Software Knowledge Base

Note ID: 000095 – Applications: PanelsPlus

Title: PanelsPlus Tutorial – Strongback example

Description: General description of the application and usage of strongback elements including a worked example

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Date Created: 12/11/2008

Date Modified: 12/11/2008

Strongback elements can be used in the PanelsPlus software when a panel’s geometry may make the panel susceptible to cracking or failure during the lifting phase. A strongback is typically made up of a steel ‘I’ section or 2 Parallel Flange Channels (PFC - or ‘C’ sections) arranged back-to-back and attached to the panel along the bottom flange.

Below is a sketch showing a strongback positioned along a tall narrow leg of a panel. The section shows a typical arrangement where a strongback is attached to the panel along the height of the panel.

Notes regarding strongback elements in PanelsPlus;

- A strongback MUST be continuously connected to the panel along its entire length (part of a strongback cannot be positioned through an opening).

- PanelsPlus does NOT use a particular brand or type of strongback. The user must enter the required section properties for the strongback.

- Out-of-plane behaviour and local buckling effects along the length of the strongback are not considered by the software, and the user needs to consider these aspects independently from the software.

- The self-weight of the strongback is not considered during the analyses or the panel weight etc.

Worked Example

The following example is based on a panel contained within the tutorial file available on the install CD. The general geometry and details are shown in the screen shot below;

The lifting analysis was performed using 2 edge lifters located at the top of the panel. This arrangement (panel thickness = 150mm) was chosen in order to produce large stresses in the panel.

The stresses in Y-Y during lifting are shown in the screen shot below;

In order to determine the size of the strongback required, the bending moment diagram where the strongback is to be located needs to be extracted. The moment results in the Y-Y direction produce a maximum positive moment for the example panel of 37.2kNm/m. As PanelsPlus produces the moment results as ‘kNm/m’, this result needs to be multiplied by the perpendicular distance of the section where the moment diagram was produced. In this case, the width of the left leg is 990mm, so the total maximum bending moment in the panel is: 37.2 x 0.99 = 36.8kNm.

The next step is to generate a strongback element and enter properties of a suitable section considering the results that were calculated in the previous step.

To create a strongback the ‘Strongback icon’ needs to be selected from the main interface of the software. The software will then show that the drawing mode is set to ‘Ortho Mode’ meaning that when the user clicks on the panel creating a line (2 points), the strongback will be generated orthogonal to Y-Y or X-X (depending on relative location of the second point to the first point).

For this example the strongback is to be positioned along the entire height of the panel, approximately centred about the left narrow leg.

Before clicking on the two points shown as ‘1’ and ‘2’ in the screen shot below, the user needs to ensure that the snapping mode is set to ‘snap to edge’. While this snapping mode is selected, the user needs to click on point 1 and the software will position the end of the strongback at the base of the panel.

The location of point 2 can be anywhere along the top edge of the panel as the Ortho mode will set the x co-ordinate of point 2 to as the same as the x co-ordinate that was generated for point 1.

Once the second point is defined, the software will display the strongback as a bold purple coloured line as shown in the screen shot below;

The next step is to enter the properties of the strongback. Selecting the strongback will bring up the Property window that contains the co-ordinates or the strongback and the other required input parameters: Moment of Inertia, Cross section Area, and Section Depth.

A suitable strongback for this panel needs to have an ultimate moment capacity greater than the moment calculated in the previous step (36.8kNm). There may be many suitable I section or PFC sections, however the chosen strongback for this example is a pair of 200PFC sections that are to be positioned back-to-back.

The properties for the strongback are entered as shown in the screen shot below;

The section depth is required in order for the software to calculate the transformed section that will represent the strongback and the panel.

A sketch of the Section depth parameter is shown below. Note that because the panel thickness is know (in this case 150mm), the distance ‘y’ is calculated by the software.

The Transformed section is then calculated as:

Note: the Ec value for the concrete is internally set to 20MPa as it is assumed that the panel will be lifted when the concrete has a reduced Modulus of Elasticity.

Using the transformed Moment of Inertia calculated in the step above, the panel is then analysed incorporating the influence of the strongback when the ‘Analyse and Design’ button is pressed.

Once the analysis has been successfully performed, displaying the stresses in the direction that the strongback is orientated will display the stress results along with the maximum moment in the strongback. The user needs to check that the moment result shown in the Information window below is smaller than the moment capacity of the strongback – ie: [0.8Mu for 2x200PFC] > M* = 114.6kNm > 49.7kNm.