Restraint Loads

Related Topics

This table displays support and restraint loads. Support loads are displayed as projections on coordinate axes. External support loads corresponding with the coordinate axes direction are positive. Counter-clockwise moments (looking from the end of the axis on which the moment acts) are positive. See also "How to Reduce the Nozzle Loads in START-PROF"

Table view and contents depend on four properties, which must be input:

Property

Description

Operating Mode

Choose operation mode for which the results will be displayed

Maximum - the maximum value will be displayed in every cell from all operation modes

Here you can see analysis results from each of additional force-based loading, seismic, wind, and ice loading

Submode

For every operating mode software calculates several submodes (piping states)

  • Maximum - maximum load values (for the absolute value) are displayed for each axis in all states (Operation state, Cold state, Test state, Cold state after relaxation)

  • Maximum and minimum - maximum and minimum load values in all states are displayed. Non-stressed and non-deformed state where all forces are zero is added for all states. Maximum and minimum values considering the signs of all forces are selected for each support based on all load components in all states. If all values are negative, 0 is the maximum value; is all values are positive, 0 is the minimum value. Data is displayed in two lines: upper line - minimum value, lower line - maximum value. Maximum and minimum value for different axes are calculated separately for the same support, meaning that the 6 calculated loads for a support (forces PX, PY, PZ and moments MX, MY, MZ) can act in different states and not simultaneously. Therefore, if supports, equipment and structure do not meet safety conditions for the calculated minimum and maximum values, analysis should be run for various separate load combinations (in operating mode, cold mode, cold mode after relaxation, test state), which will minimize unnecessary safety margins.

  • Maximim + Seismic. Seismic load cases are considered

  • Maximum and minimum + Seismic

  • Operation state

  • Cold state

  • Test state

  • Cold state after relaxation

Occasional Loads

 

  • Maximum+seismic maximum static+seismic

  • Maximum and minimum + seismic

Axis

Loads and moments are displayed as projections on coordinate axes:

  • Global axes (X, Y, Z) - Px, Py, Pz, Mx, My, Mz (fig. 1.a)

  • Support local axes (for support construction Xmm, Ymm, Zmm) - ΔXmm, ΔYmm, ΔZmm, φXmm, φYmm, φZmm (fig. 2). Local restraint axes do not match local axes of pipe elements adjoining the support. Restraint axes are always in horizontal and vertical planes. In other words, regardless of the Piping slope, the local restraint coordinate system remains the same. Support local axes are usually used for determining of loads on supports, because we need the load along the Piping direction, vertical load and horizontal load. If the pipe has a slope then pipe local axes loads will be inclined, that can not be accepted.
    Support local loads for supports where the pipe direction change more than 0.5 degrees, and nodes containing more than two pipe elements are not displayed in the table because program can't determine the Piping direction.
    Support local loads for supports where the pipe slope is greater than 45 degrees are not displayed in the table because it doesn't make sense. For example - what is the Piping direction (north, south, west, east) for a vertical pipe?

  • Pipe local axes (for vessels, equipment, pumps Xm, Ym, Zm) - in local coordinate system Pxm, Pym, Pzm, Mxm, Mym, Mzm, connected to the axes of elements adjoining the support (fig. 1.b)
    Pipe local axes are usually used to determine the nozzle loads, because we need the load along the pipe axis and perpendicular to pipe axis.

Fig. 1. Support loads in global (general) and local coordinate systems

Fig. 2. Loads in local restraint axes

Support type

Only loads for support types selected in the menu will be displayed.

Load factor

This option is available only if the local restraint axes  coordinate system is selected. Support load factor k must be input (usually set as  k= 1.0 or k=0.8 according to SNIP 2.05.06-85 section 8.44).

If support load factor k is not 1.0, load is calculated as follows:

  • applied only for fixed anchors and moment free anchors

  • if loads from pipes to the left and right of the support  (N1 and N2) are in the same direction, they are combined  N1+N2

  • if loads  N1 and N2 are in different directions, the lower values is multiplied by k and then combined as  N1+N2*k (|N2|<|N1|)

  • if the support is on an end node, factor  k is not used

Standards do not indicate loads for which factor k  must be applied. Factor k is included in standards to consider possible errors in friction forces and uneven Piping heating, so it is used in START-PROF only for loads in the horizontal plane. In other words, factor k is used for forces along the Xmm and Ymm axes, and moment around the  Zmm axis. It is not applied for forces along the  Zmm axis and moments around the  Xmm and Ymm axes.

For more information read How to Avoid Zero Anchor Loads?

Menu Access

After analysis: Output > Restraint Loads