According to IS 800 : 2007, under classification of cross-sections, Class 1 sections are also called as _____.
Plastic
IS 800: 2007 Cross-Section Classification
According to the Indian Standard code for steel structures, IS 800 : 2007, structural steel cross-sections are classified based on their ability to resist local buckling when subjected to moment or axial force. This classification helps engineers determine the maximum strength a section can achieve before failure.
The code classifies cross-sections into four main categories:
- Class 1: Plastic
- Class 2: Compact
- Class 3: Semi-compact
- Class 4: Slender
Let's look at the characteristics of each class according to IS 800: 2007:
| Class | Description | Moment Capacity |
|---|---|---|
| Class 1 (Plastic) | Can reach plastic moment capacity and sustain plastic hinges over a significant rotation. Local buckling does not occur before plastic moment is reached and plastic hinge is formed. | Can reach \(M_p\) and sustain rotation |
| Class 2 (Compact) | Can reach plastic moment capacity but cannot sustain large plastic hinge rotation due to local buckling. Local buckling occurs at or after plastic moment is reached. | Can reach \(M_p\) |
| Class 3 (Semi-compact) | The extreme fibre stress can reach the yield stress, but local buckling prevents the development of plastic moment capacity. | Can reach \(M_y\) but not \(M_p\) |
| Class 4 (Slender) | Local buckling occurs even before the yield stress is reached in one or more parts of the section. | Cannot reach \(M_y\) |
Understanding Class 1 (Plastic) Sections
As per IS 800 : 2007, Class 1 sections are specifically defined as those that can develop plastic hinges and have the rotation capacity required for plastic analysis. This means they can achieve their full plastic moment capacity (\(M_p\)). Because of this ability to reach and sustain the plastic moment, these sections are also known as Plastic sections.
The classification depends on the width-to-thickness ratio of the elements (like flange and web) that make up the cross-section, compared against limits specified in the code (Table 2 of IS 800: 2007).
Therefore, according to IS 800 : 2007, Class 1 sections are also called as Plastic sections.
Important Questions from Plastic Analysis
The shape factor for a solid circular section of diameter D is equal to:
If the shape factor of a section is 1.5 and the factor of safety to be adopted in 2, then the load factor will be
Shape factor for most rolled I-section in flexure about strong z-axis ranges from ______.
In a steel beam, when the width to thickness ratio of the compression flange is sufficiently large, local buckling of compression flange may occur even before extreme fibre yields. Such sections are generally known as
The plastic theory is generally used for
