1
CONSTRUCTION-VI
TASK-1
LONG SPAN
STRUCTURES IN
TIMBER
SECTION-B GROUP-3
BA19ARC049 RAJASHEKAR N.
BA19ARC057 PRIYAM H.
BA19ARC069 ABHISHEK B.
BA19ARC070 DHEERAJ VELTHURI
BA19ARC074 ALLA REVANTH
BA19ARC077 DARSHAN M.
BA19ARC080 AKSHAY KUMAR
BA19ARC081 ABHISHEK G.
BA19ARC082 SAKETH REDDY
BA18ARC016 VENKAT SUNIL
SEM-VI, DEPARTMENT OF ARCHITECTURE & PLANNING, VNIT.
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SHORT LENGTH TIMBER
This is a type of timber derived from the waste piece of wood left after sawing of the logs
in a mill used for timber construction.
CHARACTERISTICS
The product of timber cut into board is referred as lumber-Each piece is not more than 2M in length.
Engineered wood used for structural use like beams,column arches,etc.
Thoroughly seasoned lumbers
Standard joinery techniques
Economical carpentry work.
REQUIREMENTS
DIMENSIONS
Length : 1.2 m. ,1.5m , 1.8m , 2.0m
Width:. 0.10m, 0.12m , 0.15m
Thickness: 0.020m , 0.025m , 0.040m , 0.050m
STRUCTURAL ARRANGEMENT SYSTEM
Single layer system - one piece of wood butts into another (most often at a right angle, or square to the other board)
and is fastened using mechanical fasteners. This type of joint is often used in wall framing on construction
Double layer system Multilayer systemBoxing system-
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UTILIZATION
Home furnitures
scaffoldings
Sheet piles
Cladding
Temporary shelters
Sport structures
Auditorium & exhibition hall
Portal frames lamella roofing
JOINING TECHNIQUES
The most common ways to reinforce this type of wood joint are the following:
Fasteners – nails, screws, and even metal brackets can be used to strengthen the joint.
Glue added along with your fastener of choice.
Dowels – drill holes and glue/insert wooden plugs.
Biscuits – eye-shaped thin pieces of wood attached by using a biscuit joiner tool that will cut a half-moon-shaped
groove in the two boards to be joined. The biscuit is put in after gluing the grooves, and the wood joint is clamped.
Biscuits are especially good with plywood and other manufactured pieces and provide a lot of gluing surface in a
small amount of space.
Pocket joinery – such as Kreg joinery tools where holes are pre-drilled to toe-nail fasteners in. This is stronger
than just screwing into the end grain, and the advantage is that it can be hidden. Pocket joinery is pretty fast and
secure, if performed with required tools.
LAMINATED TIMBER
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*Laminated timber is the result of joining two boards to form a single unit, making the unit stronger and
to add o to the strength.
*But with the advancing technology, laminated timber was just not restricted to one type; in fact, there
were many new forms, types and varieties of laminated timbers.
* These different types of mass timber have different uses and properties, making each one unique yet
connected together.
Types of Laminated timber and their differences
1. Cross Laminated Timbers
*Generally there are three, five or seven layers, which after gluing are compressed and set to dry. It is
basically a plywood made of boards that can reach enormous dimensions, 2.4 m to 4.0 m in height and
up to 12.0 m in width.
*Cross Laminated timber used in building construction
Advantages of Cross Laminated timbers
*It is strong and stable and overcomes the inconsistencies inherent in unmodified wood
*It requires lesser to no additional modifications when brought to site.
*It requires a smaller foundation since Cross laminated Timber is lighter.
*Installation of prefabricated Cross laminated pieces is faster.
Disadvantages of Cross LamiNated Timbers
*Creation of wall cavities is limited hence there might be an increase in costs of electrical and plumbing
services
*Since it is prefabricated, if the production site in not in close vicinity then there can be higher material
transportation costs.
*Future renovations and changes
2 Glue laminated Timber (Gulam)
*Glulam is a versatile engineered wood that is known for its strength, aesthetics and reliability.
*It constitutes of several layers of timber bonded together using adhesives, in order to form a bigger and
stronger piece of wood.
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*It is often specified as a viable
replacement of structural concrete and
steel.
Advantages of Glue Laminated Timber
*It is perfect for long span and curved
designs.
*It offers strength with no compromise on aesthetics.
*It is locally available and environmentally sustainable material.
