Structural Steel Example #1 - Use piping loads to calculate support stiffness - CAESAR II - Help

CAESAR II Users Guide

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CAESAR II
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CAESAR II Version
12

Determine the stiffness of the structural steel support shown below. Use the estimated rigid support piping loads from the piping analysis to back-calculate each stiffness.

A U-bolt pins the pipe to the top of the channel at node 20. The piping loads output from the pipe stress program are:

Fx= -39.0 lbs.

Fy= -1975.0 lbs.

Fz= 1350.0 lbs.

Complete the initial specifications for Example #1

  1. Click File > New from the CAESAR II main window ribbon.

  2. Enter a job name (for example, SUPP), click the Structural Input option, and browse to select the data directory. Then, click OK.

    The software displays the Units Selection page.

  3. Specify the units to use with this job, then click Next.

    The software displays the Vertical Axis Selection page.

  4. Verify that the vertical axis is set to the Y-axis, and then click Next. Selecting the Y-axis means that the gravity works in the Y--axis direction on this model.

    Be sure this coordinate system matches the piping model.

    The software displays the Material Selection page.

  5. Click Next in the Material Selection dialog box to use default material properties.

    The software displays the Cross Section Selection page.

  6. Specify the cross section by typing in the name exactly as it appears (including exact capitalization and trailing zeros) or by clicking Select Section ID and selecting the name from the list.

    For this example, enter the Section ID 1 name as W16X26.

  7. Click Add Another Section to create other cross sections. Enter Section ID 2 as MC8X22.8 and Section ID 3 as L6X4X0.5000. Repeat this until you have three sections specified in this example, then click Next.

    The software displays the Model Definition Method Selection page.

  8. Select Method 1 - Element Definitions Method Selection (the default setting) to use the Element Dimension (EDim) option to define individual elements that span between two node points. Then, click Finish. This input works similarly to piping input, where elements are defined by their end points and delta X, Y, Z distances between those end points.

    The Method 2 - Node/Element Specifications option uses commands to define an array of nodes in space and commands to add elements bounded by these nodes.

    The software opens the CAESAR II Structural Modeler dialog box, where you can interactively input data. Click the arrow on each line in the modeler to expand or condense the information.

Specify the structural steel model input for Example #1

  1. Click on the Commands toolbar to enter commands and parameters that define the model input.

  2. Click EDim to add the first element to the end of the list, then click the arrow to the left to expand the data for that group, and enter the column data.

    Struc Steel Ex 1 First Element

    Notice that the first element is at node 5 to node 10 and runs 12 feet in the Y direction and has a section number of 1 (the default section).

    Press TAB to move quickly from one Card Stack box to the next.

  3. When you complete the first element, click EDim and repeat the entry process to add the next four elements.

    Structural Steel Ex 1 - All Elements

    Structural Steel Ex 1 - All Elements Pt 2

    Use the Input Card Toolbar functions to copy, paste, or delete a card from the Structural Modeler. Alternatively, you can copy or delete a card element by selecting Edit > Copy Card or Edit > Delete Card.

    After you complete the element entry, the software displays the current model.

    Structural Steel Ex 1 - Comp model no fix or loads

    Select O343611 Reset View to return the model to a default view each time the model refreshes. When activated, this function appears highlighted. You can use Reset View to zoom in and out on the model to make changes, and then quickly return to your default view.

  4. Click Fix to add the restraint at the base of the column.

    strucsteelex1fix

  5. Click Loads to enter the loads on this support. You can use a previous CAESAR II analysis for these loads.

  6. Enter the loads at Node 20 [(FX, FY, FZ) = (-39, -1975, 1350)].

    O454597

    The software displays the completed model.

    Struc Steel Ex 1 - Full model

  7. Add comments to the model by first setting where CAESAR II inserts comments from the Insert menu option. You can specify for comments to appear before or after the currently selected element, or at the end of the model elements list. Click Comment to add comments to the model.

    After you insert a comment, you must click the down arrow to expand the comment element and add the comment text. The following example shows the completed model with new comments inserted.

  8. Click File > Save to check and save the model. Then, click OK.

    CAESAR II checks the input. If the error checker does not find any fatal errors, the software writes the execution files. You can use the model in a piping analysis, or you can analyze the model singularly. For the purposes of this example, you will analyze the model by itself.

  9. Close the CAESAR II Structural Modeler dialog box and return to the CAESAR II main window.

  10. With the SUPP file still open as the current model, click Analysis > Statics on the toolbar.

    Remember to replace the Weight load in Load Case 1 (L1) with F1 (the applied loads).

  11. Click Run the Analysis.

    CAESAR II performs the structural steel analysis, just as a piping analysis.

The output from a structural analysis is comprised of displacements, forces, and moments. The results from the analysis of the SUPP model show the displacements at Node 20.

Structural Steel Ex 1 - Displacements

These displacements are excessive for a support, which is to be assumed rigid in another analysis. The translational stiffness for the support can be computed as follows:

Kx = 39 lb. / 10.125 in. = 3.85 lb./in
Ky = 1975 lb. / 0.4228 in. = 4671 lb./in.
Kz = 1350 lb. / 0.8444 in. = 1599 lb./in.