Steel Special Moment Frames Research Articles

Seismic Responses of Isolated Structures with Mass Asymmetry Mounted on TCFP Subjected to Near-Fault Ground Motions

This study is devoted to investigate the effects of mass eccentricity on seismic responses of base-isolated structures subjected to near-field ground motions. Superstructures with 3, 6 and 9 stories with aspect ratios equal to 1, 2 and 3 have been idealized as steel special moment frames resting on a reasonable variety of triple concave friction pendulum bearings considering different period and damping ratios for the isolators. Three-dimensional linear superstructures mounted on nonlinear isolators have been subjected to three components of near-field ground motions. Under 25 near-field ground motions, effects of mass eccentricity on the main parameters of the systems have been studied. These parameters have been selected as the main engineering demands including maximum isolator displacement and base shear as well as peak superstructure acceleration. The results indicate that the mass eccentricities do not have a remarkable effect on isolator displacement. In contrary to displacement, torsional effect of mass eccentricity has raised the base shear up to 1.75 times in a three-story superstructure. Additionally, mass eccentricity can amplify the roof acceleration of a nine-story model approximately 3 times in comparison with a symmetric one. It is also concluded that eccentricity in the direction of the subjected earthquake has the most impact on the base shear, while the isolator displacement and roof acceleration are mostly influenced by the eccentricity perpendicular to the earthquake path.

The influence of gravity column continuity on the seismic performance of special steel moment frame structures

This paper investigates the influence of the stiffness and strength of gravity columns on the collapse performance of buildings that utilize steel special moment frames as the main seismic lateral load resisting system. The research centers on the development of a simple lumped column approach, where all the gravity columns are combined into one elastic, continuous, and pinned-base element. Once this approach was validated, 2-, 4- and 8-story buildings that were originally analyzed without the influence of gravity columns in the ATC 76-1 project were re-analyzed including gravity columns. The FEMA P-695 methodology was used to assess the collapse performance. The effect of having a different number of gravity columns and different column sections was modeled by varying the moment of inertia of the lumped gravity column. The results show that the gravity columns have a profound influence on the collapse performance of buildings, especially for taller structures. Moreover, it was found that the correlation between the results of the nonlinear static analyses and the nonlinear dynamic analysis, based on collapse evaluation, provides insight into the choice of an optimal section for the lumped column. This means, in turn, that the designer can determine the number and the size of gravity columns that are required to significantly improve the building's collapse performance.

Application of Simplified Analysis Procedures for Performance-Based Earthquake Evaluation of Steel Special Moment Frames

This paper evaluates the effectiveness of single and multi-mode nonlinear static procedures (NSPs) as well as the FEMA P58 simplified approach versus rigorous nonlinear response history analyses (NRHA) for estimating seismic demands of steel special moment frames (SMFs). This work was mostly conducted within the framework of the ATC-76-6 project and indicates the level to which simplified analysis procedures in combination with commonly used nonlinear component models can reliably predict story-level engineering demand parameters (EDPs) such as, story drift ratios, story shear forces, overturning moments, residual deformations and peak floor absolute accelerations. It is advisable to employ a combination of NSP and NRHA to understand the seismic performance of steel SMFs and quantify important EDPs.

A superelastic viscous damper for enhanced seismic performance of steel moment frames

This study proposes a hybrid passive control device and investigates its performance in improving response of steel frame structures subjected to multi-level seismic hazards. The proposed superelastic viscous damper (SVD) relies on shape memory alloy (SMA) cables for re-centering capability and employs a viscoelastic (VE) damper that consists of two layers of a high damped (HD) blended butyl elastomer compound to augment its energy dissipation capacity. First, experimental tests are conducted to characterize behavior of SMA cables and VE damper and to assess the influence of various parameters such as displacement amplitude and loading frequency on their mechanical response. Then, an analytical model of a six-story steel special moment frame building with the installed SVDs is developed to determine the dynamic response of the structure. Nonlinear response history analyses are conducted to evaluate the behavior of controlled and uncontrolled buildings under 44 ground motion records. Results shows that SVDs can effectively mitigate dynamic response of steel frame structures at different seismic hazard levels and enhance their post-earthquake functionality.

