Axially Loaded Column
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The document discusses different types of columns based on bracing, length, and reinforcement. It describes braced and unbraced columns, long and short columns, and tied, spiral, and composite columns. Requirements for minimum reinforcement, lateral ties, and selection of column size are also summarized.
Axially Loaded Column
- 1. PREPARED BY: Asst. Prof. GAURANG PRAJAPATI CIVIL DEPARTMENT AXIALLY LOADED COLUMN Mahatma Gandhi Institute Of Technical Education & Research Centre, Navsari (396450) ELEMENTARY STRUCTURAL DESIGN 6TH SEMESTER CIVIL ENGINEERING
- 2. INTRODUCTION Column : • If for a compression member, effective length > 3 x least lateral dimension, it is called column. Pedestal : • If for a compression member, effective length < 3 x least lateral dimension, it is called pedestal. ESD 2160607 2 AXIALLY LOADED COLUMN
- 3. TYPES OF COLUMN ESD 2160607 3 AXIALLY LOADED COLUMN A. As per Bracing: 1. Braced column: 2. Unbraced Column: B. As per Length: 1. Long column: 2. Short column: C. As per Lateral reinforcement & Longitudinal reinforcement: 1. Tied column: 2. Spiral column: 3. Composite column
- 4. TYPES OF COLUMN ESD 2160607 4 AXIALLY LOADED COLUMN A. As per Bracing: 1. Braced column: In braced frames, lateral loads like wind, earthquake, etc. Are resisted by some special arrangements like shear wall, bracing, etc. Side sway is not possible in such columns.
- 5. TYPES OF COLUMN ESD 2160607 5 AXIALLY LOADED COLUMN A. As per Bracing: 2. Unbraced Column : In unbraced frames, No special bracing systems are provided to resist horizontal forces. Side sway occurs in such columns. Such columns shall have to be designed to resist horizontal loads.
- 6. TYPES OF COLUMN 1. Long column : (slender column) If 𝐿𝑒 𝐷 > 12 & 𝐿𝑒 𝑏 > 12 → long column Where D= depth, b= width , Le= eff. Column length It is failed by material failure & buckling together. Bucking is dominant. ESD 2160607 6 AXIALLY LOADED COLUMN B. As per Length:
- 7. TYPES OF COLUMN 2. Short column : If 𝐿𝑒 𝐷 < 12 & 𝐿𝑒 𝑏 < 12 → short column Where D= depth, b= width , Le= eff. Column length It is failed by material failure only. Buckling is negligible. ESD 2160607 7 AXIALLY LOADED COLUMN B. As per Length:
- 8. TYPES OF COLUMN ESD 2160607 8 AXIALLY LOADED COLUMN C. As per Lateral reinforcement & Longitudinal reinforcement: Longitudinal reinforcement is provided in the column to increase its load carrying capacity. When column is subjected to compressive force, length of column decreases and lateral dimensions increases. Thus, the longitudinal bars assume the shape of bow and developing cracks on the outer face of column. It may cause failure of column.
- 9. TYPES OF COLUMN 1. Tied column : When lateral ties are provided as transverse reinforcement in columns, they are called tied columns. They may be used for square, rectangle, circular, L, T-shape columns. ESD 2160607 9 AXIALLY LOADED COLUMN C. As per Lateral reinforcement & Longitudinal reinforcement:
- 10. TYPES OF COLUMN 2. Spiral Column : When longitudinal bars are covered laterally by a wire in the form of helix or spiral, they are called Spiral columns. They are normally provide in circular columns. Due to higher ductility, spiral columns are suitable for earthquake resistance. ESD 2160607 10 AXIALLY LOADED COLUMN C. As per Lateral reinforcement & Longitudinal reinforcement:
- 11. TYPES OF COLUMN 3. Composite column : When column are provided with structural steel sections like I, H, steel tube, etc. In place of longitudinal rein, it is called composite column. ESD 2160607 11 AXIALLY LOADED COLUMN C. As per Lateral reinforcement & Longitudinal reinforcement:
