I. Overview of the Project
K 135+ 199.445 separated overpass is located in Yuncheng Interchange, which spans 338 provincial highway with an intersection angle of 90, a span of 22-28-22m and a total length of 72m. The bridge foundation is in the form of bored piles, with a total of 30 piles * * *. The diameter of bored piles at abutment is 1.2m and the length is 38m, and the diameter of bored piles at pier is1.5m. The length of bored piles on the right is 47m, and that on the left is 48m. Pile caps are arranged at the top of piers and abutments. The abutments are ribbed abutments, and the piers and abutments are columns with the diameter of1.3m. The superstructure is cast-in-place continuous box girder, the left box girder 13.5m wide is a three-room structure, and the right box girder 17.0m wide is a four-room structure. Box girder height 1.4m, beam room height 0.98m, bottom plate thickness 0.2m, top plate thickness 0.22m and web width 0.45m. The box girder is made of C50 concrete, * * *1381.56m3. ..
Second, the cast-in-place box girder construction scheme
Cast-in-place box girder bracket adopts full-hall bowl-buckle bracket. When the full-house support is erected, the traffic of provincial highway 338 is closed, and the road is diverted from No.3 subgrade to ensure the safety of the full-house support construction. Vertical and horizontal squares are erected on the bowl rack. The box girder bottom formwork and side formwork are made of high-strength bamboo plywood with a thickness of 1.5cm, and the indoor formwork of the box body is made of wood formwork. Box girder concrete is poured in two times, the first time to the joint of web and flange plate, and the second time to the top plate. When the concrete strength of box girder reaches 100%, prestressed tensioning will be carried out.
Ⅰ. Foundation treatment
1, foundation treatment
Backfilling treatment of drainage ditches on both sides of provincial highway 1 and 338.
Dig out the loose eluvial soil and silt in the drainage ditch, and then backfill the mountain skin stone 50cm in layers, the backfill height is slightly lower than the height of the provincial road surface, and roll it by layers with a roller until there is no settlement. Then fill 6% lime soil with a thickness of 40cm, backfill it in two layers, the degree of compaction will reach above 93%, the top surface of backfill soil will be flush with the provincial road surface, and 2%-4% cross slope will be made to facilitate drainage.
2, within the scope of the bridge subgrade surface treatment
Use graders and bulldozers to clean and level the surface. Then loosen the 30cm-thick topsoil with a plow, add 10% quicklime powder, and stir evenly with a rotary tiller. When the water content is appropriate, it will be compacted with a road roller, and the compactness will reach over 90%. Then fill in 30cm thick 10% lime soil, and make 2%-4% transverse slope, with a degree of compaction above 93%, which is higher than the ground and is not affected by rain soaking.
3. Drainage ditch excavation
Dig a 50×50cm drainage ditch around the foundation treated with 10% lime soil, and connect it with the natural drainage ditch on both sides of the provincial road on the right side of the route. The rainwater will be introduced into the drainage ditch to prevent the rainwater from soaking the foundation and avoiding the uneven settlement of the bowl buckle bracket.
Ⅱ. Scaffolding
K 135+ 199.445 Cast-in-place box girder of separated overpass is constructed as a whole with single span and three spans, and the supporting method is full bowl buckle bracket. The bowl buckle bracket adopts WDJ bracket with an outer diameter of 4.8cm, a wall thickness of 0.35cm and an inner diameter of 4. 1cm. The longitudinal spacing along the bridge support is 0.9m, the longitudinal spacing at the diaphragm is 0.6m, the transverse spacing at the bottom of the beam is 0.9m, the bottom of the flange plate is 1.2m, and the vertical spacing between the longitudinal and transverse rods is1.2m. Considering the overall stability of the support, diagonal steel tube shear braces are set in the vertical and horizontal directions.
1, survey lofting
The surveyors used the total station to set out the vertical projection line of the box girder on the basis, and sprinkled the marking line with white ash. On-site technicians determined the center line of a single box girder according to the projection line, and marked it with a white gray line. Bowl buckle brackets are symmetrically arranged on both sides according to the center line.
