Full Scale Cyclic Large Deflection Testing of Foundation Support Systems for Highway Bridges
Principal Investigator: Jonathan P. Stewart (UCLA)
This research involved analysis and field testing of several foundation support components for highway bridges. Two classes of components were tested - cast-in-drilled-hole (CIDH) reinforced concrete piles (drilled shafts) and an abutment backwall. The emphasis of this document (Part I of the full report) is CIDH shafts.
CIDH shafts are among the most common support structures in highway construction. Typically, drilled shafts have simple, prismatic geometries; yet, they display a complex, inelastic response under applied loading. The two major factors that affect their behavior are the interaction between the shaft and surrounding soil media, and the material inelasticity of the shaft itself. In this report we document the results of two single shaft tests and one shaft group test. All specimens are two-feet diameter reinforced concrete drilled shafts that extend approximately 24ft below ground line. The single shaft specimens include one in a flagpole configuration extending 13.3ft above ground line and the other capped at the surface in a fixed-head configuration. The group test specimen had 9 individual shafts in a 3 by 3 configuration anchored at the ground surface (with a moment connection) in a reinforced concrete cap. The test site consists primarily of low plasticity alluvial clay that is expected to exhibit an undrained response to the cyclic lateral loading. The quasi static loading was applied with a hydraulic control system in displacement-control mode, with the full suite of loading taking several days to complete for each test. The test data have been reduced to provide complete load-deflection backbone curves for loading in both directions, curvature profiles at pre-yield deflection levels, hysteresis curves documenting the cyclic behavior of the shaft soil system at pre-yield displacements, p-y curves for the single shaft specimens, and group interaction factors for the group specimen.
Structural Health Monitoring of Tall and Important Buildings
Principal Investigator: John Wallace (UCLA)
This research will provide critically needed field data to address fundamental issues associated with modeling of complex structural systems, including system interactions. These data cannot be generated in controlled laboratory experiments due to issues of scale, materials, boundary conditions, system interactions, and most significantly, cost. The research vision is to make the true built environment the laboratory - to collect the wealth and diversity of data not otherwise possible. The project will provide vital data to improve modeling capabilities for wind events, low-to-mid level amplitude shaking in relatively frequent earthquakes, and ultimately, the "Big One". The systems and tools will be developed in an open-source environment. The project team, along with the NEES@UCLA and UCLA CENS resources and technologies, are uniquely qualified to carry out the proposed research.
Mitigation of Collapse Risk in Vulnerable Concrete Buildings
Principal Investigator: Jack Moehle (UC Berkeley)
One of the greatest overall seismic risks in the United States is the risk of collapse of older concrete buildings in a major urban earthquake, yet there are no solutions to how to address this in a cost-effective manner. Policy makers and building owners are frustrated by the costs of retrofitting large inventories of existing buildings. Engineers need tools to accurately assess the risk of individual buildings and to differentiate between adequate buildings and potentially hazardous ones, so building owners can prioritize mitigation expenses. Regulatory agencies need better information on the regional extent of the risk so that effective policy measures can be put in place to effect regional mitigation efforts. This project will study the collapse potential of older nonductile concrete buildings, which are pervasive and high risk, to improve and disseminate effective engineering assessment and retrofit tools and to define appropriate incentive or policy measures to mitigate the risk. The research will investigate four areas: 1) Exposure - a single urban region will be selected to serve as a model for other regions, and an inventory model suitable to study the regional collapse risk of older type concrete buildings will be developed; 2) Component and System Performance - laboratory and field experiments will be conducted on components, subassemblies, and soil-foundation-structure systems to better understand conditions that lead to collapse; 3) Building and Regional Simulation - models will be developed and implemented in nonlinear dynamic analysis software useful to earthquake engineers, and results will be extended through regional dynamic simulations to help understand the regional distribution of building collapses in a major earthquake; and 4) Mitigation Strategies - effective mitigation strategies and coalitions involving engineers, planners, policy experts, and stakeholders will be developed to promote action for risk reduction. The program features a significant education component aimed at increasing diversity in earthquake engineering, international collaborations, and outreach to disseminate results to a broad community.
The intellectual merit lies in the multi-disciplinary challenge of understanding the conditions and mechanics of collapse under three-dimensional loading, implementing that understanding in software usable for individual building analysis, and extending the understanding to the regional level where the intersection among engineering science, economics, and public policy will provide a rational basis for recommending the best mitigation strategies.
