Steel Moment Resisting Frame Structures Research Articles

The effect of far field and near field earthquakes on the hysteresis energy and relative displacement of steel moment resisting frame structures

Various types of research studies show that other parameters are also involved in seismic response of structures and only the force–displacement issue in elastic or even bilinear elastic perfectly plastic states is not capable of justifying the entire seismic behaviors of structures. Therefore, researchers are seeking to propose a new method in the seismic design of structures. In this regard and during the last two decades, the subject of energy has been highly taken into consideration, because by advances obtained in this method a lot of proposed parameters and behaviors in seismic design of structures have become justifiable and applicable in design process. In the current research, nonlinear dynamic analysis has been conducted under Loma Prieta, Landers, and Northridge earthquakes in far and near field on three ordinary moment resisting frames structures with 3, 6, and 12 stories in SAP2000 (VER 16.0.0) software. Hysteresis energy distribution and maximum relative displacements in buildings stories were extracted. The obtained results showed that near-fault earthquakes result in larger relative displacements of stories than far-fault.

Multi-objective seismic design optimization of steel frames by a chaotic meta-heuristic algorithm

In this study, multi-objective optimization is applied to implement performance-based design of steel moment-resisting frame (SMRF) structures. In order to efficiently achieve this purpose, a chaotic multi-objective firefly algorithm (CMOFA) is proposed to find the Pareto optimal front for the multi-objective performance-based optimum design (MO-PBOD) problem of SMRFs. The structural weight and the maximum inter-story drift at performance levels are taken as the conflicting objective functions of the MO-PBOD problem which should be optimized simultaneously subject to serviceability and ultimate limit-state constraints. In order to illustrate the efficiency of the proposed CMOFA meta-heuristic, two benchmark truss examples and three MO-PBOD examples of SMRFs are presented. The numerical results demonstrate the better computational performance of the proposed CMOFA meta-heuristic in comparison with some existing multi-objective algorithms.

Numerical study of an innovative SMA based beam-column connection in reducing the seismic response of steel MRF structures

During recent years, Shape Memory Alloys (SMAs) have been e ectively used to control the seismic response of structural systems. Recovering the residual strains upon unloading (super-elasticity) or by heating (shape memory e ect) is the main characteristic of SMA materials. This paper explores the eciency of a proposed application of steel & SMA bolts in improving the seismic behavior of connections in steel Moment Resisting Frame (MRF) structures. A new semi-rigid, end-plate, beamcolumn connection is introduced, which is based on parallel application of steel and austenite-phase SMA bolts. A number of 3-D steel MRF structural models with di erent numbers of stories and mass eccentricities are considered. These structural models that are designed by employing the conventional rigid and the proposed semi-rigid connections are subjected to bi-directional earthquake records that have been scaled according to ASCE7-05 procedure. Extensive nonlinear dynamic time history analyses are conducted to evaluate the eciency of the steel & SMA based connections in enhancing the seismic performance of the structural models. The obtained results indicate that the proposed steel-SMA connection is highly promising and can eciently reduce the seismic response parameters of the structural systems. Steel bolts of the end-plate connections contribute both to shear force transfer (from beam to column) and dissipation of the input seismic energy through hysteresis behavior. On the other hand, parallel application of steel and SMA bolts in the connections reduces the story drifts as well as the induced forces in the structural elements while decreasing the permanent story displacements. The main goal obtained is to keep the beams away from the formation of plastic deformation. OpenSees platform is used for generating the structural models and performing the numerical analyses.

Comparison of code-specific non-linear seismic performance

This paper reports a comparative study conducted on the non-linear performance of steel moment-resisting frame structures designed with the Iranian, European and Japanese seismic design codes of practice. To this end, typical three-, six-, nine- and 12-storey steel moment-resisting frames of the high-ductility category are designed based on the requirements adopted in the codes. The structural performance of each frame is then evaluated extensively based on Fema 356 provisions for life safety performance level utilising non-linear static procedure. Comparisons are made regarding the elastic stiffness, peak strength, target displacement, plastic hinge rotations of elements at the target displacement, sequences of hinging in various elements, global lateral response, as well as the total amount of materials used in each structure. Results reveal differences in global and local performances of the structures designed according to regulations relevant to each code. Moreover, in some cases, the requirements for life safety performance level are violated. Finally, recommendations are provided based on the results of the study.

