Moment Resisting Frame System Research Articles

Investigations of elastic vibration periods of reinforced concrete moment-resisting frame systems with various infill walls

The fundamental period of vibration is a crucial characteristic in assessing the dynamic performance of reinforced concrete (RC) buildings because it is not only directly related to the mass and stiffness of the structure, but also to the lateral actions applied, e.g. earthquakes and winds. In this study, the RC moment-resisting frame (MRF) systems designed under gravity and wind loading have been evaluated by utilising 3D FE modelling incorporating eigen-analysis to obtain the elastic periods of vibration. The parameters considered include the number of storeys, the number and length of bays, plan configurations, mechanical properties of infill walls, and the presence of openings in the uncracked and cracked infill walls. These analyses provide a sound basis for further investigating the effects of these parameters and exploring the possibility of proposing new formulas for predicting the fundamental vibration period by utilising regression analyses on the obtained results. The proposed numerically based formula for vibration periods of bare RC frame models reasonably agrees with some cited formulas for vibration period from design codes and standards due to disregarding contributions of infills’ stiffness towards the structural systems. Meanwhile, the proposed formulas for RC MRF buildings with uncracked infills agree well with most cited experimentally based formulas and some numerically based ones. However, the proposed formulas for RC MRF buildings with cracked infills only reasonably agree with some cited numerically based formulas.

Evolution of High-rise Buildings in Vancouver, Canada

The potential for a large earthquake to cause significant ground shaking has had a defining influence on the evolution of high-rise buildings in the City of Vancouver. However, unlike other major cities along the seismically active west coast of North America, structural steel systems and reinforced concrete moment-resisting frame systems have rarely been used. Virtually all high-rise buildings in Vancouver are concrete shear wall buildings. Older buildings, constructed up until the mid-1980s, typically have thin (200 mm or less) lightly reinforced concrete walls distributed throughout the buildings. A number of factors, such as increased seismic demands and the changing requirements of the Canadian building code, caused a paradigm shift in the 1980s so that today, almost all new high-rise buildings in Vancouver have a large central core that is designed to resist all lateral loads. Typical modern high-rise cores have three independent cantilever walls in one direction that are coupled together in the transverse direction by ductile coupling beams above the door openings on each story. The City of Vancouver has recently declared that the designs of high-rise buildings must attain a new benchmark of architectural creativity. The recent designs that have been proposed for the city include very irregular buildings that are much less likely to be habitable after an earthquake.

Energy-factor-based damage-control evaluation of steel MRF systems with fuses

The primary objectives of this research are to investigate the energy factor response of steel moment resisting frame (MRF) systems equipped with fuses subject to ground motions and to develop an energy-based evaluation approach for evaluating the damage-control behavior of the system. First, the energy factor of steel MRF systems with fuses below the resilience threshold is derived utilizing the energy balance equation considering bilinear oscillators with significant post-yielding stiffness ratio, and the effect of structural nonlinearity on the energy factor is investigated by conducting a parametric study covering a wide range of parameters. A practical transformation approach is also proposed to associate the energy factor of steel MRF systems with fuses with classic design spectra based on elasto-plastic systems. Then, the energy balance is extended to structural systems, and an energy-based procedure for damage-control evaluation is proposed and a damage-control index is also derived. The approach is then applied to two types of steel MRF systems with fuses to explore the applicability for quantifying the damagecontrol behavior. The rationality of the proposed approach and the accuracy for identifying the damage-control behavior are demonstrated by nonlinear static analyses and incremental dynamic analyses utilizing prototype structures.

Collapse Resistance of RC Moment-Resisting Frame and Shear Wall Structural Systems Exposed to Blast

AbstractVarious characteristics of a structure influence its response when subjected to a blast load. This has important implications for survivability and resistance to progressive collapse. In this study, the effect of the type of lateral load resisting system on reinforced concrete (RC) building resistance to progressive collapse when exposed to blast load was examined. Fourteen different reinforced concrete structures were considered for analysis, with five structures designed as moment-resisting frames and nine designed as shear wall systems. Buildings with 3, 6, and 10 stories with 3-, 4-, and 5-bay symmetric configurations were considered. The structures were exposed to external and internal charges, whereas the nonlinear, transient dynamic analysis of collapse behavior was investigated with a finite-element-based approach, the applied element method (AEM). The results show that the shear-wall structures and structures larger in height and plan generally provide greatest resistance to blast damage ...

