4-32 解：取整体：∑MA=0 F1×1.5+F2×3+F3×4.5+F4×6+F5×7.5-FRB×9=0

∑Fy=0 FRA+FRB-(4×30+40)=0 ∴FRA=80kN

S1?1.51.5?0.6622取A点：∑Fx=0

FRA?S1??S2?0

0.661.5?0.6622∑Fy=0

?0

联立后解得：S1=-197kN S2=180kN

(S3?S4)?1.51.?52取Ｃ点：∑Fx=0

?S1?20.661.5?2?01. 520.66 ∑Fy=0

S4?0.661.?52?(?S1?S)320.66?20.66?F10?21.5 0.66 联立后解得：S3=-37kN S4=-160kN

S6?1.51.5?0.6622取Ｅ点：∑Fx=0

??S41.51.5?0.6622?0

∑Fy=0

S6?0.661.?52??S420.66?20.66?S521.5?0F2?0 .66 联立后解得：S5=-30kN S6=-160kN

S7?S?81.51.?52取Ｄ点：∑Fx=0

2?2??S2?S31.5?022?1.5 0.66

∑Fy=0

S8?21.?522?2?S30.66?2?1.52??S500. 66 联立后解得：S7=１１２kN S8=56.3kN 由对称性可知：S9=S8=56.3kN S10=S6=-160kN S11=S5=-30kN S12=S4=-160kN S13=S2=180kN S14=S3=-37kN S15=S1=-197kN

4-33 解：取整体：∑MA=0 FRB×4-P1×2-P2×3=0 ∑Fy=0 FRA+FRB-P1-P2=0 ∴FRA=62.5kN 取A点：∑Fx=0 S1+S2cos45°=0 ∑Fy=0 FRA-S2sin45°=0 解得：S1=-62.5kN S2=88.4kN 取C点：∑Fx=0 S4-S2cos45°=0 ∑Fy=0 S3+S2sin45°=0 解得：S3=-62.5kN S4=62.5kN 取D点：∑Fx=0 S6+S5cos45°-S1=0

FRB =87.5kN ∴

∑Fy=0 -S3-S5sin45°=0 解得：S5=88.4kN S6=-125kN 取F点：∑Fx=0 S8-S6=0 ∑Fy=0 -P1-S7=0

解得：S7=-100kN S8=-125kN

取E点：∑Fx=0 S9cos45°+ S10-S5cos45°-S4=0 ∑Fy=0 S7+S5sin45°+ S9sin45°=0 解得：S9=53kN S10=87.5kN 取G点：∑Fx=0 S12cos45°-S10=0 ∑Fy=0 S12sin45°+ S11=0 解得：S9=-87.5kN S10=123.7kN 取H点：∑Fx=0 S13-S8-S9sin45°=0 ∴S13=-87.5kN

4-34解：取整体：∑MA=0 -FRA×6a+G×(5a+4a+3a+2a+a)=0 ∴FRA=2.5G

∑Fy=0 FRA +FRB +5G=0 ∴FRB=2.5G 取A点：∑Fx=0 S1+S2cos45°=0 ∑Fy=0 S2sin45°+FRA=0 解得：S1=2.5G S2=-3.54G 取C点：∑Fx=0 S4-S1=0 ∴S4=2.5G ∑Fy=0 S3-G=0 ∴S3=G 截面Ⅰ-Ⅰ，取左半部分

∑Fy=0 S5sin45°+FRA-3G=0 ∴S5=0.707G ∑MD=0 -FRA×4a+G×3a+G×2a+G×a+S6×a=0 ∴S6=4G