Design of Timber Structures

1. Lecture 1 Design of Timber Structures

Prepared by: Niyetbay S.E.

2. Industrial Timber Structures and Their Applications

Timber is one of the oldest structural materials used in
construction.
Industrial
Timber
Structures
and Their
Applications
The objective is not to revive traditional construction methods, but
to determine the main directions for the progressive development
of industrial timber structures and identify their efficient
applications.
Industrial timber structures must meet modern requirements for:
• reliability and durability in service;
• comprehensive mechanization;
• cost-effective mass production.
Compared with reinforced concrete structures, timber structures
are particularly effective in lightweight roofs and buildings where
the low unit weight and high strength of timber can be fully utilized.

3. Physical and Mechanical Properties of Timber

The properties of timber are
determined by its natural
tubular-fibrous structure.
Timber has high strength
and elasticity along the grain
and low thermal conductivity
across the grain.
The strength of wood
substance along the grain is
almost equal to that of steel.
The unit weight of wood
substance is approximately
1.5, which is about 5 times
lower than that of steel.
Dry, glued, metal-free timber
structures have high
chemical resistance and are
suitable for chemical
industry buildings and
mineral fertilizer
warehouses.
Figure 1. Macrostructure
and microstructure of pine
wood:
a — longitudinal tangential
section, scale: 0.5 mm;
b, c, d — cross-sections,
scales: 10 mm, 1 mm, and
0.1 mm;
a.r. — annual rings;
m.r. — medullary rays;
40% and 20% — indicators
shown for individual
structural zones in the
cross-section.

4. Limitations and Improvement of Timber Structures

In buildings with humid operating conditions and in damp
underground parts, the unit weight of timber increases, while its
strength and elasticity decrease.
Limitations
and
Improvement
of Timber
Structures
Under alternating moisture conditions, timber is exposed to
biological deterioration.
Due to its combustibility and the risk of fire spread, timber is
generally unsuitable for densely developed multi-storey
construction.
These natural disadvantages significantly restrict the efficient
application of timber structures.
Their performance can be improved by combining timber
structures with:
• reinforced concrete elements;
• bio-resistant and non-combustible structural materials;
• thermal insulation and roofing materials.

5. Timber Structures in Agricultural Construction

Agricultural production is
distributed over large
territories; therefore,
individual farms require
local storage facilities for
grain, dry fodders.
Lightweight prefabricated
glued timber arches and
frames are used for
warehouses and shelters.
Such structures weigh
several times less than
comparable reinforcedconcrete structures.
They reduce steel and
cement consumption,
transportation costs, and
eliminate the need for
heavy lifting equipment
and special access roads.
The structures can also
be used for livestock
buildings and repair
workshops.
Figure 2. Typical
lightweight
prefabricated structures
for rural warehouses
(dimensions in metres):
a — earth-covered
structure: 10–20 m;
b — arched warehouse:
15–45 m;
c — arched earth-covered
structure: 20–50 m;
d, e — framed structures:
12–18 m;
f — framed structure: 18–
30 m;
a, b, c — longitudinal
transportation
arrangement;
d, e, f — transverse
transportation
arrangement.

6. Roof Structures for Rural Industrial Buildings

• Three-hinged arched and framed structures allow the use
of lightweight column foundations installed in drilled holes.
• Framed or pile foundations may also be combined with
prefabricated reinforced-concrete plinth enclosures of the
strip type.
• The most accessible systems are timber–steel lattice
structures.
• Prefabricated reinforced-concrete supporting columns
rigidly fixed into foundations are recommended, especially
where overhead cranes are used for internal transport.
• Figure 3. Typical roof structures for rural industrial
buildings (dimensions in metres):
• frame and truss systems with spans of 12–24 m;
• large-span structure: 12–24 m, with an overall width of up
to 36 m;
• arched system: 15–18 m;
• asymmetric industrial building: 9–18 m.

7. Roof Structures for Rural Public Buildings

Timber–steel trusses and glued timber arches can be used for public buildings in rural areas.
These structural systems provide large column-free interior spaces and allow the use of lightweight roof solutions.
Figure 4. Typical roof structures for rural public buildings:
a — timber–steel trusses supported on brick walls: span 12–30 m;
b — glued timber arches supported on reinforced-concrete buttresses: span 15–60 m.

