Need a book? Engineering books recommendations...

Return to index: [Subject] [Thread] [Date] [Author]

Re: Test, Longitudinal cracks in double TEE, and Cracks in Concrete Column

[Subject Prev][Subject Next][Thread Prev][Thread Next]
        Listers,
                Curiously, I have not been kicked off the list either at work or at home during the last few months. However, I cannot sign up for digest mode at a gmail account – the same gmail account can easily get the normal mode, though. And the server thinks I am signed up at the gmail account even though it does not send me the digest.
 
                There are many reasons for a crack at the joint of a double tee stem and flange. The foremost reason is the dramatic change in section there, so if there are any stresses, the stress risers will be there.
                If there is any lateral force or restraint at the bottom of the stem near the end it may crack the flange on the inside of the stem. There are enough of these that we could probably all think of different ones.
                A 2 thick flange will almost certainly crack on the outside, if the driver uses a wrench extender to tighten the chains before hauling. Many tees these days have sleeves through the stems near the flange for pipes and conduit. They are a better place for chains.
                Many tees are now cast with straight strand, not draped. This substantially increases the tensile force in the flange at the ends at stripping. This will cause a horizontal crack in the stem at the bottom of the flange, and can cause a transverse crack across the flange at the lifting inserts. Your description sounds like you have not seen this.
                A warping crack can occur if one of the four stems deviates by more than 1” or more from the plane of the other three stems (three points defining a plane). This starts as flange crack at the inside of a stem. It usually extends to the other end, and runs diagonally to the inside of the other stem, but may just show at one end.
 
                I did not follow the description of the cracked columns well enough to understand it. While there is some remnant creep and shrinkage after most precast is set, most of those volume changes have occurred before the structure is built. If the walls are restraining the columns from temperature movement to the extent of causing cracking, I would expect a horizontal crack at the top of the wall. This would require that the CIP wall was poured up against the column after the precast concrete had been completed, and wall top corner concrete crushing might be evident, too. Both CIP pours after precast concrete setting and lack of a caulked gap are unusual. What I would really expect is column rotation at the base, with no sign of distress. I have seen and heard of precast concrete structures creating their own expansion joints, but the distress has always been in the horizontal members or their connections to vertical members, not the columns.
                Rich, you can pick up my email address from the post and send me photos if you like, but I cannot receive more than a few in any one email.
 
        Regards,
        Jim Getaz
        Precast Concrete Engineer