Joints In Steel Structures Research Articles

Impact fracture energy of structural steel welds constructed at low ambient temperatures

Welding at low atmospheric temperatures is frequently needed for the construction of steel structures in cold regions. In this work, the Charpy impact test in parallel with metallurgical observation was carried out to evaluate the low temperature impact fracture energy of structural steel welded joints constructed at low ambient temperatures. The impact fracture energy at low temperatures of structural steel joints welded at room temperature was also investigated for comparison. Standard V-notch Charpy impact specimens were prepared and tested under dynamic loading condition. The effects of low climatic temperatures during welding on the low temperature impact fracture energy of structural steel welded joints were explored based on the absorbed energies and the microstructures, from which the feasibility of welding in cold weather was assessed. Referring to the results, significant drop of the low temperature impact fracture energy at the heat affected zone occurs due to the rapid cooling effects. Nevertheless, it is confirmed that the impact fracture energy of structural steel welded joints constructed at low ambient temperatures can be guaranteed for use in cold regions provided that proper precautions such as the use of low-hydrogen electrodes and suitable thermal control are taken during the welding process.

Research on performance of high-strength bolted connection in fire and after fire

Experiments on the tensile performance and the shear performance in high temperature and shear performance after fire have been carried out to study the fire-resistant performance of high-strength bolted connection. The experimental research on the shear performance of the connection in high temperature reveals the effect of temperature on the mechanical performance of high-strength bolted steel. A formula for the mechanical performance index can be obtained through a comparative analysis. The research on the shear performance of high-strength bolt in high temperature presents the effect of temperature on the bolt's sliding load and limit load. The formula for calculating the sliding load and limit load for shear connection at high temperature can be put forward through a comparative analysis on the basis of the test results. The test results for the shear property of post-firing high-strength bolted connection reveal the change law of the sliding load in different fire temperatures, fire processing methods and types of cooling. Moreover, the calculation formula of the reduction coefficient of the sliding load is given. Research findings provide theoretical basis for research on fire-resistant performance of steel structure joints and the prerequisite for overall fire-resistant design of steel structures and act as an important reference for compiling and revising relevant codes. This paper can promote the improvement and development of fire-resistant design methods of steel structures.

Major factor causing improvement in fatigue strength of butt welded steel joints after laser peening without coating

Laser peening without coating (LPwC) can introduce compressive residual stress to the surface and, therefore, is effective in enhancing the fatigue strength. This study used butt welded structural steel joints to investigate changes in the residual stress and the hardness near the toe of the welded zone and to examine the major factor causing the improved fatigue strength due to LPwC. It is concluded that the generation of compressive residual stress by LPwC is the major factor improving the fatigue strength, because the reduction in compressive residual stress due to stress relief annealing decreased the fatigue strength to the same level as that of butt welded joints without LPwC.

Finite Element Analysis of the Combined Connection with Bolts and Welds

The combined connection with welds and bolds has advantages of both welds and bolts connections, and can be widely used in reinforcing the joint in steel structure. In this paper, the Finite Element Method (FEM) was taken to analyze the carrying capacity of the combined connection with bolts and welds, and the results ware compared with those come from experimental investigation. Further analysis based on FEM ware performed to research the failure mode and bearing performance of the combined connection and the contribution of bolts and welds .Advice was provided for related design.

Proposed Design Method of Combined Connections with Bolts and Longitudinal Welds

The combined connection with welds and bolds can be widely used in reinforcing the joint in steel structure. In this paper, proposed design method of combined connection with bolts and longitudinal welds was given based on the tests and finite element analysis (FEA). The method considers the effect of the strength ratio between bolts and welds. The safety and reliability of the method were verified by FEA and comparison with other design method. The design method can contribute to the promotion of the application of the combined connections.

Analysis of Mechanical Performance Considering Damage Accumulation of Intersecting Joints in Steel Structures

The mechanical behaviors of intersecting joints considering damage accumulation in steel tube structures is analyzed through the FE-program ABAQUS. The stress characteristic and failure modes of these joints are concluded. Especially, it has been analyzed influence of the change of geometric parameters to mechanical behavior of joints. Finally, the results indicate the joints have a good mechanical performance and good plastic deformation as to excessive local buckling of chord under the loads.