*It is far superior to solid timber due to its high strength and dimensional stability
Disadvantages of Glue Laminated Timber
*Prices compared to solid timber are higher
*Manufacturers tend to use sub-standard timber, which might cause defects later.
*Due to the usage of glue, adhesives and other treating chemicals, which if not used properly, can cause
the loss of natural look
elements
Nail laminated Timber (NLT)
*Nail laminated timber (NLT), is a mass timber product constructed by turning dimensional lumbar on
the edge and mechanically fastening the laminations together with nails
* It is most commonly used for floor and roof systems.
*The adjoining panels are laid in one direction and require support from beams or other structural
elements
Advantages of Nail Laminated Timber
*It delivers flexibility since it is relatively easy to fabricate it
*It is light weight compared to other materials used for floor and roof systems like concrete, steel etc.
*It can be used for both residential and commercial projects.
SEM-VI, DEPARTMENT OF ARCHITECTURE & PLANNING, VNIT.
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Disadvantages of nail Laminated Timber
*Once nailed completely and permanently, there is no possibility for rearrangement of timber panels.
To make any possible changes, one has to use a saw leading to disfigurement of the actual constructed
element.
4. Dowel Laminated Timber (DLT)
*Dowel laminated timber or DLT is one of the most recent developments.
‘Dowel’ refers to the inclusion of wooden dowels, used to replace the nails or adhesives, making the
laminated timber more flexible to changes and arrangements.
*This system was designed to utilise a moisture content variation between the posts and dowels.
Advantages of Dowel Laminated Timbers
*It is flexible in terms of attachment and construction. In order to make changes, dowels can be removed
the posts can be rearranged.
*DLT members are more diverse and make up advanced structural applications
*It is very well suited for horizontal spans.
Disadvantages of Dowel Laminated Timbers
Over time, hardwood fasteners or dowels lose
*their stiffness causing dimensional instability.
Market Survey
Companies Manufacturing Laminated Timber
* Floor studio
* Action Tesa (Balaji Action Build well )
* jagadamba Wood industries
* jp insulation Private limited
* Dhanuka Enterprises
Sizes
* Cross laminated is Available in 2.4 m to 4.0 m in
and up to 12.0 m in width.
*Glue Laminated Timber is available in 45 mm x 45 mm to 250 mm x 1800 mm x 30 m
SEM-VI, DEPARTMENT OF ARCHITECTURE & PLANNING, VNIT.
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SOLID TIMBER BEAMS
INTRODUCTION :
● Solid timber beams are made of a single piece of wood. As their name implies, they
are very sturdy. They have been used for centuries to make buildings and structures
of all kinds.
● The rugged appearance of these beams gives them an undeniable charm, but they can
be quite expensive. Their considerable weight can also make them more complicated
to install.
WHERE TO USE ?
● They are used for timber framing that is highly common in construction projects.
SOME SPECIES OF TIMBER
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Yellow Bald Cypress
Eastern Red Cedar
Red Oak
Southern White Oak
Post Oak
Aromatic Cedar
Douglas Fir
Western Cedar
Reclaimed Heart Pine
Southern Yellow Pine
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PROS AND CONS
OF SOLID TIMBER BEAMS
Pro: Structural Advantages
Because the weight of the structure is supported by posts that are spaced relatively far apart,
post and beam construction allows for large expanses of glass.
Consequently, post and beam houses often feature large windows.
Furthermore, post and beam houses usually feature high vaulted ceilings, creating a large,
roomy living space.
Pro: Fire Resistance
●
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Because the timber used in constructing a post and beam structure must be denser and
stronger than in light frame buildings (post and beam wood is typically Type IV grade), it is
more fire resistant.
Light frame buildings are often built from softwood, which is less dense and more porous,
making them more susceptible to fire.
Con: Cost
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As opposed to light frame construction, building and beam home requires large pieces of
high quality timber cut from large trees.
Moreover, these heavy pieces of wood must be moved into place using some kind of crane,
whereas light frame construction can be assembled from a large quantity of light pieces.
In addition, because post and beam construction relies on a fewer number of structural
elements, their placement must be more precise.
This expertise is often difficult to come by and, therefore, is expensive.
Con: Susceptibility to Rotting
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Another disadvantage of post and beam buildings is their susceptibility to rotting.
If beams are on the outside of the home and are not covered. This exposure allows the
beams, which are essential structural elements, to rot over long periods of time.
Furthermore, the large amounts of exposed wood on the exterior of the house are more
susceptible to infestation by a variety of harmful pests, especially termites and carpenter
ants.
