- 2072 Chaitra · 12 marks
Frame AFD, SFD, BMD (60 kNm, 50 kN)
Short answer
Reactions: Ha=0, Va=43.64 kN↑, Ve=36.36 kN↑. AB: N=-30.86, V=30.86, M linear 0→87.27 kN·m. At B a 60 kN·m couple jumps moment to 147.27 kN·m (right face) on BC. CD: V linear -6.36→-36.36, M parabolic max 128.18 bottom at C. DE: N=-36.36, V=0, M=0.
Draw axial force, shear force and bending moment diagrams for the frame given in figure below. [Figure: inclined member A-B-C rising from a hinged support at A to C (A to B horizontal projection 2 m, B to C 3 m); a 50 kN force and a 60 kNm couple at B; horizontal member C-D of 6 m carrying 5 kN/m UDL; right column D-E of height 4 m with E on a roller support.]
Assumptions (taken from the figure):
- A(0,0) hinged; inclined member A–B–C at 45°: B = (2,2), C = (5,5); 50 kN downward and 60 kN·m clockwise couple at B.
- Beam C–D = 6 m with 5 kN/m downward; column D–E = 4 m with E on a roller (vertical reaction only).
Sign convention: N is positive in tension; V is positive when the forces on the part before the section (travelling A → end) point along the left-hand normal of the member axis (upward on a left-to-right beam); M is quoted as a magnitude with the tension face named. Support reactions are drawn on the free-body of the whole frame.
/C------------------------D
/ |
/// |
/ |
/// |
/ |
/B/ |
/ |
/// E
/
A/
Support reactions
Equilibrium of the whole frame gives , and .
- = 0.00 kN →
- = 43.64 kN ↑
- = 36.36 kN ↑
Check: the three equilibrium equations of the complete frame (and the hinge condition, where present) are satisfied to rounding (residuals below ).
Axial force, shear force and bending moment at the key sections
| Section | N (kN) | V (kN) | M (kN·m) |
|---|---|---|---|
| AB at A | -30.86 | 30.86 | 0.00 |
| AB at B | -30.86 | 30.86 | 87.27 (right face) |
| BC at B | 4.50 | -4.50 | 147.27 (right face) |
| BC at C | 4.50 | -4.50 | 128.18 (right face) |
| CD at C | 0.00 | -6.36 | 128.18 (bottom) |
| CD at D | 0.00 | -36.36 | 0.00 |
| DE at D | -36.36 | 0.00 | 0.00 |
| DE at E | -36.36 | 0.00 | 0.00 |
Shape of the diagrams
- AB: V constant (steps at point loads), M linear
- BC: V constant (steps at point loads), M linear
- CD: V linear, M parabolic
- DE: V constant (steps at point loads), M linear
- AFD: constant between loads on a member, changing only where a load component acts along the member.
- BMD is drawn on the tension side of each member; it is continuous at rigid joints (moment is transferred) and zero at hinges and at free ends.
Salient features
- Maximum bending moment = 147.27 kN·m at B, tension on the right face
✓ Answer checked by Claude Opus 5.5 (high effort)
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