Analysis of Fracture Behavior of Large Steel Beam-Column Connections

[EN] Recently completed experimental steel beam-column connection tests on the largest specimens of reduced-beam section specimens ever tested have shown that such connections can meet current seismic design qualification protocols, allowing to further extend the current AISC Seismic Provisions and the AISC Provisions for Prequalified Connections for Special and Intermediate Steel Moment Frames. However, the results indicate that geometrical and material effects need to be carefully considered when designing welded connections between very heavy shapes. Understanding of this behavior will ease the use of heavier structural shapes in seismic active areas of the United States, extending the use of heavy steel sections beyond their current use in ultra-tall buildings. To better interpret the experimental test results, extensive detailed finite element analyses are being conducted on the entire series of tests, which comprised four specimens with beams of four very different sizes. The analyses intend to clarify what scale effects, at both the material and geometric level, influence the performance of these connections. The emphasis is on modeling of the connection to understand the balance in deformation between the column panel zones and the reduced beam section, the stress concentrations near the welds, the effects of initial imperfections and residual stresses and the validity of several damage accumulation models. The models developed so far for all four specimens have been able to accurately reproduce the overall load-deformation and moment-rotation time histories.These studies were made possible by a grant from the National Scholarship Council of China to Mr. Qi and by the generosity of the Advanced Research Computing Center at Virginia Tech.Qi, L.; Paquette, J.; Eatherton, M.; Leon, R.; Bogdan, T.; Popa, N.; Nunez, E. (2018). Analysis of Fracture Behavior of Large Steel Beam-Column Connections. En Proceedings of the 12th International Conference on Advances in Steel-Concrete Composite Structures. ASCCS 2018. Editorial Universitat Politècnica de València. 521-526. https://doi.org/10.4995/ASCCS2018.2018.7122OCS52152

Steel Deck Diaphragm Test Database V1.0

Front material and Excel database of test results.From the 1950’s to the present, a substantial number of large-scale tests have been conducted on steel deck diaphragms or concrete on metal deck diaphragms. The data, papers and reports for these tests are located in scattered references and many are not publically available. As part of the Steel Diaphragm Innovation Initiative (SDII), a database of over 750 past experiments on metal deck diaphragms was created. The information contained in this database can be useful for several applications including evaluating strength and stiffness prediction equations, assessing resistance and safety factors, and investigating ductility of diaphragms. The database contains fields related to 1) specimen identification and reference, 2) the test setup including information about the geometry, loading type, deck orientation, beam sizes, steel deck geometry, and concrete slab information if applicable, 3) fastener information including sidelap fasteners, structural fasteners, and shear studs, 4) information about materials including deck material and concrete fill material, and 5) test results for selected specimens including stiffness, strength, and ductility.American Institute of Steel Construction (AISC), American Iron and Steel Institute (AISI), Steel Deck Institute (SDI), Steel Joist Institute (SJI), Metal Building Manufacturers Association (MBMA), National Science Foundation (NSF

Large-Scale Cyclic and Hybrid Simulation Testing and Development of a Controlled-Rocking Steel Building System with Replaceable Fuses

Current U.S. building codes and earthquake engineering practice utilize inelasticity in the seismic force resisting system to dissipate seismic energy and protect against collapse. Inelasticity in conventional structures can lead to structural damage distributed throughout the building and permanent drifts after the earthquake motion ceases which can make the structure difficult if not financially unreasonable to repair. A controlled rocking system has been developed which virtually eliminates residual drifts and concentrates the majority of structural damage in replaceable fuse elements. The controlled rocking system for steel-framed buildings consists of three major components: 1) a stiff steel braced frame that remains virtually elastic, but is not tied down to the foundation and thus allowed to rock, 2) vertical post-tensioning strands that anchor the top of the frame down to the foundation, which brings the frame back to center, and 3) replaceable structural fuses that absorb seismic energy as the frames rock. The controlled rocking system is investigated and developed through analytical, computational, and experimental means. First, the mechanics of the system response are described based on decomposing the system into a restoring force component and an energy dissipating component which are then combined in parallel to create a flag-shaped self-centering load-deformation response. A large-scale experimental program was then conducted in the MUST-SIM facility at the University of Illinois at Urbana-Champaign including quasi-static cyclic and hybrid simulation tests. Nine specimens were tested representing three-story frames at approximately half scale. The hybrid simulation tests included computational components that considered the destabilizing effects of gravity loads on leaning columns and the effect of the lateral resistance of gravity framing and interior wall partitions on the self-centering capabilities of the controlled rocking system. These large-scale experiments validated the performance of the system, allowed the investigation of detailing and construction methods, provided information on frame member forces, and provided data to confirm and calibrate computational models. After developing computational models that can represent system behavior, two computational studies were conducted. A single degree-of-freedom study consisting of over 25,000 analyses was performed to investigate system proportioning including defining the amount of restoring force that is necessary to provide reliable self-centering in the presence of ambient building resistance. A multi-degree-of-freedom study consisting of approximately 1500 analyses was performed to investigate the application of the controlled rocking system in different configurations, heights, and system proportioning. This study was also used to investigate the probabilities of reaching limit states for earthquake events with varying recurrence period. This work is part of a multi-institution, international research project to develop the controlled rocking system for implementation in practice. Phases of the larger research project that are not included in this dissertation include development of steel fuse plates at Stanford University, large-scale shake table testing at E-Defense in Miki, Japan, related computational studies, and development of displacement based design procedures. The experimental and computational studies described in this dissertation demonstrate that the controlled rocking system for steel-framed buildings can satisfy the performance goals of virtually eliminating residual drift and concentrating structural damage in replaceable fuses even during large earthquakes. The results of all phases of this work were synthesized into design recommendations which summarize the practical application of this system to building structures

