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Cork Institute of Technology
Bachelor of Engineering (Honours) in Structural Engineering- Award
(NFQ Level 8)
Summer 2006
Advanced Structural Design
(Time: 4 Hours)
Section A
Instructions Attempt two questions from Section A and the questions from Sections B and C. Use separate Answer books for each Section. Candidates may refer to: BSI-PP7312: - Extracts from British Standards for students of Structural Design and other approved design aids
Examiners: Mr. L O’Driscoll Mr M P Mannion Mr. S P Lowe Mr. T Corcoran Prof P O’Donoghue
A1 Fig.QA1 gives details of a reinforced concrete canopy and its supporting beam. Design the beam to the requirements of BS 8110. With the aid of cross-sectional sketches at the supports, mid-span and quarter points show the reinforcement. Design information: Canopy loading:- Finishes = 0.5 kN/m^2 Imposed = 1.0 kN/m^2 Fire resistance = 1 hour Exposure = moderate fcu = 35 N/mm^2 f (^) y = 460 N/mm^2 WRConcrete = 24 kN/m^3 The canopy support beam is to have an overall depth of 750 mm and a 300 mm wide rib. The torsion centre may be assumed to lie on the centroidal axis of the rib. The columns are capable of providing full restraint to the ends of the beam. Neglect loading from the glazing and its framework. Neglect wind and assume that stability requirements are satisfied. (25 Marks)
A2 Pinned based steel portal frames, of span 30 m, are symmetrical about their centre-line. The frames, which are spaced at 6 m centres, have a height to eaves of 6.5 m and a height to ridge of 10.5 m. The eaves have haunches of length 3 m and depth 0.7 m. The purlins are at 1.0 m centres on plan. Refer to Fig. QA2 with regard to dimensions. Using S275 structural steel, check the suitability of 533 x 210 x 82 UBs for the stanchions and 457 x 152 x 60 UBs for the rafters. The following checks are to be undertaken: (i) Check which of these two is the critical collapse mechanism:- (a) one with plastic hinges at the bottom of an eaves haunch and at the second purlin point below the ridge, or (b) one with plastic hinges at the same point relevant to the haunch but at the first rather than the second purlin point below the ridge. (12 Marks) (ii) Check that the maximum moment at any section of the rafter does not exceed the plastic moment provided. (5 Marks) (iii) Check the sway stability of the frame. (8 Marks)
Loading (on plan): Sheeting and insulation = 0.18 kN/m^2 Purlins = 0.07 kN/m^2 Frame = 0.20 kN/m^2 Imposed = 0.75 kN/m^2 (Attached information:- Clause 5.5.4.2.2 ex BS 5950:Part 1:2000; pp 26 & 27 ex Constrado Section Property Tables)
A3 The glued ply-webbed box-beam of Fig. QA3, of effective span 6 m, is to be used in service class 2 conditions. Using BS 5268:Part 2, check the adequacy of the beam to carry a long- term uniformly distributed load of 2 kN/m (including self-weight). The beam is non-load sharing and the bearing may be taken as adequate. In using a transformed section take Emean for the timber. Design data: Timber flanges: 120 x 60 in Strength Class C Plywood webs: 490 x 12 Finnish birch of 9 plies with face grain parallel to span. Sanded. Deflection due to shear = M/GwAw (Roark’s formulas for stress and strain) Panel shear = Fv Q/It. Rolling shear = FvQ (^) r /2hI. (Attached information:- Clause 4.7, Tables 39 and 49 ex BS 5268:Part 2) (25 Marks)
Section B
B1(a) A covered underground reinforced concrete water storage tank is required. The capacity of the tank shall have a capacity of 500,000 litres. The walls should not include movement joints. Assume an internal wall height of 5.5m, with a 500mm freeboard. Base thickness is 500mm, and roof thickness is 200mm. Assume a sliding joint between wall and roof.
Design the main and distribution steel for each wall to BS 8007, using the following checks: (i) Check for flotation at maximum groundwater level. (^) (4 marks) (ii) Calculate the maximum moments in the walls for serviceability limit states, for all load cases. (^) (8 marks) (iii) Calculate the maximum crack width in the walls for mature concrete. This must be less than 0.2mm. (6 marks) (iv) Calculate minimum thermal steel requirements. (2 marks)
Clearly state any design assumptions made.
Design information: fcu = 35 N/mm^2 fy = 460 N/mm^2 αconc = 12 x 10-6^ / 0 C (coefficient of thermal expansion of mature concrete) Es = 200 KN/mm^2 Ec = 13.3 KN/mm^2 ∆T = 30^0 C = Temperature change Assume soil bearing capacity is adequate. Maximum design crack width = 0.2mm The surcharge load on both roof and surrounding ground is 10 KN / m^2. Soil Properties Granular soil density = 18 KN/m^3 Angle of repose (φ) = 30^0 Maximum groundwater level is 2m below ground.
B1(b) Explain the mechanism of cracking in concrete due to temperature and moisture effects. How is this dealt with in the design and construction of movement joints for water-retaining structures? Use sketches where necessary. (5 marks)
- DSE4 Advanced Structural Design - Section B – Attachment B
- DSE4 14 Advanced Structural Design - Section B – Attachment B
DSE4 Advanced Structural Design - Section B – Attachment B
Limiting moments (kNm), service steel stresses (N/mm^2 ) and ultimate shear capacity (kN/m)
Section C
C1 Design the prestressing strand layout for the precast, prestressed concrete beam indicated in figure C1. The precast beam is made composite with the in-situ reinforced concrete slab also indicated in figure C1. The precast beams are 11.0m long. The beams are simply supported over a single span on bearings with a centre to centre span of 10.0m for both construction (i.e. casting of the in-situ slab) and working (i.e. superimposed dead and live load) conditions. The precast beams are not propped during the casting of the in-situ concrete slab.
Loading: Dead Loads: Precast concrete beam and in-situ concrete slab unit weight γ = 24 kN/m^3
Superimposed Dead and Live Loads (following application of SLS factors): w = 7 kN/m (uniformly distributed over 10.0m span)
Material Properties: Prestressed Concrete: fcu = 60 N/mm^2 fci = 40 N/mm^2 Class 1 member Prestressing Strands: 12.9mm superstrands initially prestressed to 140kN per strand
Stress Limits: Use the recommendations given in BS 8110-1:1997 Section 4 to determine the tensile and compressive stress limits at both transfer and working conditions.
To Do: Determine and sketch an acceptable prestressing strand layout for the midspan of the beam. Use Magnell Diagrams. The Magnell Diagram inequalities for a composite section are given in the attached. Assume a prestress loss factor of R = 0.8. Select strand positions from the available positions indicated in figure C2. Note the indicated mandatory strands.
Calculate the minimum (i.e. largest negative – tensile – value if relevant) and maximum stresses in the beam (consider both transfer and working conditions).
(25 marks)
