STRENGTH OF BUTT WELDED BUTT JOINT OF REINFORCEMENT OF CLASS A500C

The paper presents the results of experimental studies of the strength of cross-shaped welded joints of types К1-Кт and К3-Рр [1] of thermomechanically hardened reinforcement of class A500C [2] for hardening during welding of the main bar [3]. Experimental studies included testing three series of samples of welded joints and reinforcement samples in the initial state. The first series included testing welded joints of type К1-Кт to strengthen the main bar during welding. Reinforcement Ø14A500С was accepted as the main (working) bar, and reinforcement Ø12A500С and Ø8A240С were accepted as the transverse bar. For each joints, 6 samples were tested on the lower and upper limits of the carbon equivalent values of the grade steel class Ст3пс, 0.245% and 0.346%, respectively. The second series included testing of welded joints of the K3-Pp type to strengthen the main bar during welding. To directly compare the test results of different types of cross-shaped welded joints, the diameter of the main and transverse rods, the number of samples and the  value of equivalent were the same as in the first series. The third series included testing welded joints of type К1-Кт for cutting. Reinforcement Ø14A500С was taken as a longitudinal bar, and reinforcement Ø12A500С and Ø8A500С was taken as a transverse rod. For each joints, 12 samples were tested at the lower and upper limits of the carbon equivalent values. As a result of testing samples of welded joints of types К1-Кт and К3-Рр of reinforcement A500C for strengthening during welding, it was established that the destruction occurs along the main bar and in the zone of thermal exposure, the amount of hardening was up to 4% for the К1-Кт compound, and for the К3-Рр type connection - 4... 10%. Failure of samples of welded joints of type К1-Кт reinforcement A500C with reinforcement Ø12A500C and Ø8A240C during the cut test usually occurred in the zone of thermal exposure, or in some cases, in the presence of both rods from reinforcement of class A500C - directly at the welding site. The average value of cut strength for a sample of 24 samples of reinforcement connections of class A500C with reinforcement A240C was 356.5 MPa, or 0.89 of the temporary resistance of the reinforcement in the initial state, with a coefficient of variation - 0.08 and a span of 107.4 MPa. The average cut strength for a sample of 24 samples of reinforcement connections of class A500C with reinforcement A500C was 541.1 MPa, or 0.80 of the temporary resistance of the reinforcement in the initial state, with a coefficient of variation – 0.152 and a span of 280.0 MPa. The first series included fittings Ø12A500C, Ø14A500C, Ø16A500C from steel of the ST3ps brand and Ø18A500C, Ø20A500C, Ø22A500C from steel of the Ст3пс brand. A total of 278 samples of welded joints were tested. The second series included samples of C1-Co welded joints from the rest of the nomenclature of diameters and grades of steel reinforcement class A500C, namely Ø16A500C from steel grade St3ps, Ø20A500C, Ø22A500C from steel grade St3Gps and Ø25A500C, Ø32A500C, Ø32A500C, Ø32A500C. For each of the diameters, 6 samples were tested in the initial state and 6 samples of C1-Co welded joints. It was found that the destruction of the butt contact connection type C1-Co thermomechanically reinforced reinforcement class A500C of all diameters, from 12 to 32 mm, and steel grades, takes place in the zone of thermal impact and is plastic. Experimental data on the strength of the butt contact weld type C1-Кo reinforcement class A500C for the entire range of diameters and grades of steel produced in Ukraine. It is established that the greatest degree of hardening within 19-20% takes place at diameters of armature of 12… 16 mm from steel of the Ст3пс brand, at diameters of armature of 18… 22 mm from steel of the Ст3Гпс brand of marking made 15-17%, and at diameters of 25… 32 mm from steel of the 25Г2С brand - 2,5… 8%.