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JOINERY DETAILS
END-TO-END JOINTS
●
This wood beam joint technique is very simple. It involves joining the pieces end to end
with the least modification possible.
SCARF JOINTS
● Scarf joints join two ends that are cut obliquely.
● The main varieties of scarf joints are nibbed scarf joints, which have ends cut
vertically or on an angle to prevent them from sliding.
● Other nibbed varieties, called “hooked,” can also keep the beams from sliding. They
are designed with a notch in the middle that interlocks perfectly with their
counterpart, which has the same notch facing the opposite direction.
● These types of joints are generally used for large structural members such as rafters,
because they are effective at transmitting compression force.
SEM-VI, DEPARTMENT OF ARCHITECTURE & PLANNING, VNIT.
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LAP JOINTS
●
This joint technique consists of creating pieces of wood where the end or another part of one covers
part of the other. There are several different varieties.
Mortise and tenon joints
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This method consists of creating a piece of wood with a smaller end bit (the tenon) shaped so that it
can be inserted into a slot (the mortise) made on the other piece of wood
HALF LAP JOINTS
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Half lap joints involve removing some material from a part of both pieces of wood in order
to interlock them.
This type of joint has many possible configurations:
● T-joint
● Cross joint
● L-joint
● Dovetail joint
SEM-VI, DEPARTMENT OF ARCHITECTURE & PLANNING, VNIT.
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RABBET JOINT
●
For this type of joint, only one beam has a notch to fit the end of the other beam.
MITERED RABBET JOINT
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This is a type of joint where both the receiving piece and the covering piece have a miter.
SEM-VI, DEPARTMENT OF ARCHITECTURE & PLANNING, VNIT.
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MARKET SURVEY
SIZES:
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All types of sizes available in market
Customised sizes can be available by pre ordering to the suppliers
PRICES:
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Prices may vary according to its size and thickness
Generally available in square feet
Price ranges from 500 - 1500 rupees / square ft
MANUFACTURERS
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Nav nirman manufacturers and suppliers, Hyderabad.
Wood Barn India private limited, Haryana.
Karnataka wood packers , Banglore
SEM-VI, DEPARTMENT OF ARCHITECTURE & PLANNING, VNIT.
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TIMBER WEB BEAMS
INTRODUCTION :
●
●
I-Beams are high-strength, long-span structural timber beams which are used for residential
and commercial applications. They offer exceptional straightness, uniform depth and
dimensional stability.
I-Beams are generally not considered to be an appearance product due to the visibility of
gluelines but can be finished accordingly for architectural and design applications.
WHERE TO USE ?
● They are used for timber framing that is highly common in construction projects.
● Required in building simple shelters, wooden framing has played an important role in
shaping structures of many kinds. One of the most popular types of wooden framing is
known as lightweight timber construction.
SOME SPECIES OF TIMBER
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Red Oak
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Southern White Oak
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Post Oak
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Douglas Fir
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Western Cedar
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Reclaimed Heart Pine
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PROS AND CONS
OF SOLID TIMBER BEAMS
PROS :
● Longer spans and higher loads are achievable
● More efficient use of the material
● Quick installation and light to handle
● Fast installation of services
● Available in long lengths
● Cost advantages
● Web beams are less likely to bow, crown, twist, Cup, check or a split as would a
dimensional piece of lumber
● Web beams dimensional soundness and least little or no shrinkage helps eliminate Squeaky
floors
CONS :
● The disadvantage is very rapid structural failure during a fire reducing the time
advantage for residents to escape and increasing the danger of firefighters.
JOINERY DETAILS
TIMBER FRAME JOISTS & PURLINS :
● Timber purlins and joists form the roof and floor framing in timber framed buildings. The
old school way to do the joinery is to dovetail them in.
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● The lap joint allows us to maintain cross sectional area in the girts (main carrying beams).
STEEL TIE RODS :
● Steel tie rods solve the age-old problem of roof construction; they hold the walls
from bending out as the roof is loaded with wind or snow.
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● The buttresses eliminated the need for a bottom chord on a timber truss, which gave
the truss a great open feeling.
● A steel tie rod is the solution. It acts as the bottom chord of the truss and gives a very
open and light feeling.
●
Economical to produce, the I-Beam is made from a combination of timber products. The top
and bottom flanges - which make the distinct ‘I' shape, - are made from material with a high
tension strength such as LVL or even graded solid timber.
