• Journal of the Korea institute for structural maintenance and inspection
• /
• v.8 no.2
• /
• pp.259-267
• /
• 2004

Most steel frame structures are constructed to one side without considering the arrangement of major-minor axis of column and bracing. This research presents more safety and economic efficiency can be obtained by just rearrangement of major-minor axis. Because most of steel-frame structures are excessively designed with Allowable Stress Design, and it needs to be changed to other specifications. The arrangement of major-minor axis of column is partly referred in AISC-LRFD, but still insufficient. This study compared with the each result from rearrangement of major-minor axis of column, arrangement of bracing, the connecting method of bracing, and consequence with different specifications. Moreover it demonstrated the direction of more economically optimized design.

• Journal of Korean Society of Steel Construction
• /
• v.21 no.5
• /
• pp.537-544
• /
• 2009

The design standards, such as AISC-LRFD (2005) and KBC-2005, specify the maximum width-to-thickness ratio that can be used for computing the strength of the concrete-filled tube (CFT), and do not include any formula for computing the strength when the width-to-thickness ratio is over the limit. This paper proposes a strength equation for CFTs with a large width-to-thickness ratio by acknowledging the fact that the stiffened slender steel platehas substantial postbuckling strength, and that it therefore can be more economical to use it. The equation adopts the concept of effective width,which is very useful for plate analysis. By comparing the strengths of AISC2005, KBC2005, and the proposed method with the results of the experiment, where the width-to-thickness ratio was regarded as the main parameter, the applicability of the proposed method was verified.

• Journal of the Korea Academia-Industrial cooperation Society
• /
• v.10 no.8
• /
• pp.2038-2043
• /
• 2009

This study investigates elastic lateral-torsional buckling(LTB) of T-beams subjected to pure bending using finite element analysis(FEA). The results from the FEA are compared with those from the current American Institute of Steel Council(AISC) Load and Resistance Factor Design(LRFD) Specifications. The comparison indicates that AISC-LRFD provide unsafe values for T-beam subjected to pure bending. Therefore, a new design equation are presented using results from the FEA. The new equation could be easily used to calculate the elastic lateral-torsional buckling moment resistance of T-beam for beam design and to expand the new equation for developing LTB equations of T-beam subjected to general loading conditions such as a concentrated load, distributed load, or a seres of concentrated load.

• Steel and Composite Structures
• /
• v.30 no.5
• /
• pp.483-492
• /
• 2019

In the current study, the influence of the initial lateral (sweep) shape and the cross-sectional twist imperfection on the lateral torsional buckling (LTB) response of doubly-symmetric steel I-beams was investigated. The material imperfection (residual stress) was not considered. For this objective, standard European IPN 300 beam with different unbraced span was numerically analyzed for three imperfection cases: (i) no sweep and no twist (perfect); (ii) three different shapes of global sweep (half-sine, full-sine and full-parabola between the end supports); and (iii) the combination of three different sweeps with initial sinusoidal twist along the beam. The first comparison was done between the results of numerical analyses (FEM) and both a theoretical solution and the code lateral torsional buckling formulations (EC3 and AISC-LRFD). These results with no imperfection effects were then separately compared with three different shapes of global sweep and the presence of initial twist in these sweep shapes. Besides, the effects of the shapes of initial global sweep and the inclusion of sinusoidal twist on the critical buckling load of the beams were investigated to unveil which parameter was considerably effective on LTB response. The most compatible outcomes for the perfect beams was obtained from the AISC-LRFD formulation; however, the EC-3 formulation estimated the $P_{cr}$ load conservatively. The high difference from the EC-3 formulation was predicted to directly originate from the initial imperfection reduction factor and high safety factor in its formulation. Due to no consideration of geometric imperfection in the AISC-LFRD code solution and the theoretical formulation, the need to develop a practical imperfection reduction factor for AISC-LRFD and theoretical formulation was underlined. Initial imperfections were obtained to be more influential on the buckling load, as the unbraced length of a beam approached to the elastic limit unbraced length ($L_r$). Mode-compatible initial imperfection shapes should be taken into account in the design and analysis stages of the I-beam to properly estimate the geometric imperfection influence on the $P_{cr}$ load. Sweep and sweep-twist imperfections led to 10% and 15% decrease in the $P_{cr}$ load, respectively, thus; well-estimated sweep and twist imperfections should considered in the LTB of doubly-symmetric steel I-beams.

