1, the phenomenon
The improper preparation of the bottom formwork and formwork of the construction hanging basket causes difficulties in construction operation, the bottom plate joint of the box girder changing section by section is not smooth, the bottom formwork is deformed, the side formwork joint is not smooth, the beam bottom is uneven, and the longitudinal axis of the beam body is not smooth.
2. Cause analysis
(1) The cantilever pouring is generally constructed by the hanging basket method, and the plane size of the hanging basket bottom formwork fails to meet the requirements of formwork construction.
(2) The setting of the bottom formwork did not take measures according to the characteristics of the gradual change of the cross section of the box girder, so that the bottom joint of the beam was uneven, slurry leakage and the bottom line shape of the beam was not smooth.
(3) The joints of the side formwork are not closely attached, resulting in slurry leakage and uneven wall joints.
(4) When positioning the hanging basket template, the high value is not considered enough, or the tightening force of the suspension belt before and after the hanging basket is uneven.
(5) The template of the hanging basket is not positioned according to the longitudinal axis of the bridge.
(6) The vertical and horizontal beam connection of the bottom formwork of the hanging basket is unstable and geometrically deformed.
3. Prevention and control measures
(1) The plane size of the bottom formwork shall meet the operating width required for supporting and dismantling during formwork installation and pouring concrete.
(2) The bottom formwork shall consider the gradual change of box girder section and construction pre-camber, and set up movable steel stranding at the connection between the longitudinal beam and the transverse beam of the bottom formwork to adjust the bottom formwork and make the bottom joint of the beam smooth.
(3) In order to prevent the deformation of the geometric dimensions of the bottom formwork between the parallel longitudinal beams and parallel cross beams under the bottom formwork, the vertical and horizontal beams shall be firmly connected with the shear-shaped arrangement of steel bars or section steels to prevent the deformation of the bottom formwork.
(4) After the hanging basket is in place, when correcting the bottom formwork, the throwing height of concrete pouring must be reserved (which shall be obtained through the equal load test of the hanging basket). When installing the formwork, the elevation shall be checked strictly according to the measured position, and the center line shall be corrected. The concrete surface of the formwork and the previous section shall be flat and tightly pasted.
(5) After the hanging basket is in place, the fulcrum shall be stabilized, the rear sling shall be tightened, the rear anchor shall be fixed, and the elevation of the beam end shall be measured again. When the sling is retreated, it shall be evenly synchronized. After the sling is tightened, it shall be checked whether the force is balanced, otherwise it shall be readjusted.
