Moment Frame Structures Research Articles

Dynamic Disproportionate Collapse in Flat-Slab Structures

AbstractDisproportionate collapse of structures can lead to catastrophic economic loss and casualties, and thus, it is of utmost concern to mitigate the risks of such events. Flat-slab structures are much more vulnerable to disproportionate collapse than moment-frame structures as there are no beams to redistribute the loads initially resisted by the lost column. Moreover, the propagation of punching-shear failure at slab–column connections due to load redistribution may result in the collapse of the entire slab. Thus, increased attentions should be paid toward assessing the disproportionate collapse performance of flat-slab structures. However, to date, limited knowledge exists regarding the risks of disproportionate collapse in flat-slab structures, especially in terms of dynamic tests. For this purpose, a series of one-third-scaled flat-slab substructures were subjected to the simulated sudden-column-removal scenario and the failure mode, acceleration, and displacement responses were presented and disc...

Life-cycle cost optimization of steel moment-frame structures: performance-based seismic design approach

In recent years, along with the advances made in performance-based design optimization, the need for fast calculation of response parameters in dynamic analysis procedures has become an important issue. The main problem in this field is the extremely high computational demand of time-history analyses which may convert the solution algorithm to illogical ones. Two simplifying strategies have shown to be very effective in tackling this problem; first, simplified nonlinear modeling investigating minimum level of structural modeling sophistication, second, wavelet analysis of earthquake records decreasing the number of acceleration points involved in time-history loading. In this paper, we try to develop an efficient framework, using both strategies, to solve the performance-based multi-objective optimal design problem considering the initial cost and the seismic damage cost of steel moment-frame structures. The non-dominated sorting genetic algorithm (NSGA-II) is employed as the optimization algorithm to search the Pareto optimal solutions. The constraints of the optimization problem are considered in accordance with Federal Emergency Management Agency (FEMA) recommended design specifications. The results from numerical application of the proposed framework demonstrate the capabilities of the framework in solving the present multi- objective optimization problem.

Effect of viscous damping devices on the response of seismically isolated structures

SummaryViscous and other damping devices are often used as elements of seismic isolation systems. Despite the widespread application of nonlinear viscous systems particularly in Japan (with fewer applications in the USA and Taiwan), the application of viscous damping devices in isolation systems in the USA progressed intentionally toward the use of supplementary linear viscous devices due to the advantages offered by these devices. This paper presents experimental results on the behavior of seismically isolated structures with low damping elastomeric (LDE) and single friction pendulum (SFP) bearings with and without linear and nonlinear viscous dampers. The isolation systems are tested within a six‐story structure configured as moment frame and then again as braced frame. Emphasis is placed both on the acquisition of data related to the structural system (drifts, story shear forces, and isolator displacements) and on non‐structural systems (floor accelerations, floor spectral accelerations, and floor velocities). Moreover, the accuracy of analytical prediction of response is investigated based on the results of a total of 227 experiments, using 14 historic ground motions of far‐fault and near‐fault characteristics, on flexible moment frame and stiff braced frame structures isolated with LDE or SFP bearings and linear or nonlinear viscous dampers. It is concluded that when damping is needed to reduce displacement demands in the isolation system, linear viscous damping results in the least detrimental effect on the isolated structure. Moreover, the study concludes that the analytical prediction of peak floor accelerations and floor response spectra may contain errors that need to be considered when designing secondary systems. Copyright © 2014 John Wiley & Sons, Ltd.

Collapse simulation of reinforced concrete moment frames considering impact actions among blocks

A simulation system based on the Discrete Element Method (DEM) was developed to model the collapse behavior of reinforced concrete (RC) moment frame structures subjected to seismic loads or explosions. This system mainly consists of two parts: a numerical analysis part that simulates the collapse process of RC moment frame structures quantitatively, and a visualization system that vividly shows the dynamic responses obtained from the numerical analysis. Using this system, the whole damage process of a structure can be numerically analyzed and visually simulated. Consequently, the collapse mode, mechanism and duration and the distribution of the debris after the collapse can be obtained. The numerical analysis is based on the DEM, in which the element shape is assumed to be cuboid, and the elements are connected by dummy concrete springs and steel springs. The impact actions among elements, particularly after breaking of the connecting springs, are taken into account with the application of impulse-based impact models, which are derived from the results of the experiments and the numerical tests. Finally, two examples, including a frame building demolished by a controlled explosion and a scaled model structure of an RC moment frame subject to an earthquake, are presented to verify the impact models and simulation system and to reveal the collapse mechanism of RC moment frame structures subjected to abnormal loadings.

