© The Hong Kong Polytechnic University
THE HONG KONG POLYTECHNIC UNIVERSITY
DEPARTMENT OF CIVIL AND ENVIRONMENTAL ENGINEERING
Programme:
Higher Diploma in Civil Engineering (31363)
Subject:
Structural Steel Design
Subject Code:
CSE28362
Session:
2019/20
Date:
20 January 2020
Time:
3:15 pm - 5:15 pm
Time Allowed:
Two Hours
This question paper has SIX pages.
Instructions to Candidates:
This paper contains FIVE questions.
In Part 1, answer both Q1 and Q2.
In Part 2, answer two questions only.
All questions carry equal marks.
Additional information provided:
Supplementary Information Sheets
DO NOT TURN OVER THE PAGE UNTIL YOU ARE TOLD TO DO SO.
1
© The Hong Kong Polytechnic University
PART 1
ANSWER BOTH Q1 AND Q2
Q1 Design methodology [25 marks]
a)
What is limit state design? What are partial safety factors? Please explain in terms of
both actions and resistances. Please give examples on their use.
[ 12 marks]
b)
Figure Q1 shows a typical framing plan which is subject to a factored load of 10 kN/m2.
i) Sketch the shear force and the bending moment diagrams of the following beams:
 Beam DEF
 Beam ADG
Also evaluate the maximum shear force (in kN), and the maximum bending moment
(in kNm) of these two beams.
ii) Determine the total load (in kN) on Column A.
[13 marks]
Notes:
1. Adopt the equal distance method in assessing the contributive areas of the beams.
2. As the self-weights of the beams and the columns are small, they may be neglected
in loading assessment.
A
B
C
2.5m
F
D
E
2.5m
H
G
12m
Figure Q1
2
I
© The Hong Kong Polytechnic University
Q2
Section Analysis [25 marks]
Figure Q2 illustrates a cross-section of a fabricated section under various forces.
a.
Refer to Figure Q2a, evaluate the following section capacities of the fabricated
section:
i. Compression capacity, Pc
ii. Shear capacity, Pv
iii. Moment capacity, Mc , assuming Class 1 Plastic section.
Assume S275 steel with a yield strength, py , at 265 N/mm2 and a shear strength, pv ,
at 0.577 py .
[ 8 marks]
b.
Refer to Figure Q2b, evaluate the moment capacity, Mc , of the fabricated section
under an axial force, Fc , at a value of 300 kN.
[ 6 marks]
c.
Refer to Figure Q2c, evaluate the moment capacity, Mc , of the fabricated section
under an axial force, Fc , and a shear force, Fv , both at a value of 300 kN.
Hint: In the presence of shear force, the design yield for combined axial and
bending actions of the web is reduced from the yield strength, py , to the
reduced yield strength py,v , as shown in the figure.
[ 11 marks]
Figure Q2
200
20
160 + 10 = 170
320
he
10
(b)
(a)
py
py2 – 3 fv2
py,v =
where
(c)
3
fv = Fv / Av
py
© The Hong Kong Polytechnic University
PART II
Q3
ANSWER TWO QUESTIONS ONLY
Design of a Fully Restrained Steel Beam [25 marks]
Consider a simply supported beam subject to the following uniformly distributed
loads:
Uniformly distributed loads
Dead load, qd
Imposed load, qi
=
=
8.0 kN/m with a load factor of 1.4
7.0 kN/m with a load factor of 1.6
The beam is 8 m long. Try UB406x140x39 kg/m S275.
a)
Ultimate limit state design
i) Evaluate the total factored distributed load (in kN/m), the maximum shear force
(in kN) as well as the maximum moment (in kNm) of the beam.
[ 8 marks]
ii) Perform section classification of the beam section, and check structural adequacy
of the beam against bending as well as shear actions.
[ 11 marks]
b)
Serviceability limit state design
iii) Evaluate the total unfactored load (in kN/m) for deflection check. [ 2 marks]
iv) Check structural adequacy of the beam against the following deflection limit:
≤ L / 200
Mid-span deflection
under total load
where L is the span of the beam.
[ 4 marks]
Hint: The mid-span deflection of a single span beam is given by:
5 q L4
 =
under a uniformly distributed load, q [kN/m].
384 EI
where
E = 205 kN/mm2
Design data for UB406x140x39 S275
D
=
398.0 mm
B
t
=
8.6 mm
T
d
=
360.4 mm
A
rx
Ix
Zx
Sx
u
=
=
=
=
=
=
49.7 cm2
15.9 cm
12500 cm4
629 cm3
724 cm3
0.858
ry
Iy
Zy
Sy
x
=
=
141.8 mm
10.2 mm
=
=
=
=
=
2.87 cm
410 cm4
57.8 cm3
90.8 cm3
47.5
4
© The Hong Kong Polytechnic University
Q4
Design of an Unrestrained Steel Beam [25 marks]
Consider a simply supported beam with an overhang as shown in Figure Q4, i.e.
Beam ABC. At the free end C, a point load of 37.5 kN (factored) is applied. Assume
Class 1 Plastic section.
a)
Evaluate the maximum internal forces of the beam, and sketch
i) the bending moment diagram, and
ii) the shear force diagram.
[ 4 marks]
b)
The beam member is simply supported between Supports A and B, and the effective
length of Beam AB is assumed to be equal to its system length, i.e. LE = 1.5 m.
Check structural adequacy of Beam AB against lateral torsional buckling.
[12 marks]
c)
The beam member is continuous over Support B with partial torsional restraint while
the free end C of the beam member is free, and the effective length of Beam BC is
assumed to be twice of its system length, i.e. LE = 6.0 m. Check structural adequacy
of Beam BC against lateral torsional buckling.
[9 marks]
Use the Slenderness Buckling Strength Table in the Supplementary Data Sheets as
appropriate.
37.5 kN
UB406x140x39 kg/m S275
A
B
C
1.5 m
3.0 m
Figure Q4
Design data for UB406x140x39 kg/m S275
D
=
398.0 mm
B
=
t
=
8.6 mm
T
=
d
=
360.4 mm
A
rx
Ix
Zx
Sx
u
=
=
=
=
=
=
49.7 cm2
15.9 cm
12500 cm4
629 cm3
724 cm3
0.858
ry
Iy
Zy
Sy
x
=
=
=
=
=
5
141.8 mm
10.2 mm
2.87 cm
410 cm4
57.8 cm3
90.8 cm3
47.5
© The Hong Kong Polytechnic University
Q5
Design of an Unrestrained Steel Column [25 marks]
a) It is decided to measure the failure load of a slender steel column, and an experiment
is proposed to apply an axial (concentric) load to the steel column. Please describe
the following details of the test:



typical test set-up to achieve a pinned-fixed condition
typical testing procedures and measurements
possible load-displacement curves and failure modes
[ 10 marks]
b) Consider a 8.1 m high steel column with a UB406x140x39 kg/m S275. Determine its
compression resistance according to the following conditions:

LEx =
8.1 m

LEy =
2.7 m
Use the design tables for flexural buckling in the Supplementary Data Sheets to obtain
the compressive strength, pc .
[ 15 marks]
Design data for UB406x140x39 kg/m S275
D
=
398.0 mm
B
=
t
=
8.6 mm
T
=
d
=
360.4 mm
A
rx
Ix
Zx
Sx
u
=
=
=
=
=
=
49.7 cm2
15.9 cm
12500 cm4
629 cm3
724 cm3
0.858
ry
Iy
Zy
Sy
x
141.8 mm
10.2 mm
=
=
=
=
=
-End of Paper-
6
2.87 cm
410 cm4
57.8 cm3
90.8 cm3
47.5