- 2073 Shrawan · 14 marks
AFD, SFD, BMD for frame with mixed loads
Short answer
Reactions: A_x = 7.98 kN ←, A_y = 48.51 kN ↑, G_y = 3.51 kN ↓. Maximum hogging moment is 116.04 kN·m at C. Contraflexure in BC at 0.89 m above B. Right column FG is in tension.
Draw AFD, SFD and BMD for the given frame and loading. Indicate salient points, if any. [Figure: frame with supports A and G; column heights 4 m and 2 m; spans 2 m, 2 m, 2 m; loads: 20 kN at D, 20 kN/m on the vertical member near C, 30 kN at 30° at B, 5 kN/m UDL on E-F, and a triangular load of up to 6 kN/m on the right column.]
Reading of the figure: A is a hinge at the base (0, 0) and G is a roller at the base (4, 0). The left column rises to C at (0, 6); B is 2 m above A, and D is a cantilever end 2 m to the left of C. Beam C–E–F: C(0, 6), E(2, 6), F(4, 6). The right column FG is 6 m high. Loads: 20 kN downward at D (cantilever tip); a 20 kN·m couple at C (counter-clockwise; the label reads 20 KN/m but is drawn as a curved arrow); 30 kN at B at 30° (down and to the right); 5 kN/m UDL on EF (2 m); a horizontal triangular load on FG, zero at F and 6 kN/m at G, acting to the left. G is a roller (vertical reaction only).
Support reactions
Loads: 30 kN → (25.98 →, 15 ↓) at B; UDL 5 × 2 = 10 kN ↓ at x = 3 m; triangular load = ½ × 6 × 6 = 18 kN ←, at 2 m above G.
ΣM_A = 0 (anticlockwise +):
+20×2 (cantilever, 20 kN ↓ at x = −2) = +40
+20 (couple) = +20
−25.98 × 2 (horizontal part at B) = −51.96
−10 × 3 = −30
+18 × 2 (leftward load at 2 m height) = +36
+4 G_y
=> 4 G_y = −14.04, G_y = −3.51 kN (acts downwards, ↓ 3.51 kN)
ΣFx = 0: A_x + 25.98 − 18 = 0 -> A_x = −7.98 kN (7.98 kN ←)
ΣFy = 0: A_y − 20 − 15 − 10 − 3.51 = 0 -> A_y = 48.51 kN ↑
Member forces
| Member | N (kN) | V (kN) | M (kN·m) |
|---|---|---|---|
| Cantilever DC | 0 | 20 (constant) | 0 at D → 40 at C (hogging) |
| AB | −48.51 (compression) | 7.98 | 0 at A → 15.96 at B |
| BC | −33.51 | −18.00 | 15.96 at B → −56.04 at C (zero at 0.89 m above B) |
| CE (beam) | −18.00 | 13.51 | −116.04 at C → −89.02 at E |
| EF (UDL) | −18.00 | 13.51 → 3.51 | −89.02 at E → −72.00 at F |
| FG (column) | +3.51 (tension) | 18 at F → 0 at G | 72.00 at F → 0 at G |
- At joint C the moment in the beam (116.04) = column (56.04) + cantilever (40) + couple (20).
- At F the moment in the beam (72.00) equals the moment at the column top (72.00).
- Column FG: with y up from G, V = 6y − 0.5y², M = 3y² − y³/6; check M(6) = 108 − 36 = 72 kN·m.
BMD (kN·m, tension side drawn)
D --40-- C(116)------E(89)---F(72)
| |
(56) | 72 at F, curving to 0 at G
| |
15.96 B |
| |
0 A 0 G
Salient features: the maximum moment is 116.04 kN·m (hogging) at C, just to the right of the cantilever junction; M = 0 at A, D and G (pinned and free ends); the BC column changes the sign of its moment at 0.89 m above B (point of contraflexure); the shear in the beam is 13.51 kN, then falls linearly to 3.51 kN under the UDL; the roller G has a negative reaction (3.51 kN downwards), so the frame must be anchored there, and the right column is in tension.
✓ Answer checked by Claude Opus 5.5 (high effort)
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