What are the stress characteristics of steel truss bridge structure? What is Truss? What are the str

Trusses are one of the most reasonable forms of force in planar structures. A truss bridge is a form of bridge. Truss bridges are generally found on railways and highways; It is divided into two types: upper chord force and lower chord force.

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. Since the spans of the bridges are large, and the stiffness of the single trusses "out of plane" is relatively weak, therefore, "out of plane" needs to be supported.

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. Some bridge decks are set on the top chord, so the force is mainly transmitted through the top chord; There are also bridge decks set in the lower chord (such as more highway bridges now adopt this form), due to the requirements of out-of-plane stiffness, the upper chord still needs to be connected to reduce the out-of-plane calculation length of the upper chord. 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".

Stress characteristics The cross-sectional centroid of each member of the steel truss.

The axes should meet at a point at the nodes, and the internal forces are generally hinged.

Trusses are carried out. When the truss is only subjected to nodal loads, all members are only subjected to axial tension or compression; If a load is also applied to a member internode, the member will be bent at the same time. Steel truss members are generally thinner, and local bending moments should be avoided or reduced as much as possible when arranging nodes.

For steel trusses with a large cross-sectional height to length ratio, the secondary stress of the member caused by the rigidity of the joint should be considered if necessary.

All nodes are articulated. All members are two-force bars (axial forces only under tension or compression).

(1) By the balance system, fey + fby-40-60 = 0n (fey represents the vertical support reaction force at point e).

fby*15+40*20+60*5=0n*m (find the moment of bending the shirt at point e), and calculate fey=

2) Vertical section of the truss H-G section is dissected and stress analysis is carried out

fh-g+f2+f1*cos45=0 (the sum of transverse stresses is 0); The sum of the vertical stresses is 0); fh-g*5+60*5-f1*sin45*5=0 (me=0), the above three formulas are obtained f1=tensile force), f2=Danzen dust tension). According to the law of the two-force rod, it is easy to tell that it is a zero rod and the f3 stress is 0.

Structural characteristics: The force of each member is mainly unidirectional tension and compression, and the bending moment and shear force distribution can be adapted to the internal 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 has a wide range of applications. Compared with the solid belly beam, in terms of bending resistance, the tension and compression sections are concentrated at the upper and lower ends, and the internal force arm is increased, so that with the same amount of material, greater bending strength is realized.

The above content reference: Encyclopedia - truss structure.

The stress characteristics of the girder bridge are as follows:

Beam bridge refers to the bridge with beam or truss girder as the main load-bearing structure, is a kind of structure without horizontal reaction force under the action of vertical load, and its superstructure only produces vertical reaction force under the action of plumb vertical load.

Since the direction of action of the external forces (dead load and live load) is close to the axis of the load-bearing structure, the bending moment generated in the beam is the largest compared to other structural systems with the same span, and it usually requires materials with strong bending resistance (steel, wood, reinforced concrete, etc.) to construct.

The beam bridge is one of the basic systems of the bridge, which is very convenient to manufacture and erect, widely used, and occupies a large proportion in the bridge construction.

Stress characteristics of arch bridges and suspension bridges:

1. Arch bridge.

The main load-bearing structure of an arch bridge is the arch ring or arch rib. Under the vertical load of this structure, the pier or abutment will be subjected to horizontal thrust, and this horizontal thrust will significantly cancel out the bending moment action in the arch ring (or arch rib) caused by the load. The load-bearing structure of the arch bridge is mainly composed of hypothetical compression differential limbs, which are usually constructed with strong compressive resistance of dock materials (bricks, stone fallacia, concrete) and reinforced concrete.

2. Suspension bridge.

The suspension bridge takes the suspension cable as the main load-bearing structure, the structure is light, the structure is simple, the force is clear, and the long-span bridge can be built economically and reasonably with a small building height. Due to the light weight of the structure of this kind of bridge and poor stiffness, there is a large deformation and vibration under the action of vehicle dynamic load and wind load.

The steel truss girder bridge is a structural form that hollows out the steel plate girder bridge with solid belly according to certain rules, and the structure as a whole is the stress mode of the beam, that is, the knot Lachang structure that mainly bears the bending moment and shear force.

The steel truss girder bridge is composed of truss members, and each truss member is mainly subjected to axial forces. Compared with the solid web beam, the web of the whole is replaced by the sparse web member, thereby saving steel and reducing the weight of the structure, and because the amount of web steel is reduced compared with the web of the solid web beam, the steel truss girder can be made into a larger height, thereby having greater stiffness and greater spanning capacity. However, the rods and crack preparation joints of steel truss girder are more, the structure is more complex, and the manufacturing is more labor-intensive.

The rack structure corresponds to the frame structure and the portal rigid frame structure, which is classified according to the calculation model and is a professional term.

The truss structure is to say that the transverse member is to replace the beam with a truss, and it is used in the row frame structure, and 'truss structure' is not a professional term, let alone a type of structural type.

The nodes of the beam and the column of the portal rigid frame structure are just connected, which are mostly used in the single-storey Zaohushu light steel structure workshop. The joints between the beams and the columns of the row frame structure are hinged and are used for single-storey workshops.

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The deformation characteristics of the wheel of the bending steel truss beam are as follows: when the member is subjected to an external force perpendicular to the rod shaft or is subjected to a force couple action in the longitudinal plane of the burning; The rod axle is bent into a straight curve steel truss (STLT machine USS), and the truss made of steel is used for roof structures, crane beams, bridges and hydraulic gates of industrial and civil buildings, etc., and steel trusses are commonly used as the main load-bearing components. All kinds of towers, such as mast towers, TV towers and transmission line towers, etc., are commonly used as space steel trusses composed of three-sided, four-sided or multi-sided plane trusses.

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