The introduction of the four truss bridge, the difference between the bridge and the truss

In the bridge structure of the overhead crane, it is composed of two main beams and two end beams on the left and right, and the two main beams are space four truss structures, which are composed of the main truss, the auxiliary truss, the upper horizontal truss and the lower horizontal truss and the diagonal brace, and each truss is composed of an upper chord, a lower chord and a web member (oblique rod or vertical rod). This type of crane tray structure is known as a four-truss bridge.

The four-truss bridge is a kind of empty structure, and the co-partition frame causes many times of super-static determination, and if the calculation is carried out in strict accordance with the spatial structure, it is too complex and cannot be adopted in the general practical calculation. The four-truss type bridge is bent and torsional as a whole in the working process, because the bridge is torsional, so that the auxiliary analysis frame that does not directly bear the trolley load also shares part of the load.

Hello, bridge and truss are commonly used forms in connecting members, but they are different in structural form and application. Bridge is a kind of bridge connection structure composed of straight sections as the main body. Its structural composition mainly includes upper and lower layers of beams and vertical rods, and the periphery is strengthened with diagonal braces, so that the bridge deck has good rigidity and stability.

Bridge is widely used in steel structure buildings, billboards and other long-span suspension structures, such as power towers, viaducts, etc. A truss is a spatial structure consisting of many interconnected members or tubes. Its structural composition mainly includes crossbars, vertical rods and diagonal supports, which are commonly found in steel structure workshops, large warehouses, stadiums and other buildings.

The spatial rigidity and stability of the truss are high, which can provide good support and safety for large buildings. At the same time, due to its flexible structure, it can be adjusted and changed according to needs, which provides convenience for building customization. The differences in structure, application and material selection between bridges and trusses make them widely used in different fields.

In fact, there is a big difference between the bridge and the truss in the difficulty of its engineering construction. In construction, the bridge is easier to assemble, install and disassemble, while the bright truss is generally more difficult to construct due to the complexity of its structure and the particularity of the space structure, and it is often necessary to make a model or a simulation model to find the best construction technology. In addition, there is a significant difference in the optimal design and material selection of the bridge and truss.

The material of the bridge is mainly alloy steel with high strength, corrosion resistance and fatigue resistance, which can adapt to various harsh natural environments, such as ocean, snow, desert, etc. The frank imitation material selection of truss tends to use thin-walled steel pipes or square pipes. On the whole, the difference between bridge and truss is mainly considered from the aspects of structural design, application occasions, engineering construction difficulty and material selection.

Of course, for the selection of other components, it is also necessary to consider many factors.

China's truss structure bridge front: 1975 In 1977, Henan combined the advantages of T structure cantilever construction and truss, with the Longjugou 25-meter truss cantilever bridge as the test bridge, and then built a 9x50m arch bridge in the Yitala River in Song County, and later built bridges such as Ninghai and Ancheng in Zhejiang.

In 1979, Hubei built the Huanglingji truss T-frame bridge, which has a span of 90 meters. The Hangzhou Qiantang River Bridge built in 1988 is a prestressed simply supported truss girder bridge with a span of 55 meters, which was used for the first time in the domestic large-span highway bridge.

The Wuhu Yinluzhi Yangtze River Bridge, which was completed and opened to traffic in September 2000, is an upward-bearing composite truss girder bridge, and its design and construction level have refreshed a number of domestic bridge construction records.

Wuhan Tianxingzhou road and railway dual-purpose Yangtze River Bridge was completed and opened to traffic on December 26, 2009, and it is the first passenger dedicated undercarriage steel truss combined girder bridge built in China.

1. A truss bridge is a form of bridge. 2. Truss bridges are generally found in railways and highways; It is divided into two types: upper chord force and lower chord force. 3. The truss is composed of an upper chord, a lower chord and a web member; The form of the web is divided into oblique and straight web; Due to the large slenderness of the members themselves, although the connections between the members may be "fixed", the actual bending moments at the end of the members are generally small, so the design analysis can be simplified to "hinged".

In the simplified calculation, the members are all "two-force bars" that are subjected to pressure or tension. 4. Because the spans of the bridges are large, and the stiffness of the single truss "out of plane" is relatively weak, therefore, "out of plane" needs to be set up with support. When designing bridges, "out-of-plane" is generally designed in the form of trusses, so that the bridge forms a whole with good stiffness in both directions.

5. Some bridge decks are set on the upper chord, so the force is mainly transmitted through the upper chord; There are also bridge decks that are set on the lower chord, and due to the requirements of out-of-plane stiffness, the upper chords still need to be connected to reduce the out-of-plane calculated length of the upper chord. 6. The chord of the truss is stressed relatively large in the middle part of the span, and gradually decreases in the direction of the support; The force of the web member is mainly the largest in the support attachment, and the force of the web member in the middle of the span is relatively small, and there is even a theoretical "zero rod".

Trusses can be classified according to different characteristics.

First, according to the shape of the truss, it is divided into:

1.Parallel chord trusses (for easy arrangement of double-layer structures; It is conducive to standardized production, but the rod force distribution is not uniform enough);

2.Folding string truss (such as parabolic truss girder, bending moment diagram of simply supported beam under uniform load with the same shape, uniform distribution of rod force, economical use of materials, and complex structure);

3.Triangular truss (the rod force is more unevenly distributed, and the structural arrangement is difficult, but the slope meets the needs of roof drainage).

Second, according to the truss geometric composition of the division:

1.a simple truss (consisting of a basic hinged triangle with a sequential addition of binary bodies);

2.a joint truss (consisting of several simple trusses united according to the simple composition rules of a geometrically invariant system);

3.Complex trusses (different from other statically determined trusses of the first two).

3. According to the horizontal thrust received:

1.Beam truss without thrust (compared with the corresponding solid beam structure, the hollowing rate is large, the upper and lower chords are bending-resistant, the web members are mainly shear resistant, the force is reasonable, and the materials are economical);

2.Arch truss with thrust (arch ring and arch structure are integrated into one, good integrity, easy to construct, strong spanning capacity, saving steel materials).

The rack structure corresponds to the frame structure, which is classified according to the calculation model and is a professional term, and the portal steel frame structure is also one of the classifications of the calculation model of the steel structure, which is a professional term. The truss structure means that the transverse members are replaced by trusses, and it is used in the row frame structure, and the "truss structure" is not a professional term, let alone a type of structural type.

The main structural features of the span.

The force of each member is mainly unidirectional tension and compression, and the bending moment and shear force distribution can be adapted to the structure through the reasonable arrangement of the upper and lower chords and web members. Due to the self-equilibrium of the tension and compression forces in the horizontal direction, the whole structure does not produce horizontal thrust on the support. The structure layout is flexible and the application range is very wide.

Compared with the truss beam and the solid web beam (i.e., the beam we generally see), in terms of bending resistance, because the tension and compression sections are concentrated at the upper and lower ends, the internal force arm is increased, so that with the same amount of material, greater bending strength is realized. In terms of shear resistance, the shear force can be gradually transmitted to the support through the reasonable arrangement of the web members. In this way, whether it is bending or shear resistance, the truss structure can give full play to the strength of the material, so that it can be suitable for building roof structures of various spans.

More importantly, it converts the complex stress state inside the solid web beam under the action of transverse bending into a simple tensile and compressive stress state in the truss member, so that we can intuitively understand the distribution and transmission of force, which is convenient for the change and combination of the structure.