Thermal Behaviour of Beams with Slant End-Plate Connection Subjected to Nonsymmetric Gravity Load

Research on the steel structures with confining of axial expansion in fixed beams has been quite intensive in the past decade. It is well established that the thermal behaviour has a key influence on steel structural behaviours. This paper describes mechanical behaviour of beams with bolted slant end-plate connection with nonsymmetric gravity load, subjected to temperature increase. Furthermore, the performance of slant connections of beams in steel moment frame structures in the elastic field is investigated. The proposed model proved that this flexible connection system could successfully decrease the extra thermal induced axial force by both of the friction force dissipation among two faces of slant connection and a small upward movement on the slant plane. The applicability of primary assumption is illustrated. The results from the proposed model are examined within various slant angles, thermal and friction factors. It can be concluded that higher thermal conditions are tolerable when slanting connection is used.

Evaluation of Progressive Collapse of Special Steel Moment Frames

The point of this study was to assess the progressive collapse resisting capacity of special steel moment frame structures and the behaviour of buildings which have different height when they are losing one of their exterior columns. Two buildings were considered for this research, 7-storiy and 12-storiy buildings. Corner column as well as one of the middle columns was removed to evaluate the importance and the effect of the location of removed column in structural response. General Services Administration (GSA) and Department of Defence (DoD) guidelines are considered for choosing the method of analysis. Nonlinear dynamic analysis procedures were carried out to investigate the behavior of structures. Thus, maximum vertical displacement in the point of column removal for each structure was measured. In addition, both buildings have cover plate connections which are cosidered to be rigid in modelling.

Fragility analyses of mid-rise T-stub PR frames in the Mid-America earthquake region

Mid-America region is defined as the region of the central and southeastern United States compromising those states that have expected large but infrequent seismicity. Although earthquakes in this region are less frequent than in western U.S., they affect much larger areas than those of similar magnitude in western U.S. due to the deep and loose subsurface conditions. However, as little research has been carried out for partially restrained (PR) steel moment frame structures in this region, it is necessary to evaluate their seismic performance. To achieve this, seismic performance of three proto-type 6-story steel moment frames with T-stub PR connections was evaluated in accordance with FEMA 273/356 limit state criteria using fragility analyses. Three PR frames were designed using the appropriate design codes representing mid-1950s, late 1980s, and current practice. Two different types (“Conventional” and “New”) of fragility curves are developed and compared. In addition, the fragility curves at Los Angeles site representing western U.S. were generated and compared with those at the Mid-America region. Two different fragility analysis results show the same trends. Three proto-type 6 story PR frames in the Mid-America earthquake region performed well and may not collapse. It can be concluded that the seismic performance of the mid-rise PR frames in the Mid-America region will be satisfactory even under large but infrequent ground motions.

A Study of Reduced Beam Section Profiles using Finite Element Analysis

Reduced beam section (RBS) is one of the several connection types, which is economical and popular for use in new steel moment frame structures in seismic zone. To form RBS connection, some portion of the beam flanges at a short distance from column face is purposefully trimmed so that the yielding and plastic hinge occurs within this area of flanges. Use of RBS connection is found advantageous due to: a) the shear force in the panel zone is reduced; b) the force demand in column continuity plates i.e. stiffeners are reduced; and c) strong-column - weak-beam requirement is satisfied. Although, radius cut RBS is qualified by ANSI/AISC, FEMA codes, various flange cut shapes like constant, tapered, radius cut, drilled holes are possible to reduce the cross sectional area of beam flanges. The purpose of this study is to understand behavior of RBS beam-to-column moment connections for various flange cut geometries. This document represents nonlinear finite element analysis of the connection models performed using the computer program, ANSYS/Multiphysics Keywords - Steel structures, steel connections, reduced beam section, RBS profiles