2. Layout stud pads
According to the position of the vertical rod, the vertical rod plate is laid, and the plate is made of 5cm wood, so that the vertical rod is in the center of the plate, and the plate is placed flat and firm, without hanging at the bottom.
3, bowl bracket installation
According to the design combination of vertical pole and cross bar, the vertical pole and cross bar are installed in turn from bottom to top. During installation, the upright post should be in the center of the pad. Generally, the bottom upright post and some crossbars of a working face should be installed first, and then installed step by step. All crossbars should be installed at the same time. After the installation of vertical poles and cross bars, diagonal braces shall be installed to ensure the stability of the support. The diagonal braces are connected with the bowl buckle bracket through fasteners, and should be arranged on the frame nodes as far as possible during installation.
4, jack-up installation
In order to facilitate the aerial work of the support, it is safe and time-saving. The jacking amount can be roughly adjusted on the ground, and then transported to the top of the bracket for installation. According to the change of beam bottom elevation, the section spacing is determined in the transverse bridge direction, and three control points, left, middle and right, are set along the bridge direction to accurately adjust the jacking elevation. Then, the protruding amount of jacking is marked with obvious marks for verification. Finally, the elevation of each jacking is called out in turn by cable interpolation method, and the jacking extension is generally controlled within 30cm.
Ⅲ. Installation of longitudinal beam and transverse beam
After the jack-up elevation adjustment is completed, place 10× 15cm square timber longitudinal beam on it, and place 10× 10cm square timber beam on the longitudinal beam with a spacing of 30 cm. The length of the cross beam depends on the width of the bridge, which is at least 50cm wider than each side of the roof to support the external formwork support and inspectors to walk. When installing vertical and horizontal square timber, it should be noted that the joint position of horizontal square timber is staggered from that of vertical square timber, and any two adjacent horizontal square timber joints are not on the same plane.
Ⅳ, support preloading
In order to reduce the influence of bracket deformation and foundation settlement on the alignment of cast-in-place box girder, bracket preloading construction is carried out after the installation of longitudinal and transverse beams is completed. Sand bags are used for preloading, the preloading range is at the bottom of the box girder, and the weight is not less than 1.2 times of the total weight of the box girder. Due to the light weight of the cantilever plate itself, the pre-camber of the cantilever plate template can be adjusted accordingly according to the measured preloading results.
1. Loading sequence: loading in three stages, with the first and second loading accounting for 30% of the total weight and the third loading accounting for 40% of the total weight respectively.
2. Preloading observation: the observation position is set at L/2, L/4 and pier of each span, and at the left, middle and right points of each component. Fixed observation poles at each point to facilitate settlement observation.
Observe the settlement with a level. After arranging the observation pole, determine the pole top elevation before loading. During settlement observation, each observation shall be sampled by the survey supervision engineer, and the observation results shall be reported to the supervision engineer for approval. After the first loading, observe it every 2 hours. When the settlement observed for two consecutive times is less than 3mm and the settlement is zero, carry out the second loading. Follow this procedure until the third loading is completed. After the settlement is stable after the third loading, it can be unloaded with the consent of the supervision engineer.
3. Unloading: manually cooperate with the crane to lift the sand bag and unload it evenly, and continue to observe while unloading. After unloading, record the observed values, so as to calculate the comprehensive deformation of the bearing and foundation. According to the observation records, the preloading settlement results are sorted out, and the pre-arching height of beam bottom plate and cantilever is controlled by adjusting the top support elevation of bowl buckle bracket.
ⅴ, template installation
1, bottom template
The bottom die is made of high-strength bamboo veneer with a thickness of 1.5cm, and the formwork should be fully coated with release agent before installation. The transverse slope of the bottom plate shall be 2% of the transverse slope specified in the design drawings, and the transverse width shall be greater than the width of the beam bottom. Formwork on both sides of the bottom of the beam should be not less than 5cm beyond the bottom edge of the beam, so as to facilitate the erection of side formwork on the bottom formwork. Sponge rubber strips should be used at the joint between templates to prevent slurry leakage, and the staggered platform between templates should not exceed 1 mm ... The flat-fell seam of templates should be connected vertically and horizontally to avoid staggered joints.
