• Journal of the Korea Concrete Institute
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• v.15 no.6
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• pp.856-865
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• 2003

Current design provisions and guide for performance-based design do not accurately evaluate seismic performance of flat plate system. In the previous companion studies, parametric studies using nonlinear finite element analyses were performed to investigate behavior of the flat plate, and based on the numerical results, design methods that can predict the bending moment-carrying capacity and the corresponding deformability of the flat plate was developed. In the present study, a generalized moment-rotation relation of the flat plate was developed based on the previous studies and the numerical analyses. The proposed method was verified by the comparisons with existing experiments. In addition, the effective stiffness of the flat plate corresponding to 0.2 percent of lateral drift that is generally regarded as the serviceability limit was proposed, so as to evaluate conveniently deflection of the structure subject to wind load.

• Steel and Composite Structures
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• v.16 no.2
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• pp.157-185
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• 2014

This paper examines the behaviour of two types of practical open beam-to-tubular column connection details subjected to combined moment, axial and/or shear loads. Detailed continuum finite element models are developed and validated against available experimental results, and extended to deal with flexural, axial and shear load interactions. A numerical investigation is then carried out on the behaviour of selected connections with different stiffness and strength characteristics under various load combination scenarios. The influence of applied levels of axial tensile or compressive loads on the bending stiffness and capacity is examined and discussed. Additionally, the interaction effects between shear forces and co-existing bending and axial loads are examined and shown to be comparatively insignificant in terms of stiffness and capacity in most cases. It is also shown that the range of connections considered in this paper can provide rotational ductility levels in excess of those required under typical design scenarios. Based on these findings, a simplified component-based representation is proposed and described, and its ability to represent the connection response under combined loading is verified using results from detailed numerical simulations.

• Steel and Composite Structures
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• v.20 no.4
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• pp.913-930
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• 2016

It is common practice to use Reduced Web Beam Sections (RWBS) in steel moment resisting frames. Perforation of beam web in these members may cause stress and strain concentration around the opening area and facilitate ductile fracture under cyclic loading. This paper presents a numerical study on the cyclic fracture of these structural components. The considered connections are configured as T-shaped assemblies with beams of elongated circular perforations. The failure of specimens under Ultra Low Cycle Fatigue (ULCF) condition is simulated using Cyclic Void Growth Model (CVGM) which is a micromechanics based fracture model. In each model, CVGM fracture index is calculated based on the stress and strain time histories and then models with different opening configurations are compared based on the calculated fracture index. In addition to the global models, sub-models with refined mesh are used to evaluate fracture index around the beam to column weldment. Modeling techniques are validated using data from previous experiments. Results show that as the perforation size increases, opening corners experience greater fracture index. This is while as the opening size increases the maximum observed fracture index at the connection welds decreases. However, the initiation of fracture at connection welds occurs at lower drift angles compared to opening corners. Finally, a probabilistic framework is applied to CVGM in order to account for the uncertainties existing in the prediction of ductile fracture and results are discussed.

• Steel and Composite Structures
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• v.17 no.6
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• pp.851-865
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• 2014

Full penetration welded steel moment-resisting frame (SMRF) structures with welded box sections are widely employed in steel bridges, where a large number of steel bridges have been in operation for over fifty years in Japan. Welding defects such as incomplete penetration at the beam-column connections of these existing SMRF steel bridge piers were observed during inspection. Previous experiments conducted by the authors' team indicate that gusset stiffeners (termed fillets in this study) at the beam-web-to-column-web joint of the beam-column connections may play an important role on the seismic performance of the connections. This paper aims to experimentally study the effect of the fillet radius on seismic performance of the connections with large welding defects. Four specimens with different sizes of fillet radii were loaded under quasi-static incremental cyclic loading, where different load-displacement relations and cracking behaviors were observed. The experimental results show that, as the size of the fillet radius increases, the seismic performance of the connections can be greatly improved.

• Journal of the Korean Society of Safety
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• v.34 no.2
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• pp.40-47
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• 2019

The Half-depth precast deck is a structural system that utilizes pre-cast panels pre-built at the factory as formwork at the construction stage and as a major structural member at the same time after completion. These systems have joints between segments, and the detail and performance of the joints are factors that have a very large impact on the quality, such as the constructability and durability of the bridge decks. In this study, strength performance evaluation was performed for improved joints using connecting rebar by experimental method. Static loading tests were conducted on the test specimen with improved joint, those with existing joint and those without joint. The test results of the specimens were compared to each other, and the flexural strength required by the design was compared. The flexural strength required in the design was presented by finite element analysis. It has been shown that the flexural strength of the specimens with joints were more than twice that required by the design. But the flexural strength of the specimen with existing joint was about 84% of that without joint. The flexural strength of the specimen with improved joints was a nearly similar degree of that compared to the specimen without joint. And a comparison of the moment-deflection relationship curves of the two specimens also shows a very similar flexural behavior. It is confirmed that improved joint has sufficient flexural strength. In addition to strength, the bridge decks require serviceability, such as deflection and cracking, and in particular, fatigue resistance due to repetitive live loads is an important performance factor. Therefore, further verification studies are required.