Comparison of the Progressive Collapse Resistance of Seismically Designed Steel Shear Wall Frames And Special Steel Moment Frames

In this study, the progressive collapse potential of seismically designed steel plate shear wall (SPSW) systems is investigated using the alternate path method, and their performances are compared with those of the conventional special moment frame (SMF) systems. Nonlinear static and dynamic analyses are conducted to follow the progressive collapse of the structures, and their ability of absorbing the destructive effects of member loss is investigated. The obtained results show that when a corner or a middle column in the first story of the SPSWs is removed, the rest of the structure is not able to provide an appropriate alternative path for redistributing the generated loads caused by member loss, and therefore the structure presents a high potential for progressive collapse. However, by changing the lateral load resisting system of these buildings with the SMFs, the progressive collapse resisting capacity of the buildings increases significantly.

Evaluating the reliability of using the deflection amplification factor to estimate design displacements with accidental torsion effects

Some model building codes stipulate that the design displacement of a building can be computed using the elastic static analysis results multiplied by the deflection amplification factor, Cd. This approach for estimating the design displacement is essential and appealing in structural engineering practice when nonlinear response history analysis (NRHA) is not required. Furthermore, building codes stipulate the consideration of accidental torsion effects using accidental eccentricity, whether the buildings are symmetric-plan, or asymmetric-plan. In some model building codes, the accidental eccentricity is further amplified by the torsional amplification factor Ax in order to minimize the discrepancy between statically and dynamically estimated responses. Therefore, this warrants exploration of the reliability of statically estimated design displacements in accordance with the building code requirements. This study uses the discrepancy curves as a way of assessing the reliability of the design displacement estimates resulting from the factors Cd and Ax. The discrepancy curves show the exceedance probabilities of the differences between the statically estimated design displacements and NRHA results. The discrepancy curves of 3-story, 9-story, and 20-story example buildings are investigated in this study. The example buildings are steel special moment frames with frequency ratios equal to 0.7, 1.0, 1.3, and 1.6, as well as existing eccentricity ratios ranging from 0% to 30%.

Assessment of floor accelerations in special steel moment frames

The floor acceleration response of Special Steel Moment Frames subjected to earthquakes is evaluated considering different modeling options, i.e., elastic and inelastic behavior, with and without gravity frames, and considering different strength levels of the partially restrained connections in the gravity frames. The characteristics of the Special Steel Moment Frames considered in this study are based on those considered in the ATC 76-1 project. The influence of each modeling option on peak floor accelerations and on floor response spectra is then investigated. Results are also compared with the design acceleration demands on nonstructural components indicated in ASCE 7, which leads to relevant observations.

Influence of the gravity framing system on the collapse performance of special steel moment frames

This paper investigates the influence of the gravity framing system on the seismic performance of special steel moment frames (SMFs). The buildings used in this study were taken from one of the examples that form part of the ATC-76-1 project, which used the FEMA P-695 methodology to assess the collapse probability of SMF systems. Two, four and eight story SMFs were analyzed with and without the gravity frame to quantify their collapse performance. Aspects of the gravity frame that were investigated include the contribution of stiffness and strength of beam to column connections, and the location of splices in the gravity columns. Moreover, this research investigates the potential for the development of inelastic deformations in the gravity columns, and the effect of such deformations on structural response. The results show that gravity connections and gravity column continuity profoundly affect the computed response and collapse probability. The inelastic behavior in gravity columns has a less important effect but should be included in the analysis.

Analytical investigation of the cyclic behavior and plastic hinge formation in deep wide-flange steel beam-columns

This paper investigates the cyclic behavior of deep wide-flange sections, used as columns in steel Special Moment Frames (SMFs), through detailed finite element (FE) analysis. A wide range of wide-flange sections is subjected to symmetric cyclic lateral loading combined with different levels of constant compressive axial load ratios representing the loading conditions of interior steel columns in SMFs. The FE simulations demonstrate that wide-flange beam-columns, with web and flange slenderness ratios near the current compactness limits of seismic design provisions (AISC 341-10), experience rapid cyclic deterioration in flexural strength under high axial load ratios. It is also found that deep wide-flange slender sections shorten axially to about 10 % of their length due to severe flange and web local buckling. Based on the FE simulations, for bottom story columns, where axial load ratios are in the range of 20–35 %, a reduction to about two thirds of the current compactness limit for highly ductile members would achieve a 4 % chord rotation while maintaining a flexural strength larger than 80 % of the expected plastic flexural strength of a steel column. The FE simulation results also suggest that the pre-capping rotation predicted by current modeling recommendations for steel components (PEER/ATC 72-1) is overestimated for sections with high web and flange slenderness ratios undergoing monotonic and/or cyclic lateral loading combined with high axial load levels.