●
The flanges are separated by a vertical web, usually manufactured from structural plywood
or oriented strand board (OSB). The centre of the section serves to transmit shear stresses,
so a material with good shear properties is required.
●
The web and flanges create a lightweight beam which is both strong and durable. The
flanges resist bending, tension and compressive stresses, utilising LVL's enhanced strength
and stiffness properties.
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●
The web serves to transmit the shear stresses, relying on plywood's panel shear capacity and
dimensional stability.
Market survey
SIZES :
●
Customised sizes can be available by pre ordering to the suppliers
●
All types of sizes available in market
PRICES :
●
Prices may vary according to its size and thickness
●
Generally available in square feet
●
Price ranges from 350 - 1000 rupees / square ft
Manufactures :
● Magnus panel products @ 600 cubic feet
● Balaji timber and plywood @ 400 cubic feet
● Allied forest product
● Austim plywood LTD
● CADE ply system ltd
.
SEM-VI, DEPARTMENT OF ARCHITECTURE & PLANNING, VNIT.
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TIMBER PORTAL FRAME
OVERVIEW
Timber portal frames are one of the most favoured structural applications for commercial and
industrial buildings whose functions necessitate long spans and open interiors. As a material
choice, timber offers designers simplicity, speed and economy in fabrication and erection.
Timber portal frames offer a strong, sound and superior structure. Structural action is achieved
through rigid connections between column and rafter at the knees, and between the individual
rafter members at the ridge. These rigid joints are generally constructed using nailed plywood
gussets and on occasion, with steel gussets.
From material selection to finishing, this application guide provides a comprehensive overview
of the process of using timber in the specification, fabrication and erection of portal frame
structures
SPECIFICATIONS
MATERIAL OPTIONS
Glue laminated timber (Glulam), laminated veneer lumber (LVL), sawn timber and plywood
webbed beams are all common materials used for portal framing.
Glue laminated timber
Glue laminated structural timber may be considered a solid timber and is well suited to portal
frame production. With no restrictions on nails being driven on or near the glue lines, it provides
freedom in the location of moment joints as well as the secondary member arrangements. The
material is ideal for carrying gantry cranes and being a solid section it has fire resistance that can
reliably predict the survival of the frame.
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Laminated veneer lumber
Laminated Veneer Lumber (LVL) is essentially a vertically laminated glued beam comprised of
soft veneers. The product is manufactured using thick plywood technology and is supplied to a
maximum size of 1200 mm deep and 63mm thick. Lengths are limited only by handling and
transport, although 15 metres is the recommended upper bound.
Design procedures are identical to glue laminated structural timber with the exception of the
lamination factor not needing to be applied to the allowable design stress. Note that the butt
joined internal joints of LVL are suitable for portal framing.
LVL manufacturers should be consulted for specific design properties.
Plywood webbed beams
For applications involving above average portal frame spans, a more efficient section is
provided by a fabrication comprising of timber flanges, (solid timber, glued laminated structural
timber or L.V.L.) connected with plywood webs. Typically these are arranged as box-beams,
which due to good bonding strength about the ‘YY' axis, have increased buckling resistance.
Design procedures have also been formulated for 'l' and double 'I' beams. Typically construction
is nailed, however note that nailed construction results in some slip and so an equivalent
member has to be larger than the rigid glued product. Where the forces require it, it is common
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practice to reinforce the flange by adding extra flanges resulting in an efficient and light product.
An alternative construction method to nailing is gluing (resorcinol adhesive factory fabrication
only) with nails providing temporary clamping during curing.
Splices in the flanges are usually mechanically jointed using steel nailplates or lapped timber.
Splices in the plywood webs can be nailed or glued. Common design procedures call for internal
stiffeners to provide a base for fixings. These are best located at web splices and where purlins
and girts are to be connected.
Gusset materials
The most common gusset materials are plywood and steel. Plywood should comply with AS2269
and be branded under the Plywood Association of Australian Quality Control Program. Steel
should comply with AS1204.
Sawn Timber
Due to limitations of available sawn sections with low shrinkage, 12m is the practical span
limitation for sawn timber. All sawn structural timber should comply with the relevant
Australian Standard.
INSTALLATION
FABRICATION OF MEMBERS AND GUSSETS
For unseasoned timber, fabrication should not commence until the moisture content of the
timber is lower than 20%. Trial fabrication is also highly recommended to check the timber
performance and suitability of equipment before major fabrication commences.
