Dr. PAULS ENGINEERING COLLEGEDEPARTMENT OF CIVIL ENGINEERING
Unit Test ISubject Name: Prefabricated Structures Date :
16.02.2015Subject Code :ST 7008 Duration: 2 Hours Year / Sem / Dept
:I / II/ Structural Engineering Marks : 50
Part A (10 X 2 = 20)Answer All Questions1. What is Pre stressed
concrete structure?2. State the reasons for using high strength
concrete and high tensile steel in PSC.3. What are the losses
encountered in pre tensioning and post tensioning methods.4. Write
down the factors influencing deflections.5. Differentiate Pre
tensioning and post tensioning methods.6. Define partial pre
stressing.7. Differentiate bonded and un bonded tendon.8. Define
load balancing concept.9. Define short term deflection and long
term deflection.10. Define the term tendon.
Part B (2 X 15 = 30)Answer Any Two Questions
11. A pre stressed concrete beam 400x600 mm in a section has a
span of 6m and subjected to udl of 16kN/m including the self weight
of the beam. The pre stressing tendons are located at 100mm from
the base. Provide an effective pre stressing force of 960kN.Compute
the extreme fiber stresses at midspan using Stress concept,
Strength concept and Load balancing concept. (15)
12. A pre stressed concrete beam 200mm wide x 300 mm deep is pre
stressed with 7 wires of 8mm diameter located at a constant
eccentricity of 100mm and carrying an initial stress of
1200N/mm2.The span of the beam is 12m.Calculate the %loss of stress
in wires if the beam is (a) The beam is pre-tensioned (b) The beam
is post tensioned.Take Es = 210kN/mm2 & Ec= 35kN/mm2.Relaxation
of steel stress = 5% of initial stress, shrinkage of concrete =
300x 10-6 for pre tensioning and 200x 10-6 for post tensioning,
creep co-efficient = 1.6, slip at anchorage = 1mm, Frictional
co-efficient for wave effect is 0.0015per m. (15)
13. The simply supported concrete beam of span 8m and a
rectangular cross section 125mm wide and 250mm deep is pre stressed
by a single cable in which the total tensile force is 220kN. The
centre line of the cable is parallel to the axis of the beam and
75mm above the soffit over the middle third of the span and is
curved upward in a parabola over the outer-thirds of the span to a
distance of 175mm above the soffit at supports. If the modulus of
elasticity of concrete is 35kN/mm2 and the density of concrete is
24kN/m3,calculate (a) the upward deflection at mid-span due to pre
stress only(b) the deflection when the beam is supporting its own
weight and (c) the magnitude of concentrated load Q placed at the
third point of the span, which would result in limiting short-term
deflection of span /500. (15)
