Lightweight Concrete for High Strength - Expanded Shale & Clay

3. Concrete compressive strength at transfer, f ci ’
4. Square root of concrete compressive strength at transfer, √f ci ’
5. Concrete modulus of elasticity at 28 days, E c
6. Concrete modulus of elasticity at transfer, E ci
7. Prestressing strand diameter
8. Prestressing strand area
9. Stress in prestressing strand prior to transfer, f si
10. Effective prestress, f se
Based on FHWA results and their analysis of other research results, the restriction on the use of
0.6-inch strand was lifted. The FHWA proposed Equations A.13 and A.14 for “best-fit” and to
provide a 95% confidence interval, respectively.
l
t
f
pt
d
b
= 4 − 21
( A.13)
'
f
c
where
l
t
f
pt
db
= 4 − 5
( A.14)
'
f
d b = diameter of prestressing strand (in.)
f c ’ = concrete compressive strength (psi)
f pt = stress in prestressing strand just prior to strand release (psi)
c
A.9 Flexural Behavior
A review indicates that only limited research has been conducted on the flexural behavior
of composite HSLC girders. Prior to the onset of flexural cracking and the point at which
flexural cracking occurs, the behavior of the HSLC is important. Beyond the cracking state, the
behavior of the NWC deck is the governing concern. To the authors’ knowledge, no background
information was available related to the findings and conclusions identified in this research for
flexural behavior. The general flexural behavior of normal weight prestressed composite girders
made with normal strength concrete is well understood and discussed in standard text books.
A-15