QUESTION 3 (40 marks) A single pad footing supporting the axial load from a colu

Question

QUESTION 3 (40 marks) A single pad footing supporting the axial load from a column has the following data: Column load: Axial Gk 700 KN, 370 kN; Service Moment, M-40 kN-m Footing height h 650 mm, nominal cover C 35 mm, concrete grade fak 30 N/mm2 steel gradefyk-500 N/mm, concrete weight-25 kN/m, bar diameter #7-12 mm, soil bearing pressure pb-150 kN/m, column size-300 mm x 300 mm. a) Describe the failure mode of over-reinforced concrete beam and explain why it is not desired in design. [CLO1-PLO2:C2] (8 marks) b) Design the square pad footing based on the above data. [CLO3-PLO3:C5] (27 marks) c) Sketch the footing with the reinforcement details. [CLO4-PLO3:C3] (5 marks)

Explanation / Answer

Sol a). An over reinforced beam is a beam, which have so much steel that the concrete fails in compression before the steel reaches yield.

This failure mode will be sudden, and without warning.

The beam will be fine up until the point it reaches its ultimate limit, and then the concrete in the  compressive zone will fail in compression without showing any cracks. This will not provide any opportunity for the users to repair the defects or save their lives as the failure would be sudden. Also this type of beam is not economical. Therefore, this type of beam is not desired.

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