STRUCTURAL DESIGN FOR ARCHITECTURE

Structural Design for Architecture

sive collapse cannot occur and specify limits

within which the collapse which is caused by a

single incident must be contained. These

regulations apply to all types of building but

are particularly relevant to the overall planning

of masonry structures which are more vulner-

able to this form of collapse than other types.

As with all of the Building Regulations,

however, the requirement is no more difficult

to meet than that which a responsible designer

would in any case wish to impose.

In practice the satisfaction of the require-

ments in respect of progressive collapse is

not difficult with a masonry structure. Both

common sense and the Building Regulations

dictate that, in these exceptional circum-

stances, the concern should be with the

preservation of life rather than with the

preservation of the building itself. A consid-

erable amount of damage to the building is

therefore acceptable, following an incident,

so long as the occupants are neither injured

nor trapped as a consequence of it. The

factor of safety against the total collapse of a

damaged building can be very low, and a

figure of 1.05 is specified in the Building

Regulations.

Most masonry structures are capable of

'bridging' a gap in the structure with this

degree of safety if certain rudimentary precau-

tions are taken during the design. These

usually amount to the incorporation of certain

details into the wall-to-wall and wall-to-floor

junctions so as to improve the integrity of the

structure, and the insertion of a certain

amount of reinforcement into key walls and

piers. It is not usually necessary for any major

alteration to be made for this purpose to the

structural form which is required to resist the

normal gravitational and horizontal loads. For

this reason the specific design requirements in

respect of the prevention of progressive

collapse are not dealt with here.

Fig. 5.42 Plan dimensions of walls.

(a) Plain cavity wall.

(b) Fin wall.

(c) Diaphragm wall.

178

Table 5.3 Wall dimensions for tall single-storey

masonry structures

Wall Plain

height cavity Fin wall Diaphragm wall

wall

(m) ti(mm) tp (mm) T (mm) D (mm) S (mm)

3 215 - - - -

4 327.5 665 440 - -

5 440 890 440 - -

6 - 1012.5 440 557.5 1360

7 - 1340 440 557.5 1135

8 - 1340 440 557.5 910

9 - - - 665 1135

10 - - - 665 910

Fig. Fig. 5.42b Fig. 5.42c

5.42a