Aluminum advantages highlight the advantages of aluminum bridge
The appearance of the beautiful and rich aesthetic shape, high corrosion resistance, in the entire life cycle does not need maintenance, can reduce the cost of reasonable cost and maintenance cost is much lower than that of steel bridge, combined with life cycle matures, aluminium scrap almost can recycle all, more than 95% of the performance can be obtained with the original quite recycled aluminum, aluminum and steel bridge expires recycling renewable steel is less than 70%…
Aluminum, as a bridge material, has a series of superior properties that are difficult to replace, and is considered as a new material with vitality and vitality.
A study in Canada in 2008 fully demonstrated this. Of the nine Bridges built between 1946 and 1963, six are still being built.
The density of aluminum is low, so the bridge’s deadweight is lower than that of steel bridge and concrete bridge, which is conducive to manufacturing, transportation and installation. At the same time, the width of the bridge can be increased, and the supporting members can be reduced and reduced. This is especially important for the load limitation of the bridge and the restoration of historic Bridges.
Usually, aluminum bridge decks are 70 to 80 percent lighter than concrete and most other metal decks.
In recent years, the aluminum industry has made great progress in aluminum production, new alloy research and development and performance improvement, and large-section extruded material production, which has promoted the application of aluminum in bridge structures to a new level.
Matte group (MAADI, MostAdvancedAluminumDesign&Inspection) and alcan association (AluminumAssociationofCanada), according to a study by a use made of galvanized steel 3.24 meters wide, 28.6 meters long steel bridge, after 50 years the cost of 28% ~ 167% higher than aluminum bridge.
The study also showed that aluminum Bridges cost less over 33 years than galvanized steel Bridges.
This only compares the cost of the two materials in the general atmospheric environment. The corrosion resistance of aluminum is higher than that of steel under severe corrosion conditions. At this time, the advantage of aluminum bridge will be more prominent.
The advantages of aluminum are evident in the construction of pontoon and movable Bridges, as well as in the recent construction of road Bridges, such as the sardisfield bridge in west Massachusetts, USA, which was built with extruded aluminum.
In 2017, the consumption of extruded aluminum in Canada increased by 5% year on year, which has been in a growth trend for nine consecutive years. Thanks to the increase in the consumption of aluminum in buildings and structures, the consumption of extruded aluminum in Bridges is one of the factors.
The industry has been encouraged by the greater growth of aluminum in bridge construction in North America, especially as the success of Vehicularbridge construction has increased the use of structural extrusion aluminum in Bridges.
To meet this market demand, madi group has launched a system called GuarDeckR (high performance bridge panel R), which is made of extruded aluminum and can carry 15 tons. In case of a bridge or road accident, it can be transported to the site, repaired in a short time, and traffic can be resumed.
Challenges of aging Bridges
Bridge system at present, North America has entered a critical state or approaching danger, 603000 in the United States and Canada more than 56000 of the highway bridge is the most in the construction of 50 ~ 70 s, most of which are already in or about to enter a defective fault period, the federal highway administration in the near future, according to data from the United States has about 56000 Bridges in structure is more or less problems;
About $123 billion is needed to repair and strengthen broken Bridges, according to a report published by the American society of civil engineers.
Repairing these Bridges, most of which are made of steel and concrete, and more recent ones made of reinforced concrete, will significantly increase the cost of their infrastructure over the next 20 years.
Investing in the construction of Bridges, roads and other transportation facilities will undoubtedly play a huge role in developing the urban and rural economy.
Extruded aluminum will be widely used in road and bridge repair in North America.
Research and development of aluminum bridge panel
Although aluminum has many advantages, it also faces many challenges. For example, its elastic stiffness and fatigue strength are much lower than steel, the strength performance of solder joints and their heat-affected areas is greatly reduced, and the price of raw materials is also high.
In the face of these challenges, after years of research and development, madi group has designed and built hundreds of aluminum alloy bridge structures using fusion welding and selected alloys, which have been applied in practice to build new Bridges, repair and reinforce aging Bridges.
Among these structures, the famous one is the make-a-bridge, which is used in new pedestrian aluminum Bridges in the United States and Canada. Instead of welding, it is interlocked.
The group’s pedestrian aluminium bridge for the Asian market is called “Caribbean”.
At present, madi group has successfully built an aluminum bridge capable of handling 15 tons of cars.
Matty group, in collaboration with the university of Waterloo (Waterloo) research and development of “safe aluminum bridge plate (GuarDeck) concept structure have been incorporated into the Canadian standards association (CSA) in 2011 file, later, they built a bridge test, 22.9 meters long, at Waterloo university conducted a series of comprehensive assessment test, such as ultimate strength test, life test, vibration test, fatigue test and so on.
The group’s in-house engineering team has built several prototype bridge panels and conducted extensive tests in the workshop, as well as friction tests with 178kN presses to assess the force of friction, under the auspices of the aluminum industry development center of Quebec (CQRDA), which is dedicated to developing new applications of aluminum.
The GuarDeck aluminum bridge is made of extruded aluminum and all parts are machined on a large 5-axis machining center (CNC) with high accuracy, with a deviation of less than 0.5 mm on the 11.5-meter-long panel.
