• Journal of the Korean Society of Hazard Mitigation
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• v.4 no.4 s.15
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• pp.63-71
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• 2004

The centroid of rail doesn't coincide with the centroid of stringer on target truss bridge. If there is no eccentricity on the bridge, bending stress works only. But in the real design and execution, not only bending stress works but also torsional stress does because of it's eccentricity. So this study evaluates how much the torsional stress by eccentricity effects joint members on the bridge. We investigate the possibility to control torsional stress if we model longitudinal bracing between stringers.

• Steel and Composite Structures
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• v.35 no.1
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• pp.29-41
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• 2020

Cross-beams of modern through truss bridges are connected to truss chord at its nodes and between them. It results in variable rotational end restraint for cross-beams, thus variable bending moment distribution. This feature is captured in three-dimensional modelling of through truss bridge structure. However, for preliminary design or rapid assessment of service load effects such technique of analysis may not be available. So an analytical method of assessment of rotational end restraint for cross-beam of through truss bridges was worked out. Two cases - nodal cross-beam and inter-nodal cross-beam - were analyzed. Flexural and torsional stiffness of truss members, flexural stiffness of deck members and axial stiffness of wind bracing members in the vicinity of the analyzed cross-beam were taken into account. The provision for reduced stiffness of the X-type wind bracing was made. Finally, general formula for assessment of rotational end restraint was given. Rotational end restraints for cross-beams of three railway through truss bridges were assessed basing on the analytical method and the finite element method (three-dimensional beam-element modelling). Results of both methods show good agreement. The analytical method is able to reflect effects of some structural irregularities. On the basis of the obtained results the general values of rotational end restraint for nodal and inter-nodal cross-beams of railway through truss bridges were suggested.

• Structural Engineering and Mechanics
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• v.85 no.6
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• pp.825-835
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• 2023

The effective buckling length factor is an important parameter in the elastic buckling analysis of steel structures. The present article aims at developing a new method that allows the determination of the buckling factor values for frames. The novelty of the method is that it considers the interaction between the bracing and the elastic supports for asymmetrical frames in particular. The approach consists in isolating a critical column within the frame and evaluating the rotational and translational stiffness of its restraints to obtain the critical buckling load. This can be achieved by introducing, through a dimensionless parameter 𝜙_i, the effects of coupling between the axial loading and bending stiffness of the columns, on the classical stability functions. Subsequently, comparative, and parametric studies conducted on several frames are presented for assessing the influence of geometry, loading, bracing, and support conditions of the frame columns on the value of the effective buckling length factor K. The results show that the formulas recommended by different approaches can give rather inaccurate values of K, especially in the case of asymmetric frames. The expressions used refer solely to local stiffness distributions, and not to the overall behavior of the structure.

• Journal of Korean Society of Steel Construction
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• v.15 no.4 s.65
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• pp.359-368
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• 2003

Design and detailing requirements of seismic provisions for Concentrically Braced Frames (CBF) were specified based on the premise that bracing members with large KL/r and low b/t have superior seismic performance. However, relatively few tests have been done to investigate the cyclic behavior of CBF. Therefore, the question lies on whether the compression member of CBF plays as significant a role as what has been typically assumed by design providers. In this paper, existing experimental data were reviewed to quantify the extent of hysteretic energy achieved by bracing members in past compression tests as well as the extent of degradation of the compression force given repeated cycling loading.

• Steel and Composite Structures
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• v.35 no.4
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• pp.599-609
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• 2020

The tension-only braced frames (TOBFs) are widely used as a lateral force resisting system (LFRS) in low-rise steel buildings due to their simplicity and economic advantage. However, the system has poor seismic energy dissipation capacity and pinched hysteresis behavior caused by early buckling of slender bracing members. The main concern in utilizing the TOBF system is the determination of appropriate performance factors for seismic design. A formalized approach to quantify the seismic performance factor (SPF) based on determining an acceptable margin of safety against collapse is introduced by FEMA P695. The methodology is applied in this paper to assess the SPFs of the TOBF systems. For this purpose, a trial value of the R factor was first employed to design and model a set of TOBF archetype structures. Afterwards, the level of safety against collapse provided by the assumed R factor was investigated by using the non-linear analysis procedure of FEMA P695 comprising incremental dynamic analysis (IDA) under a set of prescribed ground motions. It was found that the R factor of 3.0 is appropriate for safe design of TOBFs. Also, the system overstrength factor (Ω₀) was estimated as 2.0 by performing non-linear static analyses.

