Stirrups:
As per IS456, the development and anchorage length deemed to have provided in the stirrups when
The stirrup bar is bent through an angle of at least 90° around a bar of at least its own diameter and is continued beyond the curve for a length of at least eight times the bar diameter.
Or
When the bar is bent through an angle of 135° and is continued beyond the curve for a length of at least six times the bar diameter.
When the bar is bent through an angle of 180° and is continued beyond the curve for a length of at least four times the bar diameter.
Bent Up Bars:
The development length of such bars is according to the development length of bars in tension allowing for hooks and bends if provided and measured as following:
In tension zone – from the end of sloping or inclined portion of bars.
In compression zone – from the mid depth of beam.
Hi,
Please let me know the difference between standard hooks and bend where following the curve, the bar continues for a length of 4 x dia. with a min. of 50 mm. for practical purposes. Why for stirrups, the bar continues 8 x dia for 90°, 6 x dia for 135° hook and 4 x dia for 180° hook after the curve? Should we follow same for column links or should we revert back to standard hook specification?
Also, for stirrups, what are the reasons for adopting the use of 90° bend stirrup or 135° hook stirrups? In IS code, there is a clause where the 90° bend can open up and cause spalling of concrete if there is but a thin coat of concrete onto it. Also it seems that 90° bend is much easier to make than a 135° bend.
I will also greatly appreciate if you can tell me the difference between this and the BS8666-2005 standard bend and hooks especially where the author use quite a confusing and ambiguous language where they speak of angles greater than or smaller than 150° and also do not explain how to apply same to a 135° hook.
Thanks in advance for your help.