Introduction: aluminum extruded aluminum has been used especially in bridges in a long history, but the amount is small, the development speed is not fast, one of the reasons is Aluminum Alloy strength is not high enough, can not meet the requirements of highway and railway bridge......
Especially the application of existing aluminum extruded aluminum in bridge in a long history, but the amount is small, the development speed is not fast, one of the reasons is Aluminum Alloy strength is not high enough, can not meet the requirements of highway and railway bridge, 6xxx alloys commonly used in extrusion tensile strength of Rm profiles is only 250N/mm2 to the R & D group the strength of >650N/mm2 high strength Aluminum Alloy, to meet the bearing Luqiao especially military pontoon construction needs, high strength and high corrosion resistance Aluminum Alloy extrusion has played a particularly important role in the construction of pontoon pontoon units is an important part of a strong army, the properties of 6xxx alloy current it is to build a footbridge across the street is more than sufficient; two is the price of aluminum than steel, the bridge cost rise, to some extent hindered the development of aluminum bridge.
By extrusion Aluminum Alloy profiles bridge a lot of advantages
Aluminum alloy extruded profiles are one of the excellent structural materials for bridges and floating bridges, especially for the construction of pontoon bridges:
About 1/3 of steel, the density of aluminum alloy is about 2.7g/cm3, while the density of steel is as high as 7.8g/cm3.
The strength property of 6xxx system is comparable to that of low carbon steel, so the specific strength (strength to mass ratio) and specific stiffness (modulus of elasticity) are much higher than that of steel.
Strong corrosion resistance
The corrosion of rainwater and seawater and road salt, mud can be ignored, especially the 5xxx alloys, thus not only built after no paint during the service do not need regular maintenance. The 2013 visit to the United States, via Pittsburgh City, built in 1933 to stop by the Smith Rumsfeld Street Bridge (Smithfield Street Bridge), which is a city built on the river over the car and pedestrian bridge aluminum structure, for 84 years, still The brightness dazzles the eyes. shine.
The fatigue crack propagation ability is very strong, and there is no brittleness at low temperature. Aluminum Alloy strength and plasticity decreases with the temperature rising, but more than 90% of the steel with low temperature brittleness, so Aluminum Alloy is the excellent material in alpine area of the bridge.
Is one of the best economic cycle aluminum metal materials, Aluminum Alloy bridge without loss of corrosion during use, almost completely recovered, while energy consumption is only equivalent to the original scrap aluminum extraction energy consumption 5%, recycling of resources, energy-saving emission reduction has important significance, great social benefits.
Aluminum bridges are lighter than steel bridges and have many advantages. First of all, the most important thing is to reduce the static load of the upper structure, increase the loading capacity of vehicles, while the adverse effects can be offset compensation such as steel, cable and so on the upper structure and foundation of large span bridge; it has more important significance, the total load is decreased to make the bridge; static load can reduce the earthquake relief the lateral force on the bridge in the earthquake zone, and the size of the lateral force of the bridge static load proportion.
From the history of construction of bridge, concrete bridge is the most expensive, due to its large static load, in those not suitable for construction of concrete bridge, steel bridge deck has become the first choice, the thickness of 200mm concrete under static loading 454kg/m2 negative. Although the ratio of concrete bridge deck light a lot, but the price is much higher. Building this kind of steel bridge is a hard work, labor intensive, and expensive.
The aluminum alloy bridge deck is much lighter than the steel bridge deck, and the strengthening force and the plate under the bridge deck are a whole and extruded at one time. The quality of Aluminum Alloy deck is 90.8kg/m2, than the international standard of highway capacity is much higher, so Aluminum Alloy large extrusion trimming historic bridges become the most attractive materials, because the static load is critical to the tribute deck bridge. However, the aluminum alloy bridge also has some shortcomings, which is not conducive to the large area promotion of aluminum alloy materials in bridge construction:
The original cost is high
The original cost of the aluminum bridge (initial investment) than other materials, usually according to the different 25%~100% contrast material, but the aluminum bridge in after the building without paint, while serving in the later does not need regular maintenance, so if the maintenance cost is calculated, the total cost in the whole service period aluminum bridge (investment and maintenance costs and lower than the bridge), especially in the alpine region, with no cold low temperature brittleness of alloy steel.
Connection of parts
The past is the aluminum bridge with aluminum manufacturing, using screw connection parts and rivet, in mid 90s the U.S. Reynolds Metal Co (Reynolds Metals Co., in 2005 by the Alcoa Corp merger) successfully developed several bridge aluminum extrusion, mainly by welding connection. The weakness of bolted joint or conventional welding method is that the strength of joint, especially the fatigue strength, is lower than that of base metal. Later, the advanced friction stir method was used to provide an excellent connection process for the bridge parts, welding aluminum aluminum, welding aluminum steel, the strength of the weld is almost equal to the base metal.