目前在钢筋混凝士及预应力钢筋混凝土桁架设计中,对上弦附加弯矩产生的次应力是估计不足的。在预应力桁架中,由于预应力张拉时,屋架向上起拱而大大减少了由于垂度所引起的上弦附加弯矩;对非预应力析架,当所用钢筋应力不高,屋架刚度较大时,由屋架垂度而引起的上弦附加弯矩可能不大,但是在某些钢筋应力较高的屋架中,上弦 At present, in the design of reinforced concrete and prestressed reinforced concrete trusses, the secondary stress generated by the additional bending moment of the upper winding is underestimated. In prestressed trusses, due to prestressing, the truss arches upwards and greatly reduces the additional bending moment due to sag; for non-prestressed trusses, when the stress of the steel bars used is not high, the truss stiffness is greater. At the moment, the additional bending moment caused by the truss truss may not be large, but in certain truss roofs with high stress, the winding