Page
1
HONG KONG INSTITUTE OF VOCATIONAL EDUCATION (TSING YI)
Department of Construction
2009/10
Sessional Examination
(Autumn Semester)
Course Name (Code)
:
Higher Diploma in Civil Engineering (51301
F
)
Higher Diploma i
n Civil Engineering (51301A)
Year of Study
:
L4
(51301F)
2 (51301A)
Mode of Study
:
F
T
Unit
:
Temporary Works (CBE3
0
3
3)
Date
:
21
J
anuary
20
10
Time
:
1:30
p
.
m
.
–
4:30
p
.
m
.
Time Allowed
:
THREE (3) Hours
Instructions to Candidates:
1.
Answer
ANY
FOUR (4)
questions
2.
All questions carry
EQUAL
marks.
3.
This question paper has
T
WELVE
(1
2
)
pages.
4.
This question paper contains
SIX (6)
questions.
Examination Data:
Density of Concrete
25 kN/m
3
Available from In
vigilator:
Graph papers
Page
2
Q.1
Fig.Q1
shows a
typical
panel of soffit
formwork
measuring 1800x3300
mm on plan
designed for the construction of a
4
0
0 mm thick concrete
slab
at the top
.
Use the
beam
formulas on Page
8
to c
heck the adequacy of the gi
ven
spacing of the formwork components
. Assume
the following design
and formwork material information
will be
used.
Design Information
Unit weight of concrete
25 kN/m
3
Construction operation load
2.0
kN/m
2
Deflection not to exceed
1/360 o
f span
Formwork Material Information
Formwork
Materials
Permissible
Moment of
Resistance
Permissible
Shear Load
Stiffness
EI
Plywood Sheeting
0.420 kN

m /m
7.86 kN /m
2
.50 kN

m
2
/m
B
earers each
1.800
metres long
1.
00 kN

m
6
.80 kN
7
9.14 kN

m
2
Joists
each 3.300 m
long
5
.39 kN

m
3
0
.21 kN
100
.58 kN

m
2
(25 marks)
(Ans. Max. Spacing Req
’
d : Bearer

@ 451 mm; Joist @ 1291
mm; Prop @ 1485 mm)
Page
3
Q,2
(a)
What are the major responsibilities of a
temporary works
provider under
C
ommon
L
aw?
(5
marks)
(b)
In open country area
s
, dewatering could be employed in lowering
ground water level
for excavation works
.
Explain with
illustration
the arrangement for a typical 2

stage dewatering
system indicating the ground water profile before and after
de
watering.
(
10
marks)
(c)
Briefly describe the responsibilities of a contractor who carries
out trench excavation in a carriageway according
to
the
local
Construction Site Safety Regulations.
(
10
marks)
Q.3
Fig. Q3
shows a
7 m tall, 12 m long vertical w
all formwork designed for
concrete placement in a single lift from its top. The
nonlinear
formwork consists of a single skin with a profile
comprising of straight
segments as shown in the figure
. Anticipated site conditions during
con
creting operation
wi
ll be as follows:
Concrete temperature
5
–
30
C
Unit weight of concrete
25 kN/m
3
Rate of concrete delivery
4 trucks each of 4.5
m
3
per hour.
Given the following formula in computing concrete pressure
acting on formwork,
determine
and
plot
the des
ign concrete
pressure distribution in kPa for the wall form
.
Hint:
R
H
K
R
D
P
0
.
1
45
.
0
0
.
1
max
in kPa, or
Dh
(
2
5 marks)
2
16
36
T
K
Page
4
Ans.
Conc. Pressure Diagram
0.00
75.00
101.19
100.61
98.87
0.00
1.00
2.00
3.00
4.00
5.00
6.00
7.00
8.00
0.00
50.00
100.00
150.00
Conc. Pressure (kN/m2)
Elevation above bottom (m)
Page
5
Q.4
(a)
A steel bracket anchored to an external wall is designed to
withstand a vertic
al point load of 10 kN as shown in Fig. Q4(a).
There are two anchor bolts spaced at 600 mm centre to centre to
arrest the
pull