After the bottom die is laid, carry out plane lofting, comprehensively measure the vertical and horizontal elevation of the bottom plate, detect a point at a vertical and horizontal interval of 5m, and adjust the bottom die to the design elevation according to the measurement results. After the floor elevation is adjusted, check the elevation again. If the elevation does not meet the requirements, make a second adjustment.
2. Side formwork and flange plate formwork
High-strength bamboo plywood with a thickness of 1.5cm is used for side formwork and flange plate formwork. Determine the edge line of box girder bottom plate according to survey and layout, play ink lines on bottom formwork, and then install side formwork. Stick sponge rubber strip at the joint of side formwork and bottom formwork to prevent slurry leakage. The lateral side of the side formwork is provided with vertical and horizontal square timber back ribs, which are connected with brackets by steel pipes and fasteners to support and fix the side formwork.
The installation of flange plate bottom formwork is the same as that of box girder bottom formwork, and the installation of outer baffle plate is the same as that of side formwork. After the baffle template is installed, the elevation and line type should be comprehensively tested to ensure the beautiful line type of flange plate.
3, box room template
Because the box girder concrete is poured twice, the box formwork is installed twice. For the first time, the steel formwork is used as the internal formwork, and the square timber is used as the cross brace. At the same time, positioning steel bars are used for positioning and fixing, and the position and overall linear shape of the steel formwork are corrected by pulling wires. When the concrete reaches a certain strength for the first time, dismantle the internal formwork, then set up a small bent frame with square wood, spread a 2cm thick board on the bent frame, and then spread a layer of linoleum on the board, with the joint of linoleum overlapping 5cm, and nail it with a row of nails to prevent slurry leakage. In the process of pouring concrete, assign personnel to check the position change of internal model. In order to facilitate the removal of the internal mold, a manhole is set at the design position of each hole.
ⅵ, steel processing and installation
1, rebar installation sequence
(1) Install and bind the steel mesh at the lower part of box girder bottom plate;
(2) Install the web reinforcement skeleton and reinforcement;
(3) Install the steel skeleton and reinforcement of the partition board;
(4) installing and binding the steel mesh and side angle steel at the upper part of the box girder bottom plate;
(5) When pouring concrete for the first time, after the strength is pulled up, install and bind the embedded parts such as upper and lower steel mesh, corner steel bars, guardrails and expansion joints on the roof.
2, steel processing and installation
When processing steel bars, they should be cut and shaped according to the design requirements, and the spacing, position and quantity should be controlled when installing steel bars. Those that need to be bound should be firmly bound, and those that need to be welded should be welded in batches in advance to improve work efficiency. Weld length, plumpness and other aspects should meet the specification requirements.
Reinforcement processing and installation should pay attention to the following items:
(1) Steel bars must be listed and piled up at the site according to different steel grades, specifications, brands and manufacturers. Steel bars should be stored in the lower cushion and the upper cover to prevent steel bars from rusting due to moisture.
(2) The steel bars are produced in the factory and transported to the site for installation.
(3) The reinforced concrete protective layer should be prefabricated in advance, with the same label as the main girder, and the thickness of the concrete protective layer should meet the design requirements.
(4) In the process of steel bar installation, design reserved holes and embedded parts shall be set in time, with correct setting position and firm fixation.
(5) The steel skeleton is welded by layers, that is, it is symmetrically staggered from the center of the skeleton to both ends, and the lower part of the skeleton is welded first, and then the upper part of the skeleton is welded. Steel welding should adjust the current of electric welding machine to prevent steel biting caused by excessive current or improper operation. Double-sided welding is the first choice for rebar welding. When double-sided welding does not meet the construction conditions, single-sided welding shall be adopted. After the steel bar is welded, knock out all the welding slag. After the steel bar welding is completed, the construction of the next working procedure can only be carried out after the self-inspection is qualified and reported to the supervision engineer for inspection.
