In building structure, because of its excellent structural mechanical properties, rigid column structure is favored by many structural architects. Among them, there is the combined connection between section steel and reinforcement, and the combined connection between section steel, reinforcement and section steel and reinforcement. Among them, there is reinforcement wrapped in the outer layer of section steel (steel wrapped steel), and there is section steel wrapped in the outer layer of reinforcement (steel wrapped steel).

Next, we will introduce the method and characteristics of double threaded joint in the structural connection according to the first case above.

（1）Combined connection of section steel and reinforcement

As shown in Figure 1 and Figure 2, the composite connection structure of section steel column and reinforced beam is shown.

Figure 1 (top view)

Previously, our common connection method is to use the cantilevered corbel on the steel column to connect it within the flange range of the steel column in the structural design. The flange plate of the outer steel column is 280mm wide, and the connecting plate is welded on the flange plate. For example, the reinforcement usually needs to be welded on the connecting plate to realize the connection between the reinforcement beam and the section steel column, as shown in Figure 2 (insert the photo of the connection of the method).

Using the original traditional welding connection method, the steel column flange overhanging steel corbel connecting plate is welded with the reinforcement. On site, it is not only difficult to weld the reinforcement, but also difficult to ensure the welding quality and the accuracy of the reinforcement position. Moreover, the on-site welding time is long, which often can not meet the requirements of construction period and quality.

一、Problem analysis:

Figure 3 ?? Structural diagram of flange plate welding connection between horizontal reinforcement and section steel column

The new connection method uses welded sleeves at both ends of the rigid column and double screw sleeve for butt joint in the middle!

Figure 6 ? Photo of middle end of double screw sleeve

二、Technical features

The national patented product “WL double screw sleeve reinforcement joint” independently developed by Beijing Wulongxing Technology Development Co., Ltd. is mainly characterized by “reinforcement non rotation” connection. It has the characteristics of fast connection speed, convenient construction, reliable quality, low cost and all-weather construction.

The double screw sleeve has the following technical features:

① There is no wet operation at the connection joint, and it is fully mechanically connected; ② The connection is fast and takes only 20 seconds. After the connection is completed, it can bear the force;

③ Whether the reinforcement connection quality is qualified or not can be visually inspected, which is simple and clear;

④ The field joint quality inspection is simple and fast, which is consistent with the ordinary straight thread joint;

⑤ The reinforcement connection working face does not need its machines and equipment, but only needs to connect the wrench.

Several connection methods, you can choose the connection position according to the structural needs!

三、雙螺套連接與焊接工藝對比：

Next, taking 32mm as an example, the cost of double screw sleeve connection and welding is compared in more detail.

It has passed the type inspection of hrb400e class I joint by the national construction engineering quality supervision and inspection center

Hrb500e class I connector

It has passed the “American Standard” type inspection of the national construction engineering quality supervision and inspection center

It has passed the fatigue performance test of 2 million times by the national construction steel quality inspection center

It has obtained the approval for the use of the National Nuclear demonstration project “Rongcheng nuclear power”

It has passed the “CABR” product certification of Chinese Academy of Building Sciences

[case] bottleneck technology of connection between reinforced concrete beam and steel reinforced concrete column

For the connection between reinforcement and section steel column, the quality control problems caused by connection will be encountered in many large public construction projects, as follows;

Figure 1: ? One end of the reinforcement is processed with straight thread and effectively connected with the section steel column through the welding sleeve. It has the advantages of convenient and fast, simple operation, stable and controllable quality, high efficiency and low cost.

Figure 2: because the reinforcement at the other end cannot rotate, the connecting plate welding operation is adopted. The features can solve the problem that the reinforcement can be connected with the section steel column when it cannot rotate, but there are many unqualified items of welding quality, difficult quality control, low connection efficiency, low qualified rate of flaw detection, unstable quality, large weight of connecting plate, high cost and difficult detection.

