【Haichuan Chemical Construction Technology】What are the requirements regarding the types of connections for rebar and their placement locations?

II. Location of steel bar connection joints: Whether the connection is achieved through binding, welding, or mechanical means, the location of steel bar connection joints must meet the following requirements: In concrete structures, the connection joints of load-bearing steel bars should be placed in areas where the stress is lower, and as few joints as possible should be used on the same load-bearing steel bar. \"In the important components and key load-transferring areas of a structure, longitudinal stress-reinforcing bars should not have connection joints\" (see Article 8.4.1 of the Code for Design of Concrete Structures GB50010-2010). This is the general principle for determining the placement of steel bar joints. Why are there restrictions on the location of steel bar joints? Because joints are, after all, weak points; the load-bearing strength of steel bar joints is inferior to that of intact bars without joints, and any form of steel bar jointing reduces their load-bearing strength. A straight-threaded sleeve coupling is a connection method that transfers the force from one steel bar to another through the mechanical interlocking between the steel bars and the coupling elements. Since the quality of joints is still not as good as that of the rebar itself, codes restrict the location, number, and percentage of joints; it is advisable to place joints in areas where the stress is low (i.e., where the bending moment is small). At the same time, the joints should be avoided in key stress-bearing areas such as the stirrup reinforcement zones at the column ends and beam ends of seismic structures. The term used in the standards is “it is advisable”, rather than “it is required”, indicating that it is not a mandatory requirement; if it is truly impossible to avoid the areas with increased rebar density during construction, then the rebar can be arranged differently. III. Disputes over the location of steel bar joints: The terms “preferably” and “not preferably” in the specifications do not represent mandatory requirements; some flexibility is allowed – it is possible to proceed in one way or another. When conditions permit, the preferred approach should be adopted first. If it means that it is necessary to do so, the wording used must be “must” or “strictly prohibited”. None of the provisions in the \"Technical Code for Mechanical Connection of Steel Bars\" (JGJ107-2016) regarding the location of steel bar joints are mandatory. In actual construction, the codes should not be interpreted in a dogmatic manner; the provisions must not be understood incorrectly or inaccurately, but rather with precision and clarity. IV. Percentage of reinforcement joint area: According to the \"Technical Code for Mechanical Connection of Reinforcement\" (JGJ107-2016), the percentage of reinforcement joint area in the same connection section refers to the ratio of the cross-sectional area of the longitudinal reinforcement bars with sleeves in that connection section to the total cross-sectional area of all longitudinal reinforcement bars. When reinforcing bars of different diameters are connected, the calculation is based on the area of the bar with the smaller diameter. ) When it is 100%, a grade 1 joint should be selected. When the joint percentage is 100%, only Grade I joints can be used; Grade II or Grade III joints are not permitted. JGJ107-2016, Clause 4.0.3, Sub-clause 2: “Joints should be avoided in the areas with increased stirrup density at the ends of beams and columns in frames that are subject to seismic requirements; when avoidance is not possible, Grade II or Grade I joints shall be used, and the percentage of jointed area shall not exceed 50%.” In the stirrup reinforcement zones at the ends of beams and columns required for seismic design, it is preferable to avoid using joints; if sleeve joints must be used in these critical areas, the grade of the joints should be improved and the percentage of joints should be reduced. As long as the percentage of joint area does not exceed 50%, grade II joints or grade I joints can be used in any part of the seismic structure.

The general principles for setting steel bar joints outlined by the original poster are very thorough; indeed, joints, as weak points in a structure, require strict control. A few practical details worth mentioning: First, in addition to this general principle, different types of connections have their own specific requirements. For example, the percentage of the cross-sectional area occupied by tensile steel bar joints within the same connection section should generally not exceed 25% for beams and slabs; if it is indeed necessary for construction purposes, it should not exceed 50%. All of these requirements must comply with the relevant provisions of GB50010. Furthermore, in many of our chemical engineering construction projects, the structures have additional requirements regarding seismic resistance and corrosion resistance. For special structures such as tank foundations and chemical engineering frameworks, the design of joints must be adjusted in accordance with the industry-specific standards. One final reminder: before starting on-site construction, it is advisable to follow the project’s specific plans and design drawings. In case of any uncertainties, it is necessary to consult professional structural engineers to avoid compliance issues.

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