No_6_April_1963 — Page 104

Type

(B. S. 1470-77)

Table 3

WROUGHT ALUMINIUM AND ALUMINIUM ALLOYS FOR BUILDING PURPOSES

B.S. designation

Range of minimum tensile strength (ton/in2)

Available forms

Condition (see Table 2)

(see Table 1)

Super-purity

1

(99 397)

O, H. H

1A (99.8%)

M. O. H. H

3.5-65 3.5-8.0

S. G

E, S. P. T

Commercially pure

IB (99.5%)

M. O. ¡H. H

4.0-8.5

E. S. P. T. G

1C (39.0%)

M. 0, 48, 14, H, H

4.0-9.0

E. S. P, T. R. G, Foil

Non-heat-treatable alloys

N3

M. O. ¿Í. ¿H. ¡H. H

6.0-11.5

S. G. Foil

N4

M. O. H. H

11.0-15.0

S. P. T. G

N5

M. O, H

14.0-17.0

E, S. P. 'T. C

N6

M. O, ¡H

16.0-19.0

N7

M. O

20.0-25.0

S. P. T. R. G

T.F.

N8*

M

N21

M

1 1

Heat-treatable alloys

H9

M. O, W, P, WP, WD

7.0-15.0

E. G. T, V

H19

M. O, W, WP

7.0-19.0

E. T. V

H20

M, O. W. WP

7.0-18.0

S. P. T V

H30

M, O. W. WP W

7.0-20,0

S, P. T. F. B. R. G E. S. C. P. T. F. R. G

C. T. F. G

H14 H15

in the fully heat-treated condition. will withstand high stresses and cor- rosive conditions and have now superseded HIO which was much used in the past. Alloy H19, of in- termediate strength, is suitable for producing complex shapes with a good finish after extrusion. but should not be used in stressed struc- tures.

The fact that aluminium has a better resistance to impact loading than steel makes it attractive for balustrades and railings. Sections are available designed to withstand a lateral impact force of more than 100 Ib per linear foot.

Wall cladding and roofing

Aluminium may be used as a roof covering in the form of flat sheets. fully supported, or as wall cladding and roofing in the form of corrugat. ed or troughed sheets. The flat shects are made from one or other of the four grades of pure aluminium. SI to SIC, in the an- nealed or half-hard condition, and the corrugated or troughed sheets from the alloy NS3-H.

B.S.2855, Corrugated aluminium sheets for general purposes,' shows a standard profile with corrugations at 3-in. pitch, and B.S.3428, Troughed aluminium building sheet, shows two standard profiles for troughed sheets; other profiles are available from

some manufacturers. The design and construction of roofs covered with preformed sheets is dealt with in B.S. Code of Practice C.P.143, Part 1. 'Alu- minium corrugated and troughed

102

W. WP

* To be included in 1962 revision of B.S. 1477

sheet. When laid with 1 corruga- tions (or a single trough) side lap, and a 6-in. end lap, the sheets are suitable for use on pitches of 15° or more, but flatter pitches may be adopted if the end laps are increased and, on severely exposed sites, sealed with mastic. The maximum length of sheet in the preferred range of sizes is 12 ft, but sheets up to 35 or 40 ft long are available so that end laps may be eliminated if desired. The thermal movement of sheets up to 12 ft long is accommodated by the oversize bolt holes and by the flexibility of the sheet at right-angles to the corrugations. Special provi sion may be required for the move- ment of longer sheets. Some pro. prietary patterns of preformed sheet incorporate concealed fastenings which secure the sheets to the roof structure without drilling or punching holes through the sheets.

There is at present no Code of Practice for roofing with fully-sup- ported flat sheets, but these should be laid with standing seams or bat- ten rolls in the manner traditional

24.0-26.0 24.0-30.0

for other sheet metal coverings. This form of roofing is suitable for use on nominally flat roofs and, as the material is not subject to signi ficant creep, it is also suitable for use on steeply pitched slopes.

The thickness of sheet commonly used, preformed or flat, varies from 20 s.w.g. (0.036 in.) to 24 s.w.g. (0.022 in.), but thicker sheets are available for use under severe con- ditions of corrosion or where purlin spacings may need to be increased.

In polluted and marine atmos- pheres, special precautions against corrosion may be needed, such as the use of impervious gaskets between supporting steelwork and aluminium sheeting. Metal fixings should be of aluminium or heavily galvanised steel. Non-conducting sleeves and washers should be used to insulate the sheeting from contact with other dissimilar metals.

Fixing clips should not be less than 1/8 in. thick and should pre- ferably be made from HS30-WP alloys. Clips should not be relied

Table 4

CAST ALUMINIUM ALLOYS FOR BUILDING PURPOSES

B.S. designation (B.S. 1490)

Minimum tensile strength

(tons/in2)

Sand-cast

Chill-cast

LM2-M

9.5

LM4-M

9.0

10.0

LM5-M

9.0

11.0

LM6-M

10.5

12.0

LM8-M, P. W

8.0-15.0

10.5-18.0

or WP

LM10-W

18.9

20.0

LM11-W, WP

14,0-18.0

17.0-20.0

LM18-M

7.5

9.0

LM20-M

10.5

12.0

LM21-M

10.0

11.0

LM24-M

11.5

THE HONG KONG & FAR EAST BUILDER — VOLUME 17, NUMBER 6