How to calculate the reinforcement of dowel bar
The dowel bar refers to the round steel bars arranged in the middle of the slab thickness every certain distance along the transverse joint of the cement concrete pavement. One end is fixed in one side plate, and the other end can slide in the adjacent side plate. Its function is to transfer traffic load between two road slabs and prevent platform staggering, increase stress transfer between adjacent concrete blocks, so as to prevent uneven settlement of concrete pavement caused by large local stress on concrete pavement, and transfer stress to make adjacent concrete blocks bear stress together
the equipment is also used to detect 23 joints of two cement pavement sections in Illinois, USA. here, the evaluation standard of this paper is used to summarize the joint dowel deviation of North Hei Expressway and Illinois, USA. The following conclusions can be drawn from the comparison:
(1) compared with foreign high-quality construction level, DBI construction technology is still in its infancy in China, and the dowel bar deviation control technology needs to be improved
(2) the horizontal movement deviation leads to the unacceptable level of the dowel bar, which is 0% in the United States and 1.8% in the North black highway, indicating that the horizontal movement deviation can be well controlled by DBI process
(3) the longitudinal movement deviation leads to the unacceptable level of the dowel bar, which is 1.1% and 5.6% respectively in the United States and North black highway, and the proportion between the unacceptable level and the acceptable level is 12.4% and 29.3% respectively. The longitudinal movement of the dowel bar is closely related to the position of the slit
the general practice is that one end of the dowel bar is embedded in the middle of the pavement concrete (1 / 2 of the length), and the other end is covered with a sleeve when the concrete is poured and tamped
the main function of the dowel bar is to prevent the pavement on both sides of the expansion joint from sinking. The function of casing is to improve the damage of pavement caused by thermal expansion and cold contraction
generally, the dowel bar is round steel. The distance is about 50. It is explained in detail in the specific design< br />
http://www.ldstruc.com/simple/index.php?t22772.html
http://co.163.com/forum/content/1729_ 281072_ 1. HTM
if you still don't understand, there's nothing I can do
The first thing to correct is that the pull rod is set in the longitudinal direction, and the dowel rod is set in the transverse contraction and expansion joints
1. The left and right half of pouring, the middle is set with longitudinal rod, the setting of rod is related to your panel thickness and board width, board length
take the ordinary cement concrete surface as an example: when the plate is 3M and the surface thickness is 200-250mm, the pull rod is used φ 14 rebar × 700mm length × 900 mm, and the distance from the outermost transverse joint shall not be less than 10 mm (that is, the clear distance of not less than 100 mm between the two ends of a plate with a length of 4 meters)
2. The dowel bar should be round steel bar
take the transverse expansion joint as an example: when the surface thickness is 220mm, the diameter of dowel bar is 28mm φ The minimum length of dowel bars is 400mm and the maximum spacing of dowel bars is 300mm
3. The setting of the dowel bar is based on the transverse contraction joint and expansion joint, which means that the dowel bar is set only where there are transverse contraction joints and expansion joints, not between plates. In general, an expansion joint is set every 200m, or at the intersection of other roads, which must be set at the junction with the bridge
In this way, I'll show you some CAD drawings. If you need electronic version of CAD drawing, you are asking me Moreover, I hope you can take a closer look at the code for design of highway cement concrete pavement structure JGT d40-2011
[answer] it depends on the specific design. Recently just do a quotation is: dowel core 0.5 kg; 4 kg. For reference only, hope to help you
the above contents are sorted out according to the problems encountered in the actual work of the students for reference. If you have any problems, please communicate and correct them in time.