(6) When the installation position of steel bar conflicts with the position of prestressed pipe or anchorage, the position of steel bar should be adjusted appropriately to ensure that the position of prestressed member meets the design requirements. When welding steel bars, it is necessary to prevent electric welding from burning steel strand and metal bellows, so as to prevent tension fracture and pipeline from being blocked by concrete and grouting cannot be carried out.
After reinforcement processing and installation are completed, the next working procedure can only be carried out after the self-inspection is qualified and reported to the supervision engineer for sampling inspection.
ⅶ, concrete pouring
The concrete is mixed by two concrete mixing stations, namely, the concrete mixing station K 137+600 in this contract section, 2.5km away from the construction site, and the concrete mixing station K 124+ 100 in the twelfth contract section, and1km away from the construction site. Concrete transportation adopts 5 tankers, 2 tankers in this contract section and 3 tankers in contract section 12. 1 pump truck is used for pouring concrete on site, and then contact 1 pump truck for standby.
Box girder concrete is poured twice, the first time the bottom plate and web plate are poured to the top of the rib plate, the second time the top plate and wing plate are poured, and the joints poured twice are treated as construction joints. The concrete is poured continuously from one end to the other in steps and layers, and the pouring distance between the upper and lower layers is about 2m. The upper concrete is poured before the initial setting of the lower concrete. Concrete pouring should pay attention to the following items:
1. Before concrete pouring, clean the sundries in the formwork manually and with a hair dryer, and thoroughly inspect the bracket, formwork, reinforcement and embedded parts. At the same time, check the crane, mixing station, tank car, generator, vibrating rod and other mechanical equipment to ensure foolproof.
2, concrete pouring should be symmetrical to the longitudinal center line, first to the center, and then to both sides of the symmetrical pouring. The layered thickness of concrete is 30cm. During pouring, check the slump of concrete at any time.
3. Concrete shall be vibrated with plug-in vibrator, and the moving distance shall not exceed 1.5 times of the action radius of the vibrator, which is about 8~9 times of the action radius of the vibrator.
4. When vibrating with a vibrator, keep a distance of 5~ 10cm from the side formwork to avoid the vibrator contacting the formwork and prestressed pipe. When vibrating the upper concrete, the vibrating rod should be inserted into the lower concrete about 10cm. Vibrate the vibrating parts until the concrete stops sinking and the surface is smooth and pulpy, so as to avoid vibration leakage or excessive vibration. After each vibration, the vibrator should be extended slowly.
5, in the process of concrete pouring, arrange someone to track and check the bracket and template. If the template leaks slurry, it should be filled with sponge strips. Before pouring concrete, hang lines at L/2 and L/4 sections under the bottom die, and set five vertical lines at the left, left center, center line, right center and right of each section. Tie steel bars below the vertical line, bury steel bars in the corresponding position on the ground, and mark the staggered position of two steel bars to observe the settlement of the bottom plate during concrete pouring. If abnormal conditions are found, concrete pouring shall be stopped immediately, and construction shall be continued after the reasons are found out.
6, pouring concrete for the first time, pouring to the top of the web, completes the construction joints. The concrete height is slightly higher than the top of the design web 1cm. The cement slurry and loose concrete on the top surface should be chiseled away to expose the hard concrete rough surface, and then washed clean with water.
7, secondary pouring concrete box girder roof, in the L/2, L/4 pier top and other sections, from the inside to the outside spacing of 5m layout of steel bars, steel bars are welded on the roof reinforcement, so that the top surface elevation is the roof elevation, in order to control the roof concrete pouring elevation and cross slope. After the concrete is vibrated and leveled, vacuum water absorption is carried out. The vacuum water absorption time (min) is 1~ 1.5 times of the thickness (cm), that is, 10~ 15min. The vacuum water absorption effect was tested by residual water cement ratio. After the vacuum absorber is opened, the vacuum degree will gradually increase. When the required vacuum degree (500 ~ 600 mm Hg) is reached, the vacuum degree should be kept uniform. Before the end of water absorption, the vacuum degree will gradually weaken, so as to avoid leaving a water outlet channel inside the concrete and affecting the compactness of the concrete.
