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Fatigue strength of glued anchorage of reinforcement bars of A500C class Shutenko L., Zolotov M., Sklyarov V. Kharkov National Academy of Municipal Economy 61002, Ukraine, Kharkov, Revolution st., 12 Email: zolotov@ksame.kharkov.ua Due to the use of a new assortment of reinforcement steel of crescent section [1] in construction in Ukraine experimental investigation on determining longterm strength of the anchorage of reinforcement bars of A500C class into concrete using acrylic glues of different compositions [2, 3] under the influence of shortterm and longterm pulling efforts have been carried out by the authors. The urgency of this investigation was caused by considerable difference of geometric and physical characteristics of reinforcement of AIII class applied before from modern reinforcement of A500C class. As a result of the experiments the depth of reinforcement bars embedment and their deformation ability under mentioned types of loads have been determined. The depth of anchorage of reinforcement bars of A500C class into concrete using ordinary glues (the strength at pressure R_{с}_{omp} = 70…75 MPa, at shear R_{tens} = 21…24 MPa) l_{anch} = 22,5d_{s} (where d_{s} – a bar diameter), and with the use of special modified agents (R_{с}_{omp} = 90…98,6 MPa, R_{tens} = 32…37 MPa) – l_{anch} = 17,5d_{s}. Under longterm influence of calculated load the displacement of unloaded end of the anchored bar end into concrete is not more than 100 microns. In connection with the use of mentioned above reinforcement in reinforced concrete structures under dynamic influence experimental investigation on determining fatigue strength of glued anchorage of reinforcement bars of A500C class have been carried out by the authors. Six batches of samples have been made for carrying out experiments on determining the influence of cycles frequency and asymmetry coefficient. Each batch consisted of five samples of anchor joint. A sample of anchor joint consisted of a concrete cube and a reinforcement bar with the diameter d_{s} = 16 mm of A500C class. Acrylic glue of ordinary compositions and modified glue with increased adhesive and cohesive strength have been applied for the anchorage of bars. The process of hardening lasted not less than ten days at the environment temperature 1518^{0}C. The anchorage depth was determined according to [2, 3] and l_{anch} = 17,5d_{s }was equal to 280 mm using modified acrylic glues and l_{anch} = 22,5d_{s} was equal to 360 mm using glues of ordinary compositions. Testing for determining fatigue strength of glued anchorage of reinforcement rolling of A500C class was carried out using pulser ЦДМПу 100 [4]. The scheme of testing of anchor joints under dynamic load is given in the fig. 1, 2. The maximum stress on the loaded end of embedded part of an anchor according to construction standards was equal to σ_{max} =300 MPa and the minimum – σ_{min} = 150 and σ_{min} = 100 MPa and the asymmetry coefficient of a cycle was accordingly equal to ρ = 0,5 and 0,33. Pulling efforts were accordingly equal to Ρ_{max} = 60 kH and Ρ_{min} = 39 and 20 kH. Testing was carried out at frequency of applied load equal = 600, 420 and 250 cycles/min., most frequently occurring when maintaining reinforced concrete structures.
was equal = 600, 400 and 250 cycles/min, most frequently occurring when maintaining reinforced concrete structures. The first loading of a sample by dynamic load has been carried out to 330 cycles, then the sample was loaded with the full cycle stepwise with the further endurance at each step of loading. The samples of anchor joints were loaded from 0 to 20 kH with the further endurance and reading an instrument of relative deformation and loading control. Further loading was carried out from 20 to 40 kH and then from 40 to 60 kH. After that a sample loading continued to 500 cycles and then stepwise loading of a sample with full cycle of loading from 0 to σ_{max} and with deformation measurement was carried out. Such testing of samples was carried out using a step of 500 cycles and static stepwise loading until the base number of the cycles of dynamic loading 2 10^{6} has been achieved. After that the number of cycles was increased to 6 10^{6}. In all, six batches of samples of glued anchorage of reinforcement of A500C class have been tested. Each batch consisted of five samples of anchor joint.
fig. 2 – General view of the installation for investigating effort stability of preliminary tightening under dynamic load in case of using a strip layer for the frame bearing and concrete foundation The results of the experiments are the following. Under the action of repeated pulling efforts (taking into account the characteristics of an actions cycle, asymmetry coefficients of a cycle of a glue elasticity modulus, the depth of a bar embedment) no destruction of glued anchorage of reinforcement bars has been observed. It can be explained by lower elasticity modulus of acrylic glue (4…10 times lower than elasticity modulus of concrete and reinforcement) and it offers damping resistance to oscillations. After endurance test of glued anchor samples they were destructed by shortterm static load. The destruction of all samples took place along the reinforcement bar [5]. But remainder strength was different. It depended on elasticity modulus of acrylic glue. The number of loading cycles and an asymmetry coefficient of a cycle had less influence. So, when the elasticity modulus of acrylic glue was E_{k} = 5,2 10³ MPa the remainder strength of a reinforcement bar was σ_{b} = 588 MPa, E_{k} = 6,8 10³ σ_{b} = 582 MPa, E_{k} = 9,6 10³ σ_{b} = 563 MPa, E_{k} = 10,4 10³ σ_{b} = 560 MPa and E_{k} = 12,2 10³ σ_{b} = 557 MPa. On the basis of the experimental data obtained one can come to the conclusion that the use of acrylic glues for the anchorage of reinforcement bars of A500C class provides the necessary strength and reliability of anchor joints.

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