1.单跨静定梁的反力The reactions of single span beams
常见单跨梁 The most common single span beams ：
单跨梁都是由粱和地基按两刚片规则组成的静定结构，因而其支座反力都只有三个，可取全梁为隔离体，由平面一般力系的三个平衡方程求出。
Single span beam is a statically determinate structure composed of beam and foundation according to 2-body rule, there are 3 reaction forces which can be determined by isolating free body and solving the equilibrium equation of forces.
2、内力Internal forces
符 号 规 定 Sign conventions
轴力axial force FN –tensile as positive拉力为正
剪力shear force FS— clockwise as positive 绕隔离体顺时针方向转动者为正
弯矩bending moment M—causing tension in the lower fibers-positive 使梁的下侧纤维受拉者为正