The reinforcement lap length is one of the important topics. When the size of a single bar is reduced, two bars are lapped side by side to maintain the desired design. Mechanical couplers can be used as a replacement.
Lapping is the process of overlaying two bars together up to their design length. Stock lengths of steel bars are normally limited to 12m to make it easier to deliver the steel bars to the construction site. Imagine, for example, that a 100ft high column is needed, but the steel bars are not available. The bars are, therefore, cut every second story.
The tension forces are then transmitted from the first bar to the second bar at the cut-off position. The second bar is then provided close to the first and overlapped. The “lap length” is the amount of overlap between two bars.
Lapping is usually achieved when there is little bending stress. If both bars have the same width, then the lap length will be 50d. This is equal to 50 times the diameter of the bar.
The length of the lap in tension
The anchorage value and lap length of hooks are as follows:
- If the flexural stress is greater than 30d, then Ld is used.
- Direct pressure is 2Ld or 30, whichever is greater.
The length of the straight bar must not be less than 15d or 20cm.
The Lap Length of Compression
The lap length must be the same as that of the compression length, but it cannot be less than 24d.
To Order Different Diameter Bars
The lap length will be measured using the bar with the smaller diameter if the bars are to be spliced.
Lap Splices
Lap splices are not recommended for bars larger than 36 mm in diameter. In these situations, welding should be considered. If welding is not possible in certain conditions, then lapping of bars larger than 36 mm is allowed. Lapping is permitted, but the bars must be reinforced with 6 mm spirals in addition to lapping.
Concrete of Nominal Mixture:
The lap length (MS bar, mild steel bar), together with the anchorage value, should be 58d. The lap length is = 58d + 2*9d =40d. The hook allowance is up to 25mm in 9d and k=2.
Along with the anchorage value, the voltage lapping length should be 58d. The lap length = 58d + 2*9d =40d unless the anchorage factor has been eliminated. (Where 9d is a maximum capacity of 25 mm, and k=2)
The lap length of M20 concrete
- Columns – 45d
- Beams 60d
- Slabs 60d
If you want to lap a column bar with a 20 mm diameter, then a minimum lap length of 45*20= 900 mm will be required.
Concrete spalling appears as circular or oval depressions on surfaces or joints. In cold climates, spalling can be caused by de-icing agents or seasonal freeze-thaw cycles.
Why does the splintering occur, and what can be done to prevent it?
When the rebar has been exposed, it can rust from water infiltration and humidity. The concrete joints can also be imperfectly made. The concrete extends due to changes in the weather. This causes spalling and further degradation. A strong water sealant can be applied on the finished surface to prevent water from entering the concrete.
Concrete spalls can be controlled if the concrete is properly managed and pouring concrete is done using the correct methods. As an example, rebar can be embedded in concrete by arranging the right distances and exact positions of joints. As per the suggestions of structural engineers or ACI, special attention should be paid to the corners and edges of uncovered concrete in order to maintain sufficient concrete coverage. Concrete mix is also a vital factor in spalling since excessive water content causes spalling.
Here are some tips to repair cracked concrete
The severity of the problem, the type and location of the concrete structure, and other factors will determine the best way to treat spalling.
- Concrete that has suffered spalling and is less than 1/3 the thickness will usually only need a surface fix. If the damage is greater than 1/3 depth, it’s necessary to install steel bars and perform a full-depth restoration.
- Due to exposure, rotted rebar should first be cleaned. After the rebar has been cleaned (normally using a wire brush) and the corrosion is removed, it should be coated with a rust inhibitor. This will prevent future erosion.