanger Design - CAESAR II - Help

CAESAR II Users Guide

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CAESAR II
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CAESAR II Version
12

This example illustrates the hanger selection logic when the software considers more than one operating state.

The software bases hanger selection on the dead weight load to be carried by the hanger and the range of expected travel. The load is dependent on any nonlinear supports that are active in the operating state. If a nonlinear support is active in the initial weight distribution analysis but inactive in the operating case (or vice versa), the software recalculates the weight distribution based on the nonlinear support configuration found in the operating case. With more than one operating case to satisfy, you may have more than one load and more than one travel for the hanger.

The example uses two operating cases.

  • Operating case 1: W+T1+D1

  • Operating case 2: W+T2

Operating Case 1

  1. The software runs the restraint weight case (W) to calculate the hot load of 3,174 lb (T1) supported by the hanger. The +Y non-linear vertical support at node 30 is not active, because the pipe must move down to close the 0.5-inch gap before carrying any load.

  2. The software runs operating case 1 (W+T1+D1) and calculates the deflection of 0.2905 inches at the node 20 hanger. The +Y non-linear support at node 30 is now active.

  3. The software converts the node 30 support to a linear vertical support and re-runs the restraint weight case (W).

    The hanger hot load reduces to 815 lb. The software sizes the hanger using the reduced hot load and the travel of 0.2905 inches.

Operating Case 2

  1. The software runs the restraint weight case (W) to calculate the hot load of 3,174 lb. that the hanger has to support. The +Y non-linear vertical support at node 30 is not active.

  2. The software runs operating case 2 (W+T2) and calculates the deflection of 0.2226 in. at the node 20 hanger. The +Y non-linear vertical support is still inactive.

    The software uses the hot load of 3174 lb. and travel of 0.226 in travel to size the hanger.

Determining the Load Cases

  1. Click Hangar design criteria .

    The Hanger Design Control Data dialog box displays.

  2. In the No. of Hanger Design Operating Load Cases box, type 2. In the Multiple Load Case Design Option box, select 2- Operating Case #2.

    The software bases hanger selection on two operating load cases.

  3. After running static analysis and the hanger report, the software recommends operating cases L2 and L3 during hanger selection.

L1 (Dead weight for the hanger)

The software runs a weight analysis with a +Y restraint included at node 20 to pick up the load that the hanger carries. The 0.5-inch gap at node 30 remains. With no load carried at node 30, the dead weight load assigned to 20 is 3174 lbf.

L2 (Operating case #1)

The software analyzes the operating case with an upward load at node 20 of 3174 lbf, representing the effort of the hanger. The vertical displacement at node 20 represents the required travel of the hanger. However, the -Y displacement at node 40 engages the gapped +Y restraint at node 30.

With 30 now resting on the support, the initial estimate of dead weight load at node 20 is in question. The software returns to L1 to recalculate the load at node 20, this time with the +Y restraint at node 30 (no gap) included. On this second pass, the load at node 20 is now only 815 lbf.

The software reanalyzes L2 with the upward load of 815 lbf. The vertical deflection of node 20 in this case is 0.2905 inches.

L3 (Operating case #2)

The software uses the initial dead weight estimate for the hanger at node 20. Without the displacement specified at node 40, the operating case does not engage the restraint. The vertical displacement of node 20 is 0.2226 inches and is used with the original load of 3174 lbf.

The software now has the data to select hangers at node 20 based on these two operating cases:

Operating Case

Load
(lbf.)

Travel
(in.)

1

Operating Case #1 (W+T1+D1)

815

0.2905

2

Operating Case #2 (W+T2)

3174

0.2226

Other Design Options

You can make additional selections for Multiple Load Case Design Option that use the two operating cases.

10 - Maximum Load

Uses the load and travel pair with the largest load. For this example, the software uses operating case #2.

11 – Maximum Travel

Uses the load and travel pair with the largest travel. For this example, the software uses operating case #1.

12 – Average Load & Travel

Uses the average load and travel values of the operating cases. For this example, the software uses an average load of 1995 lbf and an average travel of 0.2566 inches.

13 – Maximum Load & Travel

Uses the maximum load and travel values of the operating cases. The values can be from different operating cases. For this example, the software uses a load of 3174 lbf (from operating case #2) and travel of 0.2905 (from operating case #1).

Summary

Multiple Load Case Design Option

Load
(lbf.)

Travel
(in.)

1

Operating Case #1 (L2 = W+T1+D1)

815

0.2905

2

Operating Case #2 (L3 = W+T2)

3174

0.2226

10

Maximum Load

3174

0.2226

11

Maximum Travel

815

0.2905

12

Avg Load & Travel

1994

0.2566

13

Max Load & Travel

3174

0.2905

Hanger report:

For more information, see Multiple Load Case Design Option.