Is it possible to use hilti RE500V4 with 16 dia bar to get full tensile capacity of the bar in pull out? Embedment length will be equal to lap length required for the bar (~1000 mm for 16 dia (Grade 500)).
Hi Sandeep,
Thanks for your question.
Post-installed rebar (PIR) is not yet covered in New Zealand local standards; however, it can be used in the country as an Alternative Solution. Using Eurocode 2 as a design method, a qualification for the post-installed rebar system needs to be carried out to demonstrate that the solution behaves similarly to the equivalent cast-in alternative, and regardless o the epoxied rebar may have an increased bond strength when compared to the cast-in reinforcing bar, the bond strengths used in the calculations for a PIR is limited by the bond strength of the concrete.
The formula to calculate the basic development/anchorage length(Lb,rqd) for the full development of a PIR considers the rebar diameter (Փ), its yield strength (σ), and the bond strength (fbd) of the mortar that is being used (limited by the concrete’s bond strength), as per below:
Lb,rqd = (Փ/4) x (σ/fbd)
The bond strength is dependent on the concrete grade, on the installation method (e.g., hammer driller or diamond coring), and on the type of loading (i.e., static, seismic, etc.). Considering a HD16 rebar fixed into a 30 MPa concrete using RE500 V4 and a hammer driller for a seismic application, the bond strength to be used will be 3 MPa, as extracted below from the approval document for HILTI HIT-RE 500 V4.
Lb,rqd = (Փ/4) x (σ/fbd) = (16mm / 4) x (500 MPa / 3 MPa) = 666.7 mm
For the design anchorage length (Lbd), also known as refined development length in the NZ standards, additional “α” factors need to be considered:
Lbd = Lb,req x α1α2α3α4α5α6*
* α6 is only applicable for splices.
For a PIR joint-type connection, α1α3α4α5 = 1, and α2 is between 0.7 and 1.0, depending on the confinement provided by the concrete cover and clear spacing between the post-installed rebars. As no information has been given for this case, it is conservative to assume α2=1.0, and therefore the design anchorage length for the full development of the HD16 rebar in question would be approximately 667mm following EN1992-1.
If the connection will be used as a splice and overlap between existing rebar and the PIR rebar is needed, an additional α6 value is incorporated in the formula, increasing the required embedment by 50%, as α6 = 1.5. Hence, the new embedment required for yielding of the same rebar will be 666.7 x 1.5 = 1,000mm
Please note that the calculations above follow the rebar theory, and some conditions need to be met to use this design theory. To understand if it can be used in your design, we advise checking other articles that have been uploaded to ASK Hilti.
Hilti’s HIT-RE 500 V4 and HIT-HY 200-R V3 have been tested and approved to be used in static, fire and seismic conditions following the European Assessment Documents (EAD) of the European Organisation for Technical Assessment (EOTA), and if the right methodology is followed, the rebars are expected to achieve full development with the embedment calculated using the Eurocode methodology.
If you have any other questions, please do not hesitate to contact us on NZEngineers@hilti.com
Kind Regards,
Samuel Aguiar
Engineering Marketing Manager