All aluminum materials are produced by 50MN forward extruder, and the alloy is 6061-t6, which has higher strength performance and high corrosion resistance. There are tenons and grooves on both sides of each bridge plate, so as to interlink each other. Because the thermal expansion coefficient of 6061 alloy is 23.6×10-6/℃, twice as large as that of steel, this connection method can eliminate the thermal expansion difference.
The aluminum bridge can be treated with a variety of finishes: transparent paint, durable anodizing, baking coating, and even an anti-skid epoxy resin to prevent car tires from sliding on the surface.
For safety reasons, a safety barrier can be installed on the side of the panel.
Madi group is always concerned about environmental protection. The 6061 alloy used for GuarDeck aluminum bridge contains about 20% scrap aluminum. If such extruded aluminum cannot be purchased, renewable new energy will be used as much as possible in the processing and manufacturing of aluminum bridge.
In addition, the aluminum bridge can be 100 percent recycled and reused, with a loss of less than 2.5 percent during smelting.
Current is important to use fast comprehensive bridge structure (ABC, acceleratdbridgeconstruction) technology, the essence of the ABC technology, is in the factory will block, block with good aluminum bridge, and then transported to site assembly, it can be finished in does not affect traffic within the scheduled time of hoisting, if the bridge of long span bridge surface, bridge panel can be pre-loaded into small blocks of 55 kg, the small piece of main girder of fixed on extrusion Ι, fasteners, stainless steel, and take measures for corrosion protection, prevent damage, guard against theft.
Each fastener is solid and requires 134kN torque to loosen the panel.
Because the installation of the bridge board does not need welding process and large equipment, the installation time can be compressed very short, even if the unskilled workers install a prefabricated bridge panel as long as 10 minutes, a 30 meter span of the bridge only about 1 day can be handed in.
The manufacturing, installation and use of the GuarDeck aluminum bridge of maddie group is in full compliance with environmental regulations and standards of relevant countries and organizations, such as the Canadian national standards, the Canadian standards institute (CSA), the American society of civil engineers (ASCE), and the interstate highway and transportation administrators association (AASHTO).
Backbone material of 6061 alloy bridge
In today’s aluminum bridge materials, more than 90% of them are 6061 alloy extruded materials, especially for highway aluminum Bridges, almost all of them are made of 6061 alloy extruded materials, and the auxiliary facilities of pedestrian Bridges can be made of 6063 alloy extruded materials.
Alloy 6061 is an ai-mg-si-cu-cr alloy developed by Alcoa in 1933 and put into commercial production. It is a classic, time-tested deformed aluminum alloy and one of the four “diamond” heat-treatable aluminum alloys.
(the four “king kong” heat-treatable aluminum alloys include type 2024, type 6061, type 6063 and type 7075).
The output of type 6061 alloy is second only to that of type 6063 alloy, and much more than that of type 2024 and type 7075 alloy.
By December 2019, there are 5 members of the 6061 alloy family. Except for the 6061A developed by the European aluminum association (EAA), the other 4 are all American alloys. Their chemical composition is shown in table 1.
Only 6061 alloy is used in the production of bridge aluminum, because it has comprehensive properties and easy to control the composition. Some old aluminum can be used in the mixing.
The solid melting temperature of 6061 alloy is very wide and easy to control, ranging from 515℃ to 550℃, which can be controlled at 535℃.
Specification for artificial aging of extruded materials :(170 ~ 180)℃/8h.
The mechanical properties of 6061 alloy are shown in table 2, and the mechanical properties at low and high temperatures are shown in table 3.
Physical properties of 6061 alloy: density 2.7g/cm3, liquidus temperature 652 ° c, solidus temperature 582 ° c, linear expansion coefficient 23.6×10-6/ c from 20 ° c to 100 ° c, specific heat 896J/(kg. ° c) at 20 ° c, thermal conductivity at 25 ° c:
O state of 180 w/(m ﹒ ℃), T4 status of 154 w/(m ﹒ ℃), T6 state of 167 w/(m ﹒ ℃), 20 ℃ when the electrical conductivity of: O state of 47% IACS, T4 status of 40% IACS, T6 state 43% IACS, 20 ℃ when the resistivity, O n Ω ﹒ 37 m, state of 43 n Ω 40 n, m, T6 state Ω, m.
Corrosion resistance of 6061: the potential of SCE(saturated dry mercury electrode) in 2.67%AlCl3 solution was -876.9mV, and the pore erosion potential was -704.2mV.
No stress corrosion cracking was found in T6 material in the laboratory and in actual use. No stress corrosion cracking was found in T4 material in actual use. However, such corrosion was observed in the direction of plate thickness and peeling corrosion was observed in the laboratory test, but it had no effect on actual use.
The 6061 alloy has good welding properties and can also be brazed.
It is a kind of classic alloy which can be heat treated and strengthened with medium strength extrusion performance. It has excellent forming and processing performance and good surface treatment performance. It is widely used in general industrial structure and transportation equipment.
