Short Notes: Limit State of Compression | Short Notes for Civil Engineering - Civil Engineering (CE) PDF Download

 Page 1


 
 
LIMIT STATE OF COMPRESSION 
 
? If leff > 3B, it is called a column 
? If leff < 3 LLD, it is called a pedestal  
Note: LLD is least lateral dimension 
1. IS RECOMMENDATION REGARDING LONGITUDINAL REINFORCEMENT 
 
? Minimum percentage of longitudinal reinforcement should not be less than 0.8% to prevent 
buckling of the column. 
? Maximum percentage of longitudinal reinforcement shall not be more than 6% to avoid 
congestion of reinforcements which would make it very difficult to place the concrete and 
consolidate it. 
? The minimum no of longitudinal bars provided in a column shall be four in rectangular columns 
and six in circular columns. 
? The bars shall not be less than 12 mm in diameter 
? Maximum spacing of longitudinal bars = 300 mm 
? Minimum cover to the column reinforcement equals 40 mm or dimeter of bar, whichever is 
greater. 
2. TRANSVERSE REINFORCEMENT 
 
? Diameter shall not be less than the maximum of these values 
 
Page 2


 
 
LIMIT STATE OF COMPRESSION 
 
? If leff > 3B, it is called a column 
? If leff < 3 LLD, it is called a pedestal  
Note: LLD is least lateral dimension 
1. IS RECOMMENDATION REGARDING LONGITUDINAL REINFORCEMENT 
 
? Minimum percentage of longitudinal reinforcement should not be less than 0.8% to prevent 
buckling of the column. 
? Maximum percentage of longitudinal reinforcement shall not be more than 6% to avoid 
congestion of reinforcements which would make it very difficult to place the concrete and 
consolidate it. 
? The minimum no of longitudinal bars provided in a column shall be four in rectangular columns 
and six in circular columns. 
? The bars shall not be less than 12 mm in diameter 
? Maximum spacing of longitudinal bars = 300 mm 
? Minimum cover to the column reinforcement equals 40 mm or dimeter of bar, whichever is 
greater. 
2. TRANSVERSE REINFORCEMENT 
 
? Diameter shall not be less than the maximum of these values 
 
 
 
?  If the longitudinal bars are not spaced more than 75 mm on either side, transverse 
reinforcement need only to go around corner and alternate bars for purpose of providing 
effective lateral supports. 
 
? The diameter of  transverse reinforcement need not exceed 20 mm. 
? Spacing of transverse Reinforcement shall not exceed the least of the following 
• Least lateral dimension 
• Sixteen times the diameter of the smallest longitudinal reinforcing rod. 
• 48 times the diameter of transverse reinforcement 
 
3. EFFECTIVE LENGTH 
Case No. End condition Theoretical Leff Recommended Leff 
1 
 
0.5 L0 0.65 L0 
  
Page 3


 
 
LIMIT STATE OF COMPRESSION 
 
? If leff > 3B, it is called a column 
? If leff < 3 LLD, it is called a pedestal  
Note: LLD is least lateral dimension 
1. IS RECOMMENDATION REGARDING LONGITUDINAL REINFORCEMENT 
 
? Minimum percentage of longitudinal reinforcement should not be less than 0.8% to prevent 
buckling of the column. 
? Maximum percentage of longitudinal reinforcement shall not be more than 6% to avoid 
congestion of reinforcements which would make it very difficult to place the concrete and 
consolidate it. 
? The minimum no of longitudinal bars provided in a column shall be four in rectangular columns 
and six in circular columns. 
? The bars shall not be less than 12 mm in diameter 
? Maximum spacing of longitudinal bars = 300 mm 
? Minimum cover to the column reinforcement equals 40 mm or dimeter of bar, whichever is 
greater. 
2. TRANSVERSE REINFORCEMENT 
 
? Diameter shall not be less than the maximum of these values 
 
 
 
?  If the longitudinal bars are not spaced more than 75 mm on either side, transverse 
reinforcement need only to go around corner and alternate bars for purpose of providing 
effective lateral supports. 
 
? The diameter of  transverse reinforcement need not exceed 20 mm. 
? Spacing of transverse Reinforcement shall not exceed the least of the following 
• Least lateral dimension 
• Sixteen times the diameter of the smallest longitudinal reinforcing rod. 
• 48 times the diameter of transverse reinforcement 
 
3. EFFECTIVE LENGTH 
Case No. End condition Theoretical Leff Recommended Leff 
1 
 
0.5 L0 0.65 L0 
  
 
 
2 
HIP 
NRAR 
 
HIP RAR 
0.7 L0 0.80 L0 
3 
 
1.0 L0 1.0 L0 
4 
 
1.0 L0 1.20 L0 
5. 
 
– 1.5 L0 
6. NHIP 2.0 L0 2.0 L0 
Page 4


 
 
LIMIT STATE OF COMPRESSION 
 
? If leff > 3B, it is called a column 
? If leff < 3 LLD, it is called a pedestal  
Note: LLD is least lateral dimension 
1. IS RECOMMENDATION REGARDING LONGITUDINAL REINFORCEMENT 
 
? Minimum percentage of longitudinal reinforcement should not be less than 0.8% to prevent 
buckling of the column. 
? Maximum percentage of longitudinal reinforcement shall not be more than 6% to avoid 
congestion of reinforcements which would make it very difficult to place the concrete and 
consolidate it. 
? The minimum no of longitudinal bars provided in a column shall be four in rectangular columns 
and six in circular columns. 
? The bars shall not be less than 12 mm in diameter 
? Maximum spacing of longitudinal bars = 300 mm 
? Minimum cover to the column reinforcement equals 40 mm or dimeter of bar, whichever is 
greater. 
2. TRANSVERSE REINFORCEMENT 
 
? Diameter shall not be less than the maximum of these values 
 
 
 
?  If the longitudinal bars are not spaced more than 75 mm on either side, transverse 
reinforcement need only to go around corner and alternate bars for purpose of providing 
effective lateral supports. 
 