out
and shear mode of failures of the bracket
bolting
. Assume a factor of safety of
2.
0 for both failures,
(i)
Determine the desig
n tension and compressive force
for the anchor bolt
s
.
(5 marks)
(Ans. Tension 25 kN; Compression 25 kN; Shear 10 kN)
(ii)
If three anchor bolts
equally spaced at 300
mm
centre
to centre
are used instead, explain
by
calculation
how
the safety margin
of the steel
bracket
could be
increased.
(10 marks)
Ans.
If top bolt fails: Safe Load W=10 kN (Pull

out failure); W=20 kN (Shear
Failure)
If none of bolts fails: Safe Load W=20 kN (Pull

out failure); W=30 kN
(Shear Failure)
(b)
Formwork is one of the most importan
t temporary works in
concrete
construction.
State the general principles in design and
construction of a
high quality formwork
.
(10 marks)
Page
6
Q.5
Fig.
Q
5
shows the elevation layout of a typical transverse row of a
birdcage scaffold structure measured
7.0
m (H) and
9.1
m (W). The
re
are 12 rows of
scaffold
framework
in longitudinal direction each
co
mprising
of mild steel tubing and fittings all complying with BS1139.
The
scaffold structure
will be erected to support the construction of a
concrete slab.
Given the following configuration of the
scaffold structure
and design
loading information:
Design Loading
Concrete slab thickness
20
0 mm
Operation load
2.0 kPa
Self weight
of Formwork &
Scaffolding
1.0 kPa
Design wind speed
30
m/s
Scaffold St
ructure
Configuration
Lift Height
1.4 m
Bay Length
1.30 m c/c in transverse
direction
1.35 m c/c in longitudinal
direction
Solidity Ratio of scaffolding
exposed to transverse wind:
5%
(a)
Determine the total wind moment acting on the
scaffold structure
.
Assume that the dynamic wind pressure
q
(in
k
Pa)
for wind speed
V
d
(in m/s)
is given by
q
V
d
4
.
40
and pressure coefficient C
f
= 1.3 and 2.0 for circular scaffolding tubing and the
edge form
respectively.
(5 marks)
(Ans.11.60 kN

m per row
)
(b)
Determine the total leg load in kN in each individual verticals
(standards) of the scaffold under the combined vertical and
horizontal loading condition. Using the Table
Q
5
to check the
Page
7
axial loading capacity of the verticals against lateral buckling.
Identify if there are any verticals under tension.
Assume
scaffolding tubes of
“
USED
”
condition will be used.
(13 marks)
(Ans. Max. Leg Load 14.57 kN; Safe vs Buckling; None of Verticals
are in Tension)
(c)
Assume swivel couplers
each
of 6.25 kN in capacity w
ill be used
to fix diagonal braces
.
D
etermine the minimum number of
diagonal braces required
for each row of scaffold structure
to
resist the horizontal wind load. Draw the layout of the diagonal
braces provided.
(4 marks)
(Ans. Provide ONE diagonal brac
e per row)
(d)
Determine the safety factor against overturning for the
scaffold
structure
when the soffit formwork is standing EMPTY with
out
any
operation load
and
any
kentledge
required
to meet the
minimum
safety factor of
1.2
against overturning.
(3 marks)
(
Ans. 4.08)
Hint
:
Formulas for calculating leg loads induced by
overturning
moment M
are given as follows:
Q.6
A propped cantilever steel sheet piling cofferdam is designed to resist
a
5.5
m (H) high vertical cut as detailed in Fig. Q
6
. Given the
fol
lowing soil properties
and loading information
:
Active earth pressure coefficient K
a
0.
30
Passive earth pressure coefficient K
p
2.85
Unit weight of soil
18 kN/m
3
2
2
2
i
i
i
l
l
p
i
i
i
l
M
p
F
Page
8
Surcharge Load
15
kN/m
2
and the net earth pressure diagram shown in
the figure, use the
FREE
EARTH SUPPORT
method to determine the:
(i)
Depth of point of zero net earth pressure (Z);
(
2
marks)
(Ans. 0.75 m)
(ii)
Prop load if the props are
spaced to leave a working
clearance of 3.0 m on plan for equipment passing between
the gro
und level and the bottom of excavation
;
(1
0
marks)
(Ans.202.59 kN)
(iii)
Calculate the maximum bending moment and shear force
in the waling member.
(
4
marks)
(Ans. Bending Moment 60.78 kN

