This paper extends the model of beam with overhang to combined structure of rods and beam , introduces the Green's function and calculates the static deflection of two -span beam.When the parameter EA of two rods tends to infinity , that is to say the rods turned into rigid ones, the combined structure of rods and beam comes back to the model of beam with overhang again . The extended model of N -span beam with overhangs meets the extended Maxwell's reciprocity principle.Further more, the calcu-lation formula to the number of subsection functions pair of Green's function is given .%把外伸梁的模型推广为杆梁组合结构，引入格林函数，计算推广后的两跨梁的静挠度，当两杆的 EA趋于无穷大，即成为刚性杆时，推广后的杆梁组合结构即可回到外伸梁的模型。推广后的 n跨外伸梁满足推广后的麦克斯韦尔互易原理，并给出了满足互易关系的格林函数分段函数对数目的计算公式。
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