Large-Scale Cyclic and Hybrid Simulation Testing and Development of a Controlled-Rocking Steel Building System with Replaceable Fuses

Current U.S. building codes and earthquake engineering practice utilize inelasticity in the seismic force resisting system to dissipate seismic energy and protect against collapse. Inelasticity in conventional structures can lead to structural damage distributed throughout the building and permanent drifts after the earthquake motion ceases which can make the structure difficult if not financially unreasonable to repair. A controlled rocking system has been developed that virtually eliminates residual drifts and concentrates the majority of structural damage in replaceable fuse elements. Portions of the development related to but not contained in this report include fuse testing, fuse analysis, large-scale shake table testing, development of a displacement based design procedure, and collapse modeling. The controlled rocking system is investigated and developed through analytical, computational, and experimental means. A large-scale experimental program was conducted including quasi-static cyclic and hybrid simulation tests. Nine specimens were tested representing three-story frames at approximately half scale. These experiments validated the performance of the system, demonstrated system response when subjected to simulated ground motions, allowed the investigation of detailing and construction methods, provided information on frame member forces, and provided data to confirm and calibrate computational models. Computational models were developed based on the experimental behavior and two computational studies were conducted. A single degree-of-freedom study consisting of over 25,000 analyses was performed to investigate system proportioning including defining the amount of restoring force that is necessary to provide reliable self-centering in the presence of ambient building resistance. A multi-degree-of-freedom study consisting of approximately 1500 analyses was performed to investigate the application of the controlled rocking system in different configurations. This study was also used to investigate the probabilities of reaching limit states for earthquake events with varying recurrence period. The experimental and computational studies described in this report demonstrate that the controlled rocking system for steel-framed buildings can satisfy the performance goals of virtually eliminating residual drift and concentrating structural damage in replaceable fuses even during large earthquakes. The results of all phases of this work were synthesized into design recommendations which summarize the practical application of this system to building structures.published or submitted for publicatio

Nonlinear behavior of controlled rocking steel-framed building systems with replaceable energy dissipating fuses

This report summarizes the results of a parametric study of a controlled rocking seismic lateral resistance system that includes two steel braced frames linked by replaceable energy dissipating fuses that are engaged by controlled rocking behavior. The frames are post-tensioned vertically to the foundation so as to facilitate self-centering after rocking. The study was conducted using geometrically and materially nonlinear finite element analysis of a two-dimensional prototype of the structural system. In this study, the structure is subjected to a suite of far-field ground motions representing different hazard levels in the Western U.S. The characteristics of the structural fuses, which absorb energy through a combination of cyclic shear and localized flexure mechanisms, were based on experimental test results of steel slit shear panels and engineered cementitious composite shear panels. Three key parameters are investigated that affect the response. The first is the ratio, A/B, of the bay width of the braced frames as compared to the width of the shear fuses connecting the frames. The second is the overturning factor (OT), which is the ratio of the total resisting moment of the fuses and post-tensioning compared to the overturning forces in the design code. The third is the self-centering factor (SC), which is the ratio of restoring moment of PT to the resisting moment of the fuses. Based on the computational results, recommendations are made for appropriate ranges of values for each of these parameters for effective performance.published or submitted for publicatio

Self-Centering Seismic Lateral Force Resisting Systems: High Performance Structures for the City of Tomorrow

