Chapter I On-the-job Training Materials for Bridge and Tunnel Workers

This chapter mainly introduces the composition and classification of bridge and tunnel buildings, bridge and tunnel clearance and bridge and tunnel load.

Bridges and tunnels are the general names of bridges, tunnels, culverts, open channels, overpasses, underpasses, overpass bridges and structures for river regulation.

Composition and classification of bridges

(I) Composition of the bridge The bridge consists of superstructure, substructure, protective equipment and buildings for river regulation (Figure 1- 1).

Superstructure: including bridge deck, bridge span structure (beam arch) and bearing.

Substructure: including pier, abutment and foundation.

Protective equipment and structures for river regulation: including bridge and culvert height limiting protective frame, cone, bank protection, foundation protection, bottom protection, diversion dike, groin, pear-shaped dike, etc.

(2) Bridge classification

1. Classification by bridge length

Extra large bridge: The length of the bridge exceeds 500 meters.

Bridge: the length of the bridge exceeds100m to 500m.

Medium bridge: the length of the bridge is more than 20m to 100m.

Small bridge: the length of the bridge is 20 meters or less.

2. According to the classification of beam and arch materials

Steel bridge: the span structure of a bridge with steel as the main building material.

Reinforced concrete bridge: The span structure of the bridge is mainly made of concrete with stressed steel bars. The bridge span structure is mainly composed of prestressed steel collar concrete.

Stone bridge: a bridge with a span structure built of stone.

Wooden bridge: a bridge-span structure with wood as the main building material.

3. Classification by bridge deck position

(1) Deck bridge: the bridge with the deck located at the upper part of the bridge span structure (Figure 1-2(a)).

(2) Half-through bridge beam: the bridge deck is located in the middle of the bridge span structure (Figure 1-2(b)).

(3) Through bridge: The deck is located at the lower part of the bridge span structure.

Through bridges are divided into through bridges and semi-through bridges. Bridges with transverse connections above the deck are called through bridges (figure 1-3(a)), and bridges without transverse connections above the deck are called half-through bridges (figure 1-3(b)).

4. Load classification according to the characteristics of bridge span structure.

(1) Beam bridge: a bridge with a beam as the span structure. There are three kinds of simply supported beam bridges: continuous beam bridge and cantilever beam bridge.

(2) Arch bridge: a bridge with arch ring or arch rib as the span structure. Arch bridges can be divided into hingeless arch, double-hinged arch and three-hinged arch according to their structural forms. According to whether there is external thrust, it is divided into thrust arch and no thrust arch.

(3) Rigid frame bridge: a bridge whose span structure is rigidly connected with the pier or abutment.

(4) Frame Bridge: This bridge is an integral box bridge. (5) Suspension bridge: The cables anchored at both sides (both ends) supported by the bridge tower, and the bridge deck and beams suspended by the suspenders hanging on the cables form a bridge with a span structure.

(6) Cable-stayed bridge: A bridge with stay cables connecting the tower and the main beam as the bridge span structure.

(7) Integrated system bridge: The bridge span has several system characteristic structures, which are combined with each other, such as steel truss arch bridge.

According to the section form of the beam.

(1) plate beam: suitable for low-height beams. This form is adopted when the height of the bridge is limited.

Steel plate beam is an I-section beam composed of steel plate or section steel, which is connected by longitudinal and transverse connection systems. Concrete slab beam is a common reinforced concrete beam with wide web and small span.

(2)T-beam: T-beam is the most common cross-section form of existing concrete bridges. Concrete T-beam is a kind of concrete beam with T-shaped cross section.

(3) Box Girder: With the speed-up of the train, the requirements for the rigidity of the bridge are getting higher and higher, and more and more box girders are used on the line, as shown in figure 1-4. Steel box girder is a single-cell or multi-cell box-section girder composed of steel plates strengthened by longitudinal and transverse stiffeners. Concrete box girder refers to a concrete beam with one or several closed boxes in cross section.

(III) Dimensions and specifications of each part The dimensions of each part are shown in figure 1-5.

1. span (calculated span)

(1) Simply supported beam, continuous beam, cantilever beam, cable-stayed bridge, suspension bridge and double hinged arch are the distances between the bearing centers at both ends of each hole.

(2) Hinged arch bridges, rigid bridges and box bridges are open holes.

2. The total length of the beam

The length between the two end faces of a beam.

3. Clear span of beam (clear hole)

The distance between the full-length abutment edges of adjacent piers measured along the calculated water level.

4. Bridge length (bridge length)

(1) Beam bridge refers to the length between the front walls of abutment ballast.

(2) Arch bridge refers to the length between the outer ends of two expansion joints between the upper side wall of arch and the side wall of abutment.

(3) Rigid frame bridge (or frame bridge) refers to the length along the span direction between the outer sides of rigid frame (or frame structure).