It has become common practice to fabricate rafters, purlins and roof bracing on the ground, and
then lift the roof (in sections or fully) onto the columns. The through-rafter method facilitates
this method of erection better than the mitre joint.
The rafters are erected on the floor and adjusted to the correct pitch. To avoid interference
during lifting ensure the whole roof is laid out approximately 500mm along the building from its
designed position.
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The ridge gussets should be nailed off and the purlins installed with the exception of those in the
immediate vicinity of the columns, which should be fitted after erection.
Mark the set out on to the floor to ensure that the prefabricated roof is as specified. Hoop iron
crossed bracing is installed to preserve a square structure while lifting and this may also be
effective as the final roof bracing. The purlins should have all connections installed at this stage.
Knee gussets are first nailed completely to the columns erected onto their base plates. If the base
plate is capable of providing some fixity in both directions then that will be sufficient, if not
temporary bracing must support each column.
Lifting and erection
●
Each frame must be supported
during lifting, as the purlins are generally
discontinuous. When multiple bays are
erected, lifting beams or strongbacks must be
used.
●
The frames can be quickly erected
with the knee gussets wedged apart to
facilitate rafter entry and the columns readily
swayed to accommodate any inaccuracies of
fabrication.
●
Longitudinal bracing elements can
then be installed and note that the rod and
turnbuckle type facilitate plumbing of the end
columns. The columns have to be plumbed
across the building by props or by a jemmy
bar and then the knee gussets are ready for
nailing.
●
As cranes support the frame the
entire time, it is worthwhile investing in
suitable equipment to facilitate quick
completion of the column and nailing phase to reduce hire costs. As the full load is not acting at
this stage, not all nails have to be driven; but all gussets must be nailed before releasing the load
from the crane.
●
After crane removal, remaining nailing can be completed, together with installation of the
eaves, purlins and girts. The mullions and the end wall girts can then be installed together with
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any additional roof wind bracing. Apart from the treatment of the openings the structure is now
ready to be clad.
Erection of box-beam frames are similar with the only notable difference being the steel plates
are not as flexible as ply gussets and hand nailing is more time consuming. The lighter frame
may result in reduced crane hire costs.
KEY CONSIDERATIONS
BUILDING DESIGN
The absence of internal columns, large spans and
low profiles makes portal frame construction
particularly popular in industrial and commercial
building applications. The use of timber and timber
components in such buildings is both economic and
aesthetically pleasing and, combined with the other
inherent advantages of timber construction, have
been responsible for ensuring timber remains the
preferred material choice in this mode of
construction.
Building envelope
Timber portals may be clad with other timber products such as plywood and weatherboards. For
large-scale factories and warehouses, conventional metal or fibre cement cladding is common
and for the more commercial type applications, cavity brick and brick veneer. Internally, purlins
can be exposed as cathedral ceilings or sheeted on the underside with conventional ceiling lining
materials, alternatively the frame may remain ‘raw' and natural.
PORTAL ACTION
Portal frames have the primary objective of resisting lateral loads caused by wind acting on the
walls. They distribute the wind loading from the end walls into a wind truss or roof bracing and
from there into bracing elements located at convenient positions in the sides of walls.
Structural action for timber portal frames is achieved through rigid connections between column
and rafter at the knees, and between the individual rafter members at the ridge. These rigid joints
are constructed using a substantial number of nails with gussets of either steel or plywood,
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creating a connection that is simple yet highly efficient. Various layouts, that balance cost and
appearance, can be used to achieve the moment restraint.
STRUCTURAL DESIGN
Timber portal frames are usually designed with pinned bases as there is little structural benefit in
making the base joint fixed. Tudor arches (3 pinned portals) are effective with pitches about 20°
to 50°, with spans to 40m. Two pinned portals are generally effective up to 12m for solid timber,
35m for glue laminated structural timber and to 40m for plywood box beams. Where gussets are
used, pitches should be kept above 10° as it is difficult to design plywood ridge gussets for
low-pitched frames.
The deflections predicted during analyses by using the Short Duration Modulus of Elasticity 'E'
must be modified by 'j2', the Duration of Load Factor for Deflection relevant to loads that act for
5 months or more. This means that dead load deflections need to be increased by a factor of 2
and 3 for members of seasoned and unseasoned timber respectively, with the internal forces
remaining virtually unchanged.
For average circumstances of geometry and loadings, the dead load + live load combination
often governs member design. Eave displacements may be more critical where design wind
velocities are in excess of 40 m/s. The NZS3615, predicts the relaxation caused by the joint
moment and this may be used if a more exact analysis is appropriate.