From the point of the development of aluminum alloy Bridges, the world’s first bridge is the Pittsburgh aluminum (Pittsburgh) Smithfield, Smithfield street is about 100 m long highway bridge with 2014 – T6 aluminum alloy thick plate, which was built in 1933, renovated in 1967, the bridge panel to switch to stronger corrosion resistance of 5456 – H321 alloy thick panel, it can be think that 1953 years ago, highway bridge aluminium alloy is mostly 2014 – T6 alloy,
In addition to 2014-t6 alloy plates, some 6151-t6 alloy thick plates were used for a road bridge built in Hendon, England in 1948.
In 1950, a road bridge over the river Tummel in Scotland was built with 6151-t6 alloy sheet.
Some road Bridges built in Germany and England before 1962 (1953 ~ 1962) used 6351-t6 alloy extruded profile corrugated sheet.
Since the mid – 1990 – s, 6061 – T6 alloy aluminum extrusion materials in bridge structure material in the dominant, one of the famous Pennsylvania zhu (Juniata river suspension bridge, tower, built in 1994, using the Reynolds metals (after annexation by Alcoa, now Mr NingKe company) provided by 6061 – T6 and 6063 – T6 alloy extruded material, the road bridge is about 98 m long, a former steel bridge, only through 7 tons of cars, to aluminum bridge can pass 22 tons of cars.
It can now be said that before the emergence of aluminum alloy with better overall performance, it is advisable to consider the 6061-t6 alloy extruded material as aluminum bridge material.
Of course, such as 6063, 5083, 5086, 6082 and so on can also be used.
Aluminum is after wood, steel, concrete, stone material of construction of the bridge, this paper introduces the aluminum bridge process and various properties of 6061 – T6 alloy, hope that interested in aluminum bridge and bridge aluminum people and promote the application of aluminum and help to the development of national economy, the more hope authorities understand madden group in aluminum bridge.
The author of the following views are purely a statement, not as a lesson.
The understanding of aluminum bridge needs to be strengthened, the investment needs to be increased, and the development should be accelerated.
Compared with the United States and Canada, China has little momentum in the construction of aluminum Bridges, with insufficient research, incomplete design specifications, and the aluminum industry’s work in this area to be strengthened.
In March 2007 was China’s first aluminum bridge built in hangzhou qingchun road pedestrian overpass in the river, technology and materials all imported from Germany, in 2007, nine months completely independent intellectual property rights of state-owned pedestrian overpass in Shanghai xujiahui cao caoxibei road operation, using 6061 – T6 alloy, single span 23 meters, 6 meters wide, 2.6 meters high, the main clear height of 4.6 meters, its own quality 15 tons, about 50 tons load.
According to incomplete statistics, from 2007 to 2019, 13 years, our country built in 15 cities such as Beijing, Shanghai, a total of about 75 pedestrian crossing aluminum bridge, highway Bridges thereof not see public reporting, therefore, in terms of aluminum bridge construction, the number is less than the industry developed countries, the road bridge is less, this is not surprising, because the United States has a history of aluminum bridge built in 87, and construction of the Chinese history of 13 years, but other countries such as Canada, Britain, Germany, Denmark, Norway, Sweden and other countries of aluminium are around 80 history of bridge construction.
Some people think that the initial cost of aluminum is higher than that of steel. Economically speaking, the steel used to build a 50-meter-long pedestrian bridge is only about 40% of the price of aluminum. However, some people abroad have done research, and if the maintenance cost is included, the aluminum bridge is much more economical than the steel bridge.
Taking the manufacturing of a bridge deck of 91.4 meters long and 6.1 meters wide as an example, the manufacturing cost of steel bridge deck is 833 dollars/meter 2, and that of aluminum bridge deck is 1,388 dollars/meter 2, so the total cost of steel bridge deck is 450,000 dollars, and that of aluminum bridge deck is 750,000 dollars, and that of aluminum bridge deck is 67% more expensive than that of steel bridge deck.
The steel deck has to be maintained every 10 years, which is a labor-intensive job to clean up the rust, expose the steel and repaint it with preservatives.
If the life cycle of the bridge is 50 years, it needs to be maintained four times, and the cost of each time is about 1/3 of the initial construction cost.
In this calculation, the total cost of the steel bridge is $1.05 million over the lifetime of the bridge, while the aluminum bridge remains beautiful and beautiful after 50 years of service, even after 25 years of service, and the cost remains at $750,000.
That way, even if it is purely economic, there are advantages to building aluminum Bridges.
Establish a research and development center to promote the application of bridge aluminum.
The reason why China has not become a leader in aluminum bridge construction is related to the fact that it has not built a powerful research and development unit.
In order to promote the development and research and development of aluminum bridge bridge performance more aluminum alloy, the development of efficient aluminum bridge processing technology and assembly process, it is necessary for us to form a powerful research institute and center of aluminum bridge, increasing investment, talents, and make the bridge aluminum become a new bright spot of aluminium industry, under the “hard” kung fu dry, get dry, dry for five or six years later, carrying a banner, one of the leading enterprises in the world’s aluminum bridge team.