5. Total length of bridge

The total length of a bridge refers to the distance between the two abutment tails on the bridge axis.

6. Total length of bridge hole

Refers to the drainage width of the bridge, that is, the sum of the net span of each hole of the bridge. Inclined bridge is the sum of the vertical distances of two piers (platforms); An arch bridge is the sum of the net lengths at the arch line of each hole. When the conical fill exceeds the abutment, it is measured along the middle line between the calculated water level and the low water level.

7. Bridge height

Vertical distance from the bottom of bridge deck rail to the most concave point of river bed.

8. Clearance height under bridge

The free height between the bottom of the bridge span structure and the water surface, road surface or rail surface that can be used for traffic.

9. Temperature span

Refers to the cross-sectional length of the beam span that is lengthened and shortened due to the influence of temperature (Figure 1-6).

Second, the composition and classification of tunnels

(A) the composition of the tunnel

The tunnel consists of two parts: the main building and auxiliary equipment. The main building consists of a cave body and a cave door; Auxiliary equipment includes car-avoiding tunnels and waterproof and drainage facilities, and long tunnels also have special ventilation and lighting equipment.

(2) tunnels are classified by length

Extra-long tunnel: the total length exceeds10000m;

Long tunnel: the total length is over 3000m to10000m;

Middle tunnel: the total length is more than 500 meters to 3000 meters;

Short tunnel: the total length is 500 meters or less.

Tunnel length refers to the distance between the end walls of the entrance tunnel, that is, it is calculated by the intersection of the intersection line between the end wall and the top surface of the inner rail and the center line of the line. When calculating, the downline of the double-track tunnel shall prevail; The tunnel at the station obeys the main line.

III. Composition and Classification of Culverts

Culverts, open channels, aqueducts and inverted siphons are collectively called culverts.

Culvert consists of tunnel body, foundation, entrance and exit buildings (i.e. end wall, wing wall, etc.). ) and auxiliary equipment of retaining wall at the exit of the tunnel body (Figure 1-7).

(A) Culvert classification

According to the structural form, there are arch culvert, round culvert, frame culvert and slab culvert.

According to the hydraulic characteristics, there are pressure culvert and non-pressure culvert;

According to the number of holes, there are single holes, double holes and multiple holes.

The minimum aperture of the spillway culvert should not be less than 1.25m, and the total length should not exceed 25m. When the total length is greater than 25m, the aperture should be increased accordingly to facilitate maintenance. The diameter of irrigation culvert without siltation shall not be less than 0.75m.. When the aperture is 0.75m and the clear height h

If the existing culvert does not meet the above requirements, it should be gradually transformed according to the specific situation.

(2) the provisions of the culvert size

1. Culvert hole cleaning

(1) Arch culvert is the horizontal distance between arch lines.

(2) The frame structure culvert refers to the horizontal distance inside the culvert.

(3) The circular culvert is the inner diameter (elliptical or oblate culvert is the maximum distance in the horizontal direction).

(4) Slab culvert is the clear distance between piers.

2. Total length of culvert

(1) The total length of the culvert is the axial length of the culvert, including the end wall.

(2) The total length of the frame culvert and the slab culvert is the lateral width between the side walls, calculated as the long side.

Clearance is the outline dimension line which is stipulated by the state that railway buildings and any other equipment are not allowed to invade, and its purpose is to ensure the safe operation of railway rolling stock and overloaded goods.

First, building clearance.

Building clearance is the cross section perpendicular to the center line of the line.

(I) Basic Building Clearance The height of the basic building clearance (Figure 1-8) is calculated from the top surface of the rail, and the transverse dimension is calculated from the center line of the line.

The half-width of the single-line straight-line basic building is 2440m m. This is because the half-width of the maximum first-class overloaded goods loading clearance is 2225mm, plus the lateral movement of goods 170.5mm, plus the safety degree of 44.5mm, namely:

Half width of basic building clearance =2225+ 170.5+44.5=2440mm.

The clearance height of the foundation building is 5500mm, which is because the maximum clearance height of the overloaded goods is 5300m, plus the upward vibration offset of the goods is 46.5m, plus the safety amount is 153.5mm, namely:

Building clearance height =5300+46.5+ 153.5=5500mm.

During the period of bridge and tunnel maintenance, construction machinery and scaffolding shall not invade the basic building clearance (the clearance shall be widened according to the provisions on the curve) to ensure the safety of traffic and personnel. (B) the building clearance on the curve

On the curve, both the inside and outside of the building limit need to be widened. The widening value is calculated as follows:

Where r- curve radius (m);

H—— the height from the calculated point to the rail surface (mm);

H- superelevation of outer rail (mm).

The second is the loading clearance of out-of-gauge goods.

The loading clearance of out-of-gauge goods is shown in figure 1-9.

Third, the bridge building clearance

The bridge building clearance is slightly larger than the building clearance, as shown in figure1-10 ~1-12. Lighting, communication and signal equipment can be installed between them. The clearance of newly built, maintained and rebuilt bridges shall meet the requirements of bridge building clearance.