Figure 3: both ends are connected by welding sleeves. Because the reinforcement cannot rotate again, it is difficult to connect, so welding connection is adopted. The welding length loses raw materials, the welding quality is also uncontrollable, the welding operation time is long, the qualification rate is low, the efficiency is low, the flaw detection can not guarantee 100% qualification, and the detection cost is high, and the construction progress is difficult to guarantee.

Figure 4: a new type of fabricated mechanical connection process. The section steel and steel column are connected by welding sleeve. For the non rotating parts in the middle, the new mechanical connection method is adopted to connect the two non rotating reinforcement in situ. The connecting reinforcement will not produce displacement during connection, and only a connecting wrench is required for operation. The connection speed is one minute to complete the operation (the reinforcement is also a straight thread thread head), the on-site components are cut to reach the first-class joint strength, the batch connection quality is very stable, the operation time is greatly reduced, and the operability of quality acceptance is strong. There is no open fire operation on site, which greatly saves welder operation and cost.

Figure 5: the vertical reinforcement is connected with the section steel beam. Similarly, the upper and lower reinforcement can complete the in-situ connection through the rotating sleeve when they cannot rotate.

Figure 6 perfect combination of straight thread and new sleeve, each application has its own advantages, reducing cost and increasing efficiency.

From the above data and cases, it is not difficult to see that the advantages of choosing double screw sleeve connection scheme in rigid column connection are clear at a glance!

Field processing of connecting joints

(1) Straight thread rebar thread head processing. The processing of straight thread reinforcement thread head shall comply with the following provisions.

① The ends of reinforcement shall be cut flat by band saw, grinding wheel saw or special reinforcement cutter with arc blade.
② The upsetting head shall be free of transverse cracks perpendicular to the reinforcement axis.
③ The length of steel wire head shall meet the product design requirements, and the limit deviation shall be 0 ~ 2.0P (P is the pitch of thread, the same below).
④ The steel wire head shall meet the accuracy requirements of grade 6F, and shall be inspected with a special straight thread gauge. The through gauge shall be able to rotate smoothly and reach the required screw in length, and the screw in of the non-stop gauge shall not exceed 3p. The self inspection quantity of each specification shall not be less than 10%, and the inspection qualification rate shall not be less than 95%.

(2) Processing of taper thread reinforcement thread head. The processing of thread head of taper thread reinforcement shall comply with the following provisions.

① There shall be no local bending at the end of the reinforcement that affects the thread processing.
② The length of steel wire head shall meet the product design requirements. The tightened steel wire heads shall not contact each other. The limit deviation of wire head processing length shall be -0.5p ~ -1.5p.
③ The taper and pitch of steel wire head shall be inspected with special cone thread gauge; The self inspection quantity of each specification of wire head shall not be less than 10%, and the inspection qualification rate shall not be less than 95%.

Field installation of connecting joints

(1) Installation of straight threaded joints. The installation of straight threaded joints shall comply with the following specifications.

① When installing the joint, the pipe wrench can be used to tighten it. The steel wire heads shall be pressed against each other at the center of the sleeve. The exposed thread on one side of the standard type, positive and negative wire type and reducing type joints after installation shall not exceed 2p; For other straight threaded joints that cannot be butted, locking nuts, jacking bosses and other measures shall be added for fastening.
② After the joint is installed, the tightening torque shall be checked with a torque wrench, and the minimum tightening torque value shall meet the requirements.
③ The accuracy level of torque wrench for verification can be grade 10.

Minimum tightening torque value of straight threaded joint during installation

(2) Installation of taper threaded joints. The installation of taper threaded joints shall comply with the following requirements:

① When installing the joint, strictly ensure that the specification of the reinforcement is consistent with that of the connector.

② The joint shall be tightened with a torque wrench during installation, and the tightening torque value shall meet the requirements of table 5-2.

