⑤ Shrinkage and creep observation of concrete the shrinkage and creep of concrete shall be measured by field sampling for 7 days, 14 days, 28 days and 90 days.
Before the measurement results are available, the test data of the same grade of concrete under the same or similar conditions in the previous construction shall be used.
Then modulate the formwork, bind the reinforcement, pour the concrete, tension the prestress, move the hanging basket forward, and cycle until the construction of the cantilever section is completed.
1.0 construction process flow of cantilever section of cantilever cast-in-place continuous beam adopts the method of symmetrical casting of hanging basket cantilever.
② A special observation team shall be established to strengthen the observation of the deflection changes of the cantilever under four working conditions before and after concrete pouring and prestressed tensioning during the construction of each section.
During the suspension pouring construction, the elastic deformation of the hanging basket shall be included in the calculation of the camber of the beam section construction.
In case of no clear description, this operation instruction specifically refers to the triangular hanging basket.
Each hanging basket has two composite beams, the components are welded by hot-rolled section steel, and the parts are bolted; The formwork system adopts combined steel formwork, with channel steel as rib and support; The suspension system adopts finish rolled deformed steel bar; The whole hanging basket is light, stable and safe in stress state, and convenient for operation and construction.
(6) precautions for the assembly and disassembly of the hanging basket ① the assembly and disassembly of the hanging basket shall be carried out at the same time with basic symmetry at both ends.
Before operation, the safety inspection shall be carried out on the hoisting machinery and machines.
③ The assembly and removal of hanging baskets are high-altitude operations.
After the construction of each section, sort out the deflection curve for analysis, timely and accurately control and adjust the deviation value during construction, so as to ensure the closure accuracy of the cantilever end of the box girder and the line shape of the bridge deck.
According to the actual conditions on site, the loading method can adopt the simulated loading of stacked sand bags or the opposite tension and back pressure loading through the jack and the anchor ingot anchored in the bearing platform.
(1) determination of relevant parameters of linear control ① deformation value of hanging basket the deformation of construction hanging basket is difficult to be calculated accurately and shall be measured through hanging basket load test.
Through on-site sampling and laboratory measurement, the e values of concrete at 7, 14, 28 and 60 days are measured respectively to obtain a complete E-T curve.
The precise level is used for elevation measurement monitoring, and the measurement time is arranged to observe when the temperature change is small in a day..
The vault support in the box shall be taken out by dismantling parts, the side formwork and bottom formwork system shall be hoisted as a whole, and the main truss shall be retreated to the vicinity of the pier, and then dismantled by crane.
In order to minimize the influence of temperature, the observation of deflection is arranged before the sun comes out in the morning.
After the assembly is completed, the beam section load shall be applied to the hanging basket for preloading to fully eliminate the inelastic deformation of the hanging basket.
(5) remove the hanging basket structure after the construction of the box girder cantilever pouring beam section is completed.
(2) hanging basket assembly after the structural members of the hanging basket are transported to the construction site, they shall be hoisted to the top surface of the 0# beam section that has been poured for assembly.
The process flow is shown in Figure 1-1 Construction process flow chart of cantilever pouring beam section 2.0 construction methods and requirements 2.1 construction preparation (1) the construction of continuous beam “t” component 0# block is completed.
The temperature change includes daily temperature change and seasonal change.
The hanging basket structure is mainly divided into triangular integral main truss beam, walking system, bottom basket and formwork system, suspension system and anchorage system.
During the loading process, the deformation value of the front end of the hanging basket under various loads can be measured, and the load deflection relationship curve of the hanging basket can be obtained.
The daily temperature change is more complex, especially under the action of sunshine.
The influence of seasonal temperature difference on the deflection of the main beam is relatively simple, and its change is uniform.
According to the deflection of the hanging basket under various loads, the load deflection curve of the hanging basket is drawn, which provides a reliable basis for the linear control of cantilever construction.
During the load test, the equivalent loading shall be carried out according to the beam section load with the most unfavorable stress on the hanging basket during construction, and the deflection of the hanging basket under various loads and the internal force of the hanging basket control rod under the maximum load shall be measured.
