Reducing Earthquake Losses: From Research to Practice
A webinar series co-sponsored by the Earthquake Engineering Research Institute and the George E. Brown, Jr. Network for Earthquake Engineering Simulation
The Research to Practice webinar series focuses on the outcomes of NEES research and their significance to engineering design and construction. The content of the webinars are designed to appeal to both practitioners and researchers. Webinars are broadcast every couple of months and are archived here for continued access. Future webinars may be found in the calendar at nees.org.
Concentrically braced frames (CBFs) are practical and economical for seismic design, but the inelastic performance of CBFs is more complex and less well understood than many other structural systems. The NEESR small group research project, International Hybrid Simulation of Tomorrow's Braced Frame Systems, investigated these issues using experimental and analytical research methods. The results were combined to develop a new design method that balances the inelastic action within the CBF.
NOTE: IN THE VIDEO ABOVE, THE FIRST SLIDE DOES NOT ADVANCE FOR SEVERAL MINUTES. YOU DO NOT NEED TO ADJUST YOUR BROWSER.
Shear-wave profiling can be performed using a range of techniques including borehole methods. Surface-wave methods have become increasingly used because they are nonintrusive, economic and require the least field time. SASW (spectral-analysis-of-surface-waves) and MASW (multi-channel-analysis-of-surface-waves) methods are the two most popular. The presenters discuss the importance of shear-wave velocity profiling in seismic design, its uses, misuses and uncertainties.
The February 27, 2010 Chile earthquake was not only of very large magnitude (Mw 8.8), but also long in duration and strongly felt over a vast region. Thousands of structures designed and built to codes and standards similar to those used in the U.S. were tested by the earthquake. This webinar focuses on the performance of mid-rise concrete buildings by reviewing the test results, changes to the Chilean building code resulting from new knowledge, and implications for U.S. codes and standards.
This webinar summarizes key findings of the NEESwood project, suggested design approaches, and code implications. Findings address effects of nonstructural finishes on behavior, hold-down forces and elongation, inter-story drift limits, and accidental torsion. The discussion of the proposed design approach includes direct displacement design, use of numerical methods, rigid body calculations and diaphragm design.
Project Warehouse Development of a Performance-Based Seismic Design Philosophy for Mid-Rise Woodframe Construction
Project Warehouse Development of a Performance-Based Seismic Design Philosophy for Mid-Rise Woodframe Construction (Capstone test)
Precast concrete structures are cost-effective and durable systems that are rapidly erected and can accommodate long floor spans within a shallow profile. However, poor performance of precast floor diaphragms in recent earthquakes has limited the widespread use of precast construction. Reliable designs and details for the precast floor diaphragms are required for these systems to open up their use to a wider market.
Reinforced concrete and steel frame structures sometimes include unreinforced masonry infill walls as interior and exterior partitions. Such construction can be found in many old buildings in the western United States, such as pre-1930’s buildings in California, and is still being used for newer buildings in the midwestern and eastern parts of the country. Even though unreinforced masonry infill walls are usually considered as non-structural elements, they interact with the bounding frames when subjected to earthquake loads. This interaction may result in unintended failure mechanisms, such as shear failures of reinforced concrete (RC) columns and the crushing of the masonry infill. The seismic performance and safety of infilled frames have received much attention because of their mixed performance in past earthquakes. The lateral load resistance of an infilled frame highly depends on the frame-wall interaction and the specific failure mechanism that may result. This presents a major challenge for the performance assessment of these structures.
The NEEShub Databases (http://nees.org/resources/databases) contain spreadsheet-style data from the NEES Project Warehouse and from external data sources that are vetted by professional communities and connected to their original sources. Existing and planned databases will be a primary focus of the webinar. Currently there are nine databases available through NEEShub, ranging from earthquake reconnaissance information to data from journal articles. Partnerships with the American Concrete Institute and the Journal of Earthquake Engineering have provided a platform for authors to share the data plotted in figures in published manuscripts. Modeling parameters may be verified or developed based on information in Databases such as: the SAC Steel Project Database, the Shear Wall Database, the Shear Wave Velocity Database, and the Structural Control Database. Databases planned for the near future will publish data from ACI technical committees.
The PREcast Seismic Structural System program (PRESSS), completed about a decade ago, introduced the use of unbonded post-tensioned walls for seismic-resistant design. Since that time, several research advancements have been made and codification of unbonded post-tensioned walls has been completed. To improve cost-effectiveness and resiliency, the PREcast wall with end columns (PreWEC) was subsequently introduced. Today, an investigation of PreWEC—focusing on understanding the influence of various damping components and interaction between rocking walls and surrounding building components—is being conducted in the NEES Rocking Wall Project. The webinar will provide 1) a brief summary of the PRESSS wall system; 2) details of PreWEC and its performance; 3) analysis results that examined the interaction between a PreWEC system connected to floors and gravity columns; and 4) directions for implementing ongoing and completed research in design practice. In addition, an opportunity to provide input for the NEES Rocking wall project will be provided.
Professor Jamie Steidl and Dr. Sandy Seale presented several examples of research conducted using data collected at the NEES@UCSB permanently-instrumented geotechnical test sites in southern California. These sites are designed to improve our understanding of the effects of surface geology on strong ground motion, liquefaction susceptibility, and soil-foundation-structure interaction (SFSI). The instrumentation at these sites includes surface and borehole arrays of accelerometers and pore pressure transducers that record strong ground motions and excess pore pressure generation generated by earthquakes. An instrumented test structure is also monitored to improve our understanding of (SFSI) effects. Researchers also use the sites for active experiments where ground motions are generated by virbroseis trucks (T-Rex), large shakers, and a small remotely operable shaker and cross-hole source. Data acquired by the sites is available through the data portal on the website http://nees.ucsb.edu/. The sites have live telepresence that is available through the website. A virtual tour of the sites and a demonstration of how to view and download data was part of the webinar.
