Brief discussion on lap length of bars
Development length and lap length are two vital parts of reinforcement. But there are some basic differences among development length and lap length.
While going to arrange the steel in RC structure, if the necessary length of a bar is unavailable to produce a design length then lapping is essential. Lapping occurs because of overlapping of two bars alongside to attain desired design length.
As for instance, if it is required to construct a 100 feet tall column, but 100 ft long bar will not be available in practical and caging can’t be done in this situation. So, it is necessary to cut the bars frequently to transmit the tension forces from one bar to the other at the position of suspension of bar. So, it is essential to arrange the second bar adjacent to the first bar that is suspended and overlapping should be performed. The amount of overlapping among two bars is called lap length.
For the RCC structure, if the length of reinforcement bars has to be expanded, splicing is conducted to attach two reinforcement bars for transmitting the forces to the joined bar.
LAP LENGTH FORMULA:
LAP LENGTH IN TENSION:
The lap length along with anchorage value of hooks should have been as follow :-
1. For flexural tension – Ld or 30d either is larger.
2. For direct tension – 2Ld or 30d either is larger.
The straight length of lapping should not be under 15d or 20 cm.
LAP LENGTH IN COMPRESSION: The lap length in compression should have similarity with the development length in compression calculated but not below 24d.
FOR DIFFERENT DIAMETER BARS: In case of bars with dissimilar diameter should have been spliced, the lap length is computed based on the smaller diameter bar.
LAP SPLICES: Lap splices should not be employed for the bars with greater dia than 36 mm. In this situation, welding is needed. But, in case, welding is not possible then lapping is allowed for the bars greater than 36 mm dia. supplementary spirals should have been around the lapped bars.