• Journal of Korean Society of Steel Construction
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• v.18 no.2
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• pp.191-201
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• 2006

New design equations for calculating the lateral-torsional buck ling moment resistances of stepped I-section beams with/without continuous lateral top-flange bracing subjected to a point load, a series of point loads, and a uniformly distributed load, are suggested based on the results of elastic finite-element analyses. The new equations presented in this study are compared with the current moment gradient modifiers presented by other researchers and specifications. Although the study paper presents mainly stepped-beam cases subjected to a point load and a uniformly distributed load. The proposed equations include the length-to-height ratio effects for stepped beams with continuous lateral top-flange bracing. The new moment gradient correction factors could be easily used to calculate the lateral-torsional buckling moment resistance of stepped I-beams.

• Steel and Composite Structures
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• v.19 no.1
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• pp.59-74
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• 2015

Since there are several places located in active seismic zones in the world, serious damages and losses have happened due to major scaled earthquakes. Especially, structures having different irregularities have been severely damaged or collapsed during these seismic events. Behavior of existing structures under several loading conditions is not completely determined due to some uncertainties. This situation reveals the importance of design and analysis of structures under seismic effects. Several non-linear static procedures have been developed in recent years. Determination of the seismic safety of the existing structures and strengthening techniques are significant civil engineering problems Non-linear methods are defined in codes to determine the performance levels of structures more accurately. However, displacement based ones give more realistic results. These methods provide more reliable evaluation possibilities for existing structures with developing computer technology. In this study, non-linear performance analysis of existing and strengthened steel structures by X shaped bracing members with 3, 5 and 7 stories which have soft story irregularity is performed according to FEMA-356 and Turkish Earthquake Code-2007. Damage ratios of the structural members and global performance levels are determined as well as modal properties and story drift ratios after non-linear finite elements analysis for each structure.

• Journal of Korean Association for Spatial Structures
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• v.6 no.1 s.19
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• pp.45-54
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• 2006

A steel frame is one of the most commonly used structural systems due to its resistance to various types of applied loads. Many studies have been conducted to investigate the effects of connection flexibility, support conditions, and beam-to-column stiffness ratio on the story drift of a frame. Based on the results of these studies, several design guides have been proposed. This research has been conducted to predict the actual behavior of a double angle connection, and to establish its effect on the story drift and the maximum allowable load of a steel frame. For these purposes, several experimental tests were conducted and a simplified analytical model was proposed. This simplified analytical model consists of four spring elements as well as a column member. In addition, a point bracing system was proposed to control the excessive story drift of an unbraced steel frame.

• Advances in concrete construction
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• v.9 no.4
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• pp.423-435
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• 2020

Open ground story (OGS) reinforced concrete (RC) buildings are vulnerable to the complete collapse or severe damages under seismic actions. This study investigates the effectiveness of four different strengthening techniques representing the local and global modifications to improve the seismic performance of a non-ductile RC OGS frame. Steel caging and concrete jacketing methods of column strengthening are considered as the local modification techniques, whereas steel bracing and RC shear wall systems are selected as the global strengthening techniques in this study. Performance-based plastic design (PBPD) approach relying on energy-balance concept has been adopted to determine the required design force demand on the strengthening elements. Nonlinear static and dynamic analyses are carried out on the numerical models of study frames to assess the effectiveness of selected strengthening techniques in improving the seismic performance of OGS frame.. Strengthening techniques based on steel braces and RC shear wall significantly reduced the peak interstory drift response of the OGS frame. However, the peak floor acceleration of these strengthened frames is amplified by more than 2.5 times as compared to that of unstrengthened frame. Steel caging technique of column strengthening resulted in a reasonable reduction in the peak interstory drift response without substantial amplification in peak floor acceleration of the OSG frame.

• Steel and Composite Structures
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• v.33 no.4
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• pp.525-535
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• 2019

The seismic performance of steel frames equipped with a particular type of bending dissipative braces (BDBs) having U elements, which has recently been introduced and tested by the authors, is investigated. For this purpose, two structural systems, i.e., simple and dual steel building frames, both with diagonal BDBs and different number of stories, are considered. After providing a design method of this new BDB, the detailed structural models are developed in the OpenSees platform to perform nonlinear dynamic analyses. Seismic performance factors like ductility, overstrength, response modification and deflection amplification factors are calculated using incremental dynamic analysis (IDA). In addition, to assess the damage probability of the structural models, their seismic fragilities are developed. The results show high energy dissipation capacity of both structural systems while the number of U elements needed for the bracing system of each story in the moment frames are less than those in the corresponding non-moment (simple) frames. The average response modification and deflection amplification factors for both structural schemes are obtained about 8.6 and 5.4, respectively, which are slightly larger than the corresponding recommended values of ASCE for the typical buckling-restrained braces (BRBs).