Steel Moment Frame Structures Research Articles

Investigating post-earthquake progressive collapse resistance of irregular steel structures

Removal of load-bearing elements such as columns, can rapidly lead to structural failures and the compromise of building stability. These failures can be initiated by minor damage but can ultimately culminate in catastrophic events. In the line of progressive collapse resistance of conventional urban buildings, extensive studies have so far been performed; though relatively little attention has been paid to the impact of earthquakes on structural resilience under such failures, this is particularly the case in irregular structures as these structures have hardly received much attention. In this research, considering the presence of setback irregularities in many structures, the impact of the column removal scenario after different earthquake intensities of low, medium, and high on over 60 steel moment frame structures with 5 and 10 stories is investigated. The structures are first categorized into four vulnerability groups, from maximum to minimum resistance against progressive collapse, based on the damage percentage. After applying 12 earthquake records at the MCE level, the cases studied are assessed under column removal scenarios at different spans and stories. The results reveal that earthquakes, elevate the risk of progressive collapse. Moreover, increasing setback irregularity up to 13.33 % improves structural performance against progressive collapse, reducing responses by 21 % on average compared to regular structures. However, at higher setback irregularity percentages, responses increase by 82 % on average, diminishing structural resistance. Setting upper limits for this type of irregularity and imposing constraints on design parameters, while modifying minimum base shear and maximum period limit, can significantly reduce progressive collapse potential.

Aftershock collapse capacity assessment of special steel moment frame structures

This study assessment of the collapse capacity of special steel moment frames (SSMFs) with considering earthquake shock sequences for structures height from 4 to 20 stories. The collapse capacity is expressed in terms of the Sa(T1) value at which the system reaches the collapse state. Collapse identification relies on the capability of the model to accurately simulate damage of members and the resulting behavior deterioration. The softening in the lateral response expressed in terms of maximum interstory drift (MID) when it is expressed against the Sa(T1) values is thus used to identify collapse occurrence. The mainshock-aftershock (MS-AS) effect and the uncertainties associated with it are simulated by utilizing a set of 32 natural record pairs. The level of damage induced by MS is represented by two parameters including MID and peak residual story drift (PRSD). Using these parameters, the MS is applied so as to various pre-selected damage levels are imposed. For each MS damage level, an incremental dynamic analysis (IDA) is performed using the AS record that follows MS and a free vibration phase. The AS intensity causing the collapse state is finally identified and respected for evaluating the effect of MS damage level. The correlation between the median collapse Sa’s, called aftershock median collapse capacity, and the MS damage indicated by MID and PRSD parameters is quantified. The study results indicate that larger mainshock damages are required to reduce the collapse capacity of high-rise SSMFs compared to low- to mid-rise structures. Furthermore, the structural collapse capacity may reduce significantly when the building is subjected to a high intensity MS. A comparison between the trendlines presented by the regression equations developed in terms of the MID and PRSD variables was indicated that the MID parameter was more predictable trend.The PRSD parameter was, however, said to be useful in the sense that its value could be measured just after an MS excitation.

EESD special issue: AI and data‐driven methods in earthquake engineering – (Part 1)

EESD special issue: AI and data‐driven methods in earthquake engineering – (Part 1)

Seismic Performance of Built-In Continuous-Column Steel Moment Frame with Low-Damage CPSFC at Column Bases

Integrating the concepts of frictional energy dissipation and low-damage mechanism, this paper proposes a built-in continuous-column (BCC) steel moment frame structure with low-damage cover plate slip-friction connections (CPSFCs) at the column bases. The slip-friction connections can convert the buckling energy dissipation of the column into frictional energy dissipation, and the continuous column can improve the lateral deformation mode of the structure under seismic action. The strength and stiffness deterioration characteristics of the material were considered in the simulation of the seismic performance of the structure, and the simplified numerical models of CPSFCs and continuous columns were established in OpenSees. Comparative analyses were carried on a seven-story steel frame, steel moment frame (SMF) with CPSFCs at the column bases (CPSFC–SMF), and a built-in continuous column steel frame (BCCF) with CPSFC at the column bases (CPSFC–BCCF). The results showed that CPSFC slightly reduced the bearing capacity of the steel moment frame but minished the structural stiffness degradation and increased the ductility of the structure. The setting of CPSFC changed the plasticity hinge sequence of the structure, resulting in a homogeneous deformation between stories. The CPSFC–BCCF had the best damage pattern and the most uniform inter-story energy dissipation.

