7.6 truss deflections by energy methods aU Castigliano's Second Theorem aPi Area A dU =iF dl dLp Fpdx EA 2 dU= dx 2EA U= 0 2EA 2EA U= N Elastic Inelastic 同停大学 土本2 i=1 2EA 9 Example Ps 0.67P1-0.5P2+1.33P (-0.67P1+05P2-1.33P) (-0.5P1+0.375P2P) N ① 2115 o ③ P2 0.67P1+0.5P2 -1.33P3 P3 e 05P,+0.375P@ (-0.67P1-0.5P2-1.33P3-P) P4+1.33P3 P ⑤ 1、 5 (-P1-P3-P5 器 U= 含F U=1 2EA ((-0.67P1+0.5P2-1.33P3)2+(-0.5P1+0.375P2-P3)21 aU △= +[(-1.33P3)2+(-P3)212+[0.5P1-0.375P2+P3+Ps)23 aP +[0.67P,+0.5P2)2+(0.5P1+0.375P2)]4 +P4+1.33P3)2]5}