How many classes of cross-section are defined in IS 800: 2007 to avoid the local buckling by limiting the width to thickness ratio?
- A4Correct
- B3
- C2
- D1
Solution
Concept
Classification of Cross Sections
Formula
No mathematical formula; classification is based on limiting width-to-thickness ratios (b/t) using the yield stress factor ε = √(250/fy).
Step-by-step solution
1. Refer to IS 800:2007 guidelines for cross-section classification based on the width-to-thickness ratio. 2. Identify the four defined classes: Class 1 (Plastic), Class 2 (Compact), Class 3 (Semi-compact), and Class 4 (Slender). 3. Select Option A (4).
Explanation
According to IS 800:2007, cross-sections are classified into 4 distinct categories based on their width-to-thickness ratio to prevent local buckling: - Class 1 (Plastic): Can form plastic hinges with large rotation capacity. - Class 2 (Compact): Can develop full plastic moment capacity but limited rotation. - Class 3 (Semi-compact): Extreme fibers can reach yield stress, but local buckling prevents developing full plastic moment. - Class 4 (Slender): Elements buckle locally even before reaching the yield stress.
Shortcut
Remember the acronym PCSS: Plastic, Compact, Semi-compact, Slender (4 classes in total).
Common mistake
Students often confuse the 4 cross-section classes in IS 800:2007 with the 3 classes defined in older codes or forget to count slender sections, leading them to incorrectly select 3.
Correct answer: A) 4