![]() For this equation, ACI recognizes that, in virtually all cases, the ( c b+ K tr)/ d b value is at least 1.5. As such, the results of this calculation offer a less conservative result for development length, but with increased complexity of the calculation itself. While this equation has considerable similarity to the equations of ACI 318 section 12.2.2, it also includes a distinct difference: the ( c b+K tr)/ d b term offers the potential for explicitly including the benefits of other factors that contribute to development length, specifically bar cover/spacing ( c b) and transverse reinforcement index ( K tr). While the provisions of ACI 318 section 12.2.3 are secondary to the aforementioned section 12.2.2, fundamental research led to the development of the following empirical relationship (ACI 318, Equation 12-1): Is there another alternative?ĪCI 318 allows for a rational and simple solution. He would be happy with option D initially, but upon further consideration may wonder how much money is being wasted on the project due to your conservative design. Do you:Ī) instruct him to cancel his concrete pour until the problem can be fixed?ī) allow him to continue as planned, but add more bars (excess reinforcement) at the lap splice that will effectively lap with each of the bars in question?Ĭ) tell him that he can proceed if he splices the bars with mechanical couplers?ĭ) allow him to proceed without changes, since your design was conservative?Ĭertainly any of these options might be pursued, but the first three are not likely to be favored by the contractor and may be injurious to the good working relationship that you have been striving to foster with him for many years. Final inspection of rebar placement has occurred and the inspector has found, due to some unknown error, that the lap splices on a particular size bar in the bottom a mat foundation are short by 6 inches. Perhaps you have been a party to the following scenario, or something akin to it: You get a call from a contractor planning to place a large volume of concrete the next day. However, the simplicity introduced within this discussion does come with a price – a conservative design. This might even be the basis of standard lap splice length schedules used by your office. With this as a basis, the development of standard schedules, details and embedment length versus bar diameter relationships become fairly trivial. If we further assume that the material properties (f y and f ‘ c) are constant, the only differentiators become the fraction coefficient (which is basically the size factor) and whether more than 12 inches of fresh concrete is cast below the bar (Ψ t). From this, we can surmise that basic development lengths ( l d) follow the form: The minimum lap length for compression bars must be 12inches.For most of us, the provisions for development length and lap splices of reinforcing steel are taken from ACI 318-11, Table 12.2.2. The lap length for compression lap splice is calculated as per ACI 12.16.1 as Where, ld= development length, which is calculated as per ACI 12.2 ( Without taking into consideration the modification factor).The minimum lap length is 12 inches 3. As per ACI 318, the tension lap splices are classified into two classes Class A and Class B ( Table R12.5.2, ACI 318) for which the lap length are as follows: Hence, the lap splice, in this case, shows varied interaction depending on the concrete strength, grade of steel reinforcement, location, bar size ,and spacing. This hence results in a continuous line of reinforcement. In a tension lap, the force is transferred from the reinforcement bars to the concrete by the bond which in turn force back to the reinforcement. The lap splice length in tension reinforcement is calculated as per ACI 12.15. ![]() ![]() Also Read: Methods of Splicing Reinforcement Bars 2. ![]()
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