Effect of various span lengths on seismic demand on column splices in steel moment frames

Steel moment frames have gone through intensive investigation to understand the cause of the damage since the 1994 Northridge–California earthquake. A research conducted by the SAC Joint Venture has helped to improve the current code requirements for steel special moment frame design. One major outcome of these research efforts was on the enhanced design requirements for column splices. For example, AISC 341 Seismic Provisions require that column splices in intermediate and special moment frames, when not made using complete joint penetration welds, be designed to develop the expected flexural strength of the smaller connected column and the shear demand associated with flexural hinging at the top and bottom of the spliced column. This paper focuses on the effect of various span lengths on seismic demands on column splices in steel moment-resisting frames. A comprehensive nonlinear analytic investigation was undertaken to evaluate the seismic responses of 4- and 9-story moment-resisting frames with constant and various span lengths subject to an ensemble of 20 strong ground motions. The results indicate that the structural response is sensitive to the span length and variable span length within the frame might significantly increase the seismic demand on column splices.

Modeling of the composite action in fully restrained beam‐to‐column connections: implications in the seismic design and collapse capacity of steel special moment frames

SUMMARYThis paper investigates the effect of the composite action on the seismic performance of steel special moment frames (SMFs) through collapse. A rational approach is first proposed to model the hysteretic behavior of fully restrained composite beam‐to‐column connections, with reduced beam sections. Using the proposed modeling recommendations, a system‐level analytical study is performed on archetype steel buildings that utilize perimeter steel SMFs, with different heights, designed in the West‐Coast of the USA. It is shown that in average, the composite action may enhance the seismic performance of steel SMFs. However, bottom story collapse mechanisms may be triggered leading to rapid deterioration of the global strength of steel SMFs. Because of composite action, excessive panel zone shear distortion is also observed in interior joints of steel SMFs designed with strong‐column/weak‐beam ratios larger than 1.0. It is demonstrated that when steel SMFs are designed with strong‐column/weak‐beam ratios larger than 1.5, (i) bottom story collapse mechanisms are typically avoided; (ii) a tolerable probability of collapse is achieved in a return period of 50 years; and (iii) controlled panel zone yielding is achieved while reducing the required number of welded doubler plates in interior beam‐to‐column joints. Copyright © 2014 John Wiley & Sons, Ltd.

Assessment the Behavior of Seismic Designed Steel Moment Frames Subjected to Progressive Collapse

Recent investigations reveal that progressive collapse phenomenon is dominant behavior in the majority of steel structures. Although the design of buildings is based on the fact that they need to withstand all the loads exerted on the structure, failure occurs as a result of inadequate design and modeling techniques, particularly for abnormal and extreme loading conditions. Once one or more load bearing member is eliminated from the structure, progressive collapse, mainly in columns, will commence. By the time a column is eliminated from the structure as a result of a sudden motor vehicle strike or earthquake or fire or any other internal or external factor that could take one column out of the system, the weight of the building (gravity load) will be distributed among other columns within the structure. Failure commences in the part of the structure that has lost a column unless other columns are designed appropriately against gravity loads and are capable of redistribution of additional loads imposed on them. Failure of vertical load bearing elements will continue until the stabilization of extra loading. Hence, this could lead to serious damage and collapse of the building which will lead to higher damage to the building than the primary damage. This research is based on the regulations conforming to the specifications of UFC guidelines and the structures have been modeled using SAP2000 (2012). In order to study the effects of the progressive collapse on the seismic design of special steel moment frames, SMRF, two 5-story and 15-storystructures are modeled in SAP2000 (2012). In order to have a better understanding of progressive collapse and obtain reliable results, Linear Static (LS), Nonlinear Static (NLS) and Nonlinear Dynamic analyses (NLD) procedure for single and 2 adjacent columns removal have been implemented in this study. Having a good perception of the possibility of progressive collapse involves incorporation of demand capacity ratio, plastic hinges formation and vertical displacements of removed column’s location plus axial force in columns adjacent to the removed column. Other factors such as number of stories and the amount of local damage resulted from the removal of 2 adjacent columns could also lead to a better understanding of the structural behavior.

A Flexibility-Based Formulation for the Design of Continuity Plates in Steel Special Moment Frames

This paper introduces a rational approach for the design of continuity plates and associated welds in steel special moment frame (SMF) connections. The current AISC Seismic Provisions require welds attaching continuity plates to develop the full strength of the plate, resulting in the need to use complete-joint-penetration (CJP) groove welds. The combination of continuity plate thickness requirements, welding process and weld inspection often leads to costly detailing that may be overly conservative. The proposed design procedure, which is based on the relative flexibility between the column flange and continuity plate, aims to quantify the seismic force demand on continuity plates, thus allowing designers to efficiently size both the continuity plate thickness and the associated welded joints. In addition, the design procedure may allow the use of fillet welds or partial-joint-penetration groove welds as opposed to CJP welds, leading to a more economical design and fabrication. Formulation of the design procedure through analytical studies, including finite element analysis, is outlined.

