Hot Spot Stress Method Research Articles

An Evaluation of the Use of Fracture Mechanics Techniques for the Design of Orthotropic Decks

Although the use of fracture mechanics based techniques in the evaluation of fatigue resistance in civil engineering has expanded steadily, it’s application in the field of orthotropic bridge decks remains very small. This is remarkable, since especially orthotropic decks have numerous fatigue prone details, which could benefit from a fracture mechanics based approach, or alternatively from the hot spot stress method. Currently, all international design guidelines for orthotropic plated bridge deck are based on a traditional nominal stress S-N approach and Miner’s Rule, and, although suggested by various in field designers and bridge owners, a fracture mechanics approach is currently limited to academic research. The paper gives an overview of current practice in the field, as well as an overview of attempts made academic researchers to apply fracture mechanics techniques. The available literature suggests that the lack of implementation of fracture mechanics results from a combination of factors including the lack of experience with these methods, conservatism, but also the complexity of geometry and loading conditions resulting in numerous variables. This paper may contribute to the implementation of modern fracture mechanics based techniques in this field by pointing out the opportunities and warning for the difficulties.

SIZE EFFECT OF WELDED THIN-WALLED TUBULAR JOINTS

This paper clarifies the terminologies used to describe the size effect on fatigue behavior of welded joints. It summarizes the existing research on size effect in the perspective of newly defined terminologies. It identifies knowledge gaps in designing tubular joints using the hot spot stress method, i.e. thin-walled tubular joints with wall thickness less than 4 mm and thick-walled tubular joints with wall thickness larger than 50 mm, or diameter to thickness ratio less than 24. It is the thin-walled tubular joints that are addressed in this paper. It is found that thin-walled tube-plate T-joints do not follow the conventional trend: the thinner the section is, the higher the fatigue life. It is also found that simple extrapolation of existing fatigue design curves may result in unsafe design of thin-walled tube–tube T-joints. The effect of chord stiffness on fatigue behavior of thin-walled tubular T-joints is also discussed.

A Comparative Study on the Fatigue Evaluation for Weldments under Out-of Plane Bending Load Using Structural Stress and Hot Spot Stress

Fatigue strength assessments with two types of load carrying fillet weldment under out-of-plane bending load have been carried out by using both hot spot stress and structural stress methods. Basis for the derivation of structural stress method is discussed in detail. Finite element analyses using shell elements models have been performed for the fatigue strength assessment of weldments. As a result of the fatigue strength evaluation for load carrying transverse fillet weldment, hot spot stress method is found to be consistent with structural stress method as well as measurement. Hot spot stress, however, estimated for the load carrying longitudinal fillet weldment exhibit large variation with respect to mesh size and element type while the calculated structural stress for the longitudinal fillet weldment is relatively independent of mesh size. The fatigue life estimation according to structural stress has been introduced with the master S-N curve.

필릿 용접구조물의 피로해석을 위한 기준응력에 대한 비교 연구 -구조응력 및 핫스팟응력-

Fatigue strength assessments with two types of load carrying fillet weldment under out-of-plane bending load have been carried out by using both hot spot stress and structural stress methods. In this study, a derivation for the structural stress method using shell element models is discussed in detail. Finite element analysis using shell element models have been performed for the assessment of fatigue strength. As a result of the fatigue strength evaluation for load carrying transverse fillet weldment, hot spot stress method is found to be consistent with structural stress method and measurement. Hot spot stress, however, estimated for the load carrying longitudinal fillet weldment exhibit large variation with respect to mesh size and element type while the calculated structural stress for the longitudinal fillet weldment is relatively independent of mesh size. On the other hand, drawbacks and doubts associated with applying the structural stress method such as the guidance of virtual node method have been discussed.

함정용 배전반의 피로강도 향상을 위한 프레임 브래킷의 최적설계

Structural reliability of electrical panels installed in naval vessels is of critical importance from structural performance viewpoint. The electrical panels may be exposed to vibration and fatigue loadings from internal and external sources as well as wave loadings which result into a crack and fracture due to the decrease of fatigue strength. It is also well known that welded joints including brackets within steel structures .such as vessels and bridges are vulnerable against such repeated loadings. This study introduces a preliminary result of the optimized shape of frame bracket consisting of electrical panels in navel vessels against fatigue loading and their fatigue life at brackets of electrical panels by means of hot spot stress and structural stress methods.

Fatigue Tests and Design of Welded T Connections in Thin Cold-Formed Square Hollow Sections Under In-Plane Bending

There is an increased use of thin-walled (t<4mm) hollow sections in the manufacture of lighting poles, traffic sign supports,swing-ploughs, linkage graders, trailers and haymakers. These structures are subjected to fatigue loading. A review of current fatigue design guidelines showed that there is a lack of design rules for nodal joints made up of thin-walled (t<4mm) hollow sections. This paper describes the tests carried out on welded thin-walled (t<4mm) tube-to-tube T-connections made up of square hollow sections under cyclic in-plane bending. Different failure modes were obtained during fatigue testing. The experimental stress concentration factors determined in this investigation were found to be significantly lower than the stress concentration factors from the existing parametric equations from the International Institute of Welding. The design Sr.hs-N curves have been determined for the hot spot stress method from Sr.hs-N data based on both experimental and parametric equation stress concentration factors. Design Sr.hs-N curves have been derived from the fatigue data using least-squares method. The design Sr.hs-N curves derived from the experimental fatigue data are lower than the expected design curve resulting from the current trend for design Sr.hs-N curves for different thicknesses from the International Institute of Welding (IIW) and the International Committee for the Development and Study of Tubular Construction (CIDECT). Three design approaches are proposed for welded T-connections in thin cold-formed square hollow sections under cyclic in-plane bending.

