16m pretensioning method prestress Hollow slab construction method
Content introduction Part I Layout of prefabrication site and layout of hollow slab tensioning platform of prefabrication base: design and check calculation shall be carried out according to the corresponding stress conditions, and also according to the local geological conditions, the foundation depth of 100cm of the base shall be replaced with sandy soil within the same width of the bottom formwork, the prefabrication site shall be leveled and compacted, and then the reinforced concrete shall be poured within the foundation range of the slab beam base and the bottom formwork, Four reinforced concrete shear walls are set at the base foundation, which are respectively arranged at the center of each bottom formwork. The tensioning end and anchoring end of the pedestal are reinforced concrete stiffened walls with a foundation depth of 250cm. In addition to the normal reinforcement, several 25 # channel steel ribs are added inside. The tensioning and anchoring end faces are respectively provided with 25mm thick steel plates to facilitate the anchoring and tensioning construction. The outer side of the tensioning end is equipped with a steel beam processed from 70 type I-beam, which is used for the jack tensioning construction. The second part is the main construction method for prefabrication and installation of hollow slab. Mangeerte Medium Bridge is a 4-16m pretensioned prestressed hollow slab bridge, of which there are 88 prestressed hollow slab beams with a span of 16m. The hollow slab beam is prefabricated in the prefabrication yard. After the prefabrication, it is transferred to the beam storage yard for storage. During installation, two cranes with a lifting capacity of 25 tons are used for hoisting in place. 1、 Prefabrication of reinforced concrete hollow slab 1. First plan the prefabrication site, level and compact it, and treat the site foundation. The prefabrication yard is located 200m to the left of K58+020 road, and all prefabricated parts are prefabricated in the prefabrication yard. The size of the prefabrication yard is designed to be 90m × 60m. 2. Pedestal and formwork ① The pre-stressed hollow slab of pedestal is produced with open pedestal. It is proposed to set up two production lines, each pedestal is 76 m long, and the pedestal concrete is C40. Each production line is considered to produce four hollow slab beams at a time, and eight hollow slab beams at a time. The production of 16 m span slab beams is completed in 11 times. The tensioning pedestal must meet the design requirements, and the pedestal beam shall have sufficient rigidity, and the deflection after being stressed shall be ≤ 2mm. The tensioning bench can be used only after reaching the design strength. The deformation of the bottom beam must be observed and recorded when the tensioning pedestal is used for the first time. ② As far as the superstructure of precast prestressed bridge is concerned, due to prestress, the camber of precast slab beams will occur during construction. Generally, the camber opposite to the structural camber should be set during construction. At the same time, according to the experience of previous highway construction, in order to ensure the thickness of bridge deck pavement, the elevation of abutment cap and pier cap should be lowered by 1~2 cm from the design value. C40 terrazzo concrete is used for the inner bottom formwork of pedestal. The surface shall be waxed after troweling to ensure that the bottom mold surface is flat and smooth. The hollow plate core mold adopts inflatable capsules. The side mold and the retaining head mold are set shaped steel molds, which are produced by professional manufacturers. It is proposed to make 4 sets of formwork, and the versatility of middle plate and side plate of 16m span plate beam shall be considered when making formwork, so as to meet its requirements as far as possible. Before installing the core mold, the capsules should be inflated for inspection to prevent air leakage. Formwork removal shall be carried out after the concrete reaches 80% of the design strength.