The broader impacts of the project are extensive. The research program tackles an important and challenging problem that will advance discovery and understanding of earthquake engineering. The education program will expose a diverse population of undergraduates to the program and promote top candidates into graduate research. The results of the research will be disseminated in several ways, including: by sharing results using the NEES resources, by involving earthquake professionals and urban planners, and by disseminating educational materials. The results will benefit society by helping define appropriate engineering and public policy solutions to address the problem of existing hazardous building construction. Better understanding collapse of buildings during earthquake will also contribute to knowledge on vulnerability and toughening of infrastructure against effects of explosive and impact hazards. Mitigation strategies developed in this project also can inform strategies to mitigate for other natural hazards such as hurricanes. This project uses the NEES equipment sites at the University of California, Berkeley, the University of California, Los Angeles, the University of California, Santa Barbara, and the University of Minnesota.
Evaluation of Seismic Levee Deformation Potential by Destructive Cyclic Field Testing
Principal Investigator: Scott Brandenberg (UCLA)
The Sacramento-San Joaquin Delta levees are critical components of California's water distribution system. The Delta supplies fresh water to 22 million people in southern and central California as well as eastern portions of the San Francisco Bay area and directly supports $400 billion/year of economic activity within the State of California. The "islands" circumscribed by the network of levees are commonly 3 to 5 meters below sea level, and are protected by only about 1 to 1.5 meters of freeboard at high tide. A breach in a levee causes water from the channel to flow into the island thereby inundating farmland and wildlife habitat, and drawing saline water from the San Francisco Bay into the Delta. This is a potentially catastrophic scenario, as saline contamination could halt water delivery to central and southern California, removing the sole water source for many communities. This scenario is unlikely in the event of an individual levee breach caused by burrowing animals and other local hazards because the existing emergency response system can respond to a single breach within a matter of hours and affect repair within a matter of weeks. On the other hand, seismic hazard is an extraordinary threat because of the potential for multiple simultaneous breaches inundating many islands within the Delta. Such widespread system failure has been forecast to cause up to 28 months of time during which fresh water deliveries from the Delta would not be possible. Some in fact question whether such a sequence of breaches might permanently change the regional morphology such that either alternative water sources would need to be identified or major sectors of the California economy/population would need to be reconfigured or relocated. The influence of earthquake shaking on the behavior of the levees is uncertain because the cyclic deformation potential of the underlying peaty organic soils not well understood, and there is an urgent need to investigate the behavior of these materials. Intellectual Merit and Scope: This award will support full-scale testing of an existing earth embankment (very similar in geometry to a levee, but not currently holding water) to investigate the in situ deformation potential of peaty organic foundation soils under realistic stresses and boundary conditions. The test conditions and instrumentation will be designed to measure the deformation mechanisms that can result in a critical loss of freeboard leading to a breach. Data of this sort is essential for the development of more rational analysis tools for assessing the seismic vulnerability of levees. The field testing will be supplemented by an extensive laboratory testing program to further investigate key material response characteristics such as soil strength loss and volume reduction caused by shaking. The improved knowledge of levee seismic vulnerability will be broadly applicable wherever these earth structures are founded on organic soils. Testing activities will be closely coordinated with engineers at the California Department of Water Resources to identify a suitable site. Insights gained from this project could fundamentally alter the manner in which Delta seismic risk is assessed and retrofit decisions are made. Broader Impacts: The most important societal impact of this research will be improvement of seismic risk assessment in the Delta, which in turn will result in better informed retrofit and/or construction decisions and a water delivery system that is more likely to maintain functionality during and following earthquake shaking. This award will also support development of education modules that leverage NEES resources to contribute to the broader NEESinc goals for education, outreach and training (EOT). The modules will teach about the current water delivery system, the network of levees in the Delta, the link between water delivery and the levee network, the engineering properties of these levees, the potential seismic failure mechanisms of the levees, and the consequences on the availability of water for drinking and irrigation. Included with the modules will be a study guide containing suggestions regarding implementation of the modules at different levels (i.e., undergraduates and K-12). Data from this project will be made available through the NEES data repository (http://www.nees.org).