Effects of flashing and upset sequences on microstructure, hardness, and tensile properties of welded structural steel joints

In this study, ASTM A529 carbon–manganese steel angle specimens were joined by flash butt welding and the effects of varying process parameter settings were investigated. The resulting weld metal and heat affected zones were examined and further processed using tensile testing, Rockwell hardness testing, ultrasonic scanning, optical microscopy, and scanning electron microscopy with energy dispersive spectroscopy. Test results showed that hardness was increased in the weld zone for all specimens, which can be attributed to the extensive deformation of the upset operation. Statistical analysis of experimental data highlighted the sensitivity of weld strength and the presence of weld zone inclusions and interfacial defects to the process factors of upset current, flashing time duration, and upset dimension. Microstructural analysis revealed various phases within the weld and heat affected zone, including acicular ferrite, Widmanstatten or side-plate ferrite, and grain boundary ferrite. Fractography of tensile specimens indicated brittle cleavage fracture within the weld zone for certain factor combinations. The significance of process factor levels on microstructure, fracture characteristics, and weld zone strength, inclusions, and embrittlement was analyzed.

Study on Influences of Heat Input and Inter-pass Temperature on the Mechanical Properties and the Execution Efficiency of Weld Joints in Steel Structures

Study on Influences of Heat Input and Inter-pass Temperature on the Mechanical Properties and the Execution Efficiency of Weld Joints in Steel Structures

STUDY ON DEFORMATION CAPACITY OF SHOP AND SITE WELDING BEAM- TO-COLUMN JOINTS WITH WELD DEFECT

The weld defect of the welded beam-to-column joint in steel structure causes the brittle fracture and has possibilities to reduce the deformation capacity. It is considered that the effect of the weld defect on the deformation capacity from the difference of between shop and site welding beam-to-column joints is different. Therefore it is important to understand this difference. In this paper, full-scale welding test was done it were shop and site welding beam-to-column joints. Then, the effect of the deformation capacity of test specimens caused by the difference of the position of welding defects between two joint methods was studied. As the results, the deterioration of deformation capacity caused by the welding defect was low using shop welding beam-to-column joints, and high using site welding beam-to-column joints.

Experimental Nonlinear FE Modelling & Eurocode 3 Analyses of Steel Flush Endplate Joints

Structural steel joints form an integral part of all structural steel frames and regardless of the joint type employed the behaviour and response of the joints is of primary importance in determining the manner in which the frame resists both vertical and horizontal loading. An understanding of joint stiffness, strength and ductility is required. Eurocode 3 provides guidance for predicting the ultimate strength, rotational capacity and rotational stiffness of steel flush endplate joints. This paper examines in detail the correlation be-tween Eurocode 3 predictions and actual behaviour recorded in full scale tests and validated numerical mod-els. The detailed three dimensional finite element analysis methods used enable the significant differences to be explained by reference to the initial assumptions made in the Eurocode 3 calculations.

Behavior appraisal of steel semi-rigid joints using Linear Genetic Programming

This paper proposes an alternative approach for predicting the flexural resistance and initial rotational stiffness of semi-rigid joints in steel structures using Linear Genetic Programming (LGP). Three types of steel beam-column joints i.e. endplates, welded, and end bolted joints with angles are investigated. Models are constructed by utilizing test results available in the literature. The accuracy of the proposed models is verified by comparing the outcomes to the experimental results. LGP models are further compared to the corresponding design code (Eurocode 3), reference values and several existing models. The results demonstrate that the LGP based models in most cases provide superior performance than other models.

FEM Analysis Study on Fatigue Strength and Fracture Morphology in Spot Welded Joints of Structural Steels

In this paper, fatigue tests and finite element method (FEM) analyses are carried out on spot welded joints of mild steel (270MPa class) and ultra-high strength steel (980MPa class) in order to investigate the influence of strength level of base steels on fatigue strength and fracture morphology of spot welded joints. From the fatigue tests the following results are obtained : (1) The fatigue limit of spot welded joints is almost the same in both steels. (2) Three-dimensional morphology of crack initiation and growth around a nugget is made clear. (3) The fatigue fracture morphology of spot welded joints depends on the load level in the ultra-high strength steel, but not in the mild steel. From the discussion based on the FEM analyses the following results are obtained : (4) The fatigue limit of spot welded joints can be predicted by stress intensity factors around a nugget, fracture criterion from a mixed mode crack and threshold values for fatigue crack growth in base steels. (5) The plastic deformation around a nugget in spot welded joints strongly affects the fatigue fracture morphology.

