How to calculate the lap length and joint area percentage when two steel bars with different diameters are overlapped?
Lap length: The force transfer between the lashing lap steel bars is due to the grip and wrap bonding anchorage between the steel bar and the concrete. The two opposing reinforcing bars are respectively anchored in the concrete of the lap connection section, and both transfer the stress to the concrete, thus realizing the stress transition between the rebars. Therefore, the basis of lashing lap force transfer is anchorage. When the same stress is transmitted through the binding of two steel bars of different diameters, the thick steel bar and the concrete surface are larger, and the required length is smaller, and the thin steel bar and the concrete surface are smaller, and the required length is larger. Therefore, when the coarse and fine steel bars are lapped in the same section, it is safer to calculate the lap length according to the finer steel bars.
Head Area Percentage:
If the steel bar lap is not good, it will cause the steel bar to be connected from end to end, and the arrangement of the form of head and tail connection will cause stress concentration and local cracks on the lap end face, so the specification staggers the steel bar joint by controlling the percentage of the joint area in the same connection section, if the steel bar is of the same diameter, then it is very good to calculate, if the diameter of the steel bar of the lap is different, when calculating the percentage of the joint area, the steel bar tied together needs to be calculated according to the fine diameter steel bar with less force, and when calculated according to the smaller diameter, this percentage will be smaller. Obviously, it's safe.
Attached: relevant normative provisions
↘↘ Code for Construction of Concrete Structure Engineering GB50666-2011
↘↘ Code for Acceptance of Construction Quality of Concrete Structure Engineering GB50204-2015
↘↘ Code for Design of Concrete Structures GB50010-2010 (2015 Edition)
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