Unclosed Stirrup Cage in 1960s Era Reinforced Concrete Beam

[rsbmusicguy]

Hey all,

I am dealing with a concrete beam on a building that has some deflection (0.5" > 0.469" per L / 480) at the quarter span of the simply supported beam.

I did my calculations and the maximum deflection calculated of approximately 0.25" at the midspan matched what I measured in the field. Additionally, I confirmed that the member was overstressed in moment and shear so I provided repairs to make the section pass.

Note the stirrup cage is not closed and similar sections are at other locations in the building with no issues. My suspicion is that since the stirrup cage is not close that the rebars have split causing the maximum deflection of 0.5" at the quarter span.

Anybody have recommendations on remediation techniques for a stirrup cage that has slipped? I have used couplers in the past but do not want to start chipping away the concrete to find the stirrups which will compromise the section. The only alternative I am aware of is FRP wrap.

Thanks!

RSB

 

[KootK]

1) I'm surprised to hear that your quarter point deflection is greater than your mid-span deflection. Are you able to explain that?

2) Are you actually seeing significant shear cracking in the beam? If not, I doubt that the stirrups are contributing to your deflection issues meaninfully.

3) Open stirrups were, and in most jurisdictions still are, fine for resisting static shear so long as proper anchorage detailing is provided (max stirrup size #5 and hooked around a longitudinal bar etc).

 

[dik]

Settlement of one support?

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[JLNJ]

Maybe it’s not deflection and it was just built out of straight.

 

[rsbmusicguy]

KootK - in reference to your reply:

1) Per dik and JLNJ, I have considered the fact that the support has settled but I am not seeing significant cracking at other areas to support that therefore I have been thinking JLNJ may be correct.