MALAYAN TIMBERS
By
Mr. P. M. Barnes, P.W.D. Architect of Singapore
A considerable quantity of Malayan timber is imported into Hong Kong but its use is confined to a limited variety of work. This is probably due to the fact that there has not been sufficient information available concerning the properties of the timber. In the following abstract of an article by an acknowledged authority on the subject, the information given should make possible the free use and wider application of material which is easy to obtain in any quantity and at reason- able prices. Further sections will be published in future issues.
In response to the demand for greater economies in the timber, the Tables contained herein have been prepared with object of assisting designers to assess the values and properties of the different kinds of timbers they are frequently required to use. The Tables serve for most practical purposes, but, it is ostensible that in any large undertakings where unusual conditions predominate, fresh and more detailed calculations regarding timber sizes are necessary.
The rules governing structural mechanics in both steel and reinforced concrete construction are also applicable to timber. It is unfortunate, however, that the internal properties of any one beam or column cannot be relied upon to the same extent as steel or concrete, for timber is subject to many diseases which are not obvious to the Supervisor of Works. For this reason a fairly high factor of safety must be chosen varying according to reliability statistics of any particular timber and reference to the Malayan Forestry Department essential in this respect.
It is recommended that deflections should be given close study in any doubtful case in preference to the adoption of traditional rule of thumb methods. Badly or underseasoned timbers develop fatigue very quickly and the use of deflection formulae can offer a better guarantee of stability than many time honoured systems of calculation.
The tables arranged within this pamphlet contain the properties and load bearing characteristics of the most widely used Malayan timbers.
From an Engineer's or Architect's point of view, it is important that correct identification of timber is made for its especial purpose and the subsequent extracts from the Malayan Forest records have been added to assist the designer in his timber selections:-
Keruing
Grain. Straight or shallowly interlocked. Texture. Coarse, but even.
Sapwood. When freshly cut consists of two zones, the inner purple-red-brown and the outer cream. When dry, grey brown or purple grey.
Heartwood. Various shades of dark purple red when freshly cut which darkens on prolonged exposure,
Keruing is often mistaken for Kapur, but Kapur has a distinctive camphor like smell.
Uses. Flooring, staircases, wagon planks and moderately heavy construction work.
Defects. Heart shakes, oil shakes, end splits.
Kapur
Grain, Straight or shallowly interlocked. Texture. Coarse, but even.
Sapwood. Light yellow-brown with a pink tinge sharply
defined.
Heartwood. Light rose-red to deep red when green becoming rose-red or red-brown on exposure.
Uses. General building construction, flooring, rolling stock and lorry bodies,
Defects. Liable to termite attacks.
Red Meranti
Grain. Interlocked and occasionally wavy. Texture. Moderately coarse.
Sapwood. Yellow-brown, yellow-pink, grey-pink or grey- brown, frequently with a purplish tinge in darker species.
Heartwood. Varying shades from light-pink to purple- brown darkening upon exposure.
Uses. General utility or for those purposes which Baltic pines would be used.
Defects. Liable to attack by shot and pin hole borers.
Dark Red Meranti
Planed surface, slightly lustrous.
Uses. Heavy structural work, bridge timbers, sleepers, telegraph poles.
Defects. Seasoning checks occasionally to pin holes and borers. Should be in well ventilated positions.
Balau
Grain. Rarely straight, usually interlocked or deeply interlocked and occasionally wavy.
Texture. Fine and even.
Sapwood. Lighter in colour to heartwood, sharply defined. Heartwood. Yellow or grey-brown, brown or distinctly red, darkening upon exposure to brown, purple-brown or dark- red-brown with lighter coloured markings. Planed surface glistens.
Uses. Railway sleepers, bridge building, wharf construc- tion and other heavy structural work.
Defects. Occasionally attacked by powder post beetles and Resin pockets occur where timber has been injured in growth.
DESIGNING WITH MALAYAN TIMBER
There is considerable variation in the strength of different timbers in different pieces of the same kind and it is necessary to know the strength of wood to be used. This has been provided by the Malayan Forestry Department who have conducted numerous experiments and tests upon different timbers until they can state with confidence what the "Average" strength is according to their experience.
Factor of Safety. It is a question for the designer to decide upon the safety factor and many use 7, 8 or even 10 for permanent structures. In the case of the coloumns in the following tables, a factor of safety of 7 has been used, however, it is possible to go to 3 or 4 for temporary work.
Applying the formula. The tables show a maximum joist of 8" X 8", but, for the egregious cases the following system may be used.
(i) Where deflection is not a primary consideration— example:-
U.D. load
1258 lbs.
B.M. WL 1258 X 120 18,870 inch lbs.
8
8
F1700 (outside seasoning not in contact with ground-
see M.F.S. trade leaflet No. 7).
Z-
18,870
1700
=
11.1
-
A 6" X 2" beam has a Z of 12.00.
(ii) Where deflection is the important factor the system below must be adopted. If a beam bends or sags a certain amount when loaded it is obvious that ceilings will crack and floors creak. The deflection should not be more than 1.40′′ per ft. of span or 1/480 of span. If there is no ceiling 130" per ft. of span may be taken.
Example:- Span
480
=
5 X W X La
apply this to the 10′0′′ joist
designed for strength.
384 X EX
120 = 5 X 1258 X 120 X 120 X 120
480
bdy
=
384 X 2,310,000 X bds
5 X 4 X 629 X 3 X 3
bd8 590 b d - 6.6" practical size.
192,5
=
2"
12
590 d V/295
a 7" X 2" beam appears to be a more
As a reminder to designers the following formulae has been appended.
Type of beam & loading
B.M. Shear
Deflection
WL
W
WL:
Cantilever with load at end
Similar characteristics to Red Meranti except darker in colour and more uniform.
EI
WL
W
14
WLI
Uses. Furniture, panelling, coach work, shop fitings, flooring. Takes a high polish.
Chengal
Grain. Rarely straight, shallowly to deeply interlocked. Texture. Fine and even.
Sapwood. Light yellow sharply defined.
Heartwood. Light yellow-brown with greenish tinge when freshly cut. Darkens to dark purple-brown to rust-red.
Cantilever with U.D. load
2
EI
WL
Beam resting on end supports
(central load)
4
WL
W
Beam resting on end supports
(U.D. load)
8
NE NE
མཾ'
1
WL1
48
EI
מן
WL
384
EI
73
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