1. Gravity pier: The gravity pier of a beam bridge consists of pier cap, pier body and foundation. Pier cap should meet the needs of bearing arrangement and local bearing; Compared with the gravity pier of beam bridge, the gravity pier of arch bridge has structural facilities such as arch frame, and the gate pier is thicker than the ordinary pier, which can bear a larger horizontal thrust in one direction and prevent collapse.

2. Gravity abutment (U-shaped abutment): It consists of abutment cap, back wall, abutment body (front wall and side wall), foundation and tapered slope. The back wall, front wall and side wall are combined into a whole, which has the functions of retaining wall and supporting wall.

3. Light pier of beam bridge

(1) Reinforced concrete thin-walled pier: The masonry is small in volume and light in structure, and the specific gravity pier can save about 70% of the masonry.

(2) Column pier: It is composed of two or more separated columns (or piles) and is one of the widely used pier forms in highway bridges.

(3) Flexible bent pile pier: it is formed by connecting single or double rows of reinforced concrete piles with reinforced concrete capping beams.

4. Light abutment of beam bridge

(1) Light abutment with supporting beam

(2) Embedded abutment:

(3) Reinforced concrete thin-walled abutment:

(4) Reinforced earth abutment:

5. Lightweight pier of arch bridge

(1) triangular bar one-way thrust pier;

(2) Cantilever unidirectional thrust pier.

6. Light abutment of arch bridge

(1) splayed abutment.

(2)u-shaped abutment

(3) Back-supported abutment:

(4) Backrest frame support:

(2) Mechanical characteristics of the bridge substructure

Pier is the middle supporting structure in multi-span bridge, which not only bears the vertical force, horizontal force and bending moment generated by superstructure, but also bears the impact of wind, running water pressure, possible earthquake force, ice pressure, ships and floating objects.

Abutment is set at both ends of the bridge, which not only supports the bridge span structure, but also connects the connecting dikes at both sides. It should not only be able to retain the soil and protect the embankment, but also be able to bear the additional soil lateral pressure caused by the fill at the back of abutment and the vehicle load on the fill.

When calculating the stress of pier and abutment, the most unfavorable load combination should be carried out according to various possible load situations.

Master the classification and stress characteristics of bridge superstructure

1. Slant slab bridge

(1) load tends to shift to the direction with the shortest distance between two supporting edges;

(2) The stress on each corner can be described by comparing with the work of continuous beam. Oblique angle produces greater negative bending moment and greater reaction force, while acute angle tends to incline upward.

(3) Under the uniformly distributed load, when the axial span of the bridge is the same, the maximum span bending moment of the skew slab bridge is smaller than that of the main bridge;

(4) Under the uniformly distributed load, when the axial span of the bridge is the same, the transverse bending moment of the skew slab bridge is smaller than that of the main bridge.

2. Assembled simply supported reinforced concrete T-beam: the beam rib and wing plate (bridge deck) are combined into a load-bearing structure, and the concrete in the tension area between the ribs is hollowed out to reduce the weight of the structure. It not only makes full use of the compressive capacity of the expanded bridge deck, but also effectively exerts the tensile effect of the steel bars under the beam ribs.

3. Prestressed concrete simply supported beam T-beam: Prestressed concrete simply supported beam has the concept of core distance, and the greater the distance, the greater the resistance effect. In order to improve the core distance, the structure can adopt the form of large flange, thin rib and wide and short horseshoe. To match the distribution of positive bending moment in the beam and prevent tensile stress, the longitudinal prestressing tendons must be bent at the end of the beam or cut off in the middle. But bending can improve the shear capacity near the fulcrum.

4. Continuous system bridge

(1) Due to the negative bending moment at the fulcrum, the positive bending moment in the mid-span is significantly reduced, which can reduce the height of the main girder in the mid-span and increase the span. When the beam height near the fulcrum section increases to form a variable section, the mid-span bending moment can be further reduced;

(2) Because it is statically indeterminate structure, the factors that produce additional internal force include prestress, concrete shrinkage and creep, uneven settlement of pier and abutment, and temperature gradient change of cross section.

(3) The requirements of positive and negative bending moments should be considered during reinforcement, and the alternating changes of positive and negative bending moments of cross sections should be considered during incremental launching method construction.

5. Cable stayed bridge

(1) Stay cables are equivalent to external cables with increased eccentricity, which can give full play to the ability of resisting negative bending moment and save steel.

(2) The horizontal component of stay cables is equivalent to the prestress of concrete;

(3) The main girder is supported by multiple points of elasticity, with small height-span ratio, light dead weight and large span.

6. suspension bridge

The main cable (1) is the main load-bearing structure, and its huge tensile force needs to be borne by the solid ground anchor. For continuous suspension bridges, the horizontal thrust of the cables on both sides of the middle ground anchor is basically balanced, and the vertical force is mainly borne by its own weight.

(2) The nonlinear deformation of main cable generally adopts deflection theory or deformation theory. Deflection theory is to consider the new resistance caused by the vertical deformation (deflection) of the main cable caused by the original load (such as dead load), and then consider the internal force balance after deformation; Deformation theory regards suspension bridge as a structural system composed of single members. In mechanical analysis, the stiffness of each member is calculated first, and then it is put into the matrix of the structural system to find the overall balance.