Rafter and column design
Low pitch portal frame design is governed by bending stresses, with the critical areas being the
knee, ridge and mid-rafter length. It is usual to rely on purlins and girts to provide lateral
restraint to members and so the slenderness coefficient 'S' is based on a discrete restraint system.
Fly braces are required where secondary members are not deep enough to provide sufficient
torsion restraint to the frame. The fly braces may be simple hoop iron angle bracing,
prefabricated 'K' bracing or substantial moment generating cleats that double for the primary
purlin fixings. AS1720 gives guidance on the magnitude of the loads that the connection has to
resist.
Serviceability
Timber has a low modulus of elasticity compared to steel, and so for the relatively shallow
sections used in portal frames, deflections are more significant. If relaxed serviceability criteria
(more flexible frames) is adopted for more economical design, then the pitch has to be increased
above the roofing manufacturers minimum recommendations.
Vertical movement of the ridge should be calculated to ensure that differential movements
between the end wall and the adjacent frame are not excessive. The allowable limits are related
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to the member stiffness and their connection detailing. The horizontal movement of the eave
must be compatible with the cladding in the end wall and other elements such as windows, doors
and gantry beams. Additionally the allowable deflection must be compatible with any heavy
weight cladding on side walls. For such materials a limiting movement of eaves height/300 is
recommended.
The most significant movements of the structure occur in response to the maintenance load
(downward at mid-rafter span and ridge) and wind to the side of the building resulting in
positive pressure acting on the windward roof (horizontal movement at the eave).
Moment resisting connections
The full gusset is a simple triangle cut from a plywood sheet with a length limitation of 2400mm
or 2700mm depending on the plywood manufacturer. Similarly 1200mm is the sheet limitation
to the gusset depth. The full gusset provides more nailing area for a smaller gusset depth and so
may be an advantage when used with higher strength members. For the full advantage to be
realised, the plywood should be both a high stress grade and a joint group similar to the main
members.
Once the length limitation is reached, the truncated shape has to be used. For a most efficient
nail group, the nails should be located around the periphery of the gusset as this increases the
effective polar movement of the area more rapidly.
AS1720 specifies edge and end stances that must be adhered to in order to maintain fastener
performance. Practical experience has indicated that smaller and larger spacings will be
required, depending upon species and moisture content.
For plantation softwoods an increased nailing density leads to a more compact group. Where
nailing is laid out around the periphery of the gusset it may be reduced. There is a correlation
between joint strength and timber density and so timbers of a low density such as fast grown
Radiata Pine from New Zealand would be relegated to JD5 while the Australian grown timber of
the same species is allocated JD4 in AS1720.
Plywood and steel gusset design
Experience has shown that the stress distribution resulting from the applied moment is
non-linear. Plywood is laid up in odd numbers of veneers so that the external veneers run in the
same direction. In the design of the gusset, it is more efficient to use a plywood with a more
pronounced strength in one direction. This is known as the 'equal ply' lay out, with all plies of
relatively the same thickness. When the gusset has to resist bending, only those fibres running
parallel to the indirect tension can be effective.
The plywood gusset must be designed to resist the axial compression (and tension) that again is
resisted by the parallel plies only. The unstiffened part of the gusset is able to buckle and can be
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designed to resist this as a diaphragm. Here it can be seen that the diaphragm is acted upon by
compression shear and moment and logically is governed by an interaction equation. The only
unusual concept is that shear is resisted by all plies, while moment and axial load is taken only
by the parallel veneers.
Steel gussets are designed according to AS1250, Steel Structures Code and for economy are kept
as thick as possible. Buckling is a problem, so the nail groups have to be effective in withdrawal
to prevent it. It is normal practice for the plates to be aligned on the members centrelines and a
welded 'L' is generally more efficient than cutting to the plate shape.
Base plate connections
Base plate types are varied but preference should be given to simple connections that will
minimise steel fabrication costs. The loads to be resisted include axial load (both tension and
compression) and shear load. The function of the base is to cater for these combinations as well
as providing a minimal moment restraint as an aid to erection of the columns.
Consideration must then be given as to whether the connection should be cast into the concrete
slab or pier. Alternatively hold-down bolts may be cast in to receive base plates. A third
alternative for smaller structures, is for hold down bolts to be epoxy grouted into the concrete.