8. Timber Structures in Industrial and Civil Construction

Industrial timber structures are mainly suitable for lightweight, medium- and largespan roofs.
Timber
Structures in
Industrial
and Civil
Construction
Their weight is approximately 5 times lower than that of similar reinforcedconcrete structures. This reduces the weight of the building and its foundations,
facilitates transportation, and simplifies and accelerates installation.
Reinforced-concrete columns or frames are generally used as supports for beamtype trusses, while reinforced-concrete buttresses are used for large glued
arches.
Combining lightweight glued timber roofs with non-combustible and bio-resistant
supports provides maximum economic efficiency in large-span, low-rise buildings:
•assembly shops;
•hangars;
•garages.
Large structural elements can be installed by truck-mounted cranes without
scaffolding.

9. Glued Timber Structures for Industrial Buildings

• Metal-free timber arches are more resistant to chemically aggressive environments than steel and
reinforced-concrete structures.
• Therefore, glued timber roofs are particularly suitable for chemical plants and chemical product
warehouses.
• Figure 5. Typical glued trusses and arches in industrial roofs supported by reinforced-concrete
structures:
• a — glued truss: span 15–18 m;
• b — glued truss: span 24–36 m;
• c — multi-span glued arches: each main span 18–60 m, intermediate sections 6–12 m.
• Industrial timber structures may also be used in cultural and public buildings, including covered markets,
stadiums, tennis courts, club and concert halls, and cinemas.

10. Large-Span Roofs and Application Restrictions

• Large-span lattice domes made of glued plywood
elements are based on factory-produced standard
components known as voussoirs.
• These elements are suitable for transportation over
hundreds of kilometres and are sufficiently large for
installation by truck-mounted cranes.
• Figure 6. Typical glued timber structures for largespan public buildings:
• a — lattice dome made of glued plywood voussoirs:
span 40–60 m;
• b — dome roof: span 50–100 m.
• Application restrictions:
• Timber structures are not recommended for baths,
laundries, dyeing shops, drying chambers, and other
buildings with humid operating conditions and possible
condensation.
• Reinforced concrete should be used above glassmelting furnaces, central boiler rooms, hot foundry
shops, and other facilities where structural elements
may be heated to 50°C or higher.

11. Timber Structures in Transport Construction

• In forest-rich northern and eastern regions, timber structures
are suitable for replacing existing road bridges and
constructing new medium-span bridges.
• In severe ice conditions, permanent bridges should generally
have enlarged spans.
• The required service life of new timber bridges should be
increased from 15–20 years to 40–50 years.
• This can be achieved through rational design, industrial
production of prefabricated glued timber structures, and
factory-applied antiseptic treatment.
• The self-weight of glued timber medium-span bridge structures
is approximately 4–5 times lower than that of reinforcedconcrete structures with the same load-bearing capacity.
• Lightweight construction is especially important for rapid
bridge erection in sparsely developed areas.
• Figure 7. Typical schemes of glued laminated timber and
glued plywood road bridges:
• a — beam bridge: span 18–33 m;
• b — cantilever-beam bridge: span 24–42 m;
• c — arch bridge: span 30–60 m.

12. Timber Structures in Relocatable and Demountable Buildings

• The harsh conditions of northern and eastern regions create a strong demand for relocatable and
prefabricated demountable buildings.
• Millions of construction workers, loggers, surveyors, and utility workers require:
• warm housing and public service facilities;
• mobile power stations and radio stations;
• repair workshops, warehouses, and laboratories.
• Reusable lightweight structures significantly reduce the cost of temporary buildings.
• Mobile cabin houses and foundation-free demountable buildings shorten construction time and
considerably reduce the required workforce.
• A normal temperature and humidity regime must be maintained even when buildings are installed on
frozen lakes or marshes.
• High thermal resistance is required for walls, roofs, and lower horizontal floors.
• To prevent distortion and cracking during uneven settlement or frost heaving, the building should be
supported at three points.

13. Structural Solutions and Industrial Production

• Glued plywood structures with lightweight foam insulation best meet the requirements of minimum
weight, strength, durability, and thermal efficiency.
• Foam plastic is expanded inside box-section panels and does not settle even under prolonged
vibration and impact loads.
• Dry timber provides:
• high structural strength along the grain;
• high thermal insulation across the grain.
• Priority should be given to the mass production of:
• glued plywood panels for relocatable buildings;
• panel doors, in which plywood may be replaced with hard fibreboard;
• insulated panels for demountable roofs, walls, and door leaves;
• unified glued plywood panels made of Bakelite-treated plywood for reusable large-panel formwork.
• Serial production can make use of existing idle or reconstructed prefabricated housing factories and
quickly recover the required investment.

