Question – A simply supported rectangular concrete beam of 7 m span carries a characteristic dead load (Gk), including self-weight of the beam, and imposed load (Qk) of 7 kNm and 5 kNm respectively.
The beam dimensions are breadth b = 225 mm and effective depth d = 400 mm.
Assume fcu = 30 N/mm2 and fy = 460 N/mm2.
Calculate the area of reinforcement required.
Answer: Given b = 225 mm, d = 400 mm, l = 7.00 m,
Gk = 7.00 kNm, Qk = 5.00 kNm,
fcu = 30 N/mm2, fy = 460 N/mm2.
Ultimate load (w) = 1.4Gk + 1.6 Qk
= (1.4 x 7.00) + (1.6 x 5.00) kN/m
= 17.80 kN/m
Cross-sectional area of 01 no. 16 mm diameter bar = 201 mm2
Provide 4 nos. of 16 mm diameter bars resulting 804 mm2.
Note: However, there are other limitations before considering the size and spacing of bars. Those factors will be discussed in another example.