Trussed Rafters and Structures

Characteristic Features of the System

The system of beams connected by steel angle/connector plates with press-in pins, known under the term „Gang-Nail“, was invented in the USA by the end of 50th of the 20th century. Switzerland and Belgium were the first European countries where this system began to be used at first for the structures. The company BIOS Dobříš was the initiator and pioneer of the system in the Czech Republic.

characteristic feature of the system = connecting element = connector plate
development stage of manually nailed plates and trusses
most progressive and efficient technology in the category of light-weight truss structures
a wide scope of application in practice - roof and floor trusses, supporting frames of timber structures, formwork components for concrete industry, etc.

Materials of Rafters

wood

plank lumber, humidity of ca 20 %
usual cut-to-size sections - 50, 60 x 80 - 240 mm
wood preservation from wood borers and fungi by cold soaking - Katrit BAQ

connector (angle) plates

a wide product range - different sheet metal thickness, different lengths and pin shapes
surface finish - hot-dip galvanizing or stainless material (for aggressive environment)

Manufacture

technology

special circular sawing machine
giant stationary press ( 50 t )

working process

preparation of cut-to-size sections on the sawing machine
wood preservation by coal soaking in the tub
placing of the bottom connector plates on the press table
laying of cut-to-size sections on tie members, fixation of part geometry
placing of the top connector plates
step-by-step connection of all trusses - the table moves under the press unit
transfer of the pressed assembly on the transport truck
the table returns to the home position
manufacture of another assembly

Advantages of Trussed Rafters

dimensional and shape variability
precasting - high productivity and quality of labour
saving of material ( 20 - 40% ) and price
static „self-supporting feature" ( up to 30 m of free span ), optional layout
simple and quick erection with minimum demands for heavy-duty plants
material - wood - natural, low consumption of resources, environment-friendly and renewable raw material
light-weight, fine-features structure - minimum loading of foundations, existing structures and roofs
simple linking of other structures

Scope of Use of Roof Trusses

variable system - nearly any plan dimensions can be roofed
saddle, hip, single pitch, mansard, cradle (rainbow) roofs, etc.
family and residential houses
hall structures - agricultural, industrial, sports
warehouses, store rooms, sheds, etc.
supermarkets, shops
panel house extensions
re-roofing of the existing flat roofs
possibility of use of the attic area - the so called "studio" trusses

Roof Composition with Trussed Rafters

the trusses are installed on the reinforced concrete bond beam, wooden wall beam or steel girder
axial distance (span) - usually 1 - 1.2 m ( depending on roof cladding and load )
spatial stability of the structure is guaranteed by wind bracing - longitudinal and transverse at the roof level ( boards, bracing trusses )
accessibility of the roof cladding is usually provided by the board walkway at the level of the bottom chord
upper chord = base for the supporting roof cladding layer
bottom chord = supporting element for suspension of ceiling
erection of the trusses usually needs a crane, scaffolding in certain cases only ( mansards, etc. )

Truss Structure Designing

Designing of trussed rafters is naturally subject to structural analyses, carried out by a special computer programme due to complexity and time-consuming character of these analyses. Time for calculation of the structure can be minimized, design of individual rafter bars, size and layout of connector plates optimized, using the progressive software of the company MiTEK. At the same time software creates the complete production and erection documentation, bills of materials and price calculations.