Transcript Document
2.0 ANALYSIS AND DESIGN 2.2 STRUCTURAL ELEMENT Reinforced Concrete Column Rearrangement by :NOR AZAH BINTI AIZIZ KOLEJ MATRIKULASI TEKNIKAL KEDAH INTRODUCTION Column is defined as a structural members subjected to compressive force. Strut – a small compressive member in a framed structure. Column – a larger member, such as the main support for a beam in a building. INTRODUCTION Axially loaded compressive member can fail in two principal ways: - short fat member fail by crushing or splitting of the material. - long thin members fail by sideways buckling. Types of column i) Braced column(tiang dirembat) – the lateral loads are resisted by wall or some other form of bracing ii) Unbraced column(tiang tidak dirembat) – the lateral loads are resisted by the bending of the column iii) Short Column (tiang pendek) lex/h and ley/b < 15 for a braced column ● l /h and l /b < 10 for an unbraced column ex ey iv) Slender(Long) Column ( tiang langsing) ● ● ● lex/h @ ley/b >15 for a braced column lex/h @ ley/b >10 for an unbraced column Failure Mode Short column (p> pcr)usually fail by crushing when the material achieved its ultimate strength. Slender column is liable to fail by buckling The end moment on slender column cause it to deflect sideways exceed a critical values until the column buckles. Failure Mode Slender Column - fails by sideways buckling - The load at which a slender column buckles, is known as its critical buckling load, P crit. P crit. = ΩEI / L2 Where; E = Modulus of Elasticity I = second moment of area L = length between pins Column detail Reinforcement detail Longitudinal steel bar - - A minimum of 4 bars is required in a rectangular column and 6 bars in a circular column. The size of the bars should be not less than 10mm Links - Minimum size = ¼ x size of the largest compression bar but not less than 6mm - Maximum spacing = 12 x size of the smallest compression bar Types of Reinforced Concrete Column Rectangular column Circular column Load transfer on column for design Factored Axial Load (N) for Column Design Interior Column – 1.25 ●Edge/face column – 1.5 ●Corner column – 2 ● Corner column Edge /face column Interior column Short Axially Loaded Column Design Equation N = 0.4 fcu Aconc+0.8 fy Asc Where N – Ultimate Axial load fcu – Characteristic of concrete strength Aconc – area of concrete cross section fy – Characteristic of reinforcement strength Asc – area of reinforcement cross section N Example: A column with 200 mm x 200 mm resists a factored axial load 500kN. Calculate the area of steel required if fy = 460 N/mm2 and fcu = 30 N/mm2 Table 1 Bar dia.(mm) C/s area (mm2) Diameters and areas of reinforcing bars 6 8 10 12 16 20 25 32 40 28 50 79 113 201 314 491 804 1256 Formula for design column N = 0.4 fcu Aconc + 0.8 fy Asc 500x103 = 0.4 (30) (40000 - Asc) + 0.8 (460) Asc = 480000 – 12 Asc + 368 Asc = 480000 + 356 Asc Asc = 56.18mm2 Asc (for each bar) = 56.18mm2/4 = 14mm2 Asc = Πj2= ΠD2/4=14mm2 D = 14 x 4 / Π = 4.22mm Standard required 4 number of steel reinforcement bars size 10mm minimum) . So size column = 4 T 10 4T10