Evaluation of seismic behaviour of steel special moment frame buildings with vertical irregularities

AbstractThis paper concentrates on investigating the seismic behaviours of vertically irregular steel special moment frame (SMF) buildings by comparison with the regular counterpart. All buildings in this study were assumed to be located in Los Angeles, and subjected to 20 earthquake ground motions with a seismic hazard level of 2% probability of exceedance in 50 years. The beam–column connections of the buildings were modelled to consider the panel zone deformation. In addition, a ductile connection model accompanied by strength degradation was incorporated to the analysis programme in an effort to obtain more accurate response results. Three types of irregularities (mass, stiffness and strength irregularity) specified as vertical irregularities in the IBC 2000 provisions were imposed to the original building. Nonlinear static and dynamic analyses were performed, and the confidence levels of which the performance objective will be satisfied were calculated as well. The effects of different irregularity types and levels on the seismic behaviours of the buildings were investigated and discussed in terms of the height‐wise distribution of storey drifts, maximum storey drift demands, global collapse storey drift capacities and confidence levels. Copyright © 2010 John Wiley & Sons, Ltd.

Repairable Seismic Moment Frames with Bolted WT Connections: Part I

A moment frame lateral load-resisting system was developed in which inelastic deformations due to seismic loading were intended to be isolated to easily replaceable WT components. Fully bolted connections were utilized to facilitate simple component installation and replacement. In Part I of this series, WT components for the moment frame system were modeled using finite element analysis. Full-scale component testing was performed to verify analytical results. Parameters taken from modeling and testing results were used to develop design provisions. In Part II of this series, an example building was designed using the provisions developed and analyzed under simulated earthquake accelerations to develop appropriate seismic performance factors. WT components designed using recommended geometric parameters resulted in desirable behavior. Recommended design equations correlated well to experimental test results. Experimental results suggested WT components designed using the recommended provisions exhibit adequate low-cycle fatigue performance and deflection capacity to be used with wide flange beams up to a nominal depth of 30 in. (762 mm). Nonlinear time-history analysis suggests seismic performance factors currently published for steel special moment frame systems are appropriate for the proposed WT moment frame system.

Repairable Seismic Moment Frames with Bolted WT Connections: Part II

A moment frame lateral load-resisting system was developed in which inelastic deformations due to seismic loading were intended to be isolated to easily replaceable WT components. Fully bolted connections were utilized to facilitate simple component installation and replacement. In Part I of this series, WT components for the moment frame system were modeled using finite element analysis. Full-scale component testing was performed to verify analytical results. Parameters taken from modeling and testing results were used to develop design provisions. In Part II of this series, an example building was designed using the provisions developed and analyzed under simulated earthquake accelerations to develop appropriate seismic performance factors. WT components designed using recommended geometric parameters resulted in desirable behavior. Recommended design equations correlated well to experimental test results. Experimental results suggested WT components designed using the recommended provisions exhibit adequate low-cycle fatigue performance and deflection capacity to be used with wide flange beams up to a nominal depth of 30 in. (762 mm). Nonlinear time-history analysis suggests seismic performance factors currently published for steel special moment frame systems are appropriate for the proposed WT moment frame system.

Steel non‐orthogonal reduced beam section moment connections—a case study

SUMMARYThe architectural expressions for many modern buildings require creative and unconventional structural solutions. Columns must be taller, beams must span further, the structure must be more slender, elements must be curved, structural framing must be sloped and connections must deviate from conventional orthogonal fit‐up. Although the technology exists to analyze and design responsive structural systems, prescriptive code requirements oftentimes hinder the implementation of those technologies. Although not a ‘tall building’ by traditional definition, the Tom Bradley International Terminal (TBIT) Modernization Program at Los Angeles International Airport (LAX) provides an appropriate case study in the implementation of unconventional structural geometry subject to code requirements that prescribe contrasting conventional geometry, which is a familiar challenge for many tall buildings.The architectural expression for the LAX TBIT Modernization Program required the use of long‐span steel Special Moment Frames with non‐orthogonal moment connections between the beams and columns. The beams were sloped, some were sloped and curved and some of the columns were sloped. The reduced beam section (RBS) moment connection was selected for the project. ANSI/AISC 358, Prequalified Connections for Special and Intermediate Steel Moment Frames for Seismic Applications, provides prequalification limits for using an RBS connection. Those limits do not address non‐orthogonal moment connections. ANSI/AISC 358 implicitly limits connections to orthogonal geometry; hence, non‐orthogonal moment connections are not prequalified for use in seismic applications. This paper describes the structure and the cyclic testing program that was implemented to qualify the proposed non‐orthogonal RBS connections in accordance with ANSI/AISC 341, Seismic Provisions for Structural Steel Buildings, Appendix S for use on the LAX TBIT Modernization Project. Copyright © 2011 John Wiley & Sons, Ltd.

