• Steel and Composite Structures
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• v.7 no.3
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• pp.201-217
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• 2007

Two combinatorial optimization algorithms, tabu search and simulated annealing, are presented for the minimum-weight design of geometrically non-linear steel plane frames. 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 Load and Resistance Factor Design (LRFD) specification, maximum and interstorey drift constraints and size constraints for columns were imposed on frames. The stress constraints of AISC Allowable Stress Design (ASD) were also mounted in the two algorithms. The comparisons between AISC-LRFD and AISC-ASD specifications were also made while tabu search and simulated annealing were used separately. The algorithms were applied to the optimum design of three frame structures. The designs obtained using tabu search were compared to those where simulated annealing was considered. The comparisons showed that the tabu search algorithm yielded better designs with AISC-LRFD code specification.

• Steel and Composite Structures
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• v.19 no.4
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• pp.811-827
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• 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
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• v.58 no.3
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• pp.597-612
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• 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.

• Structural Engineering and Mechanics
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• v.10 no.4
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• pp.313-336
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• 2000

The focus of this paper is on the development and implementation of a methodology for automated design of discrete structural systems. The research is aimed at utilizing Genetic Algorithms (GA) as an automated design tool. Several key enhancements are made to the simple GA in order to increase the efficiency, reliability and accuracy of the methodology for code-based design of structures. The AISC-ASD design code is used to illustrate the design methodology. Small as well as large-scale problems are solved. Simultaneous sizing, shape and topology optimal designs of structural framed systems subjected to static and dynamic loads are considered. Comparisons with results from prior publications and solution to new problems show that the enhancements made to the GA do indeed make the design system more efficient and robust.

• Steel and Composite Structures
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• v.30 no.5
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• pp.483-492
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• 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
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• v.8 no.6
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• pp.491-510
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• 2008

This paper presents a plan and guidelines that were drawn for Korean based research carried out on the fire-resistance of CFT columns. This research was carried out by reviewing the Korean regulations related to the fire-resistance of CFT columns and examining studies which had been made in Korea as well as overseas. The first phase of the study plan was to compare the fire-resistance of square CFT columns without fire protection (obtained through fire-resistance tests and numerical analyses) with estimated values (obtained through fire-resistance design formulas proposed in Korea and overseas). This comparison provided conclusions as outlined below. Fire-resistance tests conducted in this study proved that, when the actual design load is taken into consideration, square CFT columns without fire protection are able to resist a fire for more than one hour. A comparison was made of test and analysis results with the fire-resistance time based on the AIJ code, the AISC design formula and the estimation formula suggested for Korea. The results of this comparison showed that the test and analysis results for specimens SAH1, SAH2-1, SAH2-2 and SAH3 were almost identical with the AIJ code, the AISC design formula and estimation formula. For specimens SAH4 and SAH5, the estimation formula was more conservative than the AIJ code and the AISC design formula. It was necessary to identify the factors that have an influence on the fire-resistance of CFT columns without fire protection and to draw fire-resistance design formulas for these columns. To achieve this, it is proposed that numerical analyses and tests be conducted in order to evaluate the fire-resistance of circular CFT columns, the influence of eccentricity existing as an additional factor and the influence of the slenderness ratio of the columns. It is also suggested that the overall behavior of CFT structures without fire protection within a fire be evaluated through analysis simulation.

• Structural Engineering and Mechanics
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• v.50 no.3
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• pp.323-347
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• 2014

This paper proposes a Particle Swarm Optimization (PSO) algorithm, which is improved by making use of the Harmony Search (HS) approach and called HS-PSO algorithm. A computer code is developed for optimal sizing design of non-linear steel frames with various semi-rigid and rigid beam-to-column connections based on the HS-PSO algorithm. The developed code selects suitable sections for beams and columns, from a standard set of steel sections such as American Institute of Steel Construction (AISC) wide-flange W-shapes, such that the minimum total cost, which comprises total member plus connection costs, is obtained. Stress and displacement constraints of AISC-LRFD code together with the size constraints are imposed on the frame in the optimal design procedure. The nonlinear moment-rotation behavior of connections is modeled using the Frye-Morris polynomial model. Moreover, the P-${\Delta}$ effects of beam-column members are taken into account in the non-linear structural analysis. Three benchmark design examples with several types of connections are presented and the results are compared with those of standard PSO and of other researches as well. The comparison shows that the proposed HS-PSO algorithm performs better both than the PSO and the Big Bang-Big Crunch (BB-BC) methods.

• Earthquakes and Structures
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• v.12 no.6
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• pp.713-723
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• 2017

Steel plate shear walls (SPSWs) are effective lateral systems which have high initial stiffness, appropriate ductility and energy dissipation capability. Recently, steel plate shear walls with low yield point strength (LYP), were introduced and they attracted the attention of designers. Structures with this new system, besides using less steel, are more stable. In the present study, the effects of plates with low yield strength on the seismic design parameters of steel frames with steel plate shear walls are investigated. For this purpose, a variety of this kind of structures with different heights including the 2, 5, 10, 14 and 18-story buildings are designed based on the AISC seismic provisions. The structures are modeled using ANSYS finite element software and subjected to monotonic lateral loading. Parameters such as ductility (${\mu}$), ductility reduction ($R_{\mu}$), over-strength (${\Omega}_0$), displacement amplification ($C_d$) and behavior factor (R) of these structures are evaluated by carrying out the pushover analysis. Analysis results indicate that the ductility, over-strength and behavior factors decrease by increasing the number of stories. Also, the displacement amplification factor decreases by increasing the number of stories. Finally, the results were compared with the suggestions provided in the AISC code for steel plate shear walls. The results indicate that the values for over-strength, behavior and displacement amplification factors of LYP steel plate shear wall systems, are larger than those proposed by the AISC code for typical steel plate shear wall systems.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.35 no.1
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• pp.47-52
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• 2011

In this paper, we describe the development of a finite-element model for seismic qualification. This paper presents finite-element analysis model of the electronic enclosure to be used at Arkansas nuclear power plant, USA. The verified model predicts natural frequencies within 5% error for all major modes below 50 Hz. The finite element lumped mass approach and the finite element stiffness approach using the COSMOSM finite element code is applied for static, eigenvalue, and dynamic analyses of the mathematical model of this system. The FEM model indicates that the stress levels corresponding to the specified loading conditions are below the allowable stress levels that have been specified in the AISC Code. The findings conclude that the electronic enclosure will withstand the seismic levels stated in the reference documents.

• Steel and Composite Structures
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• v.18 no.2
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• pp.519-546
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• 2015

This study addresses the load capacity prediction of circular concrete-filled steel tube (CFST) columns under axial compression using current design codes. Design methods given in the Chinese code CECS 28:2012 (2012), American code AISC 360-10 (2010) and EC4 (2004) are presented and described briefly. A wide range of experimental data of 353 CFST columns is used to evaluate the applicability of CECS 28:2012 in calculating the strength of circular CFST columns. AISC 360-10 and EC4 (2004) are also compared with the test results. The comparisons indicate that all three codes give conservative predictions for both short and long CFST columns. The effects of concrete strength, steel strength and diameter-to-thickness ratio on the accuracy of prediction according to CECS 28:2012 are discussed, which indicate a possibility of extending the limitations on the material strengths and diameter-to-thickness ratio to higher values. A revised equation for slenderness reduction factor in CECS 28:2012 is given.