CEB424-T1-S1-2005

CEB424-T1-S1-2005 - GUT Student Number Surname Given Name/s...

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Unformatted text preview: GUT Student Number Surname Given Name/s Examination Paper SEMESTER: FIRST SEMESTER EXAMINATIONS 2005 UNIT: CEB424 PROFESSIONAL STUDIES 6 (CONCRETE STRUCTURES AND GEOTECHNICAL ENGINEERING) - THEORY 1 DURATION OF EXAMINATION: PERUSAL: 10 MINUTES WORKING: 3 HOURS EXAMINATION MATERIAL SUPPLIED BY THE UNIVERSITY: EXAMINATION BOOKLETS EXAMINATION MATERIAL SUPPLIED BY THE STUDENT: STUDENTS MAY BRING ANY MATERIALS THEY WISH INTO THE EXAMINATION ROOM INSTRUCTIONS TO STUDENTS: Students are prohibited from having mobile phones or any other device capable of communicating information (either verbal or written) in their possession during the examination NOTES MAY BE MADE ONLY ON THE EXAMINATION PAPER DURING PERUSAL TIME ALL SIX (6) QUESTIONS ARE TO BE ATTEMPTED MARKS FOR EACH QUESTION ARE AS INDICATED THIS IS AN OPEN BOOK EXAMINATION THIS EXAMINATION PAPER MUST NOT BE REMOVED FROM THE EXAMINATION ROOM Queensland University of Technology GUT Gardens Point GUT Kelvin Grove GUT Carseldine Where the following Questions seek descriptive answers. keep your answers brief and to the point. Use diagrams wherever ossible to illustrate our answers. Do not writ an essa for an answer - a sim I le list of clearl ex resse key points is best. QUESTION 1 (a) List the loads, forces and actions we should consider acting on the superstructure of a building when doing the structural design of that building. (“Superstructure” means all of the structure above the footings). (2 marks) (b) Using diagrams, words or formulas, show the ways in which the loads, forces and actions on a building should be combined to design the building for all situations that an engineer should reasonably consider. (2 marks) (0) Clearly explain the difference between the limit state of strength and the limit state of serviceability. (2 marks) (d) List four main ways in which a concrete building can fail the limit state of serviceability if not designed properly. (2 marks) (e) The planned uses of a particular floor in a building are described as “a mix of ofice space and reading areas, with the likelihood of some localised areas where stacked files will be stored”. Determine a suitable single factored design load to be used over the whole floor, and describe your reasoning in deriving that load. (2 marks) W QUESTION 2 (a) A concrete spandrel beam spans over 4 columns; the columns and beams are all 400mm wide. The first span is 6.5m, the second is 6.9m, the third is 8.5m. The permanent (unfactored) load on the beam is 25kN/m plus 4kN/m superimposed permanent (unfactored) load; the imposed (unfactored) load on the beam is 32kN/m. The beam has a uniform cross section along its entire length and is reinforced according to AS3600 specifications. Which types of structural analysis in AS3600 can be used to determine the moments and shears in this beam? (2 marks) (b) The building is modified so that the three spans are now 6.5m, 7.2m and 8.5m. The loadings on the beam are the same as in (a) above. Use ASS600 to draw the design limit state bending moment and shear force diagrams for this beam. (10 marks) (0) What is meant by the expression “deemed to comply” in AS3600? (2 marks) ((1) When using the deemed to comply approach in AS3600 for checking that a beam’s deflections are acceptable, the calculation for Fur has the term (1.0 + kcs)g in the expression for total deflection, but the 1.0 part is missing in the expression for deflection which occurs after addition of partitions. Explain why that 1.0 missing from the second expression. (2 marks) (e) The beam in (b) above is 400mm wide, 600mm overall total depth and is cast monolithically with the slab it’s supporting. The beam is reinforced with 4N28 bars in tension; the concrete in the beam and slab is f ’c =32MPa. The slab exists on only one side of the beam. The slab is 200mm thick. Considering only total deflection, will the beam’s deflections be satisfactory? (6 marks) Total = 22 marks CEB424T1.051 cont/... K‘Q QUESTTON 3 (e) What is the primary purpose of ties in a reinforced concrete column? (a) Name four different characteristics of a building that need to be considered when determining the seismic forces to be applied to it. (2 marks) (b) What is the difference between the shear centre and centre ofmass of a building and why is it important to determine their locations? (2 marks) (c) In a building in which there are no shear walls or service core, what effects do seismic forces have on columns in the building? (2 marks) (d) For the columns in the building described in (c) above, which of the two moment magnifiers in AS3600 will apply when designing the columns? Give reasons for your answer. (2 marks) (2 marks) W QUESTION 4 A suspended concrete slab comprises one internal floor in a 20 storey building. It is a flat plate 250mm thick, supported by columns whose centrelines form a rectangular grid 9000mm in one direction and 7000mm in the