Cyclic Testing of Bolted Flange Plate and Double Split Tee Type Weak-Axis Steel Moment Connections

Steel beam-to-column connections are very important for steel moment-frame structures. Beam-to-column connections have a great influence not only on the seismic performance but also on construction costs and construction durations. These days in Korea, most of the connection details are comprised of the column-tree type beam-to-column connections due to the Japanese influence. But this type of connection is inefficient when it comes to transportation and requires numerous components. The Bolted Flange Plate(BFP) and the Double Split Tee(DST) type weak-axis connections on the other hand are simple in construction and the load transfer is more direct. So, in order to research their respective seismic performance, this paper prepared two specimens and conducted a full-scale test. The study obtained the story drift ratio curves and the total plastic rotation curves of the specimens. Through the analysis of the curves this paper aims to conclude that the two connections meet the requirements pertaining to the Special Moment Frame, which prescribes that the story drift ratio should reach 4%. This paper demonstrates that the BFP and DST type connections display good plastic behaviors.

Metamodel-based regional vulnerability estimate of irregular steel moment-frame structures subjected to earthquake events

Rapid seismic vulnerability assessment tools for use with existing structures not only help in quantifying their susceptibility to structural failure, but also aid decision makers with regional portfolio earthquake risk mitigation. Steel moment-frame structures are a common structure type in the United States, and most research to date on their regional assessment has focused on the fragility analysis of structures with regular configurations. Given the large number of irregular structures in use in seismically active zones, the effect of plan-form irregularity on the fragility of moment-frame structures should be examined. The focus of this study is to estimate structural fragilities for the class of L-shaped steel moment-frame (LSMF) structures in the Central United States. As part of the assessment process, L-shaped plan-forms that are most common in the region are first selected based upon input from structural and architectural experts. Significant parameters affecting the LSMF seismic responses are identified from sensitivity studies using finite element models and design-of-experiments methods to construct response surface metamodels (RSMs). Portfolio-level fragility curves for LSMF structures are generated from the RSMs joined with Monte Carlo Simulation (MCS) to treat regional uncertainty. RSM-based fragility curves are also compared with fragilities from HAzards US Multi-Hazard (HAZUS-MH). Furthermore, a fragility-based parametric study is performed to evaluate the effect of significant parameters on LSMF susceptibility. Findings indicate the extent to which different irregularity parameters such as first floor height and eccentricity impact regional LSMF vulnerability.

Damage detection algorithm based on identified system Markov parameters (DDA/ISMP) in building structures with limited sensors

In this study, a new approach for global/local damage detection in a finite element model of structures, with limited sensors, is proposed using identified system Markov parameters. The proposed damage detection is directly related to the Markov parameters, locations of actuators and sensors. Also there is no explicit relation between DDA/ISMP and mode shapes. So, it is unnecessary to install a sensor at each DOF for measuring output to identify mode shapes unlike the other damage detection techniques in which mode shapes play an important role in damage identification. The stiffness of all elements of a structure is identified using the proposed DDA/ISMP. The effects of noise, numbers and locations of sensors on the identification precision are investigated. The results demonstrate that, with the limited sensors and the noise contamination in the measured responses, the DDA/ISMP can effectively identify the locations, types and quantities of damages, both locally and globally. To illustrate the efficiency of DDA/ISMP, a four-storey steel moment frame structure and a five-storey shear building are used. Our numerical results show that the DDA/ISMP technique in damage detection is more effective than the scheme proposed by Xu et al. Also, the time consumed in DDA/ISMP is considerably less than the method introduced by Xu.

