design of concrete structures 1 2011 semester 4

8/22/2019 Design of Concrete Structures 1 2011 Semester 4

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@,TINIVERSITY OF MORATI.IWA

Faculty of EngineeringDepartment of Civil Engineering

B.Sc. EngineeringSemester 4 Examination

CE 2122 - Design of Concrete Structures ITime allowed: 3 Hours December 20l lADDITIONAL MATERIAL:Not applicable.

INSTRUCTIONS TO CAIIDIDATES :This paper contains 4 questions on 6 pages.This examination accounts for 60% of the module assessment. The total maximum mark attainableis 100. The marks assigned for each question & sections there of are indicated in square brackets.This is an open book examination.Answer only THREE questions.Assume reasonable values for any data not given in or with the examination paper. Clearly statesuch assumptions made on the script.If you have any doubt as to the interpretation of the wording of a question, make your owndecision, but clearly state it on the script.All Examinations are conducted under the rules & regulations of the University.

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cE2122Q.1.It is proposed to construct a 10 storey apartment building in Colombo suburb. Up to the 9th floor,each floor has four apartments. At each floor level, the facades facing East and West have beenprovided with a small garden area so that a green environment can be created to ensure pleasingconditions for the occupants at each floor level while ensuring better protection from the directsolar radiation. The sky garden located at 10th floor level is expected to provide adequate projectionto the fagade to protect from tropical thunder storms.Effrcient vertical circulation in the building is ensured providing fwo passenger lifts. Twostaircases have also been provided so that adequate number ofsafe passage can be ensured in caseof a fire. One such staircase is located around the lift well is shown in Figure L The stairs arespanning longitudinally and connected to the two supporting beams. The effective span is 1.9 mand the height of the flight is 1.2 m. The live load is considering as 2.5 kN/m2. The characteristicstrength of concrete is 3%trt/Jnm2 and yield strength of high yield steel (tor steel) is 460 N/mm2 andfor mild steel is 250 N/mm'. The waist thickness can be taken as 125 mm. Lateral restrained to thebuilding will be provided using the fagade and lift core wall as shown in Figure 1. A SAP2000model has already been prepared for this building. It was found that the lift core wall is subjectedto an axial load of 400 kN and the bending moment of 800 kNm.

a. Suggest suitable design load on the staircase consideringimposed load contributions. the dead, finishes and[3 Marks]b. Determine the moments and shear forces acting on the flight identified as No:l.[4 Marks]c. Design the staircase for flexure and shear and propose a suitable reinforcementarrangement[8 Marks]d. Determine whether the staircase can satisfu the serviceability design criteria for crackcontrolling and deflection.[6 Marksle. Detail the staircase showing curtailment of bars, lap lengths, etc. with proper barnotations.[6 Marks]f. Design the lift core wall in Grid line E with a length of 1.9 m and subjected to an axialload of 400 kN and a bending moment of 800 kNrn

Flight No 1

1.9 m

D I 1.5m E!:l F I i.Sm

Lift core wall

Flight No 3

[7 Marks]

Figure Q.1. Plan view of staircase IPage3 of6


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cE2122Q.2.With the opening of Southern expressway in Sri Lanka on 27'h of November 20 I 1, it is expected tohave the rapid infrastructure development taking place in the southem part of Sri Lanka. Aninvestor has proposed to construct an 8 storey building as an apartment complex with the scenicviews of the mountain located inland and some tea estates on the other side. This building will belocated in a new suburb earmarked for development to accommodate the housing needs of theemployees who will be working in the new business ventures that will immerge. For this building,the foundation selected was of inverted T type which would be designed to carry the loads of theeight storey building and all the additional features that will be mounted at the roof top levelincluding satellite antennas, wind mills, solar panels, etc.Figure 2 shows the part of I't floor plan and the beam layout. All members that are structurallyimportant would be constructed using grade 25 concrete. Yield strength of high yield steel (torsteel) can be taken as 460 N/mm2 and the latter for mild steel can be taken as 250 N/mm2. You aresupposed to design the beam identified as ABCD as shown in Figure 2. The@$6sed size of thebeam is 400 mm of depth and 300 mm of width.

a. What are the possible failure modes that could occur when the beam is subjected to auniformly distribute floor load of appreciable magnitude?[5 Marks]b.Determine the design load on beam ABCD considering that the slabs are one way andcontinuous over the beam ABCD.[5 Marks][5 Marks][SMarks]ITMarks]f. Check whether the beam reinforcement arrangement proposed in part (e) complies withthe requirement for the crack control of the beam section.