Note: H in the figure is the height of catenary structure. When elastic suspension is used, the section of 200km/h is 1 100mm, and the section below 160km/h is 700 mm. When rigid suspension is used, the height of the structure is determined separately.

The section clearance of through truss beam and half-through beam on the curve, as well as the value to be widened, are not only related to the radius of the curve, the superelevation of the outer rail and the length of the vehicle, but also related to the length of the beam.

(1) The width of the inside and outside of the monorail is within W, but outside W..

Considering the electric traction clearance:

(2) Widening the center distance of double track.

Four, the tunnel construction clearance

(1) Construction department of interval straight tunnel

See figure1-1~1-1-13 for the construction boundary outline of the interval linear tunnel.

(2) Widen the tunnel clearance on the interval curve.

(1) The method of widening inside and outside the single-track curve is the same as that of building clearance.

(2) For double-track tunnels, the line spacing on the curve is generally widened as follows.

Five, bridge and tunnel construction clearance management

Relevant departments should carefully grasp the accurate measurement section of bridges, tunnels, overpasses, overpasses, aqueducts and other buildings in the pipeline and the size of each part from the center line of the line. According to the regulations of railway technical management, the clearance of bridges and tunnels on important lines shall be inspected once every five years, and other lines shall be inspected once every 10 years.

(A) inspection methods of bridge and tunnel clearance

Inspection methods of bridge and tunnel clearance are commonly used. The inspection frame method is to install the inspection frame vertically on the center line of the bogie at the front of the vehicle, and measure its position and specific size where the gap is insufficient. Some outer tunnels also use photographic inspection, that is, the car is equipped with a fixed camera, which can shoot the light strip showing the inner contour of the tunnel at a fixed focal length under driving conditions, and after washing, interpret and convert the actual size of the tunnel section or find out the minimum comprehensive section size of the section.

(2) Draw a comprehensive minimum clearance map.

According to the data measured by the above inspection, the comprehensive clearance map of bridges and tunnels is drawn, and the railway bureau draws the comprehensive minimum clearance map of bridges and tunnels in each section of the pipeline.

When the bridge and tunnel clearance is insufficient, it should be improved in a planned way. The actual building clearance of existing bridges and tunnels can still meet the following requirements, and the extension can be postponed:

(1) When the actual building clearance exceeds the maximum loading clearance of out-of-gauge goods and there is a clear distance exceeding 100mm;

(2) In the double-track section, when the bridge and tunnel clearance of a line can meet the requirements.

There are three kinds of loads borne by bridges and culverts: main load (main force), additional load (additional force) and special load.

First, the main force

The main stress is normal, frequent or repeated, including dead load and live load.

Dead load generally refers to the dead weight of the structure, earth pressure, hydrostatic pressure, buoyancy and prestress, etc., and its size and action point are generally fixed, so it is called dead load.

Live load mainly refers to the load caused by train weight and train movement, generally referring to train weight, impact force, centrifugal force, sidewalk load, etc.

China Railway Department has made a comprehensive study on all kinds of locomotives and rolling stock, and worked out the general standard load for the whole railway.

1. Zhong Yi live load

"People's Republic of China (PRC) (PRC) Railway Standard Live Load", that is, "Medium One Live Load", includes ordinary live load and special live load (Figure 1- 14).

2.ZK live load

"China Passenger Dedicated Line Standard Live Load", namely "zK Live Load" (Figure 1- 15).

Second, additional force.

Additional force is an accidental load, and its maximum value will not appear frequently, so the probability of various additional forces appearing at the same time is even smaller. Including train braking force or traction, lateral sway force, wind force, running water pressure, ice pressure, additional force caused by temperature change, frost heaving force, etc.

Third, special load.

Special load is a load acting under special circumstances, which is often temporary or disastrous, such as the impact of ships or rafts, earthquake force, construction load, etc.

The bearing capacity of operating bridges and culverts shall be checked according to the Code for Verification of Railway Bridges, and expressed by the verification bearing coefficient "K". A is the multiple of the standard live load that the structure can bear and shall meet the following requirements:

(1) The bridge and culvert structure shall satisfy K≥ 1.

(2) The allowable live load of temporary bridges and culverts must meet the requirements of Q.

Insufficient carrying capacity (i.e. K.

The bearing capacity of rebuilt bridges and culverts shall meet the provisions of Basic Code for Design of Railway Bridges and Culverts.

? Review thinking questions

1. What parts does this bridge consist of?

2. How are bridges classified by length?

3. How long is a bridge?

4. What is the height of the bridge?

5. What are the parts of the tunnel?

6. How to determine the length of the tunnel?

7. How to classify the tunnel connection length?

8. What are the parts of the culvert?

9. What is the gap?

10. What are the types of bridge loads?