In the Classic Piping Input dialog box, click the Uniform Loads auxiliary panel and select the in G's option. On the first element, type the seismic load in Gs. Enter the X-direction acceleration in the Vector 1 box, the Y-direction acceleration in the Vector 2 box, and the Z-direction acceleration in the Vector 3 box. This makes load case generation easier.
Because a seismic event is likely to occur while the piping system is in operation, an operating case should have all operating loads plus the seismic load. This load case is then used with the standard operating case to segregate the effect of the seismic load. The seismic load is then combined with the static sustained load case for code compliance considerations.
L1 |
W+T1+P1 |
(OPE) |
L2 |
W+T1+P1+U1 |
(OPE) |
L3 |
W+T1+P1-U1 |
(OPE) |
L4 |
W+T1+P1+U2 |
(OPE) |
L5 |
W+T1+P1-U2 |
(OPE) |
L6 |
W+T1+P1+U3 |
(OPE) |
L7 |
W+T1+P1-U3 |
(OPE) |
L8 |
W+P1 |
(SUS) |
L9 |
L1-L8 |
(EXP) |
L10 |
L2-L1 |
(OCC) |
L11 |
L3-L1 |
(OCC) |
L12 |
L4-L1 |
(OCC) |
L13 |
L5-L1 |
(OCC) |
L14 |
L6-L1 |
(OCC) |
L15 |
L7-L1 |
(OCC) |
L16 |
L8+L10 |
(OCC) |
L17 |
L8+L11 |
(OCC) |
L18 |
L8+L12 |
(OCC) |
L19 |
L8+L13 |
(OCC) |
L20 |
L8+L14 |
(OCC) |
L21 |
L8+L15 |
(OCC) |
Load cases 2 through 7 include all the loads and call these operating cases. The subtracted uniform load vectors reverse the direction of the uniform load applied. Use these load case results for occasional restraint loads and occasional displacements. Load cases 10 through 15 signify the segregated occasional loads. These are called occasional load cases, but you do not need a code stress check here because these are only part of the final solution for code compliance. Because of this, you can select the Suppress option for the Output Status. Also, these combination load cases all use the Algebraic Combination Method on the Load Cases tab. Load cases 16 through 21 are all used for code compliance. Add the segregated occasional results to the sustained case results and use either the Scalar or ABS Absolute Value Combination Method. Both scalar and absolute will give the same code stress results although the displacements, forces, and moments could be different. Because you do not use any results except the stresses for combination cases, it does not matter which combination method you use.
Sometimes you want to combine the results of vertical g-loads with horizontal g-loads. A factor is often applied to the vertical g-load component of the combined load. You can accomplish this when you type the Uniform Load data on the Classic Piping Input dialog box for the vertical component, or you can do this directly in the load case editor as shown below. Using the previous example, combine .67 vertical g-load with each horizontal component.
L1 |
W+T1+P1 |
(OPE) |
L2 |
W+T1+P1+U1+0.67U2 |
(OPE) |
L3 |
W+T1+P1-U1+0.67U2 |
(OPE) |
L4 |
W+T1+P1+U1-0.67U2 |
(OPE) |
L5 |
W+T1+P1-U1-0.67U2 |
(OPE) |
L6 |
W+T1+P1+U3+0.67U2 |
(OPE) |
L7 |
W+T1+P1-U3+0.67U2 |
(OPE) |
L8 |
W+T1+P1+U3-0.67U2 |
(OPE) |
L9 |
W+T1+P1-U3-0.67U2 |
(OPE) |
L10 |
W+P1 |
(SUS) |
L11 |
L1-L10 |
(EXP) |
L12 |
L2-L1 |
(OCC) |
L13 |
L3-L1 |
(OCC) |
L14 |
L4-L1 |
(OCC) |
L15 |
L5-L1 |
(OCC) |
L16 |
L6-L1 |
(OCC) |
L17 |
L7-L1 |
(OCC) |
L18 |
L8-L1 |
(OCC) |
L19 |
L9-L1 |
(OCC) |
L20 |
L10+L12 |
(OCC) |
L21 |
L10+L13 |
(OCC) |
L22 |
L10+L14 |
(OCC) |
L23 |
L10+L15 |
(OCC) |
L24 |
L10+L16 |
(OCC) |
L25 |
L10+L17 |
(OCC) |
L26 |
L10+L18 |
(OCC) |
L27 |
L10+L19 |
(OCC) |
Sometimes you need to combine the horizontal and vertical components of seismic loading. You can do this from the Static Analysis - Load Case Editor. Set up the static seismic load cases as shown in the first example, then combine the segregated horizontal and vertical load cases together using the SRSS Combination Method. Add these results to the sustained case.
L1 |
W+T1+P1 |
(OPE) |
L2 |
W+T1+P1+U1 |
(OPE) |
L3 |
W+T1+P1-U1 |
(OPE) |
L4 |
W+T1+P1+U2 |
(OPE) |
L5 |
W+T1+P1-U2 |
(OPE) |
L6 |
W+T1+P1+U3 |
(OPE) |
L7 |
W+T1+P1-U3 |
(OPE) |
L8 |
W+P1 |
(SUS) |
L9 |
L1-L8 |
(EXP) |
L10 |
L2-L1 |
(OCC) * |
L11 |
L3-L1 |
(OCC) * |
L12 |
L4-L1 |
(OCC) * |
L13 |
L5-L1 |
(OCC) * |
L14 |
L6-L1 |
(OCC) * |
L15 |
L7-L1 |
(OCC) * |
L16 |
L10+L12 |
(OCC) ** |
L17 |
L10+L13 |
(OCC) ** |
L18 |
L11+L12 |
(OCC) ** |
L19 |
L11+L13 |
(OCC) ** |
L20 |
L14+L12 |
(OCC) ** |
L21 |
L14+L13 |
(OCC) ** |
L22 |
L15+L12 |
(OCC) ** |
L23 |
L15+L13 |
(OCC) ** |
L24 |
L8+L16 |
(OCC) *** |
L25 |
L8+L17 |
(OCC) *** |
L26 |
L8+L18 |
(OCC) *** |
L27 |
L8+L19 |
(OCC) *** |
L28 |
L8+L20 |
(OCC) *** |
L29 |
L8+L21 |
(OCC) *** |
L30 |
L8+L22 |
(OCC) *** |
L31 |
L8+L23 |
(OCC) *** |
* Use the algebraic combination method in the Static Analysis - Load Case Editor.
** Use the SRSS combination method in the Static Analysis - Load Case Editor.
*** Use the ABS or Scalar combination method in the Static Analysis - Load Case Editor.
Change the operating load cases that include seismic loads to OCC for piping codes that do not perform a sustained code stress check. Use these cases for code compliance. The combination cases are not needed in such cases.