Steel bridge structures made
of steel, was constructed to overcome the large span bridges or temporary, rapid construction, with large bearing capacity and high reliability, light weight, high mobility and the ability to fully mechanized.
The steel bridge diagram:
Steel girder bridges:
+ Cantilever girder
Steel truss bridge:
+ Simple truss
+ Continuous truss
Distinguish steel bridge road surface:
+ Above driver
+ Under driver
Classification by vertical bars
+ vertical bars
+ No vertical bars
The tendency to develop steel for today: Two developments:
• Reducing the volume of steel works themselves to a minimum (fabrication of the bridge girder reinforced concrete)
• Reducing weight and cost fabrication and construction of steel bridges
With structural composite steel bridge of reinforced concrete, continuing developed with 3 trend:
• Increase the percentage of RC structures in combined cross-sectional areas - saving steel
• Complete deferent parts: use of reinforced concrete bridge deck has a surface, long life, good quality, protects steel parts for the bottom; previously used with the steel beams or steel frame, huge drawback because the heat absorption causes cracking of asphalt overlay Concrete Wearing layers above the bridge deck, structural and watertight down to the bottom, causing destructive rust-difficult to use in VN
• The entire section is linked to the steel beams forming one combined system, structural span become one the most common structural monolithic space to work
• The effects of reinforced concrete beams work together, adjusting stress, stress causes the opposite sign to the stresses caused by the load - bearing capacity increases, and due to the reduced volume of steel reinforced concrete that one clearly, make sure the technical and economic criteria, overcome the disadvantages caused beton cracked asphalt surface for hot climates like Vietnam
2. General characteristics of the steel bridge, analyze strengths and weaknesses and the scope of application.
* General Characteristics:
• Bearing high with all kinds of stress: scissors, cut the compression bending ….
• It can be fabricated using all different types of beam bridges, platforms, arches, suspension and the conjugated system
• High-strength steels, secondary steel bridge itself should light can pass the great span
• Steel has high strength, large elastic modulus, hardness large, guaranteed stability under the effect of wind loads, cyclical load (load or load fatigue repeat)
• The plastic-destructive vandalism accompanied by large-deformation caused redistribution of internal forces and stresses for steel should be able to withstand shock loads and stresses concentrate better
* Analysis of advantages and disadvantages:
- There are large bearing capacity and high reliability. Steel bridge capable of bearing large, high reliability due to steel materials intense, most of the building materials. High reliability is due to inhomogeneous structure of the material, the elastic and plastic work of steel close to the theoretical calculations. The actual working of steel bridges in accordance with theoretical calculations.
- Lightweight. Lightest steel structure of the bridge structures, to evaluate the quality of "light" of the material often used coefficient c is the ratio of the specific gravity and the strength of its force
- Mobility in transportation, installation rap.Do lightweight, the transportation and erection of steel structures easily and quickly, can be used in the construction of temporary bridges as well as permanent bridges
- As high industrialization.Do the material production entirely in the factory, and the fabrication of steel components made mainly in specialized factories or at least use the machinery specialized equipment, like consolidated conditions thoroughly mechanized
- As of sealed, waterproof. Materials and associated structural steel secrecy, waterproof, air impermeable, so the most suitable for the construction of liquid storage tanks, gas.
- The phenomenon of corrosion by environment: Stainless makes metal corrosion, reduce load-bearing section, vandalizing links and thereby reducing project life
- The anti-rust coating paint work in a given time - the need of frequent maintenance checks, scraping rust, repaint
- Maintenance costs are quite high compared with other materials for use
* Scope of application:
- Steel materials are used in many different industries and for demand of everyday.
- The use should be considered suitable for general needs: such as aesthetics, economics, feasibility ...
- At present steel bridge structures are usually only used for large span bridges (due to large span> 30m), railway bridge (mandatory use of steel bridge load effects due to the iterative load, causing fatigue-destruction repeat fine steel load)
- Used for temporary bridges, military requirements, need quick dismantle and easy to transport.
3.General forming of 1 simple steel girder structural.
- General truss including the bar (structures) associated to any edge platforms, only a pulling force axial compression, different beam characteristics under bending momen.
- Open truss structure, easy to pose for art works
- Saving steel materials than concentrate girder when pass the long span L>30 m
- Easy standardized and prefabricated structures detailed in the works
- Assemble outside the school, many requiring special stages over girder bridges
- For a simple truss bridge roadway below, must be directly sphere system load, the load transfer to democracy and bearing down.
The simple diagram rigs and basic dimensions
- Seamless reduced plated single bar (Editor) straight or curved
- Driver above or under.
- Basic dimensions of a simple steel girder span
• Span length must be economically reasonable, and adequate drainage
• The height h of the rig selected in proportion to the length of span
+ Parallels plated bar:
+ Curver plated bar;
+ With continuous and cantilever bridges:
+ With long span bridges l> 40m height civilians choose h> 6m
• Length chamber orchestra: d = (0.6 to 0.8) h or d = (0.8-1) the triangular lattice, with no vertical bars (rails)
• Oblique angle from horizontal
• Distance between 2 hearts all platforms (b)
+ Oto Bridge roadway below, should be arranged with two rigs all distances greater than the roadway suffering from 800mm to 1000mm sure to include the wood truss rod wheel and breadth
+ Oto Bridge on the motorway can arrange the platforms all the way to another 5000 or 7000mm 4 rigs are all separated in 2500-4000mm