ສຽງ​ທີ່​ແບ່ງປັນ

UNIT 18: BRIDGES Page 85 INTRODUCTION Bridges allow us to cross rivers, valleys, and roads. There are many types of bridges. Each type is good for different situations. Bridge engineers must make sure the bridge is strong and safe. STORY 1: Beam Bridges The simplest bridge is the beam bridge. It is a flat, horizontal beam supported at each end by a pier (a strong column). The beam can be made of wood, steel, or concrete. Beam bridges work well for short distances. If the distance is too lo