Category Archives: Steel

Impact of Water and Climate When Talking About CLT

Cross-Laminated Timber (CLT) is the trendy new building material that has received a lot of attention in the northwest this year.  It is by definition a series of thick boards (usually 2×4 or 2×6) glued together in an alternating pattern and Cross-to form a solid wall, post or beam. (A similar concept is glue laminated (glue lam) timber that has been used for beam construction for many years.)

To understand how water affects wood construction, one must understand its function in a tree. Wood is designed to provide structural support for the tree, move water from roots to leaves and store the chemical results of photosynthesis (primarily sugars in the form of cellulose). These properties of wood create some challenges for its longevity when exposed to moisture.  Thus, while wood can be structurally strong, it naturally absorbs and retains water.

Depending on climatic conditions, it can take some time for CLT panels to fully dry after getting wet. So, moisture control is of utmost importance when building from wood, such as cross-laminated timber.

The first source of moisture concern is during manufacturing. While manufacturers try to have all of their boards have the same moisture content, wood is an organic material and each board reacts to moisture differently. Some take water in more quickly and some take longer to dry. The result is that boards swell and shrink at differing rates which can affect the performance of a CLT panel.

Think of the hardwood floors in older buildings where the floor buckles in places. That is what happens when one board expands against another. As the wood dries again, it shrinks. This expansion and contraction process can damage the wood causing new cracks and gaps. On a floor, one can just refinish it. But, CLT is an integrated structural component and any deformity can weaken its life-safety purposes.

Another source of moisture is environmental moisture during construction. Studies indicate that construction moisture wetting is a serious problem in rainy climates like the Pacific Northwest. It can take several years for the wood to fully dry after construction. With rainfall likely in any month of the year, it is vital that proper precautions be taken to prevent the wood from getting and staying wet.

It is not just rainfall that is a concern. Other sources of moisture must also be accounted for, such as sprinklers, groundwater, pressure washing of siding, sidewalks, driveways, etc. decorative ponds, swimming pools, or other sources of moisture.

Wet CLT panels built with wrappings that do not allow vapor to pass through (both interior and exterior) are much more likely to develop bio-deterioration. There are vapor permeable wrapping on the market that can mitigate this concern to some extent.

Exterior cladding also plays a significant role in preventing moisture penetration. Not long ago, there were significant problems with wood frame buildings experience the negative effects of prolonged moisture, especially condominiums. The resulting lawsuits bankrupted many developers and contractors. With CLT, the stakes are even higher. With wood frame, the walls can be exposed, dried and cleaned. Since CLT is a structural system, that process is much more difficult and expensive.

In comparison, concrete, masonry and block all dry very quickly when wetted. Any remaining moisture can be removed easily (similar to using your shop-vac and a floor-squeegee in your garage after a big rain). Thus, construction moisture is of much less concern. And, there is no concern with rot with concrete, masonry and block construction.

One solution is to cover the CLT panels during construction until they are clad with the exterior components (be it siding, brick or stone). This is complicated, expensive and time consuming. Thus, covering panels during construction can undermine the presumed time and cost savings of CLT construction.

Another possible solution is to install water and air barrier membranes when the panels are manufactured. To date, no manufacturer is doing this, presumably because it would be cost prohibitive.

Certainly, more research needs to be done before the public can be assured of the safety and environmental impacts of cross-laminated timber panels used in construction. Also, new additional building code standards and construction practices would need to be developed to mitigate the health, life-safety and structural concerns posed by our wet climate on CLT buildings.  Current building codes allow wood structures to be built up to five stories. The talk is some would like to go up to as many as 20 stories with CLT.

The risk of fire in a wood building has historically been the primary concern with high-rise wood construction, but, water and climatic conditions can have an equally and perhaps more insidious impact on the construction.

CLT may have the potential to be a sustainable building product that lowers the carbon impact of building.  But so do proven products like concrete, steel and masonry.

While fire is an immediate and known risk, water’s impact is subtler, but no less threatening. This is particularly true in the Northwest from the Pacific Coast to the Cascades.

Check out what’s happening in the local construction scene

VWDealershipUDistrict

 

The DJC has published its annual Construction & Equipment special section. It’s a mix of industry articles, profiles of local award-winning projects and a few interviews with the contractors who make it all happen.

Read all about it at www.djc.com/special/construct2015

 

China aims for world’s tallest building — in 90 days

Chinese company Broad Sustainable Building Corp. erects buildings on ridiculously short time frames: It built a low-rise office in nine days earlier this year and a 30-story hotel in 15 days last year.

How do you top that? You build the world’s tallest building in 90 days — duh.