Multi-objective optimization for probabilistic performance-based design of buildings using FEMA P-58 methodology

This research presents an automated performance-based optimal design process by integrating a multi-objective optimization algorithm and a comprehensive probabilistic performance assessment method. This process is used to provide a set of design options that comply with the minimum code requirements and are optimal in terms of both initial cost and mean annual repair cost. The FEMA P-58 methodology is utilized as a modern performance-based methodology to determine the various performance measures such as repair costs, repair time, casualty rates, environmental impacts, and unsafe placarding for the design alternatives. To account for uncertainties in the magnitude and intensity of future earthquakes, the time-based assessment, and to account for inherent uncertainties affecting seismic performance, the Monte Carlo procedure is performed in accordance with FEMA P-58 guideline. The optimization process is carried out using a well-known multi-objective optimization algorithm called NSGA-II for three example office buildings with 3-, 6- and 9-story steel moment frame structures. For each building, a detailed performance model including a set of fragility functions for the structural and non-structural components as well as contents typically present in the building is considered. Three optimal design options are selected from the Pareto front set obtained for each building based on different optimization objectives. They are compared with each other and with the other design alternatives in terms of various performance metrics under different ground motion intensities. The contribution of structural components as well as drift-, acceleration- and velocity-sensitive non-structural components to the repair costs of these optimal designs is investigated. It is shown that drift-sensitive nonstructural components have the largest contribution to the repair costs of optimal structures. The contribution of these components in earthquake events with a 29% probability of exceedance in 50 years (29%/50 yrs) is on average about 71%, which decreases to 55% with increasing seismic intensity to 3%/50 yrs.

Reducing the lateral displacement of lead rubber bearing isolators under the near field earthquakes by crosswise dissipaters connected to rigid support structure

The purpose of base isolation is to absorb earthquake energy, prolong the life of the structure, and enable the structure to be similar to a rigid body. However, since resonance can occur due to the closeness of the period of structures to the long period and large velocity pulses of the near field earthquakes, the stability of these buildings greatly reduces, and with the large displacement above isolation level, sometimes, tendency of overturning is created in isolators leading to their destruction. The main objective of this study is to significantly reduce the lateral displacement of base isolation subjected to near field earthquakes. In this research, seismic response calculation has been carried out for five steel moment frame structure with the 3, 5, 8, 11, and 14 stories in two states of with and without stiff core structure and energy dissipaters. The analyses has been done under fourteen scaled records of seven near-source and seven far-source earthquakes. It has been shown that the lateral displacement of base isolation system can be reduced by 87% for low-rise buildings, and 77% for high-rise buildings.

On the optimal performance-based seismic design objective for steel moment resisting frames based on life cycle cost

The present study attempts to propose an optimum performance objective in the performance-based design method based on life cycle cost. For this purpose, the optimum hazard level which corresponds to the Life Safety performance level is explored in order to minimize the total cost of standard commercial office buildings. Furthermore, the effect of some parameters such as building depreciation over time, building lifetime, and monetary discounting rate on the optimal seismic hazard level is evaluated. The uncertainties involved in seismic loss assessment are considered according to the FEMA-P-58 methodology. To achieve the objectives of this study, three buildings with steel moment frame structures having 5, 10, and 15 stories are investigated. The buildings are optimally designed at different seismic hazard levels with a performance-based approach and then evaluated for the probabilistic life cycle cost. Among the five designs with different design objectives for each building, the design with the minimum total cost is chosen as the optimal design and the corresponding seismic hazard level is presented as the optimal hazard level. The results show that an increase of up to 25.1% in initial structural cost by selecting the optimal hazard level leads to a decrease of up to 57.7% and 16% in life cycle cost and total cost, respectively.

