Steel Section Design and Connections Tutorial - Kxcad.net

The outer columns require two torsional restraints each, one at 4.200 m and the
other under the haunch at the plastic hinge locations.
T2.2.12 Rafter Lateral Restraints
We will now check the rafter for a purlin spacing of 1.8 m.
Ensure you are in Search
for Next Brief Mode
Click on the outer left hand
rafter
Click on the Lateral
Restraints tab
Enter a value of 1.8 in the
Portion 1 input box
Click on the critical
portions of the bending
moment in the output area
Purlin spacing of 1.8 m is
satisfactory for the first rafter.
Varying the Purlin Spacing
The purlin spacing will need to be reduced in some areas. It is therefore
necessary to enter the spacing for all portions and then reduce it in the critical
locations.
Enter a value of 1.8 in Portion 2 to Portion 7
Let us now reduce the spacing in the critical portions using an increment of 0.1
m.
Click on Portion 2 in the Input Data
Click on the left part of the horizontal spin button to the right of the Portion 2
value to reduce the length of Portion 2 from 1.8 to 1.7m
Purlin spacing is now satisfactory. However, let us reduce the first and second
portions to 1.4 m, so that a purlin is coincident with the end of the haunch.
Use the horizontal spin button to reduce Portion 1 and 2 to 1.4, or
alternatively
Directly type the values in Portion 1 and 2 to 1.4
Let us check the 2 nd and 3 rd bay rafters using the same brief.
Change to Copy Current Brief Mode
Select rafter members 2, 3, 4, 5, and 6 to copy the Axial with Moment brief
including the lateral restraints information to all other rafter members
Click on Search for Next Brief Mode
Click on the critical portions of the bending moment in the output area
T2 Multi-bay Portal Frame Design Tutorial
T2 - 13