基于DOL强度衰减模型的古建筑木桁架的剩余寿命预测

Residual Life Prediction of Historic Timber Truss Based on Strength Degeneracy Model

有效分析古建筑木结构长期抗力随时间变化的规律,至少要考虑木材的持续荷载效应,温湿度变化和腐朽虫蛀等因素的影响。在Gerhards损伤积累模型的基础上推导了恒载长期作用下木材残余强度的衰减模型,并应用该模型对一榀具有100年历史的古建筑木桁架的剩余寿命进行了预测。研究结果表明:恒载作用下的持续荷载效应引起木材的强度降低是有限的,构件失效是由于木材蠕变引起的过大变形造成的,减小恒载长期作用对构件抗力的影响的有效办法是减小过大变形和构件的应力水平;该木桁架的剩余寿命为30年左右,若同时考虑其他因素对结构抗力的影响,该桁架已处于危险状态,需要维修加固。

These factors must be considered such as load-duration effect, moisture content and temperature change, decay and termite attack etc. in order to obtain the relation between the long-term resistance of the historic timber structure and time. The strength degeneracy model of timber member was deduced under constant load based on the Gerhards damage accumulation model. Then the load -duration effect on the resistance of a 100-years historic timber truss under constant load was analyzed by the strength degeneracy model without regard to the other factors＇ change during the service life. Finally the strength degeneracy model was used to predict the residual life of the truss. The results indicates that the load-duration effect on the structural lumber under constant load is limited, and that it is large deformation that induces the member＇s damage, and the effective method to decrease the load-duration effect is to reduce the large deformation and stress level; although its residual life is about 30 years the truss has been in danger and should be repaired and strengthened because timber decay, termite attack, dry shrinkage crack and some critical pulses such as earthquake and hurricane also decrease the truss＇s resistance.