Structural walls are one of the most commonly used reinforced concrete seismic resisting systems. In mid-rise and taller buildings, walls are typically placed at the core of the building to frame elevators and/or stairs. As a result, core walls often have a flanged configuration with coupling beams linking the flanged walls and providing access to elevators, stairs or other elements located within the core walls. A research study sponsored by the National Science Foundation through the NEES research program, with supplemental funding provided by the Charles Pankow Foundation, was undertaken to investigate the seismic response of core wall systems. The study included integrated experimental and analytical research on planar, coupled and C-shaped walls. The talk will present research related to all three wall configurations. Experimental and analytical results will be presented with an eye towards specific design recommendations. The experimental data generated as part of the current study were supplemented with data from prior research on RC walls and a large database of walls responding in flexure was developed.
In 2005 NSF funded a 5-year NEESR research project to develop Performance Based Tsunami Engineering (PBTE). The objective of this study was to fill the gap between tsunami modeling, which had traditionally focused on tsunami generation and transoceanic propagation for evacuation planning, and the actual performance of coastal structures during tsunami inundation, which was rather unknown for U.S. construction. Experiments performed in the NEES Tsunami Wave Facility at OSU and in the Hydraulics Laboratory at UH Manoa have led to enhanced inundation modeling and improved understanding of fluid loading on structural elements. A subsequent NEES project investigated the problem of waterborne debris impact in greater detail, leading to a better understanding of loads induced on structural elements by floating logs and shipping containers.
A multi-institution combined experimental/computational NEES research program was undertaken in 2009 comprised (a) experiments on 18 full-scale slender concrete-filled steel tube beam-columns, (b) the development of new finite element formulations that enable accurate representation of the seismic response of three-dimensional composite braced and unbraced frame structures; (c) extensive use of these models in FEMA P695 studies to reevaluate the seismic performance factors of ASCE 7-10, and (d) the development of design recommendations for composite structures within the context of the AISC Specification for Structural Steel Building. The results of the investigation indicate that concrete-filled beam-columns are extremely tough and ductile elements, capable of maintain their load-carrying capacity and stiffness through very severe cyclic load histories. In addition, the advanced models indicate that structural systems with these types of members provide superior performance under nonlinear time-history analyses. The results have provided additional data to improve the design provisions for composite columns and beam-columns in both the AISC Specification and the AISC Seismic Provisions.
Coupled shear wall systems are the most commonly used seismic force-resisting system for moderate to high-rise reinforced concrete (RC) structures. This presentation highlights background research and field applications on the use of high-performance fiber-reinforced concrete (HPFRC) in coupling beams that link together adjacent shear walls. During large earthquake motions, it is anticipated that coupling beams will undergo significant inelastic deformations and it is important for these beams to have a high energy dissipation capability and good stiffness retention. Current design practice is to use heavy diagonal reinforcement in RC coupling beams, but the placement of such reinforcement is labor intensive and costly. The primary concept behind this research was that the next generation of RC structures should utilize ductile concrete in critical regions that are expected to experience plastic deformations, rather than expensive reinforcement detailing, to provide shear resistance and concrete confinement. This presentation will cover mix design information and behavior of HPFRC, observed behavior of individual precast HPFRC coupling beams subjected to large cyclic displacement reversals as well as results from tests of two four-story coupled wall systems, and design and construction procedures for buildings under construction in the Seattle area.
Seismic behavior of pile foundations is a complex problem. This complexity is further exacerbated when weak soils such as soft clays or liquefiable sands surround the pile foundations. The behavior of pile foundations in liquefiable sands has been studied extensively; however, similar investigations for soft clays and seismic response of piles in improved soils have received attention only in recent years. Ensuring satisfactory performance of pile foundations during earthquakes is critical for obtaining desirable seismic performance of structures that they support.
Seismic isolation has long been regarded as an effective technique to enhance the seismic performance of structures, but applications to new buildings has been limited in the United States. The following reasons have often been given for the slow growth of application for seismic isolation systems: the high cost premium of isolation coupled with inability to convey the potential benefit to building owners; lack of field or laboratory data on full-scale, realistic buildings; and uncertainty about the response of isolated structures in extreme ground motions that exceed design levels.
Understanding the level of seismic risks facing the Sacramento-San Joaquin Delta is of national concern given the country's two largest water diversion systems are located in the southern portion of the estuary. Recent studies of seismic risk in the Delta indicate that a moderate earthquake in the region could cause multiple simultaneous levee breaches that would flood Delta "islands" and draw in saline water from the west, thereby halting delivery. These studies focused primarily on the seismic response of liquefiable sands and silts within and beneath the Delta levees, which is widely acknowledged by experts as being a significant problem. However, most Delta levees are founded on peat soil, often in combination with sandy soils, and much less is currently understood about the seismic deformation potential of peat. This NEES/EERI research-to-practice webinar will present findings from a recently completed NEES field test of a model levee resting atop peaty organic soil, and an ongoing NEES centrifuge study of nonliquefiable and liquefiable levee fills resting atop peat.