Civil Engineering Reference
In-Depth Information
where,
σ
s
and
σ
a
are respectively stress of tensile or small compression bars and profiled
steel, which can take the same value approximately and be computed as Eq. (3.63).
3. Constitution requirement
Using encased steel method, the following requirements should be complied with:
a. The side length of rolled angle could be not less than 75 mm; the section size of batten
plate could be not less than 25 mm
3 mm, space length of which could be not larger than
20
r
(
r
is the least radius of gyration of a single rolled angle section 2) and 500 mm.
b. Rolled angle should be continuous and not cut off in slabs. The end of rolled angle
should extend to the top of foundation and be anchored with epoxy mortar or epoxy plaster.
Post cap may be equipped to weld with rolled angle, ensuring that the top of rolled angle
has enough anchorage length.
c. Batten plate should be close to concrete surface and connect with rolled angle through
flat position welding when using epoxy to grout. After it is welded, profiled steel should be
sealed by epoxy and air holes are prepared for final grouting.
d. When using latex cement in which latex should be not less than 5%, batten plate may
be welded outside rolled angle.
e. 1
:
3 sand-cement grouts with width of 25 mm or antiseptics could be used as cover of
the profiled steel.
×
4. Example
Example 3.9
Retrofitting Example 3.7 using wet-enclosing steel method.
a. Processing.
a) Sand the original column surface with hand-hold electric grinder until column surface
becomes smooth and four corners are round angles, coarsen it using wire brush, blow clear
with compressed air.
b) Smear a thin layer of epoxy resin, then stick the profiled steel which has been descaled
and wiped with dimethyl benzene on surface, and clamp with a chucking appliance.
c) Stick batten plate on surface and weld.
d) Seal the profiled steel with epoxy plaster and leave air holes, then paste grout nicks in
proper position, the spacing of which is 2
∼
3 mm.
e) Check whether the grout nick leaks, and press epoxy resin into it under pressure of
0.2
0.4 MPa.
f) Spray 1
:
2 sand-cement grouts on the surface of the column.
b. Materials. According to constructional requirement, 4
L
75
∼
×
5 is rolled angle,
A
s
=
A
s
= 741
.
2
×
2 = 1482 mm
2
,
a
s
=20
.
3 mm,
f
s
= 215 N/mm
2
; batten plate select 25
×
3,
spacing is 20
r
=20
15 = 300 mm.
c. Calculation of bearing capacity. As in Example 3.7,
M
= 410 kN
×
·
m,
N
= 600 kN,
600 mm,
A
s
=
A
s
= 1256 mm
2
,
η
=1
.
0
b
×
h
= 400 mm
×
e
0
=
e
i
= 683
.
3mm
>
0
.
3
h
01
(large eccentricity)
e
=
ηe
i
+
h
2
−
a
s
0
= 683
.
3 + 300
−
30 = 953
.
3mm
AccordingtoEq. (3.66),
10
3
N
f
cm
b
600
×
x
=
=
= 136
.
4mm
11
×
400