③ The torque wrench for verification and the torque wrench for installation shall be used separately. The torque wrench for verification shall be checked once a year, and the accuracy level shall not be lower than level 5.

Tightening torque value of taper threaded joint during installation

(3) Installation of sleeve extrusion joint. The installation of sleeve extrusion joint shall comply with the following provisions.

① The end of the reinforcement shall be free of local bending, serious corrosion and attachments.

② The end of the reinforcement shall be provided with an obvious mark of the insertion depth of the reinforcement after the extrusion sleeve. The distance between the end of the reinforcement and the midpoint of the sleeve length shall not exceed 10mm.

③ Extrusion shall start from the center of the sleeve and squeeze to both ends successively. The fluctuation range of indentation diameter or sleeve length after extrusion shall be inspected with special gauge; The outer diameter of the sleeve at the indentation shall be 0.80 ~ 0.90 times of the outer diameter of the original sleeve, and the length of the sleeve after extrusion shall be 1.10 ~ 1.15 times of the length of the original sleeve.

④ The extruded sleeve shall be free of visible cracks.

鋼筋剝肋直徑的偏差

The diameter dimension after rib stripping of reinforcement is an intermediate process value (Table 5-1). Generally, this dimension is the diameter dimension of reinforcement base circle. If this dimension is not well controlled and the processing deviation is large, it will also directly affect the subsequent wire head rolling dimension.

(1) If the rib stripping diameter is too large (the transverse and longitudinal ribs on the reinforcement surface are not completely removed), burr may appear on the thread of the thread head after rolling, and the tooth shape finish will be reduced. At the same time, because the wire rolling diameter has been set, the excessive rib stripping diameter of the reinforcement will increase the pressing amount of the wire rolling wheel and reduce the service life of the roller;

(2) If the diameter of rib stripping is too small, the tooth shape of silk head will not be full, and the possibility of bald teeth at the tip of silk head will increase.

Deviation of rib stripping length of reinforcement

(1) Rib stripping length deviation

The rib stripping length of the reinforcement shall be consistent with the length of the rolling wire. Too long rib stripping will damage the base metal of the reinforcement. Since the rib stripping at this part has not been strengthened by rolling, it is likely to be damaged in this section under the tensile state of the joint, affecting the strength of the joint;

(2) Rib stripping length is short

If the rib stripping is too short, it will affect the rolling quality of each part of the screw head. Does the overall taper of the reinforcement screw head increase, and then affect the thread fit between the screw head and the sleeve.

Deviation of nominal size of steel wire head

(1) Rib stripping length

The rib stripping length of the reinforcement shall be consistent with the length of the rolling wire. Too long rib stripping will damage the base metal of the reinforcement. Because the rib stripping at this part is not strengthened by rolling, it is likely to be damaged in this section and affect the strength of the joint under the tensile state of the joint;

(2) Rib stripping length is too short

If the rib stripping is too short, it will affect the wire rolling quality at the root of the wire head, increase the overall taper of the reinforcement wire head, and then affect the thread fit between the wire head and the sleeve.

Deviation of nominal size of steel wire head

After processing, the reinforcement wire shall be tested with a special thread ring gauge. The ring gauge shall be open and closed at both ends. The qualified screw head can be rotated smoothly, such as the through end of the ring gauge, and 0 ~ 3 BUCKLES shall be exposed by hand;

(1) If the screw head is too large, it will not rotate smoothly into the sleeve;

(2) If the screw head is too small, the fit gap between the screw head and the sleeve increases, so as to reduce the shear capacity of the screw teeth.

Deviation of effective thread length of screw head

The effective length of the screw head is consistent with that of the sleeve thread, with a tolerance of 0 ~ + 1p.

(1) The length of the screw head is too long, which will lead to more exposed threads after the screw head is tightened, and the joint is easy to break at the exposed thread when being pulled;

(2) If the length of the screw head is too short, the matching length with the sleeve cannot be reached, and the joint strength will be affected.

