Research Into Some Problems In The Design Of Parallel Strings Steel Roof Truss

State building standard atlas"parallel strings steel roof truss of light roofing"(08SG510-1)is compiled according to the new code,and basically has continued to use the former design thinking,did not take it roof trusses bottom chord's tense or compressive stress caused by the crane loads or wind loads and the impact of the horizontal thrust produced by elastic elongation of bottom chord caused by the vertical loads to the support component into consideration.This article has carried on the concrete analysis and computation to the above questions,and obtains the following conclusions:①The crane's main impact on the roof truss is making the end of bottom chords compressed.As to single-span frame,the impact can be ignored.In double-span frames,when the crane hoisting capacity Q<20t,the crane load didn't make a difference basically;but when the crane hoisting capacity Q≥20t,bottom chords at the end of roof truss compress more obviously and it is necessary to check the stability of bottom chords.②Single-span and double-span single-slope roof trusses do not have to consider the impact of wind loads in the calculation.As to double-span double-slope roof,the wind load impact is negligible when the basic wind pressure is less than 0.6kN/ m~2,but when the basic wind pressure is greater than or equal to 0.6kN/m~2,its wind load effects on roof truss bottom chords should be considered.③When the span and the roofing load are big,under the vertical load function,the roof truss will bring quite great horizontal thrust to the top of pillar in bent frame and the attached internal force at the bottom,which should be separately superposed with the members' internal force caused by the wind load,crane load and under the gravity load function.④Optimizing the design of 18m,24m-span steel roof trusses will allow the roof bars to control stress ratio around 0.8,so the bar can be fully utilized.The results of the interface are about 15% weight reduction,saving much cost.This article proposed some opinions to the design and calculation of standard atlas 05G515,which are helpful to the designers and constructors to make effective use of this atlas.At the same time,further experience for the truss engineering design in the future is accumulated.