• Structural Engineering and Mechanics
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• v.60 no.1
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• pp.51-69
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• 2016

A large number of welded steel moment-resisting framed (SMRF) structures failed due to brittle fracture induced by ductile fracture at beam-to-column connections during 1994 Northridge earthquake and 1995 Kobe (Hyogoken-Nanbu) earthquake. Extensive research efforts have been devoted to clarifying the mechanism of the observed failures and corresponding countermeasures to ensure more ductile design of welded SMRF structures, while limited research on the failure analysis of the ductile cracking was conducted due to lack of computational capacity and proper theoretical models. As the first step to solve this complicated problem, this paper aims to establish a straightforward procedure to simulate ductile cracking of welded joints under monotonic tension. There are two difficulties in achieving the aim of this study, including measurement of true stress-true strain data and ductile fracture parameters of different subzones in a welded joint, such as weld deposit, heat affected zone and the boundary between the two. Butt joints are employed in this study for their simple configuration. Both experimental and numerical studies on two types of butt joints are conducted. The validity of the proposed procedure is proved by comparison between the experimental and numerical results.

• Smart Structures and Systems
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• v.20 no.2
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• pp.219-229
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• 2017

Outlier detection is an imperative task to identify the occurrence of abnormal events before the structures are suffered from sudden failure during their service lives. This paper proposes a two-phase method for the outlier detection of Global Positioning System (GPS) monitoring data. Prompt judgment of the occurrence of abnormal data is firstly carried out by use of the relational analysis as the relationship among the data obtained from the adjacent locations following a certain rule. Then, a negative selection algorithm (NSA) is adopted for further accurate localization of the abnormal data. To reduce the computation cost in the NSA, an improved scheme by integrating the adjustable radius into the training stage is designed and implemented. Numerical simulations and experimental verifications demonstrate that the proposed method is encouraging compared with the original method in the aspects of efficiency and reliability. This method is only based on the monitoring data without the requirement of the engineer expertise on the structural operational characteristics, which can be easily embedded in a software system for the continuous and reliable monitoring of civil infrastructure.

• Earthquakes and Structures
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• v.18 no.5
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• pp.581-598
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• 2020

This paper aims to investigate the seismic behavior and influence parameters of the large-scaled thin-walled reinforced concrete (RC) tubular columns in air-cooled supporting structures of thermal power plants (TPPs). Cyclic loading tests and finite element analysis were performed on 1/8-scaled specimens considering the influence of wall diameter ratio, axial compression ratio, longitudinal reinforcement ratio, stirrup reinforcement ratio and adding steel diagonal braces (SDBs). The research results showed that the cracks mainly occurred on the lower half part of RC tubular columns during the cyclic loading test; the specimen with the minimum wall diameter ratio presented the earlier cracking and had the most cracks; the failure mode of RC tubular columns was large bias compression failure; increasing the axial compression ratio could increase the lateral bearing capacity and energy dissipation capacity, but also weaken the ductility and aggravate the lateral stiffness deterioration; increasing the longitudinal reinforcement ratio could efficiently enhance the seismic behavior; increasing the stirrup reinforcement ratio was favorable to the ductility; RC tubular columns with SDBs had a much higher bearing capacity and lateral stiffness than those without SDBs, and with the decrease of the angle between columns and SDBs, both bearing capacity and lateral stiffness increased significantly.

• Structural Engineering and Mechanics
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• v.26 no.3
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• pp.263-276
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• 2007

Steel frame structures have been widely used in multi-storey and high-rise buildings and the connections in these structures are critical. In the Northridge and Kobe Earthquake, beam-column connections suffered damage due to brittle fracture. According to seismic design codes, ductility of the beam to column connection is also necessary. A study on the behavior of a beam to column connection with the aim of improving ductility as well as preventing brittle failure was carried out. In order to control the position of a plastic hinge on the beam, a connection with a hole in the beam web was developed. Five specimens with different parameters under cyclic load were assessed. The results are presented in terms of the stress distribution of the beam, hysteretic behavior, and ultimate capacity. Furthermore, the finite element method was also used to analyze the model, and the results were compared with those obtained from the experiment. It is shown from the analysis and experimental results that this type of connection is effective in terms of improving ductility for a beam to column connection in low-rise buildings.

• Earthquakes and Structures
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• v.13 no.5
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• pp.455-464
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• 2017

This paper develops a new method for analyzing the structural seismic behavior of single-layer reticulated shells based on exponential strain energy density (ESED). The ESED method reveals a characteristic point from a relationship between ESED sum and peak seismic acceleration. Then, the characteristic point leads to an updated concept of structural failure and an ESED-based criterion for predicting structural failure load. Subsequently, the ESED-based criterion and the characteristic point are verified through numerical analysis of typical single-layer reticulated shells with different configurations and a shaking table test of the scale shell model. Finally, discussions further verify the rationality and application of the ESED-based criterion. The ESED method might open a new way of structural analysis and the ESED-based criterion might indicate a prospect for a unified criterion for predicting seismic failure loads of various structures.

