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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; E=150 kN/mm2E = 150\ \text{kN/mm}^2.]

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 ×\times 45 cm, E=150E = 150 kN/mm2=1.5×108^2 = 1.5\times10^8 kN/m2^2. 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).

I=0.25×0.45312=1.898×10−3 m4,EI=284 766 kNm2I = \frac{0.25\times0.45^3}{12} = 1.898\times10^{-3}\ \text{m}^4,\qquad EI = 284\,766\ \text{kNm}^2

Virtual load

Unit vertical load (down) at D. ss is measured from D up the right column, from C along CB, and from B down the left column (EIEI constant).

Memberss (m)MM (kNm)mm∫Mm ds\int Mm\,ds
DC0-6000
CB0-62s22s^2ss648
BA0-672+15s72 + 15s64212

Details: in CB, M=4s2/2=2s2M = 4s^2/2 = 2s^2 and m=sm = s, so ∫062s3 ds=648\int_0^6 2s^3\,ds = 648. In BA, M=4×6×3+15s=72+15sM = 4\times6\times3 + 15s = 72 + 15s and m=6m = 6, so ∫066(72+15s) ds=6(432+270)=4212\int_0^6 6(72+15s)\,ds = 6(432 + 270) = 4212. (The UDL and the 15 kN load both bend the left column in the same sense as the unit load.)

ΔDv=648+4212EI=4860EI=4860284 766=17.07 mm\Delta_{Dv} = \frac{648 + 4212}{EI} = \frac{4860}{EI} = \frac{4860}{284\,766} = 17.07\ \text{mm}

Answer: vertical deflection at D =4860/EI=17.07= 4860/EI = 17.07 mm downward.

✓ Answer checked by Claude Opus 5.5 (high effort)

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