Influence of seismicity level and height of the building on progressive collapse resistance of steel frames

Summary Influences of building height and seismicity level on progressive collapse resistance of buildings are investigated in this paper. For the height, 4-story, 8-story and 12-story steel special moment resisting frames are focused. The obtained results indicate that taller buildings are safer against progressive collapse. To study the influence of seismicity level, different four-story structures having special moment resisting frame systems are designed for different levels of seismicity, namely, very high, high, moderate and low. The structures are evaluated, using nonlinear dynamic method and two main scenarios of the codes, including sudden removal of a corner and a middle column in the first floor. Some graphs are presented for progressive collapse resistance of the structures, depending on their seismic base shears. It is shown that the structures designed for greater seismic base shears are more resistant against progressive collapse. Copyright © 2016 John Wiley & Sons, Ltd.

Nonlinear Performance Evaluation of Diagonally and X-Braced Moment Resisting Frame Systems: Buckling and Post–Buckling Responses

The inelastic post-buckling performance of braced moment resisting frame (BMRF) systems is notably affected by their strength, ductility, and stiffness which have been paid a great deal of attention in recent years. The concept of performance-based design requires a thorough appraisal of the system responses, and their improvements in conjunction with the design parameters in details. In this paper, we aim to provide insight into the above issues with an accurate evaluation of nonlinear post buckling response of BMRFs, and through a comprehensive comparison of such systems for different gusset-brace configurations, namely, diagonally braced moment resisting frames (DBMRFs) and X-braced moment resisting frames (X-BMRFs). The effect of different gusset plate connection sizes/types with linear and elliptical clearance offsets are fully considered, using high fidelity three-dimensional finite element models of the proposed system that are validated and verified globally/locally against available experimental results and numerical simulations. A number of BMRF models are developed, and the sensitivities of buckling and post–buckling states to changes in system parameters and geometric imperfections are discussed. The results of this study can be further extended to ascertain the effects of different types of beam-to-column connections. Additionally, brace-to-frame rigidities and material properties of BMRFs can be considered to determine optimum design parameters and to control interaction characteristics between different subsystems of BMRFs.

Comparison of Seismic Behavior of Eccentrically Braced Frames with Vertical and Knee Links in Retrofitting the Reinforced-Concrete Buildings with Intermediate Moment-Resisting Frame Systems

Given the fact that some reinforced-concrete (RC) buildings have not met resistance against seismic loads, it is mandatory to adopt a suitable and economically cost-efficient method to retrofit them. One appropriate method is application of steel Eccentrically Braced Frames (EBFs). This article is aimed at evaluation of seismic performance of retrofitted reinforce-concrete buildings by EBFs with single and knee links. For evaluation of modeled buildings, different editions of the Iranian Seismic Code (Standard No. 2800) were reviewed. To this end, three Moment-Resisting Frames (MRF) of four-, eight-, and twelve-story buildings with medium ductility were modeled where they were designed for seismic loads based on Standard 2800, 2nd edition. In order to evaluate buildings under modified seismic loads, models were seismically reloaded based on the Standard 2800, 3rd edition. Reanalysis showed that the stress ratios exceeded 1 in most columns. Therefore, buildings were retrofitted using EBFs with knee and single vertical links and their seismic performance were evaluated using nonlinear static analysis. Results indicate that knee bracing systems are more efficient than bracing systems with vertical link in increasing rigidity and controlling displacements, while they significantly reduce ductility. For example, application of knee bracing system in the twelve-story building can cause an 11% reduction in displacement in comparison to bracing systems with vertical links.