Identifying the Collapse Hazard of Steel Special Moment-Frame Buildings with Viscous Dampers Using the FEMA P695 Methodology

An innovative design using steel special moment frames sized per building code requirements for strength and viscous dampers to control story drift ratios results in longer period structures that limit floor accelerations with excellent performance in design-level earthquakes. However, the response of this design to extreme seismic events is not well understood. This is due to the lack of: a) limit state data for dampers, and b) data on the response of the system when subjected to large earthquakes. To address these issues, analytical investigation of the limit states of dampers was performed and the performance of the model was correlated with experimental data. This model was then implemented in a group of archetypes subjected to collapse-level loading. Analysis showed that this design had satisfactory performance when subjected to extreme seismic events. Additional significant improvement in performance was obtained with an enhanced damper design and with a damper safety factor of 1.3.

Damage Assessment of a Full-Scale Six-Story Wood-Frame Building Following Triaxial Shake Table Tests

In the summer of 2009, a full-scale midrise wood-frame building was tested under a series of simulated earthquakes on the world's largest shake table in Miki City, Japan. The objective of this series of tests was to validate a performance-based seismic design approach by qualitatively and quantitatively examining the building's seismic performance in terms of response kinematics and observed damage. This paper presents the results of detailed damage inspections following each test in a series of five shake table tests, and explains their qualitative synthesis to provide design method validation. The seismic test program had two phases. Phase I was the testing of a seven-story mixed-use building with the first story consisting of a steel special moment frame (SMF) and stories 2-7 made of light-frame wood. In Phase II, the SMF was heavily braced such that it effectively became an extension of the shake table and testing was conducted on only stories 2-7, making the building a six-story light-frame multifamily residential building instead of a mixed-use building. All earthquake motions were scalings of the 1994 Northridge earthquake at the Canoga Park recording station with seismic intensities ranging from peak ground accelerations of 0.22 to 0.88 g. The building performed quite well during all earthquakes with damage only to the gypsum wall board (drywall), no sill plate splitting, no nails withdrawing or pulling through the sheathing, no edge tearing of the sheathing, no visible stud splitting around tie-down rods, and reasonable floor accelerations. On the basis of damage inspection, it was concluded that it is possible to design this type of building and keep the damage to a manageable level during major earthquakes by utilizing the new design approach. DOI: 10.1061/(ASCE)CF.1943-5509.0000202. © 2012 American Society of Civil Engineers.

Shake table testing of a full-scale seven-story steel–wood apartment building

In July 2009, a full-scale mid-rise light-frame wood apartment building was subjected to a series of earthquakes at the world’s largest shake table in Miki, Japan. The test program consisted of two major phases: the building tested in the first phase consisted of a single-story steel special moment frame (SMF) with six stories of wood on top, and the second phase consisted of locking down the steel story and testing the six-story light-frame wood building by itself. This paper focuses on the test results for the seven-story steel–wood building tested to earthquakes having return periods of 72 and 665 years. The objective of this phase of the test program was to investigate the performance of a mid-rise light-frame wood building with a first-story moment frame when subjected to a major earthquake, essentially providing a landmark data set to the seismic engineering research community. The building consisted of 225 square meters for retail space at the first story and 1350 square meters of multi-family residential living space with 23 apartment units above. The building was instrumented with just over 300 sensors and 50 LED optical tracking points to measure the component and global responses, respectively. In this paper the seven-story test specimen is described and the resulting seismic response and behavior is summarized. Detailed damage inspection was performed following each of these tests, and representative images are presented and discussed. The building was found to perform excellently, with very little damage following an event that was slightly larger (×1.16) than the design-level event for the city of Los Angeles, California. The peak global drift at roof level was 166 mm, and the peak inter-story drifts were approximately 1.3%.