All connections should separate the timber from the concrete. Either bearing plates can be used
or a damp proof course installed. For economy, the timber connection should be a single bolt or,
if absolutely necessary, two bolts. Bearing failure of bolt to steel is generally the determinant for
the steel thickness.
Bracing
Buildings typically contain bracing elements that transmit the wind from the end walls to the
ground. The racking forces are carried from the mullions into the roof place and are transmitted
to the purlins and roof diagonals and then to the bracing walls.
The purlin-rafter connection has to transmit tension to counteract wind suction acting on the end
wall. Bracing elements are usually crossed so that wind loading at each end wall is resisted at its
end rather than transmitting it via the eaves tie to a single bracing element. This results in less
load on the connections and as a result, cheaper solutions can be used.
Purlins
Purlins may be:
●
●
Solid timber (approx 6m limit)
Nail plated built-up sections
SEM-VI, DEPARTMENT OF ARCHITECTURE & PLANNING, VNIT.
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●
Glued laminated structural timber (generally only used for appearance purposes)
●
LVL
●
Plywood webbed beams (Light, stiff and easily fabricated. Often appear as either nailed
'C' sections or glued 'I' beams. The former will require more lateral restraint.)
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Parallel chord trusses. (Similar advantages to plywood webbed beams with the added
facility to accommodate services.)
The purlins are designed to resist maintenance and wind loads and, in the vicinity of the roof
bracing, carry some compression. They can be simply designed by using published tables,
bearing in mind, AS1720.
Purlins are usually set between the frames, rather than across the top, to provide stability for the
purlin ends as well as intermediate restraint for the rafter.
ADVANTAGES
CONSTRUCTED FROM READILY AVAILABLE MATERIAL AT AN ECONOMIC
●
COST.
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LIGHT IN WEIGHT.
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EASY TO TRANSPORT AND ERECT.
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CAN BE TRIMMED AND EASILY ADJUSTED ON SITE.
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PROTECTION AGAINST FUNGI AND OR INSECT ATTACK CAN BE BY
SURFACE APPLICATIONS.
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PLEASING APPEARANCE EITHER AS AN NATURAL TIMBER FINISH OR
PAINTED.
FINISHING AND PROTECTION
Buildings with a strong visual focus, such as glue laminated commercial constructions should be
finished and (where possible) covered with building paper prior to erection. If any elements are
to be painted or treated this should also be carried out prior to erection. Steel gussets should
SEM-VI, DEPARTMENT OF ARCHITECTURE & PLANNING, VNIT.
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receive their finished coat after all nails have been driven. Throughout the assembly process it is
wise to provide all fabricated components with temporary protection from the weather.
LAMELLA ROOF
CONTENTS
What is a lamella roof
types of lamella roofs
comparison between timber
and steel
construction details and
materias
advantages and disadvantages
market survey
availability in market
methods
What is a lamella roof
a lamella roof is made up of a series of intersecting skewed arches, each arch made up of
smaller individual pieces called lamella roof. these skewed arches come together to form a curved roof profile.
the timber arched roof was made up of relatively short timbers referred to as lamellas varying
varying in thickness and depth depending upon the span but identical for any given span.
these lamellas are curved on their top edge sand beveled at the ends which are radial to the curvature and are
bolted on edge with the curvedside uppermost, to form a rhomboid network of framing timbers. in this manner
the external surface of the roof takes up the arched form.
the focus on the segmental arch, where the profile of the roof follows a segment of a circle rather than a parabola
or a gothic arch.
a lamella roof also known as the zollinger roof is a vaulted roof made up of simple, single prefabricated standard
segments as a way span large spaces.
SEM-VI, DEPARTMENT OF ARCHITECTURE & PLANNING, VNIT.
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Types of lamella roofs
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tied segmental arch
gothic arch
buttress segmental arch
parabolic arch
wooden sheathing covers the structure on the outside.
and the end support conditions, such as the tied arch or the buttressed arch, account for the resultng horizontal
thrust in the springing ends of the arch.
while such supports should be taken into consideration in the roof design, it is beyond the scope of this project to
develope into the different design calculations pertaining to each.
Comparison between timber and steel
timber
●
zollinger's lamella
roof consists of timber
pranks, about 2 metres long,
that are originally connected
with only one bolt.
●
the lacking flexural
rigidity of the connection with
only one bolt turns out to
connection
with only one bolt turns out to
be problematic.
steel
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hugo junkers patented a steel lamella roof construction, based on the wood lamella roof
design by zollinger.
