Permitted maximum slenderness ratio of steel column under dead and live load is:
180
Steel Column Slenderness Ratio Explained
The slenderness ratio is a crucial parameter in the design of compression members like steel columns. It is defined as the ratio of the effective length of a column to its least radius of gyration. This ratio helps determine the column's susceptibility to buckling under compressive loads. A higher slenderness ratio generally indicates a greater tendency for buckling, meaning the column is more slender and less stable against lateral deflection.
Mathematically, the slenderness ratio ($\lambda$) is expressed as:
$$\lambda = \frac{L_{eff}}{r_{min}}$$
Where:
- $\boldsymbol{L_{eff}}$ is the effective length of the column, which depends on its end conditions.
- $\boldsymbol{r_{min}}$ is the minimum radius of gyration of the column's cross-section.
Permitted Maximum Slenderness Ratio for Steel Columns
For a steel column, also known as a compression member, carrying primary loads such as dead load and live load (or imposed load), the Indian Standard IS 800:2007 (Code of Practice for General Construction in Steel) specifies limits on the maximum permissible slenderness ratio. These limits are set to ensure the structural integrity and prevent premature buckling of the column under service conditions.
According to IS 800:2007, Table 3 (Limiting Slenderness Ratios), for a compression member subjected to dead load and imposed loads (live loads), the maximum permissible slenderness ratio is $\boldsymbol{180}$. This value is critical for ensuring the stability and safety of structures where columns bear the primary vertical loads.
Other Important Slenderness Ratio Limits
It is important to note that the maximum permissible slenderness ratio varies depending on the type of member and the nature of the forces it resists. Below is a table summarizing some common limiting slenderness ratio values as per IS 800:2007, which helps in understanding the context of the 180 limit.
| Type of Member / Condition | Maximum Slenderness Ratio |
|---|---|
| A compression member carrying dead and imposed loads (steel column under dead and live load) | 180 |
| A member subjected to compression resulting from wind or seismic forces only | 250 |
| A tension member in which a reversal of direct stress occurs due to wind or seismic forces | 350 |
| A member normally acting as a tension member but which may experience a reversal of stress into compression due to wind or seismic forces (and not acting as a compression member under dead and imposed loads) | 350 |
| Members always in tension (other than pre-tensioned members) | 400 |
| Lacing bars or battens for built-up compression members | 145 |
Therefore, based on the specific condition of a steel column under dead and live load, the maximum permitted slenderness ratio is 180.
Important Questions from Tension Member
The following are the statements about lug angle used to connect heavily loaded tension member to gusset plates.
(i) The length of end connection is reduced
(ii) By using lug angles there will be saving in the gusset plate
(iii) Cost of connection increases due to additional fasteners and angle required.
A structural member subjected to tensile force in a direction parallel to its longitudinal axis is generally known as
When the length of a tension member is too long:
The allowable stress in axial tension is generally kept less if the thickness of the member is more than
A single angle in tension is connected by one leg only. If the areas of connecting and outstanding legs are respectively a and b, then what is the net effective area of the angle?
A) \(a-\frac{b}{1+0.35\times\frac{b}{a}}\)
B) \(a+\frac{b}{1+0.35\times\frac{b}{a}}\)
C) \(a-\frac{b}{1+0.20\times\frac{b}{a}}\)
D) \(a+\frac{b}{1+0.20\times\frac{b}{a}}\)
