Part One Chapter One
1. Generally speaking, the composition of a bridge can be divided into two parts : the upper structure and the lower structure.
2. The basic composition of girder bridge: embankment, bridge span structure, abutment, support, pier, foundation, cone slope protection
3. The basic composition of the arch bridge: conical slope protection, arch axis, arch structure, abutment, arch foot, pier, foundation, arch ring, and vault . Illustrated bridge engineering common terms and terms
4. Clear span : The girder bridge is the horizontal distance between two adjacent piers (or abutments) on the design flood level or navigable water level. Arch bridge is the horizontal distance at the arch line
5. Calculate the span : for a bridge with supports, it is the distance between the centers of two adjacent supports of the span structure; for a bridge without supports, it is the distance between the centers of supports; for an arch bridge, it is the distance between the two ends of the arch axis. distance between
6. Standard span : beam bridge and slab bridge refer to the length of the centerline of the bridge between the centerlines of two adjacent piers or the length of the centerline of the bridge between the centerline of the pier and the front edge of the back of the abutment; arch bridges and culverts are net spans
7. Overall length of the bridge : The bridge with abutments is the distance between the side walls of the abutments on both banks or the end of the eight-character wall , and the bridge deck without abutments is the length of the roadway.
8. Overall length of the bridge : for beam bridges and slab bridges, it is the distance between the front edges of the two abutment backs, that is, the total length of the porous standard span ; for arch bridges, it is the distance between the arching lines in the abutments at both ends; Bridge Deck Lane Length
9. The high water level calculated according to the design flood level frequency is called the design flood level
10. The building height of the bridge : the vertical distance between the bridge deck and the lowermost edge of the bridge span structure is not only related to the system of the bridge structure and the size of the span, but also varies with the height position of the carriage part on the bridge
11. Bridge height : Bridge height for short, refers to the height difference between the bridge deck and the low water level (river with water); or the distance between the bridge deck and the road surface of the route under the bridge (overpass bridge); The distance between the bottom of the ditch (dry bridge)
12. The allowable building height refers to the difference between the elevation of the bridge deck (or rail top) determined in the road (or railway) alignment and the elevation of the top of the navigation clearance
13. According to the position of the upper structure traffic lane, bridges are divided into upper-supported bridges , middle-supported bridges , and lower-supported bridges
14. According to the total length and span of bridges, bridges are divided into extra-large bridges , large bridges , medium bridges , small bridges , and culverts
15. According to the system, bridges are divided into: girder bridge , arch bridge , rigid frame bridge , suspension bridge, composite system bridge
Part 1 Chapter 2
1. The design principles of China's highway bridges are safety , durability , applicability , economy , environmental protection and beauty or safety, reliability, applicability, durability, economy, rationality, advanced technology, beauty, environmental protection and sustainable development
2. The design procedure of my country's bridges is divided into preliminary work and design stage. Preliminary work includes preparation of pre-feasibility study report and engineering feasibility study report . The design stage is carried out in three stages : preliminary design , technical design and construction drawing design
3. Bridge design includes plane design , elevation design and cross-section design
4. Main content of facade design: determination of approach road, approach bridge, starting and ending point of main bridge or demarcation point mileage ; determination of bridge total span, bridge sub-hole, pier number and center line mileage ; bridge deck elevation and bridge Clearance, longitudinal slopes of bridge and bridgehead approaches, and embedding depth of foundations
5. The main content of cross-section design: determine the width of the bridge deck ; the layout of the cross-section of the bridge span structure
Part One Chapter Three Bridge Design Loads
1. Usually, bridge actions are divided into four categories: permanent action , variable action , accidental action , and earthquake action
2. Permanent effect : an effect that always exists in the design reference period and whose magnitude changes are negligible compared with the average value, or whose change is monotonous and tends to a certain limit value
Variable effect : The effect whose magnitude changes with time during the design basis period, and the change value is not negligible compared with the average value
Accidental effect : It does not necessarily appear in the design reference period, but once it occurs, its magnitude is large and the duration is very short
3. The car load level is divided into highway-level I and highway-level II; it consists of lane load and vehicle load
4. The lane load is composed of uniform load and concentrated load , which is used for the overall analysis and calculation of the bridge structure ; the vehicle load is used for the analysis and calculation of the local loading of the bridge, culverts, abutments and retaining walls, etc.
