Updated: Oct 30, 2018
By virtue of the sheer beauty of timber, you can secure a masterpiece by designing, manufacturing and constructing a timber roof structure. The team at Wolf Professional Services knows this, and that is why the company offers a ‘must-attend’ workshop especially for our industry.
Despite its inherent aesthetic qualities, over time timber has become ‘forgotten’ as a preferred building material of choice. That is largely because, for many years, the built environment remained primarily focused on concrete and steel as the ‘only’ construction materials for commercial and public buildings.
Undoubtedly, architects and engineers were more confident working with these traditional construction materials, and timber was seen as a product more suited to smaller projects like residential developments.
The question can be asked: Was this due to a lack of confidence in the product, or due to a lack of knowledge?
A LOOK BACK AT TIMBER TRUSSES
The timber trusses that we commonly see today comprise of a framework of triangulated construction timber joined together with galvanised steel connector plates (also called truss plates).
While the shape of roof trusses has not changed over the years, the manufacturing process has, as has the span possibilities.
The truss shape has been in use ever since man started using pieces of logs and, later, sawn lumber. In more modern times, the first light wood frame trusses were built on a construction site, using nails or plywood gusset plates at the connections. In 1952, in Pompano Beach in Florida, USA, the metal plate connected engineered wood truss was invented and patented by A. Carroll Sanford, founder of Sanford Industries. This roof system proved to be faster and more cost-effective than earlier practices, utilizing less material and labour.
TIMBER ROOF TRUSSES TODAY
Today, timber trusses’ high strength-to-weight ratio permits long spans, which in turn offer greater flexibility in roof plan layouts.
They can be designed in almost any shape or size, restricted only by manufacturing capabilities, shipping limitations and handling considerations.
The design and manufacture of metal plate connected wood trusses in modern truss operations are achieved with computer-aided design packages. In the design, the computerisation of the process takes over. Common standard engineering principles, along with building code requirements, roofing material, ceiling, wind and snow loads, as well as any extraordinary loading or stress conditions, are all taken into consideration at the design stage.
An engineering-analysed drawing is produced by computer, detailing the forces that develop in each member under the given design loads. Rational-designed members also include the timber truss dimensions, timber sizes, and the grade for each cord and web. The plate size and orientation of each metal connector plate is precisely specified, as is the location of permanent bracing.
The truss manufacturer supplies the construction drawings to the architects, engineer, and building contractor. The contractor responsible for carpentry is also responsible for the placement of the timber trusses. To ensure that the structure will be sound and safe, the trusses must be erected in strict accordance with the construction drawings.
In South Africa there are four truss systems that manufacture metal plate connectors and ancillary materials. Each system has its own design software.
The strength and integrity of a roof truss depends on the integrity of its metal plate connectors. Timber trusses are manufactured from pine softwood or BILIGOM® hardwood, available in various profiles and grades.
Typically, the truss frame manufacturing process starts by carefully cutting optimally thick members so that they are exactly the specified length and have the exact, correct angles at the ends. Many roof truss manufacturers use computer-driven saws that produce multiple cuts quickly and precisely. The size and the grade of timber for each member on the cutting bill is based in the magnitude of force that each must resist while under potential maximum design load.
The storage and handling of a timber truss as a construction material is an important factor in the overall quality of the finished product. Improper handling during delivery and/or installation is the most frequently cited reason for failure of the wood floor or roof truss system.
THERE IS MORE TO LEARN
Wolf Professional Services has developed a special workshop with the aim of securing renewed confidence in timber as a construction material of choice, with specific reference to correct design procedures and the applicable requirements to comply with all necessary standards. All participants in the timber and building industries stand to benefit from the course.
Wolf Professional Services is an approved CPD Provider in accordance with the ECSA (Engineering Council of South Africa) requirements for this workshop, titled Workshop – Timber Roof Structure. Upon completion of the workshop, attendees will be credited with two CPD points.
All speakers are specialists in their respective fields and deliver up-to-date information on the latest developments and technologies being utilised within the timber industry.
For more information: visit the Wolf Professional Services website or contact Renée Wolfaardt on 082 304 7006