Background – Rigid connection must be done with splices

In the past, post-installed rebar connections according to EOTA TR 023 can only be executed with straight rebar, which are permitted in accordance with EN 1992-1-1. This means that the moment-resisting connections need to be executed with splices.

Execution of a post-installed, moment-resisting concrete rebar connection by splicing, as required by EAD 330087.

 
This “limitation” is based on the fact that the tension forces from the rebar transferred to the concrete by bond should be balanced either by local (e.g. splices) or global compression struts to avoid brittle concrete failure. A tension loaded rebar may cause brittle concrete cone failure by using the tensile capacity of the surrounding concrete if not balanced by compression struts. Since this ~failure mode is prevented by means of global or local compressive struts, it is not considered in the national concrete code design rules

Example: Load bearing behavior of the end support of a simple supported beam avoiding the occurrence of concrete cone failure due to compression struts

 
Challenges for execution of splice in jobsite

This requirement to construct moment-resisting rebar connections using a splice can have a crucial impact on the construction workflow, economics and safety:
 

• A splice (planned overlap of a cast-in rebar with a post-installed rebar) in new construction needs to be planned and be in place. This is not always the case.
• As concrete-pouring is done bit by bit, rebar can be exposed, which can lead to different issues: Influencing logistics, damaged rebar and also safety hazards.
• The load-bearing capacity of a splice consisting of two rebar with different properties is dependent of the capacity of the lesser rebar, i.e. the one that is cast-in. This is why the potential of the used mortar can usually not be fully leveraged. This can lead to overlap lengths that can be uneconomical.
• In renovation, a rebar connection with splice needs to be executed by partial demolition to expose the existing rebar, weld the new rebar onto it and then close the connection with concrete again, all of which is very time and thus cost-intensive.

Schematic depiction of executing a rebar connection with partial demolition

The new design concept EOTA TR 069: Design rigid connection without the use of splice

The new Technical Report TR 069, published in 2019 “Design method for anchorages of post-installed reinforcing bars (rebar) with improved bond-splitting behavior as compared to EN 1992-1-1” allows for the design of post-installed, moment-resisting reinforced concrete connections under static loading conditions without using a splice configuration. The new TR 069 combines reinforced concrete design principles (EN1992-1-1) with anchoring to concrete principles (EN1992-4).
 
The design is based on the hierarchy strength design principle, i.e., the lowest resistance of the individual failure modes is decisive. Yielding of the steel, concrete cone failure and bond-splitting failure of the post-installed rebar connection must be verified. In addition, the requirements of EN1992-1-1 in terms of minimum anchorage length must be fulfilled.
 
If you would like to start designing as per TR069, you can use the Hilti PROFIS Engineering rebar module.
 

Applications of rebar connections covered by EAD 33087 No. 1-3 (EN1992-1-1) and EAD 334202 No. 4-8 (TR 069)