●
because of its simplicity and markable rigidity it was soon used for many large roofs worldwide
which could span upto 40 mts.
the lamella roof system was devised in 1908 in dessau, germany by friedrich zollinger, the city architect. and in
the late 80s the steel structures are came to use.
Construction details and materials
fixing details of timber
SEM-VI, DEPARTMENT OF ARCHITECTURE & PLANNING, VNIT.
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in the zollinger construction system, short planks are arranged in such a way that two planks meet in the
●
middle of a vertically running plank.
a typical connection details consists of a bolt that goes through a slotted hole in the middle plank, with
●
toothed washers being placed between the planks.
a typical dimensions for the planks used in roofs constructed in the interval period are 3cm x 20cm, with
●
lenghts between 2 and 2.5m.
fixing details of steel
●
it consists of only three standardized elements. the lamellas, the gusset plates and the roof beams.
the lamellas are about 1.5 to 2.5mts long and upto 0.5mts wide like in zollinger's system.
●
the lamellas are made of sheet steel 3 to 6mm thick.
●
they go from one crosspoint to the next. four lamellas are connected flexurally rigid in one crosspoint.
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the specially shaped ends are arranged next to each other, clasped by two ‘u’ shaped gusset plates and
●
easily screwed together by one or two of three screws each.
fixing details of timber
fixing details of steel
schnit bars, gusset plates, bolts,
screws, etc
Advantages of lamella roof
●
the easy assembly of
construction
low weight of individual
●
parts makes transporting and
stocking easier.
total weight of thebroof is
●
reduced by 25%compared to the
roof truss constructions.
economical construction due to use of thinner roof planking.
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acoustical properties – suppresses the flutter echo
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aesthetically appealing
●
long span structures
●
Disadvantages of lamella roof
●
as timber is natural and cellular it moves with changes in climatic conditions. timber shrinks,
SEM-VI, DEPARTMENT OF ARCHITECTURE & PLANNING, VNIT.
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swells, twists, cracks and bends over time in different climate conditions.
●
●
●
●
most timbers are prone to pest, rot, mold and fungi attacks some are far better than others
timbers tent to silver orlook old if left natural and unpainted.
timber maintainance can seem to be higher than other building materials
steel lamella roofing members could be prone to corrosion.
Market survey
sizes
●
●
●
●
all types of sizes available in market
where the thickness is 1mm -4mm, 1mm -50mm, 48mm-100mm,1200mm-100mm etc
and these are mostly applicable for the residencial and commercial purposes.
and sizes may vary according to the construction types in such places.
prizes
●
●
●
prizes may vary from size to size and its thickness
and it is available in square feet/sq ft in market
prizes ranges from rs 450 to 800/sq ft and above for timber roofs
Manufacturers and whole sale dealers
●
●
●
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sri venkateshwara enterprises, hyderabad
lubna enterprises, hyderabad
visaka industries limited, hyderabad
omega roofing industries pvt lim, hyderabad
availability in market
type 01 :
matboard model
a proof -of- concept model was created using matboard connected with solid brass fasteners. the lamella pieces
were cut using a lasre cutter and assembled by hand. while assembling the model, the author noted as more
pieces were added to the lamella arch, the arch itself became morestiff, indicating an interaction having to do
with the interesting connection style used by lamella construction.
type 02 :
steel model
after the proof -of -concept model was made, a model made of sheet steel was fabricated and donated by the
architects, the model was precision-cut using a computer – controleed plasma cutter with the ends bent in a
machine press. the steel model was approximately a two-times scales copy of the matboard model.
matboard model
Methods
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the methods are based on the loads
SEM-VI, DEPARTMENT OF ARCHITECTURE & PLANNING, VNIT.
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●
●
the load calculates the overall structure
the loads are calculated in values and according the values the structure is planned
following are the loads
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dead load
live load
wind load
snow drift load
construction load
balanced snow load
the loads on the arch were found in intervals for rises between two and twenty feet. since, in the finite element
model, the moment capacity of the arch is dependent on the stiffness, and according to the analysis, the loads are
calculated in values and ratios, and then the structure is planned over the site, and the methods rely on such
loads where the structure is pointed out clearly, on the basis of ratios the construction is planned out with more
flexible arches which reflects the stiffness of structure on site.
the construction of timber lamella roof structure merely depends on the dead load and live load.
THANK YOU
SEM-VI, DEPARTMENT OF ARCHITECTURE & PLANNING, VNIT.