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Column Design Charts

The building structures pages have been added over the six months to Dec. 2012.     They are very much work-in-progress and I will be updating them on a regular basis over the next six months.

Estimation of Reinforcement requirement for columns withstanding axial force and bending moment using design charts.

Introduction

This page includes a number of non-dimensional charts based on symmetrically reinforced rectangular columns.     The included data is based concrete with a maximum characteristic strength (fck )of 50 N/mm2.

Consider a column with a section as shown below. d = dimension from face in compression to centroid of area of reinforcement in tension.

These charts are used to "estimate" the area of reinforcement required with the following information available

N = Design Axial force(N)
M = Design Moment (Nm)
h = depth of section (mm)
b = width of section (mm)
d = Effective depth to centroid of reinforcement in tension
fck = Characteristic strength of concrete (cylinder strength) MPa (N/mm2)
f yk = Characteristic strength of reinforcemnt (prooof stress) MPa (N/mm2)

Example
 Considering a section h =300mm x b= 150 mm with an effective depth of d = 240mm withstanding an design axial force of N = 1 MN and a design moment of M = 50 MNmm. fckis assumed to be 40 N/mm2 and fyk = 500 N/mm2 1)    d/h = 0,8 2))   N/( b.h.fck ) = 0,55 3))   M/( b.h2.fck ) = 0,185 4) )   Referring to the chart based on d/h = 0,8 the intersection of the two values coincides approx with the [ p.fy/fck = 0.75 ] 5))   p therefore = 0,75.(40 / 500 ) = 0,060) 6))   p = As /bh therfore As = 0,060*300*150 = 2700 mm2 7))   Suggested reinforcement is three bars 25mm at top and bottom. Resulting area of As = 2945mm2

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