- 12. MINIMUM ECCENTRICITY IN COLUMN: ESD 2160607 12 AXIALLY LOADED COLUMN All columns shall be designed for minimum eccentricity. emin = 𝒍 𝟓𝟎𝟎 + 𝑫 𝟑𝟎 IS 456 Clause No.: 25.4 Page No.: 42 where l = unsupported length of column (eff. Span) D = lateral dimension (overall depth) Minimum eccentricity for column should not be less than 20 mm. emin > 20 mm IS 456 Clause No.: 25.4 Page No.: 42
- 13. FORCE (LOAD) ALONG THE COLUMN (PU): ESD 2160607 13 AXIALLY LOADED COLUMN All columns shall be designed for minimum eccentricity. Pu = 0.4 fck Ac + 0.67 fy Asc IS 456 Clause No.: 39.3 Page No.: 71 where fck = Grade of concrete fy = Grade of steel Ac = Area of concrete = Ag- Asc Asc = Area of longitudinal reinforcement for column = n × 𝜋 4 d2 Ag = Gross area of column = b x D → for Rectangle column = b2 → for Square column = 𝜋 4 D2 → For Circular column
- 14. REINFORCEMENT REQUIREMENTS OF COLUMNS: ESD 2160607 14 AXIALLY LOADED COLUMN Min steel = 0.8 % of Ag IS 456, Clause : 26.5.3.1 (a), Page No.: 48 Max steel = 6 % of Ag For Rectangle column → Min. No. of bar = 4 IS 456, Clause : 26.5.3.1 (c), Page No.: 48 For Circular column → Min. No. of bar = 6 (min) Min. diameter of bar = 12mm IS 456, Clause : 26.5.3.1 (d), Page No.: 48 Spacing of bar ≯300 mm IS 456, Clause : 26.5.3.1 (g), Page No.: 48
- 15. LATERAL TIES: ESD 2160607 15 AXIALLY LOADED COLUMN Pitch : The vertical distance between two successive (consecutive) ties in column is called pitch. It is taken minimum of 1. Least (min) Lateral dimension (min of b & D) 2. 16 x ∅min 3. 300 mm IS 456 Clause No.: 26.5.3.2.d (2) Page No.: 71 Diameter of Lateral ties : It is taken maximum of 1. 𝟏 𝟒 x ∅max 2. 6 mm IS 456 Clause No.: 26.5.3.2.d (1) Page No.: 71
- 16. LATERAL TIES: ESD 2160607 16 AXIALLY LOADED COLUMN
- 17. COLUMNS WITH HELICAL REINFORCEMENT (CIRCULAR COLUMN): ESD 2160607 17 AXIALLY LOADED COLUMN Fact load = 1.05 x Design fact load (Pu) Strength of column with helical reinforcement = 1.05 x Strength of tied column Pu = 𝐅𝐚𝐜𝐭 𝐥𝐨𝐚𝐝 𝟏.𝟎𝟓 IS 456 Clause No.: 39.4 Page No.: 71
- 18. SELECTION OF SIZE OF COLUMN: ESD 2160607 18 AXIALLY LOADED COLUMN Minimum eccentricity for column should not be less than 20 mm. emin ≤ 0.05 (lateral dimension) emin ≤ 0.05 (D) IS 456 Clause No.: 39.3 Page No.: 71 20 ≤ 0.05 D 20 0.05 ≤ D D ≥ 400 mm Min. Dimension of column is greater than or equal to 400 mm.
- 19. LATERAL TIES: ESD 2160607 19 AXIALLY LOADED COLUMN They are used in columns. The load is carried by the vertical steel bars, while the ties are provided to keep the bars in their required position without getting disturbed while compacting the concrete by the needle vibrators
- 20. PROVISION OF LATERAL TIES (OPEN/ CLOSE): ESD 2160607 20 AXIALLY LOADED COLUMN If 48 ф > c/c distance between corner bars, Provide open tie. If 48 ф < c/c distance between corner bars, Provide close tie Where, Ф = diamete of lateral tie c/c distance between bar For Square column c/c distance = D – 2 (c.c) – 2 ( ∅ 2 ) For Rectangle column c/c distance = b – 2 (c.c) - 2 ( ∅ 2 ) (Along shorter side) c/c distance = D – 2 (c.c) – 2 ( ∅ 2 ) ( Along longer side) Where, c.c. = clear cover for column = 50 mm Ф = diameter of main steel at corner (Greater diameter) b = smaller dimension of column D = greater (Max.) dimension of column
- 21. PROVISION OF LATERAL TIES (OPEN/ CLOSE): ESD 2160607 21 AXIALLY LOADED COLUMN Examples of open tie:
- 22. PROVISION OF LATERAL TIES (OPEN/ CLOSE): ESD 2160607 22 AXIALLY LOADED COLUMN Examples of close tie: If along one side, open tie has to be provided and Along the other side, close tie has to be provided. (Normally in Rectangle column) If along both side, close ties are provided