Capacity design by developed pole placement structural control

To ensure safety and long term performance, structural control has rapidly matured over the past decade into a viable means of limiting structural responses to strong winds and earthquakes. Nonlinear response history analysis requires rigorous procedure to compute seismic demands. Therefore the simplified nonlinear analysis procedures are useful to determine performance of the structure. In this investigation, application of improved capacity demand diagram method in the control of structural system is presented for the first time. Developed pole assignment method (DPAM) in structural systems control is introduced. Genetic algorithm (GA) is employed as an optimization tool for minimizing a target function that defines values of coefficient matrices providing the placement of actuators and optimal control forces. The ground acceleration is modified under induced control forces. Due to this, performance of structure based on improved nonlinear demand diagram is selected to threshold of nonlinear behavior of structure. With small energy consumption characteristics, semi-active devices are especially attractive solutions for limiting earthquake effects. To illustrate the efficiency of DPAM, a 30-story steel moment frame structure employing the semi-active control devices is applied. In comparison to the widely used linear quadratic regulation (LQR), the DPAM controller was shown to be just as effective and better in the reduction of structural responses during large earthquakes.

Hope for the Best, Prepare for the Worst: Response of Tall Steel Buildings to the ShakeOut Scenario Earthquake

This work represents an effort to develop one plausible realization of the effects of the scenario event on tall steel moment-frame buildings. We have used the simulated ground motions with three-dimensional nonlinear finite element models of three buildings in the 20-story class to simulate structural responses at 784 analysis sites spaced at approximately 4 km throughout the San Fernando Valley, the San Gabriel Valley, and the Los Angeles Basin. Based on the simulation results and available information on the number and distribution of steel buildings, the recommended damage scenario for the ShakeOut drill was 5% of the estimated 150 steel moment-frame structures in the 10–30 story range collapsing, 10% red-tagged, 15% with damage serious enough to cause loss of life, and 20% with visible damage requiring building closure.

Numerical and experimental evaluation of seismic capacity of high-rise steel buildings subjected to long duration earthquakes

Occurrences of large earthquakes having a magnitude larger than eight along subduction zones have been reported worldwide. Due to large number of load reversals the effect of cumulative damage on structural components due to deterioration becomes critical for steel buildings of old construction but may also become critical for buildings designed based on current seismic provisions. A state-of-the-art analytical model that simulates component deterioration and fracture due to low cycle fatigue has been developed and implemented in the OpenSees computational framework. The model serves for seismic evaluation of steel moment frame structures subjected to long duration records. The effectiveness of the numerical model in quantification of the seismic capacity of high rise steel structures is demonstrated through validation with a full scale shaking table test of a high-rise steel building subjected to a long duration record at the world’s largest shaking table facility (E-Defense). Limitations of the proposed numerical model are also discussed.

A Model of Steel Frame for Simulating Connection Fractures

Following the 1994 Northridge earthquake, widespread damages were discovered in welded steel moment frame buildings. In order to accurately simulate the typical seismic damage of welded steel moment frame structures, a new simplified model is proposed for performing seismic evaluation of welded steel moment frame structures. In this model, the slabs effect is considered, as well as the effects of the slip between slabs and steel beams, deformation of panel zone and connection fractures. Fracture toughness demands were evaluated in terms of the mode I stress intensity factor. The model was employed in simulation of seismic damage of Blue Cross Building which experienced fractured connections in the Northridge earthquake. It indicates that the model can accurately predict the earthquake response of welded steel moment frame structures and estimate the level of damage. The approach proposed in this paper has important meaning to the research on seismic damage of steel frame which may experience fractured connections.

Seismic performance of composite reinforced concrete and steel moment frame structures – state-of-the-art

Composite reinforced concrete and steel moment frame structures are comprised of reinforced concrete (RC) columns and steel (S) beams – the so-called composite RCS frames. Extensive research over the past several decades suggests that such systems are particularly well proper and economic for use in mid- to high-rise buildings in low to moderate seismic risk regions and low to mid-rise buildings in moderate to high seismic risk regions. This paper reviews the state-of-the-art in testing, finite-element analysis and design of composite RCS systems. Development of guidelines and recommendations of RCS beam–column connections and RCS moment frames are presented and a future research on composite RCS systems is provided.

