Maximum Permissible Compressive Loads in Steel Scaffolds

shawlaskewvilleΠολεοδομικά Έργα

29 Νοε 2013 (πριν από 3 χρόνια και 7 μήνες)

51 εμφανίσεις

Page
1


HONG KONG INSTITUTE OF VOCATIONAL EDUCATION (TSING YI)


Department of Construction















200
7
/0
8

Sessional Examination















Course Name (Code) :

Higher Certificate in Civil Engineering (55401)


Higher
Diploma
in Civil Engineering (55
9
01
)


Year of Study

:

Final Year


Mode of Study

:

P
TE


Unit

:
Temporary Works (CSE4402)


Date

: XX

January

2
00
8


Time

:
XX pm
-

XX pm


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
N
ine

(
9
)

pages.

4.

This question paper contains
SIX (6)

questions.















Examination Data:

Density of Concrete

25 kN/m
3















Available from Invigilator:

Graph papers










Page
2


Q.1

(a)

Use the

formula of CIRIA Report 108 to determine the maximum
concrete pressure acting upon a vertical timber formwork panel for the
construction of a RC wall,
7
50 mm thick, 5

m high and 12 m long
.

(4 marks)

(Ans. Pmax=64.08 kPa)

(18

Use the concrete pressure obtained

in (a) to determine

the spacing of
walings, soldiers and tie rods
for
the

wall form

panel, given the following
design criteria and formwork material properties
:




Casting Conditions and Design Criteria:



Mix:




OPC with retarder added

Concrete Tempera
ture:

1
5
-
3
5


C

Pour Rate:



3

trucks of 6 m
3

each per hour


Allowable deflection:

not to exceed 1/
36
0 of span



Tie rod spacing:

minimum 900 mm (vertically and





horizontally)



Formwork
Component

Allowable Values

Moment of
Resistance

(M=f Z)

Bending

Stiffness

(E I)

Shear Load

(q A)

Plywood
Sheeting

0.4
2
0 kNm/m

3.25 kNm
2
/m

6.86 kN/m

Waling

2.025 kNm

1
0
9.14 kNm
2

9.80 kN

Soldier

10.5 kNm

200.35 kNm
2

6
5
.50 kN


(18 marks)

(Ans. Waling@175, Soldier @ 1325, Tie Rod @ 1100 mm c/c)



(c)

Calculate the ten
sion in
the

tie rods which
keeps

the double skins
in
position
against the outwards concrete fluid pressure.

(3 marks)

(Ans. 93.40 kN)

Hint:












R
H
K
R
D
P
0
.
1
45
.
0
0
.
1
max

in kPa, or
Dh

2
16
36








T
K
Page
3



Assume all formwork components are continuous beams
of multiple equal
spans and the following formulas to be used.

Max. Bending Moment for a continuous beam under
UDL





2
10
1
L



Max. Shear Force


L

6
.
0

Deflection


= 0.007
EI
L
4


for plywood



= 0.004
EI
L
4


for waling and soldier,


where ω

=
Uniformly Distributed L
oad
(UDL)
on span L

(kN per metre
run)

Page
4



Q.2

(a)

Fig. Q2 shows
the
part of the elevation of a
row of
falsewor
k assembled
from scaffolding tubes and fittings which all comply with BS 1139. The
vertical spacing of horizonta
l lacing members is neither uniform in the
arrangement nor
the projected lengths of
the upper and lower cantilever
projections. Given the Maximum Permissible Compressive Loads of
BS1139 scaffolding tub
ing in Table Q2, determine the f
ollowings:


(i)

Maximum Pe
rmissible Strut Load when the diagonal brace is
fixed to the falsework framework with couplers
at all Levels L1
to L6
;

(3 marks)

(Ans.

28 kN

)


(ii)

Maximum Permissible Strut Load when the diagonal brace is
fixed to the falsework framework with couplers
at Leve
ls L1 and
L6 only
;


(3 marks)

(Ans.

1.6 kN

)


(iii)

Maximum Permissible Strut Load when the diagonal brace is
fixed to the falsework framework with couplers
at Levels L1, L3,
L5 and L6

only
;

(3 marks)

(Ans.

28 kN

)


(iv)

Maximum Permissible Strut Load when the diagon
al brace is
fixed to the falsework framework with couplers
at Levels L1, L4
and L6 only
.

