Building an edifice that will last long is the aim of any construction engineer. Clients can spend as much as they have to be able to have a completed project that can withstand the test of time. For almost a century now, the building of concrete structures has focused on the use of steel couplers to reinforce and transfer tension and shear force.
This is mostly due to its ability to withstand pressure while been durable and also for its ability to provide load path continuity independent of the condition or existence of surrounding concrete. It also has the advantage of putting to extinction time-consuming factors especially those that will arise as a result of compliance with current construction codes like ACI and other codes.
A steel coupler is used to couple or joins two pieces of steel together in the building. When long lengths of steel bars are needed in building a column or when the need of joining additional reinforcement to existing bars arises, the general practice is to ‘lap’ (tying of bars together next to each other). This practice although old, is not advisable because it doesn’t withstand the weight load properly and hazards may arise if not properly fixed. The best alternative to this is the use of steel coupler that provides a direct connection between ends of steel bars.
Steel coupler consists of a sleeve that is threaded into which the bars to be joined can be screwed into. The coupler is built as screw connection reinforcement on a framework of working joints in concrete. With the combination of reinforced concrete components and maximum force transmission, static and dynamic loading is achieved. Steel coupler system offers a method of connecting steels even as large as 12 mm, in a simple fast and cheap way.
Lap splicing which is a mechanical means of joining steel that requires the overlapping of two parallel bars, can easily fail during impact with load condition. To avoid this, steel coupler is provided in concrete. This will among other things increase the structural performance, achieve continuity of load path and even reduce the amount of steel reinforcement that will be used in construction.
Apart from the above, steel coupler offers the following advantages;
• It offers reliable protection of socket rods with some possessing thread protection cap
• It also offers maximum force transmission in the working joint
• It enhances construction speed by replacing the slow and tedious conventional method of planting starter bars
• It reduces steel frame congestion problem.
• It makes the control of concrete crack propagation possible
• It leads to the reduction of labor and therefore the overall cost of the structure.
• There is also the possibility of joining bars of any diameter and length just as mentioned above.
• It is economical for large steel bar diameters in column construction.
• Last but not least is the aesthetics dimension steel coupler adds to a column.
Types of steel couplers
There are various types of couplers that can be used in the construction of columns, with some designed to carry both compression and tension, while others are designed to either work with compression or tension. The most common types of couplers for construction are as follows:
1. Parallel threads coupler
Coupler with parallel thread is another type of coupler that what we used in constructing a column. Here, threads are forged or rolled on the bar so that the diameter of the part threaded is equal or above but not less than the main bar. The load capacity is reduced by this and the threaded ends are screwed into the coupler.
The reason we used the coupler is to avoid the congestions inside the column when it closed with the shutter or form. The biggest size of the aggregate in the concrete should pass through in between the two vertical bars. When the vertical bar diameter gets bigger the higher the chance the congestions may observe inside the column.
2. Shear bolts coupler
The shear bolt coupler consists of a cylindrical steel coupler with a line of ‘lock shear’ bolt along its length. It does not require the bars to be threaded because of the lock shear. With the two bars to be joined placed in a coupler, the bolts are tightened making the bars to lap against hardened steel griping or locking strip until a moment of force (torque) is reached.
3. Wedge locking sleeves
As earlier stated, there are couplers that can be used for either compression or tension only. Wedge locking sleeves are used only in connecting bars in compression. It is used as follows; with the bars to be joined and held in the concentric bearing by the lateral clamping action of a sleeve and wedge. The wedge compresses the sleeves laterally clamping the bars together when driving inside. It is worthy to note that the bar faces are accurately cut and aligned before finally assembling them.
Photo by researchgate.net
4. Metal sleeves swaged onto bars
This is achieved by slipping a seamless malleable steel sleeve over the adjoining ends of the two reinforcing bars. The sleeve is subsequently deformed or swaged onto the ends of the bar with the aid of hydraulic, which compresses the sleeve over the bar, and therefore gripping the ribs. Photo by m.made-in-china.com
Columns or pillars are rigid upright structural member that is designed mainly to support axial compressive loads emanating from beams and slabs and subsequently transfer it to ground through the footing, with the footing finally transferring it to the soil. Just as the bone in the human body gives strength while also transferring weight to all parts of the body, so also a column does in a building. Therefore, having a strong column is a prerequisite for the whole load transfer mechanism in a structure and without it, the structure doesn’t exist.
Columns need rods to be firmly rooted, and most of these rods can be as long as 12 meters. In many cases, there is a need for them to be joined together. The most effective and reliable way of doing this is with the use of couplers. Couplers provide an easy and fast way of joining rods together while also maintaining the aesthetics of the structure. Couplers are cheap and can be installed quickly and easily on site without the need for specially trained personnel or a specialized, expensive machine. Couplers due to its compactness ensure stability and can be used in any situation even in a confined one where space is lacking.
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One can therefore conclusively state that couplers are very essential for a strong column and can never be relegated as long as good column construction is involved. It has the added advantage of been reliable and durable in all condition. This is part of the beauty that it adds to any construction.
Sir, Please include the RMC QA/QC blog, like role and responsibilities, what are the test we know for working there as a QA/QC Engineer and also details of Concrete Mix design in Gulf countries.