- 2071 Magh (old course) · 12 marks
Frame vertical deflection at D
Short answer
Unit vertical load at D. Actuating moments: beam 2s^3 gives 648, column 6(72+15s) gives 4212; total 4860. With EI = 284766 kNm², deflection = 4860/EI = 17.07 mm downward.
Determine the vertical deflection at point D of the frame loaded as shown in figure below. [Figure: portal frame; A (hinge) at the bottom left, B and C top joints, D at the foot of the right column; column height 6 m, beam BC = 6 m (3 m + 3 m) with 4 kN/m UDL, 15 kN horizontal load at B; cross-section 25 cm × 45 cm; .]
Given data and assumptions
Frame: A(0,0) at the base of the left column, B(0,6), C(6,6), and D at the foot of the right column, hanging from C (free end at D). Column height 6 m, beam BC = 6 m with UDL 4 kN/m (down), 15 kN horizontal at B (taken to the right). Section 25 cm 45 cm, kN/mm kN/m. Since a vertical deflection is asked for at D, D is taken as a free end; the frame is then stable only if A is fixed, so it is treated as a cantilever frame from A (a hinge at A with D free would be a mechanism).
Virtual load
Unit vertical load (down) at D. is measured from D up the right column, from C along CB, and from B down the left column ( constant).
| Member | (m) | (kNm) | ||
|---|---|---|---|---|
| DC | 0-6 | 0 | 0 | 0 |
| CB | 0-6 | 648 | ||
| BA | 0-6 | 6 | 4212 |
Details: in CB, and , so . In BA, and , so . (The UDL and the 15 kN load both bend the left column in the same sense as the unit load.)
Answer: vertical deflection at D mm downward.
✓ Answer checked by Claude Opus 5.5 (high effort)
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