In the construction of high pier (over 40m), steel pipe support (or bamboo support) is adopted around the bridge pier, and the construction platform is directly erected from the ground to the pier top; It is not economical and applicable to use tic-tac-toe frame with hoist to lift or cable to hang formwork to transport concrete pouring. First, high supports are prone to instability, and there are potential safety hazards, and support collapse accidents often occur. Second, it needs to consume a lot of materials; Cable cranes are expensive and need a working platform around them.
In recent years, with the increase of expressway construction in Yunnan, Guizhou, Sichuan and other places, the special terrain in this area determines the increase of high pier projects in these areas. Some experiences have been gradually summed up in the construction, which are summarized as follows:
1. Project overview
The span arrangement of a large bridge is 8m (abutment) +8×40m (continuous beam)+120.2m+2× 230m+120.2m (continuous rigid frame) +2×40m (continuous beam) +8m (abutment). The total length of the bridge is11/6.4m ... The highest pier of the bridge is as high as 132m, and the maximum span of the superstructure of the main span is 230m. The bridge is the main control project of the whole line, with a total construction period of 28 months. Short construction period, great technical difficulty and complicated technology.
The bridge is located in the southeast of Yunnan-Guizhou Plateau. The topography of the bridge site is undulating, and the natural landform is high, steep and deep. The elevation of the section where the bridge axis passes is1020 ~1218m, and the relative height difference is 198m. Main piers (No.8, No.9, 10, 165438, 12). Among them, Pier 8 is a double column with a cross section of 5×4m, a wall thickness of 0.5m and a height of 60m. Pier No.9 has four columns, the cross-sectional size of which is 8.5×3.5m, the height of which is 65m, and the wall thickness is 0.8m and1.2m; : 10 pier height 132m, the lower section is double columns, the section size is 10× 14m, the wall thickness is 0.9m and 1.2m, and the middle wall thickness is 0.6m. When the pier height reaches 67m, it is divided into four columns, with the section. After reaching the height of 32m, it is divided into four columns with a cross section of 8.5× 3.5m.12 pier with double columns, a cross section of 5×4m, a wall thickness of 0.5m and a height of 49m.
2. Structure and application of sliding frame
2. 1 Structure of sliding lifting frame
Sliding frame and turnover formwork are mainly used for high piers, high chimneys of factories and independent columns of houses. The construction is simple, convenient, fast and economical. The turnover formwork is all made of newly processed large steel formwork, and the concrete surface is smooth after formwork removal. The sliding frame is used as a working platform. Pier formwork is installed on the support platform, and the upper part of the support is used to facilitate the installation of steel bars, and the lower part is used to repair the defects on the poured pier concrete surface. The whole carriage is connected into a whole with steel pipes at the top of the bracket, and a safety net is installed around the bracket after the bracket is installed.
The sliding frame consists of bearing channel steel frame and steel pipe bracket. The frame is made of 2[22 channel steel by tailor welding. The support is welded with steel pipes and fixed on the channel steel frame by welding, which is suitable for aerial work without scaffolding. The self-weight and construction load of the whole carriage shall be borne by inserting φ50mm round steel (45# steel) into the pier, and holes shall be reserved when pouring concrete. After the carriage is lifted in place, the round steel is inserted into the reserved hole of the pier, and the carriage is supported by the round steel.
2.2 Processing, installation and hoisting of carriage
In order to process the sliding lifting frame, the channel steel frame is divided into two halves on the ground. After the pier shaft is poured for two heights, the formwork of the first pier shaft is removed, and then the frame is hoisted around the pier shaft by tower crane, welded into a whole, and steel pipes are welded on the frame to form an integral sliding lifting frame.
The lifting of the carriage is mainly completed by chain block. The lifting point at the upper part of the inverted chain is anchored at the inner side of the main reinforcement of the bridge pier with φ50mm round steel cross bolts, and the lifting point is hooked on the frame at the lower part of the sliding frame to lift the rings. By manually tightening the crane, it will be gradually lifted. When hoisting to the reserved hole, use φ50mm round steel (45# steel) to penetrate into the pier and fix it, and complete the hoisting work. After the concrete pouring of each pier column is completed and the appearance of the last poured section is repaired, the carriage can be hoisted.
