3D Structure, Gables, Bracing and Ties

You can now move on to generate the full 3D structure, including bay spacing, gable end frames, side and roof bracing, longitudinal ties and purlin types, followed by global wind and snow loading.

3D Structure 

Selecting the Generate 3D Frame button  will add the 3D Bays, Gable, and Bracing tabs in which you can enter the relevant data. If the structure has global symmetry in the longitudinal direction, select the North-South Bracing Symmetry button also , as this will reduce the number of entries required.

The spacing of the frames is entered in the left column. You can enter unequal spacing’s for the first few frames, separating each value by a space. Then enter the number of equal spaced frames and the distance between them. Finally, add any unequal spacing’s at the north end of the structure.

Enter the Current Portal number. This is the portal frame that will be used in your design. You can change this number later in the design end of the program if required.

For the program to evaluate the wind loading on the whole structure, the overall length of the building should be entered – even though you may be using a lesser number of spacing’s to reduce the analysis time, see below.

Tip - Analysis of the structure can take time for a long building with numerous bays, therefore to reduce the analysis time, the length of the building can be reduced to twice the column height, or a minimum of 5 bays, whichever is greater.

This allows the wind loads to be correctly evaluated, and, with a minimum of 5 bays, the full portal action to be obtained in the central two portal bays. The full length of the structure can be entered when you reach the drafting end of the program.

You can manipulate the grid lines if you are not happy with the automatically generated layout. You may switch the grid lines on using the Grid Lines button  in the top toolbar.

You can also swap grid lines, simply interchange the letters and numbers separated by a semi-colon. You can omit grid lines on a specific column line if desired using Y (to keep the grid line) and N (to delete the grid line).

The right data entry column gives you the option to alter the section sizes for the rafters and columns of both the South and North gable frames, with the option to make them independent from one another.

The purlin type, name, section depth and width can be entered. These will only be relevant to the drafting of the structure later.

The spacing of the purlins and rails is dictated by the restraint spacing’s specified in steel design for each group of members. Initially these default to 1.8 metres for roof purlins and 1.4 metres for the cladding rails.

In the table the purlin type can be set for the following purlin shapes.

At this stage the frame views are automatically generated – the 3D view, elevations, plan and sections – for each grid line.