CVEN 4301
Advanced Concrete Structures
Prestressed Concrete Lecture 3
Professor Stephen Foster
Flexural Behaviour Post Cracking
Losses of Prestress
Cracking Moment
Flexural cracking occurs when the tensile stress at the
extreme tensile fibre is just large
CVEN4301 Advanced Reinforced Concrete Design
Introduction to Time Effects
Introduction
sh
e
P
c
When concrete sets in time, it shrinks (as it loses water). The strain at a
time t due to shrinkage is sh(t)
When load is applied to a concrete element and
CVEN4301AdvancedConcreteStructures
PrestressedConcrete Lecture2
FlexuralBehaviourofUncrackedMembers
InitialStrains
Consider a section in a prestressed member that is
subjected to its self-weight + prestress at time = 0
strain reference points
initial elas
Week 4 ProblemFor a prestressed concrete beam with a T cross-section shown in Figure below, calculate
Assume that prestress area is 1380mm2, the section has 2N32 reinforcement with
650
. effective prestress level in 980MPa, = 32
.
=
Solution:
Calculate ne
Question1
A prestressed concrete beam with a T cross-section shown in figure 1 has a span of 12 metres.
It is post-tensioned by a cable that has a cross-sectional area of 1000 mm2 and an eccentricity
e that varies parabolically from the ends to a maximum
Week 3 ProblemFor a prestressed concrete beam with a T cross-section shown in Figure below, calculate .
Assume:
1. There is no tensile reinforcement in the section
2. There are 2N32 bars in the section assume d=600
Other data:
Ag 3.6 105
mm2 ; I g 1.56 10
Tutorial Problem
For the simply supported beam shown Below which spans 12m with dead load of 9 kN/m(SW) and live
load of 25 kN/m:
1. Determine the presstress needed to ensure that the section remains uncracked under the dead load
plus 70% of the live load
Solved Example
Loss of Prestress
Question: The post-tensioned beam shown in Figure-1 is stressed by two tendons. Each
tendon contains eighteen 7 wire compacted strand and the diameter of each strand is 18 mm.
The initial prestress induced in the strands i
RECOMMENDED PRACTICE
Reinforcement Detailing Handbook
Errata:
The existing section 13.2.3 (a) and Figure 13.4 on page 13:4 should be replaced with:
(a) At all simple supports, a primary calculation is
required in accordance with Clause 8.1.10.4(a)
of AS36