After vacuum water absorption, roll it with a pulp lifting rod to make the surface pulp, which is convenient for plastering. After winding the pulp lifting rod, manually wipe the pulp. When plastering, the board should be erected, and it is not allowed to step on the concrete surface, so as not to affect the flatness. About half an hour after plastering, it will be leveled again with plastering machine, and finally it will be plastered manually.
After the concrete is plastered, it shall be brushed manually, and the depth of brushing in the transverse direction of the bridge with steel wire brush shall be controlled at 1~2mm. It is necessary to master the nap time. If it is too early, the sizing will be serious, which will affect the flatness. If it is too late, the nap depth will not be enough. Generally speaking, it is based on experience. When the concrete surface is slightly hard by pressing with fingers, it should be trimmed. Make plaster twice. The first plastering is used to level the concrete, and the second plastering is used to collect light when the concrete is near the final setting and there is no bleeding on the surface. Then brush the direction across the bridge.
8, before pouring box girder roof concrete reserved hole, should remove the clutter in the box, so as not to block the floor drain hole. The wall of the reserved hole at the top of the main girder should be chiseled, and the concrete filling the reserved hole should be vibrated and compacted.
9, concrete curing using geotextile cover sprinkler maintenance, ensure that the concrete surface is always in a wet state, maintenance time is not less than 7 days. The concrete strength test blocks used to control the frame stretching and descending are placed in the box girder room and maintained under the same conditions. During the curing period, it is forbidden to pile materials on the bridge deck.
Eight, prestressed engineering
As the most important part of cast-in-place box girder, prestressed engineering can not be ignored from the arrangement of reserved channels, the installation of anchor pads, the vibrating, tensioning and grouting of concrete under anchor. Once something goes wrong, it will cause quality problems.
Prestressing engineering is divided into five steps: grooving, blanking and bundling, stringing, tensioning and grouting;
1, pore formation
Metal bellows should be used for prestressed pipe forming, and the metal bellows should be inspected one by one before use. Corrugated pipes covered with rust, oil stain, dirt or impact, indentation and crack shall not be used. When placing metal bellows, positioning ribs should be set according to the coordinate values of the pipeline and the requirements of the design drawings, and they should be firmly tied with wire. The bending part is fastened with U-shaped locating ring and locating rib to clamp the corrugated pipe. At the joint of corrugated pipe and its joint with anchor pad horn, use wide adhesive tape to ensure its sealing and no slurry leakage.
When installing the anchor head, put the anchor head into the groove, and don't place it at will. When installing the limit plate, pay attention to the one-to-one correspondence between the steel strand and the hole to prevent dislocation and cause the steel strand to break during tensioning. The depth of the groove of the limit plate should be appropriate to prevent the steel strand from being seriously scratched and the clip from being exposed for a long time or dislocated because it is too deep.
2. Blanking and binding
First, check whether the quality of steel strand meets the design requirements, and ensure that the surface of steel strand is free of cracks, burrs, mechanical damage, iron scale and oil stains. The blanking length of steel strand is determined by calculation, and L= (designed length between two anchor heads) +2 (anchor thickness+limit plate thickness+jack length+reserved length). The steel strand is cut by a grinder and then bundled. When binding, each steel strand should be parallel and not twisted. Tie a lead wire every 1- 1.5m, and buckle the lead wire inward. Bundled steel strands shall be stacked in numbers, kept dry off the ground and covered to prevent rain.
3, wear beam
Steel sleeve traction method is adopted for steel strand of box girder, and the steel strand head is wrapped with adhesive tape when passing through the beam to prevent the steel strand head from being caught.
Step 4 be nervous
(1) the choice of tensioning equipment:
The tensioning equipment consists of two 350-ton jacks and two ZB4-500 oil pumps. In order to ensure the safety, reliability and accuracy of tensioning, the rated tensile force of the selected equipment is greater than that of tensioning prestressed tendons. The tension of prestressed tendons is calculated as follows:
Ny=N×δk×Ag× 1/ 1000
Where: ny-tensile force of prestressed reinforcement;
N-the number of prestressed tendons tensioned at the same time;
Δ k —— tensile control stress of prestressed tendons;
Ag—— the cross-sectional area of a single steel strand.
