Civil Engineering Reference
In-Depth Information
7. Example for sticking steel reinforcement
Example 3.5
Two groups of 185 m long heavy-duty crane girders whose tonnage is
respectively 25 t and 50 t had to be retrofitted for serious damage in the Anshan steel
factory after a long operational life. Inspection found that the crane girder with 10
∼
60 mm
carburized depth was densely covered with more than 50 cracks of 0.5
∼
10 mm width and
150
1200 mm length. Covering layer had been peeled off in four places of the beam bottom,
where the major rebars had been corroded, rusted, and even broken. There were 17 hollows
10
∼
600 cm
2
.
∼
150 mm high and with area of 50
∼
Solution:
a. Retrofitting method and process.
After identification, steel sticking reinforcement was chosen to retrofit the crane girder,
and epoxy resin perfusion was used to patch the cracks.
A
3
steel plates which were 2
3mm
thick, 800 mm wide, 6600 mm (or 3000 mm) long were attached to beams with rust-broken
reinforcing bars. Four layers of epoxy glass fiber reinforced plastic that were 900 mm wide
were pasted at the end of plates near support to enhance the bonding of steel and bearing
capacity of oblique section.
Process: coarsening concrete—rust removing of the exposed steel using steel brush—
clearing dust with compressed air—coating YJ-302 concrete finishing agent—plastering high
strength and fast hardening mortar of M15—wiping the surface with acetone when
f
c
10 MPa—smearing the structural adhesive on the surface of concrete and dealt steel plates—
sticking plates and fixing—pasting four layers of epoxy glass fiber reinforced plastic after 16
hours curing—48 hours curing —regular service.
b. Identification of retrofitting.
Five analog experiments had been done before retrofitting, four beams of which were
reinforced with 1.2 mm thick, 1.86 m long steel plates and two layers of epoxy glass fiber
reinforced plastic were pasted and coiled at the end of steel. Fatigue test and static test
were applied on one beam, while only static test on the others. Tests showed that bearing
capacity of the former was increased 2.15 times, the latter were increased 1.24
∼
∼
3.7 times.
Several years after retrofitting, this project is still operating normally.
3.3
Concrete Column Retrofitting
Reinforced concrete columns are the most popular in China along with steel columns and
brick columns. This chapter covers retrofitting and retrofitting design of reinforced concrete
columns. Brick columns will be discussed in Chapter 4.
3.3.1
Problems in Reinforced Concrete Columns and Analysis
Generally, column destruction occurring suddenly without any signs is brittle failure.
Therefore, we should understand the failure features and reasons. Analysis is needed to
decide whether to retrofit the columns or not.
1. Failure features of concrete columns
Destruction of concrete columns could be divided to compression failure (including axial
and small eccentric compression columns) and tensile failure (large eccentric compression
columns).
(1) Failure of axial compression columns
When columns are subjected to relatively large external forces, longitudinal cracks appear
in the direction of forces, then concrete in covering layer is shelled, peeled off, crushed and
broken. This process has slight differences with different position of rebar. For example,
when concrete coverage is thin and the space between stirrups is too large after concrete
