Network For Earthquake Engineering Simulation Research Articles

Uncertainty analysis of system identification results obtained for a seven-story building slice tested on the UCSD-NEES shake table

A full-scale seven-story reinforced concrete building section/slice was tested on the Network for Earthquake Engineering Simulation (NEES) shake table at the University of California San Diego during the period of October 2005 to January 2006. Three output-only system identification methods were used to extract the modal parameters (natural frequencies, damping ratios, and mode shapes) of the test structure at different damage states. In this study, the performance of these system identification methods is investigated in two cases: (Case I) when these methods are applied to the measured dynamic response of the structure and (Case II) when these methods are applied to the dynamic response of the structure simulated using a three-dimensional nonlinear finite element model thereof. In both cases, the uncertainty/variability of the identified modal parameters due to the variability of several input factors is quantified through analysis of variance (ANOVA). In addition to ANOVA, meta-models are used for effect screening in Case II (based on the simulated data), which also capture the effects of linear interactions of the input factors. The four input factors considered in Case I are amplitude of input excitation, spatial density of measurements, length of response data used for system identification, and model order used in the parametric system identification methods. In the second case of uncertainty analysis, in addition to these four input factors, measurement noise is also considered. The results show that for all three methods considered, the amplitude of excitation is the most significant factor explaining the variability of the identified modal parameters, especially the natural frequencies. Copyright © 2013 John Wiley & Sons, Ltd.

Supporting Shared Resource Usage for a Diverse User Community: the OSG Experience and Lessons Learned

The Open Science Grid (OSG) supports a diverse community of new and existing users in adopting and making effective use of the Distributed High Throughput Computing (DHTC) model. The LHC user community has deep local support within the experiments. For other smaller communities and individual users the OSG provides consulting and technical services through the User Support area. We describe these sometimes successful and sometimes not so successful experiences and analyze lessons learned that are helping us improve our services. The services offered include forums to enable shared learning and mutual support, tutorials and documentation for new technology, and troubleshooting of problematic or systemic failure modes. For new communities and users, we bootstrap their use of the distributed high throughput computing technologies and resources available on the OSG by following a phased approach. We first adapt the application and run a small production campaign on a subset of “friendly” sites. Only then do we move the user to run full production campaigns across the many remote sites on the OSG, adding to the community resources up to hundreds of thousands of CPU hours per day. This scaling up generates new challenges – like no determinism in the time to job completion, and diverse errors due to the heterogeneity of the configurations and environments – so some attention is needed to get good results. We cover recent experiences with image simulation for the Large Synoptic Survey Telescope (LSST), small-file large volume data movement for the Dark Energy Survey (DES), civil engineering simulation with the Network for Earthquake Engineering Simulation (NEES), and accelerator modeling with the Electron Ion Collider group at BNL. We will categorize and analyze the use cases and describe how our processes are evolving based on lessons learned.

Integrated Analytical and Experimental Research to Develop a New Seismic Design Methodology for Precast Concrete Diaphragms

AbstractA new seismic diaphragm design methodology has been developed for precast concrete floor diaphragms. The knowledge required to create the design methodology was obtained through an integrated analytical and experimental research project using two Network for Earthquake Engineering Simulation (NEES) equipment sites. The activities of the project involved a sequence of integrated research tasks that systematically developed knowledge about diaphragm behavior from the reinforcement detail level to the structural system level. These tasks included the use of state-of-the-art experimental techniques made possible through the NEES facilities including hybrid simulation and large-scale shake table tests. Such techniques were crucial to the research as the complex behavior of precast diaphragms is not well described by simple analytical models or idealized experiments. Valuable industry oversight in the planning, execution, and technology transfer stages of the project guided the research activities, incl...

Performance-Based Seismic Design of Midrise Woodframe Buildings

The understanding of, and ability to predict, the seismic behavior of woodframe structures has improved immensely in the last 10 years. Two notable projects occurred in succession, the Consortium of Universities for Research in Earthquake Engineering (CUREE) and California Institute of Technology (Caltech) CUREE-Caltech Woodframe Project, and the Network for Earthquake Engineering Simulation (NEES) NEESWood Project, which provided greater understanding, improved analytical modeling, and advances in force- and performance-based seismic design (PBSD) of woodframe buildings, respectively. The NEESWood project focused on the development of a PBSD philosophy (and procedures) for midrise woodframe buildings and included full-scale system-level validation. To date, the complete design procedure has not been systematically explained, which serves as the impetus for this paper. While the method was shown to be quite viable, some challenges remain, including identifying a format that would facilitate widespread adoption and use by engineers. Thus, this paper examines the progress, current state, and challenges for PBSD of midrise woodframe buildings.

