U and inverted U lapped stirrups in a beam 2

[VoyageofDiscovery]

I typically do not use stirrups in this fashion, however I am checking a design of a beam, adjacent to a re-entrant corner with a typical crack. I would note that as the crack crosses the lap area, the development length of these stirrup U and inverted U bars either side of the crack is obviously less than the lap length, should this be of concern? Lap lengths are as per Code in my situation.

 

[hokie66]

Yes, it is of concern, as stirrups typically depend on anchorage by way of hooks around longitudinal bars. Development is not the same as anchorage.

 

[VoyageofDiscovery]

Thanks hokie66, this was my thought as well, however upon further reading the Code, such a configuration of paired U stirrups is permitted with 1.3 ld for lap length.

VoD

 

[TXStructural]

When using overlapping U-stirrups, you need to be sure that the crack intersects a sufficiently-developed stirrup, hence the 1.3 ld requirement. Only one "U" needs to be developed (the top or the bottom) at the crack location. However, the danger is that loss of cover will render this configuration useless, so you should never permit them in seismic systems or where cyclic loading, the presence of deleterious materials, or the likelihood of mechanical damage could compromise the integrity of cover.