Structures designed in accordance with even the most modern buildings codes are expected to sustain damage during a severe earthquake; however; these structures are expected to protect the lives of the occupants. Damage to the structure can require expensive repairs; significant business downtime; and in some cases building demolition. If damage occurs to many structures within a city or region; the regional and national economy may be severely disrupted. To address these shortcomings with current seismic lateral force resisting systems and to work towards more resilient; sustainable cities; a new class of seismic lateral force resisting systems that sustains little or no damage under severe earthquakes has been developed. These new seismic lateral force resisting systems reduce or prevent structural damage to nonreplaceable structural elements by softening the structural response elastically through gap opening mechanisms. To dissipate seismic energy; friction elements or replaceable yielding energy dissipation elements are also included. Post-tensioning is often used as a part of these systems to return the structure to a plumb; upright position (self-center) after the earthquake has passed. This paper summarizes the state-of-the art for self-centering seismic lateral force resisting systems and outlines current research challenges for these systems

Steel Diaphragm Innovation Initiative Workshop Report

Summary report of technical workshop and user survey.Researchers from the Steel Diaphragm Innovation Initiative (SDII) led a one day workshop in Burlingame California on 10 January 2019 for thirty-five engineering participants to discuss progress to date in the SDII effort, receive feedback on existing and planned future work, and to collectively identify key challenges and innovation opportunities related to the seismic performance of buildings employing bare or concrete-filled steel deck diaphragms. The SDII research team summarized current efforts in structural experiments across a variety of scales, modeling across scales, codes and standards for demand and capacity, and innovation opportunities. The presentation slides are provided in Appendix 1 and 2. For bare steel deck diaphragms existing testing, new testing, and simulation have been employed to develop improved design provisions for AISC 342/ASCE 41, AISI S310, AISI S400, and NEHRP/ASCE7. These new provisions recognize the conditions in which bare steel deck diaphragms can provide adequate ductility, deformation, and residual force capacity – and when these performance conditions are met, provide appropriate reductions in diaphragm demands. For concrete-filled steel deck diaphragms, new testing including: monotonic pushout tests, cyclic pushout tests, and full-scale cantilever diaphragm tests are all underway. Combined with existing testing the results are providing improved stiffness and strength provisions for AISI S310, and will also impact AISC 341, AISC 360, and ASCE7. The workshop participants were brought up to speed on all of these issues and more, expressed support for the SDII effort, and then engaged in an active exercise to explore challenges and opportunities in steel deck diaphragms. Workshop participants were provided a questionnaire in advance and given time during the meeting to individually answer ten questions related to challenges and nine questions related to innovation (see Appendix 3). Participants provided their complete response to the SDII team for later analysis, and then during the workshop engaged in small groups to develop an initial set of priorities. The prioritized challenges developed during the workshop covered: codification needs related to capacity prediction; improved models, particularly for diaphragm demands; workflow and practice-oriented (time and fee) challenges, detailing challenges, and how to better handle irregularities. The deeper analysis of the complete participant responses highlighted two major additional specific challenges: (1) even the nation’s most accomplished seismic building engineers do not have a consistent understanding of whether or not inelasticity is expected in the seismic response of building diaphragms, (2) while some engineers rely extensively on supplemental reinforcement in concrete-filled steel deck diaphragms both to improve the strength and provide the necessary chord and collector capacity, other engineers have specific concerns about confinement in these systems and will not employ them in their designs. A similar process was followed during the workshop and in later analysis for the questions related to innovation. During the workshop the prioritized points regarding innovation centered on three groups: technological innovation, overall innovation, and engineer support/workflow innovations. The primary ideas for technological innovation focused on improved connectors, and the potential for the integration of discrete energy dissipation devices (structural fuses). A significant point of discussion with respect to innovation is the need to have strong engineering support and efficient and simple workflows. Engineers found that the tools to model diaphragms were lacking in nearly every regard, and innovation is needed. A deeper analysis of the participant responses identified that innovation in diaphragms is hampered by a definitive lack of knowledge with respect to the behavior of building systems with inelasticity in both the vertical and horizontal lateral force resisting system. If this behavior is understood then software improvements (that support design) and specific technological innovation (isolation, improved damping, optimized deck profiles) can have impact.American Institute of Steel Construction (AISC), American Iron and Steel Institute (AISI), Steel Deck Institute (SDI), Steel Joist Institute (SJI), Metal Building Manufacturers Association (MBMA), National Science Foundation (NSF

