Question

A fixed beam AB of span 10 m is subjected to a concentrated load of 72 kN acting at mid span C. The maximum bending moment in the beam is

• A. 60 kNm
• B. 90 kNm
• C. 120 kNm
• D. 180 kNm

Hint:

Memorize the key formulas for fixed beams:
- Point Load at Center: Max Moment = $PL/8$ (at center and supports).
- UDL over entire span: Max Moment = $wL^2/12$ (at supports). The center moment is $wL^2/24$.

Answer 1

The Correct Option is B

Step 1: Understanding the Question:
Fixed beam 10m span, 72kN at center. Find max BM.

Step 2: Key Formula (Alternate):
Fixed-end moments M_A=M_B=-PL/8. Mid-span moment M_C=+PL/8. Both have magnitude PL/8.

Step 3: Detailed Explanation:
PL/8 = 72×10/8 = 720/8 = 90kNm. Supports: -90kNm (hogging). Center: +90kNm (sagging). Max magnitude = 90kNm.

Step 4: Final Answer:
Maximum bending moment is 90 kNm.