other direction. The slab is prestressed in both directions. There are no drop panels or beams supporting this slab. There is 0.5kPa permanent partition load applied to this slab and 4.0kPa imposed load. Minimum cover for corrosion is 30mm and for fire is 25mm; f ’c = 32MPa. Each prestressing tendon consists of four 12.7mm diameter regular stress-relieved strands in flat ducts which have internal dimensions of 19mm by 74mm; the ducts are made of 0.5mm thick galvanised steel. (61) (b) (C) (d) CEB424T1.051 For a balanced slab design, choose a suitable load to be balanced. Explain the reasons for your choice. (2 marks) For this slab, determine the maximum possible drape of the tendons in an end span and an interior span for the slab spanning the 7000mm direction only, considering all possible factors that might affect the amount of drape of this tendon. (4 marks) For the 9000mm direction, the load to be balanced is set at 4.0kPa. Using an interior span only in this direction, and assuming that the maximum drape for these tendons in an interior span is 175mm, determine the required prestress force per metre width of slab. (4 marks) Consider an end span in the 9000mm direction. Assume at the live end anchorage that the tendons exit the slab at the mid height of the slab cross section. Near the mid-point of the end span, the centroid of the tendons is located 45mm above the soffit of the slab. Where these tendons pass over the centreline of the first internal column, the centroid of the tendons is 50mm below the top of the slab and the tendons are horizontal at this point. If the jacking force applied to each strand in these tendons is lSOkN, what will be the force in the strands at the point where they pass over the centreline of that first internal column? Assume appropriate values of parameters where appropriate. (7 marks) Total = 17 marks cont/ b.) QUESTION 5 A new building 35m by 55m in plan is to be constructed. The maximum column load applied to any footing is 7OODkN. The following questions relate to the building’s foundations, (a) What issues need to be taken into consideration when deciding between spread footings, bored piles, or driven piles? (2 marks) (b) What factors would you take into account in determining appropriate movement limits for the building? (2 marks) (c) A suitable investigation of the proposed site will be needed. The gently sloping site on which the building is to be located is 50m by 70m in plan. There are outcrops ofrock showing on the surface in various places along one 70m boundary of the site. An old deep creek bed runs along the other 70m boundary. What sort of geotechnical sub-surface investigations might be needed? Give reasons for your answer. (6 marks) Total = 10 marks QUESTION 6 At a certain site for a new building, 600mm diameter circular prestressed concrete piles are planned to be driven to refusal. The site is also going to be excavated to 3m depth for a basement. A particular footing at the site is called “Footing A”. The maximum factored vertical load on Footing A is 8000kN. Boreholes at the site indicate the following strata beneath Footing A; the watertable is at a depth of 1m across the whole site: Depth of Stratum Descriptipn of Stratum Properties of Stratum 0m to 1.5m Ash fill, lightly compacted, N = 2 low lasticity. 1.5m to 4m Clay, high plasticity, dark CD = 90kPa grey, trace of fine grained sand, stiff. 4m to 7m Clay, medium plasticity, pale Cu = lSOkPa brown and grey, stiff. 7m to 10m Clayey sand, light brown N = 7 L > 10m Slightly weathered sandstone l N =30 for 75mm (a) What length of piles would you need at Footing A? Explain your answer. (2 marks) (b) Make an initial approximate estimate of how many piles you might need at Footing A. Explain your answeri (2 marks) (c) Determine the geotechnical capacity of 932. of the piles supporting Footing A. (10 marks) (d) What geotechnical matters would you bring to the attention of the contractor before excavation of the basement commences? (3 marks) (e) If there are three piles supporting Footing A, and the service load on the footing is S700kN, determine the settlement of the pile cap. ' (8 marks) (0 What type of retaining wall do you think would be needed for the basement of the finished building? Sketch a suitable retaining wall cross section showing possible dimensions and any other elements that may be needed to make this wall effective for this basement. (3 marks) (g) For the retaining wall you proposed in (f) above, what geotechnical soil parameters would you advise to the structural engineer in order to design this retaining wall? In your answers, give clear reasons for your choices. (3 marks) Total = 31 marks END OF PAPER CEB424T1.051 ...
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This note was uploaded on 04/26/2010 for the course EN 40 taught by Professor Mcgregor during the Two '10 term at Queensland Tech.

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CEB424-T1-S1-2005 - GUT Student Number Surname Given Name/s...

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