Seismic Design Of Steel Frames Research Articles

The Mechanical Behavior Study on Reduced Beam Section and Widened Beam Section Connections of Steel Frames

In the paper, finite element models are established by using numerical methods to study the mechanical behavior of these kinds of connections. By discussing the range of design parameter of reduced beam section connection and widened beam section connection, stress distribution of connections and the influence of design parameter on bearing capacity at elastic stage and plastic stage are studied. The FEM models of these two kinds of connections behaved good ductility behavior. The purpose of moving plastic hinge outward from the beam and column interface is realized. Stress concentration near welds at the end of beam is reduced significantly. The bearing capacity of widened beam section connection increase obviously due to expanding the local area of beam flanges at the end of beam, but that of reduced beam section connection decrease due to trimming beam flanges. After studies, the range of design parameter of reduced beam section connection and widened beam section connection are given in the paper, and comparing with FEMA-350 [14] of American. The suggestion parameters would be useful for seismic design of steel frames.

Analytical expressions for preliminary design of dissipative bracing systems in steel frames

In this paper a direct displacement-based design (DDBD) method for seismic design of steel frames equipped with dissipative braces is proposed. Attention is focused on concentric braced steel frames with pinned beam-to-column joints in which the bracing system (with viscoelastic or elastoplastic dissipative devices) is the main seismic resistant component. The proposed design method uses an equivalent continuous model where flexural deformability and shear deformability are related respectively to columns and diagonals of the bracing system. In this way, analytical expressions of the required flexural and shear stiffness distributions are obtained. These expressions are quite simple and can be conveniently used in preliminary design of dissipative diagonal braces and columns. Examples are shown for steel frames with dissipative braces based on elastomeric dampers (viscoelastic devices) and steel frames with buckling-restrained braces (elastoplastic devices). Results of time history analyses are illustrated and discussed in order to evaluate the effectiveness of the proposed DDBD procedure.

Performance-based seismic design of steel frames using ant colony optimization

In this paper, a performance-based optimal seismic design of frame structures is presented using the ant colony optimization (ACO) method. This discrete metaheuristic algorithm leads to a significant improvement in consistency and computational efficiency compared to other evolutionary methods. A nonlinear analysis is utilized to arrive at the structural response at various seismic performance levels, employing a simple computer-based method for push-over analysis which accounts for first-order elastic and second-order geometric stiffness properties. Two examples are presented to illustrate the capabilities of ACO in designing lightweight frames, satisfying multiple performance levels of seismic design constraints for steel moment frame buildings, and a comparison is made with a standard genetic algorithm (GA) implementation to show the superiority of ACO for the discussed optimization problem.

Assessment of European seismic design procedures for steel framed structures

This paper assesses the fundamental approaches and main procedures adopted in the seismic design of steel frames, with emphasis on the provisions of Eurocode 8. The study covers moment-resisting as well as concentrically-braced frame configurations. Code requirements in terms of design concepts, behaviour factors, ductility considerations and capacity design verifications, are examined. The rationality and clarity of the design principles employed in Eurocode 8, especially those related to the explicit definitions of dissipative and non dissipative zones and associated capacity design criteria, are highlighted. Various requirements that differ notably from the provisions of other seismic codes are also pointed out. More importantly, several issues that can lead to unintentional departure from performance objectives or to impractical solutions, as a consequence of inherent assumptions or possible misinterpretations, are identified and a number of clarifications and modifications suggested. In particular, it is shown that the implications of stability and drift requirements as well as some capacity design checks in moment frames, together with the treatment of post-buckling response and the distribution of inelastic demand in braced frames, are areas that merit careful consideration within the design process.

Multiobjective heuristic approaches to seismic design of steel frames with standard sections

AbstractSeismic design problem of a steel moment‐resisting frame is formulated as a multiobjective programming problem. The total structural (material) volume and the plastic dissipated energy at the collapse state against severe seismic motions are considered as performance measures. Geometrically nonlinear inelastic time‐history analysis is carried out against recorded ground motions that are incrementally scaled to reach the predefined collapse state. The frame members are chosen from the lists of the available standard sections. Simulated annealing (SA) and tabu search (TS), which are categorized as single‐point‐search heuristics, are applied to the multiobjective optimization problem. It is shown in the numerical examples that the frames that collapse with uniform interstorey drift ratios against various levels of ground motions can be obtained as a set of Pareto optimal solutions. Copyright © 2007 John Wiley & Sons, Ltd.

