In the following tutorial, we will explore how to model, analyse and design custom concrete sections using the SkyCiv Section Designer. In the tutorial, we will be checking a concrete column with a custom section.

This tutorial includes a step-by-step guide on:

• Modelling a column in Structural 3D (S3D),
• Assigning loads and load combinations to the model,
• Creating a custom section,
• Applying section reduction multipliers,
• Solving the model and viewing results
• Complete section design checks using the General Section Designer (GSD)

The Problem

We have been given the following problem to solve for this example:
An 18′ tall concrete column with a custom cross section is subjected to the following loads:

• A permanent compression load of 150 kip
• A lateral load of 10 kip along the X-axis and -24 kip along the Z-axis

The column is a cantilever, with a fixed base and the loads are applied at the top of the column.
Check the column for deflection (Height / 200) and complete a section check on the base of the column.

The column is to be checked with the following section dimension:

We will be modelling the column using S3D. From the SkyCiv dashboard, launch a new file of S3D and make sure your unit system is set to imperial (Settings > Units > Unit System = “Imperial“). The first step will be to define the nodes for the column. To create the nodes go to the Nodes menu. From this menu, we can input the X, Y and Z coordinates for each node individually, clicking Apply for each node to add them into the model.

Nodes will be applied at the following coordinates (X, Y, Z):

• 0, 0, 0
• 0, 18, 0

Next, we will assign loads to our model. We have been given a few loads to apply to the top of the column. Go to the Point Loads menu and input 2 in the Node ID input box. Our first load to apply is a permanent compression load. Enter a value of -150 kip in the Y Magnitude input box. We will also rename the load to be “Permanent” in the Load Group input box to denote that this is a permanent load. Click Apply to apply the load.

We will also apply a lateral load to the module. Still in the Point Loads menu, again, set the Node ID to be 2. This time set the X Magnitude to be 10 kip and the Z Magnitude to be 24 kip. Set the Load Group name to be “Lateral” and hit Apply. Your model should now show two individual point loads in the model, one with the compression load of 150 kip and another with the resultant lateral load of 26 kip.

We will also assign a gravity load to the model to account for the self-weight of the column. Go to the Self Weight menu and select On to enable self-weight in the model. By default, this will apply a -1 g (9.81 m/s2) self-weight in the y-direction across the entire model.

With loads applied to the model, the next step is to define load combinations. Go to the Load Combos menu. In this example we will define two load combinations, one for strength and one for serviceability. For the strength case, enter the following data into the input boxes:

• Name: Strength
• Criteria: Strength
• Lateral Factor: 1
• Permanent Factor: 1.2
• SW1 Factor: 1.2

Click Apply to add the load combination. For the serviceability case, input the following data into the input boxes and select Apply:

• Name: Deflections
• Criteria: Serviceability
• Lateral Factor: 0.7
• Permanent Factor: 1
• SW1 Factor: 1

Next we can define the custom section for the column. We will be using the Section Builder to create a custom shape for the section. To access the Section Builder in S3D, got to the Sections menu and click the green Builder button at the top of the menu.

The section builder will open. As our shape is not a standard template available in the section builder, we will need to create a custom shape. In the menu on the left side of the screen, select Custom Shapes > Add Points Shape. A default shape with 6 points will appear. The coordinates for the points in the shape can be modified by going to the Dimensions tab in the menu on the right side of the screen. Based on the section dimensions provided above, we will assign the following four coordinates (Z, Y) with the Radius set to 0 for each coordinate.

• (0 , 0)
• (5, 36)
• (15, 36)
• (20, 0)

When we have set the coordinates, click Apply to make the changes. The section should now look like this:

We also need to assign a material to the section. Still in the Section Builder, in the menu on the right side of the screen select the Material tab and select the Add From Database button. This will open a window where we can select from a database of standard materials. For this example, we will be using 4000 PSI concrete, which can be selected from the drop downs with the following selections: Imperial > Concrete > General > CONC 4000 PSI. Click Submit to apply this material to the section.

With the section material applied, we can now save our section to be used in the model. In the Section Builder, click Submit to save the section and return back to S3D. The section will automatically apply to the column as it is our first section in the model. We can review the column in the 3D renderer to check that it looks correct by clicking the Cube icon on the right side controls.

From reviewing the 3D view, we can actually see that our section is currently rotated incorrectly. The column taper should be parallel to the Z axis as per the section dimension drawing. If we leave this as is, our loads will be incorrectly applied along the column, so we need to rotate the column. To fix this, We can then select the member in the model to bring up the member properties menu on the left side of the screen. Set the member Angle of Rotation to be -90 degrees and click Apply. Your member should reorientate to the correct direction per below:

Now that we can see that the column is orientated correctly, we can exit the 3D renderer (click the Cube symbol again).

Depending on what you are analysing and your specific design code requirements, you may need to apply section reduction factors. These can be important for concrete sections where a reduction in values may occur due to the loading of the structure, for example, you may want to account for a reduction in section stiffness due to cracking in a concrete section.

This can be done in SkyCiv by applying section reduction factors. These parameters can be accessed by hovering over Edit > Members > Section Reduction Factors. In this example, we will reduce the Moment of Inertia by a factor of 0.7 for both the Iz and Iy. For simplicity, we will leave the other parameters set to the default of 1, which means the software will use the gross section properties for these parameters. Click save to make apply the changes to the section.

• Modelling with Plates documentation
• Plate Design Module documentation
• More about SkyCiv Structural Analysis Software – S3D