I.D. Number __________________________________ Desk Number ________________

Faculty of Science, Engineering and Computing

Postgraduate Modular Scheme

Semester 1, January Examinations 2012/2013

Level 7

MODULE: CEM 081: Steel Buildings Design

DURATION: Three Hours

Instructions to Candidates

This paper contains SIX questions inTWO sections: Section A and Section B

Answer FOUR questions onlySection A: Answer at least ONE question

All questions carry equal marks

CANDIDATES ARE PERMITTED TO BRING ONE APPROVED CALCULATOR INTO THIS EXAMINATION: from either Casio FX83 or Casio FX85 series (with any suffix), FX115MS, FX570ES or FX991ES

Invigilators are under instruction to remove any other calculators

Candidates are reminded that the major steps in all arithmetical calculations are to be set out clearly.

Stationery Pink Answer BookProvided Design Extracts and Data Sheet

Number of Pages: 1 – 6

+ Design Extracts to be supplied separately+ Structural Analysis Data sheet

SECTION A

1. A 3-spans continuous beam with a uniformly distributed load and two point loads is shown in Figure Q1a. The cross section of the beam is made up of a UB strengthened with a plate on the top of the UB as shown in Figure Q1b. The yield stress of steel is 275N/mm2.

(a) Determine Mp, the fully plastic moment, for the beam.(8 marks)

(b) Using Plastic Analysis method, investigate two possible collapse mechanisms and determine the actual collapse load and the corresponding collapse mechanism.

(10 marks)

(c) For the collapse load in (b), draw the bending moment diagram showing all significant values.

(7 marks)

6q 6q

2q/unit lengthA

B CD

12m 7m5m 5m 7m

Figure Q1a

8mm

13mm

380mm

13mm

10mm

Figure Q1b

178mm

230mm

1

Continued…

2

2 A rigid joint plane frame with a horizontal point load, a vertical point load and a vertical uniformly distributed load is shown in Figure Q2. The relative plastic moments (Mp) are marked next to the members. Assume the plastic hinge along member CD occurs at mid-span.

(a) Examining four collapse mechanisms with sway, determine the collapse load for the frame using Plastic Analysis method.

(16 marks)

(b) If supports E and F are pinned supports, determine the reduction in the collapse load capacity for the chosen collapse mechanism in (a).

(9 marks)

Continued…

B

5m Mp

2Mp

MpMp

2MpC D

EFA

7W

2W/unit length

Figure Q2

3m 3m 6m

5W

3

SECTION B

3. The column shown on Figure Q3 is part of braced framing system and is made from steel S275. It is subjected to following nominal loads: axial compression force F = 600 kN as permanent load and bending about major (y-y) axis My = 300 kNm as variable load. The column is pinned top and bottom. The height of the column is 3.5 m. Check the adequacy of universal column UC 305x305x137 for the indicated loading.

Perform the following design calculations based on EC3:

(a) Check the resistance of the cross section to bending and compression acting simultaneously.

(10 marks)

(b) Check the buckling resistance of the column about the major and the minor axes.

(5 marks) (c) Check lateral torsional buckling and combined buckling effects.

(10 marks)

Figure Q3

Continued …

4

4 A composite beam is part of ComFloor 51 system, supporting trapezoidal steel decking spanning in perpendicular to the axis of the beam direction. It is supporting concrete slab with 130 mm maximum depth. The thickness of concrete above steel decking profile is 79 mm. Shear connectors 19 mm diameter and 100 mm in length are expected to be used.

The top flange of the composite beam is loaded with design UDL of 70 kN as total load during the construction stage of loading and 190 kN as total load during the composite stage of loading. The beam is simply supported with span of 7 m. The spacing between the beams is 3 meters.

The properties of the materials used are: structural steel S275, reinforcement and shear connectors fy = 460 N/mm2, concrete class C25/30, fck = 25 N/mm2, Ecm = 31 kN/mm2.

Design the composite beam following the indicated below procedure according to BSEN 1994-1-1:

a) Calculate construction and composite stage maximum design bending moments and corresponding maximum shear forces and conduct initial section selection.

(5 marks)

b) Evaluate the class of the section and calculate the compression resistance of the slab and tensile resistance of the steel section for composite stage of loading. Estimate the position of neutral axis.

(8 marks)

c) Calculate the moment resistance of the beam and design the shear connectors as numbers and positioning.

(10 marks)

d) Check vertical shear resistance of the beam. (2 marks)

Continued…

5

5 The beam-to-column connection indicated in Figure Q5 is ‘bolted end plate’ type of connection. It is designed to transfer vertical design load Ned, of 300 kN from the beam (UB356x171x67) to the column (UC254x254x73), both of them made of S275 steel. The endplate size 240x160x10 is welded to the web of the beam and is made of S275 steel as well (fu = 410 N/mm2).

The bolts are M20 HSFG bolts class 8.8 (fu = 800 N/mm2) and are positioned as indicated in Figure Q5. The distances are as follows: end distance e1 = 30 mm, edge distance e2 = 35 mm, pitch p1 = 60 mm and gauge p2 = 90 mm.

Check the following elements of the resistance of ‘bolted end plate’ connection:

(a) Limitations for positioning of the holes.(8 marks)

(b) Bearing resistance of the bolt group assuming γM2 = 1.25.(10 marks)

(c) Shear resistance of bolt group with αv = 0.6.

(7 marks)

Figure Q5.

Continued…

6

4 mm

6. A steel beam 406x178x74 UB (grade S275) is protected on 3 sides with a mineral fibre board. The critical temperature of the unprotected beam determined by an iteration procedure was found to be 500°C. For the applied load given in Figure Q6 check the moment capacity of the beam. Calculate the required minimum thickness of the protection if the fire resistance time is 90min, having in mind that ψ=0.3 and A/V = 150m-1. The mineral fibre board properties are λp= 0.25 W/mK and ρp= 530 kg/m3.

Conduct the following calculations:a) Determine for ambient temperature and and for the

critical temperature of 500°C. (10 marks)

b) Calculate the moment capacity of the steel beam and compare with the applied load if the combination coefficient is ψ=0.3.

(7 marks)c) Calculate the minimum required thickness of the protection, if the

fire resistance time is 90min and A/V=150m-1. (8 marks)

Figure Q6

END OF EXAMINATION PAPER

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