Civil Engineering Reference
In-Depth Information
stirrups were anchored at the upper and lower flange of the beam and transverse frapping
were used to stretch.
The method of releasing the load on the beam was to replace the partition walls on the
fifth and sixth floors by light-weight materials, and replace original floor slabs with ceramic
concrete floor slabs.
The performance of the building in later service period has been good based on the above
comprehensive retrofitting method.
3.2.5
Sticking Steel Reinforcement Method
1. Introduction
Sticking steel reinforcement is used to retrofit structures through sticking steel plates to
the exteriors of members. Conventional adhesive, the
structural adhesive
, is an epoxy-based
material mixed with proportional curing agent, flexibilizer and plasticizer.
In recent years, sticking steel reinforcement method has been developed for structural
retrofitting and repairing. Steel plate pasted in concrete tensile region will improve the
tensile and flexural strength remarkably. Currently, this method has become so mature that
the United States has established a construction standard for structural adhesive, Japan has
compiled a structural adhesive quality test standard, and China has also put this approach
into a
Technical Specification for Strengthening Concrete Structures
.
Sticking steel reinforcement method has won the favor of engineering technical person-
nel and owners because it has following advantages compared with traditional retrofitting
methods:
a. Short construction period, little or no downtime due to fast hardening of adhesive,
which has special appeal to owners.
b. Simple process, fast and convenient construction, without open flame, which is ex-
traordinarily suitable for high fire-protection workshop.
c. Since the strength of adhesive is higher than concrete itself, attachment and original
members can work cooperatively without stress concentration in concrete.
d. Pasted steel plates occupy small space and scarely increase the section dimension and
weight of the strengthened member. Therefore, structural clearance and member shape will
not be altered.
2. Properties of structural adhesive
(1) Components of structural adhesive
Structural adhesive is an epoxy-based material and its advantages are as follows:
a. Epoxy resin has high adhesiveness and good bond strength with most materials such
as metal, concrete, ceramics and glass.
b. Epoxy resin has good processing property and stable storage performance. It can be
prepared as thick paste or thin grouting materials, whose curing time would be adjusted
appropriately according to needs.
c. Cured epoxy adhesive has excellent physical and mechanical properties, corrosion
resistance capacity, and small curing contraction.
d. Epoxy material has low cost, nontoxicity and plentiful material resources.
Only by adding the curing agent can epoxy resin be cured. Because curing epoxy resin
alone is brittle, flexibilizer and plasticizer are needed before curing to improve plasticity,
ductility, shock strength and freeze resistance.
Epoxy curing agent types include ethylenediamine, diethanoltriamine, and triethanolte-
traamine. Conventional plasticizers, which do not participate in the curing reaction, are