The appearance of thread head profile is unqualified

The steel wire head shall meet the accuracy requirements of grade 6F. Within the effective length of the thread, the cumulative number of bare teeth or broken threads shall be more than 2 turns, with low tooth profile finish and rough tooth profile.

Insufficient joint connection

The screw head cannot be screwed into the sleeve completely, resulting in insufficient thread matching length and affecting the connection strength.

High efficiency steel rigid column mechanical connection, welding sleeve + double screw sleeve + welding sleeve reduces a large number of welding operations, saves the expensive cost of connecting plate, and the on-site operation is convenient and fast.

Bottleneck technology of connection between reinforced concrete beam and steel reinforced concrete column

Construction pain points of tunnel reinforcement works:

Low construction efficiency of reinforcement works;
Large number of on-site construction personnel and high labor intensity;
The mechanical connection of the last joint of the “ring reinforcement” in the tunnel is difficult and the quality is difficult to guarantee;
The degree of mechanization of reinforcement engineering operation is low.

Industrialized construction scheme of tunnel reinforcement works:

• Adopting the prefabrication, installation and connection technology of lined double-layer reinforcement mesh can greatly improve the mechanization, prefabrication and industrial construction of reinforcement engineering.
• The industrialized construction method can improve the on-site construction efficiency by more than 70%, reduce the on-site construction personnel by about 70%, and improve the comprehensive benefits of construction.
• The production of double-layer reinforcement mesh lining can be made by special forming machinery, with low cost, high efficiency and excellent quality.

• Mesh prefabrication can be carried out in prefabrication plant or tunnel.
• The mesh lifting installation device can be transformed by tunnel construction trolley.

New mechanical connection joints can also be used for the connection of longitudinal main reinforcement of lining reinforcement. In order to facilitate the connection between the inner arc reinforcement and the main reinforcement, it is recommended to stagger the positions of the inner and outer arc reinforcement and the main reinforcement in the design.

Solution

Before connection

When the reinforcement is connected, the general reinforcement sleeve cannot be connected because the reinforcement gap at both ends of the reinforcement parts is too large

After connection

WL double screw sleeve reinforcement connection technology can completely solve the problem of reinforcement connection of parts in building industrial construction.

WL double screw sleeve reinforcement connection technology

There are several main types of reinforcement mechanical connection in China:

At present, in China’s Construction Engineering, since the 1980s, the mechanical connection technology of reinforcement has been widely popularized and applied. Among the commonly used types of reinforcement joints, such as sleeve extrusion joint, conical thread joint, upsetting straight thread joint, direct rolling straight thread joint and rib stripping rolling straight thread joint, the commonly used standard joints are of reliable quality due to their simple processing technology and equipment, low connection cost and convenient connection, It accounts for more than 90% of the market share of reinforcement mechanical connection joints.

?Main types of rib stripping rolling joint:

The main joint types of rib stripping and rolling straight thread joints are: standard type, reducing type, flared type, welding type, positive and negative screw thread type, extended thread type, etc. different types of joints can be selected for different application scenarios. Among them, the extended threaded joint is widely used.

Connection characteristics and main application scenarios of extended threaded joint:

Connection process of extended threaded joint: first connect the straight thread sleeve to the reinforcement on the long thread side. After the connected reinforcement is in the butt joint position, rotate the sleeve to the reinforcement to be connected on the short thread side

Connection features of extended threaded joint: the connection of reinforcement can be completed without rotating the reinforcement, or slightly rotating and tightening the reinforcement after connection. In the connection of reinforcement parts of reinforcement cage, because the connecting reinforcement cannot rotate, the middle of the connecting reinforcement cannot be tightened.

Main application scenarios of lengthened threaded joint: foundation reinforcement cage, ground connecting wall, reinforcement connection with “knee reinforcement”, etc.

