| Timber materials are light-weight and environment friendly,however,the mechanical properties of timber are inferior to concrete materials.Due to the defects of the timber itself and the aging characteristics,the timber structure needs regular maintenance and reinforcement.Fiber reinforced polymer(FRP)is widely used in structural reinforcement due to its high strength to weight ratio.Basalt fiber reinforced polymer(BFRP)has attracted much attention in recent years due to its excellent mechanical properties and high economic efficiency.At present,the research on creep behavior of timber structures strengthened with BFRP is not enough,which limits the extension of BFRP reinforcement technology.Based on creep theory,this paper studies the creep properties of timber beams strengthened by BFRP sheets bonded with organic adhesive under the coupling effects of sustained load,temperature and humidity.The timber beams were strengthened by BFRP sheets bonded with inorganic adhesive and the creep behavior of multi-layer BFRP externally bonded timber beams was predicted by simulation.The work of this paper provides suggestions for popularizing the existing BFRP strengthening technology.The effects of temperature,humidity and sustained load on creep behavior of wood beams strengthened with BFRP are studied.Creep tests were carried out under high humidity and dry conditions respectively at high temper ature(50 oC),room temperature(23 oC)and low temperature(-10 oC)with self-made load holding device and environmental test chamber.The creep test lasted 180 days and the residual mechanical properties were tested.The results show that the creep deformation of the reinforced specimens increases with the increase of load level and the residual mechanical properties decrease with the increase of temperature and humidity during the 180-day test period.At 50 oC,cracks appeared in some specimens during creep test,leading to debonding of BFRP sheets.Due to the aging problem of organic adhesive,this paper carried out an experimental study on inorganic adhesive bonded with BFRP to strengthen timber beams.In creep test,the performance of organic adhesive degraded and the BFRP cloth was debonded due to the wet and hot environment.Magnesium oxychloride and alkali slag inorganic adhesive were selected to be used for externally bonded BFRP to strengthen timber beams.The results showed that the resistance of inorganic adhesive to moisture and heat and UV aging was better than that of organic adhesive,and the resistance of magnesium oxychloride to UV aging was better than that of organic adhesive to BFRP.A simulation model of creep behavior of BFRP reinforced beams is established.In order to accurately predict the creep deformation of BFRP-strengthened timber beams under different working conditions,the creep parameters of the strengthened timber beams were obtained based on the Norton-Bailey theory and strain data,and the results were converted into creep coefficients by using COMSOL software.Based on this model and the creep parameters of the BFRP layer,the creep behavior of the multi-layer BFRP sheet reinforced timber beams is predicted,which provides a reference for the actual reinforcement design. |