Experimental study on seismic performance of partial penetration welded steel beam-column connections with different fillet radii

Full penetration welded steel moment-resisting frame (SMRF) structures with welded box sections are widely employed in steel bridges, where a large number of steel bridges have been in operation for over fifty years in Japan. Welding defects such as incomplete penetration at the beam-column connections of these existing SMRF steel bridge piers were observed during inspection. Previous experiments conducted by the authors' team indicate that gusset stiffeners (termed fillets in this study) at the beam-web-to-column-web joint of the beam-column connections may play an important role on the seismic performance of the connections. This paper aims to experimentally study the effect of the fillet radius on seismic performance of the connections with large welding defects. Four specimens with different sizes of fillet radii were loaded under quasi-static incremental cyclic loading, where different load-displacement relations and cracking behaviors were observed. The experimental results show that, as the size of the fillet radius increases, the seismic performance of the connections can be greatly improved.

Application of Reliability-Based Robustness Assessment of Steel Moment Resisting Frame Structures under Post-Mainshock Cascading Events

This paper proposes a reliability-based framework for quantifying structural robustness considering the occurrence of a major earthquake (mainshock) and subsequent cascading hazard events, such as aftershocks that are triggered by the mainshock. These events can significantly increase the probability of failure of buildings, especially for structures that are damaged during the mainshock. The application of the proposed framework is exemplified through three numerical case studies. The case studies correspond to three SAC steel moment frame buildings of three, nine, and 20 stories, which were designed to pre-Northridge codes and standards. Two-dimensional nonlinear finite-element models of the buildings are developed with the Open System for Earthquake Engineering Simulation framework (OpenSees), using a finite length plastic hinge beam model and a bilinear constitutive law with deterioration, and are subjected to multiple mainshock-aftershock seismic sequences. For the three buildings analyzed herein, it is shown that the structural reliability under a single seismic event can be significantly different from that under a sequence of seismic events. The reliability based robustness indicator shows that the structural robustness is influenced by the extent to which a structure can distribute damage.

Simplified Method for Estimation of Beam Plastic Rotation Demand in Special Moment-Resisting Steel-Frame Structures

It is necessary to predict the plastic deformation demand of members and the story drift ratio for seismic design. In the present study, a simple method of estimating the plastic rotation of beams in special steel moment-resisting frame structures designed by the strong column-weak beam philosophy was developed. The plastic rotation of beams was calculated as the function of the story drift ratio based on the result of elastic analysis. The effects of the design parameters, such as moment redistribution, joint dimension, plastic mechanism, panel zone deformation, and the rocking effect of lateral bracing were addressed. For verification, the proposed method was applied to 6-story special moment frames with and/or without lateral bracing. The plastic rotations of beams in the same floor significantly varied according to the design parameters, although the story drift ratio was the same. The plastic rotations of beams predicted by the proposed method correlated well with those from nonlinear static analysis.

Multi-objective seismic design method for ensuring beam-hinging mechanism in steel frames

Previous research efforts have shown that the column-beam flexural strength ratios of joints in moment resisting steel frames should be higher than 1.0 or even 2.0 for a beam-hinging collapse mechanism. However, it has been pointed out that, in order to prevent a weak story mechanism in a structure, it is not practical to use a specific single value as a limit for the column-beam flexural strength ratio for all joints of a structure. Therefore, an optimal design technique is needed to determine the column-beam flexural strength ratios for joints in a structure. In this paper, a multi-objective seismic design method for ensuring beam-hinging mechanism in steel moment resisting frame structures is presented and applied to optimal seismic design of well-known steel moment frames. In addition to the constraint for ensuring beam-hinging mechanism, the relationship between the structural cost and the energy dissipation capacity of structures is provided by considering the two conflicting objective functions. In order to select the best design among the candidate designs, as a guide for structural engineers, a simple rule is presented in the form of dissipated energy density defined by the ratio of the energy dissipation capacity to the structural weight.

