PORTLAND CEMENT CONCRETE - Materials for Civil and Construction Engineers - page 301

7.16 Discuss the creep response of concrete structures. Provide examples
of the effect of creep on concrete structures.
7.17. On one graph, draw a sketch showing the typical relationship be-
tween the stress and strain of concrete specimens with high and low
water-cementitious materials ratios. Label all axes and curves. Com-
ment on the effect of increasing the water-cementitious materials
ratio on the stress-strain response.
7.18 Using Figure 7.29,
a. Determine the ultimate stress at each water-cementitious materials
ratio.
b. Determine the secant modulus at 40% of the ultimate stress at
each water-cementitious materials ratio.
c. Plot the relationship between the secant moduli and the ultimate
stresses.
d. Plot the relationship between the moduli and the ultimate stresses
on the same graph of part (c), using the relation of the ACI Building
Code (Equation 7.3).
e. Compare the two relations and comment on any discrepancies.
7.19 A normal-weight concrete has an average compressive strength of
4500 psi. What is the estimated modulus of elasticity?
7.20 Discuss the significance of the compressive strength test on concrete.
Draw a graph to show the relationship between compressive
strength and water-cementitious materials ratio for different curing
times (Label all axes and curves).
7.21 What is the standard size of PCC specimens to be tested for com-
pressive strength? If a smaller size is used, which size is expected to
provide higher compressive strengths? Why? Which size provides
strengths close to that of an actual concrete structure?
7.22 A short plain concrete column with dimensions of
is to be constructed. If the compressive
strength of the concrete is 5000 psi, what is the maximum load that
can be applied to this column using a factor of safety of 1.2?
7.23 What is the purpose of performing the flexure test on concrete?
How are the results of this test related to the compressive strength
test results?
7.24 What are the advantages of using a third-point loading flexure
test over a center-point loading flexure test? Draw a shear force
diagram and a bending moment diagram for each case to support
your answer.
7.25 Consider a standard flexural strength specimen of length L , width a ,
and depth a . Assume third point loading where the load at failure
from the test machine is P , which is distributed evenly (1/2 to each)
over the two loading points. Derive the equation for calculating the
modulus of rupture of the beam in terms of P , L , and a .

12 in. * 12 in. * 36 in.