?Main problems of extended threaded joint connection:

(1) Low joint strength (broken on exposed thread):

Because the rib stripping and rolling process is adopted, the cross-sectional area of reinforcement is reduced due to rib stripping and cutting. Even if the cold rolling and rolling process is adopted to slightly improve the surface strength of reinforcement, it is not enough to compensate for the reduction of reinforcement cross-section and strength caused by rib stripping.

The damage of this joint is basically at the exposed thread part of the joint section. Due to low strength, class II joints specified in standard jgj107 are mostly used in the design of such joints, and the joints are not arranged in the same section. Even so, when there is not much super reinforcement, the joint strength is still difficult to meet the qualified requirements.

(2) Low joint strength (sleeve internal thread pulled off):

Due to the equipment and technology of some manufacturers, it is easy to form excessive taper and pitch error in the processing of long thread of reinforcement (the error exceeds 0.2-0.3mm within the length range of sleeve). In order to facilitate the smooth screw in and installation of long thread end sleeve, the on-site operators can only reduce the diameter of reinforcement thread head, and often thread at the end of long thread reinforcement (connection part) The fit clearance with the connecting sleeve is out of tolerance, which weakens the strength of the end thread of the long threaded reinforcement and causes the joint to pull off in the sleeve.

(3) Difficult connection and joint quality assurance:

This situation is often seen in the overall connection of “reinforcement parts” such as reinforcement cage and ground connecting wall.

In order to ensure the accurate position of the upper and lower reinforcement threads during joint connection, the prefabrication process of “long line method” and “short line method” is mostly adopted during reinforcement cage prefabrication, that is, the ground mountain is paved for tens of meters or hundreds of meters, the main reinforcement is connected first, then the main reinforcement is welded and fixed with the stirrup, and then the butt mark is made to open each joint. When the reinforcement cage is connected, it is hoisted and connected according to the prefabrication position.

In this case, the main reason for the difficulty of connection is not the radial position deviation and deformation of stirrups, but the small deviation in the axial position of upper and lower connecting reinforcement during prefabrication, hoisting and installation of reinforcement cage, and the thread trace lines of upper and lower reinforcement are not collinear.

鋼筋籠（鋼筋部品）中上下鋼筋的

螺紋軌跡線 的圖示說明：

The thread pitch of domestic 25-40mm reinforcement straight thread joints is generally 3.0mm. When the processing accuracy of reinforcement and connecting sleeve thread is guaranteed, and the over tolerance of upper and lower thread trajectory is greater than 0.3mm, the connection is very difficult. Even if the joint is connected with super large torque (which may exceed more than 10 times the specified torque value), the connection thread has actually been damaged, Resulting in low strength of threaded connection.

At present, many employees in the industry are not very clear about the causes of this potential quality hazard.

According to 7.0.2 of the current industry standard technical specification for mechanical connection of reinforcement jgj107-2016 Article 1 clearly requires that “all types and types of joints shall be subject to process inspection, and the inspection items include unidirectional tensile ultimate tensile strength and residual deformation”.

If the joint process inspection is carried out in strict accordance with the standard requirements, the residual deformation in the process inspection cannot meet the qualified requirements when the “extended thread” joint cannot be tightened in the middle of the connecting reinforcement!

Because the ordinary straight thread reinforcement joint is not suitable for the “part” reinforcement connection under the background of building industrialization, the double screw sleeve reinforcement joint came into being in 2017.

Composition of double screw sleeve reinforcement joint: the double screw sleeve reinforcement joint is composed of connecting reinforcement 1, inner short sleeve, inner long sleeve, outer screw sleeve, lock nut and connecting reinforcement 2.

The biggest feature of double screw sleeve reinforcement joint connecting reinforcement: by simply adjusting the relative position of the connector during connection, the track lines of the upper and lower threads of the butt reinforcement can be adjusted from non collinear to collinear!