there are many kinds of steel bars, which are usually classified according to chemical composition, proction process, rolling shape, supply form, diameter size, and use in structure:
(1) plain steel bars: Grade I steel bars (Q235 steel bars) are rolled into smooth round section, and the supply form is round, with diameter no more than 10 mm, The length is 6m ~ 12m
(2) ribbed bars: there are spiral, herringbone and crescent shapes. Generally, grade II and III bars are rolled into herringbone, while grade IV bars are rolled into spiral and crescent shapes
(3) steel wire (including low carbon steel wire and carbon steel wire) and steel strand
(4) cold rolled and twisted steel bars: cold rolled and cold twisted< (2) steel wire (diameter 3-5mm), fine steel bar (diameter 6-10mm) and thick steel bar (diameter more than 22mm)
(3) grade I steel bar (235 / 370) according to mechanical properties; Grade II reinforcement (grade 335 / 510); Grade III steel bar (370 / 570) and grade IV steel bar (540 / 835)
(4) according to the proction process, there are hot-rolled, cold-rolled and cold drawn steel bars, as well as heat-treated steel bars made of grade IV steel bars, which have higher strength than the former
(5) according to the role in the structure: compression reinforcement, tension reinforcement, erection reinforcement, distribution reinforcement, stirrup, etc
according to their functions, the steel bars in reinforced concrete structures can be divided into the following categories:
(1) stressed steel bars: the steel bars bearing tensile and compressive stresses
(2) stirrups, which bear part of the cable-stayed stress and fix the position of the reinforcement, are mostly used in beams and columns
(3) erecting reinforcement is used to fix the position of steel hoop in the beam and form the reinforcement framework in the beam
(4) distributed bars are used in roof slabs and floor slabs, which are arranged vertically with the load-bearing bars of the slabs, so as to evenly transfer the weight to the load-bearing bars, fix the position of the load-bearing bars, and resist the temperature deformation caused by thermal expansion and cold contraction
(5) others - structural bars configured for structural requirements of components or construction and installation. Such as waist bar, embedded anchorage bar, ring, etc.
the upper layer of concrete is composed of a certain thickness of concrete panel, which has the property of thermal expansion and cold contraction. Due to the change of air temperature in all seasons of the year, concrete slabs will expand and contract in different degrees. In a day and night, the temperature of the top surface of the concrete slab is higher than that of the bottom surface when the temperature rises in the daytime, which will cause the middle part of the slab to protrude. When the temperature decreases at night, the temperature of the top surface of the concrete slab is lower than that of the bottom surface, which will make the surrounding and corner of the slab tilt up;. These deformations are constrained by the friction and adhesive force between the slab and the foundation, as well as the dead weight of the slab and the wheel load. It results in the excessive stress in the plate and the fracture or arching failure of the plate. The cracks caused by warping will not completely separate the two plates after the cracks occur, and also have the ability to transfer the load. If the temperature of the plate decreases evenly and causes shrinkage, the two plates will pull apart, thus losing the ability to transfer the load
in order to avoid these defects, cement concrete pavement has to set many joints in both vertical and horizontal directions, and divide the whole pavement into many plates. The joints of cement concrete pavement can be divided into longitudinal joints and transverse joints. The joints parallel to the middle line of the route are called longitudinal joints, and the joints perpendicular to the route are called transverse joints. The joint design should be able to: (1) control the position of cracks caused by shrinkage stress and warpage stress; ② Provide sufficient load transfer through joints; ③ Prevent hard debris from falling into the seam
< 2. Longitudinal joint and its structure
1. Longitudinal contraction joint
when the width of one-time paving is greater than 4.5m, longitudinal contraction joint should be added. The longitudinal contraction joint can adopt the type of false joint and pull rod. The pull rod should be set at 1 / 2 of the plate thickness; Generally, the notch set at the upper part of the contraction joint should be cut by the joint cutter after the concrete pouring and when it reaches a certain compressive strength (6.0 ~ 12.0mpa for crushed stone concrete and 9.0 ~ 12.0mpa for gravel concrete), or the wooden bar should be vibrated ring the concrete pouring. If the depth of the slot door is too shallow, the strength of the concrete section will not be weakened enough, so that the future cracking can not be guaranteed at the joint position; If the depth is too deep, the area of irregular fracture surface is too small, and the load transfer capacity of joints is reced. According to the experience, the groove depth is generally 1 / 4-1 / 5 of the plate thickness, and the groove width should be as narrow as possible according to the construction conditions, usually 3-8mm
2. Longitudinal construction joint