m; Shear 121.55 kN)
Hint:
Max. Bending Moment for a continuous beam und
er
UDL
2
10
1
L
Max. Shear Force
L
6
.
0
(iv)
Minimum depth of embedment (D) that the pile has to be
driven if the factor of safety for moment equilibrium is
designed to be not less than 2.0. (
Hint start D=X+Z =
2.
75
m for ite
rations
).
(
9
marks)
(Ans. 2.85 m)

End of Paper

Page
9
Continuous Beam
of more than 3
spans
Max. Bending Moment= 0.107
L
2
Max. Shear
= 0.607
L
L
L
L
L
L
Max. Deflection
=
EI
L
4
00632
.
0
2

span Continuous Beam
Max. Bending Moment= 0.125
L
2
Max. Shear
= 0.625
L
L
L
Max. Deflection
=
EI
L
4
00521
.
0
Max. Support Reaction = 1.25
L
Single

span Si
mply Supported Beam
Max. Bending Moment=
2
8
1
L
Max. Shear
= 0.5
L
Max. Deflection
=
EI
L
384
5
4
L
Where
= Uniformly Distributed Load
L
=
S
pan
EI
= Stiffness of Beam
Page
10
TABLE Q
5
Maximum Permissible Compressive Loads in Steel Scaffolds
(which are manufactured in accordance with BS 1139: Section 1.1:1990
with a yield stress of 225 N/mm
2
)
Effective Length
(mm)
Permissible Axial Compressi
ve Load (kN)
As “New” Tubes
As “Used” Tubes
250
76.4
70.0
500
74.5
63.3
750
70.7
60.1
1000
64.3
54.7
1250
55.3
47.0
1500
45.3
38.5
1750
36.4
30.9
2000
29.3
24.9
2250
23.9
20.3
2500
19.8
16.8
2750
16.6
14.1
3000
14.1
11.9
3250
12.1
10.3
3500
10.5
8.9
3750
9.2
7.8
4000
8.1
6.9
4250
7.2
6.1
4500
6.4
5.5
4750
5.8
4.9
5000
5.2
4.4
5250
4.7
4.0
5500
4.3
3.7
5750
4.0
3.4
6000
3.6
3.1
8000
1.3
1.1
Page
11
A
Joist
Bearer
P
lywood
Spacing
Sheeting
at
4
00 mm c/c
1100
1100
1100
Prop
Spacing
A
Joist
Bearer
900
900
ELEVATION A

A
(All dimensions are in mm unless otherwise stated)
Fig.
Q1
4
00 mm Thick Concrete Slab to be cast in

situ
Page
12
2 m
3 m
Wall Form
Profile
2.5 m
2 m
2.75 m
1 m
3 m
1 m
4 m
Fig. Q3
10 kN
750
Anchor
Steel Bracket
Bolt
600
Fig. Q4 (a)
(All dimensions are in mm unless otherwise stated)
Page
13
Edge Form for
20
0 mm
thick
Concrete
Slab
20
0
mm
5
lifts each
1.
4
m high
Wind
Ground Level
7 bays each 1.3 m wide
Fig. Q
5
(Not to Scale)
15
kPa
Prop
4.50
kPa
1 m
Waling
5.5
m
34.20
kPa
Z
D
X
Steel Sheet Piling
Fig. Q6
(Net Lateral Earth Pressure Diagram)
(Not to Sca
le)
Page
14
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