Abstract
Present paper deals with the evaluation of fatigue strength at crack initiation stage in the double angle elements of lattice steel structures. The current construction norms for steel structures do not include check for fatigue strength at crack initiation stage, and the calculation of elements endurance limit does not account actual stress-strain state in stress concentration zones, material deformation characteristics in these areas, and strength properties of steel. Experimental study of the stress-strain state kinetics in the areas of gusset plate breakage of double angle welded joints was carried out by strain gauge method. Results were obtained regarding the stress state stabilization under cyclic loading and stress intensity factor. During cyclic tests, maximum load level varied depending on the yield stress. The formation of fatigue cracks was detected in the zone of gusset plate breakage. The curve at fatigue cracks initiation stage, by deformational fracture criteria at 'stiff' loading, was described by the equations presented in the 'Standards of strength calculation of equipment and pipelines of nuclear power plants'. Calculation analysis of results for number of cycles before fatigue crack initiation has been made and good agreement with test results has been obtained.
Highlights
Welded steel structures and constructions have found wide application in various branches of industry
For steel lattice structures, which operate under cyclic loads, the presence of structural stress concentration, residual welding stresses and initial technological welding defects is characteristic
Operating experience of building structures under cyclic load shows that the elastoplastic material deformation is accompanied with a damage accumulation and leads to the fatigue crack initiation in stress concentration zones [10, 11]
Summary
Welded steel structures and constructions (reservoirs, gas tanks, pipelines, pressure vessels, masts, towers, crane beams, load-bearing structures of industrial buildings, etc.) have found wide application in various branches of industry. For steel lattice structures, which operate under cyclic loads (truss structures of industrial buildings with underslung cranes, bunker structures and unloading racks, towers, masts, power lines supports, etc.), the presence of structural stress concentration, residual welding stresses and initial technological welding defects is characteristic. For design of structural elements considering the operating conditions of such structures, additional analysis of fatigue strength must be performed [06,07]. Operating experience of building structures under cyclic load shows that the elastoplastic material deformation is accompanied with a damage accumulation and leads to the fatigue crack initiation in stress concentration zones [10, 11]
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