Design Of Steel Frames Research Articles

Enhancements of Genetic Algorithm for Minimum Cost Design of Steel Frames Considering Fabrication Cost

Enhancements of Genetic Algorithm for Minimum Cost Design of Steel Frames Considering Fabrication Cost

Displacement-Based Seismic Design of Steel Frames Strengthened by Buckling-Restrained Braces

This study presents a displacement-based design procedure for seismic retrofitting of steel frames using buckling-restrained braces (BRB) to meet a given target displacement in the framework of the capacity spectrum method. The seismic performance of a six-storey steel frame equipped with BRB is investigated. Different storey-wise BRB distribution methods are proposed and the influence on the results of the design procedure is analyzed. Nonlinear dynamic analyses demonstrate the efficacy of the design procedure showing the improvements achieved by the retrofitting intervention using BRB. The maximum top displacement registered for the retrofitted frame under earthquake excitation coincides with the target displacement obtained in accordance with the design procedure. The introduction of buckling-restrained braces enhances the earthquake resistance of the steel frame, providing significant energy dissipation and the stiffness needed to satisfy structural drift limits.

Computational Framework for Automated Seismic Design of Steel Frames with Self-Centering Connections

AbstractA computational framework is proposed as an automated design cycle for the optimal seismic design of steel frames with self-centering connections. This paper demonstrates the approach by co...

The effects of construction related costs on the optimization of steel frames

This paper presents a computational study that explores the design of rigid steel frames by considering construction related costs. More specifically, two different aspects are investigated in this study focusing on the effects of (a) reducing the number of labor intensive rigid connections within a frame of given geometric layout, and (b) reducing the number of different member section types used in the frame. A genetic algorithm based optimization framework searches design space for these objectives. Unlike some studies that express connection cost as a factor of the entire frame weight, here connections and their associated cost factors are explicitly represented at the member level to evaluate the cost of connections associated with each beam. In addition, because variety in member section types can drive up construction related costs, its effects are evaluated implicitly by generating curves that show the trade off between cost and different numbers of section types used within the frame. Our results show that designs in which all connections are considered to be rigid can be excessively conservative: rigid connections can often be eliminated without any appreciable increase in frame weight, resulting in a reduction in overall cost. Eliminating additional rigid connections leads to further reductions in cost, even as frame weight increases, up to a certain point. These complex relationships between overall cost, rigid connections, and member section types are presented for a representative five-story steel frame.

A Simplified Approach for Evaluating Second-Order Effects in Low-Rise Steel Framed Buildings

Consideration of second-order effects is one of the most involved tasks in the analysis and design of steel framed buildings. More specifically, the evaluation of amplified moments due to frame level second-order effects is a very time consuming task because, depending on the method used, it may require an additional first order analysis or the introduction of additional notional loads for each considered load case. Although the use of such methods may not present a problem when the design process is fully automated, hand calculations can be quite complicated for checking the results of a computer generated design or for designing a small structure in which second-order effects may not even be significant enough to affect the selection of member sizes. This paper presents a simplified approach for the incorporation of second-order effects in the design of low-rise steel framed structures. The development of this approach involved the design and analysis of a number of systems with various numbers of bays, floors and beam-span to floor-height ratios and included a thorough investigation of the effect of moment amplification on final member sizes. To facilitate this task, a spreadsheet application was developed to automate the design of a typical low-rise steel frame under given loading conditions. A parametric study was then performed to understand the effect of the various design parameters on member-level and frame-level second-order forces and moments. This led to the development of the simplified design approach proposed in this paper.

Optimum design of geometrically non-linear steel frames using artificial bee colony algorithm

An artificial bee colony (ABC) algorithm is developed for the optimum design of geometrically non-linear steel frames. The ABC is a new swarm intelligence method which simulates the intelligent foraging behaviour of honeybee swarm for solving the optimization problems. Minimum weight design of steel frames is aimed under the strength, displacement and size constraints. The geometric non-linearity of the frame members is taken into account in the optimum design algorithm. The performance of the ABC algorithm is tested on three steel frames taken from literature. The results obtained from the design examples demonstrate that the ABC algorithm could find better designs than other meta-heuristic optimization algorithms in shorter time.