Survey on different factors influencing small-scale milking practices in a peri-urban area

The main objective of this paper is to evaluate the load-displacement capacity of steel moment-resisting frame structures using the conventional non-linear static analysis method and incremental dynamic analysis approach. Emphasis was put on the influence of different lateral load patterns on the plastic hinge of structural components and also on the seismic behavior of the structures which is influenced by the behavior of their components [(EEsof, electronic engineering software)]. Firstly, to get an idea, two simple frames were selected and analytically tested using the conventional push-over and then the results were compared with dynamic analysis approach using a simple harmonic time-history. The results show that the axial forces in columns obtained from dynamic approach are smaller than those of the other non-linear static methods and this influences the plastic hinge lengths. Then three sets of steel moment-resisting frames were loaded under different load patterns frequently used in conventional push-over analysis methods. The outputs of the structural analysis, in the forms of story shear versus story drift ratios of upper, middle and lower portions show that in general, nonlinear static analysis results in smaller axial forces in columns which cause smaller component deformations, thus weaker structural load-deformation capacities. Key words: Performance- based engineering,nonlinear static analysis, lateral load pattern, plastic hinge.

Reliability-based assessment of deteriorating steel moment resisting frames

One of the objectives in performance-based earthquake engineering is to quantify the seismic reliability of a structure due to future random earthquakes at a designated site. For that purpose, two performance evaluation processes that do incorporate the effect of aleatory and epistemic uncertainties are illustrated and used in order to calculate the reliability of different height Special Moment Resisting frames through two probabilistic-based measures. These two measures are the confidence levels for satisfying the desired performance levels at given hazard levels and mean annual frequency of exceeding a specified structural capacity. Analytical models are employed including panel zone and a comprehensive model for structural components that not only include strength and stiffness degradation in back bone curve, but also incorporate gradual deterioration of strength and stiffness under cyclic loading. Incremental dynamic analysis is then utilized to assess the structural dynamic behavior of the frames and to generate required data for performance based evaluations. This research is intended to contribute to the progress in improvement of the performance knowledge on seismic design and evaluation of special steel moment resisting frame structures.

Effects of connection deformation softening on behavior of steel moment frames subjected to earthquakes

In the years since the 1994 Northridge earthquake, the profession has paid significant attention to the potential effects of various forms of deterioration in connection strength and stiffness that steel moment-resisting frames can experience during severe seismic excitations. The brittle connection fractures that a number of welded steel moment-resisting frame structures experienced during recent earthquakes have been the most extensively studied to date. However, cyclic testing of post-Northridge beam-column connections demonstrates that ductile connections may suffer other forms of deterioration. Negative post-yield tangent stiffness or capping, hereafter referred to as deformation softening, is a behavior of particular interest because it may have significant adverse effects on frame system behavior. The effects of deformation softening on frames subjected to pulse excitations were examined as part of an integrated experimental and analytical investigation of the effect of various forms of hysteretic deterioration on the overall system behavior of moment resisting steel frames. Pulse excitations, and the near-field ground motions they represent, can be highly damaging to structures and are therefore the primary focus of the results presented in this paper. The experimental portion of this study consisted of a series of thirty-two shaking table tests, which were performed on a one-third scale, two-story, one bay, steel moment frame with idealized, mechanical connections. These tests and subsequent analytical studies show that, in general, significant loss of connection strength capacity, whether from deformation softening or other types of deterioration, leads to large residual drifts and, for large pulse excitations with durations longer than the fundamental period of the structure, to collapse. In particular, frames with connections exhibiting negative post-yield stiffness tend to have substantially increased peak and residual displacements when subjected to pulse excitations.

Evaluating the Damage in Steel MRF under Near Field Earthquakes from a Performance Based Design Viewpoint

This study is about the performance assessment of steel moment resisting frame structures under nearfield strong ground motions. A number of 3 and 9-story, 3-D structural models being designed using the strength method, are considered. A set of 7 near-field earthquake records, scaled according to ASCE-7(05), are considered for nonlinear dynamic time history analyses using OpenSees program. Park and Ang damage index is considered for quantitative measurement of the performance of structural models. Maximum values of inter-story drifts along with the local and global damage indices are determined to be used in the performance assessment process. Considering the average results of different scaled ground motions, it is observed that nearly all the structural models cross the limit of repairable damage for the 10/50 hazard level with many of them close to collapse under MCE level ground motions.

