CLT PROJECT SPURS NEW EQUIPMENT DESIGN
THE JOHNSON family operates a lumber mill and a glulam plant in the Pacific Northwest region of the US, and wanted to expand their product line to include crosslaminated timbers. They tapped USNR for a solution. The result is a unique modular CLT press that is meeting their needs today, and can be expanded to meet future needs.
The Johnson family has been in the wood products business in Oregon for over 50 years. Valerie Johnson and her sister Jodie Westbrook are secondgeneration owners of the business and are involved in the day-to-day operations.
The company owns and operates three plants. Umpqua Lumber is located at Roseburg. The company’s mainstay, D.R. Johnson, is located at Riddle, where the company was founded in 1951. Riddle Laminators was added on the same site at Riddle in 1967.
The mills produce dimension lumber, structural joists, planks, laminated beams, utility poles (up to 135 feet), and their latest product is cross-laminated timbers, or CLTs. Riddle Laminators was built to manufacture glue-laminated beams. Going forward, both the glulam beams and the cross-laminated timber panels will be produced and sold under the name D.R. Johnson.
While CLT has been produced and used in structural projects in Europe for about 20 years, D.R. Johnson has received the first U.S. certification to manufacture the panels under a new standard approved last year by the American National Standards Institute (ANSI) (PRG 320-2012). The company’s products were tested and certified by the Engineered Wood Association (APA).
Revolutionising the use of timber in construction
“This is not merely a new engineered composite panel product,” Lech Muszynski, a professor in the OSU Department of Wood Science and Engineering, said in a news release. “It’s an entirely new building technology that is revolutionising the use of timber in construction and dramatically cutting the overall time for construction projects.”
The certification paves the way for D.R. Johnson to market its 3-lam, 5-lam, and 7-lam CLT panels to an emerging U.S. wood building market. CLTs are engineered wood panels typically consisting of three, five or seven layers of dimension lumber oriented at right angles to one another and then glued to form structural panels with exceptional strength, dimensional stability and rigidity. The maximum panel size currently produced is 10’ x 24’ x3, 5, or 7 layers.
These panels are components of a construction system commonly referred to as “Mass timber construction,” a revival of building taller buildings with wood, greatly reducing the carbon footprint of the project. These buildings have high seismic resilience, and although it’s counter-intuitive, a better fire resistance than steel. It is also possible to combine CLT with other building materials in a hybrid system.
D.R. Johnson first got involved with CLT in response to a plea for test panels from Thomas Maness, Dean of the College of Forestry and Director of the Oregon Forest Research Laboratory. He had organized an industry meeting in which University researchers, Mass timber architects, and industry producers came together to discuss the market potentials of CLT.
“They put on an amazing presentation to around 40 industry CEOs,” Valerie Johnson remembered. “It was exciting and looked like an amazing opportunity.” The academic research group was looking for industry support to help kick start the production of CLT in the Pacific North West. The researchers just needed some test panels to get the process going.
Having operated a glulam plant for many years, Valerie was confident that her team could figure it out. “Several of our people have PhDs in common sense,” she quipped. Under the keen eye of John Redfield, COO of D.R. Johnson, the company made 15 test panels that were evaluated and tested by APA against specific criteria
including structural performance, design properties, and appearance classifications. A set of standards was issued by ANSI to the industry, and D.R. Johnson received official certification to produce CLT. “It’s a real big deal” Valerie exclaimed, “and the fact that a US manufacturer is a major collaborator makes it a big story.”
Unique machine design
USNR was commissioned to design and manufacture D.R. Johnson’s CLT press. USNR is accustomed to producing presses for the manufacture of OSB, MDF, and plywood, but this is the company’s first press for the manufacture of cross laminated timbers, and it’s a different animal altogether.
But the mill had the cart before the horse. D.R. Johnson was getting ready to break ground in Riddle, and USNR had already begun manufacturing the press plates when somebody suggested that John Redfield take a team to Europe to investigate the processes of a more mature market. They took the trip and confirmed the European presses looked a lot like USNR’s design. But there are some key differences.
One difference is the use of compressed air instead of hydraulics. USNR’s CLT press uses pneumatic pressure to produce 10’ wide CLT panels up to 24’ long and 10.5” thick. The panels are assembled using between three to seven layers of cross-laid timbers. Adhesive is applied between the layers prior to the panel entering the press.
This press follows a “window frame” design consisting of 16 identical steel frames spaced 18” apart, with each frame having an opening (or “window”) which allows CLT panels to pass through the press. Once the panel has been fed into the press via a set of pop-up rolls, it comes to rest on platens within the press opening.
A set of pneumatic cylinders then applies pressure from the sides to ensure minimal gap between timbers within a given layer. Meanwhile, a set of channels carrying 8 large diameter pneumatic hoses is lowered to rest on top of the CLT panel. Once the panel is configured correctly within the window of the press, the 8 hoses are brought to pressure (typically to 100 psi, though it’s capable of delivering up to 150 psi of pressure). Press time depends largely on the time it takes to lay-up the panel, with a ratio of approximately 2.5:1 (press time to layup time).
The unique curvature of USNR’s press opening allows it to redistribute stress and withstand the tremendous pressures required to produce APA-certified CLT panels. While most CLT presses utilize hydraulic cylinders to achieve the necessary pressures, the USNR press applies pressure pneumatically instead, thanks to a heavy-duty hose which takes advantage of recent material advancements in the oil and gas industry.