• Steel and Composite Structures
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• v.18 no.3
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• pp.793-809
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• 2015

In this scientific work, constructing of a novel shear deformation beam model including the stretching effect is of concern for flexural and free vibration responses of functionally graded beams. The particularity of this model is that, in addition to considering the transverse shear deformation and the stretching effect, the zero transverse shear stress condition on the beam surface is assured without introducing the shear correction parameter. By employing the Hamilton's principle together with the concept of the neutral axe's position for such beams, the equations of motion are obtained. Some examples are performed to demonstrate the effects of changing gradients, thickness stretching, and thickness to length ratios on the bending and vibration of functionally graded beams.

• Proceedings of the Korea Concrete Institute Conference
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• 2006.11a
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• pp.365-368
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• 2006

RBSN Method, Rigid-Body-Spring Network Method, is a structural analysis method that overcomes the problems faced in FEM analysis of concrete or crack forming structures. In RBSN, irregular lattices are used to model structural components consisting of bulk material, curvilinear reinforcements, and their interfaces. Because reinforcements and their interfaces in the bulk material are freely positioned, meshing is irrespective of the geometry of the representing bulk material. In this paper, RBSN method of 3D is applied in simulating the pull-out test of FRP (Fiber Reinforced Polymer) embedded in concrete. The comparison of analysis results to experimental results shows that RBSN method simulates the shear-slip behavior very precisely. From the analysis results, 3D RBSN method is proven to be an effective and accurate analysis method for concrete structural analysis. Also, the results show that RBSN method can be a potential analysis method for concrete structures that can replace the current FEM analysis.

• Steel and Composite Structures
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• v.25 no.6
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• pp.705-716
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• 2017

The objective of this study is to investigate the actual behavior of studs in structures under earthquake load through laboratory tests and numerical simulation. A test program including eighteen specimens was devised with consideration of different concrete strengths and stud diameters. Six of specimens were subjected to monotonically increasing loading while the others were subjected to cyclic loading. Mechanical behavior including the failure mechanism, load-slip relationship, stiffness degradation, energy dissipation and the damage accumulation was obtained from the test results. An accurate numerical model based on the ABAQUS software was developed and validated against the test results. The results obtained from the finite element (FE) model matched well with the experimental results. Furthermore, based on the experimental and numerical data, the design formulas for expressing the skeleton curve were proposed and the simplified hysteretic model of load versus displacement was then established. It is demonstrated that the proposed formulas and simplified hysteretic model have a good match with the test results.

• Steel and Composite Structures
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• v.33 no.3
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• pp.433-444
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• 2019

Fatigue failure of a grid structure using bolt-sphere joints is liable to occur in a high-strength bolt due to the alternating and reciprocal actions of a suspension crane. In this study, variable amplitude fatigue tests were carried out on 20 40 Cr steel alloy M30 high-strength bolts using an MTS fatigue testing machine, and four cyclic stress amplitude loading patterns, Low-High, High-Low, Low-High-Low, and High-Low-High, were tested. The scanning electron microscope images of bolt fatigue failure due to variable amplitude stress were obtained, and the fractographic analysis of fatigue fractures was performed to investigate the fatigue failure mechanisms. Based on the available data from the constant amplitude fatigue tests, the variable amplitude fatigue life of an M30 high-strength bolt in a bolt-sphere joint was estimated using both Miner's rule and the Corten-Dolan model. Since both cumulative damage models gave similar predictions, Miner's rule is suggested for estimating the variable-amplitude fatigue life of M30 high-strength bolts in a grid structure with bolt-sphere joints; the S-N fatigue curve of the M30 high-strength bolts under variable amplitude loading was derived using equivalent stress amplitude as a design parameter.

• Smart Structures and Systems
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• v.15 no.1
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• pp.41-55
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• 2015

This study proposes a laser based impedance measurement system and impedance based pipe corrosion and bolt-loosening monitoring techniques under temperature variations. For impedance measurement, the laser based impedance measurement system is optimized and adopted in this paper. First, a modulated laser beam is radiated to a photodiode, converting the laser beam into an electric signal. Then, the electric signal is applied to a MFC transducer attached on a target structure for ultrasonic excitation. The corresponding impedance signals are measured, re-converted into a laser beam, and radiated back to the other photodiode located in a data interrogator. The transmitted impedance signals are treated with an outlier analysis using generalized extreme value (GEV) statistics to reliably signal off structural damage. Validation of the proposed technique is carried out to detect corrosion and bolt-loosening in lab-scale carbon steel elbow pipes under varying temperatures. It has been demonstrated that the proposed technique has a potential to be used for structural health monitoring (SHM) of pipe structures.