Discussion on concept design of long span special steel roof structures

This paper deals with the problem about the conceptual design of long span special steel roof structures.For those large-scale buildings with close walls around,the shape factor of the buildings under wind load are often negative,resulting uplift in the roof.For those large-scale buildings wihtout close walls around,the uplift or pressure wind on the roofs should be determined by the roof shape and tis relative position to the wind direction.Cautions should also be paid to the draining problem of special roof to avoid accumulation of water.Thus,the drainage path should be short enough,and water should be led to structual supports and should not be accumulated on the end of suspending elements.whether a roof structure is a space structure or a plain one is determined by the force in the roof.A roof structure with mainly bending effect can be considered as a plain roof,and its ratio of span and thickness is large.A spatial roof typically is formed by the effects of compression and tension,and the span to depth ratio is relatively small.Cast-steel nodes can be used where there are more members and the angles between neighboring members are small.Cast-steel nodes can have less stress concentration.For those nodes where only a few elements linked together,welding connection can meet the requirement of load-bearing instead of cast-steel node.