In case of applying axial tensile force to a high strength bolt, in general, stress is concentrated at the bottom of the threaded portion. As a result, its failure mode is brittle due to lack of ductility. In this study, the mechanical behavior of high strength bolts with waisted shank subjected to axial tensile force has been analyzed numerically by FE analysis considering both material and boundary nowlinearity. Based on these numerical results, an optimal diameter of the waisted shank of the bolts is discussed paying attention to their energy absorption capacity.
A hot spot stress (HSS) concept is expected to be widely used in a fatigue assessment of welded steel structures. In order to investigate an influence of welded attachment size on HSS, finite element analyses were conducted on longitudinally stiffened joints. As a result, it was revealed that weld leg length affects HSS values but not local stress concentration field. Based on this fact, revised two-point extrapolating method for HSS calculation was proposed. In case of a very small stiffener, both the length and height of a stiffener influence HSS. But for a lager stiffener, the influence is saturated. Furthermore, the fatigue strength grades in the existing fatigue design recommendations were compared with the HSS values.
This paper proposes a chemical composition parameter for estimating the heat-affected zone toughness of building column-beam welding. HAZ toughness of steels with various chemical compositions was examined using the one-bead welding proposed by the authors. From the series of tests, the following parameter, fHAz, has been derived. Considering a relationship between toughness of the one-bead welding and that of multi-pass welding, upper bound value of fHAz for maintaining a HAZ toughness level for the standard beam-column multi-pass CO2 arc welding has been determined. fxaz = C+Mn/8+6(P+S)+12N-4Ti≤0.577 ( for vEo(multi-pass welding)≥70J )
A method for evaluation of the horizontal ultimate strength and displacements of steel piers or frames with box sections is proposed. The concept of plastic deteriorating hinge is introduced to the versatile a-e model so that it can be used to study local buckling in pushover analyses. A hardening-softening stress-strain relation is used in a beam element, which has the maximum compressive stress calculated as the buckling stress of a stiffened plate under uniaxial compression. The horizontal ultimate strength and displacement of steel frames will be predicted by finite displacement analyses with linear Timoshenko beams, which give a good approximation of the strain distribution in the beam section.
In low-rise steel structures, tension channels are widely adopted for earthquake resistance. Failures of the tension channels at joints with high-strength bolts have three modes: net section fracture, inner tearing fracture, and end fracture. In the current design method, the ultimate strength of the joints is supposed to be examined only for the net section fractures and the end fractures. But, the design values obtained by this method are not always accurate for edge distances and arrangements of bolt holes. Furthermore, as the inner tearing fractures actually occur in tension channels in addition to these other two fracture types, we need to make a design formula for the inner tearing fracture. In this research, we examine experimentally the effects of the bolt-hole arrangement and edge distance of the bolted joints on the ultimate strength of the tension channels and the failure modes. We propose formulas to predict the ultimate strength of joints for the net section, the inner tearing and the end failure modes.
In order to develop design of the hollow ball joint in roof trusses, tensile tests and Finite Element (FE) analysis were carried out on screw connection, which consist of a bolt and a flat nut subjected to outof- plane bending. Test results show that the ultimate capacity of connection is smaller than calculated value using shear strength of screw in the case of small bending stiffness of nut, which agree well with FE analysis. Based on results of a parametric FE analysis, an assessment of the ultimate tensile capacity of screw connections has shown in the form of a relationship between the ultimate capacity and bending stiffness of nut.