The welding requirements of all parts of the carriage are firm, and the corners are welded with triangular steel plates. The support pipe should be cut and inserted into the channel steel of the frame for welding, especially the lifting point. The hole should be cut with 2cm thick steel plate, and the hole should be polished smooth to avoid cutting the steel wire head; Hoisting hoist requires long-chain 10t new hoist, and it is forbidden to use threaded steel bars as rings to prevent brittle fracture; The welded joint of steel pipe adopts sleeve type, the top of the bracket is connected into a whole with transverse steel pipes, and the side faces are cross-connected with oblique steel pipes. The bracing arrangement is reasonable, and the hanging points of wire rope and chain block are reliable.
2.3 Unloading of sliding lifting frame
After the pier pouring is completed, the tower crane will gradually cut off the carriage from top to bottom, and the rest of the frame columns will be lowered to the bottom of the pier with a hoist, and then removed.
3. Template processing and installation
3. 1 template structure and construction technology
The turnover formwork is designed as a fillet formwork with the radius of the four corners of the pier R=3cm, and the design specifications of the middle standard formwork are 150× 150cm and 200×200cm. After being transported to the construction site, it will be assembled into a large mould, and one side will be divided into 1 ~ 2 pieces, which is convenient for hoisting and dismantling and saves time.
Template design panel adopts 5mm thick steel plate, welded with 63×63×6mm angle steel, and the square is 35×35cm. Between the formwork joints, use rubber sponge with thickness of 1cm, and connect and clamp with M 16 bolts. The outer skeleton is divided into horizontal and vertical layers with 8# channel steel, and the distance between tie rods is set to 1 degree with 80cm. Mechanically germinate with φ 22 round steel bar, and the gasket is 2cm thick. Φ φ25mmPVC rigid pipe shall be placed between the internal and external templates with tie rods, so that the tie rods can be reused after being pulled out. The inner and outer formwork are supported by the same grade of concrete pipe jacking to control the wall thickness of pier.
The main pier is constructed by large formwork turnover and tower crane, and tower crane and elevator are set to facilitate the construction personnel to get up and down. The standard section height of the formwork is assembled into a large formwork with a height of 3m, and the casting height is 6 ~ 7.5m at a time. Each pier consists of three parts, with a height of 9m. When dismantling, turn up the lower formwork, leaving a section for height fixing. This cycle is repeated until the designed construction height is reached.
During construction, the external formwork is installed on the pile cap with elastic lines, and the formwork is erected according to the lines. The installation sequence is as follows: first install the first template, then install the second template, first fix some bolts, then correct the centerline, and then fix all bolts and tie rods.
According to this, the process flow of circular operation is formed: steel bar connection and binding → formwork removal → formwork cleaning and release agent coating → lifting and assembling formwork → centerline and elevation measurement and inspection → washing and cleaning → concrete pouring and maintenance → concrete appearance repair → lifting the carriage until it reaches the designed pier height.
Strictly control the inclination of pier during construction. After the formwork installation is completed, use total station to retest and check the center line, determine the center deviation of pier shaft, and control the deviation value of formwork within the allowable range of specifications.
3.2 Pier concrete pouring
First of all, we should choose the gradation of materials and make the mixture ratio in advance; Because of the large pier height and pumping vertical distance, it is necessary to control the slump and water cement ratio of concrete at the same time to prevent cracks from occurring in the process of creep and shrinkage of concrete.
The pier concrete is poured horizontally in layers, and the thickness of each layer is about 40 cm. Vibrate with an internal vibrator, which requires compactness. Pay attention to the stability of the formwork when pouring. After pouring concrete, keep in good health in time, and do a good job of concrete insulation in winter construction. When the concrete strength reaches above 10MPa, and the concrete edges and corners can be guaranteed not to be damaged, the formwork can be removed.
3.3 Time required for each working procedure
60 hours of steel binding → 72 hours of formwork dismantling and installation → concrete pouring 12 hours → concrete curing and carriage hoisting for 24 hours.
In this way, when all the work is well prepared and the weather is relatively normal, three shifts are connected day and night to complete a pier (6-7 days for the next big pier and 4-5 days for the last small pier) as a cycle.
4. Internal force analysis and calculation of sliding frame
4. 1 Load weight of sliding lifting frame
According to the space frame calculation, the steel pipe length of the sliding lifting frame is 17.50m, and the weight of * * * is 6.58t；; No.22 channel steel * * * is 49.7m long and weighs1.24t; The operation floor is divided into ten floors, each with 60 bamboo splints, weighing1.2t; ; Considering the load of construction crowd and construction machines and tools, it is 50k g/m2；; Temporary stowage of 6t. The calculation adopts SAP2000 calculation software, and the program automatically calculates the self-weight of materials, so the stress analysis of the carriage only considers the temporary stacking weight of bamboo plywood, construction crowd, machines and tools and a section of formwork.