? The diameter of  transverse reinforcement need not exceed 20 mm. 
? Spacing of transverse Reinforcement shall not exceed the least of the following 
• Least lateral dimension 
• Sixteen times the diameter of the smallest longitudinal reinforcing rod. 
• 48 times the diameter of transverse reinforcement 
 
3. EFFECTIVE LENGTH 
Case No. End condition Theoretical Leff Recommended Leff 
1 
 
0.5 L0 0.65 L0 
  
 
 
2 
HIP 
NRAR 
 
HIP RAR 
0.7 L0 0.80 L0 
3 
 
1.0 L0 1.0 L0 
4 
 
1.0 L0 1.20 L0 
5. 
 
– 1.5 L0 
6. NHIP 2.0 L0 2.0 L0 
 
 
RAR 
 
7. 
 
2.0 L0 2.0 L0 
 
4. SHORT COLUMNS AND LONG COLUMNS 
? If  
?  If  
5. SLENDERNESS RATIO (SRxx) 
? It is the ratio of the length of a column and the least Radius of gyration of its cross section. 
?  
 
 
?  Maximum slenderness ratio for column = 60 
?  If one end is restrained, unsupported length 
Page 5


 
 
LIMIT STATE OF COMPRESSION 
 
? If leff > 3B, it is called a column 
? If leff < 3 LLD, it is called a pedestal  
Note: LLD is least lateral dimension 
1. IS RECOMMENDATION REGARDING LONGITUDINAL REINFORCEMENT 
 
? Minimum percentage of longitudinal reinforcement should not be less than 0.8% to prevent 
buckling of the column. 
? Maximum percentage of longitudinal reinforcement shall not be more than 6% to avoid 
congestion of reinforcements which would make it very difficult to place the concrete and 
consolidate it. 
? The minimum no of longitudinal bars provided in a column shall be four in rectangular columns 
and six in circular columns. 
? The bars shall not be less than 12 mm in diameter 
? Maximum spacing of longitudinal bars = 300 mm 
? Minimum cover to the column reinforcement equals 40 mm or dimeter of bar, whichever is 
greater. 
2. TRANSVERSE REINFORCEMENT 
 
? Diameter shall not be less than the maximum of these values 
 
 
 
?  If the longitudinal bars are not spaced more than 75 mm on either side, transverse 
reinforcement need only to go around corner and alternate bars for purpose of providing 
effective lateral supports. 
 
? The diameter of  transverse reinforcement need not exceed 20 mm. 
? Spacing of transverse Reinforcement shall not exceed the least of the following 
• Least lateral dimension 
• Sixteen times the diameter of the smallest longitudinal reinforcing rod. 
• 48 times the diameter of transverse reinforcement 
 
3. EFFECTIVE LENGTH 
Case No. End condition Theoretical Leff Recommended Leff 
1 
 
0.5 L0 0.65 L0 
  
 
 
2 
HIP 
NRAR 
 
HIP RAR 
0.7 L0 0.80 L0 
3 
 
1.0 L0 1.0 L0 
4 
 
1.0 L0 1.20 L0 
5. 
 
– 1.5 L0 
6. NHIP 2.0 L0 2.0 L0 
 
 
RAR 
 
7. 
 
2.0 L0 2.0 L0 
 
4. SHORT COLUMNS AND LONG COLUMNS 
? If  
?  If  
5. SLENDERNESS RATIO (SRxx) 
? It is the ratio of the length of a column and the least Radius of gyration of its cross section. 
?  
 
 
?  Maximum slenderness ratio for column = 60 
?  If one end is restrained, unsupported length 
 
 
 
?  For a short column,  
?  For a long column,  
6. MINIMUM ECCENTRICITY 
 
7. DESIGN OF COLUMNS 
All columns shall be designed for 
? Axial load = P0 
?  Moment about x – x = Mux    Mux > Muxmin 
?  Moment about y – y = Muy 
 
(a) IS code method – WSM method 
? The safe load on a short column is given by 
 
WC
 
= scc × Ac + ssc
 
× As 
Ac = (BD – ASC) = net area of concrete 
? Safe stresses in concrete 
 M20 M25 M30 M35 M40 
scc 5 6 8 9 10 
 
? Safe stresses in concrete 
 Fe 250 Fe350 Fe415 Fe500 
ssc 130 N/mm
2
 130 N/mm
2
 190 N/mm
2
 190 N/mm
2
 
 
? Load carrying capacity of a long column 
         P = Cr (scc Ac + sscAsc) 
Cr = reduction coefficient  
 
 
? For Rectangular or square coulmn 
1.25
48
eff
r
L
C
B
=-
  
B= Least lateral dimension