During construction, the pipe friction loss of longitudinal prestressed steel strand is mainly measured to verify whether the value of design parameters is consistent with the actual situation, and the cantilever deflection caused by prestress construction is calculated according to the effective prestress.
Monitor the state of box girder during construction, and arrange professionals to carry out linear control measurement for each construction condition.
The main flow chart of hanging basket structure assembly is shown in Figure 3-2 below.
E-T curve.
(4) after the construction of the previous beam section is completed, release and relax each lifting point to separate the formwork from the beam body, release the rear anchor point on the beam, carry out anchorage conversion, transfer the supporting force of the traveling trolley to the slideway, drag the main truss through the chain block to move the whole hanging basket to the position of the next beam section.
⑥ Temperature observation temperature is one of the most important factors affecting the deflection of the main beam.
Step loading.
Therefore, in order to specifically understand the temperature difference inside and outside the box girder section and the distribution of temperature on the section, temperature observation points are arranged on the beam body for observation, so as to obtain accurate temperature change law.
④ The measurement of prestress loss is divided into several types.
③ Before closure, the last 2 ~ 3 segments on both sides of the closure section shall be jointly measured during formwork erection to ensure the closure accuracy.
② Construction temporary load measurement construction temporary load includes construction hanging basket, personnel, machines and tools, etc.
The cantilever pouring shall be carried out symmetrically and balanced on both sides, and the construction load deviation on both sides of the “t” structure shall be kept within the allowable range of the design.
Each process must be carefully checked before the next process can be carried out.
③ Determination of bulk density and elastic modulus of box girder concrete the test of elastic modulus of concrete is mainly to determine the variation law of elastic modulus E of concrete with time, i.e.
During cantilever construction, when the same T-structure hanging basket is constructed, the hanging baskets at both ends shall be constructed symmetrically.
(3) Remove 0# the construction materials, machines and tools of block compartment and beam top, and put the materials and equipment used for hanging basket construction to the beam top in order; 2.2 hanging basket construction (1) hanging basket structure the commonly used hanging baskets are cable-stayed, triangular, rhombic, truss and other structural forms.
According to the internal force of the hanging basket control rod under the maximum load, the actual bearing capacity of the hanging basket can be calculated, and the actual safety factor in the use of the hanging basket can be understood to ensure safety and reliability.
(2) The hanging basket enters the site and is trial assembled.
2.2 alignment control in order to ensure the reliability and safety of the structure during construction and ensure that the bridge alignment and stress state meet the design requirements, the bridge cantilever construction is controlled.
② The hanging basket assembly shall be carried out one by one according to their own sequence.
Figure 3-2 Hanging basket assembly flow chart (3) hanging basket static load test after the hanging basket is assembled, the load test shall be carried out to determine the actual bearing capacity of the hanging basket and the deformation under the load of the beam section.
(2) calculation of construction camber calculation of box girder camber is calculated by professional program according to various parameters measured on site.
(4) elevation monitoring two symmetrical elevation control points are arranged on each box girder section to monitor the deflection of each section of box girder construction and whether torsional deformation occurs during the whole box girder construction process.
After the hanging basket is in place, first convert the anchor on the main truss beam to the anchor bar of the beam body, install and convert the rear anchor of the bottom basket on the beam body, then measure and locate the center line and elevation through the measuring instrument, adjust the elevation, and finally conduct comprehensive anchorage after it is determined to be qualified through inspection.
The removal sequence is: vault support in the box → side formwork system → bottom formwork system → main truss, sling system and walking anchorage system.
During the operation, there shall be special personnel on the ground and in the air for command and guidance.
(3) construction deflection control of cantilever box girder ① determine the formwork erection elevation of the beam section to be cantilever poured according to the pre camber and design elevation, and erect the formwork in strict accordance with the formwork erection elevation.
After the hanging basket is assembled, the back pressure loading method is used for load test, and the loading amount is calculated and determined according to the weight of the most unfavorable beam section.