Random material variability effects on full-strength end-plate beam-to-column joints

In the seismic design of steel frames, beam-to-column joints are generally designed as full strength joints in order to avoid their engagement in the plastic range promoting the location of plastic hinges at the ends of the connected beams. In this paper, the reliability of the criteria to design full strength beam-to-column joints is investigated. In particular, in the first part of the work, starting from probabilistic analyses accounting for random material variability of connecting elements, the reliability of the design criteria suggested by codes is analyzed. Successively, on the basis of the obtained results, a new design criterion able to account for both the random material variability and the overstrength exhibited by the beam before the occurrence of local buckling is proposed.

SEISMIC DESIGN OF STEEL FRAMES WITH PARTIAL STRENGTH JOINTS

In the seismic design of steel frames, beam-to-column joints can be designed either as full strength joints, forcing the location of the plastic hinges at the beam ends, or as partial strength joints which have to dissipate the seismic input energy. Seismic codes provide specific design criteria for full strength joints, but there are no detailed recommendations dealing with partial strength connections. Therefore, in this paper, by means of a simplified model, such as a SDOF system, the requirements which partial strength joints have to possess, for designing steel frames characterised by seismic performances equivalent to those of steel frames with rigid full strength joints, are pointed out. Successively, starting from the above requirements, a new method for designing seismic resistant steel frames with extended end plate connections leading to the complete definition of the geometrical and mechanical parameters of the joints is proposed.

In-Plane Properties and Modeling of Reduced Beam Sections

In the seismic design of steel frames, one of the objectives is to provide ductile beams capable of energy dissipation through the formation of plastic hinges (or "fuses"). With wide-flange shapes, it is desirable to force these hinges away from the brittle zones near the column faces by reducing the beam section at some specified distance from these faces. Obviously, the cuts change the overall elastic properties of the reduced beam sections (RBS). However, the cuts also affect the fixed-end actions used in the elastic analysis of the structure. The first objective of this paper will be to compute not only the stiffness properties of RBS, but also the fixed-end actions. Most structural analysis programs found in design offices do not let the designer input stiffness matrices and fixed end actions. Input of beam elements is usually limited to prismatic or tapered beams. The second objective will be to show how this difficulty may be overcome by modeling a RBS with three prismatic beam elements of suitable properties. Some very simple frames will be used as examples to compare interstory drifts, and examine the Q33 method proposed by Iwankiw and Mohammadi in an earlier paper. Coincidentally, these calculations lead to the observation that beam shear deformation is not always negligible.

The establishing of performance level thresholds for steel moment‐resisting frame using an energy approach

AbstractIn this study, an energy design approach is proposed within the framework of the performance‐based seismic design of steel frames. Accumulated plastic rotation is selected as a parameter to establish the performance level thresholds. The test results of steel connections are investigated to quantify the performance level thresholds. The hysteretic energy input is acquired from a previous statistical study of twelve six‐storey steel moment‐resisting frames. The seismic performance of three‐storey steel moment resisting frames using the energy approach is examined. The research concluded that the structure designed by the energy method performed better than the steel frame designed by the equivalent lateral force (ELF) of UBC‐97 in view of accumulated plastic rotation. Performance levels such as functional, life safety and collapse are discussed based on the ductility level and the performance characteristics. Copyright © 2001 John Wiley & Sons, Ltd.

A simple approach to the seismic design of friction damped braced medium-rise frames

This paper is concerned with the seismic design of steel frames using friction damped slotted bolted connections (SBCs) in the diagonal braces as a means for passive control. A dynamic model that uses bilinear hysteretic behavior for the damper describes the response of a single degree of freedom (SDOF) steel frame and constitutes the basis for the design. A design procedure that attains the stiffness of the individual braces and their elongation at the threshold of activation is then applied to 10-story and 3-story steel frames. This design procedure is a two-phase iterative scheme of the analysis/redesign type, the analysis of which is modal. Finally, a full nonlinear dynamic analysis that uses a generalized version for MDOF's of the bilinear hysteretic SDOF model assesses the design.