The maximum tension required for prestressed tensioning during this construction period is:
ny = 15× 1370× 182× 1/ 1000 = 374(t)
Two 400-ton jacks are used for synchronous tensioning, which can meet the needs of field production through the above calculation.
According to the specification and the requirements of tensile stress, the measuring range of the oil pressure gauge is 0~ 100Mpa, and the accuracy is 1.5, and the diameter of its reading disk is required to be greater than150 mm.
② Calibration of equipment:
The acting force of hydraulic jack is generally measured and controlled by oil pressure gauge. In order to control the tension correctly, it is necessary to calibrate the oil pressure gauge and jack. First of all, the oil pressure gauge should be inspected in the Bureau of Metrology, and it can only be used in construction after passing the inspection. Then the universal testing machine with large tonnage weight is selected for loading test, and the system composed of jack and oil pump is calibrated. Only after the calibration is qualified can it be used for construction.
(3) the tensioning construction personnel arrangement:
The tensioning class consists of two technical directors, two pump drivers, two recording drivers and two jack operators, each with his own duties. Before tensioning, conduct technical training for the tensioning class to understand the equipment performance, operating procedures and safety essentials.
④ Tension of prestressed tendons
Prestressed tendons are tensioned according to technical specifications and design drawings, and the tensioning procedure is 0→ initial stress → Δ k (anchorage with load for 2min). During tensioning, the elongation value is measured while tensioning, and the stress and strain are both controlled. Compared with the theoretical elongation value, the error of the actual elongation value is controlled within 6%. If the elongation value is abnormal, suspend tensioning and notify the supervision engineer. The tensioning site records shall be sorted out in time, reported to the supervision engineer, and handled according to the measures instructed by the supervision engineer. Each batch of steel beams is tensioned symmetrically.
Unified command during tensioning, and the tensioning speed at both ends can be consistent. If there is any noise or abnormal phenomenon, the construction shall be stopped immediately, inspected, and the tensioning shall be carried out after finding out the reason.
Calculation of theoretical elongation value △L of steel strand
△ L=PpL/(ApEp)
Where: PP-tensile force (n);
L- the length of prestressed reinforcement (mm);
AP-the cross-sectional area of prestressed reinforcement (mm2);
Ep—— Elastic modulus of prestressed reinforcement (N/ mm2).
The actual elongation value△ L of prestressed reinforcement is calculated by the following formula:
△ L=△L 1+△L2
△ l1-measured elongation from initial stress to maximum tensile stress;
△L2—— the calculated elongation value lower than the initial stress, and the elongation value of the adjacent stage can be used.
Because the jack and other equipment are not in place, the L value cannot be calculated, and the δL value will be calculated after the equipment is in place.
5, hole grouting
Before grouting, in order to make the hole grouting smooth and make the slurry well combined with the hole wall, high-pressure water should be used to flush the hole before grouting, and then grease-free compressed air should be used to dry it. The vacuum grouting technology shall be used for grouting in time, and the grouting shall be carried out continuously while stirring until fresh cement slurry with the same consistency as pressure grouting appears at the outlet. After the grouting construction is completed, the anchor sealing concrete construction will be carried out immediately.
ⅸ. Dismantle the frame
After the completion of prestressed engineering construction, scaffolding should be unloaded. When unloading, scaffolding should be removed evenly in the order of crossing first and then on both sides. Barbaric construction is strictly prohibited, and the scaffold after unloading should be neatly stacked to facilitate future construction.
Third, quality assurance measures
1. Quality objective: Strictly implement the current Technical Specification for Construction of Highway Bridges and Culverts (JTJ04 1-2000) of the Ministry of Communications and the relevant provisions in the bidding documents, meet the design requirements and strive for high-quality projects.
2, before construction, first of all, the survey lofting data recorded.
