Received date: June 11, 2018; Accepted date: June 29, 2018; Published date: July 05, 2018.
The use of timber in technologic bridges in Brazil started with the Emerging Timber Bridge Program in the state of São Paulo, Brazil(ETBPSP) and was started in 2001 with the main objective of research and development of new technologies for timber bridge construction. After five years of this program, eleven demonstration timber bridges were constructed in the State of São Paulo. Also, eight composite timber/concrete bridges, one log timber girder bridge with transverse sawn deck, one transverse lumber prestressed timber bridge, and one transverse cellular plywood box prestressed bridge were constructed. A final objective is divulgation of the structural systems in extension courses to municipal engineers and in a complete publication of timber bridge project plans with the different structural systems. This paper describes the goals of the ETBPSP, accomplishments of the program in the first five years, information sheet for each of the bridges, and outlines some obstacles and opportunities.
Most timber bridges in Brazil are not designed and constructed by engineers and builders familiar with timber structures. This lead to expensive, unsafe, and low durability timber bridges. The actual state of degradation of these bridges shows a very negative picture of the use of wood as a structural material. Therefore, it is very important to develop wood technology for the construction and rehabilitation of timber bridges on county and state roads.
If one considers that the São Paulo state road system has 220,000 km of vicinal roads and 0.5 % of bridges, this translates to 2,200 km of bridges. Assuming a span of 10 meters per bridge would mean 111,000 bridges. Recent research conducted by the Laboratory of Madeiras in number of counties in the state showed that for each 1,000 bridges and pedestrian bridges, 30% must be reconstructed or rehabilitated. Since São Paulo State doesn’t have native wood species, the use of reforested species is a natural solution. In reforested areas, pines and eucalyptus are best suited for use in construction and their availability are very good. Timber used for log or sawn beams in timber bridges normally includes the application of preservative treatment.
Objectives of ETBPSP include: the development of new technologies for timber bridge construction; analysis and improvement of the actual structural and construction systems; and adaptation of existent international technologies to national conditions.
The goal is to develop technology to construct safe timber bridges with simple and modern constructive techniques, with good durability like others structural materials at a competitive cost.
After five years of this program, eleven demonstration timber bridges were constructed mainly in the State of São Paulo. This included eight composite timber/concrete bridges, one log timber girder bridge with a transverse sawn deck, one transverse lumber prestressed timber bridge, and one transverse cellular plywood box prestressed bridge.
Predicted deflections based on analytical modeling were also determined for comparison with static load test results. An orthotropic plate computer program adapted for highway bridges was used to simulate the deck behavior of each bridge under actual test truck axle loads. This software named Orthotropic Timber Bridge(OTB) was used to analyze five types of plates: composite timberconcrete plate; stress laminated sawn lumber plate, stress laminated T-section plate, stress laminated cellular box plate, and stress laminated truss plate. Figure 18 show a theoretical-OTB and experimental results comparison.
Load test behavior
Static-load tests were conduct during construction and after some time period to determine the response of the bridges to full truck loading. Each test consisted of positioning a fully loaded truck on the bridge deck and measuring resulting deflections at a series of transverse locations at midspan. Measurements of bridge deflections were taken prior to testing (unloaded) for each load position (loaded), and at the conclusion of testing (unloaded). In addition, analytical assessments were conducted to determine the theoretical bridge response. The test vehicle consisted of a fully loaded three axle dump truck with a gross vehicle weight of about 25 tons, (Figure 15). The vehicle was positioned longitudinally on the bridge so that the two rear axles were centered at midspan. Transversely, the vehicle was placed for three load positions, (Figure 16). Measurements of the bridge deflection from an unloaded to loaded condition were obtained by placing a calibrated rule on the deck underside and reading values with a surveyor’s level. Figure 17,18.
Results of the emerging program include bridge construction, five courses of design and construction of timber bridges for engineers in the Department of Roads of São Paulo State and for construction engineers of São Paulo Provinces, four class note publications for the courses, and the software OTB (Orthotropic Timber Bridge) for the design of timber bridges. The final report will take the form of the Manual for Timber Bridge Design and Construction.
The author thanks of the Foundation of Support of Research of São Paulo State – FAPESP for their financial support in the Timber Bridge Program.
CALIL CJ (2001) Long term field performance of seven stress laminated deck hardwood wood bridges in Pennsylvania. Research Report: Foundation of Support of Research of São Paulo State – FAPESP. São Carlos, 2001. 145p.
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