Evaluation of seismic performance of rotational-friction slip dampers in near-field and far-filed earthquakes

In this study, the performance of rotational-friction slip dampers in steel structures with different heights is investigated by the use of fragility curves. The use of dampers is one of the methods for vibration control of structures by simultaneously increasing both the structural stiffness and damping. Rotational-friction slip dampers are among the passive control devices that dampen the earthquake energy through their stable cyclic behavior. To study the performance of these devices in steel structures, 3, 6 and 9-story steel moment frame structures are designed, and the mentioned dampers are attached to the structure by Chevron braces. To account for the earthquake uncertainty, with the aid of incremental dynamic analysis (IDA), the damper-equipped structure is subjected to both near-field and far-field ground motion records. The acceleration and drift engineering demand parameters are selected as the functions to quantify the damage states, and the design, modeling and material properties uncertainties are considered in accordance with FEMA P-695. Evaluation of statistical results and comparison of the fragility curves, shows that the probability of failure at different damage states decreases when the dampers are added to the structure. This decrease is more remarkable in low-rise structures and near-fault ground motions.

State-of-the-art of Research Progress of Self-centering Structure System

Traditional building structures dissipate seismic energy through the plastic deformation of members in the earthquake, which may lead to a large residual deformation after the earthquake. Those structures are very difficult to repair. Traditional building structure can become a new structure with self-centering ability by using a special energy dissipation component, adding prestressed tendons or supplementing dampers. Compared to the traditional building structure, this new self-centering structure can more effectively reduce the residual deformation caused by the earthquake, and it has a desirable capability to dissipate seismic energy so as to enable itself to be of more security. In this study, the domestic and foreign self-centering structures are classified and summarized. This study deals with research progress of self-centering structures including self-centering concrete shear wall structure, self-centering concrete frame structure, self-centering steel moment frame structure, self-centering braced steel frame structure, self-centering steel plate shear wall structure and self-centering offshore platform structure. Besides, this study introduces the related research progress of other research fellows.

Sensitivity of the Fragility Curve on Type of Analysis Methods, Applied Ground Motions and Their Selection Techniques

Fragility curves are the primary way of assessing seismic risk for a building with numerous studies focused on deriving these fragility curves and how to account for the inherent uncertainty in the seismic assessment. This study focuses on a three-story steel moment frame structure and performs a fragility assessment of the building using a new approach called SPO2FRAG (Static Pushover to Fragility) that is based on pushover analysis. This new approach is further compared and contrasted against traditional nonlinear dynamic analysis approaches like Incremental Dynamic Analysis and Multiple Stripe Analysis. The sensitivity of the resulting fragility curves is studied against multiple parameters including uncertainties in ground motion, the type of analysis method used and the choice of curve fitting technique. All these factors influence the fragility curve behavior and this study assesses the impact of changing these parameters.

Mainshock–aftershock low-cycle fatigue damage evaluation of performance-based optimally designed steel moment frames

Considering the widespread damages of connections in steel moment frame (SMF) structures due to destructive earthquakes, seismic assessment of these structures for cumulative low-cycle fatigue (LCF) is of utmost importance and must be carefully taken into account in the design process of SMFs. To calculate the LCF damage index for SMFs, the Palmgren-Miner’s rule is applied on the history of relative drift of the stories based on non-linear response history analysis and existing experimental fatigue curves. On the other hand, repeated earthquakes strongly affect the inelastic response of structures and can increase building vulnerability. Therefore, the primary objective of this study is to numerically assess the mainshock-aftershock LCF damage index for performance-based optimally designed SMFs. Two illustrative design examples of 6- and 12-story SMFs are presented and designed for optimal initial and total costs in the context of performance-based design. The LCF damage index is evaluated for these structures by conducting nonlinear response-history analysis for a suite of real strong multiple earthquakes. The results showed that the optimally designed SMFs are highly vulnerable against LCF damage due to mainshock-aftershock seismic sequences. Subsequently, a simple procedure is proposed to increase the safety of optimally designed SMFs against the LCF damage. To this end, performance-based optimization process is performed for 6- and 12-story SMFs by considering higher seismic confidence levels and the results demonstrate the effectiveness of this strategy in controlling the LCF damage of SMFs caused by seismic sequences.

