What is the concrete content of how to place the longitudinal prestressing steel bar? Here is your answer.
(1) Net distance of prestressing steel bar. The net distance between pre-tensioned tendons should be determined according to the requirements of pouring concrete, applying prestressing force and reinforcing bar anchorage. The net distance between prestressing steel bars should not be less than 1.5 times of their nominal diameter or equivalent diameter, and should conform to the following rules: for heat treated steel bars and steel wires, it should not be less than 15 mm; for three strands, it should not be less than 20 mm; and for seven strands, it should not be less than 25 mm.
(2) Anchorage of steel bar and steel wire. The pre-tensioned pre-stressed concrete members should ensure that there is a strong bonding force between reinforcement and concrete. Generally, deformed steel bars, notched steel wires and steel strands should be selected. When choosing smooth circular steel wire as prestressing reinforcement, appropriate methods should be selected according to the strength, diameter and stress characteristics of steel wire, so as to ensure that steel wire is firmly anchored in concrete and prevent steel wire from sliding, and the obscure effect of low crack resistance in the scale of prestressing transfer length should be considered.
(3) The reserved passages of post-tensioned prestressing tendons and stranded tendons shall conform to the following rules:
For prefabricated members, the net horizontal distance between the channels should not be less than 50 mm, and the net distance between the channels and the edge of the components should not be less than 30 mm, and should not be less than half of the diameter of the channels.
(2) In the frame beam, the net distance of the reserved channel in the vertical direction should not be less than the outside diameter of the channel, and the net distance in the horizontal direction should not be less than 1.5 times the outside diameter of the channel; the thickness of the concrete protective layer calculated from the hole wall should not be less than 50 mm at the bottom of the beam and less than 40 mm at the side of the beam.
(3) The inner diameter of the reserved channel should be 10 mm to 15 mm larger than the outer diameter of the prestressing steel wire or strand bundle and the outer diameter of the connector that needs to pass through the channel.
(4) Grouting holes or exhaust holes should be installed at both ends and spans of components, and the spacing of holes should not be greater than 12 M.
Where pre-arched components are required during fabrication, the reserved channel should be arched together with the components.
(4) Reinforcement bars should be placed evenly at the end of the pre-stressed concrete members. Together, the following requirements should be noted:
It is advisable to bend a part of the prestressing steel bar near the support, and the bending prestressing steel bar should be evenly placed along the end of the member.
(2) When the pre-stressed steel bars at the end of a member need to be assembled at the lower part of the section or at the upper and lower parts, additional vertical welded steel nets, closed stirrups or other structural steel bars should be installed within the scale of 0.2h (h is the height of the section at the end of the member).
(5) For pre-tensioned pre-stressed concrete members, the concrete around the end of the pre-stressed steel bar should adopt the following strengthening methods:
For a single pre-stressed steel bar, it is advisable to install spiral bars with length not less than 150 mm and no less than 4 circles at the end; when there is solid experience, the insertion bars on the support cushion plate can also be used to replace the spiral bars, but the number of insertions should not be less than 4, and the length should not be less than 120 mm.
(2) Three to five pieces of steel mesh with straight prestressing bars should be set at the end of the member for 10 days (d is the nominal diameter of the prestressing bars).
(3) The transverse reinforcing bar should be properly encrypted in the 100mm scale of the plate end for the thin plate with prestressing steel wire reinforcement.
(4) For grooved slab members, additional transverse reinforcement should be installed along the slab surface of the member within the 100 mm scale at the end of the member, and the number of reinforcement should not be less than two.
_For prefabricated ribbed slabs, transverse ribs should be set to strengthen their integrity and transverse stiffness. The reinforced bar of the end transverse rib should bend into the longitudinal rib. When the pre-tensioned long-line method is used to produce the prestressed concrete ribbed slabs with end transverse ribs, a useful method to prevent cracks in end transverse ribs should be adopted in design and fabrication.
(6) Curvature radius of curved prestressing steel wire bundle and strand bundle should not be less than 4m in post-tensioned prestressed concrete members, and the curvature radius of folded-wire reinforced components can be reduced appropriately at the bending point of prestressing steel bar. In the pre-tension zone and pre-compression zone of post-tensioned pre-stressed concrete members, longitudinal non-pre-stressed structural steel bars should be installed; in the bending zone of pre-stressed steel bars, stirrups should be tightened or steel meshes should be installed along the inside of the bending zone.