5. The direction of the braking force of the car is the driving direction ; the focus point is 1.2m above the bridge deck
6. Combination of bearing capacity limit state action effect is divided into: ① basic combination: combination of permanent action design value and variable action design value , ② accidental combination: permanent action standard value and variable action certain representative value, a random action Design value phase combination , ③ action earthquake combination
7. Combinations of normal service limit state action effects are divided into: ① frequent combination: combination of permanent action standard value and vehicle load frequent value, and other variable action quasi- permanent values; Combination of quasi-permanent values
Chapter 1 and Chapter 2 of Part Two
1. Concrete girder bridges are divided into simply supported girder bridges , continuous girder bridges , and cantilever girder bridges according to the structural system
2. Concrete girder bridges are divided into slab bridges , rib girder bridges , box girder bridges and composite girder bridges according to the cross-sectional shape of the main girder
3. Under the action of uniformly distributed dead load, draw the schematic diagrams of the bending moments of simply supported beams, cantilever beams and continuous beams (P65 Figure 2-1-2: Mechanic characteristics of beam bridges under uniformly distributed loads)
4. The structure of the bridge deck system includes: bridge deck pavement, expansion joints, sidewalks (or safety belts) and curbs, car separation belts, railings (guardrails), waterproof and drainage facilities, lamppost lighting equipment, etc.;
5. The role of bridge deck pavement: to protect the roadway slab or the main load-bearing structure from directly bearing the wear of the wheel load and the erosion of rain and snow, and has a certain effect of evenly distributing the concentrated load of the wheels
6. Commonly used bridge deck pavements include asphalt concrete , cement concrete and asphalt surface treatment
7. The method of cross slope setting and their respective applicability :
① For slab bridges or cast-in-place ribbed girder bridges, make the top of the pier inclined, and cover the bridge deck on it
②For prefabricated rib-slab bridges, pavement layers of different thicknesses including concrete triangular cushions and pavement layers of equal thickness can be used
③When the bridge width is large, directly make the roadway slab into a double slope
- The role of bridge deck expansion joints :
Adapt to the deformation needs of the bridge superstructure under the influence of temperature changes, live loads, concrete shrinkage and creep, etc., and ensure the stability of vehicles passing through the bridge deck
9. Commonly used telescopic devices are: docking telescopic device , steel supporting telescopic device , rubber combined shearing telescopic device , modular supporting telescopic device , seamless telescopic device
Part Two Chapter Three
1. Explain the mechanical characteristics of simply supported inclined-slab bridges, and what are the characteristics of reinforcement?
(1) Force characteristics
①The load tends to be transmitted in the direction of the shortest distance between the two supporting sides
②The force situation of each corner point can be described by comparing the work of continuous beams
③Under the action of uniform load, for the same span bridge and inclined bridge, the maximum bending moment M oblique max < M positive max in the span , and the position of the maximum bending moment or maximum stress in the span changes with the increase of the skew angle Move from center to obtuse angle
④Under the action of uniform load, for the same span bridge and oblique bridge, the mid-span transverse bending moment M oblique > M positive, it can be considered that the increase of the transverse bending moment is equivalent to the decrease of the bending moment in the span direction
(2) Reinforcement characteristics : When the skew angle is not greater than 15°, the main reinforcement can be arranged parallel to the longitudinal axis of the bridge. When the skew angle is greater than 15°, the main reinforcement should be arranged perpendicular to the direction of the support axis of the slab. At this time, a steel belt parallel to the free edge of no less than three main reinforcements should be installed on the top and bottom of the free edge of the slab, and stirrups should be used. tight
2. The maximum reaction force of the inclined slab bridge occurs near the obtuse angle
3. The horizontal connection methods of prefabricated slab bridges include groove-and-groove concrete hinge connection and steel plate welding connection ; the horizontal connection methods of prefabricated girder bridges include welded steel plate joints, bolt joints, buckle joints, cast-in-place wet joints, and tongue-and-groove hinged joints
4. Common block division methods for prefabricated girder bridges include longitudinal vertical joints, longitudinal horizontal joints, and vertical and horizontal vertical joints
5. Why are some prestressed steel bars near the end of the pre-tensioned beam insulated from the concrete?
In order to adapt to the change of internal force (mainly bending moment) in the beam along the bridge span, the bending moment generated by the self-weight and live load of the beam end is very small, so as to prevent the cracking of the upper flange concrete at the end due to excessive prestress eccentricity
6. Why is the prestressed tendon in the post-tensioned prestressed reinforced concrete beam arranged in a curved line?
① The change of the suitable bending moment along the bridge span, the bending moment is large in the middle of the span, and the bending moment near the two ends is small
② Adapt to the change of shear force, the shear force near the beam end is large, and the pre-shear force provided by bent ribs can meet the shear resistance requirements
③It is convenient for the scattered arrangement of prestressed steel anchors
7. According to the stress diagram of the combined girder bridge and the prefabricated T-girder bridge, what is the difference in the force characteristics of the two? p 126
The dead load of the combined girder bridge is borne by the beam rib and the live load is borne by the whole section under the action of dead load and live load.