• Journal of Korean Society of Steel Construction
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• v.13 no.4
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• pp.351-361
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• 2001

The connections are classified as rigid, semi+rigid, or pinned. There are two classification systems, EC3 adn Bjorhovede et al., representatively. The EC3 boundary between rigid and semi-rigid connections is in on the whole restrictive in term of the stiffness as well as the moment capacity of connections. The boundary specified by Bjorhovede et al. may not be sufficient to assure the behavior of rigid frames in some cases. In this study, it is proposed the new classification system for steel connection that depends on the reduction factor(R) of critical buckling load for unbraced semi-rigid frame expressed by the stiffness ratio($\rho$) of beam to column and the stiffness ratio(k) of connection to beam. Finally, it is examined by experimental data that new classification criteria provides a practical boundary compared wit hteh existing classifications.

• Journal of Korean Society of Steel Construction
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• v.29 no.2
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• pp.169-180
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• 2017

Cyclic loading tests for beam-to-column weak-axis connections were performed to investigate the seismic performance. In this study, the connections were developed to improve the constructability on the basis of investigation for existing small-size steel structures. The primary test parameter is the number of high-tension bolts which are used to connect steel beam and column using exterior and interior flange plates. Test results showed that the number of bolts had a significant effect on the cyclic behavior of beam-column weak-axis connections. From the analysis of test results, it is concluded that more than four bolts in the connections can satisfy the requirements of semi-rigid connection presented in current design codes. All of specimens showed the bearing failure around bolt holes and fracture at the beam flange. However, when the web height and the flange width is relatively small, the number of the bolts used in the connections might be limited. Thus, the additional research in this area is needed.

• Journal of Korean Society of Steel Construction
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• v.25 no.6
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• pp.601-612
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• 2013

In the present study, details of the TSC beam-to-PSRC column connection for low and middle seismic zones were developed. For ease construction, the top and bottom flanges of the steel section of the TSC beam were discontinuous at the joint face on purpose, while the web passes through the joint. Thus, tensile resistance of the top and bottom flanges is not considered in the calculation of nominal strength of the connection. Cyclic loading tests on two interior connections and an exterior connection were performed to verify the seismic performance. The test parameter for two interior connections was the depth of the TSC beams: 600 and 700 mm including the slab depth. The test results showed that the nominal strength of the connections predicted by KBC 2009 correlated well with the test results. The connection specimens exhibited relatively good deformation and energy dissipation capacities, greater than the requirements for the ordinary and intermediate moment frames. Ultimately, the connection specimens were failed at the story drift ratios of 3.0 to 4.0 % due to local buckling and tensile fracture of the web of the TSC beam passing through the joint. By modifying the existing provisions of ASCE, the joint shear strength of the TSC beam-PSRC column connection was evaluated.

• Steel and Composite Structures
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• v.28 no.5
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• pp.559-571
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• 2018

In current engineering practice, circular concrete-filled steel tubular (CFST) columns have been used as effective structural components due to their significant structural and economic benefits. To apply these structural components into steel-concrete composite moment resisting frames, increasing number of research into the column-base connections of circular CFST columns have been found. However, most of the previous research focused on the strength, rigidity and seismic resisting performance of the circular CFST column-base connections. The present paper attempts to investigate the demountability of bolted circular CFST column-base connections using the finite element method. The developed finite element models take into account the effects of material and geometric nonlinearities; the accuracy of proposed models is validated through comparison against independent experimental results. The mechanical performance of CFST column-base connections with both permanent and demountable design details are compared with the developed finite element models. Parametric studies are further carried out to examine the effects of design parameters on the behaviour of demountable circular CFST column-base connections. Moreover, the initial stiffness and moment capacity of such demountable connections are compared with the existing codes of practice. The comparison results indicate that an improved prediction method of the initial stiffness for these connections should be developed.

• Journal of Korean Society of Steel Construction
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• v.17 no.1 s.74
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• pp.103-113
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• 2005

In the present study, the Direct Inelastic Design (DID) for steel structures developed in the previous study was improved to expand it applicability. The proposed design method can perform inelastic designs that address the design characteristics of steel structures: Group member design, discrete member sizes, variation of moment-carrying capacity according to axial force, connection types, and multiple design criteria and load conditions. The design procedure for the proposed method was established, and a computer program incorporating the design procedure was developed. The design results from the conventional elastic method and the DID were compared and verified by the existing computer program for nonlinear analysis. Compared with the conventional elastic design, the DID addressing the inelastic behavior reduced the total weight of steel members and enhanced the deformability of the structure. The proposed design method is convenient because it can directly perform inelastic design by using linear analysis for secant stiffness. Also, it can achieve structural safety and economical design by controlling deformations of the plastic hinges.