The double screw sleeve reinforcement joint solves the problem that the trajectory lines of the upper and lower connecting reinforcement threads are collinear in the straight thread connection of reinforcement. Therefore, the connection is smooth and efficient!

It takes 2-5 hours for the double screw socket joint to connect the ordinary straight thread joint to the connecting surface of a reinforcement cage to about 20 minutes, and the connection quality is 100% qualified!

Main engineering cases of double screw sleeve reinforcement joints: since 2017, the products have been introduced to the market, with specifications ranging from 22-50mm and a cumulative consumption of more than 700000 pieces.

The application types of double screw socket joints are: PC precast bridge bent cap, roof beam horizontal reinforcement connection

Combined connection technology of concrete beam reinforcement and rigid steel column

The application of these projects fully proves that the double screw socket joint can completely solve the problem of reinforcement connection of parts in building industrial construction. The main problems of rib stripping rolling straight thread lengthened threaded reinforcement joint in the reinforcement connection of ordinary reinforcement and parts are as follows:、

(1) Low joint strength;

(2) For the reinforcement connection of parts, it is difficult to connect and the connection quality is unqualified due to the non collinearity of the connecting thread track line;

(3) It is applied to the reinforcement connection of parts, and the residual deformation in the process inspection does not meet the standard requirements;

Therefore, the straight thread joint is not suitable for the reinforcement connection of “parts”, and the double screw sleeve reinforcement joint will be one of the alternative products!

For the connection between reinforcement and section steel column, the quality control problems caused by connection will be encountered in many large public construction projects, as follows;

Figure 1: One end of the reinforcement is processed with straight thread and effectively connected with the section steel column through the welding sleeve. It has the advantages of convenient and fast, simple operation, stable and controllable quality, high efficiency and low cost.

Figure 2: because the reinforcement at the other end cannot rotate, the connecting plate welding operation is adopted. The features can solve the problem that the reinforcement can be connected with the section steel column when it cannot rotate, but there are many unqualified items of welding quality, difficult quality control, low connection efficiency, low qualified rate of flaw detection, unstable quality, large weight of connecting plate, high cost and difficult detection.

Figure 3: both ends are connected by welding sleeves. Because the reinforcement cannot rotate again, it is difficult to connect, so welding connection is adopted. The welding length loses raw materials, the welding quality is also uncontrollable, the welding operation time is long, the qualification rate is low, the efficiency is low, the flaw detection can not guarantee 100% qualification, and the detection cost is high, and the construction progress is difficult to guarantee.

Figure 4: a new type of fabricated mechanical connection process. The section steel and steel column are connected by welding sleeve. For the non rotating parts in the middle, the new mechanical connection method is adopted to connect the two non rotating reinforcement in situ. The connecting reinforcement will not produce displacement during connection, and only a connecting wrench is required for operation. The connection speed is one minute to complete the operation (the reinforcement is also a straight thread thread head), the on-site components are cut to reach the first-class joint strength, the batch connection quality is very stable, the operation time is greatly reduced, and the operability of quality acceptance is strong. There is no open fire operation on site, which greatly saves welder operation and cost.

Figure 5: the vertical reinforcement is connected with the section steel beam. Similarly, the upper and lower reinforcement can complete the in-situ connection through the rotating sleeve when they cannot rotate.

Figure 6 perfect combination of straight thread and new sleeve, each application has its own advantages, reducing cost and increasing efficiency.

The diameter is 2.2M, the reinforcement specification is 50, the total length of pile foundation is 72.5m, and the total weight is nearly 70t. The reinforcement cage is hoisted

Site acceptance and stirrup binding after connection

All connections completed

Hoisting of section II of 24m 50 specification HRB500 reinforcement cage

The lower connection point at the 24m interface completes the docking.

48m overall connection completed

End to be connected at the upper part of 48m reinforcement cage
End to be connected at the lower part of 72m reinforcement cage

The overall butt joint of three 72.5m reinforcement cages is completed.