14. Main Types of Industrial Timber Structures: Beams

• Industrial timber structures include glued beams and built-up beams with plate dowels.
• Beams with plate dowels are assembled from 2–3 timber members or squared logs.
• Maximum spans without joints:
• sawn timber beams — 6.5 m;
• squared-log beams — 9 m.
• Plate dowels are made of hardwood with a moisture content of no more than 8–10%.
• Dowel thickness: 12 or 16 mm; length along the grain: 54 or 72 mm.
• For timber with moisture content above 20%, longitudinal cuts should not exceed 1/6
of the member depth.

15.

Figures:
Figure 1. Beams with plate
dowels: a — two timber members,
span 6 m; b — three members,
span 9 m; c — two squared logs,
span 9 m; beam depth h = l/10–
l/14.
Figure 2. Arrangement and
standard dimensions of plate
dowels: through and blind dowels;
spacing s = 9δ; member width b ≤
15 cm or b ≥ 15 cm.
Figure 3. Workbench for
manufacturing built-up beams: 1
— supports; 2 — rotating
longitudinal beam; 3 — electric
chain mortiser; 4 — clamps; 5 —
packing for camber; 6 — end
clamp.

16. Glued Timber and Glued Plywood Beams

Glued timber beams with spans of 6–12 m may have I-shaped or rectangular cross-sections and single- or double-pitched profiles.
I-shaped beams are produced from boards 40–50 mm thick.
Typical proportions:
beam depth: h = l/12–l/18;
beam width: b = h/6;
roof slope: approximately 1:10.
Rectangular beams are stable when the depth-to-width ratio does not exceed 6.
Glued beams are manufactured using waterproof phenol-formaldehyde or alkyl-resorcinol adhesives.
Figures:
Figure 4. Glued timber beam configurations: a — lattice and I-shaped section; b — single-pitched polygonal I-section; c — doublepitched rectangular section.
Figure 5. Board arrangement and jointing schemes in glued beams.
Figures 6–7. Joints of large-span beam components: plywood or timber side plates on steel dowels and bolts; wedge-shaped
laminated-plastic inserts.
Table 1. Material consumption for rectangular glued beams: spans 6, 7, 9 and 12 m; design loads 4.5, 6 and 9 kN/m; beam mass
approximately 105–760 kg.

17. Glued Timber and Glued Plywood Beams

18. Glued Timber and Glued Plywood Beams

Figure 5. Board arrangement and jointing
schemes in glued beams.
Figures 6–7. Joints of large-span beam
components: plywood or timber side plates on
steel dowels and bolts; wedge-shaped laminatedplastic inserts.
Table 1. Material consumption for rectangular
glued beams: spans 6, 7, 9 and 12 m; design
loads 4.5, 6 and 9 kN/m; beam mass
approximately 105–760 kg.

19. Glued Plywood Beams and Reinforced Beams

• Glued plywood box beams with double-pitched or parallel chords are used for spans up to 12 m.
• The frame is formed as a lattice truss and covered with plywood on both sides.
• Plywood web thickness: 6–10 mm.
• Corrugated plywood webs considerably improve beam stability and provide low weight, low material consumption, and
convenient transportation and installation.
• The standard range includes 35 beam sizes:
21 parallel-chord beams with spans of 6, 7.5 and 9 m;
14 double-pitched beams with spans of 6 and 7.5 m.
• Design loads range from 2 to 9 kN/m.
• Steel reinforcement ratio: 2–4%; reinforcement classes A-III and A-IV with design resistances of 31 and 54 MPa.
• Reinforcement reduces timber consumption by 30–40%.
• Figures:
• Figure 8. Glued plywood beams with corrugated webs: spans 6, 7.5 and 9 m.
• Table 2. Material consumption: beam mass approximately 50–300 kg, depending on span and load.

20. Glued Plywood Beams and Reinforced Beams

• Figures:
• Figure 8. Glued plywood beams with
corrugated webs: spans 6, 7.5 and 9 m.
• Table 2. Material consumption: beam mass
approximately 50–300 kg, depending on
span and load.