取截面I-I1.075个 以左: Nax ∑M4=0 3 F×3+100×6 225 40×3=0 A Fr F=-160kN ax 10040F FN=(F)×L=-164.92kN Fay=(Fax)×l1=-40kN ∑F、=0Fby-Fay+40-100=0Fby=20kN Nb (Fbby)×b=3333kN FNa=-16492kN,FN=3333kN,FN=-28.28kN NaFNa=(Fax/lax)×l a= –164.92 kN Fay=(Fax/la )×l ay= –40 kN ∑Fy=0 Fby–Fay+40–100=0 Fby=20 kN FNb=(Fby/lby)×lb =33.33kN FNa = –164.92kN, FN =33.33kN, FNc = –28.28 kN 取截面Ⅰ－Ⅰ 以左： ∑M4=0 Fax×3+100×6 –40×3=0 Fax= –160kN