TECBEAM JOISTS / BEAMS
TECBEAM® joists are composite structural ‘I’ Beams.
THE CORE TECHNOLOGY
Tecbeam is a composite I-beam made up of timber flanges mechanically fastened to a continuous heavy gauge sheet metal web, which has press-formed stiffening ribs and web holes. The timber flange is fabricated from two pieces of LVL placed each side of a steel web and fastened together through the web forming a typical I-beam composite section. In the assembly process the flanges and steel web are clamped together and mechanically fastened using nails at 100mm centres on each side.
The nails act in double shear and achieve the development of full composite action in the section; the nails also maintain the clamping action that allows the steel web to develop full compressive stresses within the flange area of the steel web. The bending stress developed in the steel web makes a significant contribution to the total bending strength and stiffness of the beam. This structural behaviour has been confirmed by extensive testing of numerous beam samples of varying spans. Load versus deflection plots consistently show linear elastic behaviour up to a point where non-linear action begins to occur (the Limit state load is within the elastic range).
In significant contrast to solid timber and other timber engineered lightweight beams and floor trusses which may undergo brittle fracture, no sudden collapse of any of the samples tested to destruction has been observed in extensive testing. Tecbeam ‘ductility’ – due to the continuous steel web, provides for a superior floor construction for heavily loaded floors.
Craig Kay
Engineering Manager
Tilling Timber
The large, regularly spaced service holes in TECBEAM joists, provide time saving convenience for all trades to install services such as: pipework, air conditioning ducts and cabling; eliminating the need for tradesmen to cut holes in the joist webs or build bulk heads.
A TECBEAM designed floor can often obviate the need for structural steel beams in point load, or long span applications. Significant savings in time and cost can be achieved. The joists have been extensively tested and proven as a structural beam in thousands of buildings since it was first introduced to the competitive Victorian market. The joists are suitable for use in all types of floor and roof construction in: houses, multi-storey units, offices, schools, gymnasiums, hotels, hospitals, warehouses, car parks, etc.
STRUCTURAL PROPERTIES
▼ Stiffness
The continuous steel web in a Tecbeam joist enhances beam stiffness, reducing creep by over 60% compared to a seasoned timber beam, trussed joist or plywood I beam, and over 80% for an unseasoned timber beam. No other engineered timber beam achieves comparable results.
▼ Strength
The continuous steel web enhances beam strength by up to 20%. Floors can be designed for loads exceeding 10kPa.
▼ Ductility
At the ultimate load capacity, testing shows that web tensile yielding and shear buckling generally occurs before flange stresses reach the timber capacity. Web yielding occurs at the point of maximum bending moment. This action forms a local mechanism which is analogous to the ductile action in a steel beam. The Tecbeam joist undergoes an increased deflection but continues to carry significant load; this is an important safety feature in the structural integrity of a floor. In comparison, truss type joists and plywood I beams all undergo catastrophic collapse at their ultimate strength limit states.
▼ Creep Factor
Long term load testing has established the creep or duration factor to be in the order of 1.3. In comparison, for solid seasoned timber the creep factor is 2.0 and for unseasoned timber it is 3.0. This lower creep factor means TECBEAM joists can often be used to replace steel beams, with significant cost savings. Benefits also include less sticking doors, cracks and emerging gaps. Less post-construction maintenance is a boon for the builder.
▼ Point Loads
High concentrated loads can be placed anywhere along the length of a TECBEAM flange because of the continuous steel web support. Open web truss joists can experience excessive local bending stresses where point loads occur between the nodes. TECBEAM joists are ideally suited to residential, commercial industrial and car park structures in which there can be high point load conditions.
▼ Vibration
In longer spans, all lightweight joists exhibit vibration; in a TECBEAM floor, this is easily controlled by using secondary beams installed at right angles to the joists (strongbacks). These strongbox are securely fixed into the TECBEAM holes by wedges. The timber and steel web combination in TECBEAM joists provides better dampening characteristics than either floor trusses, plywood I beams, steel purlin sections or lightweight all-steel joists.