Design optimization of moment frame structures by the method of inscribed hyperspheres

In this study, the method of inscribed hyperspheres (IHS) is presented and applied for the optimal design of 2-D steel moment frame structures. The weight of the structures, which is a function of the design variables (cross-sectional areas), is optimized subject to stress, displacement, size limits, and the variables’ linkage constraints. The IHS approach is employed to find the acceptable centers. The basic idea of this method is to inscribe the largest possible sphere in a closed space that has been created by the objective function and linearized constraints in each step. The obtained results were presented in discrete and continuous variables and compared to the results reported in the literature. This comparison showed the efficiency of this method. Also, a new mixed method of combining the optimality criteria (OC) method and the IHS method is presented in this study. It was observed that the number of iterations needed to reach the optimal solution using this new method is less than that of the above two methods when used individually, and the problem is converged to the optimal answer with extremely low iterations.

Comprehensive 3D numerical study on interaction between structure and dip-slip faulting

Investigations on the effects of fault permanent deformations on surface and subsurface engineering structures are important owing to their direct impact on the reduction of earthquake damage. This study presents the methodology and results of a comprehensive, three-dimensional, nonlinear numerical modeling of the interaction between dip-slip faulting in soil and a four-story steel moment frame structure founded on different types of shallow surface foundations. A modified Mohr–Coulomb constitutive model was implemented in the numerical modeling, where the softening/hardening behavior of soil and an elasto–plastic model that provided a more accurate description of the stress–strain response of steel elements were considered; both were adopted in a finite element program. The results demonstrate that modeling the structural elements, in comparison with only modeling the footing as a rigid plate and compromising the effect of the structure by applying its weight, significantly affects the soil–structure interaction and displacements of the footings. The results indicate that a strip footing oriented perpendicular to a fault strike yields results similar to a mat footing, whereas a strip footing parallel to a fault strike resembles a spread footing. This suggests that not only the stiffness of the footing to tolerate the vertical loads of the structure, but also its continuity or freedom to move in the direction of fault displacement is important. In the absence of rigid connection between structure footings, the excessive freedom of a footing to comply with the quasi-static deformation of soil due to fault-induced movements results in a considerable deformation and rotation of the columns, primarily in the columns between the footing and the first floor.

Seismic Behavior of Welded Beam-to-Column Joints of High-Strength Steel-Moment Frame with Replaceable Damage-Control Fuses

AbstractThis paper first proposes a high-strength (HS) steel-moment frame structure with replaceable damage-control fuses, which utilized the very large elastic deformation capacity of HS steel and...

A combined control strategy using tuned liquid dampers to reduce displacement demands of base-isolated structures: a probabilistic approach

This paper investigates a hybrid structural control system using tuned liquid dampers (TLDs) and lead-rubber bearing (LRB) systems for mitigating earthquake-induced vibrations. Furthermore, a new approach for taking into account the uncertainties associated with the steel shear buildings is proposed. In the proposed approach, the probabilistic distributions of the stiffness and yield properties of stories of a set of reference steel moment frame structures are derived through Monte-Carlo sampling. The approach is applied to steel shear buildings isolated with LRB systems. The base isolation systems are designed for different target base displacements by minimizing a relative performance index using Genetic Algorithm. Thereafter, the base-isolated structures are equipped with TLDs and a combination of the base and TLD properties is sought by which the maximum reduction occurs in the base displacement without compromising the performance of the system. In addition, the effects of TLD properties on the performance of the system are studied through a parametric study. Based on the analyses results, the base displacement can be reduced 23% by average, however, the maximum reduction can go beyond 30%.

Reliability-based design of steel moment frame structures isolated by lead-rubber bearing systems

This paper puts forward a reliability-based approach to seismic design of steel moment frame structures isolated with lead-rubber bearing (LRB) devices. The system is modeled as an equivalent two-degree-of-freedom system in which the superstructure is assumed to remain elastic, while a bilinear behavior is assigned to the isolation level. Furthermore, the uncertainties associated with the superstructure properties including mass and stiffness are taken into account by adopting appropriate probability density functions. To design the base-isolated structure, the paper proposes “reliability curves” that given a target reliability, return the two key design parameters: the natural period of the super-structure and the target base displacement. Given these two key parameters, the paper proposes a regression equation that predicts the optimal design variables of the base-isolation system, i.e., the initial stiffness and the yield force. This equation is calibrated against a set of optimally-designed base-isolated systems using the genetic algorithm. The proposed approach is showcased for an example steel moment frame structure located in Los Angeles, California.

