Civil Engineering Reference
In-Depth Information
The braced bays are required to be continuous for the full height
Where the braced bays do not coincide with the shear centre
then torsion effects should be taken into account. As far as
possible the braced bays should be arranged at the extremities
of the building to resist the torsion effects. The loads carried
by an asymmetric arrangement of bracing or shear walls can
be determined by hand calculation (refer to Section 15.3.2.3).
Alternatively the loads can be determined by modelling the bra‑
cing system as a stiff beam supported by spring supports with
a stiffness k representative of the vertical bracing or shear wall
stiffness (units of k are typically kN/mm) (
Figure 15.22
).
■
of the building.
If a braced bay is interrupted for any reason then the forces carried
■
by the bracing or shear wall should be transferred to other braced
bays.
If movement joints are present then each portion of the building
■
must be stable within itself.
The braced bays should be arranged such that the lateral force act‑
■
ing on the building should coincide with the centre of shear.
2
1
3
2
4
1. Longitudinal runner at apex
2. Longitudinal runners at intermediate nodes, may be omitted if this does not leave more than 4.2 m of unbraced rafter or more than
3.7 m of unbraced ceiling tie.
3. Further bracing is required on these internal members for spans over 8 m in duopitch roofs, 5 m in monopitch roofs.
4. Under-rafter diagonal brace at approximately 45° to the rafters.
Figure 15.21 Trussed rafter stability bracing. Reproduced from TRADA Technology (2006) with permission
Stiff Floor Diaphragm
Plan on Floor
Vertical Bracing
or Shear Walls
Spring Supports
Stiffness k (kN/mm)
Wind
Stiff Beam
Wind
Figure 15.22 Distribution of wind load on asymmetric layout of bracing
