lower beam

例句：

1. 1.The lower beam of the bridge is in poor condition.
   这座桥的下梁状况很差。
2. 2.The lower beam of the roof is rotting away.
   屋顶的下梁正在腐烂。
3. 3. The lower beam was damaged during the storm.
   暴风雨期间，下梁受损了。