Performance analysis and macromodel simulation of steel frame structures with beam-column joints using cast steel stiffeners for progressive collapse prevention

Progressive collapse is an important failure mechanism that must be considered in the design of critical and essential buildings. For steel moment structures, beam-column joints, which act as transportation hubs of forces, are crucial members to resist progressive collapse. This research investigated the effectiveness of beam-column joints with cast steel stiffeners (CSS) in steel moment frames for progressive collapse resistance. A computationally efficient macromodel that can be used for routine design of steel moment frame buildings with CSS was developed in this paper. The developed model, which considers the deformation of joints with CSS and the catenary action effects during progressive collapse, was validated using a 3D solid finite-element model. Subsequently, the macromodel was utilized to calculate the proper dynamic increase factor for steel moment frame structures with beam-column joints using CSS. The results show that the frame with CSS is less vulnerable to gravity-induced progressive collapse than frames with welded beam-column joints without stiffeners. The proposed macromodel is effective and a dynamic increase factor of 1.6 is suitable for dynamic progressive collapse analysis of steel moment frame structures using beam-column joints with CSS.

Seismic reliability-based design of inelastic base-isolated structures with lead-rubber bearing systems

In this paper, a seismic reliability-based approach is proposed to design inelastic steel moment frame structures isolated by lead-rubber bearing (LRB) systems. An equivalent two-degree-of-freedom system is assumed in which a bilinear behaviour is assigned to both the superstructure and the base. Furthermore, uncertainties associated with the equivalent superstructure mass, stiffness, and yield properties are taken into account by employing proper probability density functions. The proposed design approach is twofold: 1) Reliability curves that return the key design parameters of the inelastic base-isolated structure including: the period of the superstructure, the target base displacement, and the ductility-dependent strength reduction factor for a given target reliability. 2) Regression equations, which estimate the displacement ductility demand of the inelastic superstructure and the optimal design properties of the lead-rubber bearing system including: the total initial stiffness and the total yield force. These regression equations are calibrated against a large set of optimally-designed base-isolated buildings using Genetic Algorithm.

Numerical evaluation of the effects of fire on steel connections; Part 1: Simulation techniques

Steel connections are used to connect between beam and column in steel moment frame structures. As of present time, there is a huge lack of understanding of the performance of steel connections and their response to fire especially the uncontrolled fires. Therefore, in this paper, by using a finite element program ABAQUS and with the static analysis of coupled temperature- displacement and to fully understand the behavior of such connection under the fire scenario, developed a temperature-dependent models for different types of steel connections are implemented. Finite Element Analyses (FEA) of selected experimental models are performed to verify the implementation of these models. Fully detailed, field-variable-dependent conductivity element models of the connections are developed, and analyses are performed to determine the effects of heat on the behavior of the materials in the elastic and plastic areas are considered. Moreover, severe deformation in the nonlinear region was investigated.

Consequences of Modeling Choices in Seismic Performance Assessment of Buildings

Performance-based approaches utilizing nonlinear analyses have become increasingly popular for seismic evaluation of buildings. Nonlinear simulations of building response require various assumptions and modeling decisions—from choice of software to model parameters—which opens the door to differences in demand assessments from what essentially could be very similar computational models. This study examines nonlinear response sensitivity of three steel moment frame structures to variations in basic nonlinear modeling parameters using three different software platforms: OpenSees, Perform-3D, and SAP2000. The building models were analyzed in the inelastic range using a suite of near-fault and far-fault ground motions, and response sensitivity was assessed using interstory drift and plastic rotation demands. Findings from the study indicate that sensitivity to modeling assumptions and choice of software are more pronounced at the local/element level than at the global/system level and can have an impact in performance-based seismic assessment.