Numerical modeling and analysis of RC frames subjected to multiple earthquakes

Earthquakes occur as a cluster in many regions around the world where complex fault systems exist. The repeated shaking usually induces accumulative damage to affected structures. Damage accumulation in structural systems increases their level of degradation in stiffness and also reduces their strength. Many existing analytical tools of modeling RC structures lack the salient damage features that account for stiffness and strength degradation resulting from repeated earthquake loading. Therefore, these tools are inadequate to study the response of structures in regions prone to multiple earthquakes hazard. The objective of this paper is twofold: (a) develop a tool that contains appropriate damage features for the numerical analysis of RC structures subjected to more than one earthquake; and (b) conduct a parametric study that investigates the effects of multiple earthquakes on the response of RC moment resisting frame systems. For this purpose, macroscopic constitutive models of concrete and steel materials that contain the aforementioned damage features and are capable of accurately capturing materials degrading behavior, are selected and implemented into fiber-based finite element software. Furthermore, finite element models that utilize the implemented concrete and steel stress-strain hysteresis are developed. The models are then subjected to selected sets of earthquake sequences. The results presented in this study clearly indicate that the response of degrading structural systems is appreciably influenced by strong-motion sequences in a manner that cannot be predicted from simple analysis. It also confirms that the effects of multiple earthquakes on earthquake safety can be very considerable.

Seismic Loss and Downtime Assessment of Existing Tall Steel-Framed Buildings and Strategies for Increased Resilience

AbstractIn areas of high seismicity in the United States, the design of many existing tall buildings followed guidelines that do not provide an explicit understanding of performance during major earthquakes. This paper presents an assessment of the seismic performance of existing tall buildings and strategies for increased resilience for a case study city, San Francisco, where an archetype tall building is designed based on an inventory of the existing tall building stock. A 40-story moment-resisting frame system is selected as a representative tall building. The archetype building is rectangular in plan and represents the state of design and construction practice from the mid-1970s to the mid-1980s. Nonlinear response history analysis (NLRHA) are conducted with ground motions representative of the design earthquake hazard level defined in current building codes, with explicit consideration of near-fault directivity effects. Mean transient interstory drifts and story accelerations under the 10% in 50-year...

Çelik Çaprazla Güçlendirilmiş Dolgu Duvarlı Betonarme Çerçevelerin Doğrusal Olmayan Davranışı

Improperly designed and constructed reinforced concrete (RC) buildings with moment-resisting frame (MRF) systems have proven to perform poorly in earthquakes. During recent earthquakes, particularly during the Marmara (1999), Bingol (2003), and Van (2011) earthquakes, large number of RC MRF buildings either sustained severe damage or collapsed. In most of these buildings, masonry infill walls were installed in the structural frames. These so-called non-structural infill walls can interfere with the structural system and may cause premature failure of the latter especially during stronger ground shaking. If infill walls are used to improve strength, stiffness and the overall performance of a structural system, they need to be designed and constructed accordingly. Diagonal strut FRP/steel strip system is one of the preferred retrofit techniques with its mechanical properties, ease of application and low disturbance to inhabitants

Suitability of CFT columns for New Zealand moment frames

Composite steel-concrete construction uses steel and concrete together to provide the possibility of a system with better performance, and/or lower cost, than using either material alone. This paper firstly subjectively evaluates the advantages and disadvantages of a number of composite concrete filled tubular (CFT) column-connection systems proposed/used around the world in terms of their likely acceptance in moment frames in New Zealand. Then, the cost of a conventional one-way moment-resisting steel frame system is compared with a similarly behaving frame using rectangular concrete filled steel tubular (CFT) columns. It is shown for these studies conducted on one-way frames that composite CFT column construction with beam end-plate connections is generally more expensive than conventional steel column construction.

Direct Displacement Based Design on Moment Resisting Frame with Out-of-plane Offset of Frame

Direct displacement based design (DDBD) has been widely applied in several structural systems including moment resisting frame (MRF), the most common type of structures used in design practices. Due to architectural demand, recently many buildings involving some out-of-plane offset of frames in MRF system. The existence of out-of-plane offset in frame system raises differences force distribution among frames compared with the regular one without the offset. This study will observe the effect of out-of-plane offset of frame in a concrete regular MRF designed using DDBD method for two different earthquake level. Nonlinear time history analysis is used to verify the structural performance based on three parameters: story drift, damage indices and structural failure mechanism. The offset frame is assumed to be in-plane with the adjacent frame, the existence of offset is ignored, and the structure is designed as a regular MRF. The study shows that the main structural problem arises from the beams at the offset area due to high shear demand. DDBD procedure enable to adjust the ductility demand of these beams in order to improve the structural performance without involving design repetition as usually done in traditional seismic resistant design. In conclusion, DDBD performed well in predicting the seismic demands of the MRF system with out-of-plane offset of frame. The existence of offset frames in MRF system can be ignored during the design process as long as the ductility demands of beams at the offset area is well adjusted.

