Composite bridges stationed in the US military base pave the way for heavy tanks
challenges faced by the project:
bridges are mainly used to carry heavy tracked military vehicles. It is hoped that low-cost, sustainable use and low maintenance solutions will be applied to replace those traditional wooden bridges that are easy to decay
the construction of the bridge beam and longitudinal beam is connected with the bridge pile and the I-beam (insoluble polymer combined with high-density polyethylene and fiber reinforced polypropylene) manufactured by special extrusion process
a new low-cost composite material "super base" was born with the efforts of the US Army. The Fort Bragg ① base of the US Army is the headquarters of the 18th airborne army, the 82nd Airborne Division, the US Army Special Operations Command and the US parachute jumping team. At present, the base is using M-1 Abrams tank to test the bearing capacity of the traffic infrastructure of Fort Bragg base, especially the bearing capacity of the wooden structure bridge located near the base. The theoretical bearing capacity of the bridge is 6 tons, but some beams of the bridge body have been highly damaged. Therefore, when the engineer research and Development Center (erdc), relevant professionals from the U.S. Army Construction Engineering Laboratory (cerl) and Richard LAMPO, the material engineer of the U.S. Army Corps of engineers, came to Fort Bragg base together. The bridge improvement scheme proposed after research is to use recycled plastics to rebuild a new bridge to replace the original wooden structure bridge. After consideration, the public works bureau (DPW) of Fort Bragg base accepted this proposal and proposed that after the completion of the new bridge, the normal operation of heavy tank vehicles in Fort Bragg base should be ensured first. In addition, the Deputy Secretary of the corrosion prevention and control program of the Ministry of defense promised to provide financial support for the design, construction, initial load test, etc. of the program. The recent research report of the US Department of defense shows that the US Department of defense has invested about US $22.5 billion annually in combating the corrosion of base equipment and infrastructure. Therefore, the Ministry of national defense has promulgated the "green" procurement policy and corresponding federal laws and regulations to vigorously develop the construction quality of US military base facilities
the result of such strong support from the government finally led to the birth of this unprecedented composite bridge. The I-beams, slabs, railings and solid prototype piles of this bridge are all made of composite materials without exception. A total of 39 tons of raw materials were used to build these components, including corrosion-resistant raw materials, water, wear-resistant high-density polyethylene and fiber-reinforced polypropylene
the hardness of I-beam constructed by blending immiscible polymer with the strength of high-density polyethylene and the hardness reinforced by glass fiber is even higher than that of steel
each component of composite bridge is produced under the guidance of ③ professionals of Axion international holding company. The company has set up the amipp advanced polymer R & D center at Rutgers University ④, and has a patented manufacturing process and a license for composite materials. Lead researcher Dr. Thomas noskers is responsible for supervision and guidance in the R & D process. Glass fiber reinforced propylene is recycled from used automobile bumpers. It can meet the requirements of durability testing, testing the relationship between tightening range and pressure, and testing the spring tightening under specific pressure. Although there is no strict limit on the length of the fiber, the optimal fiber length is between 5mm and 10mm
using Rutgers processing program, Axion's extruder first combines high-density polyethylene and fiber-reinforced propylene by blending immiscible polymers. In short, two or more immiscible polymers are mixed to produce composites. Therefore, the strength of HDPE can be well combined with the stiffness of glass fiber reinforced polypropylene. Generally, HDPE has a certain strength, but under normal circumstances, there is no oil dripping or intermittent oil dripping at high tonnage, but it does not have very good stiffness. George Nagle, manager of the Engineering Department of Axion, said, "in a sense, our current technology for the application of high-density polyethylene materials has achieved the result that one plus one equals three."
rutgers machining program can greatly improve the mechanical properties of extruded parts. In the traditional extrusion process, the fibers usually extend along the surface structure, which is easy to cause uneven stress. Researchers at Rutgers University have overcome this shortcoming. They have developed a method that can make the added fibers in the same direction during the processing, which can not only reduce the use of fibers, but also have greater coaxial properties. For example, because the fiber direction of traditional products is random, in order to achieve the same strength of products produced by the two methods, 34% of the fiber weight must be added when processing traditional products, while the new Rutgers processing program only needs to add 11% of the fiber weight. Thus, the production cost is greatly reduced
nagle said, "once the extrusion process is completed, the resulting composite parts can have the same or even higher strength than the steel of the same weight."
I-beams pave the way for U.S. tanks.
the existing wooden structure bridge at Fort Bragg base has been highly corroded, with an initial rated load capacity of 4 tons. Nagle explained, "the bridge we are facing has to withstand greater load test than the traditional bridge mainly used for automobiles." "Therefore, in the process of evaluating the design scheme of the bridge, the load capacity, elasticity resistance, durability and corrosion resistance of the bridge are particularly important."
m.g. McLaren engineering consulting company undertook the design of the bridge. At the same time, LAMPO, a material engineer, and relevant technicians from the engineer research and Development Center (erdc, a lightweight material with excellent properties such as lightweight, safety, comfort and reliability) and the U.S. Army Construction Engineering Laboratory also provided assistance to the design scheme of the bridge. The new design concept is basically consistent with the construction method of traditional wooden bridges: 1) pile driving at both ends of the bridge to prevent water and soil loss caused by rising water level in the rainy season; 2) There are four rows of bridge piles under the bridge slab. Each circular bridge pile is made of composite material solid casting, with a diameter of 305mm and a height of 14-20 meters; 3) Every four bridge piles are fixed with a 3.7m beam. Every four beams support a 12.2m longitudinal beam. Of course, the longitudinal beam is installed in the same direction as the tank
"each longitudinal beam of the bridge is connected to and supported by each other, so that each beam can be stressed evenly," green explained. Finally, composite bridge slabs, bumpers and railings were installed and completed (all parts of the bridge, except bridge slab bolts and fasteners, were completed by the trade protectionism capacity enhancement department through the composite production of Axion company)
for the bridge at Fort Bragg base, the most critical part in the design is the 457mm wide engineering composite I-beam (including longitudinal beam and transverse beam)
the tensile tolerance of all structural composite materials used in the bridge is designed to be 600psi, which provides a great degree of safety guarantee for compression and bending stress. It is a material insensitive to strain rate. The failure strain of the composite is 3%, which is much higher than 0.7% of wood
composite bridges under construction
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