Timber Portal Frame Construction Andrew Kemp 500238299
The Timber Portal Frame • a planar frame where the lateral and bending forces are transferred by moment resisting connections (knee joint) from the portal rafters to the columns. • Timber portal frames are cost effective, easy accommodation of services such as lighting, plumbing and can be erected quickly and efficiently. • The overall appearance is aesthetically pleasing. • Timber portal frames are particularly suitable for use in high visual impact applications. • No problem with supply of timber. • Timber has a fair fire rating
Design Of Timber Portal Frames • Designed by architects in conjunction with an engineer • Engineer my also seek advice from timber supplier • Timber portal frames can be built using several different types of sawn timbers Glulam, LVL and plywood box beams, ESL, OSB
Designing Timber Portal Frame • Mainly used in commercial or industrial structures. • Depending on knee joint and member size timber portals can handle large spans up to and above 50m. • Timber can be formed into any shape desired creating flexibility for the architect.
Designing Timber Portal Frame • For large span timber portals steel hinges can be used for efficient erection and added strength • The use of steel gussets can also be used to add strength to knee joints • Nailing is a very important and set out part of design of structure. • Poor nailing can result in failure in structure.
Designing Timber Portal Frame • Timber portal frames are also able to support large weights on the members which allows extra attachments needed by the clients such as cranes, machinery etc to be designed in. • There is a number of different external claddings that can be applied to a timber portal frame some of the popular options are corrugated steel sheet, brick veneer skin and pre cast tilt up concrete panels. Ref:jjham
Timber Portal Model Plywood gusset Timber Box Beam Mild steel shoe Steel Bolts Concrete Pad Footing
Manufactured Timber Portal Members • LVL (Laminated Veneer Lumber), has a high strength on a linear axis, can be manufactured in large depths and long lengths. • Glulam (Glued Laminated Timber) –a versatile members made of small pieces of timber glued together, that can be fabricated in large depths, widths, lengths, and formed into a number of shapes, including curves. • Plywood is often selected to act with other timbers to create a member which shear stresses must be carried. Such as the web of a built up box beam section in which shear forces will be transmitted. It can be used as feature paneling or for floors in which it carries out-of-plane loads.
Manufactured Timber Portal Members • ESL (Engineered Strand Lumber), a versatile product made from clumps of wood fiber arranged in a mainly linear pattern and held together in a glue. • OSB (Oriented Strand Board), a panel product manufactured from thin wafers of wood held in a glue. The wafers are oriented during manufacture so that the grain is mainly parallel to the length of the board. • Box Beam similar to a small stud wall which is covered with plywood, basically you build the stud to the size beam needed then it is boxed in with plywood the longer the span the deeper the beam and the more studs.
Manufacture Of Timber Portal Frame • In the past large sections of timber were used to span large distances • Timbers of this are now to hard and expensive to obtain • Timber portal members are made up of several structural elements to form one single timber structural member. • These are manufactured to provide a single timber member that will span long distances which a solid timber form could not. • All timber portal members are manufactured under strict Australian Product Standard.
Manufacture Of Timber Portal Frame • Timber portal members can be manufactured out of several timber stress grades depending on length of span. • For large spanning timber portals high stress grade timbers like F17 would be used. • Large spanning beams can be made into sections for easy transportation and allows sections to be lifted into place instead of the use of cranes. • Members can also be tapered which is much more economical and will reduce the weight of member, this method will not weaken the member it will reduce stress on the apex. Ref: jjham
Manufacture of Timber Portal Frame • Timber memberscan be built on or pre-fabricated off site depending on the type of timber. • Pre fabrication will allow slab to be poured while frame being built off site, time saving • On site building will mean frame can be assembled on the ground and then raised into place using cranes, saving cost of safety issues Ref: jjham
Construction and Erection • After construction of footings and of members ether on-site or off-site erection of frame will begin. • Depending on the size of the frame cranes my have to be bought in to lift the structure into place. • Slab can be poured when footing are being poured or after frame has been risen. Ref:jjham
Construction and Erection • Once frame has been raised portal columns are fixed into mild steel shoe which have be bolted to the footing. • Mild steel shoe prevents the timber from sitting on the concrete which would allow seeping of water into the timber causing rotting. • Also creating a solid connection between the timber and the concrete footing.
Construction and Erection • After the portal is attached to footings and is free standing gusset plates can be nailed to the knee joint. • Gusset plates, often steel or plywood, fixed by nails, bolts or other means to connect timber members in a truss or other frame structure. Gusset plates may be applied to one or both sides of a joint
Basic Timber Portal Frame Plan and Section Ref: P.J.Yttrup and Associates Pty Ltd / www.timber.org.au
Timber Portal : Belmont Timber Shed Timber LVL rafters Housed in timber purlins External wiring for lighting Clear fiberglass sheet (added light) Plywood Gusset at knee joint and apex Corrugated steel sheet cladding Steel Cross Bracing
Timber Portal : Belmont Timber Shed • Timber portal knee joint • Built in brick skin • Safety mesh under sarking
Timber Portal : Belmont Timber Shed 2 1 • 1- timber portal column connected to footing with mild steel bracket, bolted into footing. • 2-Timber portal supports large roller door attached with steel bracket and bolts.
Timber Portal Frame Construction • Hope this has given an in depth insight into the processes involved in the construction of timber portal frames, from the design stage to the finished frame. Andrew Kemp - 500238299