- What is the mathematical interpretation of the assumption “ plane section normal to the axis before bending remains plane after bending” and where you have used it in reinforced concrete structural analysis?
2. In working stress design method, we use permissible stress in bending of M15 concrete as 5 instead of 15, there by having a factor of safety = 15/5 =3. Similarly for steel Fe 415, the factor of safety = 415/230=1.80 (in bending).
Then what is the factor of safety of a reinforced concrete beam made of concrete M15 and steel Fe 415? Are you trying to calculate it by means of weighted average method? Then , think again.
3. Is minimum reinforcement in column 0.8% of the actual (gross) area provided? If not, then what else?
4. Have you designed the column section having eccentric loading?
If not, then this is for your kind information that there does not exist any axially loaded column in real structures.
If yes, then you must adhere to the provision of clause 46.3 of IS: 456, which makes it mandatory that design of eccentric compression by working stress method, based on cracked section analysis should be further checked for their strength under ultimate load conditions to ensure the desired margin of safety. This condition effectively makes working stress method redundant, as it suffices to design in accordance with limit state method.
Then, have you learnt design of short and long column under compression with uniaxial bending/biaxial bending by Limit state method?
5. The ultimate moment of resistance of a reinforced concrete beam section having width=300 mm, effective depth=550 mm, Ast=1963 sq.mm (Fe 415) and Fck=20 MPa is 287 KNm.
Then, how much ultimate moment of resistance is contributed by concrete and how much by steel out of 287 KNm.
- Sanjay, 88C20
E-mail - sanjaybws@rediffmail.com
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