Beirut Arab University-BAU Dept. of Civil Engineering
P r estr stre essed C oncret oncrete e Ass A ssii gnme gnment I I , D ue date: 30/ 30/10/ 10/2013 2013
Problem I:
A prestressed concrete sleeper produced by pre-tensioning method has a rectangular cross-section of 300mm × 250 mm (b × h). It is prestressed with 9 numbers of straight 7mm diameter wires at 0.8 times the ultimate strength of 1570 2
N/mm . Estimate the percentage loss of stress due to elastic shortening of concrete a- If the prestressing steel is not considered for the centroid of the section. b- If the prestressing steel is considered for the centroid of the section. Consider n = 6. Problem II:
A pretensioned simply supported T beam has a span of 20.5 m and the geometry shown in the following figure. The ten 12.7 mm diameter strands has an eccentricity at midspan of ec = 58.83cm. Assume that prior to transfer, the jacking stress on the tendon was 1395 Mpa. Compute the magnitude of loss in prestress due to the effect of elastic shortening of the concrete. Concrete material f′c =40Mpa f′ci =30Mpa Properties of section A = 3548 cm2 I = 3,415,803 cm4 ct = 32.77 cm c b = 68.83 cm St = 104,254 cm3 S b = 49,620 cm3 Wd = 8.516 KN/m (own weight)
1
Dr. Zaher Abou Saleh – Dept. of Civil Engineering, Engineering, Beirut Beirut Arab University-Debbieh University-Debbieh Campus Campus P r estresse stressed d Con C oncr cre ete Structure Structur es, Fall 2013