An evaluation of the seismic response modification factor R for RC special moment-resisting frame system

Many countries still adopt the seismic design approach in UBC97 for RC special moment-resisting frame buildings (SMRFs), which suggests a fixed value of the seismic response modification factor R of 8.5 for all types of SMRFs. This paper investigates, using two case studies comprising 25 numerical analyses, the R factor for SMRFs by performing pushover analysis and focusing on the effect of the number and span of bays and the number of stories. The analysis results show that the R factor is significantly dependent on the number of stories in which it decreases with the increase in the number of stories. Conversely, the number and length of bays had insignificant effect on R in comparison to the number of stories. The calculated R values range from 5 to 12. Thus, the results suggest that the use of a fixed value for R could result in unsafe or uneconomic building designs.

Seismic fragility analysis of conventional and viscoelastically damped moment resisting frames

This paper presents the results of an analytical study on seismic reliability of viscoelastically damped frame systems in comparison with that of conventional moment resisting frame systems. In order to exhibit the reliability of the frame systems with viscoelastic dampers, seismic reliability analyses were carried out for steel framed buildings, 5 and 12 storeys in height, designed as: (a) Case 1: Conventional moment resisting frame, (b) Case 2: Frame with viscoelastic dampers providing supplemental effective damping ratio of 10%, and (c) Case 3: Frame with viscoelastic dampers providing supplemental effective damping ratio of 20%. Nonlinear time history analyses were utilized to develop seismic fragility curves whilst monitoring various performance objectives. To obtain robust estimators of the seismic reliability, a database including 15 natural earthquake ground motion records with markedly different characteristics was employed in the fragility analysis. The results indicate that depending upon the supplemental effective damping ratio, frames designed with viscoelastic dampers have considerably lower annual probability of exceedance of performance limit states for structural components, showing up to a five-fold reduction in comparison to conventionally designed moment resisting frame system.

The wall–frame interaction effect in steel plate shear wall systems

The overall behavior of steel plate shear wall (SPSW) dual systems comprises the contributions of the infill plate tension field and boundary frame moment resisting actions. In the literature, a moment frame acting as SPSW boundaries (SPSW boundary frame) is treated as the same frame acting alone (bare frame). However, due to an interaction effect between the infill wall and the boundary frame, the actual behavior of SPSW boundary frame is different from the behavior of the same bare frame. In the present paper, a number of code designed single and multi-story SPSWs and the corresponding bare frames are numerically analyzed (a) to study the influence of infill walls on the behavior of boundary frames and (b) to evaluate the effectiveness of infill walls. Results show that the presence of infill walls can significantly improve the performance of moment-resisting frame systems, especially for multi-story ones, in terms of strength, stiffness, ductility and energy dissipation capability. In turn, the better performance of the SPSW system than the corresponding bare frame is not only due to the contribution of the infill wall, but also due to the improvement in the performance of the frame resulted from the wall–frame interaction.

Utilizing Base-isolation Systems to Increase Earthquake Resiliency of Healthcare and School Buildings

In the recent large earthquakes in Chile, New Zealand, and Japan, a great number of critical facilities, including hospitals, schools, bridges, factories, airports, and utility systems, experienced extensive damage resulting in their loss of their function, and consequently substantial economic losses. Heavily affected communities were paralyzed for months following these large seismic events. The recovery process is estimated to last from several years to few decades. As a result, increased attention is being placed on strategies to design facilities that are both safe and damage resistant. It is often presumed that such an approach increases costs to an unacceptable level. The study reported herein compares the repair costs and repair times considering two designs for a typical three-story steel building: conventional fixed-base and damage resistant base-isolated moment resisting frame system. Performance-based earthquake evaluation tools are used to estimate repair costs and times for five different hazard levels considering two occupancy types critical for recovery: healthcare and school. The buildings are located in a seismic region in western North America. It is shown that using seismic isolation to enhance damage resistance results in significantly smaller repair cost, repair time, and improved resilience for the base-isolated alternative compared to a conventional fixed-base design.