e to construction conditions and other reasons, when the one-time paving width is less than the pavement width and needs to be poured more than twice, longitudinal construction joint should be set. According to the different structure, the longitudinal construction joint can be divided into two forms: flat joint and tongue and groove joint. Generally, the flat joint is used, and the pull rod should be set in the center of the plate thickness to prevent the joint from opening and the plate from moving up and down. According to the practical experience at home and abroad, the tongue and groove joints are easy to be damaged. The reasons are as follows: (1) the too large size of the tongue and tenon reces the strength of the joint and may lead to the failure of the tongue and tenon; ② Large and deep tongue and groove often cause early damage to the tongue and groove, sometimes even damage the tongue and groove, and need to be repaired. Under repeated loading, the local stress concentration leads to crack development and even failure. In addition, the construction is troublesome< The transverse joints are generally divided into transverse contraction joints, expansion joints and transverse construction joints
1. Expansion joint
the concrete panel is completely broken at the expansion joint, so it is also called true joint. The purpose of expansion joint is to provide room for expansion of concrete slab, so as to avoid excessive thermal stress. The structure of expansion joint. The expansion joint must run through to the end, and the seam wall is vertical: the seam width is 2.0 ~ 2.5cm, and the dowel bar is set in the center of the plate thickness. More than half of the dowel bar should be coated with asphalt or added with plastic sleeve, and the small sleeve should be lengthened by 10cm, and a 3cm gap should be left between the bottom of the sleeve and the head of the dowel bar (filled with gauze). The lower part is provided with joint plate (the wood board is coated with asphalt), and the upper part is filled with joint filler within 3 ~ 4m for sealing. When the expansion joint at the junction of the structure or the intersection with other highways can not be set with dowel bar, the edge reinforcement type or thick edge type can be used:
the expansion joint can be set, which brings inconvenience to the construction. At the same time, e to the improper setting of dowel bar (not correctly positioned) or poor sealing of joints, the concrete slab at the expansion joint often appears cracking and other diseases. The application experience and observation data show that the expansion joint gap often increases in the section with short expansion joint spacing (less than 100m), which greatly reces the load transfer capacity of the joint relying on the interlocking effect of aggregate; And because the joint filler is difficult to maintain its efficiency, sand and other debris are easy to fall into the joint, causing the concrete in the joint area to break or arch when the expansion is hindered. On the one hand, it facilitates the construction, on the other hand, it restricts the displacement of the slab, reces the joint gap, increases the load transfer capacity, and reces the diseases such as dislocation, fragmentation and arching. Therefore, expansion joints are only set in the following situations: adjacent to bridges or other fixed structures; Joint with flexible pavement; The change of plate thickness; Tunnel entrance; Small radius horizontal curve and concave vertical curve longitudinal slope transformation. At least two expansion joints shall be set at the adjacent structures according to the construction temperature. In addition to the above positions, expansion joints should not be set or set as few as possible, and the spacing can be determined according to the construction temperature, the expansion of concrete aggregate and local experience.
The longitudinal joint is only responsible for the temperature shrinkage deformation of concrete. In order to prevent the dislocation of the road and the expansion of the longitudinal gap, the reinforced bar is added The longitudinal joint is not allowed to expand)
the transverse joint is responsible for the temperature shrinkage deformation of concrete. It is also necessary to consider the transverse joint deformation expansion (large deformation) caused by the pavement bending under the action of load, so the smooth round reinforcement is used to only prevent the pavement from staggering. The transverse joint is allowed to expand and shrink (the transverse joint is allowed to expand), generally one end is anchored and the other end is movable
The surface quality of rebar is specified in the relevant standards, which requires that the end should be cut straight, the surface should not have cracks, scars and folds, and there should be no harmful defects in use. The allowable value of dimension deviation. The requirements for the bending degree of rebar and the geometric shape of rebar are specified in relevant standards
extended data:
the total gap (including longitudinal rib width) between the ends of transverse ribs on two adjacent sides of reinforcement shall not be greater than 20% of the nominal perimeter of reinforcement; When the nominal diameter of reinforcement is not more than 12mm, the relative rib area shall not be less than 0.055; When the nominal diameter is 14mm and 16mm, the relative rib area should not be less than 0.060; When the nominal diameter is larger than 16mm, the relative rib area should not be less than 0.065
after the segment assembly, the ovality of the whole segment must be tested. The purpose of controlling ovality is to ensure smooth assembly of the lower segment (especially staggered seam assembly), and to control the shape of the segment for stress; From the waterproof point of view, it is more important to control the angle between segments at the joint to ensure that the gasket can have enough contact area and enough contact pressure to resist the external water pressure