[4 Marks]g. Check whether the beam satisfies serviceability limit state requirements for deflection.[3 Marksl

7.0 m

7.5 m

c. Design and detail the beam ABCD for flexured. Design and detail the beam ABCD for sheare. Propose a suitable reinforcement arrangement

3.3 m 3.3 m 4.5 m.J+


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t cE2122Q.3A five-storey office building with a storey height of 3.6 m (totalheight is l8 m) is proposed as partof an office building complex at new Mattala air port. The building consists of ordinary momentresisting frame of reinforced concrete. The building has a rectangular plan with dimensions of 20 mx 35 m. The plan of a part of this rectangular framed building is shown in Figure 3. The buildinghas a cenhal core. The floor system consists of beam and slab construction. The beams will spanbetween the concrete columns. Since the client is interested in marketing the apartments with aguarantee on quality, it is decided to use Grade 30 concrete for the whole structure. Yield stress ofhigh yield steel can be taken as 460 N/mm2 and for mild steel, it is 250 N/mm2.A SAP2000 model has already been prepared for this building. It was found that the reinforcedconcrete column Cl at grid B/3 canies a total factored ultimate axial load of 500 kN at secondfloor level. Due to the approximate symmetry of loading, the column is subjected to a negligiblebending moment about Y axis. The slab thickness is 125mm. The primary beam and secondarybeam sizes are 500mmx300mm and 40Ammx3A0mm, respectively. The column has beenselected as350mmx350mm. Reinforcements for the column between levels 2 and I are to bedesigned. Relative sway between the floors is not prevented.

a.What are the possible failure modes if the column Cl is subjected to an axial load ofappreciable magnitude and the floor to floor height is increased to 5.2 m for aestheticrequirements?[6 Marks]b.Find the effective height of this internal column if the floor to floor height is 3.6 m.[4 Marks]c. Design and detail the column section between first and the second floors.

[10 Marks]d.It is proposed to construct a pad footing (1.8 m x 1.8 m) as the base of column Cl. If thesoil bearing capacity is about 150 kN/m2 and the proposed thickness for the footing is500 mm. Design the column footing following the steps given below;a. Design the footing for axial load and sketch the reinforcement[8 Marks]b. Check the shear capacities of the footing.

(11 (2) (3) [6,{farksl6.5 m 6.5 m 7.0 m(A)

I.f

t$=------llv.lJ-

I

5.5(BT

4m(c)

II

Page 5 of 6Figure Q.3: Plan view


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cE2122Q.4.It is proposed to construct a five storey-office complex in Colombo city limit. The investor wishesto promote this as a green lroject with the certification from Sri Lanka Green Building Council(SLGBC). This building is expected to have a roof top with only part accessible due to theinstallation of a wind turbine with 5 m long blades to hamess the wind power. The tower of thewind turbine is of 10.0 m height will be mounted on the concrete walls of the lift shaft. Figure 4shows the part of a 3'd floor slab layout.

a. Describe two alternative and cost effective slab systems that can be proposed for thisbuilding with neat sketches and discuss advantages and disadvantages of each system.b. The allowance for live load was taken as 2.5 kN/m2 for office buildings. ttlit*Yfff:

actual meaning of this allowance and hence indicate whether you agree with this value?[4 Marks]c. Find the design loads that are acting on the slab. Clearly state your assumptions.[4 Marks]d.Find the critical Ultimate Limit State bending moments and shear forces for slab panelsI and214 Marksle. Find the fleiural reinforcement requirement to resists bending moments in slib panel 1

as a one way spanning slab and panel 2 as a two way spanning slab.[6 Marks]f. Prepare a detail drawing (sketch only) for the slab clearly indicating the bar notations,curtailment and lap lengths.[6 Marks]controlling and[6 Marks]

g. Check whether the slab satisfies serviceability requirements for crackdeflection. (A)! g.om (c)I4.5m i

0m

m

IIIIIII

Panel 1IIII

Panel 2Slab thickner

IIIIIIII

/

(B)II

(1) -7.

= 125 mm

(2\

7.4

IFigure Q.4.: Plan view at first floor level(3)

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design of concrete structures 1 2011 semester 4

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