Eccentrically Braced Steel Frame Design Theory and Application Research in China

Eccentrically braced steel frame is a good anti-seismic structure which can be used in seismic area. A series of experiments and theoretical researches have been conducted in developed countries. However, research on this kind of structure in China is at an early stage. This paper reviews experimental, theoretical and practical application researches in China. The aim is to contribute to a better understanding of the development of the structure for designers in China, to provide a reference for researchers in this area, and to accelerate practical usage of the structure in seismic areas.

Optimum design of steel frames using Cuckoo Search algorithm with Lévy flights

SUMMARYIn the last two decades, many researchers have implemented various kinds of meta‐heuristic algorithms in order to overcome the complex nature of the optimum design of structures. In this paper, the optimum design of two‐dimensional steel frames for discrete variables based on the Cuckoo Search (CS) algorithm is developed. The CS is one of the recently developed population‐based algorithms inspired by the behavior of some cuckoo species in combination with the Lévy flight behavior of some birds and insects. The design algorithm is supposed to obtain minimum weight frame through suitable selection of sections from a standard set of steel sections such as the American Institute of Steel Construction (AISC) wide‐flange (W) shapes. Strength constraints of AISC load and resistance factor design specification and displacement constraints are imposed on frames. In order to demonstrate the effectiveness and robustness of the CS, low‐weight design and performance comparisons are made between the CS and other algorithms for some benchmark frames. Copyright © 2011 John Wiley & Sons, Ltd.

Design of planar steel frames using Teaching–Learning Based Optimization

This paper presents a design procedure employing a Teaching–Learning Based Optimization (TLBO) technique for discrete optimization of planar steel frames. TLBO is a nature-inspired search method that has been developed recently. It simulates the social interaction between the teacher and the learners in a class, which is summarized as teaching–learning process. The design algorithm aims to obtain minimum weight frames subjected to strength and displacement requirements imposed by the American Institute for Steel Construction (AISC) Load and Resistance Factor Design (LRFD). Designs are obtained selecting appropriate W-shaped sections from a standard set of steel sections specified by the AISC. Several frame examples from the literature are examined to verify the suitability of the design procedure and to demonstrate the effectiveness and robustness of the TLBO creating of an optimal design for frame structures. The results of the TLBO are compared to those of the genetic algorithm (GA), the ant colony optimization (ACO), the harmony search (HS) and the improved ant colony optimization (IACO) and they shows that TLBO is a powerful search and applicable optimization method for the problem of engineering design applications.

Using genetic algorithm for the optimization of seismic behavior of steel planar frames with semi-rigid connections

Beam-column connections have a significant role in the results of the analysis and the design of steel frames. In this paper, a genetic algorithm has been used for the non-linear analysis and design of steel frames. For minimizing the weight of frames, while satisfying the applied constraints and restraints such as the limits of normal and combined stresses, criteria such as target displacement(s) and the number and locations of plastic hinges were used. To analyze and design the frame elements, I and box-shaped standard sections were used for beams and columns, respectively. Finally, some clues for finding optimizing semi-rigid connection stiffness values for beam-to-column connections have been obtained. The degrees of these rigidities are obtained by a genetic algorithm during the procedure of optimization in order to reach a frame with the minimum weight. SAP2000 structural analysis program was used to perform modal analysis and linear and non-linear static solutions as well as the design of the elements. A MATLAB program was written for the process of optimization. The procedure of optimization was based on a weight minimization carried out for 9 steel frames. Thus, the optimum connection stiffness could be obtained for minimizing the weight of the structure. The results show that the non-linear analysis gives less weight for short period frames with semi-rigid connections compared to those of linear ones. However, by increasing the periods of frames, much less weights are obtained in the case of non-linear analysis with semi-rigid connections.