(3 marks)

(Ans.
5.8 kN

)


(v)

If the horizontal lacing members are re
-
arranged
in 5 equal lifts of
uniform vertical spacing together with a 150 mm cantilever
projection in
accommodating

the upper forkhead and lower base
jack
, what will be the Maximum Permissible Strut Load?

(6 marks)

(Ans.
30.9 kN

)


Hint:

Le = L + 2mL (
BS5975
)



(b)

State the construction considerations for safe erection of falsework in a
construction site.

(7 marks)


Page
5




Page
6



Q.3

(a)

The
width of a
10 m tall
concrete pier detailed in Fig. Q3
(a)

increases

from
1.8

m at its

top

to
3

m

at the
middle 3
-
m high portion and then

tapers
to 2 m at its
bottom
.
The
column
depth is 1.75 m
constant
throughout

as shown
.
A v
ertical formwork is proposed for
the pier

construction

by placing concrete
in one go
from the

top.




Anticipated site conditions during concrete placement will be as follows:



Concrete temperature

1
0




32

C



Unit weight of concrete

25 kN/m
3



Rate
of concrete delivery

20

m
3

per hour




Given the following formula
e

in computing concrete pressure acting on
formwork, determine the design concrete pressure in kPa for the form in
every 1
-
m intervals and hence plot its variation along the height of the
fo
rm.












R
H
K
R
D
P
5
.
1
45
.
0
5
.
1
max

in kPa, or
Dh

(18 marks)


Concrete Pressure Diagram (All in kPa)
0.00
2.00
4.00
6.00
8.00
10.00
12.00
0.00
50.00
100.00
150.00
200.00
Conc. Pressure (kPa)
Elev. above ground (m)
Concrete Pressure Diagram
(All in kPa)







2
16
36








T
K
Page
7




(b)

Explain

standard and design solutions in the co
ntext of temporary works
design.

(7 marks)





Q.
4

(a)

Explain

briefly the
following terms

in the context of formwork

construction:


(i)

B
ackpropping

(ii)

S
triking
P
rocedures for
a
RC slab on beam form


(
9

marks)


(b)

Discuss the advantages and disadvantages of using sheeting, waling,
strut support system in excavation works



(
8

marks)



(c)

Prepare a checklist for design
ing a roadworks layout if a proposed
trenching is to be carried out on an existing carriageway.



(
8

marks)




Q.
5


Fig. Q5 shows a

single
-
propped cantilever steel sheet piling cofferdam
designed to resist a
4.
5 m high vertical cut. Given the following so
il
properties and design information:




Height of soil to be retained



4.
5

m




Depth of the prop below ground level


0.
9

m



Horizontal spacing of props




2.50

m



Active Earth Pressure Coefficient K
a


0
.2
5



Passive Earth Pressure Coefficient K
p


3
.30



Unit weight of soil





18 kN/m
3



Surcharge Load





1
5

kN/m
2




Use
FREE EARTH SUPPORT METHOD

to determine the:


(i)

Depth of point of zero net earth pressure

Z



(
4

marks)

(Ans.

0.44m)

(ii)

Determine the strut load





(1
2

marks)

(Ans.
9
3.55 kN)

Page
8


(iii)

Minimum depth of embedment
D

that the pile has to be driven.

(

Hint
: Try

the depth below point of
zero net earth pressure X
=
2.0

m for

the first

iteration

)

(
9

marks)

(Ans. 1.92 m)


Q
.
6

(
a)

Prepare

a checklist for formwork construction on s
ite
.


(
6

marks)



(
b)

Explain the site safety regulations for
scaffolding
works under the Law
of Hong Kong.



(
1
4

marks)



(
c)

Draw annotated sketches to show
the construction details of a:




(i) Kicker; and



(ii) Coil Tie for wall form.

(
5

marks)

---
End of Paper
---

Page
9


TABLE Q2


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 Compressive 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
10









Strut Load



Forkhead

Cantilever Projection









200












L6












1450














L5











1450


Diagonal Brace













L4


Standard








1450


(BS1139)













L3











1350













L2











1350

Base Jack











L1

Cantilever Projection









150



Fig. Q2

(Not To Scale)




Page
11








3 m




1.75 m







1.8 m










3 m
















10

m







3 m


















4 m









2

m





Fig. Q3

(a)

(Not to Scale
)

































0.
9

m

















Prop













4.
5

m


















































Z
































D














Steel Sheet Piling













X




Fig. Q
5

(Net Lateral Earth Pres
sure Diagram)


(Not to Scale)