Understanding and Improving the Seismic Behavior of Pile Foundations in Soft Clays
Principal Investigator: Kanthasamy Muraleetharan (University of Oklahoma)
This project will utilize the NEES equipment sites at the University of California, Davis and the University of California, Los Angeles. Pile foundations are an integral part of many civil engineering structures. The seismic behavior of pile foundations is a very complex problem with interactions between soils (solid skeleton, pore water, and pore air), piles, and superstructure. This complexity is further exacerbated when weak soils such as soft clays and liquefiable loose sands surround the pile foundation. The behavior of pile foundations in liquefiable sands has been studied extensively; however, similar investigations for soft clays or seismic response of piles in improved soils have been rarely performed. The current seismic design practice calls for avoiding inelastic behavior of pile foundations by restricting their lateral displacements because it is difficult to detect damage to foundations following an earthquake. Limiting the lateral displacement of a pile foundation is relatively easy to achieve in competent soils. In the case of weak soils, the current practice is to use an increased number of more ductile, larger diameter piles that are difficult to design and expensive to construct. An innovative, and perhaps more cost-effective, solution to this problem is to improve the soil surrounding the pile foundation. For structures undergoing seismic retrofit with existing pile foundations in weak soils, in certain instances, improving the soils may be the only option to improve the seismic behavior of the foundation. This technique is not widely used in seismic regions due to lack of fundamental understanding of the behavior of improved and unimproved soils and the interactions between them as well as with the piles during earthquakes. As a first step in a long term objective of understanding and improving the seismic behavior of pile foundations in all weak soils, the proposed research will focus on soft clays. Soft clays are quite prevalent in earthquake prone areas of the U.S., but have received little attention from the research community. Following are some of the unanswered research questions that have to be addressed before ground improvement can be used as a viable option to enhance the seismic response of pile foundations in soft clays in routine design practice: (1) What are the effective techniques for improving soft clays around pile foundations for both seismic design and retrofit? (2) How can we analyze, simulate, and design pile foundations in soft clays with ground improvement for earthquake loads? (3) How do individual piles and pile groups, with and without ground improvement, behave during seismic events and how can we validate our analysis and simulation tools and designs? And (4) how can we translate our understanding into a useful design methodology to benefit the broader earthquake engineering community? The intellectual merit of this work is that the above mentioned research questions will be systematically addressed using a multidisciplinary team consisting of structural and geotechnical engineers and industrial partners who have extensive experience in ground improvement techniques and seismic design of pile foundations. Innovative centrifuge and full-scale field tests using NEES facilities and equipment, simplified analysis methods, and sophisticated fully coupled simulation techniques will be utilized to understand and improve the seismic behavior of pile foundations in soft clays. The research results will be translated into a useful design methodology and tools that will benefit the entire earthquake engineering community immediately as well as influence the long term practices. Simple analysis methods will serve the immediate needs of the industry while sophisticated simulation techniques are expected to show the limitations of the simple analysis methods and impact the long term industry practices. In addition to benefiting the earthquake engineering community, the broader impacts of the proposed project include the integration of the proposed research into education at K-12 and undergraduate and graduate levels using the knowledge gained from innovative curriculum projects currently underway or already implemented. The proposed education plan includes a seismic design project that spans multiple courses for undergraduate and graduate students, a web-based simulation competition for high school students, and an adventure scenario based learning module for middle and elementary school students. Data from this project will be made available through the NEES data repository (http://www.nees.org).
Characterization of Dynamic Soil-Pile Interaction by Random Vibration Methods
Principal Investigator: Jeramy Ashlock (Iowa State University)
This Payload project will be led by Iowa State University (ISU) and will utilize NEES equipment from the University of California, Los Angeles and the experimental field-test setup from the NEESR-SG project entitled "Understanding and Improving the Seismic Behavior of Pile Foundations in Soft Clays" (Award #0830328). The overall goal of the project is to contribute to improved experimental and computational tools to bridge the gap between theory and observation for soil-foundation systems under realistic multi-directional loading. Despite many years of significant advances in theoretical and experimental research, significant discrepancies remain between experimental measurements and theoretical predictions of general three-dimensional dynamic pile-soil interaction. These discrepancies may be partially attributed to a host of contributing factors such as complicated soil-pile contact conditions, difficulties in performing full-scale dynamic tests, and the statistical variation of the engineering properties of soils coupled with the challenge of their in-situ measurement. Such shortcomings in current prediction capabilities can lead to unsafe under-design or costly over-design.
The focus of this Payload project is to expand the existing NEES technologies and testing capabilities for characterizing dynamic soil-pile interaction, and to improve the accuracy of current analytical and computational simulation tools. Field vibration tests will be performed on piles installed in improved and unimproved soft clays to gain a fundamental understanding of the seismic response of piles in these soil conditions. Specific goals of the project are to; (1) evaluate the effectiveness of using a servo-hydraulic inertial mass shaker and broadband random excitation for characterizing the dynamic behavior of piles in improved and unimproved clays, (2) improve the efficiency of current testing techniques by combining the traditionally separate vertical and horizontal harmonic excitation cases into a single multi-modal random-vibration test with synchronous vertical and coupled horizontal-rocking motions, (3) investigate the use of an experimental technique involving chaotic impulse loading which has shown great success in scaled-model centrifuge tests, (4) compare the relative effectiveness of using sinusoidal, random and chaotic impulse excitation types for characterizing the elastodynamic response of the soil, (5) evaluate the predictive capabilities of current analytical and computational techniques against the measured responses of piles in improved and unimproved clays and develop corrections if necessary, and (6) investigate whether experimental behavior observed in recent centrifuge studies of piles in sands extends to piles in clays.
