Recent fire test is a win for cross laminated timber
Portlands showcase of cross-laminated timber, the 12 story Framework building due to rise in the Pearl District at 430 N.W. 10th Ave. has passed a major milestone.
The wood recently passed tests to prove that it could be in a fire for two hours and not burn so much that it would lose its structural integrity. Two hours is the time a high rise must maintain structural integrity. It is also considered adequate time to evacuate a burning building.
The test was of a mass timber assembly using Cross-laminated Timber (CLT) and Glue-laminated timber (glulam), with steel brackets holding them together. Both floor panels and posts/beams were tested.
Although the architects and engineers at Lever and KPFF knew the wood would survive a fire, it had to be tested to be approved by the State of Oregons building code.
Tall wood buildings using CLT and glulam have already been permitted in Europe, Australia, and Canada.
The results were announced during a Spotlight on Design talk at the National Building Museum Timber City exhibition in Washington, D.C. by architect Thomas Robinson, Principal at Lever Architecture.
A year ago Lever has just received its grant to find the testing and staff were optimistic. The tests were made possible by a $1.5 million grant from the USDA, Softwood Lumber Board, and Binational Softwood Lumber Council as part of the 2014 U.S. Tall Wood Building Prize Competition.
The real estate developer, Anyeley Hallova, a partner at Project^ said Framework Could create a model for future CLT projects.
They had to show they had support from Oregon and Portland, show the team had the technical expertise to work with mass timber (the architect, KPFF engineers and Walsh Construction) and that there was a big idea behind the project.
The teams had to have an idea of the processes in which the project could catalyze Oregon rural economic development.
The two-hour fire rating achieved for the project glulam beam to glulam column connection is a fundamental breakthrough in mass timber construction, exceeding results conducted anywhere in the world, said Robinson. Combined with the two-hour fire rating achieved for the cross laminated timber floors, this construction system allows mass timber to be used for high-rise construction, with some of the timber exposed.
In previous CLT projects, the structural frame of timber has been concealed under layers of fire-resistant gypsum board.
The Framework Project, LLC, as its known, conducted tests on local Oregon CLT from DR Johnson Wood Innovations in Riddle, Oregon, to confirm the feasibility of sourcing wood from nearby sources, fulfilling the USDA grant mission to leverage. It also tested wood products from other suppliers..
Jonathan Heppner, Project Manager for Framework with Lever Architecture, observed the tests over two days. They were done using a gas oven which he said was about 8 x 4 x 6 feet. The assembly was tested in a full load scenario. It was put under 24,000 pounds of pressure from an actuator to simulate the load it would bear in a building over 75 feet tall.
Weve been preparing for a long time, he said. The first round of tests was in July, and had successful results. The second round was this month.
Between the two they fine-tuned the thickness of the wood member, and also the way the steel bucket, metal screws and hangers connected to the wood (they contributed to the charring).
Heppner says it wont affect the construction schedule. They have planned for success and expect the building to open in early 2018.
Thermocouples were placed at different points in the assembly to read temperature change.
Actual flames lick around the wood in the furnace, and fans circulated the air, feeding and modulating the fire. It followed the ASTM E119 fire test standard over two hours, based on how a real fire would behave. The heat ramps up fairly quickly then plateaus. Scientists can watch on camera, and also see screens full of graphs.
Not only did the dense wood retain its strength after burning for two hours, it proved a very good insulator.
The fire was between 1,700 and 1,900 Fahrenheit, and the floor slab is seven inches thick with two inches of gypcrete. Well the temperature was just 95 F on top, thats like body temperature.
The team is working with more suppliers than just DR Johnson Wood Innovations. It is considered practical to source materials from different locations, as a way of hedging bets to make sure the project has all it needs at the right price and time.
They have also been fine-tuning the species of wood which is pressed into giant woven panels, varying between spruce in some regions and Douglas Fir in Oregon.
Exposed wood in high rise buildings doesnt exist in the US, Heppner adds, talking of structural lumber. (People who work in buildings with exposed structural lumber are likely in buildings where the last occupiable floor is less than 75 feet from the ground.)
The design of Framework deliberately shows off the connections between the beams, columns and floor panels, as an advertisement for itself.
The International Building code may make changes in 2018 based on the work going on at Lever. Mass timber could be taken way more seriously.
Heppner said the Framework building is using an earthquake resistant design which was informed by this decades earthquakes in New Zealand, and Japan.
The core of the building is solid wood and has the capacity to rebound where concrete would be damaged or crushed. Steel rods act as rubber bands to bring the building envelope back into position after the shaking.
CLT construction has the advantage of being fast and not too noisy. Heppner has seen CLT floor panels craned into position in a morning. At Albina the floors could be placed in a morning. It would take a week or so between floors to set the columns and beams.
I think the neighbors will appreciate it, the construction is so quiet, he said.
CLT construction started 20 years ago in Switzerland and was developed in Austria and Germany. Its big in London, where it earns owners carbon credits. It is also good for building where time and space are limited prefab construction means you can add one floor per day. According to naturallywood.com, the nine-story Murray Grove residential tower was erected in just nine weeks using CLT panels about four months less than conventional on-site concrete construction. Its growing in Vancouver, B.C., where they also make the timber. The University of British Columbia has an eight-story Bioenergy Research and Demonstration Project with CLT walls and roof construction off of a concrete foundation.
Frameworks building design passed Design Review approvals from the City of Portland in July 2016. Construction is planned to begin in March 2017 and be completed by March 2018. Framework is slated to be the first and tallest mass timber high rise in the U.S.
According to Lever Architecture, as a condition of the Tall Wood Building grant, the test results will be made public, thus reducing the financial burden on mass timber projects to carry out their own tests and accelerating the adoption of CLT in the building industry.