• Steel and Composite Structures
• /
• v.19 no.4
• /
• pp.811-827
• /
• 2015

This paper presents a probabilistic investigation of American and European specifications (i.e., AISC and Eurocode 4) for square concrete-filled steel tubular (CFT) stub columns. The study is based on experimental results of 100 axially loaded square CFT stub columns from the literature. By comparing experimental results for ultimate loads with code-predicted column resistances, the uncertainty of resistance models is analyzed and it is found that the modeling uncertainty parameter can be described using random variables of lognormal distribution. Reliability analyses were then performed with/without considering the modeling uncertainty parameter and the safety level of the specifications is evaluated in terms of sufficient and uniform reliability criteria. Results show that: (1) The AISC design code provided slightly conservative results of square CFT stub columns with reliability indices larger than 3.25 and the uniformness of reliability indices is no better because of the quality of the resistance model; (2) The uniformness of reliability indices for the Eurocode 4 was better than that of AISC, but the reliability indices of columns designed following the Eurocode 4 were found to be quite below the target reliability level of Eurocode 4.

• Structural Engineering and Mechanics
• /
• v.58 no.3
• /
• pp.555-576
• /
• 2016

In this paper an efficient approach is introduced for design and analysis of double-layer grids including both geometrical and material nonlinearities, while the results are compared with those considering material nonlinearity. Optimum design procedure based on Enhanced Colliding Bodies Optimization method (ECBO) is applied to optimal design of two commonly used configurations of double-layer grids. Two ranges of spans as small and big sizes with certain bays of equal length in two directions are considered for each type of square grids. ECBO algorithm obtains minimum weight grid through appropriate selection of tube sections available in AISC Load and Resistance Factor Design (LRFD). Strength constraints of AISC-LRFD specifications and displacement constraints are imposed on these grids.

• Structural Engineering and Mechanics
• /
• v.58 no.3
• /
• pp.597-612
• /
• 2016

This paper presents an optimization process using Harmony Search Algorithm for minimum weight of steel space frames under earthquake effects according to Turkish Earthquake Code (2007) specifications. The optimum designs are carried out by selecting suitable sections from a specified list including W profiles taken from American Institute of Steel Construction (AISC). The stress constraints obeying AISC-Load and Resistance Factor Design (LRFD) specifications, lateral displacement constraints and geometric constraints are considered in the optimum designs. A computer program is coded in MATLAB for the purpose to incorporate with SAP2000 OAPI (Open Application Programming Interface) to perform structural analysis of the frames under earthquake loads. Three different steel space frames are carried out for four different seismic earthquake zones defined in Turkish Earthquake Code (2007). Results obtained from the examples show the applicability and robustness of the method.

• Proceedings of the Computational Structural Engineering Institute Conference
• /
• 2005.04a
• /
• pp.97-104
• /
• 2005

The seismic behavior of framed structure with Chevron-type bucking restrained braces were investigated and their behavior factors were evaluated following the procedure proposed in ATC-19 & ATC-34. Two types of structures, building frame systems and dual systems, with 4, 8, 12, and 16 stories were designed per the IBC 2000, the AISC LRFD and the AISC/SEAOC Recommended Provisions for BRBF. Nonlinear static pushover analyses were carried out to observe the plastic hinge formation and to identify the loads and the displacements at the yield and the ultimate states. Time history analyses were also carried out to compute the permanent displacement md the dissipated hysteretic energy. According to the analysis results, the response modification factors of model structures fumed out to be larger than what is proposed in the provision in low story structures, and a little smaller in medium-story structures. The dual systems, even though designed with smaller seismic load, showed superior static and dynamic performances.

• Structural Engineering and Mechanics
• /
• v.27 no.5
• /
• pp.575-588
• /
• 2007

In this paper, two algorithms are presented for the optimum design of geometrically nonlinear steel space frames using tabu search. The first algorithm utilizes the features of short-term memory (tabu list) facility and aspiration criteria and the other has long-term memory (back-tracking) facility in addition to the aforementioned features. The design algorithms obtain minimum weight frames by selecting suitable sections from a standard set of steel sections such as American Institute of Steel Construction (AISC) wide-flange (W) shapes. Stress constraints of AISC Allowable stress design (ASD) specification, maximum drift (lateral displacement) and interstorey drift constraints were imposed on the frames. The algorithms were applied to the optimum design of three space frame structures. The designs obtained using the two algorithms were compared to each other. The comparisons showed that the second algorithm resulted in lighter frames.

• Steel and Composite Structures
• /
• v.22 no.4
• /
• pp.733-744
• /
• 2016

In this study, optimum structural designs of braced (non-swaying) planar steel frames are investigated by using one of the recent meta-heuristic search techniques, teaching-learning based optimization. Optimum design problems are performed according to American Institute of Steel Construction- Allowable Stress Design (AISC-ASD) specifications. A computer program is developed in MATLAB interacting with SAP2000 OAPI (Open Application Programming Interface) to conduct optimization procedures. Optimum cross sections are selected from a specified list of 128W profiles taken from AISC. Two different braced planar frames taken from literature are carried out for stress, geometric size, displacement and inter-storey drift constraints. It is concluded that teaching-learning based optimization presents robust and applicable optimum solutions in multi-element structural problems.