Performance
Rebar performance is about more than meeting a stated strength requirement. To achieve robust reinforcement detailing, the complete assembly — including the rebar, couplers and anchorages — must provide sufficient capacity and ductility. Below, we explain why capacity matters, how weak links can affect structural performance and what is required to secure high rebar performance.
High Rebar Performance: Why Capacity Matters
Many standards and certification schemes specify minimum tensile strength requirements for rebar products, such as rebar couplers and mechanical anchorages. Product data sheets and specifications often reference a specific strength level. However, rebar performance is not defined by strength alone. Capacity and ductility must also be considered.
- To select the right performance level, it is important to understand the relationship between rebar strength and ductility
- It is necessary to assess the performance of the complete assembly: rebar + rebar product (coupler or anchorage)
- A helpful way to illustrate this relationship is a stress–strain curve
Rebar performance: avoid the weak link
Almost every rebar heat exceeds the characteristic stress and strain requirements defined in rebar standards. The “actual” strength and strain capacity of the rebar is therefore often higher than the “specified” values.
When rebar products are used together with real rebar, the performance of the complete assembly is governed by the interaction between the two: rebar + rebar product (coupler, anchorage, splice, etc.). If an anchorage or splice has lower capacity than the rebar, it becomes the weak link and may fail before the rebar reaches its potential—sometimes even before the specified strength and strain levels are achieved. This limits the ductility of the reinforcement, and the failure mode may shift from ductile behaviour to sudden rupture.
Reduced ductility in the reinforcement reduces the robustness of the entire structure under extraordinary load situations such as overload, fire, earthquakes, accidents or attack.
Conclusion
A rebar product with a capacity level equal to the specified rebar tensile strength is not sufficient to guarantee the specified ductility of the reinforcement.
100% continuity – no weak link – high rebar performance
Projects of great importance to society, and structures with high hazard potential, must be designed and built to be robust. Examples include infrastructure projects, buildings with many occupants, and structures in the energy sector.
Ductility is one of the key ways to achieve robustness. To achieve this, rebar products must maintain high ductility in the complete assembly (rebar + rebar product) and provide a capacity level above the specified rebar tensile strength.
The ultimate rebar performance level is to develop the real, “actual” strength and ductility of the rebar—100% continuity, no weak link, high performance. This should be required for structures with high demands for robustness.
The development of actual ductility (or at least a large portion of it) can be specified:
- For headed bars: by referring to ISO 15698, category B3
- For mechanical couplers: by requiring development of Agt,spec outside the splice, or by specifying a higher strength level than the specified value (e.g. 130% fy,spec)