Specification for steel binding lap joints

The Code for Design of Concrete Structures stipulates that binding lap joints are not allowed for longitudinal reinforced bars and small eccentric reinforced bars under axial tension.

When the diameter of the tensile reinforcement is d >; 25mm, and the diameter of compressed steel bar d> When it is 28mm, it is not suitable to adopt binding lap joint (the new Mixed Code of 20 10 has made stricter requirements on these two data, while the old code is set at 28mm and 32mm).

The lap length of steel bars generally refers to the lap length of steel bar binding connection, and some refer to the length of loose weld seam of steel bar welding.

Minimum lap length of longitudinal tensile reinforcement

Reinforcement lap refers to the connection method that two reinforcement bars have a certain lap length and are bound with binding wires, which is suitable for the connection of reinforcement bars with smaller diameters. Generally used for steel mesh in concrete, the warp and weft are evenly arranged, without welding, and only fixed by iron wire.

Application example

Example d2. 1 The seismic grade of a member is Grade II, and the concrete strength grade is C35. The longitudinal tensile reinforcement adopts RRB400(III) grade φ 28 epoxy resin coated reinforcement, and the percentage of binding joint area is between 40%. Try to determine its lap length.

Solution: the minimum lap length = 40d×1.4×1.1×1.25x1.15 = 88.55d = 2479.4mm.

Each rebar joint can be prepared by increasing the length by 2150 mm.

Example d2.2 A member has no seismic fortification requirements, and the concrete strength grade is C25. The longitudinal compression reinforcement adopts HRB335(II) grade φ 18 ribbed reinforcement, and the percentage of binding joint area is between 60%. Try to determine its lap length.

Solution: minimum lap length = 45d×1.6× 0.7 = 50.4d = 907.2mm. ..

Each steel bar joint can be increased by 800mm in length.

Example d2.3 For foundation beam members without cushion, the minimum thickness of concrete protective layer is 70mm, which is fortified according to the requirements of seismic level III. The concrete strength grade is C30, the longitudinal tensile reinforcement is HRB400(III) grade φ 22 ribbed reinforcement, and the percentage of binding joint area is 40%. Try to determine its lap length.

Solution: minimum lap length = 40d×1.4× 0.8×1.05 = 47.04d =1034.88mm.

Each rebar joint can be prepared by increasing the length by 900 mm

Reinforcement lap refers to the connection method in which two reinforcement bars have a certain lap length and are bound with iron wire, which is suitable for the connection of reinforcement bars with smaller diameters. Generally used for steel mesh in concrete, the warp and weft are evenly arranged, without welding, and only fixed by iron wire. When the diameter of the tensile reinforcement is d >; 25mm, and the diameter of compressed steel bar is d & gt28mm, so binding lap joint is not suitable.

Arc welding of steel bar

Discussion on arc welding connection in fusion welding.

Steel arc welding can be divided into lap welding, surfacing welding, groove welding, groove surfacing welding and narrow gap welding.

1. lap welding head

Lap welded joints are suitable for welding HPB235, HRB335 and HRB400 steel bars with diameters of10 ~ 40mm. Double-sided welding shall be adopted for lap welding of steel bars. When double-sided welding is not possible, single-sided welding can be used. Before welding, the steel bars should be pre-bent to ensure that the axes of the two steel bars are in a straight line and the joint has good mechanical properties.

2. Welded joint of side bar

The upper steel bar welding joint is suitable for welding HPB235, HRB335 and HRB400 steel bars with diameters of 10 ~ 40mm. Steel bar welding should adopt double-sided welding. When double-sided welding is not possible, single-sided welding can also be used. Help should be made of steel bars of the same grade or diameter as the main reinforcement; If the grade of the upper reinforcement is the same as that of the main reinforcement, the diameter of the upper reinforcement can be smaller than that of the main reinforcement by one specification; If the diameter of the batten is the same as that of the main reinforcement, the reinforcement level of the batten is one level lower than that of the main reinforcement.

The weld thickness h of lap welded joint of reinforcement or welded joint of side reinforcement shall not be less than 0.3 times of the diameter of main reinforcement; Weld width b should not be less than 0.7 times the diameter of main reinforcement.

For hot rolled steel bars with a diameter greater than or equal to 10mm, the joints shall be overlapped, and the following requirements shall be met during arc welding:

1) Welded joints shall adopt double-sided weld when the design requires it, and generally adopt single-sided weld when there is no special requirement. The total length of lap welding or side welding of Grade I rebar shall not be less than 8d; For secondary and tertiary steel bars, the total weld length of lap welding or lath welding shall not be less than 10d, and the weld lengths on both sides of the joint shall be equal during lath welding.

2) The total cross-sectional area of the battens shall meet the following requirements: when the main reinforcement is Grade I reinforcement, it shall not be less than 1.2 times of the cross-sectional area of the main reinforcement; When the main reinforcement is Grade II and III reinforcement, it should not be less than 1.5 times of the cross-sectional area of the main reinforcement. In order to facilitate welding and make the center lines of upper reinforcement and main reinforcement on the same plane. The slats shall be made of steel bars of the same grade and diameter as the main bars. If the batten is different from the main reinforcement, it should be converted according to the design strength. The length of slats shall meet the requirements of corresponding welds.

Refer to Baidu Encyclopedia-Rebar Lapping