By Sun Kim
Posting in Architecture
Designers reconsider wood for taller structures amidst growing ecological concerns of steel and concrete.
If environmentally-minded architects have their way, more mid and high rise buildings will be constructed with wood instead of concrete and steel. An article in CNN's Eco Solutions coverage asks, Can wooden skyscrapers transform concrete jungles?
Architect Michael Green is designing a 30 story building constructed with wood in Vancouver and advocates for more tall wood buildings:
"We think we can go higher than 30 stories," says Green. "We stopped exploring wood around 100 years ago (with the advent of steel and concrete); now we're looking at a whole new system using mass timber products." Green says that the modern wood materials have been around for around 20 years, but until recently they've been quite niche or used only in low-rise buildings. What has changed is the way in which architects and builders are thinking about using wood. "The real change came when we started thinking about climate change. Steel and concrete are great but not environmentally friendly," he says.
The modern wood materials that Green mentions are laminated strand lumber (a composite of wood strands glued together) and cross-laminated timber (layers of wood fused together at right angles to each other). Since the newly developed materials use wood fibers, they eliminate the need for cutting down large trees. Sourcing wood from sustainably managed forests also creates a more environmentally sensitive process.
As for concerns of fire risk, large timbers are naturally fire-resistant and perform better in fire than structural steel. Timbers form an insulating and fireproof layer of char that also protects the structural integrity.
Of course, as Green points out, any building material has to be cost effective to catch on in a big way. His firm's research and designs of tall wood structures (pdf here) are offered for public use via a Creative Commons license.
Image: Michael Green Architects
Mar 19, 2012
Can you imagine being in one of these things burning from the bottom up?! One would hopefully be using 'engineered wood' where flammability had been either 'engineered out' or greatly reduced, otherwise structure like this would be a good candidate for Towering Inferno II or III or ???
Some things I see in this article just do not make sense. Perhaps the article is too short or assumes one has read extensively about these "environmental" issues. First WHY is steel and concrete unacceptable to an environmentalist? Both can be recycled - the steel can be remelted and reformed, the concrete crushed and used as filler or base material (as presently done in several concrete pads, driveways, roads... It is mentioned that "large timbers are naturally fire-resistant" and "Timbers form an insulating and fireproof layer of char" however there is NOTHING natural about these wooden processed products that are intended for this construction use, they are stated to be "a composite of wood strands glued together" or "layers of wood fused together" (I can only assume that some type of binder is still needed). Since these are not natural timbers would not the glue itself be flammable and negate the char effect? Finally the energy cost to manufacture these 'new' timbers. Are they more efficient overall or does the process of stripping the wood to fibers then reforming them add to environmental concerns such as energy usage and use of chemical treatments during the processing?? Looking forward to further discussion to 'clear' the air... so to speak ;)
How resistant to earthquakes are these wood buildings? Modern high-rises in earthquake country have to be able to "give" without toppling over.
The current unofficial record holder is a house in Russia at 13 stories. It is not very pretty. http://sightbywalk.blogspot.com/2010/08/worlds-tallest-wooden-skyscraper-1.html The tallest wooden structure ever built was the Muhlacker antenna built in Germany in 1933 was 190 meters tall. (623 feet) http://en.wikipedia.org/wiki/Transmitter_M%C3%BChlacker
Fire resistance is touched on in the 2nd to last paragraph. These aren't big pieces of natural wood, they're wood fibers & sheets glued together. Fire retardant chemicals would be added at the same time as, or just before, the glue. I thought wood was limited to 3 story buildings. There's no mention, though, of how this compares to steel frame construction or reinforced concrete frame construction in cost.
Apologies, there is a fair amount of material on the carbon impacts of steel and concrete on SmartPlanet, so I did assume readers had read previous posts. (If you haven't, I highly recommend it). The evironmental friendliness of wood vs. steel vs. concrete is an ongoing debate, since they each consume energy to source, produce, and manufacture. All the materials have their own advocates (who have their own agendas). As for the manufactured wood products not acting like "natural" timbers, even composite wood will act like large timbers because of mass and size. The binders used are non-flammable.
Properly designed modern wood buildings are much more forgiving (flexible) than either steel or concrete.
It's called fire doors/firewalls my friend. Current fire code addresses this each floor is separated.
The Tall Wood design relies on steel and concrete. Obviously not as much as a traditional high rise, but the floors use concrete topping - 2"+ - and a steel wide flange along the perimeter and back to the core. The charring rate was calculated at 0.65mm / min, or 78mm total depth (3 inches) after 2 hours without intervention. Much of the detailing shows traditional gypsum wallboard sheathing, so it's not all that different from protecting steel structural elements, to overcome the reduction of structural strength of timber, resulting from fire. I can think of many ways that the proposed savings / sf would be diminished, if not entirely used up: 1. Cost of familiarity of construction. Unless this style of construction caught on, everyone from Architect, Engineer to Contractor will find it difficult to design and build without stumbling along the way and incurring high revision costs / delays. 2. IBC and complete test documentation. Without revisions to the IBC, in the US the difficulty will be providing the necessary information and proof of the system, to building code officials. Without complete test documentation from UL and a series of unified means of construction / materials from ASTM and others, the argument from the code official will be: You're asking me to trust you? 3. Software. BIM would require a dedicated Tall Wood library. Someone needs to get the ball rolling on this, if complex high rises are ever to catch on. These aren't insurmountable obstacles, but they will need to be addressed fully, and that will take some time.