Tales from the Test Floor: Glulam Arches

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Researchers here at the Forest Products Laboratory (FPL) wrapped up testing a set of glued laminated (glulam) arches with a bang by breaking the last arch in a series of three. The arches measure 30-feet tall by 30-feet wide. Only ten arches have been tested worldwide.

This experimental work is evaluating the seismic design parameters of glulam arches by simulating the forces of an earthquake and measuring how the arches perform under such stress. The collected data will be analyzed and results published in the near future to serve as a reference for architects and engineers looking to design buildings using glulam arches.

The test took place on the strong floor in FPL’s Engineering Mechanics and Remote Sensing Laboratory (EMRSL). Here, researchers conduct physical and mechanical tests on a wide range of materials, building systems, and structures – from houses to bridges. Results inform the development of building codes and structural design standards.

 

Back to Basics Training on Engineered Wood Products: Free Webinars Begin in April

APA – The Engineered Wood Association is hosting a series of free webinars in April and May 2016 focusing on engineered wood products.

Composit-framingAccording to APA’s website, “Manufacturers, distributors, and builders are all reporting a critical need for training as they rebuild from the recession and hire new employees. New hires often lack knowledge and understanding of engineered wood products, design considerations, and installation recommendations. Even experienced sales personnel can benefit from a refresher. APA’s new, comprehensive training series includes six “back to basics” modules that cover key topics related to I-joists, Rim Board®, laminated veneer lumber, and glulam. This training targets distribution sales staffs who can, in turn, share the knowledge and training with their retail and builder customers.”

Six training modules will be offered as a weekly series beginning Friday, April 8. Modules run between 30-90 minutes. The first four are designed to be completed in sequence with progressively complex content, while the last two can be taken as stand-alone presentations.

For detailed information on the webinars and to register as a participant, visit www.apawood.org/back-to-basics

Better Bridges: Considering Wood-Concrete Construction

The United States is facing an infrastructure crisis. According to the American Road & Transportation Builders Association, over 61,000 bridges in America are structurally deficient. Although expensive to maintain, particularly in these tough economic times, when these vital pieces of our transportation system fail, the human toll is incalculable.

One needs to look no further for a reminder than the 2007 collapse of the Interstate 35 bridge near Minneapolis, Minnesota. The steel truss arch bridge suddenly failed under the load of rush hour traffic, plunging into the Mississippi river below. The bridge had consistently ranked near the bottom of nationwide federal inspection ratings, and its collapse claimed 13 lives. In the disaster’s wake, fearing similar incidents, federal and state governments mobilized to assess the condition of their own bridges.

As states continue to evaluate and improve their transportation infrastructure, researchers at the Forest Products Laboratory (FPL) are working hard envisioning the future of durable and cost-effective bridges. They believe that the answer may lie in wood, one of mankind’s oldest construction materials, used in conjunction with another time-tested material, concrete.

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An example of a composite timber girder–concrete deck bridge

In cooperation with Iowa State University, Research General Engineer Jim Wacker from the Engineering Properties of Wood, Wood Based Materials, and Structures unit at FPL, has set out to investigate the state-of-the-practice related to the use of concrete decks supported by glued-laminated (glulam) timber girders for highway bridge applications. Glulam timber bridges have already proven themselves in our nation’s National Forests, but the practice of using them in conjunction with concrete decks is relatively scarce across the highways of America. The project, which commenced earlier this year, is expected to be finished June 2017.

A composite timber-concrete bridge consists of a concrete slab rigidly connected to supporting timber sections so that the combination functions as a unit. There are two types of composite timber-concrete bridges: T-beam decks and slab decks.

T-beam decks are constructed by casting a concrete deck, which forms the flange of the T, on a glulam beam, which forms the web of the T. Composite slab decks on the other hand are constructed by casting a concrete layer on a continuous base of longitudinal nail-laminated sawn lumber.

Recent research has found that performance of timber bridges constructed 50 to 70 years ago is above average, but despite this, only a small percentage of new bridges built every year are built with graded and engineered lumber. This project hopes to change that.

Composite slab decks have been used as far back as the 1930s, and Wacker’s reassessment of concrete-timber bridge construction will arm bridge engineers with a wealth of knowledge on the best practices of the past — so that bridges of the future can be as cost-effective, durable, and safe as possible.

For more information, please see the FPL Research in Progress publication Investigation of Glulam Girder Bridges with Composite Concrete Decks.

Newest Forest Products Journal Features Adhesives: Many FPL Researchers Present

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Photomicrograph of an adhesive bond of two pieces of wood. The blue areas show the adhesive penetration into the wood structure.

The latest issue (Volume 54, No. 1/2, 2015) of The Forest Products Journal is all about adhesives. Featuring 10 selected articles addressing a theme of efficient use of wood resources in wood adhesive bonding research presented at the 2013 International Conference on Wood Adhesives in Toronto, Canada, we hear from several FPL scientists.

FPL has played an integral role in developing technical understanding of adhesives and setting product and performance standards by organizations such as the ASTM International (formerly American Society for Testing and Materials), American Institute of Timber Construction (AITC), APA–The Engineered Wood Association (APA), and the American Forest and Paper Association (AF&PA).

The first glue development research at the FPL in 1917 was to improve water resistance of the best glues available for manufacture of WWI aircraft components. At that time, FPL began to develop composites in an attempt to conserve our forests and make use of waste wood. Adhesives for housing, other buildings, timber bridges, and other structures has always been important.

In the Introduction to Special Issue: Wood Adhesives: Past, Present, and Future, Team Leader, Wood Adhesives, Forest Biopolymer Science and Engineering, Charles Frihart provides a comprehensive history and explanation of the important role that adhesives have played in the efficient utilization of wood resources.

Speaking about wood products, Frihart says: “Adhesives will continue to be a growing part of efficient utilization of forest resources. However, acquiring suitable wood resources will continue to be a challenge because of a diminished supply of high-quality wood and competition for wood from wood pellet and biorefinery industries. The challenges involve dealing with species that are not currently being used and with a greater mixture of species. More plantation wood could involve increased porosity and lower strength because of increased proportion of earlywood. The wood may also have increased or more variable moisture content as a result of efforts to reduce drying costs.

Wood products volume should continue to increase especially if engineered wood products replace other building materials for multi-story buildings and if there are sufficient housing starts. One challenge could be in bonding wood to other materials if glulam or laminated veneer lumber start using layers of stronger polymers or composites for greater strength. There also might be markets for bonding to modified wood, such as acetylated wood or heat-treated wood.”

Challenges in our changing forests and in changing construction practices will keep Frihart and his team busy for years to come as they find ways to use their adhesive research to adjust to change and best utilize our natural resources.

 

 

Throwback Thursday: Building With Glued Arches

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Laboratory utility building of plywood with glued arches, the first structure of this type in the United States.

The first research at FPL on engineering design data for glued laminated arches was undertaken in 1934, when a number of three-hinged arches were fabricated and installed in what was called Building 2, the packaging research building.

It was no ordinary building—it was built using laminated arches and also included other arches made from wood. The purpose was to provide a useful building but also one in which a visitor could observe different types of arches and see the advantages of design to decrease material and improve aesthetics. It included tests of structural units to check such factors as design formulas and working stresses, and the effect on strength of curvature, scarf joints, and knots in the inner laminations.

Results of this research are presented in United States Department of Agriculture Technical Bulletin 691, The Glued Laminated Wooden Arch, which provides the technical data necessary for the use of laminated arches on a sound basis.

The building suffered a major fire in later years, but when the firefighters learned the building was built with wood beams, they were able to save the structure. In 2010, this building was dismantled and the arches were saved for testing.