The dead load and live load of the prefabricated T -beam are both full-section under the action of dead load and live load. The maximum stress is at the top of the bridge deck.
Chapters 4 and 6 Cantilevers and Continuous Systems
1. Why do most highway long-span prestressed concrete continuous girder bridges adopt the form of unequal span and variable section? (Take three spans as an example)
The layout of continuous beam spans generally adopts the form of unequal spans. If an equal-span arrangement is adopted, the internal forces of the side spans will control the design of the full bridge, which is uneconomical. In addition, the side span is too long, which weakens the stiffness of the side span, increases the amplitude of the bending moment change of the live load in the mid-span section of the mid-span, and increases the number of prestressed tendons. From the analysis of the mechanical characteristics of prestressed concrete continuous beams, it is advisable to adopt the arrangement of variable cross-sections for the facade of continuous beams. Since the long-span continuous beam generally adopts the cantilever construction method, under the action of transverse load, the fulcrum section of the continuous beam will have a large negative bending moment. From the absolute value, the negative bending moment of the fulcrum section is often greater than the positive bending moment of the mid-span section. moment, so the variable cross-section beam can better conform to the law of internal force distribution at two points
2. Which dimensions of variable cross-section prestressed concrete continuous box girder bridges change along the length of the girder? Why change?
① Beam height: Under the premise of not being affected by the building height limit in section design, the girder height of continuous box girder should adopt variable height, and its bottom curve can adopt quadratic parabola, broken line and 1.5-1.8 in between. For subparabolic form, the specific selected form should be determined according to the uniform force on the upper and lower edges of each section and the ease of bundle distribution. According to the analysis of the completed bridge data, the beam height H of the fulcrum section is about (1/16-1/20) L (L is the length of the middle span), and the mid-span beam height H is about (1/1.6-1, 2.5) H branch. In the specific design, it is also determined by comparing several schemes according to the ratio of the side span to the middle span, load and other factors.
②Web thickness: The main function of the box girder web is to bear the main tensile stress caused by the bending shear stress and torsional shear stress of the structure. Thin, but the minimum thickness of the web should consider the requirements of the pipe arrangement of the steel bundle, the arrangement of the steel reinforcement and the pouring of concrete
③Thickness of top and bottom slabs (1) Top slab: Generally, two factors should be considered, that is, to meet the requirements of transverse bending moment of bridge deck; increase and gradually thicken to the top of the pier to meet the requirements of the lower edge of the box girder under compression. Scratch more. The thickness of the floor at the top of the pier should be 1/140-1/170 of the span, and the thickness of the floor in the middle of the span should be 20-25cm
3. Cantilever construction continuous beams or longitudinal steel beams of continuous rigid structures include types and their main design purposes
① Roof bundle: bear the negative bending moment of the cantilever construction stage
② Web bundle (bent bundle of top plate, bent bundle of bottom plate): provide pre-shear force and reduce main tensile stress
③ Mid-span floor bundle: bear the positive bending moment of the mid-span
④ Side-span floor bundle: bear side-span positive bending moment
⑤ Closing beam: bear the positive and negative bending moments of the closing section
⑥Continuous beam: strengthen the structural integrity and withstand positive and negative bending moments during use
4. The continuous girder bridge adopts cantilever construction, try to draw the schematic diagram of dead load internal force at each construction stage.