Steel Diaphragm Innovation Initiative Workshop Report

Summary report of technical workshop and user survey.Researchers from the Steel Diaphragm Innovation Initiative (SDII) led a one day workshop in Burlingame California on 10 January 2019 for thirty-five engineering participants to discuss progress to date in the SDII effort, receive feedback on existing and planned future work, and to collectively identify key challenges and innovation opportunities related to the seismic performance of buildings employing bare or concrete-filled steel deck diaphragms. The SDII research team summarized current efforts in structural experiments across a variety of scales, modeling across scales, codes and standards for demand and capacity, and innovation opportunities. The presentation slides are provided in Appendix 1 and 2. For bare steel deck diaphragms existing testing, new testing, and simulation have been employed to develop improved design provisions for AISC 342/ASCE 41, AISI S310, AISI S400, and NEHRP/ASCE7. These new provisions recognize the conditions in which bare steel deck diaphragms can provide adequate ductility, deformation, and residual force capacity – and when these performance conditions are met, provide appropriate reductions in diaphragm demands. For concrete-filled steel deck diaphragms, new testing including: monotonic pushout tests, cyclic pushout tests, and full-scale cantilever diaphragm tests are all underway. Combined with existing testing the results are providing improved stiffness and strength provisions for AISI S310, and will also impact AISC 341, AISC 360, and ASCE7. The workshop participants were brought up to speed on all of these issues and more, expressed support for the SDII effort, and then engaged in an active exercise to explore challenges and opportunities in steel deck diaphragms. Workshop participants were provided a questionnaire in advance and given time during the meeting to individually answer ten questions related to challenges and nine questions related to innovation (see Appendix 3). Participants provided their complete response to the SDII team for later analysis, and then during the workshop engaged in small groups to develop an initial set of priorities. The prioritized challenges developed during the workshop covered: codification needs related to capacity prediction; improved models, particularly for diaphragm demands; workflow and practice-oriented (time and fee) challenges, detailing challenges, and how to better handle irregularities. The deeper analysis of the complete participant responses highlighted two major additional specific challenges: (1) even the nation’s most accomplished seismic building engineers do not have a consistent understanding of whether or not inelasticity is expected in the seismic response of building diaphragms, (2) while some engineers rely extensively on supplemental reinforcement in concrete-filled steel deck diaphragms both to improve the strength and provide the necessary chord and collector capacity, other engineers have specific concerns about confinement in these systems and will not employ them in their designs. A similar process was followed during the workshop and in later analysis for the questions related to innovation. During the workshop the prioritized points regarding innovation centered on three groups: technological innovation, overall innovation, and engineer support/workflow innovations. The primary ideas for technological innovation focused on improved connectors, and the potential for the integration of discrete energy dissipation devices (structural fuses). A significant point of discussion with respect to innovation is the need to have strong engineering support and efficient and simple workflows. Engineers found that the tools to model diaphragms were lacking in nearly every regard, and innovation is needed. A deeper analysis of the participant responses identified that innovation in diaphragms is hampered by a definitive lack of knowledge with respect to the behavior of building systems with inelasticity in both the vertical and horizontal lateral force resisting system. If this behavior is understood then software improvements (that support design) and specific technological innovation (isolation, improved damping, optimized deck profiles) can have impact.American Institute of Steel Construction (AISC), American Iron and Steel Institute (AISI), Steel Deck Institute (SDI), Steel Joist Institute (SJI), Metal Building Manufacturers Association (MBMA), National Science Foundation (NSF

Steel Deck Diaphragm Test Database V1.0

Front material and Excel database of test results.From the 1950’s to the present, a substantial number of large-scale tests have been conducted on steel deck diaphragms or concrete on metal deck diaphragms. The data, papers and reports for these tests are located in scattered references and many are not publically available. As part of the Steel Diaphragm Innovation Initiative (SDII), a database of over 750 past experiments on metal deck diaphragms was created. The information contained in this database can be useful for several applications including evaluating strength and stiffness prediction equations, assessing resistance and safety factors, and investigating ductility of diaphragms. The database contains fields related to 1) specimen identification and reference, 2) the test setup including information about the geometry, loading type, deck orientation, beam sizes, steel deck geometry, and concrete slab information if applicable, 3) fastener information including sidelap fasteners, structural fasteners, and shear studs, 4) information about materials including deck material and concrete fill material, and 5) test results for selected specimens including stiffness, strength, and ductility.American Institute of Steel Construction (AISC), American Iron and Steel Institute (AISI), Steel Deck Institute (SDI), Steel Joist Institute (SJI), Metal Building Manufacturers Association (MBMA), National Science Foundation (NSF