Modeling of Sway Braces in Caesar II for stress analysis

# Modeling of Sway Braces in Caesar II for stress analysis

I have already published a post explaining the basics of Sway Braces in my earlier posts. Click here to visit it again. In this article I will explain the procedure for modeling Sway Braces in Caesar II.  As I have mentioned already that Sway braces are spring (pre-loaded) loaded units to limit the swaying or vibration induced by external forces by applying an opposing force on the pipe. The sway brace is simulated by use of bi-linear restraint available in CAESAR II. It will be discussed in the following section.

Note: Refer this article along with the earlier article on Sway Brace for proper understanding.

Modeling in Caesar II:

The steps involved in modeling a sway brace in Caesar are as follows: Select the sway brace from catalogue depending on given pipe nominal diameter or depending on the force calculated to restrain the pipe work. (Fig. SB45 as per C&P catalogue, reproduced in Fig. 1)

Fig.1: Sway Brace selection Table from C&P Catalogue. Mark a node (Node 10-Fig.2) at the location in the piping system where sway brace will be installed. Run Caesar analysis and note down the displacement of the point in specified direction from cold to operating condition. For the sake of example, let’s assume that CAESAR II calculated displacement from cold to operating position is 0.5 inch in +X direction. Now in CAESAR II input spread sheet (See Fig. 2) check the restraints box and define bi-linear restraint (X2 for the assumed case) at Node 10 with CNode at 101. Here, K1 is the initial stiffness of a bi-linear restraint. Do not enter anything on this cell as the restraint is assumed to be rigid. The value of K2and Fy to be obtained from catalogue. Where, K2= Post yield stiffness of a bilinear restraint. When the load on the support restraint exceeds Fy then the stiffness on the support restraint changes from K1 to K2. Fy = Yield Load. If the load on the support restraint is less than “Fy” then the initial stiffness K1 is used. If the load on the support restraint is greater than “Fy” then the second stiffness ” K2″ is used. Define restraint X at node 10 with CNode at 101. Provide a gap of 3 inch (=distance the sway brace is able to move in both positive and negative direction before it gets locked/ become fully rigid depending on manufacturer= 3 inch as per C&P catalogue) Check the displacement box and define the displacement for Node 101. It is the displacement for node 10 as noted earlier (0.5 inch in X direction, leave other cells i.e., DY, DZ, RX, RY, RZ blank.). Add D2 in sustained and operating load cases. Now run the analysis to obtain results.

Fig. 2: Caesar II Spread sheet for Sway brace modeling.