P256 Diagram a and diagram i Others are too difficult
Chapter 5 Calculation of Simply Supported Beam Bridges
1. One-way plate : a rectangular four-sided support plate, the plate when the side length ratio or aspect ratio l a / l b ≥ 2
2. Two-way plate : plate with aspect ratio l a /l b <2
3. Effective distribution width of the slab : under the load of the bridge deck, not only the slabs with a width of a directly bear the force, but also the adjacent slabs also participate in the work, and jointly bear the bending moment generated by the wheel load
4. Load lateral distribution : refers to the distribution of vehicle loads acting on the bridge among the main girders
5. Pre-camber : In order to eliminate the deflection caused by the long-term effect of the transverse load and the often acting live load, the reverse deflection is set
6. Driveway slabs are divided into one-way slabs and two-way slabs according to different force transmission
7. According to the force diagram, the bridge deck can be divided into one-way slab, cantilever slab, hinged cantilever slab , and two-way slab
8. The calculation methods of load lateral distribution coefficient include lever principle method , eccentric pressure method, transverse hinged plate method, transverse rigid beam method, and comparative orthotropic plate method
9. What is the basic assumption of the leverage principle method? How applicable is this method?
Basic assumption: Ignore the connection effect of the transverse structure between the main girders, assume that the bridge deck is broken at the ribs of the main girders, and consider it as simply supported beams or cantilever beams supported on the main girders along the transverse direction
Scope of application: It is used for the calculation of load lateral distribution when the load is close to the fulcrum of the main girder, and it can also be used for double main girder bridges or bridges without intermediate diaphragms with weak lateral connections
10. What is the basic assumption of the rigid beam method ( eccentric pressure method)? How applicable is this method?
Basic assumptions: ① Under the action of vehicle load, the intermediate diaphragm can be regarded as a rigid beam with infinite stiffness approximately, and the entire length of the diaphragm deforms in a straight line; ② Ignore the torsional stiffness of the main beam
Applicable conditions: Bridges with reliable lateral connections and bridge width-span ratio B/l≤0.5 (ie narrow bridges)
11. What is the basic assumption of the hinged plate method ? How applicable is this method?
Basic assumptions: ① Under the action of vertical load, only vertical shear force is transmitted in the joint; ② The lateral distribution of mid-span load satisfies the law of half-wave positive rotation
Applicable conditions: prefabricated slab bridges connected by cast-in-place concrete longitudinal groove joints, and prefabricated transverse hinged beams without intermediate diaphragms
12. What are the conditions and characteristics of the load lateral distribution coefficient changing along the bridge span?
Features: The greater the stiffness of the lateral connection, the more significant the lateral load distribution, and the more uniform the load on each main beam
- When calculating the following internal forces, it is necessary to consider the variation of the lateral distribution system along the span ( B )
A. Mid-span bending moment B. Mid-span shear force C. Quarter-point bending moment D. Pivot point shear force
14. The size of the pre-camber is usually equal to the vertical deflection value generated by all dead loads and 1/2 static and live loads
15. How to calculate the internal force of the main girder of the prefabricated simply supported girder bridge?
①Calculation of transverse load internal force ②Calculation of live load internal force ③Girder internal force combination and envelope diagram
Part III Concrete Arch Bridge Chapters 1 and 2
1. According to the structural system, arch bridges can be divided into two types : simple system arch bridges and composite system arch bridges
2. Stress characteristics of simple system arch bridge
① The main arch ring alone bears all the loads on the bridge span
② The horizontal thrust is directly borne by the pier
3. Stress characteristics of composite system arch bridge
① The roadway beam and the main arch ring jointly bear all the loads on the bridge span ② The transmission of horizontal thrust is restricted by the combination mode
4. Arch bridges can be divided into solid-belly arch bridges and empty-belly arch bridges according to the form of the arch structure
5. Simple system arches are divided into three-hinge arches , two-hinge arches , and no-hinge arches according to different static patterns.
6. Arch bridges can be divided into slab arch bridges , rib arch bridges , box arch bridges , and double-curved arch bridges according to the cross-sectional form of the main arch ring.
7. The role of expansion joints and deformation joints
① Expansion joints: mainly to prevent damage caused by excessive thermal expansion and contraction of the pavement structure caused by temperature changes; it also plays a role in preventing excessive displacement of the beam body
② Deformation joints: to meet the needs of the bridge superstructure deformed under the influence of temperature changes, live loads, concrete shrinkage and creep, etc., and to ensure that vehicles pass the bridge smoothly
8. The difference between expansion joints and deformation joints
① Expansion joints: Expansion joints must be set at the joints with a certain width, arch feet, main arch rings, and abdominal arch rings. The prefabricated panels made of sawdust and asphalt at a ratio of 1:1 are embedded in masonry or buried In-situ concrete
② Deformation joints: broken joints without joint width, the joints can be dry-laid and separated by asphalt felt
9. The upper structure of the truss arch bridge: truss arch pieces , transverse connecting systems , bridge deck
10. The truss arch generally consists of upper chord , lower chord , web , and solid web section
11. Rigid frame arches generally consist of main beams , secondary beams , main arch legs , and secondary arch legs
12. Why is the rise-span ratio of the main arch of an arch bridge one of the main parameters in the design of the arch axis?
