Question

Design of a prestressed beam in the service limit state

Loads:

Service load p = 40 kN/m

Self weight from adjacent structures g1 = 30 kN/m

Self weight of beam g2 = 7 kN/m

Dimensions:
b = 300 mm, h = 900 mm, d = 800 mm,

L = 8000 mm Ap = 12 tendons a 100 mm2

Material data:
Tendons:

fp0,1k = 1550 N/mm2

fpk = 1700 N/mm2

fpk = 1700 N/mm2

p,max = min{0,8fpk ; 0,9fp0,1k}= 1360 N/mm2

Concrete:

B45, Exposure class XC1, XC2 etc, T = 20 C, RH = 50 %

It is assumed that the prestressing and the self-weight of the beam are applied three days after casting, while the self-weight of adjacent structures and service load are applied after 28 days. 50% of the service load is assumed to be long term load and the relaxation class may be set to 2 (i.e. low relaxation).

Tasks:

a) Check that the concrete stresses at prestressing in the lower edge of the beam are within the limits given by EC2. Assume rapid cement (s=0.2)

Answer 1