by Pay attention to the official account [Lanchen Talk about Cost], and get more information about the project.
The difference between pre tensioning and post tensioning construction is I.
The pre tensioning method refers to a construction method of pre tensioning prestressed steel before pouring concrete.
That is, first tension the steel tendon on the pedestal according to the design tension, and then temporarily anchor it with clamps, and then pour the component concrete.
After the concrete reaches the required strength (generally not less than 70% of the design strength), release it, The retraction force of the steel tendon is transferred to the concrete through the bond between the steel tendon and the concrete, so that the concrete can obtain the prestress.
This method is only applicable to the construction of precast concrete components.
2、 Post tensioning method refers to the construction method of post tensioning prestressed steel for cast-in-situ concrete.
That is to say, the component concrete shall be poured first, and the duct shall be reserved in it.
After the concrete reaches the required strength (generally not less than 70% of the design strength), the tendon shall be penetrated into the reserved duct, and the tendon shall be tensioned with a jack supported at the end of the concrete component to make the component receive the reaction compression.
After the tension reaches the control tension, the tendon shall be anchored to the concrete component with an anchorage device to make the concrete obtain and maintain its pre stress.
This method is not only applicable to the construction of cast-in-situ concrete components, but also applicable to the construction of precast concrete components.
As reflected in the bill of quantities of bridge works, the post tensioning method usually requires anchorage and bellows, while the pre tensioning method does not.
Selection of transportation quota for prefabricated components ① Cart and cushion roller stranding: Cart: a small transportation tool without power, which can be made of wood or steel.
It is generally pushed forward or backward by people with a lifting and transportation capacity of 2~10kN.
It is applicable to the transportation of small structures on the site.
Pad roller stranding: place the prefabricated components on the upper walking board, and use the forward movement of the walking board on the roller to drive the components to move horizontally.
The power is a hand winch, which is suitable for short distance on-site transportation.
② Rail flat car transportation: use rail flat car to transport components along the temporary track laid from the prefabrication yard to the construction site.
The rail flat car transportation quota is generally applicable to the on-site transportation of prefabricated components, and the cost of its track shall be calculated separately.
③ Truck transportation: generally applicable to the construction and transportation of prefabricated components with medium and small spans and small prefabricated components for factory production.
④ Flat trailer transportation: generally applicable to the transportation of large-span components and large-scale components for factory centralized prefabrication.
⑤ Barge transportation: large engineering barges are used to transport prefabricated components, generally used for river transportation.
⑥ Cable transportation: when cable hoisting equipment is used for the installation of prefabricated components, cableways are used for the high-altitude transportation of prefabricated components.
Beam carrier transportation refers to a kind of prefabricated beam transportation machinery in bridge erection, which is the most ideal prefabricated component transportation tool in the current bridge erection process.
The beam carrier is divided into tire type beam carrier and rail type beam carrier.
The type of beam carrier is selected according to the prefabrication site, transportation distance and prefabricated beam tonnage.
The beam transport vehicle can solve the problem of safe transportation of prefabricated components with long distance and large tonnage, and can realize the process of beam transport and beam feeding in one step.
The beam transport vehicle should be suitable for bridge erection sites, precast beam yards, especially for the erection and transportation of bridges such as highways, railways, and intercity light rails.
Track slab transportation is applicable to on-site transportation of prefabricated components; It is mainly applicable to the transportation of T beam, small box beam and hollow slab beam, and the transportation distance should not be too long.
It can be transported to the position to be erected by laying rails on the erected beam surface or on the ground.
Truck transportation is applicable to the transportation of components with small and medium spans and small components that are prefabricated in a factory.
The flat trailer transportation is applicable to the transportation of large-span components and large-scale components that are prefabricated in a factory.
Truck crane, rubber tyred crane, crawler crane and gantry can be used to load and unload components.
The laying of transportation road, track, gantry and cable are not included in the norms…
