Expert: Babak Esmailzadeh Hakimi - 1/16/2012

Question
QUESTION: Sir,

My house is in foundation stage. There are 12 RCC colums out of which 3 columns are misaligned (the centres are not exactly in straight line). There is 2'' - 3'' misalignment. To connect the columns with plinth beam, workers bent the steal rods of RCC columns. Please suggest how to proceed.

ANSWER: Dear   ramamurthy

Intentional and unintentional misalignments of columns are very common in buildings due to architectural considerations. No serious problem will arise from bending reinforcement to run along beams. But I cant understand why bending of columns reinforcement has occurred.  Can you give me some details , pictures drawings , to help me to get your situation?

If bending of tension rods happens in not suitable situation , it may cause to a dowel action , splashing concrete covers in ultimate situations, but I guess this is not your case. Please give me more details to discuss more efficient.

Regards
Babak E Hakimi

---------- FOLLOW-UP ----------

QUESTION: Hi,
Thanks. i am not able to upload an image. The bending happenedd because of improper marking before starting foundation. But misalignment of colums is not given in structural design. By mistake the columns were mialigned. To run the plinth beam along columns,workers bent the steel rods of RCC columns. Finally we can observe the misalignment of columns(2'' to 3''). Does it leads serious problem. Kindly suggest.

Regards
Ramamurthy

ANSWER: Dear ramamurthy

Plinth Beams are not load bearing members in normal situations. They provide a basis to transfer forces between footings, in the case of differential settlements, or seismic actions. Then no problem to have limited misalignments in footings. Your case is not critical.

Regards
Babak Esmailzadeh Hakimi



---------- FOLLOW-UP ----------

QUESTION: Is pit sand suitable for concrete ?

For RCC columns, plinth beam, slab and columnfootings, we are using 1:2.5:3.5   concrete
(i.e ratio  1(cement):2.5(sand):3.5(20mm sized stones )

The volume mix for the above concrete preparation is as follows
4 Pans of cement : 10 pans of pit sand : 14 pans of 20mm sized stones   

Is the above ratio fine for concrete?
sand type - pit sand.

pit sand contains small amount of clay, is it ok?

Answer
Dear Ramamurthy

Concrete admixture is very serious even for moderate range of strength. Pit sand cant replace sand in concrete and sand cant replace gravel. I suggest this formula to be tested ( this is not very accurate  but a guide)   :

600-800 kg gravel with maximum size of 1/2-3/4 inch
1100- 1300 kg sand  
300 kg cement type 1 or 2
250-300 lit water

In the case you would have 28 days strength less than what you expected you can add some more cement to your admixture.

Please give me information about your tests. Looking foreward to hear from you.

Best Regards
Babak Esmailzadeh Hakimi