Seismic reliability of steel moment resisting framed buildings retrofitted with buckling restrained braces

SUMMARYThe present paper investigates the seismic reliability of the application of buckling restrained braces (BRBs) for seismic retrofitting of steel moment resisting framed buildings through fragility analysis. Samples of regular three‐storey and eight‐storey steel moment resisting frames were designed with lateral stiffness insufficient to comply with the code drift limitations imposed for steel moment resisting frame systems in earthquake‐prone regions. The frames were then retrofitted with concentrically chevron conventional braces and BRBs. To obtain robust estimators of the seismic reliability, a database including a wide range of natural earthquake ground motion records with markedly different characteristics was used in the fragility analysis. Nonlinear time history analyses were utilized to analyze the structures subjected to these earthquake records. The improvement of seismic reliability achieved through the use of conventional braces and BRBs was evaluated by comparing the fragility curves of the three‐storey and eight‐storey model frames before and after retrofits, considering the probabilities of four distinct damage states. Moreover, the feasibility of mitigating the seismic response of moment resisting steel structures by using conventional braces and BRBs was determined through seismic risk analysis. The results obtained indicate that both conventional braces and especially BRBs improve significantly the seismic behavior of the original building by increasing the median values of the structural fragility curves and reducing the probabilities of exceedance of each damage state. Copyright © 2011 John Wiley & Sons, Ltd.

Technical Note: New Z-BREAKSS: Post-tensioned Rocking Connection Detail Free of Beam Growth

This technical note concisely presents the details of a post-tensioned rocking moment connection (PT-RMC) concept that could be implemented in steel plate shear wall (SPSW) and moment-resisting frame (MRF) systems, along with preliminary results from limited SAP2000 cyclic nonlinear static pushover and time-history analyses that verify its anticipated behavior. The partial research results presented here could be of benefit in ongoing discussions about practical implementation and design codification of PT-RMCs [aka post-tensioned energy dissipating (PTED) or self-centering moment-resisting (SC-MRF) connections].

A simplified method for collapse capacity assessment of moment-resisting frame and shear wall structural systems

A simplified methodology for predicting the median and dispersion of collapse capacity of moment-resisting frame and shear wall structural systems subjected to seismic excitations is proposed. The method is based on nonlinear static (pushover) analysis. Simple mathematical models denoted as “generic structures” are utilized to model moment-resisting frames and shear walls. After examining a wide range of structural parameters of the generic structures, a comprehensive database of collapse fragilities and pushover curves (using ASCE 7-05 lateral load pattern) are generated. Based on the obtained pushover curves, closed-form equations for estimation of median and dispersion of building collapse fragility curves are developed using multivariate regression analysis. Comparing the estimates of the median collapse capacity calculated from the closed-form equations with the actual collapse capacities determined from nonlinear response-history analysis indicates that the simplified methodology is reliable. The effectiveness of this methodology for predicting the median collapse capacity of frame and wall structures is further demonstrated with two case studies of structural systems designed based on current seismic provisions.

RBS-B 접합부 설계식 개선에 따른 철골모멘트골조 시스템의 내진성능평가

In current seismic design provisions, a reduced beam section with bolted web (RBS-B) connections is only permitted for intermediate moment frames (IMF). This study evaluated the seismic performance of steel moment resisting frame systems having RBS-B connections designed according to current seismic design provisions. For this purpose, 12 archetypal IMF systems having two different span lengths (9m, 6m) were designed considering two design load levels (SDC , SDC ). A nonlinear analytical model that can simulate hysteretic behavior of an RBS-B connection was also developed in this study. The procedures specified in ATC 63 are used to conduct a seismic performance evaluation. Moreover, this study conducts the seismic performance evaluation of IMF systems designed according to a new design method proposed by the authors in the previous study. It was observed that several model frames designed according to current seismic design provisions did not provide satisfactory collapse margin ratios (ACMR). This study also showed that the model frames designed according to the new design procedures had a sufficient ACMR.