Civil Engineering Reference
In-Depth Information
COMMENTARY
Since 1936, the building code has required that the minimum reinforcement
ratio be 0.01 of the gross area of concrete section. This minimum reinforce-
ment area was intended to prevent “passive yielding” of the steel, which
occurs when load is transferred gradually from concrete to the reinforcement
as the concrete creeps under sustained axial load [25]. Even though it appears
to have become an outdated restriction for modern concrete and steel [26]
and notwithstanding the consideration that GFRP does not yield, this require-
ment has been retained also for the case of GFRP reinforcement for analogy.
5.5.2 Equivalency under compression between
GFRP and concrete
Available test results indicate that the equivalency under compression
between GFRP and concrete can be assumed.
COMMENTARY
With reference to the behavior of FRP bars in compression, it is known that
their testing is complicated by the anisotropic and nonhomogeneous nature
of the FRP material, which can lead to inaccurate measurements [27]. For
the case of GFRP bars in particular, reductions in the compressive strength
and elastic modulus by up to 45% and 20% with respect to the values in ten-
sion, respectively, have been reported [28]. Similar results were reported for
GFRP bars by Deitz, Hark, and Gesund [29], who indicated that the com-
pressive to tensile strength and modular ratios were approximately 50% and
100%, respectively. Accordingly, GFRP mechanical characteristics exceed
those of concrete in compression and, therefore, the equivalency between
the two materials when performing analysis and design is justifiable [6].
5.5.3 Limit on maximum tensile strain in GFRP
The tensile design strain of the longitudinal GFRP bars is limited to 0.01.
This provision is made more general by defining the ultimate design strain,
ε
fd
and corresponding design strength,
f
fd
,
as
ε=
Min
(,0.010)
ε
(5.2)
fd
fu
f
=
Min f
( 0.010
E
)
(5.3)
fd
fu
f
Search WWH ::
Custom Search