Abstract: A bi-steel ladder framework is formed by two parallel longitudinal reinforcements and short transverse reinforcements plumbing longitudinal reinforcement.In theory adopting bi-steel technique can improve bonding function between reinforcement and concrete and decrease width and space of cracks of bending member,thus producing fine cracks appear slight and dense.However,at present bi-steel is made from cold-drawn wire or cold-rolled ribbed steel,and is often used in some members such as small span one-way concrete slab,lintel and stairs.The study on bisteel made of Ⅲ grades big-diameter hot rolled ribbed steel has not been reported at present in China and abroad.In order to take enough advantage of bi-steel and extend application,it is analyzed the bi-steel structure which is welded by hot rolled ribbed steel,and emphasized the methods of calculating the cracking and deformation,and also analyzed the feature of cracking completely.At the same time,it is presented the suggested formula of calculating cracks on a bi-steel concret structure with hot rolled ribbed steel by the observation and theoretical analysis.A nice technical and economic benefit may be got by comparing it with common beam.