Experimental Study On Fatigue Performance Of Anchor Bolts In External Thermal Insulation System Of Concrete Walls

The external thermal insulation technology of building is an effective way to achieve building energy conservation.However,with the popularization of concrete external insulation system,the problem of cracking and falling off of external thermal insulation panels has continued to emerge.The main reason is caused by the lack of tensile bearing capacity of external insulation anchor bolts or the fatigue damage of anchor bolts under wind load.Therefore,studying the tensile bearing capacity and fatigue performance of the external thermal insulation anchor bolts is of great significance to improve the safety and durability of the external thermal insulation system of concrete external walls.In this paper,the tensile bearing capacity and fatigue performance of the anchor bolts in the external thermal insulation system of concrete exterior wall are studied by combining experimental research,numerical simulation and statistical analysis,and then the safety performance and fatigue life of the external thermal insulation system are evaluated.The main contents and conclusions are as follows:(1)The tensile test and fatigue test of the anchor bolts in the external thermal insulation system of concrete external walls were carried out.The tensile test and fatigue test were carried out on the anchor bolts with different strength bases,different anchoring depths,different types and different cyclic load peaks to study their tensile bearing capacity and fatigue performance.The results show that the standard value tensile bearing capacity of anchor bolts increases with the increase of anchoring depth and concrete strength,and the tensile bearing capacity of percussive anchor bolts is the largest.The fatigue times of the anchor bolts are negatively correlated with the peak cyclic load,and the fatigue times decrease greatly in the peak cyclic load section of 0.2F-0.6F.The fatigue times of the anchor bolts are greatly affected by the fatigue load.In the peak period of 0.2F-0.8F cycle load,the maximum difference between the fatigue times is 72 times.(2)The variation law of the load-displacement curve and tensile bearing capacity of the anchor bolts in the external insulation system of concrete exterior wall were explored.The finite element software ABAQUS was used to numerically simulate the anchoring performance of the anchor bolts in the concrete base.Parametric analysis was carried out by changing the anchoring depth,concrete strength and the distance between the anchor bolts.The variation law of the load-displacement curve and the tensile bearing capacity of the anchor bolts under different conditions were compared and analyzed.The results show that the numerical simulation results of the tensile bearing capacity of the anchor bolts are in good agreement with the experimental results,and the errors are all within 10%.The anchoring depth,the strength of concrete and the distance between anchor bolts are negatively correlated with the descending speed of the load-displacement curve after the peak load,and positively correlated with the tensile bearing capacity of anchor bolts.When the distance between anchor bolts is 60 mm,there is overlap area in the adjacent tensile cone range of concrete base.(3)The fatigue life evaluation method of the anchor bolts in the external thermal insulation system of concrete external walls has been established.Based on the fatigue test data of the external thermal insulation anchor bolts,the S-N curve of the anchor bolts was obtained,and the actual wind speed was analyzed by frequency and the wind pressure height variation coefficient was considered to obtain the cumulative damage value of the anchor bolts at different heights and different anchoring depths.And then through the fatigue damage theory evaluated the fatigue life of anchor bolts.The results show that the fatigue times of the anchor bolts decrease with the increase of the building height.When the anchoring depth is35 mm,the fatigue times of the anchor bolts at a height of 100 m from the ground are reduced by 26.5% compared with the anchor bolts at a height of 20 m from the ground.The fatigue life of the anchor bolts increases with the increase of the anchoring depth.When the anchoring depth is 65 mm,the fatigue life of the anchor bolts is about 5.6 times that at the depth of55 mm.