Civil Engineering Reference
In-Depth Information
Sufficient fixings must be installed where laps occur in the sheet‑
The structure must be adequately braced during erection.
■
■
ing to ensure continuity.
Flange forces in edge members resulting from the diaphragm
■
Sheeting panels must not be removed without full consideration
of the effects.
■
action must be considered.
The diaphragm actions must be transmitted to the main frame via
For detail recommendations for stressed skin design refer to
BS EN1993‑1‑3:2006.
■
suitable structural connections.
15.3.2 Low‑rise masonry structures
15.3.2.1 Lateral stability of masonry structures
Lateral stability of low‑rise masonry structures is usually
achieved by means of cross wall construction. Lateral wind
load on the side or gable of a building is transmitted to the
floor or roof structure. The floor or roof acts as a stiff plate or
diaphragm and the wind loads are in turn transferred to the
gable or side walls and then to the foundations (
Figure 15.10
).
If the roof or floor is an
in situ
reinforced concrete slab cast
on the inner leaf of a cavity wall then the slab will act as a
diaphragm and usually no further checks are required. If the
roof or floor consists of pre‑stressed concrete planks then lat‑
eral and longitudinal ties will need to be incorporated in an
in situ
structural topping in the form of a light steel fabric.
Where the planks run parallel to the cross walls anchor ties
will also be needed. A lightweight steel or timber roof will
require bracing members and anchors to transmit the lateral
wind loads from the diaphragm to the gable or cross walls
(
Figure 15.11
).
For more on stability in masonry design, please see
Chapter 20:
Masonry
.
Single Brace
(Tension and Compression)
Cross Bracing
(Tension only)
'K' Brace
(Tension and Compression)
Portal Frame Bracing
Cross wall construction
The cross walls (gable walls in
Figure 15.10
) act as shear
walls and should preferably be positioned parallel to the dir‑
ection of loading. The layout of the walls should provide lat‑
eral stability for the building in two orthogonal directions.
Referring to
Figure 15.12
, plan arrangement A is unstable in
the longitudinal direction since there are no longitudinal walls
Portal Bracing
Figure 15.8 Types of bracing for single storey steel buildings
Roof sheeting acting as
shear diaphragm
Purlins
Flange forces
Adequate
connection
required
Braced bay
Figure 15.9 Stressed‑skin gable bracing
