单板层积梁弯曲蠕变特性

在自制的弯曲蠕变试验台上对桦木和椴木单板层积梁进行弯曲蠕变试验,蠕变测试采用简支梁中部集中加载的方式。选用的加载应力水平分别为层积梁弯曲极限强度的40%、50%和60%,用百分表记录蠕变数值。实验周期为40～60d。试验结果表明,单板层积梁弯曲蠕变特性受树种、加载应力水平的影响较大,与树种的材性有较大关系:桦木单板层积梁的抗蠕变性能要明显好于椴木单板层积梁;同时,相同树种不同应力状态下,蠕变曲线为非线性的,蠕变过程由于加载应力水平不同而呈不同的规律。蠕变变形量和曲线上的跳跃点随着应力水平的增加有增大的趋势。试验测试过程中,60%应力状态下,椴木单板层积梁在连续加载60d时突然断裂。

Bending Creep Properties of LVL Girders

An experiment was conducted to determine the bending creep of the girders of laminated veneer lumber(LVL)from birch and basswood in a self-designed test bench.The mode of concentrated load on the middle part of simply supported girder was adopted for creep deformation test,and the loading stress levels were selected as forty percent,fifty percent and sixty percent of the ultimate bending strength of LVL girder,respectively,and the creep deformation values were recorded with a centesimal-millimetre watch.The experiment lasted forty to sixty days.Results show that wood species and loading stress level have significant impacts on the bending creep properties of LVL girders.The creep deformation properties of birch LVL girder are obviously better than those of basswood.The creep deformation curves of the same wood species are non-linear under different stresses,exhibiting different changing patterns.Both the creep deformation value and the number of jump points on curves increase with stress level increasing.Basswood LVL girders abruptly ruptured under sixty percent of loading stress after continuously loaded on it for sixty days.