60.螺钉受力如图所示,已知螺钉和钢板的材料相同,拉伸许用应力[σ]是剪切许可应力[t]的2倍,即-|||-[ alpha ] =2[ pi ] ,钢板厚度t是螺钉头高度h的1.5倍,则螺钉直径d的合理值为 () 。-|||-D-|||-d-|||-TF-|||-题60图-|||-A. d=2h-|||-B. d=0.5h-|||-C. ^2=2Dt-|||-D. ^2=0.5Dt