Prestressed concrete slab often need to carry out the two openings because of the retrofitting requirements, especially floors and the roof of industrial housing, public places; the type, size, location of the slab openning is different, involve to lift (staircase) opening, the pipeline equipment (air duct, pipe hole, cave roof lighting) additional opening, and change the position of the stairs stairs. The size of the hole is different, and its position may be located in the slab, the edge of the slab and the corner of the slab, and the stress system of the prestressed floor is mostly two-way.

The force category of prestressing tendons inside of the concrete floor

1.Flexural prestressing tendons

The prestressed tendons in the floor affect the flexural capacity and deflection of the floor. Therefore, for the pre-stressed floor slab opening, we should consider the influence of the prestressed reinforcement on the floor's flexural bearing capacity when the floor is strengthened.

2.Temperature prestressing tendons

For some super long concrete structures, in order to solve the temperature stress caused by the temperature difference between the super long concrete structure and the shrinkage stress of the concrete, the structural design is often applied in the concrete slab to set up the unbonded prestressed reinforcement to solve the above problems. Because the design of the unbonded temperature prestressing tendon coincides with the center line of the plate section, it does not provide bending moment resistance arm, that is, it has no influence on the bending capacity of the floor. Therefore, only the pre-stressed reinforced concrete floor openings and reinforcement need to be reinforced according to the ordinary concrete floor.

3. After the opening of the concrete floor, the stress conditions of the concrete floor have changed, and the stiffness and bearing capacity of the floor slab should be reduced. How large holes are opened or not to be reinforced depends on the specific conditions and the size of the function load of the floor. Slab opening and the reserved holes are not the same, the opening of the opening of the floor more impact on the floor, generally need to reinforce.