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Reinforced concrete has been profoundly applied to the construction of widely varied structures due to its unique properties of strength, durability, ductility and economical construction cost. A structural element of reinforced concrete is just like any other structural member in terms of its design, which means that the forces applied to it must be resisted and the resulting stresses and deformations must be within acceptable limits for serviceability and safety considerations. The elaboration on the requirement of steel reinforcement anchorage length is discussed in the following.
Anchorage length can be defined as the length of free end of the reinforcing bar that must be embedded or fixed in concrete. The anchoring distance should be sufficient to ensure that the bar is properly embedded and that full bond between the steel and the concrete is established. This process is critical in order to develop the structural full capacity.
The steel reinforcement anchorage length is determined based on the development length and splice length. Development length is the embedment length of the bar that is required to develop the full strength of the specified bars. Its value is related to the characteristic bond strength of the specification and the type of bar utilized. Splice length is the length of the bar laps and welding joints. The required splice length depends on the strength of the bars, the type of splicing system, and the characteristic bond strength of the specification.
In reinforced concrete construction, the steel reinforcement anchorage length depends on a certain combination of factors such as: bar type, bar size, bar diameter, minimum clear cover of concrete, the nature of reinforcement (whether it provides confinement to the concrete or not, etc.), the type of connection, type of concrete, type of soil and its characteristics, strength of the materials, and so forth.
Types of anchorage:
1. Hooks: commonly used for horizontal bars and lintel bars, in which the hook takes the form of one or half-enclosed circles.
2. Bent bars: commonly used for vertical bars and X-bars, in which the bar has to be bent and secured in the form of a hook.
3. U-shaped stakes: used for reinforcing bars at the ends of walls, pillars and beams, where a U-shaped opening provides the perfect friction surface for the bars to hold onto.
4. Mechanical connections: often used as an alternative to hook or bent bars, especially in situations where one type of hook or bent bar cannot satisfy the desired working capacity. Mechanical connections include the use of bolts and clamps.
Steel reinforcement anchorage length is determined based on the type of the bar, the method of anchorage and the load applied to the reinforced concrete structure. The methods used by the designer to determine the steel reinforcement anchorage length should depend on the design standard, strength characteristic and materials used besides the type of steel bar.
The steel reinforcement anchorage length depends mainly on the design standard and the strength characteristics of the steel reinforcement and concrete. If the designer is aware of these factors and uses safe anchorage practices, the structure will be delivered without any major issues. Additionally, it is important to account for the combined effect of stress and strain on the steel reinforcement. The most frequently used codes of practice suggest that the steel reinforcement anchorage length should be greater than the sum of the development length and the splice length.
In conclusion, the ratio of the steel reinforcement anchorage length should be greater than the sum of the development length and the splice length to ensure proper bond between the steel bar and the concrete. The designer should consider the highest design load, the material’s strength and the appearance of the structure when determining the anchorage length. This allows for reinforced concrete structures to be designed with respect to the performance expectations and steel reinforcement demands.
