steel\guaidian1.m .....\guaidian2.m .....\ks_bilinear.m .....\linear.m .....\main_a20.m .....\main_a20ttt.m .....\main_b20.m .....\main_b20ttt.m .....\main_vidc.m .....\newmark_single.m .....\nonlinear.m .....\response_l.m .....\response_n.m steel