CE6505 – DESIGN OF REINFORCED CONCRETE ELEMENTS
UNIT – UNIT – I I
METHODS OF DESIGN OF CONCRETE STRUCTURES Concept of Elastic method, ultimate load method and limit state method
Advantages of Limit State Method over other methods
Design codes and specification specification
Limit State philosophy as detailed in IS code
Design of beams and slabs by working stress method
Compiled by: Mr. by: Mr. S. MANIKANDAN, Assistant Professor, Department of Civil Engineering, Shanmuganathan Engineering College.
CE6505 – DESIGN DESIGN OF REINFORCED CONCRETE ELEMENTS
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2 Marks [Questions & Answers] 01) What is the expression recommended by the IS 456 – 2000 2000 for modulus of elasticity? Ans.:
(i) for Steel: As per clause 5.6 of IS 456:2000, the modulus of elasticity of steel (E s) shall be taken as 2
200 kN/mm .
(ii) for Concrete: As per clause 6.2.3.1 of IS 456:2000, the modulus of elasticity of concrete (E c) can be assumed as follows: Ec = 5000 f ck ck 2 Where, f ck ck = Characteristic strength of concrete (in N/mm ).
02) Define partial safety factor. Ans.: Partial safety factor is defined as the ratio between the design load and the characteristic load.
Design load Partial safety factor (m)
= Characteristic load
03) What are the classifications available in serviceability limit state? Ans.: As per clause per clause 35.3 of IS 456:2000, the classification in serviceabilit y limit state are following:
(i) Deflection (ii) Cracking 04) Enlist different factors that are influencing the durability of concrete as per BIS? Ans.: The following different factors that are influencing the durability of concrete as per Clause
8.1.1 of IS 456:2000 (i) the environment; (ii) the cover embedded steel; (iii) the type and quality of constituent materials; (iv) the cement content and water / cement ratio of the concrete; (v) workmanship, to obtain full compaction and efficient curing; and (vi) the shape and size of the member.
S.M.K./A.P./CIVIL/S.E.C.
UNIT I - METHODS OF DESIGN OF CONCRETE STRUCTURES
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05) What is the main concept of Elastic method? Ans.: The main concepts of Elastic method are following:
(i) It deals only with the elastic elas tic behavior of the member. (ii) The permissible stress for concrete and steel are not exceeded anywhere in the structure when it is subjected to the worst combination of working loads. 06) Write any two assumptions of working stress method. (or) What are the assumptions made in the elastic theory of reinforced concrete structures? Ans.: In the working stress method, the following assumptions shall be made As per Clause B-1.3 of
IS 456:2000 (i) At any cross section, plane plane sections before bending remain plain after bending. (ii) The stress-strain relationship of steel and concrete, under working loads, is a straight line. 07) What are the advantages of Elastic method? Ans.: The advantages of Elastic method are following:
(i) It is simple. (ii) Reasonably reliable and (iii) As the working stresses are low, the serviceability requirements are automatically satisfied and there is no need to check them. 08) What is meant by modular ratio? Ans.: Modular ratio is defined as “the ratio between modulus of elasticity of steel and modulus of
elasticity of concrete”. Mathematically, Modulus of Elasticity of Steel (E s) Modular ratio (m)
= Modulus of Elasticity of Concrete (E c)
09) Determine the modular ratio of M 25 grade concrete. Ans.: As per Clause B-1.3 of IS 456:2000, the modular ratio (m) for M25 concrete is following:
280 m =
280 =
3 cbc
= 10.980 3 x 8.5
Where, cbc value taken from Table No:21 of IS IS 456:2000.
TWO MARK Q & A and BIG QUESTIONS
CE6505 – DESIGN DESIGN OF REINFORCED CONCRETE ELEMENTS
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10) ‘The working stress method is unrealistic in many ways’. Justify with any two points. Ans.: The working stress method is unrealistic in many ways as following:
(i) In this method, we assume that both steel and concrete are perfectly elastic at all stages. But in practical the concrete is not an elastic material. (ii) The modular ratio plays important role in working stress method of design, but in practice, it is an imaginary quantity. 11) How are the safety margins assigned in Elastic method and Ultimate load method? Ans.: The safety margin assigned in Elastic method is to multiply the factor of safety ( for concrete =
3, for steel = 1.78) 1.78 ) in to the material strength for design. The safety margin assigned in Ultimate load is to multiply the load factor value in to the working load to obtain the ultimate load for design.
12) What is the basic concept of Ultimate load method? Ans.: The basic concepts of Ultimate load method are following:
(i) The working loads are increased by suitable fac tor to obtain ultimate loads. (ii) The designer is able to predict the excess load which a given structure can carry beyond the working load without collapse. 13) Define collapse load? Ans.: The collapse load is defined as the working load multiply with the load factor. f actor.
i.e., Collapse load
=
Load factor
X
Working load.
14) Write any two assumptions of limit state method. Ans.: In the limit state design, the following assumptions shall be made As per Clause 38.1 & 39.1 of
IS 456:2000 (i) Plane sections normal to the axis remain plane after bending. (ii) The tensile strength of concrete is ignored. 15) List the advantages of limit state design. Ans.: The advantages of limit state design are following:
(i) Limit state design is more economic and safer than working stress and ultimate load method of design. (ii) It shall satisfy the serviceability requirements, such as limitations on deflection and cracking. S.M.K./A.P./CIVIL/S.E.C.
UNIT I - METHODS OF DESIGN OF CONCRETE STRUCTURES
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16 Mark [Questions] CE2306 (R 2008) - April / May 2015 (A.U. Chennai) – Chennai) – Q.P. Q.P. Code: 71258
(or)
CE2306 (R 2008) – 2008) – November November / December 2014 (A.U. Chennai) – Chennai) – Q.P. Q.P. Code: 91243
(Or)
CE2306 (R 2008) – 2008) – May May / June 2014 (A.U. Chennai) – Chennai) – Q.P. Q.P. Code: 51242
(or) TWO MARK Q & A and BIG QUESTIONS
CE6505 – DESIGN DESIGN OF REINFORCED CONCRETE ELEMENTS
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CE2306 (R 2008) – 2008) – November November / December 2013 (A.U. Chennai) – Chennai) – Q.P. Q.P. Code: 31210
(or)
CE2306 (R 2008) - May / June 2013 (A.U. Chennai) – Chennai) – Q.P. Q.P. Code: 21210 (a) Explain the concept of elastic method and ultimate load method. And write the advantages of limit state method over other methods.
(16) (Or)
(b) Derive the expression for the depth of neutral axis and moment of resistance of a rectangular singly reinforced balanced beam section under flexure. Use M-15 concrete and mild steel?
CE2306 (R 2008) – 2008) – November November / December 2012 (A.U. Chennai) – Chennai) – Q.P. Q.P. Code: 11194
(or)
S.M.K./A.P./CIVIL/S.E.C.
UNIT I - METHODS OF DESIGN OF CONCRETE STRUCTURES
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CE2306 (R 2008) - May / June 2012 (A.U. Chennai) – Chennai) – Q.P. Q.P. Code: 10229
(or)
CE1354 (R 2004) - April / May 2011 (A.U. Chennai) – Chennai) – Q.P. Q.P. Code: 55232
(or)
Compiled By:
Mr. S. MANIKANDAN M.E. (Stru (Stru ctural Engg.) Assistant Professor, Department of Civil Engineering, Shanmuganathan Engineering College, Arasampatti, Pudukkottai – Pudukkottai – 622507. 622507. Email:
[email protected] Email:
[email protected] TWO MARK Q & A and BIG QUESTIONS
