Civil Engineering Reference
In-Depth Information
(2)Testresults
Repeat step 3) and step 4) and stop testing until the values of
σ
s
obtained in two repeats
are very close. The present value of
σ
s
is regarded as practical stress of rebar.
(3) Note
a. The reduced amount of the tested rebar diameter after ground should not exceed one
third of the original diameter.
b. The grinding of rebar should be finished in two to four repeats and for every one the
reduced amount of rebar section and strain increment at ground area should be recorded.
c. The ground surface should be smooth and the rebar section area after ground should
be measured with a square caliper. Record the numerical reading of strain gauge until the
temperature of ground surface is identical to that of environment.
d. After the test, weld a rebar of
φ
20 with length of 200 mm to the damaged area of
ground rebar, then make up the cover with concrete of fine aggregate.
In addition, for a compressive member, with the practical stress
σ
s
of rebar in it ob-
tained by the method mentioned above, the practical compressive stress
σ
c
of concrete on
corresponding section could be acquired by
σ
c
=
E
c
σ
s
(2
.
2)
E
s
where
E
c
and
E
s
are the elasticity moduli of concrete and rebar, respectively.
2.2.3
Material for Masonry Structures
Inspection of material strength of masonry structures focuses on mortar, brick or building
block of other materials, and integral masonry strength. In comparison with that for concrete
material, the technique for material strength inspection of masonry structures is still under
development. In recent years, however, considerable research work has been done on it and
some standards for inspection are now under the process of approval. And the
Technical
Standard for Site Testing of Strength of Masonry Structures
will be issued shortly as a
national standard, in which many methods such as the in situ axial compressing method
and flat jack are specified for site calculation of compressive strength of mortar, service stress,
elastic modulus, compressive and shear strength of masonry. The apparatus of model SQD-1
for testing of mortar strength by point load has been developed by the China Academy of
Building Research for supporting the standard. In general the technique for inspection of
material strength of masonry structures is approaching maturation day by day. The current
inspection methods in common use are briefly introduced as follows.
1. Inspection of integral masonry strength
Integral masonry strength is the main mechanical index of masonry structure. The in-
spection method for it is as follows.
(1) Site inspection method
Similar to the drilled core method for concrete, the test sample is taken during inspection
according to stipulated method directly from field walls-often under sills, and delivered to
a laboratory for compressive testing. Since it is dicult to cut samples from walls, and
the strength of samples with mortar of low strength is prone to be influenced under even
slightest movement, the site testing method is usually replaced by the following methods.
(2) Indirect inspection method
Masonry structure, as a complex body, is composed of mortar and bricks or building blocks
of other materials. Therefore its strength may be directly determined on the basis of tested
strengths of mortar and brick or building blocks of other materials related to requirements
of valid codes.