① The ratio of the horizontal thrust to the vertical reaction force of the arch bridge increases with the decrease of the rise-span ratio
② When the rise-span ratio decreases, the arch thrust increases, otherwise, the horizontal thrust decreases
③ As the rise-span ratio of the hingeless arch decreases, the additional internal force generated by elastic compression, temperature change, concrete shrinkage and pier displacement increases.
④ It is difficult to construct the arch foot section when the rise-span ratio of the arch exceeds that of the ambassador
⑤ The rise-span ratio affects the shape of the arch bridge and the coordination of the surrounding landscape
13. Explain the treatment method and principle of unequal-span continuous arches
①Tie arches without thrust are adopted to avoid the influence of horizontal thrust on adjacent spans
② Reduce the effect of double arch:
A. Use different rise-span ratios: when the span is constant, the rise-span ratio is inversely proportional to the thrust. Therefore, in two adjacent holes, the arch with the rise-span ratio is selected for the large span (the large arch is steep), and the small span Choose an arch with a small rise-span ratio (small arch tank) to make the horizontal thrust of two adjacent holes roughly equal under the action of dead load
B. Use different arch foot elevations: the arch feet with a large horizontal thrust can be placed at a lower position, and the arch feet with a relatively small horizontal thrust can be placed at a higher position, so that the horizontal thrust on both sides can affect the base of the pier The resulting bending moments are balanced
C. Adjust the dead-load weight of the building on the arch: For the upward-supporting arch bridge, the purpose of adjusting the horizontal thrust can be achieved by adjusting the dead-load weight of the building on the two adjacent arches
D. Use different types of arch span structures: Adjacent spans can adopt different types of arch span structures, such as mid-span rib arches for large spans and top-span slab arches for small spans, plus other design parameters such as rise-span ratio Adjustment, the horizontal thrust of the arch feet of adjacent spans can be adjusted appropriately
Chapter 3 Calculation of Arch Bridges
1. Arch axis: the line connecting the centers of gravity (or centroids) of each section of the arch ring
2. Reasonable arch axis: By adjusting the shape of the arch axis, the shear force V = 0 and the bending moment M = 0 on each section of the arch ring . At this time, each section of the arch ring is in a state of uniform compression. The coincidence of the axial pressure lines is called the rational arch axis
3. There are three types of commonly used arch axes: circular arc , parabola and catenary
4. Arch axis coefficient: refers to the ratio of the dead load concentration of the arch foot to the dead load concentration of the vault
5. Arch axis equation y = f / ( m -1) · ( chkξ -1)
6. The change characteristics of the arch axis coefficient m and y1 of the catenary arch bridge are: y1 decreases with the increase of m, and increases with the decrease of m
7. Briefly describe the steps of determining the arch axis coefficient of the solid belly arch bridge
① First assume the value of m according to the span l and height f of the arch, and check the "sine and cosine function table of the inclination angle of each point of the catenary arch" in the "Highway Bridge and Culvert Design Manual-Arch Bridge" (above) from m and f / l , Get the cos φ j value at the arch foot
② Substituting the formula g j = h d γ 1 + hγ 2 + dγ /cos φ j , after obtaining g j , then substituting the formula m = g j / g d together with g d to calculate the value of m'
③ Then compare with the assumed m value, if the two match, that is, the assumed m is the real value; if the two do not match, then use the calculated m' value as the new hypothetical value, and recalculate until the two are close
8. Briefly describe the steps of determining the arch axis coefficient of the fasting catenary arch bridge
9. Five-point coincidence method : When calculating the arch axis coefficient of a catenary arch, it is required that the five key control sections of the arch ring, namely the vault top, two arch feet and two quarter points reach the pressure line and the arch axis must coincide. So that the cross-section of each arch ring does not produce excessive peak bending moments, this design method is called the five-point coincidence method
10. Why it is more reasonable to use the catenary line for the arch axis of the fasting hingeless arch than the dead load pressure line
Since the catenary has a better force bearing condition and a complete calculation form is available, the catenary is often used as the arch axis. The arch axis of the hollow hingeless arch bridge calculated and determined by the five-point coincidence method only ensures that five points of the full arch coincide with the dead-load pressure line of the three-hinged arch (excluding elastic compression), and there are differences in other cross-section points degree of deviation. The calculation shows that, from the vault top to the 1/4 section point, the general pressure line is above the arch axis; while from the 1/4 section point to the arch foot, the pressure line is mostly below the arch axis, and the arch axis and the corresponding three-hinge The deviation of the arch dead load pressure line resembles a sine wave
11. After considering the elastic compression of the catenary arch under constant load, what bending moments will be produced on the arch top and arch foot respectively?
