层板胶合木拱的蠕变屈曲

目的研究蠕变对层板胶合木拱的稳定承载力的影响规律．方法通过建立层板胶合木的蠕变本构模型，推导应力-应变的迭代计算公式，结合ABAQUS有限元软件，编制描述胶合本蠕变行为的用户材料子程序UMAT，提出判断拱发生蠕变屈曲的双重条件，用有限元法分析不同跨度、矢跨比和截面规格的层板胶合木拱的蠕变屈曲特性．结果得到了层板胶合木拱的荷载水平与蠕变屈曲临界时间呈指数衰减的关系．当荷载水平为40％时，蠕变屈曲临界时间接近15N；当荷载水平为35％时，蠕变屈曲临界时间增大到接近60N；蠕变屈曲承载力-临界时间曲线在35％的荷载水平处出现一条水平渐进线，荷载水平在35％以下，木拱不会发生蠕变屈曲．结论层板胶合木拱蠕变屈曲临界时间只与荷载水平相关，不受跨度、矢跨比和截面规格的影响．胶合木拱的长期稳定荷载为瞬时稳定荷载的35％．

Creep Buckling of Glulam Arches

Creep constitutive model of glulam is developed and the related iteration formula for stress and strain is derived. The model is incorporated into the commercial FE software ABAQUS and a user defined material subroutine UMAT is encoded. The double creep buckling criteria are used to make correct judgment of buckling of Glulam arches. Creep buckling analysis of the arches is then conducted, taking the effects of span, ratio of rise to span and cross-sectional dimensions into account. The exponent-decay relationship between the buckling load and critical time is thus revealed. When load level is 40%, the critical buckling time is about 15 years;while the load level is 35% ,the critical buckling time becomes about 60 years. There is a horizontal asymptote on the curve of load level versus critical buckling time. Creep buckling will not occur when load level is under the asymptote. The critical buckling time is only affected by the load level, and it has nothing to do with the span, ratio of rise to span, and cross-section dimension of arch. Therefore the long-term buckling load for wood arch is 35 % time of instantaneous buckling load.