Research On The Durability Of Glued Laminated Timber After Service

In the context of advocating low-carbon environment and promoting green building,coupled with people's increasing demand for returning to nature and improving the quality of life,wood structures are increasingly widely used at home and abroad and have a broad space for development,of which glued laminated timber(glulam)as a typical modern deepprocessed wood is gradually occupying a place in the field of construction engineering.As an important wood composite material used in wood construction,glulam not only retains the natural texture of solid wood,but also has the characteristics of lightweight and highstrength,good structural integrity,flexible finished product specifications,corrosion and flame resistance,etc.It can better use the advantages of wood and overcome its shortcomings,so that the application of wood in the structure is more reasonable.As wood structures are increasingly used outdoors,they suffer from different types of outdoor environments due to different climatic conditions,which places strict requirements on their durability.Therefore,this paper takes glulam as the research object,and investigates the influence laws of apparent wood color,mass variation,size variation,parallel-to-grain elastic modulus,parallel-to-grain compression strength and shear strength under three different environments,namely high temperature environment(with treatment time of 2,4and 6 h and treatment temperature of 60,100,120,160,200 and 240 ? as environmental parameters),salt spray environment(with salt spray corrosion time of 12,24,36 and 48 d as environmental parameters)and freeze-thaw environment(with the freeze-thaw cycles of60,120,180 times as environmental parameters).The results indicates that,(1)For the high temperature environment,with the increase of treatment time and temperature,the glulam color deepened(progression from light brown to brown to dark brown),mass loss rate and volume shrinkage rate tended to increase,parallel-to-grain compression strength increased and then decreased,and shear strength decreased.The compressive properties changed significantly at 160 ?.According to the experimental results,the influence laws of treatment time and temperature on various physical and mechanical properties was analyzed,and it was found that the influence of treatment temperature was greater than that of treatment time.Based on the experimental study,the prediction models of mass loss rate,dimensional shrinkage rate,parallel-to-grain compression strength and shear strength of glulam after high temperature were established,and the prediction expressions of compressive constitutive model and shear constitutive model under the influence of treatment time and temperature were constructed.(2)For the salt spray environment,the physical and mechanical properties of the original material and the aging material under the effect of salt spray corrosion were studied in comparison.The tests showed that the changes in apparent material color,mass growth and volume expansion of the original and aged materials were most obvious at the end of the first salt spray corrosion stage(12 d),while the values indexes increased in the subsequent stages(24,36 and 48 d),but at a smaller rate.Compared with the original material,the physical properties of the aged material changed relatively little after the salt spray corrosion due to the reduction of activity,while the decline of its mechanical properties was more obvious with the increase of salt spray corrosion time.According to the test results,the influence of salt spray corrosion time on the physical and mechanical properties of the original material and the aged material was analyzed.The prediction models for the effects of salt spray corrosion time on parallel-to-grain elastic modulus,parallel-to-grain compression strength and shear strength were established,and the prediction expressions for compressive constitutive model and shear constitutive model under the influence of salt spray corrosion time were constructed.(3)For the freeze-thaw environment,the glulam specimens showed different degrees of tackless phenomenon after freeze-thaw cycles,indicating that the freeze-thaw cycles caused serious damage to the gluing properties of the glulam specimens.The tests showed that the changes in apparent material color,mass growth and volume expansion were most obvious at the end of the first freeze-thaw cycle stage(60 freeze-thaw cycles),while the values indexes increased in the subsequent stages(120 and 180 freeze-thaw cycles),but at a smaller rate.The mechanical properties of glulam showed different degrees of decrease with the increase of the freeze-thaw cycles.According to the test results,the influence of the freeze-thaw cycles on the physical and mechanical properties was analyzed.The prediction models for the effects of salt freeze-thaw cycles on parallel-to-grain elastic modulus,parallel-to-grain compression strength and shear strength were established,and the prediction expressions for compressive constitutive model and shear constitutive model under the influence of freeze-thaw cycles were constructed.