Figure 3: Tee dimensions
A path for transferring the flange forces from the chord to the
bracing member is necessary (because the forces are obviously
too large to transfer through the webs) and an additional load
bearing stiffener is necessary to carry the resultant force at the
change in direction. As the forces are in tension, full strength
welds would be required. The butt welds between the flanges are
substantial and require cope holes through the web to achieve
them. The webs would need to be checked for shear as well as
axial load in the joint zone. This arrangement is not favoured.
Rotating the members so their flanges are vertical (Figure 4)
provides a more direct path for the flange tension forces.
The connections between the members in the node can be
made by butt welds between the edges of the flanges. The flow of
force through the joint is smoother but the web force still needs
to be transferred, and the junction where the webs of the three
members come together is complicated.
A refinement of this arrangement, using two plates to form the
node, separated by intermittent webs is the favoured solution
(Figure 5).The plates toward the centre of the joint are wide
enough to carry half the chord force so a web is only required
close to the connecting member to transfer the web force into the
plates. The plates are butt welded to the chord flanges and the
tension diagonal is connected using a bolted splice. The column
member is connected using a bearing splice.
The tension splice in the bracing member will be effected using
M30 preloaded bolts of category B in double shear, of grade 10.9.
The slip resistance assumed for design is for a friction coefficient
μ = 0.5 and is 357 kN.
The member is a 356 UC 340 with 42.9 mm thick flanges and
26.6 mm thick web and has an area of 433 cm2. The area of one
flange is 40% of the total and carries 5.2 MN in tension. The
number of bolts required is indicated in Table 2:
Force (MN) No of Bolts Adopt
Flange 5.2 14.6 16 bolts
Web 2.6 7.3 8 bolts
Bottom chord joint -
Bottom chord joint –
Figure 6: Bolted splice arrangement