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Column design as Per BS 8110-1:1997

Column design as Per BS 8110-1:1997. PHK/JSN. Contents :-. General Recommendations of the code Classification of columns Effective Length of columns & Minimum eccentricity Design Moments in Columns Design. General Reco’s of the code. g m for concrete 1.5, for steel 1.05

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Column design as Per BS 8110-1:1997

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  1. Column design as Per BS 8110-1:1997 PHK/JSN

  2. Contents :- • General Recommendations of the code • Classification of columns • Effective Length of columns & Minimum eccentricity • Design Moments in Columns • Design

  3. General Reco’s of the code • gm for concrete 1.5, for steel 1.05 • Concrete strength – CUBE STRENGTH • Grades of steel Fe250 & Fe460 • Primary Load combination 1.4DL+1.6LL • E of concrete Ec = 5.5√fcu/ gm 10% less than IS • Ultimate stress in concrete 0.67fcu/ gm • Steel Stress-strain curve – Bilinear • E of steel 200 kN/mm2

  4. Classification of columns SHORT – both lex/h and ley/b < 15 for braced columns < 10 for unbraced columns BRACED - If lateral stability to structure as a whole is provided by walls or bracing designed to resist all lateral forces in that plane. else – SLENDER else – UNBRACED Cl.3.8.1.5

  5. Effective length &minimum eccentricity Effective length le = ßlo ß – depends on end condition at top and bottom of column. emin = 0.05 x dimension of column in the plane of bending ≤ 20 mm

  6. Contd.. Deflection induced moments in Slender columns Madd = N au whereau = ßaKh ßa = (1/2000)(le/b’)2 K = (Nuz – N)/(Nuz – Nbal) ≤ 1 Nuz = 0.45fcuAc+0.95fyAsc Nbal = 0.25fcubd Value of K found iteratively

  7. Contd.. Design Moments in Braced columns :- • Maximum Design Column Moment Greatest of a) M2 b) Mi+Madd Mi = 0.4M1+0.6M2 c)M1+Madd/2 d) eminN Columns where le/h exceeds 20 and only Uniaxially bent Shall be designed as biaxially bent with zero initial moment along other axis.

  8. Braced and unbraced columns

  9. Design Moments in UnBraced columns :- The additional Moment may be assumed to occur at whichever end of column has stiffer joint. This stiffer joint may be the critical section for that column. Deflection of all UnBraced columns in a storey auav for all stories = Σ au/n

  10. Design Moments in Columns Axial Strength of column N = 0.4fcuAc + 0.8 Ascfy Biaxial Bending Increased uniaxial moment about one axis Mx/h’≥ My/b’ Mx’ = Mx + ß1 h’/b’My Mx/h’≤ My/b’ My’ = My + ß1 b’/h’Mx • Where ß1 = 1- N/6bhfcu (Check explanatory hand book) • Minimum Pt =0.4% Max Pt = 6%

  11. Shear in Columns • Shear strength vc’ = vc+0.6NVh/AcM • To avoid shear cracks, vc’ = vc√(1+N/(Acvc) • If v > vc’, Provide shear reinforcement • If v ≤ 0.8√fcu or 5 N/mm²

  12. Design – Construction of Interaction Curve A1 A2 Section Stress Strain DistributionofstressandstrainonaColumn-Section 0.67fcu/gm 0.0035 e1 d1 f1 0.5h 0.9x M d x h N e2 f2

  13. Equilibrium equation from above stress block N = 0.402fcubx + f1A1 +f2A2 M =0.402fcubx(0.5h-0.45x)+f1A1(0.5h-d1)+f2A2(0.5h-d) f1 and f2 in terms of E and f1 = 700(x-d+h)/x f2 = 700(x-d)/x The solution of above equation requires trial and error method

  14. THANK YOU

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