Casting position effects on bond performance of reinforcement bars

In design codes, the top-bar effect is considered in most cases for calculation of the bond trength of embedded  reinforcement [159]-[161]. This is typically performed by defining regions of good or poor bond conditions. 
For instance, EN 1992-1-1:2004 [159] considers good bond conditions those of a reinforcement having an inclination between 45°~90° with respect to the horizontal surface or bars inclined less than 45° which are up to 250 mm above the formwork or at least 300 mm below the free-surface during casting (Fig. 31a).
All other locations are considered as having poor bond conditions and the bond strength is reduced by 30%, thus causing an increase of the anchorage length of 43% with respect to the bottom bars. 
A similar recommendation is also proposed in fib MC 2010 [160]. The topbar effect is also considered in the provisions of ACI 318 [161] which defines as poor bond condition those of horizontal reinforcing bars or laps having more than 305 mm (12 inches) of fresh concrete beneath them (Fig. 31b). In this case, ACI 318-19 [161] proposes an increase of the development length of 30%.

 

Fig. 31 Definition of locations with good and poor bond conditions as function of the member’s depth according to: (a) EN 1992-1-1:2004 [159] and fib MC 2010 [160]; and (b) ACI 314-19 [161] (dimensions in [mm]).

 

 

 

 

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Contribution to the updating of detailing rules for concrete structures

 

3 Casting position effects on bond performance of reinforcement bars