4.2 Safety checking calculation of sliding lifting frame
The calculation results of the carriage are modeled by the engineering structure calculation software SAP2000.
(1) The maximum shearing force assigned to each bearing round steel shall be calculated as a round steel bearing the largest weight:
τ = 5399.9/3.14× 52/4 = 275.2kg/cm2.
Less than allowable shear τ = 850kg/cm2
Check the security.
(2) Bending moment and stress of frame channel steel.
Two 22 # channel steel w = 217.6× 2 = 435.2cm3.
The calculated maximum bending moment m = 3.33t.m
Stress checking calculation
σ= M/W = 3.33× 105/435.2 = 758kg/cm2
Less than allowable stress σ= 1200kg/cm2
Check the security.
5. Precautions and safety measures for high pier construction
(1) Formulate safety technical measures, organize all technicians, constructors and labor teams participating in high pier construction to learn safety operation knowledge, and conduct special training before taking up their posts; And by the full-time security officer for hierarchical safety technical disclosure.
(2) Formulate strict operating procedures, and operators must strictly observe their respective posts and wear safety protection articles according to regulations. When working at his post, fasten the safety rope and wear the safety helmet.
(3) Safety guardrails shall be set around the construction platform, a closed safety net shall be set below the platform, and ladders shall be set on the upper and lower floors to facilitate the construction personnel to work up and down. Assign special personnel to carry out regular and irregular inspections, and the sidewalk board should take anti-skid measures. The steel bars are pressed on the springboard and tied together with iron wires.
(4) When the upper and lower floors are alternately operated, iron pieces and tools should be prevented from falling. When operating tools are not used, they must be packed in tool bags to prevent falling objects from injuring people.
(5) It is forbidden to pile up heavy objects on the operating platform, and always check the lifting point position of the lifting frame, the safety of the lifting wire rope and the chain block; Whether the load-bearing round steel is stable and balanced ensures foolproof.
(6) When the formwork is lifted and turned up, it should be lifted smoothly and balanced in place to prevent large swing and collision. Template demolition, should be removed from top to bottom, according to the level and order. The dismantled formwork shall be piled up smoothly, and deformation caused by stacking weight is strictly prohibited.
(7) The installation of each unit shall be completed within one working shift, and the bolts shall be fixed in time after completion.
(8) Construction at night must ensure sufficient lighting, and some work may not be carried out at night, such as carrying carriages and hoisting heavy components.
(9) In case of strong wind, rainstorm, thunder and lightning, snowy days and other bad weather, the construction shall be stopped.
(10) Electrical equipment for temporary electricity use shall be installed by certified electricians, and it is strictly prohibited to pull or connect them randomly.
(1 1) Machines and tools used (such as pulleys, chain block, winches, steel ropes, etc. ) check it frequently and have enough safety factor.
6. Safe lifting operation of tower crane
The main pier is constructed with large turnover formwork and tower crane, with 4 tower cranes and 2 elevators, which is convenient for construction personnel to get up and down. In ...
8# pier requires a lifting height of 75m；;
9# pier requires a lifting height of 90m；;
10# pier required lifting height160m; ;
1 1# pier required lifting height125m; ;
Tower crane requires arm length of 50m and maximum lifting capacity of 6t; Mainly consider installing 0# bracket and hanging basket.
(1) Tower crane drivers should receive professional training, hold qualified operation certificates, and understand the working principle, mechanical structure and technical performance of tower cranes.
(2) When the tower crane is lifting heavy objects, it should be commanded by special personnel, and the objects must be tied firmly with wire rope before lifting.
(3) When lifting, try lifting first. Only after the brake is sensitive and reliable can lifting be carried out.
(4) In case of heavy fog, rainstorm, thunderstorm, snowy day and gale above level 6, the hoisting operation should be stopped.
summary
The scheme is safe and reliable in high pier construction. When the lifting frame is hoisted, eight cranes are used for lifting. Because the channel steel frame of the lifting frame is only 5 cm away from the concrete of the pier, if the hoist is decoupled or broken, the pier will be stuck when the lifting frame is tilted, so as to ensure the safety of construction personnel and avoid major safety accidents. Moreover, it has the effects of saving materials, simple operation, accelerating construction progress, shortening subsection construction period, improving work efficiency and getting twice the result with half the effort.
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