This method is robust, extremely cost-effective, and more environmentally friendly than the hydraulic alternative. An additional advantage to the USNR design is its modularity – although the press is currently configured to produce 24’ panels, it could easily be modified to any desired length by simply adding or removing window frame segments.
“The real genius of USNR’s design is putting the window frames in 18-inch increments,” Valerie said. USNR’s modular press design enables it to be expanded infinitely along its length, giving D.R. Johnson the flexibility to grow their press.
“If USNR had not come up with that, I don’t know if we would have ever pulled the trigger because we didn’t know exactly what we needed at the time,” she remembered. “We started out wanting to make an 8 x 16’ panel, then it went up to 10 x 16’, and over time we finally settled on 10 x 24’. The fact that USNR designed it with frames that could be added in a modular way is sheer genius. It was the answer for us.” Laura Meeker, USNR Mechanical Engineer on the project explained, “The modularity evolved from the fact that the project began with a smaller press, and when we realized they needed a bigger press, it seemed like a natural solution.”
The outlook is bright for D.R Johnson’s CLT product with several jobs in the pipeline. “The market fo r CLT is growing,” said Valerie. “We are either under contract or in design conversations for over a dozen projects along the West Coast. Demand is there, and we expect other manufacturers to enter the market soon. Competition would give the market more confidence and it would make more supply available.”
D.R. Johnson is currently manufacturing CLT panels for the Richard Woodcock Education Centre at Western Oregon University. Western Oregon University was the first project to contract with D.R. Johnson and provided the momentum to build the CLT plant and press. The company is also manufacturing CLT for a mixeduse building in North Portland being developed by the Albina Yard Project.
In addition to those projects, the company is in design consultations with many other West Coast developers. Combined, the contracted work and project pipeline represents nearly a half-million square feet of CLT panels that may require adding an additional labor shift for the Riddle plant.
“Response to the product has been very positive,” Valerie said. “This reaction from the market is showing there are projects ready to design with CLTs. Having a source now where the product can be bought will help build the market for it.”
Valerie said the panels can be delivered to construction sites with windows and doors pre-cut. She also noted the company will be installing a Hundegger 5-axis CNC computeraided panel fabricator early this year. That addition will provide the ability to customize each CLT panel with precise routing and cutting based on the project’s computer-aided design (CAD) files, which can include electrical and plumbing.
The customization of panels to precise specifications will further reduce construction timelines and costs. D.R. Johnson expects the market to require this level of prefabrication because there isn’t an economical way to move these panels around on the jobsite to do this work. A 10 x 24’ panel of 5-ply weighs almost 5,000 lbs.
How does it compare?
One of the biggest ways CLT beats concrete, steel and other alternatives is that it assembles like a Lego set. The material is lighter and easier to handle. In addition, there are a lot less trades on a CLT jobsite compared to those using materials that require a variety of expensive tradesmen. CLT doesn’t require the skilled manpower or the time. It can basically be constructed with a crane operator and someone to handle a screw gun.
But it puts a lot of pressure on the mill to get the staging and delivery right. If you can imagine a 4-storey building constructed with CLT, they will literally have to keep track of where every panel goes in the construction process. The first truck that leaves the mill should have the first panel needed on the top of the load. It has to be sequenced exactly so they can lift that panel off the truck and put it right into place. They don’t want to be stacking them on the jobsite.
Promotional materials on the CLT panels emphasize that the product reduces the carbon footprint of a project, has high seismic resilience and comparable fire resistance to steel. Fire is a major concern, and one reason no doubt, that codes have limited the height of wooden structures. But solid CLT panels do not ignite as easily as 2 x 4s. Even if panels do burn, charring on the outside protects the interior wood, leaving the panel structurally sound. Finishing the panels with wallboard or another material further improves fire protection.
In Europe, cross-laminated timber has been around long enough that standards for fire protection and acoustics are being incorporated into building codes. In North America, a more basic understanding of the product is needed first.
Valerie says that contractors are currently familiarizing themselves with cross-laminated timbers. Building with CLT panels brings a learning curve that requires adjustments to the traditional bidding process and building methods, since the installation process is as new as the product itself. Valerie suggests that academics and government officials arrange classes and seminars where contractors, engineers and architects can learn how to work with CLT.
“There were a number of things that fell into place for us to make this a reality,” Valerie said, “but without USNR we’d be nowhere yet.”
The new CLT press at D.R. Johnson uses a modular window frame design that can be expanded to accommodate the needs of the market.
*A glulam beam at D.R. Johnson under compression. The company uses a USNR Mann Russell RF Gluing machine to cure the glue in large beams and finger-joint stock.
Laura Meeker (left), USNR Mechanical Engineer and Valerie Johnson, President of D.R. Johnson stand by a 5-ply CLT panel produced on the mills’ new press.
A worker manually lays up a 5-ply CLT panel just prior to loading in the press. The panel consists of dimension lumber oriented at right angles to each other and then glued to form structural panels with exceptional strength, dimensional stability, and rigidity. Update: DR Johnson has since installed a lay-up machine to automate the lay-up process. This increases production capacity, allowing the plant to meet increasing market potential.
Close-up of a 5-ply CLT panel. A 10 x 24’ panel of 5-ply weighs almost 5,000 lbs.
The 5-ply CLT panel being cured in the USNR press.