![]() In case such bars have to be lapped then they should be welded. Lap splicing of a reinforcement bar more than 36mm in diameter should be avoided. When two different diameters of bars have to be lapped, the lap length should be calculated based on the diameter of the smaller bar. When columns are subjected to bending, lap length may be also increased to the value in bending tension if the bar is found to be in tension. Lap length is compression should be more than 24 or Ld in compression. Hooks are also to be provided at the end of the tension bars. Tension splices should be enclosed in spirals made from 6mm bars with the pitch not more than 100mm. Lap length in direct tension should be 30 times the diameter of the bar or 2 Ld whichever is greater. in flexural tension should not be less than 30 times the diameter of the bar of the full development length Ld as calculated, whichever is greater. The total lap length of bars including bends, hooks, etc. The bars to be lapped should be provided either vertically one above the other or horizontally one beside the other. The center to center distances of laps should not be less than 1.3 times the required lap length of the bars. Laps splice in reinforcement should always be staggered. The important points to be noted while providing lap rebar splices in reinforcement bars: So in cases such as the one pictured above, an increase to the splice length may be necessary to satisfy this requirement.įor reasons I can't quite fathom, though, the Brazilian code explicitly states that splices between different diameters must adopt the larger diameter, so that's what I'm stuck with.The lap rebar splice is the most common and economic rebar splice used in the construction project. Compared to lap rebar splicing , the welded rebar splices and mechanical rebar splices require more labor and skill. However, both codes do allow distances larger than this limit so long as the splice length is increased accordingly. In this case, there's the question of which $\phi$ to use, and I honestly don't know. The Brazilian code NBR-6118 and EC2 both put that limit at $4\phi$ or 50 mm. The codes usually define a maximum distance between lapping rebars. The arrows roughly represent the furthest distance that tension needs to travel from each bar. In the figure below, for instance, assume this is a splice section, with the tension from the large red bars being transferred to the small blue ones. ![]() However, if you are splicing multiple rebars in the same position, going from a few large diameter bars to many smaller ones, an incremement to the splice length may be required. So there's no reason to design your splice to withstand a force larger than the yield strength of the smaller bar. If the tensile force is larger (say, equal to the yield strength of the larger rebar), then the smaller rebar will rupture immediately after the splice. Therefore, if you are splicing two rebars of different diameters, the maximum tensile force that can be transferred via the splice is equal to the yield strength of the smaller rebar. However, once the splice is over, all the tension from the first rebar has been transferred to the other one, which must also be capable of withstanding that same tension. Since concrete is very weak against tension, large lap lengths are required such that the stress at any point in the concrete is not excessive. What is a splice? It is when tension force in a rebar is transferred to the concrete via adhesion and then to another rebar. The use of the smaller diameter is theoretically correct. ![]()
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