①A positive bending moment is generated on the vault, and the pressure line moves ②A negative bending moment is generated at the arch foot, and the pressure line moves down
13. When the average temperature of the bridge position is greater than or less than the construction closing temperature, what kind of additional internal force will the main arch bear?
When the average temperature of the bridge position is greater than the construction closing temperature, the axis of the arch will elongate, pressure will be generated in the arch, negative bending moment will appear on the vault top, and positive bending moment will appear on the arch foot
When the average temperature of the bridge position is lower than the construction closure temperature, the axis of the arch will be shortened, tension will be generated in the arch, positive bending moment will appear at the top of the arch, and negative bending moment will appear at the arch foot
14. Arch stability checking is divided into longitudinal stability checking and transverse stability checking
15. Discuss the adjustment method and principle of the arch ring stress
①Adjust the internal force with the false load method : change the arch axis by changing the arch axis coefficient, thereby improving the internal force distribution of the arch
②Adjust the internal force with a jack : build the two halves into two cantilever curved beams on the arch frame, reserve a niche-shaped gap at the vault, and set up two rows at the upper and lower joints of the arch before the construction of the arch. The jack forms an eccentric force, which can cause the vault to generate a negative bending moment, and the arch foot to generate a positive bending moment, so as to eliminate the internal force generated by elastic compression, shrinkage and creep
③Use temporary hinges to adjust the internal force : when building the main arch, temporary hinges are made with lead pads at the cross section of the vault and arch feet. After the building on the arch is completed, the hinges are sealed to form a hingeless arch. That is to say, the dead-load internal force of the main arch can be calculated as a three-hinged arch, and the live load and temperature internal force can still be calculated as an unhinged arch. In this way, the additional internal force generated by the elastic compression of the dead load can be eliminated, and a part of the additional internal force caused by the settlement of the pier and the shrinkage of the concrete material that has occurred before the hinge sealing can be reduced.
④Adjust the internal force by changing the arch axis : By changing the arch axis, the arch axis and the dead load pressure line will have a favorable deviation, which can eliminate the large bending moment of the arch top and arch foot, and achieve the purpose of adjusting the stress of the arch ring
16. What is joint action? What is the relationship between its size and the type of architectural structure on the arch?
Combined action : refers to the role of the building on the arch and the main arch ring sharing the load
Relationship : ① When the building on the arch is a belly arch, the joint effect is greater; when the building on the arch is a beam-slab, the joint effect is small
② When the relative stiffness of the belly arch ring and the belly arch pier to the main arch is greater, the joint effect is greater
③ The smoother the abdominal arch, the greater its thrust stiffness and the greater the combined effect
④ The combined effect of the section of the arch foot and the quarter span is greater than that of the arch top
17. What is the double arch effect? How do the horizontal thrust and the positive bending moment of the vault change after considering the action of the arch?
①The effect of multiple arches : consider the interaction between the arch span structure of each hole and the bridge piers
② Calculated on the basis of continuous arches, the horizontal force in the arch is smaller than that calculated on the basis of the fixed arch, while the control design is that the negative bending moment at the arch foot and the positive bending moment on the vault top are larger than those calculated on the fixed arch; The force is smaller than that calculated according to the fixed arch
18. Calculation questions
It is known that the bending moment ∑M 1/4 = 2680 kN·m and ∑M j = 12980 kN·m produced by the dead load of a catenary vierendeel arch bridge with constant cross-section , try to find the arch axis coefficient m.