Practical Advanced Analysis for Seismic Frame Design

This paper presents the use of advanced analysis in the practical seismic design of steel frames. The proposed approaches to refine the elastic-plastic hinge method will be described. The LRFD-based static seismic design procedure for Special Moment Frames, utilizing advanced analysis, will be developed. A design example will be provided. The advanced analysis eliminates tedious member capacity checks and directly captures the overall system response, including the system overstrength factor, critical areas, and excessive deformation demands. Therefore, the proposed method provides a reliable and convenient alternative design procedure for the present static seismic design procedure.

PLASTIC DESIGN OF SEISMIC RESISTANT STEEL FRAMES

A new method for designing moment resisting steel frames failing in a global mode is presented in this paper. Starting from the analysis of the typical collapse mechanisms of frames subjected to horizontal forces, the method is based on the application of the kinematic theorem of plastic collapse. The beam section properties are assumed to be known quantities, because they are designed to resist vertical loads. As a consequence, the unknowns of the design problem are the column sections. They are determined by means of design conditions expressing that the kinematically admissible multiplier of the horizontal forces corresponding to the global mechanism has to be the smallest among all kinematically admissible multipliers. In addition, the proposed design method includes both the influence of distributed loads acting on the beams and the influence of second-order effects. In particular, the influence of second-order effects, which can play an important role in the seismic design of steel frames, is accounted for by the mechanism equilibrium curves of the analysed collapse mechanisms. Moreover, in order to show the practical application of the proposed design procedure, a worked example is presented. Finally, the inelastic behaviour of the designed frame is compared to that obtained when the simple member hierarchy criterion or a similar rule is applied. © 1997 by John Wiley & Sons, Ltd.

Discussion of “ Disposable Knee Bracing: Improvement in Seismic Design of Steel Frames ” by J. Dario Aristizabal‐Ochoa (July, 1986, Vol. 112, No. 7)

Discussion of “ <i>Disposable Knee Bracing: Improvement in Seismic Design of Steel Frames</i> ” by J. Dario Aristizabal‐Ochoa (July, 1986, Vol. 112, No. 7)

Disposable Knee Bracing: Improvement in Seismic Design of Steel Frames

A new and practical technique of lateral bracing for single‐ and multistory steel frame construction is presented and discussed. Disposable Knee Bracing (DKB) technique, as it is called in this paper, is made up of two structural elements, the knee element and the diagonal brace element. The knee element is a fuse‐like element that dissipates energy by the formation of plastic flexural hinges at its ends and midspan when the building is subjected to severe lateral loads. The diagonal brace element, on the other hand, provides the required level of lateral stiffness and remains in the elastic range at all time. The knee element is a disposable beam element that can be replaced once its energy dissipation capacity is utilized. Standard limit analysis of low‐ and high‐rise steel frames are presented to demonstrate the advantages of the DKB against traditional bracing and eccentric bracing.

Shear in Beam-Column Joints in Seismic Design of Steel Frames

In unbraced steel frames, structural stability and resistance to lateral loads require the transfer of bending moments between beams and columns. Depending upon stiffness and strength requirements, this transfer of bending moments can be achieved by either semi-rigid or rigid beam-column connections. In both cases, the intersection between beams and columns (the beam-column joint) will be subjected to high shears whenever a significant unbalance of beam moments is present at the joint. A significant unbalance usually exists at exterior and corner joints, and at interior joints in the case of lateral load application such as wind or seismic effects. Somewhat simplified, the effect of an unbalance of beam moments on the moment and shear force diagram along the column is illustrated in Figs. 1a and 1b. Figure 1c shows the forces acting on a free body of an interior joint. The effect of the shear forces in joints must be accounted for in the design of frames. In the design for strength, the joints must be capable of transmitting the high shear forces through the columns in accordance with the selected design procedure, which may be based on allowable stresses or ultimate strength. In the design for stiffness, it may be necessary to verify that the joint distortions caused by the shear forces do not excessively affect the story drift under lateral loads.