 Do you cross a bridge in your daily travels? If so, you should know you've got a 40% chance to be on a bridge, rated deficient. Now that doesn't mean it's about to fall down, but that it cannot handle current traffic because of width, height, or lane restrictions, or is restricted to reduced vehicle weights, or is simply closed. Even with massive efforts by federal, state, and local agencies, the number of bridges identified as deficient continues to grow, as they continue to age and wear, subject to traffic volume and vehicle weight never anticipated when they were designed. In other words, they're being identified faster than they can be fixed. And even when they are fixed, it's not the most popular activity with the motoring public. What can be done? How can available money, personnel, and time be stretched to meet the problem? This program is about something that's being done. By taking the steps from theory to traffic, by stepping back to go forward, by researching, designing, fabricating, and erecting modern timber bridges. That's right, wooden bridges. Not the terrorist idea of a wooden bridge, but a modern, unrestricted structure like this, or this. Did you know there are over 70,000 timber bridges nationwide that the U.S. Forest Service alone maintains about 12,000 of these bridges, adding 100 to 250 bridges annually. That modern timber bridges can have lower costs than conventional bridges. Or that they can be installed by small local construction firms or the municipal employees themselves. Or they can be erected in less time, reducing public inconvenience. To prove the feasibility of modern timber bridges, the Pennsylvania Department of Transportation embarked on a demonstration timber bridge program. Construction began with a 48-foot two-lane bridge in College Township, Pennsylvania. This stressed timber bridge was built of western Douglas fir. And while satisfactory, it did not address one of the top priorities of Pennsylvania Governor Robert Casey. Better utilization of the hardwood resources in the Commonwealth. Hardwood, traditionally used as furniture veneer, is an abundant, renewable resource. In fact, the states in the northeast, to produce most of the nation's oak, maple, and poplar, are growing twice as much timber as is being harvested. This is a raw material in abundant supply. Pendot was instrumental in the design and construction of a timber bridge with a hardwood steel composite deck. And then, went to what many feel could be the design for modern timber bridges. Glue laminated hardwoods. Glue laminated, usually referred to as glue lamp. A familiar example is the kitchen butcher block, constructed of thin strips of wood, sometimes of varying shades, and glued together. This glue lamp design seemed to answer the needs for producing a bridge from a renewable resource, hardwoods, and making it of such a design that it could be constructed by local forces. The entire project went through many stages. Many of these activities occurred simultaneously, so it will be easier to look at each part of the project as a single piece and then to bring them together when we build our bridge, when we have actually progressed from theory to tracking. View the program as if you were considering the installation of a modern timber bridge, asking, what do I get? Let's begin with design. Bridge design was the task of Gwen Dobson and Forman Incorporated. This was to be the first red oak glue lamp bridge designed for highway use. And it was to be a demonstration bridge, not an experimental bridge. As such, it had to have capacity. The final product was to have no weight restriction, competitive cost, an overall dollar value that helped to stretch local budgets, and construction methods that promoted the use of small construction firms or municipal employees. Listen to Richard Hughes, the design engineer, as he describes the process. The Department of Transportation along with Penn State University and Gwen Dobson and Forman searched Central Pennsylvania to find an ideal site for the implementation of a glue laminated hardwood bridge. After looking at several sites, we settled on one that was very close and proximity to the university and to Gwen Dobson and Forman's office so that monitoring could occur with ease. The location that we picked was in Ferguson Township in Center County. The bridge is located in the community of Baileyville, just off of Route 45 in Center County. The structure was a existing bridge of 40-foot span, two-lane structure, had a low volume of traffic across it. It was a township road. It was ideal bridge for what we were trying to achieve. The existing bridge was a reinforced concrete single span bridge that had deteriorated due to attack from salts. The bridge was approximately 50 years old with stone abutments. We recommended coming into that site with a single span, red oak, glue laminated hardwood bridge, two-lane structure. We approved the alignment a little bit. We maintained the same hydraulic opening, and at the same time we economically came back with a structure that was very competitive to the only other alternative they would have, which would be a steel or concrete superstructure. We took our standards that we were developing for PennDOT and put it into a package that consists of 15 sheets. And the 15 sheets basically gives any engineering firm a standard to follow. Now, we have designed these bridges up to 90-foot spans. So we know that this type of bridge concept will work up to 90-foot spans. We also know that it's competitive versus steel and concrete structures of similar spans and sizes. And that's the intent. We want to make these structures competitive price-wise. We want to ensure our clients that the bridges will last approximately 40 years, like any other structure that might be on the market. And at the same time, it's durable. The agricultural engineers and wood scientists at Penn State University focused their research efforts on assuring the quality of the glue-laminated hardwood components. The industrial adhesive, the glue, was selected by the Penn State research team and InSpec Incorporated at Pittsburgh, Pennsylvania, a national leader in industrial adhesive production. Since the fabricated bridge parts were made of individual laminates, which had been made by joining random-length boards together, the adhesive had to be at least as strong as the wood itself. Shear block