The Simplified Calculation of the End Moments for Steel Frames with Semi-Rigid Connections

In the structure design, the definition of the joints had a great impact on the structure internal force distribution, thus affecting the whole structure design. In the traditional design of steel structures, the beam-column joints were always considered as completely rigid connections or ideal hinged connections, but it is usually not in accord with the practical situations. According to the existing formulas, the simplified formulas for the end moments of semi-rigid connections have been proposed, the semi-rigid connections will also be discussed. The formulas proposed in this paper are applied to the auxiliary beam-column joint design, which is part of the counterforce frame design. It is hoped that the formulas can provide a reference for the steel frame design. Keywords: semi-rigid connections, end moments, internal forces distribution, steel frame design

Optimum design of unbraced steel frames to LRFD–AISC using particle swarm optimization

Particle Swarm method based optimum design algorithm for unbraced steel frames is presented. The Particle Swarm method is a numerical optimization technique that simulates the social behavior of birds, fishes and bugs. In nature fish school, birds flock and bugs swarm not only for reproduction but for other reasons such as finding food and escaping predators. Similar to birds seek to find food, the optimum design process seeks to find the optimum solution. In the particle swarm optimization each particle in the swarm represents a candidate solution of the optimum design problem. In the optimum design algorithm presented the design constraints are imposed in accordance with LRFD-AISC (Load and Resistance Factor Design, American Institute of Steel Construction). In the design of beam-column members the combined strength constraints are considered that take into account the lateral torsional buckling of the member. The algorithm developed selects optimum W sections for beams and columns of unbraced frame from the list of 272W-sections list. This selection is carried out such that design constraints imposed by the LRFD are satisfied and the minimum frame weight is obtained. The efficiency of the algorithm is demonstrated considering a number of design examples.

Practical Advanced Design Considering Random Distribution of Initial Geometric Imperfections

Current advanced analysis and design of steel frames, allows for the most unfavorable combination of initial imperfections. In fact, however, the initial geometric imperfections and their combinations are all random distributions. Recognising this situation, the sway installation tolerances and bow imperfections of both columns and beams are all considered to be the randomly distributed and simulation analyses for imperfections are made using Monte Carlo sampling method in this paper. A large number of parametric studies on twelve-storey single-bay frames with random imperfections have been carried out using the finite element method. Results indicate that both lateral drift values and girder deflections of the frames are distributed normally in the probability statistics terms. The characteristic values of these variables based on many simulation analyses, are extremely close to the results obtained for ideal frames which have on initial imperfections, so that the effects of initial imperfections can be neglected in the advanced design for similar structures. Moreover, a practical advanced design method is proposed, in which the serviceability state of the structure is first investigated under the required characteristic load combinations, and then the ultimate strength capacity is checked under the fundamental load combinations.

A genetic algorithm for design of moment-resisting steel frames

This paper presents computational approaches that can be implemented in a decision support system for the design of moment-resisting steel frames. Trade-off studies are performed using genetic algorithms to evaluate the savings due to the inclusion of the cost of connections in the optimization model. Since the labor costs and material costs vary according to the geographical location and time of construction, the trade-off curves are computed for several values of the ratio between the cost of rigid connection and the cost of steel. A real-life 5-bay 5-story frame is used for illustration. Results indicate that the total cost of the frame is minimal when rigid connections are present only at certain locations. Finally, Modeling to Generate Alternatives--MGA, is proposed to generate good design alternatives as the solution from optimization may not be optimal with respect to the unmodeled objectives and constraints. It provides a set of alternatives that are near-optimal with respect to the modelled objectives and that are also farther from each other in the decision space. Results show that a final design could be chosen from the set of alternatives or obtained by tinkering one of the alternatives.

Topology Optimization of Bracing Systems for Multistory Steel Frames under Earthquake Loads

Application of continuum structural topology optimization methods to the layout design of bracing systems for multistory steel frame buildings under earthquake loads is explored in this work. A weighted average strain energy sensitivity of element is formulated to be served as the element removal criterion in the optimization process, and then an ESO-based continuum structural topology optimization method for the layout design of multistory steel frame bracing systems subjected to earthquake-induced ground motions is presented. In each iterative design, an approximate reanalysis technique named CA method is adopted to reduce the computational effort. Finally, a design example is given to demonstrate the effectiveness of the presented optimization method for the optimal layout design of steel frame bracing systems under earthquake loads.

