Adding a Haunch in Frame
Haunches are usually added at the eaves and/or apex of a rigid portal frame. Haunches enhance the economical design of rafters of portal frames, by reducing the required depth of the rafter. The greatest bending moment occurs at the eaves of a portal frame and haunches play the major role of increasing the bending resistance of the rafter. Haunches also add stiffness, assists in reducing deflections and facilitate rigid bolted moment connections between the rafter and the column. The apex haunch is not needed to enhance the bending resistance; it is only used to facilitate a bolted connection.
A haunch can be added to a rafter section in Frame by appending the haunch depth in the section designation. To explain how to go about adding a haunch, a work example will be used.
Scenario: Adding a haunch of 300 mm to a 305x102x33 I-section.
- Click on the Input tab in Frame, under the heading Input types located on the ribbon find and click on the Beam Section icon, open the Section database
- From the list of available I-sections, locate and click on the section 305x102x33, assign the Section Name RFTR to the section
- Open the section database again, tick the box next to Haunched and define a haunch depth of 0.300m, click on the section 305x102x33 and assign the Section Name HNCH
Note: The overall depth is then taken to be 305mm + 300mm = 605mm
- Under the heading Input types located on the ribbon find and click on the Beams icon
- To add the haunch section, two section names are assigned to the Beam element
Note: The section names are separated with a comma and the section properties will vary linearly along the length of the beam element
- The first and second section names designate the section at the near and far node numbers respectively, i.e., if the hunched section starts at node 6 and ends at node 79 (in this case), the Section Name will be defined as RFTR,HNCH
Suggestion: Verify the haunched section by enabling 3D rendering in the Graphics Options.