Part Four Just Build a Bridge
1. The bridge whose span structure and piers are integrally connected is called a rigid frame bridge, and its stress is between the arch bridge and the beam bridge
2. Try to compare the differences between continuous girder bridge and continuous rigid frame bridge in terms of structure and force
①Differences in structure: continuous girder bridges are provided with supports at the pier abutments; the main girder of continuous rigid frame bridges is consolidated with the pier
②Differences in force: both are statically indeterminate structures; however, continuous beams have no redundant constraints in the longitudinal bridge direction, and longitudinal displacements caused by pre-loading, concrete shrinkage and creep, and uniform temperature do not produce secondary internal forces; continuous rigid structures are statically indeterminate The higher the number of times, it is necessary to use the flexibility of the high pier to adapt to the longitudinal displacement, otherwise, the inner force of the second time will be very large. The continuous rigid frame piers participate in the bending action, which further reduces the bending moment of the main girder. However, as the flexibility of the pier increases, the bending moment on the main girder tends to that of the continuous beam.
Part five
1. According to different combinations of beams, towers and piers, the structural system of cable-stayed bridges can be divided into: floating system , support system , tower-beam consolidation system , and steel structure system
2. The force characteristics of the floating system
①Multi-point elastically supported continuous beam with main beam free to drift in the longitudinal direction
② There is no negative bending moment peak value in the main beam at the tower column
③ The secondary internal force caused by temperature and concrete shrinkage and creep is small
④ The deformation and internal force of each section of the main beam change smoothly and the force is uniform; in addition, the longitudinal swing of the main beam during an earthquake can play a role in seismic energy dissipation
⑤Temporary consolidation should be provided between the main beam and tower column during construction to resist unbalanced bending moment and longitudinal shear force during construction
⑥ Certain lateral constraints must be imposed on the main girder of the floating system at the junction of the tower and girder to resist the lateral horizontal force caused by wind force, earthquake force, etc.
3. Stress characteristics of the support system
①The main girder is vertically supported on the tower pier and has a certain horizontal constraint along the bridge direction (the semi-floating system has no constraints along the bridge direction), becoming a multi-span continuous beam with multi-point elastic support
②Generally, the smaller the restraint stiffness is, the smaller the horizontal seismic action on the structure is, but the horizontal deformation along the bridge direction increases
③The disadvantage is that the fulcrum with high rigidity makes the main girder have relatively large negative bending moment at this place
4. The mechanical characteristics of the tower-beam consolidation system
①The tower girder is fixed and supported on the pier, and the stay cables become elastic supports
②Remarkably reduce the bending moment of the cable tower and the axial tension on the central section of the main girder, and the structural temperature stress caused by the overall temperature rise and fall is small
③When the middle hole is fully loaded, the angular displacement of the main beam at the top of the pier will cause the tower column to tilt, causing a large horizontal displacement at the top of the tower, thereby significantly increasing the mid-span deflection of the main beam and the negative bending moment of the side span
5. Stress characteristics of steel structure system
①Towers, beams, and piers are fixed to each other to form a steel structure with multi-point elastic support within the span
② The overall rigidity of the structure is good, and the deflection of the main beam is small
③The negative bending moment at the fixed connection of the main girder is large, and the section near the fixed connection needs to be enlarged, and the cable tower also needs to bear the temperature stress generated by the fixed connection system and the horizontal earthquake action
6. The layout of stay cables in the plane includes radial shape , harp shape , fan shape and star shape
7. Three commonly used symmetrical anchor structures for cables on tower columns are self-anchored , ground-anchored , and partially ground-anchored
8. The suspension bridge consists of four main structures: cables , bridge towers , anchorages , and stiffening beams
9. According to different cable anchoring methods, suspension bridges can be divided into ground-anchored suspension bridges and self-anchored suspension bridges
Title VI Bridge Bearings
1. The function of the bridge support is
①Transfer the supporting reaction force of the upper structure, including vertical force and horizontal force caused by dead load and live load
② Guarantee the free deformation of the structure under the action of factors such as live load, temperature change, concrete shrinkage and creep, so that the actual stress of the upper and lower structures conforms to the static calculation diagram of the structure
2. The support can be divided into fixed support and movable support according to its allowable displacement mode , and the movable support can be divided into one-way movable support and two-way movable support
3. The bearings can be divided into steel bearings , rubber bearings and concrete bearings according to their production materials.