In early 2013, Broad will start building Sky City in the city of Changsha in the Hunan province. At 2,749 feet tall, it will be nearly 33 feet taller than the Burj Khalifa, the current height champion.

Sky City is a fitting name: The building will have apartments for more than 30,000 people, schools, a hospital and more than a dozen helipads.

But, what will be sacrificed by using pre-fab components to construct the world’s tallest building in record time? In a word: style.

Sky City looks like a massive block built from Legos. In contrast, the Burj Khalifa resembles a giant stalagmite reaching for the stratosphere.

More interesting architecture can be found in some of China’s other skyscrapers: the 2,073-foot-tall Shanghai Tower (under construction), the 1,667-foot-tall Taipei 101 and the 1,476-foot-tall Nanjing Greenland Financial Complex.

Sky City

Burj Khalifa

Shanghai Tower

Taipei 101

Nanjing Greenland

Watch a 30-story hotel get built in 15 days

 

The Chinese are at it again. Last year, they built a 15-story hotel in 6 days. Now, the Broad Group has built a 30-story hotel in 15 days.

A big question that immediately pops up: “Is the building safe?” Well, Broad Group claims it can withstand a 9 magnitude earthquake and is 5 times more quake resistant than traditional buildings, thanks to a unique diagonal steel bracing system.

It also is 5 times more efficient than a traditional building, with 4-pane windows, exterior solar shading and interior window insulators. Building air is 20 times purer, thanks to a heat recovery system with 3-stage filtration.

Pretty cool stuff.

 

http://www.youtube.com/watch?v=t2Tz86YBLOM

Check out “tool library” coming to West Seattle

How many times have bought a special tool, only to use it once? Or, maybe you can’t afford a garage full of tools or don’t have space for them. Well, along comes a really cool idea — a tool library.

Folks at Sustainable West Seattle have been working for months on how to pull that off. Now, with the help of a $20,000  Seattle Department of Neighborhoods’ Neighborhood Matching Fund and other donations, the West Seattle Tool Library is slated to open on June 12 at South Seattle Community College.

The library will be more than a place to check out tools, it will offer classes and provide information on tool usage.

“So far we’ve partnered with organizations such as the West Seattle Nursery and Community Harvest of South Seattle, and have gathered tools from generous donors throughout West Seattle. Our biggest tool drive was held on May 8 at the West Seattle Community Garage Sale, which put our number of tools up over 300,” said coordinator Patrick Dunn of Sustainable West Seattle in a press release. “We’d like to encourage everyone to come out and join in the effort to provide community resources for West Seattle.”

The next tool drive will be held on June 5 at the Refresh Southwest festival. Tools can also be donated at the West Seattle Farmers’ Market and at South Seattle Community College. The library will be located at the college’s Garden Center, which is on the north end of campus at 6000 16th Ave. S.W.

Organizers are still looking for more tools (not gas-powered) and have put together a “wish list” that includes clamps, a pressure washer, portable table saw, portable planer, wet vacuum, wheelbarrows and more. Check out the full list: Tool Library Wish List.

Pincer on prices?

For public and private owners, an upside to the downturn is that dollars are buying more construction.  For example, in recognition of the favorable bidding climate, on May 5 Governor Gregoire certified changes to 12 project budgets that will make nearly $900,000 available for other projects.  More projects, more work for contractors and their employees, more infrastructure built. But, are contractors headed into a “pincer movement” of lower project prices combined with higher material costs?  AGC of America thinks so.

First, regarding prices for the construction inputs:  AGC economist Ken Simonson noted that compared to March, the April data shows that diesel fuel was up 6.5 percent (not seasonally adjusted), steel mill products were up 5.2 percent, lumber and plywood were up 4.7 percent, copper and brass mill shapes were up 4.3 percent, aluminum mill shapes were up 3.6 percent and gypsum products were up 2.4 percent.  Over the past year, increases in materials costs by structure type have ranged from 3.9 percent for single-unit residential construction to 8.3 percent for inputs to highway and street construction.

Second, regarding the producer price index for finished nonresidential buildings, reflecting what contractors would bid to construct a new building:  This was little changed for the month and down significantly from a year earlier.  Prices for new office buildings fell 0.1 percent from March and 4.3 percent from April 2009.  The index for new industrial buildings was unchanged from a month ago but down 4.0 percent from the year before. The index for new warehouses was up 0.2 percent for the month but down 4.6 percent over 12 months, and the index for new schools was up 0.7 percent in one month but down 1.5 percent over 12 months.

These are national stats.  Is this what people are seeing in this region?  If nothing else, this data should encourage owners to get more work on the streets now!