Fatigue design of welded very thin-walled SHS-to-plate joints under in-plane bending

The existing fatigue design S– N curve for SHS-to-plate T-joints under in-plane bending is given in the Canadian Standard, CAN/CSA-S16.1-M89, in terms of the classification method. That S– N curve is however based on the class of longitudinally loaded plates with welded non-load carrying attachments, which are different from the SHS-to-plate T-joints. The increased use of welded thin-walled ( t<4 mm) tubular joints in the road transport and agricultural industry for applications such as lighting poles, traffic sign supports, truck trailers, swing ploughs, haymakers and linkage graders, means that there is a need to develop fatigue design curves for tubular joints where the tube wall thickness is less than 4 mm. This paper aims to determine fatigue design curves for SHS-to-plate T-joints where the thin-walled tubes have a thickness of less than 4 mm. Tube-to-plate T-joints, made up by welding a square hollow section tube to a plate, are tested under fatigue loading. Constant stress-amplitude cyclic loading is applied to these connections as in-plane bending load. Stress concentration factors (SCFs) have been determined from strain distributions obtained using strain gauge measurements. Analysis of the fatigue test data using least squares method is carried out to determine the design curves of the tube-to-plate T-joints under in-plane bending, for both the classification method and the hot spot stress method. A class of 44 is recommended for the classification method. An S r. hs– N curve is proposed, with a recommended SCF of 2.0 for the hot spot stress method.

Neural network-based estimation of stress concentration factors for steel multiplanar tubular XT-joints

The hot-spot stress method for fatigue design of tubular joints relies on the accurate predictions of the stress concentration factors (SCF) at the brace to chord intersection areas. At present, SCFs are predicted based on established empirical equations. An alternative approach using a neural network-based model has been developed in this paper to estimate the SCFs of multiplanar tubular XT-joints. The neural network software, Stuttgart Neural Network Simulator, was used for the purpose. To train and test the network, an SCF database was built up using the finite element method (FEM). The database covers a wide range of geometrical parameters for the XT-joints. Three axial load cases were considered. The geometrical properties of the tubular joints were used as the training input data. The FEM SCFs are used as the training output data. Different network configurations are also tested for the best possible results. The results show that a trained neural network can indeed predict the SCFs for the various load cases with a higher level of accuracy.

Fatigue design of welded aluminum rectangular hollow section joints

Fatigue design methods for welded aluminum joints are reviewed, including various approaches to fatigue life estimation currently adopted in design codes across a range of industrial applications. The applicability of these established methodologies to the fatigue design of automotive space frame structures is critically assessed. The hot spot stress method is identified as the most promising in terms of providing a coherent and comprehensive approach to design. Particular problems related to implementation are considered such as failure sites and determination of appropriate stress concentration factors from physical models, finite element calculations or parametric equations. Preliminary results from finite element stress analyses and fatigue tests are also presented for rectangular hollow sections welded in a T-joint configuration. Recommendations are made for a design methodology for welded rectangular hollow-section joints in aluminum space frames, including use of a single hot spot S–N curve.

Weld profile and thickness effects on fatigue of welded joints applicable to offshore structures: Arockiasamy, M., Reddy, D.V. and Jani, J.S. Conf. Fatigue and Fracture in Steel and Concrete Structures, ISFF '91, Madras, India, Dec 1991 Vol 2 (Oxford & IBH Publishing Co. Pvt. Ltd, New Delhi, India, 1991) 993–1014

The verification of the Master S-N curve approach using an equivalent structural stress parameter, has been carried out for welded joints with different geometries, thickness and loading modes, mainly representative of pressure vessels and piping components. The application of the Master S-N curve to a new field requires the reassessment of the relevant fatigue data, due to different manufacturing conditions, detailing techniques across industries and typical loading modes. In this paper, the referred verification will be further extended by means of available fatigue strength data from large-scale tests of typical bridge structural details, mainly based on girder-type specimens. The reassessment can allow the consideration of loading modes and stress conditions closer to those which develop in actual girder steel bridges. An approach based on experimental S-N data is also useful because it can take into account residual stresses, construction misalignments, local notch and weld bead geometry effects in the estimated fatigue lives. In this manner, the aim is to reassess the robustness and effectiveness of the equivalent-structural stress technique combined with the Master S-N curve approach through the finite element numerical modelling of large-scale tests of welded bridge details subjected to in-plane and out-of-plane loading. The approach is applied to four fatigue test setup programs representative of welded bridge details, which were used as the basis for the establishment of the current nominal S-N curves available in American codes. A performance comparison with the nominal and the hot-spot stress method is carried out. The method proved to collapse nearly 300 datapoints of fatigue failures of welded bridge details into a narrow scatter band.

Model fatigue test result of welded structural element and proposal for fatigue design procedure

For carrying out the fatigue design of welded structures, the design S-N diagram to be used may be prepared either by the joint classification method or by the hot spot stress method. The former has a long history in design of bridge, but it is not so clear how to select the S-N diagram in design of a large marine structure using nominal stress or hot spot stress.In this paper, using the experimental data of the model tests which have been carried out by SR202 Committee of Shipbuilding Research Association of Japan, proposal for fatigue design procedure of plate type structures (bracket, stiffener and doubler pad connections) was discussed.