4. The support can be divided into: arc -shaped steel plate support , roller support, rocker support , plate rubber support , basin rubber support , spherical support according to its structural form
5. Explain the working principle of the plate rubber bearing
Use the uneven elastic compression of rubber to realize the rotation angle θ; use its shear deformation to realize the horizontal displacement Δ
6. Explain the working principle of the basin rubber bearing
Use the three-way restraint of the bottom steel basin to the rubber block to obtain a large bearing capacity; use the low friction coefficient of the polytetrafluoroethylene plate on the middle liner and the stainless steel plate on the top plate to obtain the horizontal displacement of the hammer; use the three-way in the steel basin Uneven compression to the stressed elastic rubber mass for large corners
7. Briefly describe the bearing arrangement of simply supported beam bridges on highways
① Façade setting : set a fixed support at one end and a movable support at the other end
②Plane setting : On the bridge pier set with fixed support, generally one fixed support is set, and the adjacent support is set as one-way movable support which is movable laterally and fixed vertically; while on the pier set with movable support, generally Set a longitudinal movable support (corresponding to the fixed support), and the rest are set as two-way movable supports
8. Briefly describe the layout of continuous girder bridge supports
①Facade setting : Generally, a single row of supports is set on the top of the pier along the facade, that is, a fixed support is set on one pier or platform of each joint, and movable supports are required on other piers and platforms; when the continuous length When it is longer, the fixed support should be set on the pier in the middle of the bridge length to reduce the displacement of the supports at both ends. In order to reduce the negative bending moment peak at the support, double-row supports can also be used.
②Plane setting : For continuous straight girder bridges, if there are two or more supports horizontally under the girder body, then set fixed supports and one-way movable supports or two-way movable supports as required to meet the structural longitudinal and transverse requirements. The need for displacement; for continuous curved girder bridges, it is determined according to the structure needs to move radially toward a fixed point or the structure moves along the tangent direction of the curve radius
Title VII Bridge Piers
1. Bridge piers are mainly composed of three parts: pier cap , pier body and foundation .
2. Column piers are composed of pier caps and pier columns , and the pile foundation or enlarged foundation are connected under it
3. Under what circumstances should the cover beam be installed?
When the bridge span structure is a prefabricated girder bridge, the top cap of the column pier adopts the cover beam type
4. Under what circumstances should the pier cap be set?
When the bridge span structure is an integral girder bridge, the top cap of the column pier can be designed as a beam with a cap or a beam without a cap according to the needs of setting the support.
5. What is the main difference between gravity piers and light piers?
① Gravity abutment: The commonly used type is U-shaped abutment, which consists of three parts: abutment cap, abutment body and foundation. The earth pressure behind the abutment is mainly balanced by its own weight, so the abutment itself is mostly constructed of masonry materials such as masonry, chip concrete or concrete, and is constructed by pouring in situ
②Light abutment: Commonly used types are divided into light abutment with supporting beams, reinforced concrete thin-walled abutment and embedded abutment. It is light in size and light in weight. It is generally constructed of reinforced concrete materials. It bears external forces with the help of the overall rigidity and material strength of the structure, thereby saving materials, reducing the requirements for foundation strength and expanding the application range. Abutments open up economically viable avenues
6. When the ratio of the line stiffness of the cover beam to the column is greater than 5, in order to simplify the calculation, the double-column cover beam can be calculated as a simply supported beam or cantilever beam , and the multi-column cover beam can be calculated as a continuous beam
7. According to the structure, the abutment can be divided into several types such as gravity abutment , light abutment and embedded abutment .
8. The difference in force between piers and abutments
① Stress of the bridge pier : In addition to bearing the vertical force, horizontal force and bending moment transmitted by the superstructure, it also bears wind force, water pressure, wave force (in the marine environment) and possible ice loads, ships, rafts or The impact of floating objects
②The force of the abutment : it bears the vertical force and horizontal force transmitted by the superstructure, and at the same time, it also needs to retain the bank revetment, bear the lateral earth pressure generated by the filling soil behind the abutment and the load on the filling soil
- One-way thrust pier : refers to the pier in a porous arch bridge that can bear one-way dead-load thrust. The piers mainly bear the horizontal force transmitted from the superstructure. It has certain rigidity and strength requirements along the bridge direction. In a porous arch bridge, if one hole is destroyed, other bridge holes will be destroyed. In order to prevent this situation, brake piers are set every few holes to bear the one-way horizontal thrust, so as to ensure that the damage of one hole will not affect the safety of the whole bridge. In the porous continuous beam, the fixed support is often set on a certain pier, so that the horizontal force of the superstructure is mainly borne by the pier.