3, responsible for key prestressed engineering personnel, personnel management.
4. Before construction, the person in charge of construction technology should organize technicians and construction management personnel to read the design documents carefully, understand the design intent, clarify the key points and difficulties of construction technology, and make technical disclosure.
5. In the process of construction, the system of self-inspection, mutual inspection and full-time inspection shall be strictly implemented, and the internal supervision shall exercise the veto power.
6, the process handover system, the key working procedure team inspection qualified, after the internal supervision engineer inspection, confirmed to meet the requirements, fill in the inspection records, and then ask the supervision engineer to review and identify, so as to carry out the construction of the next working procedure.
Fourth, the progress guarantee measures
1, guarantee the construction quality, and only when the quality is guaranteed can the construction progress be guaranteed;
2, the establishment of cast-in-place box girder production project leadership responsibility area, the project manager is responsible for, strengthen the macro management of box girder construction.
3, the implementation of personal responsibility system, the responsibility to the people, the establishment of construction quality and progress of the reward and punishment system;
4. Raw materials such as steel bars, sandstone and cement are fully prepared to avoid delays;
5. Check the mechanical equipment such as mixing station, crane and generator in time to ensure that the mechanical equipment is always in good working condition;
6, strengthen the training of construction personnel, so that they can quickly and skillfully master the operation essentials, and ensure the close connection of working procedures.
Five, safety and civilized construction guarantee measures
1, strictly implement the relevant provisions of the safety guarantee system of the project manager department.
2. Before the box girder construction, the security department shall make safety technical disclosure to the on-site personnel.
3.338 When the provincial highway is closed, sandbags will be piled at both sides of Mantang support 10m, and special personnel will be arranged to direct traffic.
4. When the steel strand is tensioned, warning signs shall be set at both ends, which shall be attended by special personnel, and other personnel shall not get close to it to ensure the safety of tensioning.
5. Construction personnel must wear safety helmet and safety belt, and set railings and safety nets above the support.
6, mechanical operation must abide by the safety operation procedures, shall not be illegal operation.
7, the construction site should be clean and standard, all kinds of warning signs and construction nameplate set is complete.
Calculation of supporting force of box girder
K 135+ 199.445 Force calculation of box girder support of separated overpass Take the box girder support on the right for force calculation.
First, the load calculation
1, box girder load: box girder reinforced concrete deadweight: G=777m3×26KN/m3=20202KN.
For safety reasons, take the safety factor r= 1.2, and calculate the pressure per unit area with the total weight acting on the bottom plate:
f 1 = g×r÷S = 20202 kn× 1.2÷( 12.4m×72m)= 27. 153 kn/m2
2. Construction load: F2=2.5KN/m2.
3. Load generated by concrete vibrating: F3=2.0KN/m2.
4. Box girder mandrel: F4= 1.5KN/m2.
5. Bamboo veneer: F5=0. 1KN/m2.
6. Square timber: F6 = 7.5/m3.
Second, the bottom die strength calculation
The box girder bottom formwork is made of high-strength bamboo veneer with a thickness of t= 15mm and a spacing of back ribs of bamboo veneer of 300mm, so the flat bamboo veneer with a width of b=300mm is used to check the formwork strength.
1, mechanical properties of the template
(1) elastic modulus E=0. 1× 105MPa.
(2) Moment of inertia of section: I = bh3/12 = 30×1.53/12 = 8.44cm4.
(3) sectional resistance moment: w = bh2/6 = 30×1.52/6 =11.25cm3.
(4) Cross-sectional area: A=bh=30× 1.5=45cm2.
2, template stress calculation
(1) uniformly distributed load of bottom die: f = f1+F2+F3+F4 = 27.153+2.5+2.0+1.5 = 33.153kn/m2.
Q = f×b = 33. 153×0.3 = 9.946 kn/m.
(2) Maximum bending moment in midspan: m = ql2/8 = 9.946× 0.32/8 = 0.112knm.
(3) Bending and tensile stress: σ = m/w = 0.112×103/1.25×10-6 = 9.9 MPa.