ANALYTICAL SIMULATION OF PROGRESSIVE COLLAPSE OF PERIMETER FRAMES DUE TO OUT-OF-PLANE BEHAVIOR IN MOMENT FRAME STRUCTURES

Typical steel moment-resisting frame structures in the United States, similar to many super-high-rise framed-tube structures being constructed in Japan, have stiff beams and columns only around perimeters and often have none or few seismic beams inside the building. The lack of strength and stiffness of connections between perimeter frames and floors to support the out-of-plane behavior of perimeter frames may cause unstable behavior when perimeter frames are separated from the floors due to accidental or earthquake loading. This study analytically simulates progressive collapse when the attachment of perimeter frames to floors is lost and predicts the strength of the connections required to prevent progressive collapse during earthquakes.

Life cycle cost oriented seismic design optimization of steel moment frame structures with risk-taking preference

Life cycle cost is considered in this paper for multiobjective design optimization of seismic steel moment-resisting frame (SMRF) structures. Initial material/construction cost and lifetime seismic damage cost, which are usually added up in the existing literature to form the total life cycle cost measure, are considered as two separate cost measures. The number of different standard steel section types is used to roughly account for the degree of design complexity related additional construction expenses. These three merit measures are subject to balanced minimization. The maximum interstory drift ratio is selected as the single seismic performance parameter for a code-compliant SMRF design and is evaluated through a static pushover analysis. Effects of randomness and uncertainty in estimating seismic demand and capacity as well as in describing seismic hazards are considered in accordance with SAC/FEMA guidelines. The lifetime seismic damage cost is then computed with designer-specified confidence level dependent percentile exceedance probabilities of prescribed drift ratio limits that demarcate a spectrum of performance levels with varied damage states. Using a multiobjective genetic algorithm, the proposed automated optimization procedure produces a set of alternative designs that exhibits optimized tradeoff among the three conflicting objectives. Therefore, designers have much freedom to choose the final structural solution with a preferred balance of initial cost and lifetime seismic damage cost while taking into due account of the degree of design complexity.

梁端下端フランジに高力ボルト摩擦すべりダンパーを設置したH形鋼梁の曲げせん断実験

In this paper, we proposed a new seismic hinge, which was applied to the beam end regions of steel moment resisting frame structures. The hinge consists of a narrow vertical slot which cuts the beam bottom flange, the bolted frictional slippage damper which connects the beam bottom flange cut, and the inclined stiffeners which transfer the beam shear force beyond the vertical slot. It is planned that the frame which has the hinge mechanism does not produce the large plastic deformation at the beam end region, but resists against seismic action with the frictional slipping behavior of the bolted dampers. This paper presents the result of the static and dynamic loading tests on the wide flange steel beams with the bolted frictional slippage damper. The beams with the proposed hinge mechanism behaved with the perfect elasto-plastic type of the load deformation response as planned during the loading.

Probabilistic seismic demand analysis of controlled steel moment‐resisting frame structures

AbstractThis paper describes a proposed methodology, referred to as probabilistic seismic control analysis, for the development of probabilistic seismic demand curves for structures with supplemental control devices. The resulting curves may be used to determine the probability that any response measure, whether for a structure or control device, exceeds a pre‐determined allowable limit. This procedure couples conventional probabilistic seismic hazard analysis with non‐linear dynamic structural analyses to provide system specific information. This method is performed by evaluating the performance of specific controlled systems under seismic excitations using the SAC Phase II structures for the Los Angeles region, and three different control‐systems: (i) base isolation; (ii) linear viscous brace dampers; and (iii) active tendon braces. The use of a probabilistic format allows for consideration of structural response over a range of seismic hazards. The resulting annual hazard curves provide a basis for comparison between the different control strategies. Results for these curves indicate that no single control strategy is the most effective at all hazard levels. For example, at low return periods the viscous system has the lowest drift demands. However, at higher return periods, the isolation system becomes the most effective strategy. Copyright © 2002 John Wiley & Sons, Ltd.

