A modern twist

Summary
• The theme of the conference was “Traditional into modern”.
• All-timber connections are having a revival in timber building.
• Oakwrights has taken delivery of a second Hundegger K2 beam processing machine.
• Research has been carried out on Sitka spruce logs for timber piling.

In recent history it has been a common misconception among those not in the know that timber is a low-tech material. Over the years the Institute of Wood Science (IWSc) has worked hard to dispel that myth and its recent annual conference, held at the University of Bath on September 18-19, set down another marker.

Around 70 delegates, including architects, structural engineers and housebuilders, along with wood scientists, attended the conference, which was themed “Traditional into modern”: its context was construction.

Joints were the focus of Buro Happold structural engineer Jon Shanks and University of Bath PhD student Andrew Thomson and specifically the pegs or dowels that secure them and what could make them fail.

Four hundred year old timber frame buildings may still be standing and are a testament to the skill of the craftsmen of the day, but as “non-engineered” structures built using nothing more than “rule of thumb”, they have a tendency to lean at some fairly crazy angles.

“We can’t afford this kind of sort of trial and error in the current design climate and so now we do destructive testing,” said Mr Shanks. “The aim of the research is to develop a better engineering understanding of how connections work by working with craftsmen and producing pragmatic tools through modelling and physical testing.”

Peg prediction

In traditional oak connections, he said, connection failure is through peg failure, but models have now been developed to predict pegged connection strength and stiffness in both pull-out and rotation.

“All-timber connections are having a revival,” Mr Shanks said. “Carpenters like them; there are no compatibility problems (no metal equals no corrosion); they offer fire protection (metal conducts and has to be treated if exposed); the cost is less significant; and they have low embodied energy and sequester carbon.”

Andrew Thomson’s research into non-metallic timber connections supports those contentions. “The main problem with metal connectors is corrosion and while stainless steel is an option it’s more expensive and is weaker than mild steel,” he said.

Along with their non-corrosive nature, the other advantages of non-metallic connections, he continued, are that they can be made in-house by the timber frame manufacturer, they provide a lightweight structural solution and the structural members they connect can easily be recycled or re-used as they don’t contain any metallic elements.

The ultimate aim of his research, Mr Thomson added, is to develop a non-metallic plate connector for in-plane connections and he is currently investigating the potential of birch plywood and crosswise densified veneer wood.

Using technology

Oak framing company TJ Crump Oakwrights Ltd is constantly testing different types of joints, according to production manager John Lloyd. And the company has state-of-the-art technology to help it do so.

The company has just taken delivery of its second Hundegger K2 beam processing machine – £500,000-worth of kit that is even more accurate and twice as productive as its predecessor, which was bought in 2002. And speed is key for the company which produces about one bespoke house (average size 800ft²) for the self-build market a week.

The Hundegger works in tandem with the Dietrich CAD/CAM software package and has taken “80% of the grunt work” out of the manufacturing process. “You can guarantee that all your joints will be consistently cut to the same parameters every single time – and that’s very relevant for quality control,” said Mr Lloyd.

However, he added, the human skill factor is still vital. “We invest a lot of time and money in training designers on the Dietrich software,” he said. “The jointing is very complex and we have to define exactly how they will be cut. And we still have 14 framers to hand finish and cut curved stock.”

Oakwright’s contention is that to live in one of its homes is “a life enhancing experience” – an assertion that is recognised and shared by German house manufacturer Baufritz, which combines an ecological philosophy with incredibly sophisticated and efficient production techniques.

Baufritz in Bath

The company’s managing director Helmut Holl gave delegates an insight into Baufritz’s production and assembly methods, while Tiffany Wood provided an account of the construction of her Baufritz house in Bath – a project which was covered by Channel 4’s Grand Designs.

Featuring many curves in the design, the house was a challenge for Baufritz, particularly when it came to the elliptical solid walnut staircase rising through six half-floors, but the result is breathtaking.

“The use of timber was essential for the homely feel the family was after,” said Ms Wood. “We feel timber transforms a building more than any other material,” she said. “The air quality inside the house is superb and we sleep brilliantly.”

Oak and walnut predominate in the Wood’s house, but Chris Holland and Barny Freke, both of BRE made the case for Douglas fir and Scots pine respectively.

Chris Holland has researched the reasons why glulam made from Douglas fir is under-used in the south-west and his project aims to improve its potential.

In a Catch-22, the lack of use of the material has lead to a lack of suitable strength classes, so the plan is to conduct structural testing to derive data and make strength graded Douglas fir more available in the grades that the market need and can use.

Scots pine falling boards have been the focus of Barny Freke’s research. Falling board material often goes to lower value markets such as fencing and pallet production, but Mr Freke’s contention is that this material is some of the better quality material in the log, being stronger, stiffer and clearer than most centre material. He believes potential end uses are flanges for I-beam and metal web beams, bottom cords for attic truss rafter components, ring beams and solid wood panelling.

Civil engineering potential

The BRE’s Tim Reynolds also explored potential markets for timber. Historically, timber has been used as piling material in the UK and is widely used as a civil engineering material in other countries today. Mr Reynolds outlined pile driving trials that had been conducted with Green Piling Ltd, including full scale load tests (to 760kN) on Sitka spruce logs and said that the project also involved a review of the UK’s geology and cost and environmental comparisons.

As Nick Milestone, director of B&K Timber Structures, a trading division of B&K Steelwork Fabrications Ltd, explained, another end use for timber is in hybrid construction. His company’s projects include supermarkets for Tesco, Sainsbury and Asda.

Claiming a “religious conversion” after reading “the good book of wood”, Mr Milestone said his experience was that “all the techniques used in steel frame can be transferred to timber frame”. And, he said, “shape is key – there are things you can do with timber that you can’t do with steel”.

Added benefits, he said, were that the premium for glulam was reducing as steel prices soar, making hybrid steel/timber systems more attractive. “Current demand for glulam is 20,000m³ per year and this is likely to rise,” he said. “We need a UK manufacturer and I believe the next five years will see a resurgence of glulam manufacture in this country,” he added.