This project will generate a number of practical experimental methods and a substantive database towards a more complete understanding of the fundamental behavior of dynamic soil-pile interaction. Specific tools to be developed include an innovative method for dynamic in-situ characterization of soil-pile interaction using non-destructive random vibration techniques, improved computational simulation tools to incorporate effects of pile installation and stress-dependence on the soil's shear modulus and damping, and modifications to current engineering theories which can be immediately applied in practice. In the long term, lessons learned in this project will be extended to understanding the dynamic behavior of a greater range of soil conditions as well as pile groups. The experimental and computational simulation techniques generated by this research will improve our understanding of fundamental soil-foundation-structure interaction, enabling more accurate models for foundation design and leading to improvements in earthquake hazard mitigation.
This project will involve the NEES community through teleparticipation, and a web site will be created with sections tailored for disseminating the research results to K-12 students, the general public, and the earthquake engineering community. Preliminary dynamic field-tests of a pile will be incorporated into a graduate course in soil dynamics at ISU, where students will have the option of analyzing the data for credit in a term project. Data from this project will be archived and made available to the public through the NEES data repository.
Field Testing of a Non-ductile Reinforced Concrete Building in Turkey
Principal Investigator: Ertugrul Taciroglu (UCLA)
This project brings together the technical expertise and advanced testing capabilities of a group of researchers from U.S.A. and Turkey to provide unique data on behavior and performance of older reinforced concrete buildings. This type of construction comprises the majority of residential, public service (i.e., schools, hospitals), and commercial buildings in the industrial heartland of Turkey; and there are a significant number of similarly vulnerable buildings within more active seismic regions in the USA (e.g., California, Washington, Utah, South Carolina, etc). In California, the vulnerable buildings are typically pre-1973 vintage. Therefore, the collaborative study will bring benefits to both countries. The project comprises the forced vibration and destructive testing of a full-scale building that exist in Turkey. Turkish partners will provide part of the testing equipment and the specimen structure; U.S. researchers will participate by providing technical expertise, personnel, and equipment for forced vibration testing. The project will leverage the technical resources of the George E. Brown, Jr. Network for Earthquake Engineering Simulation (NEES) equipment site at UCLA (nees@UCLA), Kandilli Observatory & Earthquake Research Institute (KOERI), and Bogazici University (BU).
Full-Scale Structural and Nonstructural Building System Performance During Earthquakes
Principal Investigator: Tara Hutchinson (UC San Diego)
This project includes the University of California, San Diego (lead institution), San Diego State University (subaward), and Howard University (subaward). It will utilize the NEES equipment sites at the University of California, San Diego (UCSD) and the University of California, Los Angeles (UCLA). Additional core project team members include industry members leading code development activities and researchers at Worcester Polytechnic Institute.
Intellectual Merit: Nonstructural components and systems (NCS) are those elements within a building that do not contribute to the building's load bearing system. NCSs are generally categorized as being either an architectural, mechanical, plumbing, or content item or system of items. Since the 19th century, NCSs have demonstrated their potential to create a dangerous environment for building occupants during earthquake shaking. Since these elements generally represent more than 80% of the total investment of a building, even minor damage can translate to significant financial losses. In fact, over the past three decades, the majority of earthquake-induced direct losses in buildings are directly attributed to NCS damage. Of the handful of full-scale building experiments conducted in the United States, none have specifically focused on evaluating the response of nonstructural component and systems (NCSs) during earthquake shaking. This project involves a landmark test of a full-scale, five-story building completely furnished with NCSs, including a functioning passenger elevator, partition walls, cladding and glazing systems, piping, HVAC, ceiling, sprinklers, and other building contents, as well as passive and active fire systems. The NEES-UCSD and NEES-UCLA equipment combine to realize this unique opportunity and hence advance understanding of the full-scale dynamic response and kinematic interaction of complex structural and nonstructural components and systems. While most NCSs in these experiments will be designed to the latest state of the art building code seismic provisions, non-seismic detailed designs widely used in low-seismic regions of the United States will also be included. Furthermore, this research will investigate the potential for protecting critical NCS systems using, for example, damping and/or isolation methods. Data from these unique experiments will be used to compare earthquake performance predictions determined using available commercial and research computational modeling platforms. Research at the system level that incorporates the structure and the NCSs and addresses issues such as detrimental kinematic and dynamic interaction between systems components is lacking. This research will enable, for the first time, tests of complex systems, which look closely at multidisciplinary issues, using facilities that are fully equipped to investigate, in a controlled environment, the effects of earthquakes on building-NCS system performance.i
Broader Impacts: Outcomes from this research will have broad and immediate impacts on the performance-based design of NCSs, including NCS fire protection systems. This research will support doctoral students in the earthquake engineering area and master students in construction management and protective systems areas. The project has developed unique partnerships to attract a diverse student group to earthquake engineering via educational activities that engage faculty and students from Howard University, as well as high school students from the Construction Tech Academy (an engineering and construction magnet program in San Diego). Data from this research will be archived and made available to the public through the NEES data repository.