Lifting a Precast beam 12 m length

[XinLok]

Base on ACI code, If I did a precast one beam 60 cm x 60 cm x 1200 cm.

the compressive strength used during design is design be 50 mpa. if I use hardener during precast, and I got 30 mpa compressive strength after 24 hours.
Can I lift the beam up if the strength of concrete reach 30 mpa after 24 hours or 48 hours?, or should reach full strength which is 50 mpa

 

[HTURKAK]

Can I lift the beam up if the strength of concrete reach 30 mpa after 24 hours

Yes.. but lift with overhangs at both sides say 2.5 m. Check tension stresses at span and lifting points. A preliminary calculation for allowable tension stress ( using 4 *SQRT* fc ) is 1.8 mPa . Check lateral stability also.

 

[XinLok]

Thanks a lot for your reply and for the attached document, interesting.
For the preliminary calculation for allowable tension stress ( using 4 *SQRT* fc ) is 1.8 mPa, this 1.8 should be compared to what to check if okay or not?

Also for Check lateral stability, what check need to do??

 

[HTURKAK]

For the preliminary calculation for allowable tension stress ( using 4 *SQRT* fc ) is 1.8 mPa, this 1.8 should be compared to what to check if okay or not?

You will find the developing tension stresses and check with allowable tension stress .Assume uncracked section.
The stresses during stripping , lifting and transport should be checked .

 

[Lomarandil]

You will find the developing tension stresses and check with allowable tension stress .Assume uncracked section.
The stresses during stripping , lifting and transport should be checked .

To calculate those tension stresses during transport and lifting, refer to the excellent articles by Mast (which are now incorporated into some PCI materials, but I find Mast's original articles do a better job explaining the reasoning). There are more potential causes of tensile stresses than Mc/I would suggest.