Civil Engineering Reference
In-Depth Information
dibutyl phthalate, dioctyl phthalate, tributyl phosphate, etc. Flexibilizers (active plasti-
cizers) participate in curing, and generally are polyamide, butadieneacrylonitrile rubber,
polysulfide rubber, etc. In addition, in order to thin the consistency of epoxy resin, a
diluent, such as acetone, benzene, toluene or xylene is needed.
Currently, all structural adhesive sold on the market has two components. Component A
is an epoxy resin with added plasticizer, a kind of modifier and filler. Component B is made
from a curing agent and other auxiliary component. According to a certain proportion of
components A and B, structural adhesive will be prepared.
(2) Physical and mechanical properties testing of structural adhesive
Whether steel plate can effectively work with original beams and fill the retrofitting role
mainly depends on the shear strength and tensile strength of adhesive between steel plate
and beam.
Structural adhesives JGN I and II are recommended in
Technical Specification for Strength-
ening Concrete Structures
. Their bonding strengths are shown in Table 3.6.
Table 3.6 Bonding strengths of structural adhesive JGNs
Shear Strength (MPa)
Axial Tensile Strength (MPa)
Test
value
f
t
Nominal
value
f
tk
Factored
value
f
t
Test
value
f
t
Nominal
value
f
tk
Factored
value
f
t
Bonded Material
Failure
Steel-Steel
Adhesive
18
9
3.6
18
16.5
6.6
f
v
f
ct
Steel-Concrete
Concrete
f
cvk
f
cv
f
ctk
f
ct
Concrete-Concrete
Concrete
f
v
f
cvk
f
cv
f
ct
f
ctk
f
ct
Bonding strength of structural adhesives should be tested and disqualified adhesives must
not be used. Currently, there is no such test specification in the construction industry.
Manufacturers in China test their products in accordance with the national
Test Method for
Shear Impact Strength of Adhesive Bonds
and
Test Method for Tensile Strength of Adhesive
Bonds
.
In fact, qualified adhesive strength is far higher than that of concrete. Tests show that in
bond-shear test and bond tensile test, failure occurred in concrete.
(3) Stick steel reinforcement beam tests
Tongji University, Research Institute of Structural Engineering of the China Academy of
Building Research, Southeast University, Shanghai Institute of Architectural Science and
others have conducted various forms of stick steel reinforcement beam tests. Based on test
data at home and abroad, the following conclusions apply:
a. Reinforcing with sticked steel plate can increase the cracking load of original beam.
The plate, located in the margin of the beam, can effectively control the concrete tensile
deformation, and is far more valid than the reinforcing bar in the original beam in improving
the beam crack resistance.
b. It enhances flexural stiffness and reduces deflection.
c. It improves bearing capacity. The upgraded range shall be increased along with the
increasing section area of sticked steel plate and the increasing reliability of the steel plate
anchorage.
3. Failure features and force analysis of stick steel reinforcement beam
(1) Failure features
Tests show that steel plate stuck at the bottom of a beam can achieve yield strength
when damaged. In proper reinforced concrete beams, as load increases, the reinforced beam
is destroyed when concrete has been crushed after steel plate and rebar yield.
