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ILD for SF and BM at C of beam

Short answer

Using influence lines, bending moment at C is -190 kN m (hogging). Shear force is -67.5 kN just left of C and +70 kN just right of C.

Determine the shear force and bending moment at C in the given loaded beam using ILD. Take EI constant throughout the beam. [Figure: beam with hinge A at the left and a roller support C; AB = 2 m, BC = 2 m, then D, E, F at 1 m each; 40 kN load at B, 5 kN/m UDL over the portion around C to E, 60 kN load at F at the free end. Details partly unclear.]

Assumptions (figure partly unclear): beam AA–BB–CC is supported by a hinge at AA and a roller at CC (AB=BC=2AB = BC = 2 m, span AC=4AC = 4 m), with an overhang CC–DD–EE–FF of 3 m (1 m each). Loads: 40 kN at BB; 5 kN/m UDL from CC to EE (2 m); 60 kN at FF (free end). The section is taken at the support CC.

Reactions (for checking)

ΣMA=0\Sigma M_A = 0: RC×4=40×2+10×5+60×7=550⇒RC=137.5R_C\times 4 = 40\times 2 + 10\times 5 + 60\times 7 = 550 \Rightarrow R_C = 137.5 kN; RA=110−137.5=−27.5R_A = 110-137.5 = -27.5 kN (uplift).

ILD for bending moment at C

Load at distance ss from AA. For s≤4s\le 4, MC=0M_C = 0 (the load is carried directly by the supports). For s>4s>4, MC=−(s−4)M_C = -(s-4) (hogging).

 A o---B-----o C---D---E---F
 ILD(M_C):  0  0   0  -1 -2 -3
MC=5×2×(−1)+60×(−3)=−10−180=−190 kN mM_C = 5\times 2\times(-1) + 60\times(-3) = -10 - 180 = -190\ \text{kN m}

ILD for shear at C

Just left of C: ordinate =−s/4=-s/4 for 0≤s<40\le s<4 (so −0.5-0.5 at BB and −1-1 as the load approaches CC); −(s−4)/4-(s-4)/4 for the overhang (−0.25-0.25 at DD, −0.5-0.5 at EE, −0.75-0.75 at FF).

Using ordinates: UDL area from CC to EE =12(0+(−0.5))×2=−0.5=\tfrac12(0+(-0.5))\times 2 = -0.5, so

VC−=40(−0.5)+5(−0.5)+60(−0.75)=−20−2.5−45=−67.5 kNV_{C^-} = 40(-0.5) + 5(-0.5) + 60(-0.75) = -20 - 2.5 - 45 = -67.5\ \text{kN}

Just right of C: ordinate 0 for loads on the span, and 1 for loads on the overhang:

VC+=5×2×1+60×1=70 kNV_{C^+} = 5\times 2\times 1 + 60\times 1 = 70\ \text{kN}

Check by statics: VC−=RA−40=−27.5−40=−67.5V_{C^-} = R_A - 40 = -27.5-40 = -67.5 kN and VC+=−67.5+137.5=+70V_{C^+} = -67.5 + 137.5 = +70 kN.

Answer: MC=−190M_C = -190 kN m (hogging); VC=−67.5V_C = -67.5 kN just left and +70+70 kN just right of CC.

✓ Answer checked by Claude Opus 5.5 (high effort)

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