European design recommendations for simple joints in steel structures

In the last twenty years, numerous researches have been devoted throughout Europe to the behaviour of semi-rigid and partial-strength joints in steel structures. These efforts progressively led to the publication of normative documents, design recommendation and guidelines and to the development of various design tools for practitioners. On the contrary rather little attention has been paid to the design of simple joints. In this paper, design recommendations for such joints are presented. They result from deep comparative studies of existing national codes and extensive discussions within the Technical Committee 10 “Connections” of the European Convention for constructional Steelwork (ECCS). The publication of this material as “European recommendations for the design of simple joints in steel structures” should be achieved in 2008.

Friction Coefficient in High Tension Bolt Joints Using a Zn/Al Metal Spray Corrosion Resistance Method

In recent years, the friction coefficient decline in the joints of steel structures caused by corrosion has drawn public attention. Therefore, this study investigated the friction coefficient and surface roughness of high tension bolt joints using a Zn/Al metal spraying corrosion resistance method to estimate the application possibility of the Zn/Al metal spraying corrosion resistance method on the joints of steel structures. According to results, the friction coefficient of Zn/Al metal spraying was 0.50 or more. In addition, the friction coefficient increased according to the decrease in surface roughness (Sm/Rz). Therefore, the Zn/Al metal spraying is applicable to a corrosion resistance method for high tension bolt joints.

310 構造用鋼スポット溶接継手の疲労強度と疲労き裂進展の3次元形態(OS4-2 技術革新に向けた新しい材料力学)

310 構造用鋼スポット溶接継手の疲労強度と疲労き裂進展の3次元形態(OS4-2 技術革新に向けた新しい材料力学)

2336 構造用鋼スポット溶接継手における疲労き裂進展形態に及ぼす強度レベルの影響(S07-4 疲労き裂進展,S07 構造材料の疲労強度とき裂進展問題)

2336 構造用鋼スポット溶接継手における疲労き裂進展形態に及ぼす強度レベルの影響(S07-4 疲労き裂進展,S07 構造材料の疲労強度とき裂進展問題)

Experimental behaviour of a steel structure under natural fire

Current design codes for fire resistance of structures are based on isolated member tests subjected to standard fire conditions. Such tests do not reflect the behaviour of a complete building under either normal temperature or fire conditions. Many aspects of behaviour occur due to the interaction between members and cannot be predicted or observed in tests of isolated elements. Performance of real structures subject to real fires is often much better than that predicted from standard tests due to structural continuity and the provision of alternative load paths. This paper reports on the results of a collaborative research project (Tensile membrane action and robustness of structural steel joints under natural fire, European Community FP5 project HPRI—CV 5535) involving the following institutions: Czech Technical University (Czech Republic), University of Coimbra (Portugal), Slovak Technical University (Slovak Republic) and Building Research Establishment (United Kingdom). It consists of an experimental programme to investigate the global structural behaviour of a compartment on the 8-storey steel–concrete composite frame building at the Cardington laboratory during a BRE large-scale fire test, aimed at the examination of the temperature development within the various structural elements, the corresponding (dynamic) distribution of internal forces and the behaviour of the composite slab, beams, columns and connections.

Enhancement of the service life of welded metal structures by high-frequency mechanical peening

We generalize the results of investigations into the high-frequency mechanical peening of welded joints of structural steels of different strength grades and aluminum alloys. As a result, we show the high efficiency of using high-frequency mechanical peening for enhancing the fatigue resistance of welded joints of metal structures at the stages of their manufacture and operation.

P64 構造用鋼スポット溶接継手の疲労強度と疲労き裂進展形態(GS1)

P64 構造用鋼スポット溶接継手の疲労強度と疲労き裂進展形態(GS1)

繰返し大ひずみ負荷後の高張力鋼溶接継手の疲労強度について

Earthquakes cause damages by fatigue at welded joints of steel structures. Structures which were not seriously damaged would be continuously used even after earthquakes. The fatigue strength of those structures, however, might have been decreased due to the cyclic straining during earthquake. In order to clarify the effect of large cyclic straining on the fatigue strength of the welded joint, low cycle fatigue crack propagation test under large straining as well as high cycle fatigue tests after large cyclic straining were performed on welded joint made of 780 MPa class high strength steel. Experimental results showed that the high strength steel welded joint exhibited an excellent fatigue limit characteristic in the case of reversal stressing. However, the fatigue limit is quite sensitive to mean strain. The application of positive mean strain substantially decreased the fatigue limit. Moreover, the cyclic application of large strain caused fatigue crack, which caused the substantial decrease of fatigue strength. The amount of reduction in fatigue limit was larger in the case of high strength steel compared to that in the case of low strength steel.