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Structural Design - III (October 2010)

5 pages, 15 questions, 1 questions with responses, 1 total responses,

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Total No. of Questions : 8] [Total No. of Pages : 5 P1020 [3864]-104 B.E. (Civil) STRUCTURAL DESIGN - III (2003 Course) Time : 4 Hours] [Max. Marks : 100 Instructions to the candidates: 1) Answer Q.1 or Q.2, Q.3 or Q.4 in Section - I. 2) Answer Q.5 or Q.6, Q.7 or Q.8 in Section - II . 3) Answers to the two sections should be written in separate books. 4) Figures to the right indicate full marks. 5) Use of IS 1343, IS 456, IS 3370 & non programmable calculator is allowed. 6) Neat diagrams must be drawn wherever necessary. 7) Assume any other data if necessary & mention it at the starting of the answer. 8) Mere reproduction from IS code as answer, will not be given full credit. 9) Assume any other data if required. SECTION - I Q1) a) A mild steel plate of cross section 12 mm 60 mm, of length 1.5 m is supporting a load of 160 N through a spring having stiffness k = 100 N/mm as shown in fig(1). Calculate the natural frequency of the system if modulus of elasticity of mild steel is 200 Gpa. [8] P.T.O. b) A post tensioned prestressed concrete beam section has top flange 450 150, web 120 450 and bottom flange 300 250 mm, is simply supported over a effective span of 16 m and carries a super imposed load of 13 kN/m over entire span. Calculate extreme fiber stresses in concrete at midspan at initial and final stage. The 3 No. of 12/7 Freyssinet cables having zero eccentricity at supports and c.g. area of steel at 90 mm from soffit of the section and are stressed to initial prestress of 930 Mpa. Take loss ratio as 0.85 and unit weight concrete as 25 kN/m3. [17] OR Q2) a) b) Explain in brief with sketches [8] i) Multiple degree of freedom system. ii) Critical damping. A post tensioned prestressed concrete beam section has top flange 500 150, web 125 550 and bottom flange 280 250 mm, is simply supported over a effective span of 17m. The beam is prestressed with 5 No. of 12/5 Freyssinet parabolic cables with their c.g. at 100 mm from extreme bottom fiber, stressed one at a time from only one end. Calculate total loss of prestress at the age of 90 days, if initial prestress is 1030 Mpa, coefficient friction = 0.28, k = 0.0026/m length of cable, slip of anchorage = 1.5mm, Cc = 2.0, Es = 2 105 Mpa, concrete grade = M45, Creep and relaxation of steel = 2% of initial prestress. [17] Q3) Design a post tensioned prestressed concrete rectangular or I section beam for flexure to carry a live load of 14kN/m over entire simply supported span of 14.6m with M40 grade of concrete and Freyssinet cables of 12/5(fy = 1750 Mpa) or 12/7(fy = 1500 Mpa), including the design of end block. Draw sketches showing cable profiles and end block reinforcement details. Checks for deflection and shear are required. [25] OR [3864]-104 2 Q4) a) b) Write a short note with sketches losses in balanced cantilever PSC beams. [8] A post tensioned prestressed concrete continuous beam ABC as shown in fig(2) is prestressed with initial prestressing force of 1180 kN. The cross section of the beam is 250 mm 850 mm the loads shown are exclusive of dead load. Locate centerline of thrust under prestress plus dead load also & make it concordant stating the shift of cable at salient points find the stresses in concrete at extreme fibers at intermediate support take loss ratio of 0.82, AD = DB = 10m and BE = 8m EC = 12m. The eccentricities at A & C = 0, at D = 230 mm (downwards), at B = 160 mm (upwards), and at E = 280 mm (downwards). [17] SECTION - II Q5) a) b) Write detailed note on Substitute frame methods of analysis. [8] Analyze a rigid jointed frame shown in fig(3) by portal method for lateral loads. Flexural rigidity for all members is same. Analyze beam GHI using proper substitute frame, if it is subjected to vertical ultimate live & dead load incl. of its self wt. intensities of 14kN/m & 12kN/m on GH and 16kN/m & 13kN/m on HI respectively. The horizontal forces are F1 = 24 kN, F2 = 18 kN & F3 = 12kN. Calculate max. span moment for span HI and support moment at H. Design section for combined effect of vertical and horizontal loads. Adopt 15% redistribution of moments for vertical load moments Use M20, Fe500. [17] [3864]-104 3 OR Q6) a) b) Write detailed note on method of calculation of earth quake forces on building. [8] Analyze a rigid jointed frame shown in fig(4) by cantilever method for lateral loads. Flexural rigidity for all members is same. Analyze beam GHI using proper substitute frame, if it is subjected to vertical ultimate live & dead load incl. of its self wt. intensities of 20 kN/m & 18 kN/m on GH and 15 kN/m & 13 kN/m on HI respectively. The horizontal forces are F1 = 20 kN, F2 = 16 kN & F3 = 10 kN. Calculate max. span moment for span HI and support moment at H. Design section for combined effect of vertical and horizontal loads. Adopt 10% redistribution of moments for vertical load moments Use M20, Fe500. [17] [3864]-104 4 Q7) a) b) Draw exaggerated bent shape of long wall of water tank fixed at base & vertical sides and free at top showing faces having bending tension. [5] Design reinforced concrete combined rectangular footing for two columns A & B carrying working loads 450 kN and 650 kN respectively. Column A is 300 mm 300 mm size and column B is 300 mm 400 mm size. Centre to centre distance of columns is 3.5 m safe bearing capacity 180 kN/m2. Use M20 and TMT steel. Draw all details of reinforcements. [20] OR Q8) Design a T shaped retaining wall for slopping backfill with the following data. Height = 5m above GL, Slope backfill = 15 , Angle of friction of backfill = 30 , unit weight of backfill = 18 kN/m3 Safe bearing capacity of the underlying strata = 170 kN/m2 Material M20 TMT steel The coefficient friction between the base slab and the underlying strata = 0.55. Draw lateral pressure diagram and details of reinforcement of stem and base showing curtailment if any. [25] vvvv [3864]-104 5

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