tests were conducted to measure the efficiency of the adhesive, as well as the efficiency of the finger joints. Actual test readings were well over the required strengths. The usual quality assurance process for wood relies on what is termed VSR, Visual Stress Rated. An experienced lumber grater can sort wood by visual characteristics known to influence its behavior. Knots, decay, slope of grain, density are just some of the items rapidly and efficiently evaluated. So efficient that a professional grater will have less than one out of 800 pieces misidentified. The red oak lumber was visually graded using this VSR method by the Penn State research team. But with the bridge design calling for bridge beams 35 feet in length and deck panels 28 feet long, a more scientific testing method had to be used. The overall objectives of that project include development of methods for gluing, structurally gluing Pennsylvania hardwoods, methods for preservative treating those hardwoods so that they don't rot when they're exposed to the elements in bridge applications and also for developing the allowable stresses that designers can use when they're designing hardwood glue laminated bridges in the field. The Penn State research team conducted the testing in accordance with the American Society of Testing Materials. The goal was to determine the strength of the red oak glue lam beam and to compare results for the untreated beam as well as the preservative treated beam. The load, the failure did occur in the vicinity or right at the location of the load point and it appears it was a tensile failure that initiated in this region and then traveled once it started to fail there it traveled back through that lamination. The failure occurred in the wood rather than in the glue line and that is important and that is critical. Over 100 beams were successfully broken by the Penn State research team. Their data confirmed that treated and untreated glue laminated northern red oak is a viable construction material. Unlike softwoods, most hardwood lumber is not generally available in standard dimension sizes. You've got to go to the source. And the members of the Penn State research team were able to procure the needed red oak from the nearby state correctional institution at Rockview, Pennsylvania. The research team supervised the selection of approximately 26,000 board feet. The trees were felled, trimmed, and taken from the forested area of the institution to an on-site sawmill. Here the red oak was rough cut, trimmed into board lengths, and once the rough cutting was finished the red oak was moved to a pre-drying facility in Lewisburg, Pennsylvania. Before the bridge components could be fabricated the moisture content of the wood had to be reduced. The wood had to be dried. This was done by allowing the cut boards to dry to a predetermined moisture content of 12% plus or minus 2%. This design value took into consideration the timber. Once assembled in place over the stream would ultimately reach a moisture content of approximately 19%. Once the wood reaches the initial dry level the boards were ready for shipment to the fabricator. UNIDILA laminated products, Sydney, New York, was the nearest plant certified by the American Institute of Timber Construction. UNIDILA was experienced in softwood timber bridge construction and willing and able to use their expertise in fabricating the first Lulam hardwood bridge designed for highway use. UNIDILA's fabricated products go beyond bridges. They are a major manufacturer of structural support beams. These arch beams are used extensively in the construction of churches, youth clubs, anywhere the architect wants an open, uncluttered interior design. To underscore UNIDILA's faith in their product the main support beam in the plant is a Lulam softwood construction. Normally lumber received at the plant is graded. Marked for trimming with a graphite marker the trimming machine will sense and separated by grade, banded and moved to a storage area. But the red oak for the Ferguson bridge had already been graded, trimmed, separated and stored. As part of the research project each board that had been selected as part of a bridge beam was tested for stiffness what the researchers term MOE Modulus of Elasticity. These values were used to determine in theory how much each beam would bend that is deflect under a live traffic load. These values were to be used as comparison against the actual values to be obtained when the finished bridge was tested. There were a lot of volts. The actual fabrication of the individual laminates into beams or deck pieces begins here. The boards are loaded into this turntable conveyor. The turntable positions the board against a locking plate and is finger jointed and encoded with the industrial adhesive, the glue, at both ends. Move to a conveyor belt where the individual pieces are joined. Note how easily. Then to cure the end joints, moved again along the conveyor under a radio frequency dryer, what the plant personnel called a microwave for wood. And then the boards are cut into the ordered lengths. The boards are then fed into a planer. The planer has three sixteenth inch exposed cutting edges and is programmed to reduce the eight and one half inch to nine inch entry width to an eight inch width at exit. With the surface spoil and dirt removed and the board clean, the chance for successful adhesion is increased immeasurably. The board then moves into the gluer. The glue is an especially formulated alcohol based product. Then to the assembly area where the individual pieces are formed into a unit. The individual laminates are stacked against a form wall. There is a window of time of up to 40 minutes where the adhesive works best. So there is a concertive effort to move this process along. Tension bars are attached, tightened, and retained in that position until the form pieces are ready to have the tension bars removed and moved to the finishing area. Where it emerges is a smooth finished piece. All required drilling was done, the product was checked again and then ready for shipment. While the bridge being constructed is a modern timber bridge, the construction process is very similar to that of a conventional steel or concrete bridge, especially in the early stages. The bridge site is on a local collector road with a posted 40 mile per hour speed limit and an average daily traffic of 200. The old