Project contacts are James Wacker at the Forest Products Laboratory, Justin Dahlberg and Brent Phares at Iowa State University
The use of cross-laminated timber (CLT) has gained popularity over the past decade, with many advances stemming from completed research and construction projects in Europe. Many inherent advantages of CLT (such as, it is prefabricated, relatively lightweight, dimensionally stable, and environmentally sustainable) have been utilized in vertical construction projects. Despite these advances, the use of CLT in bridge structures has been limited, and the adoption of CLT into governing design codes has been slow. However, CLT shows promise as a complementary or alternative construction material in bridge decks, and additional research would help characterize the structural attributes of CLT decks to guide their use in bridge projects.
IOP Conference Series: Materials Science and Engineering
The timber bridge design although economical, often has difficulty producing enough rigidity so that a solution is needed to solve it. The use of CFRP (Carbon Fiber Reinforced Polymer) as a reinforcement of structural elements if properly designed and implemented can produce an effective and efficient composite structure. The experimental study aims to analyse the strength, stiffness and ductility of flexural strengthening composite bridge glued laminated timber beams-concrete plates using CFRP layers. The dimensions of the composite glued laminated timber beams 100/180 mm and concrete plate 75/300 mm with a length of 2,480 mm. The number of specimens is 3 composite glued laminated timber beams-concrete plate consisting of 1 test beam without CFRP reinforcement, 1 test beam with one layer CFRP reinforcement, and 1 test beam with three layer CFRP reinforcement. Experimental testing of flexural loads is done with two load points where each load is placed at 1/3 span length. The test results show that the strength of composite laminated timber beams glued - concrete plates BN; BL-1; BL-2 in a row 81.32; 82.82; 82.69 kN/mm; stiffness in a row 7.51; 8.22; 6.32 kN/mm and successive ductility of 16.67; 28.83; 20.21.
In this study market opportunities for treated glue-laminated (glulam) products were investigated in the industrial wood sector. The main benefits of treated glulam are through-product treatment and the ability to manufacture treated products in shapes and sizes that do not fit into common treating chambers. These attributes provide for very durable and large glulam structures that are appropriate for outdoor use. For these reasons bridges, power poles, and sound abatement barriers were investigated. These are markets where wood has lost market share to or is being challenged by concrete and steel substitutes.
The vehicular bridge market was once heavy to the use of wood. Today wood accounts for only 7% of the number bridges in the US and less than 0.9% of the actual surface area of bridges in place. In interviewing municipalities in Canada it is clear that wood is not the preferred material with many wood bridges being replaced by concrete. Further, none of the municipalities contacted were planning wood bridges. However, wood bridges are still being installed. In the US 0.9% of the bridges installed by area in 2007 were wood. This is good news as wood is holding its market share. Steering clear of high volume or large bridges, local bridges are well suited for wood as they are plentiful, small in scale, and many are in disrepair. If 20% of local bridges were built with wood in Canada this would have equalled approximately $51 million in wood bridge construction in 2007.
Municipalities are much more open to the use of wood for pedestrian bridges and overpasses. Their quick construction and aesthetics are positive attributes in this application. One municipality contacted is planning multiple wood pedestrian bridges in the next five years. However, for the purpose of this market review there is little published information on pedestrian bridges.
Noise abatement barriers are a good high-volume technical fit for treated glulam. Increases in traffic and current road infrastructure improvements will lead to more demand for sound abatement in the future. This market is dominated by concrete, but at a very high price. If treated glulam can give adequate durability and sound performance properties it would be approximately 20% cheaper than concrete. The market for sound barriers in Canada could utilize up to 10 mmbf of wood per year to construct 80 km of barrier. This product can also be marketed as a high-performance acoustic fence for residential markets.
Treated glulam was also considered for utility poles. It is transmission grade poles where glulam would best fit the market as the demand is for longer poles which are more difficult to get in solid wood. This type of pole is where wood is currently being displaced by tubular steel. If glulam poles were used in 25% of the replacement transmission poles per year this could equal 8 mmbf. Light poles or standards are another market to consider. While this is a relatively low volume market glulam light standards are a premium product in European markets.