Structural Column
A structural column is a vertical compression member that transmits axial compressive loads from beams, slabs, and other upper-structure elements down to the foundation, and may also resist bending moments arising from lateral loads or eccentric loading. Columns are classified by their slenderness ratio (effective length divided by radius of gyration) into short columns, which fail by material crushing, and long (slender) columns, which fail by elastic or inelastic buckling before the material reaches its yield stress. In reinforced concrete design to IS 456, columns are also classified as axially loaded, uniaxially bent, or biaxially bent based on the combination of forces they carry.
Key Formula
Slenderness ratio = Effective length / Radius of gyration
LaTeX: \lambda = \frac{L_{eff}}{r}
| Symbol | Meaning | Unit |
|---|---|---|
| \lambda | Slenderness ratio (dimensionless) | — |
| L_{eff} | Effective (buckling) length of the column | mm |
| r | Radius of gyration of the cross-section | mm |
Worked Example
Problem
A steel hollow circular column has an outer diameter of 200 mm, wall thickness 10 mm, and an effective length of 4 m. Calculate the slenderness ratio. (Radius of gyration r = √(I/A); for a hollow circle, r ≈ √((D² + d²)/16) where D = outer, d = inner diameter.)
Solution
Step 1: Inner diameter d = 200 − 2×10 = 180 mm. Step 2: r = √((D² + d²)/16) = √((200² + 180²)/16) = √((40000 + 32400)/16) = √(72400/16) = √4525 ≈ 67.3 mm. Step 3: Effective length L_eff = 4000 mm. Step 4: Slenderness ratio λ = L_eff / r = 4000 / 67.3 ≈ 59.4.
Answer
Slenderness ratio λ ≈ 59 (slender column — buckling must be checked)
Classification of Columns by Slenderness Ratio
| Classification | Slenderness Ratio (λ) | Failure Mode | Design Approach |
|---|---|---|---|
| Short column | λ < 12 | Material crushing (yielding) | Direct compression check |
| Intermediate column | 12 ≤ λ ≤ 120 | Inelastic buckling | Interaction formula |
| Slender (long) column | λ > 120 | Elastic buckling (Euler) | Euler critical load |
| Stocky RC column (IS 456) | lex/D < 12 | Axial + bending failure | P-M interaction chart |
| Slender RC column (IS 456) | lex/D ≥ 12 | Additional moments due to deflection | Additional moment method |
Interactive Tools
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Related Terms
Structural Beam
A structural beam is a horizontal or inclined load-bearing member that resists transverse loads primarily through bending and shear, transferring forces from the loaded surface to the supports at its ends or along its length. Beams develop internal bending moments and shear forces that determine the distribution of tensile and compressive stresses across the cross-section, with the neutral axis experiencing zero direct stress. Beams are among the most fundamental structural elements and are constructed from steel, reinforced concrete, prestressed concrete, timber, or aluminium depending on the application.
Structural Load
A structural load is any force or collection of forces that acts on a structure, causing internal stresses, deformations, or displacements within the members. Loads are classified by their nature (static or dynamic), their source (gravity, wind, seismic), and their duration (permanent or transient). Accurate load estimation is the foundation of structural design, ensuring that every member can safely resist the demands placed on it throughout the life of the structure.
Foundation (civil engineering)
A foundation is the lowest part of a structure that transfers all superstructure loads safely to the underlying soil or rock, ensuring stability against settlement, sliding, and overturning. Foundations are broadly classified as shallow foundations (spread footings, combined footings, raft/mat foundations) when the depth of embedment is small relative to width, and deep foundations (piles, caissons, well foundations) when loads must be transferred to deeper, stronger strata. The design of foundations requires knowledge of both the structural loads imposed from above and the geotechnical properties of the soil below, making it an interdisciplinary activity bridging structural and geotechnical engineering.
From Latin "columna" (pillar, column), related to "columen" (summit, top), implying the column as the element that supports the highest point of a structure. The Latin root is cognate with "collis" (hill). Engineering usage has been continuous from Roman architecture through modern structural codes.