bridge was a 44 year old reinforced concrete T-beam with a 12 ton rating. The required traffic control was established and the old bridge was removed. The existing stone abutments were kept. This has been a common approach for the demonstration bridge project. While the old bridges themselves are in need of replacement, the abutments have usually proved to be usable with only minor repairs. This is a significant cost savings. A front end loader was placed in the stream within a copper dam made of a line of sandbags to contain any disturbed sediment. The loaders smooth the area in preparation for the placement of the riprap. The loader got into and out of the stream with the aid of this small crane. Rural bridge construction means small work areas. You'll find you cannot get along without the crane. The loader was removed. The sediment disturbed by the loader was pumped into a holding basin. The riprap was started and placed stone by stone. Repairs on the old abutments consisted of burring off the ends of the embedded pins using mortar to bring the abutment level and checking that it was. Next the construction of the gabion baskets opened mesh wire baskets filled with aggregate. While gabions have been around a long time this is fairly new. Geotextile fabrics have long been used on larger construction projects but now they are becoming quite common on smaller ones. The baskets were placed and joined together and filled. The bridge beams arrived. After their departure from the fabricating plant at Unadilla the bridge components had been shipped to Coppers Incorporated of Muncie, Pennsylvania for treatment with the commercial preservative. All of the wood was treated to a minimum penetration depth of 0.25 inches. The beams were removed from the truck and set to the side. The bridge design called for the beams to be anchored to the abutments with a galvanized steel plate. Construction plans had the plate first secured to the abutment then the beams seated. But it was found to be easier to first attach the plate to the beam and then attach the beam and plate to the abutment. Once all the beams were seated they were checked for elevation and some minor adjustments were made. Next the plans called for the installation of mid span diaphragms designed to provide lateral stability to the beams. Diaphragm installation required some field drilling. Here and wherever field drilling was done every field drill hole was coated with preservative as were the bolts themselves. Once the mid span diaphragms were installed the end wall diaphragms were next. The end wall diaphragms were critical as the bridge skew was severe a full 45 degrees. The end wall diaphragms were 39.5 feet long and extended the full skew length. Again each piece of galvanized hardware was coated prior to installation. Now the deck. The deck pieces were 6 inches thick in lengths of the 28 feet long. The deck was designed as a non-interconnected deck. However one half of the deck was constructed with one and one quarter inch diameter dowels. This was done so that PENDOT could observe the performance differences if any between the interconnected panels and the non-interconnected panels. Heavy duty felt was placed on the end wall diaphragms and on the beams. Again the crane proved its worth as the deck panels were swung out and placed into position. All pre-drilled and field-drilled holes were filled with preservative. The bolts were coated and tightened. This continued until the deck was in place. Spacing of one half inch between the deck panels was left to allow for the anticipated expansion due to moisture absorption. These one half inch openings were filled with oakum to prevent the asphalt paving material filling the space. Once the deck panels were placed the only remaining timber work was the guide rails. The design called for ten inch by twelve inch glue laminated posts spaced six feet on center. Six inch by eight inch glue laminated rails and a ten inch by twelve inch glue laminated curb. With full length the geotextile membrane between the guide rail system and the deck. As with the deck the holes and the bolts were coated prior to insertion. As the guide rail work was being completed material was being placed for final grading. Conventional concrete wing walls were installed in the area prepared for the asphalt paving. The bridge project had a couple of interested bystanders and as it turned out they had influence. The grass seed used had to be of a type that would not adversely affect them. While construction methods differed common to all of PennDOT's demonstration bridge projects is the live load test. Research at Penn State predicted the live load deflection values. Those figures were further checked by the testing of the individual boards prior to fabrication. Now the research team had to find out how the bridge would actually perform. Previously identified measuring points were selected and marked. The test used two tri-axle trucks loaded at over 70,000 pounds each. Each truck was weighed and scale readings were taken and recorded for each bearing axle. Measurements were taken with the bridge unloaded with one truck in position A, position B, and with both trucks on the bridge and again with the bridge unloaded. Predicted live load deflection was 0.85 inches. Actual live load deflection was 0.55 inches. The total cost of the bridge including design and construction was $250,000 and that will decrease significantly when standard designs and specifications are available in 1993. The bridge was built successfully by a small local construction firm using a minimum of specialized equipment. The notice to proceed was given on September 6, 1991. The bridge was opened to traffic November 1, 1991, just eight weeks later. So what do you get with a modern timber bridge? From the guy who built one and working with small contractors and doing municipality work which would be very important to the economy because we can do small bridges like this at low cost. And the man who bought one? We believe that this timber bridge will provide an alternative to traditional concrete bridge construction and should be more economical than the traditional concrete bridge construction. Maybe it is time for the construction business to stop talking about the thousands of yards of concrete and the miles of steel and look at a neglected renewable resource. Trees make timber. Timber can make bridges.