Nonlinear Finite Element Analysis on the Steel Frame with Semi-Rigid Connection under Periodic Load

In this paper, nonlinear finite element analysis on the steel frame with top-seat angle and double web-angles semi-rigid connection were carried out with ANSYS finite element software. In the analysis, connective, geometrical and material nonlinear were considered. Compare analysis results with experimental results, the influence of semi-rigid connection’s flexibility on steel frame was studied and some references to the design of steel frame with semi-rigid connection were supplied.

The Seismic Experiment of Steel Frame with GRC Lath

Two 1:4 scale wall specimen was tested under cyclic load to determine its seismic behavior, the responses of the steel frame with GRC lath are studied such as the failure modes, hysteretic behavior, ductility, energy dissipation, and the experimental results were compared with the steel frame. The testing data analysis indicated that bearing capacity, lateral stiffness, ductility and energy dissipation of the steel frame with GRC light hollow lath are superior to the steel moment frame, the steel frame with GRC lath is an ideal lateral resistant system. The prolapse of GRC lath from the frame did not appear, so the steel frame with GRC lath could be better used in the earthquake zone. Due to the collapse of connection of lath with frame, the ductility coefficient of the system is generally between 2 and 3, it is less than requirement of the seismic design specifications, and therefore a suggestion is that the seismic design of steel frame with GRC lath can be according to non-filled wall frame structure.

Optimum design of steel frames using a multiple-deme GA with improved reproduction operators

In this paper, the performance of the genetic algorithm is improved by introducing some new crossover and mutation operators. The new operators are incorporated into a multiple-deme genetic algorithm in which population is divided into subpopulations and communication between different demes is established through migration of individuals, enhancing diversity and resulting in better solutions. This algorithm is applied to the minimum weight design of steel frames subjected to actual strength and ductility constraints of AISC–ASD specifications as well as other serviceability and constructability constraints. The efficiency of the proposed method is demonstrated through optimising two benchmark problems including a three-bay, three-storey steel frame and a five-bay, 22-storey special steel frame. Significant improvements in the optimum solutions are obtained with reduced number of finite element analyses, resulting in less computational effort.

Modal strength reduction factors for seismic design of plane steel frames

A new method for the seismic design of plane steel moment resisting frames is developed. This method determines the design base shear of a plane steel frame through modal synthesis and spectrum analysis utilizing different values of the strength reduction (behavior) factor for the modes considered instead of a single common value of that factor for all these modes as it is the case with current seismic codes. The values of these modal strength reduction factors are derived with the aid of a) design equations that provide equivalent linear modal damping ratios for steel moment resisting frames as functions of period, allowable interstorey drift and damage levels and b) the damping reduction factor that modifies elastic acceleration spectra for high levels of damping. Thus, a new performance-based design method is established. The direct dependence of the modal strength reduction factor on desired interstorey drift and damage levels permits the control of deformations without their determination and secures that deformations will not exceed these levels. By means of certain seismic design examples presented herein, it is demonstrated that the use of different values for the strength reduction factor per mode instead of a single common value for all modes, leads to more accurate results in a more rational way than the codebased ones.

Heightwise Distribution of Stiffness Ratio for Optimum Seismic Design of Steel Frames with Metallic-Yielding Dampers

Metallic-yielding type of dampers is one of the oldest and most widely used passive energy dissipation devices to decrease dynamic response of buildings subjected to strong ground motions. These devices utilize the yielding of mild-steel plates, like Added Damping and Stiffness (ADAS) elements. The proper selection of design parameters of these devices has an important effect on the structural inelastic behavior. One of these parameters is ratio of the bracing member stiffness to the damper devise stiffness (B/D). Previous studies recommended that a B/D ratio of about 2 be used for the design of the ADAS elements in all stories of the buildings. In this paper, it is shown that using a fixed amount of B/D ratio for all stories may not lead to the uniform distribution of ductility. Therefore, the employment of such a B/D distribution does not guarantee the optimum use of dampers in the nonlinear range of behavior. Here, a method based on the concept of uniform distribution of deformation is implemented to optimize the dynamic response of building frames with bracing members and ADAS devices subjected to several strong ground motion records considering non-fixed B/D ratio in different stories. The results of nonlinear dynamic analyses for several buildings with different heights show that a B/D ratio more than 2 is needed in the upper stories, whereas a ratio less than 2 is needed in the lower stories for optimum dynamic behavior of the building.