Collapse risk of tall steel moment frame buildings with viscous dampers subjected to large earthquakes

AbstractThe design approach for tall steel moment frame structures with viscous dampers entails sizing steel members per code‐level strength forces, and sizing viscous dampers to limit storey drifts. This method has been used extensively in new and retrofit applications. This methodology has resulted in structures that have longer periods than those using the code‐designed approach, are economically competitive and have excellent performance in design‐level earthquakes. However, the efficacy of this design in extreme events is not well understood because of the lack of limit states data for dampers and the absence of a field or analytical database of such structures subjected to large earthquakes. Mathematical modelling of viscous dampers with limit states was developed, correlated with experimental results and then used to analyse 10‐storey archetypes. This analysis showed that the design had satisfactory performance during extreme seismic events. There were significant improvements in reducing collapse hazard by using an enhanced damper design with an increased damper safety factor. Copyright © 2010 John Wiley & Sons, Ltd.

Study on Vibration Characteristics of a High-rise Building using results of Microtremor, Manpower Excitation Measurements, Earthquake Observations and Simulations of a 3D Moment-frame structure

近年首都圏に建つ超高層建築では巨大地震に対する対策の重要性が指摘されている。巨大地震に対する被害想定や被害低減案を示すには、地震時における正確な振動性状の把握が不可欠である。本論文では新宿副都心に建つ最高高さ143mの超高層建築物である工学院大学新宿校舎を対象とした観測記録および立体フレームモデル解析結果の比較検討による振動性状の評価を示す。はじめに常時微動観測および人力加振観測より得られた固有周期およびモード形を表す変位振幅図を立体フレームモデル固有値解析結果と比較を行い両者が一致する事を確認した。続いて対象建築物の強震観測システムより得られた地震観測記録と立体フレームモデル応答解析結果との比較を行い両者が良い対応を示す事を確認した。解析に用いる減衰は人力加振観測より算出した減衰および超高層建築に一般的に用いられる、初期剛性比例減衰の2種類を用い比較検討を行った。これより初期剛性比例減衰では高次モードの減衰を過大に評価している事を確認した。さらに、モーダルアナリシスを用いた最大応答値の評価や、観測記録の振幅レベルによる固有周期の変化についても考察した。

Erratum: CONTINUOUS COLUMN EFFECTS OF GRAVITY COLUMNS IN U.S. STEEL MOMENT-RESISTING FRAME STRUCTURES [Journal of Structural and Construction Engineering (Transactions of AIJ) Vol. 75 (2010) , No. 650 pp.761-770

Typical steel moment-frame structures in the United States comprise a few seismic frames and many gravity frames, which include “continuous columns” that are pin-connected to beams. These continuous columns, which are often ignored in seismic design, can improve the seismic performance of the structure. This study investigates the effects of continuous columns on the structural stability and seismic response of building frames. Stability coefficients representing the separate and combined effects of geometric and material nonlinearities are used with a simplified modeling technique, which separates the shear-type and flexural-type lateral-force-resisting systems in moment frames. Relationships between continuous column stiffness ratio and the stability coefficients, inter-story drift, and the drift concentration factor are presented. It is shown that for realistic structures, the columns in the seismic frames are generally sufficient to prevent unstable response and large drift concentrations, and the inclusion of gravity continuous column stiffness tends to decrease both the drift concentration and inter-story drift.

CONTINUOUS COLUMN EFFECTS OF GRAVITY COLUMNS IN U.S. STEEL MOMENT-RESISTING FRAME STRUCTURES

Typical steel moment-frame structures in the United States comprise a few seismic frames and many gravity frames, which include “continuous columns” that are pin-connected to beams. These continuous columns, which are often ignored in seismic design, can improve the seismic performance of the structure. This study investigates the effects of continuous columns on the structural stability and seismic response of building frames. Stability coefficients representing the separate and combined effects of geometric and material nonlinearities are used with a simplified modeling technique, which separates the shear-type and flexural-type lateral-force-resisting systems in moment frames. Relationships between continuous column stiffness ratio and the stability coefficients, inter-story drift, and the drift concentration factor are presented. It is shown that for realistic structures, the columns in the seismic frames are generally sufficient to prevent unstable response and large drift concentrations, and the inclusion of gravity continuous column stiffness tends to decrease both the drift concentration and inter-story drift.