Estimation of seismic drift demands for frame structures

A process is outlined and evaluated for the estimation of seismic roof and storey drift demands for frame structures from the spectral displacement demand at the first mode period of the structure. The spectral displacement demand is related to the roof drift demand for the multi-degree-of-freedom (MDOF) structure using three modification factors, accounting for MDOF effects, inelasticity effects, and P-delta effects. Median values and measures of dispersion for the factors are obtained from elastic and inelastic time history analyses of nine steel moment resisting frame structures subjected to sets of ground motions representative of different hazard levels. The roof drift demand is related to the storey drift demands, with the results being strongly dependent on the number of stories and the ground motion characteristics. The relationships proposed in this paper should prove useful in the conceptual design phase, in estimating deformation demands for performance assessment, and in improving basic understanding of seismic behaviour. Copyright © 2000 John Wiley & Sons, Ltd.

Dynamic P-Delta Effects for Flexible Inelastic Steel Structures

Inelastic seismic response of steel moment resisting frame structures, which are usually quite flexible and subject to large displacements under severe ground motions, may be severely influenced by the structure P-delta effect. For structures in which this effect induces a negative postyield story stiffness, as seen from a pushover (story shear-story displacement) curve, the response becomes very sensitive under ground motions that are sufficiently strong to drive the structure into this negative postyield stiffness range. The response under such conditions may be highly nonsymmetric with progressive displacements to one side, which increases the collapse potential of the structure in a sidesway mode. This paper focuses on two case studies that (1) illustrate P-delta sensitive behavior; (2) demonstrate the sensitivity of predicted behavior to ground-motion characteristics and analytical modeling; and (3) contribute to the development of engineering guidelines for protection against excessive P-delta effects. A relatively simple procedure is proposed for identifying P-delta sensitive cases, and recommendations are made for improving the P-delta response of flexible steel frame structures.

Effects of Connection Fractures on SMRF Seismic Drift Demands

A central portion of an extensive investigation into the effects of beam-column connection fractures on seismic interstory drift demands for steel moment-resisting frame (SMRF) structures is summarized. Nonlinear dynamic analyses are carried out for six SAC Phase II buildings modeled with brittle connections and subjected to the SAC ground motions at two probability levels. Story drift demand statistics for the model structures with brittle connections are compared with those for the model structures with ductile connections. An empirical analysis model for connection fracture is employed, with values for the parameters of the model calibrated by field and laboratory data. The sensitivities of story drift demands to variations in the fracture parameters are explored. In particular, the case when only bottom beam-flange-connections fracture is contrasted with the case of both top- and bottom-flange fractures. Whereas the effects of single-flange (e.g., bottom-flange) fractures alone on story drift demands ...

Evaluation of the seismic level of protection afforded to steel moment resisting frame structures designed for different design philosophies

Steel moment resisting frames have been considered as excellent systems for resisting seismic loads. However, after recent earthquakes (e.g., Northridge, California, in 1994 and Kobe, Japan, in 1995) the confidence in this structural system was reduced as a result of various types of damage that moment resisting steel frames suffered. This paper presents the results of the evaluation of seismic level of protection afforded to steel moment resisting frame buildings designed in accordance with the National Building Code of Canada. Six- and 10-storey office buildings located in a region of intermediate seismic hazard are designed in accordance with the current Canadian code provisions. Three different design philosophies are considered, namely strong column - weak beam (SCWB), weak column - strong beam (WCSB), and strong column - weak panel zone (SCWP). The performance of these frames is evaluated dynamically by subjecting an inelastic model to an ensemble of 12 actual strong ground motion records. The model takes into account both connection flexibility and panel zone shear deformation. The results are presented in terms of response parameters determined from static pushover analyses, as well as statistical measures of the maximum response parameters determined from the inelastic dynamic analyses. The computed performance of the frames is evaluated in order to assess both the overall level of protection of the frames and the preferred design philosophy. It is concluded that a well-designed and well-detailed ductile moment resisting frame designed using either the SCWB or SCWP design philosophy can withstand ground motions of twice the design level with very little likelihood of collapse, whereas a frame designed using the WCSB approach is ill-conditioned and may develop a collapse mechanism at an excitation level well below twice the design level.Key words: seismic, ductile, steel, frame buildings, performance, design, ductility, damage, inelastic, dynamic.