A fully dynamic magneto-rheological fluid damper model

Control devices can be used to dissipate the energy of a civil structure subjected to dynamic loading, thus reducing structural damage and preventing failure. Semiactive control devices have received significant attention in recent years. The magneto-rheological (MR) fluid damper is a promising type of semiactive device for civil structures due to its mechanical simplicity, inherent stability, high dynamic range, large temperature operating range, robust performance, and low power requirements. The MR damper is intrinsically nonlinear and rate-dependent, both as a function of the displacement across the MR damper and the command current being supplied to the MR damper. As such, to develop control algorithms that take maximum advantage of the unique features of the MR damper, accurate models must be developed to describe its behavior for both displacement and current. In this paper, a new MR damper model that includes a model of the pulse-width modulated (PWM) power amplifier providing current to the damper, a proposed model of the time varying inductance of the large-scale 200 kN MR dampers coils and surrounding MR fluid—a dynamic behavior that is not typically modeled—and a hyperbolic tangent model of the controllable force behavior of the MR damper is presented. Validation experimental tests are conducted with two 200 kN large-scale MR dampers located at the Smart Structures Technology Laboratory (SSTL) at the University of Illinois at Urbana-Champaign and the Lehigh University Network for Earthquake Engineering Simulation (NEES) facility. Comparison with experimental test results for both prescribed motion and current and real-time hybrid simulation of semiactive control of the MR damper shows that the proposed MR damper model can accurately predict the fully dynamic behavior of the large-scale 200 kN MR damper.

Corotational Model for Cyclic Analysis of Light-Frame Wood Shear Walls and Diaphragms

AbstractThis paper presents a new two-dimensional shear-wall and diaphragm model developed as part of a Network for Earthquake Engineering Simulation (NEES) Project entitled NEES-Soft: Seismic Risk Reduction for Soft-Story Woodframe Buildings. A large portion of the older multistory buildings in the California region were constructed with a deficiency that makes them vulnerable to collapse in the first story during earthquakes. This deficiency is referred to as soft-story. The new model presented in this paper was developed using a corotational formulation, which makes it suitable for modeling the side-sway collapse of wood shear walls under large displacement as well as estimating the in-plane stiffness of floor diaphragms. To achieve high computational efficiency, a nodal condensation technique is used to eliminate the degrees of freedom (DOFs) associated with the nail connections from the global DOFs of the model. To verify the validity of the new model, the model was coded into a computer program and ...

The NEEShub Cyberinfrastructure for Earthquake Engineering

The US Network for Earthquake Engineering Simulation (NEES) operates a shared network of civil engineering experimental facilities aimed at facilitating research on mitigating earthquake damage and loss of life. The NEEShub gateway was created in response to the NEES community's needs, combining data, simulation, and analysis functionality with collaboration tools.

System Identification Study of a 7-Story Full-Scale Building Slice Tested on the UCSD-NEES Shake Table

A full-scale 7-story reinforced concrete building slice was tested on the unidirectional University of California–San Diego Network for Earthquake Engineering Simulation (UCSD-NEES) shake table during the period from October 2005 to January 2006. A rectangular wall acted as the main lateral force resisting system of the building slice. The shake table tests were designed to damage the building progressively through four historical earthquake records. The objective of the seismic tests was to validate a new displacement-based design methodology for reinforced concrete shear wall building structures. At several levels of damage, ambient vibration tests and low-amplitude white noise base excitation tests were applied to the building, which responded as a quasi-linear system with dynamic parameters evolving as a function of structural damage. Six different state-of-the-art system identification algorithms, including three output-only and three input-output methods were used to estimate the modal parameters (natural frequencies, damping ratios, and mode shapes) at different damage levels based on the response of the building to ambient as well as white noise base excitations, measured using DC-coupled accelerometers. The modal parameters estimated at various damage levels using different system identification methods are compared to (1) validate/cross-check the modal identification results and study the performance of each of these system identification methods, and to (2) investigate the sensitivity of the identified modal parameters to actual structural damage. For a given damage level, the modal parameters identified using different methods are found to be in good agreement, indicating that these estimated modal parameters are likely to be close to the actual modal parameters of the building specimen.

Reusing Scientific Data: How Earthquake Engineering Researchers Assess the Reusability of Colleagues’ Data

Investments in cyberinfrastructure and e-Science initiatives are motivated by the desire to accelerate scientific discovery. Always viewed as a foundation of science, data sharing is appropriately seen as critical to the success of such initiatives, but new technologies supporting increasingly data-intensive and collaborative science raise significant challenges and opportunities. Overcoming the technical and social challenges to broader data sharing is a common and important research objective, but increasing the supply and accessibility of scientific data is no guarantee data will be applied by scientists. Before reusing data created by others, scientists need to assess the data's relevance, they seek confidence the data can be understood, and they must trust the data. Using interview data from earthquake engineering researchers affiliated with the George E. Brown, Jr. Network for Earthquake Engineering Simulation (NEES), we examine how these scientists assess the reusability of colleagues' experimental data for model validation.

Simplified Direct Displacement Design of Six-Story Woodframe Building and Pretest Seismic Performance Assessment

This paper presents a simplified direct displacement design (DDD) procedure which was used to design the shear walls for a six-story woodframe structure. The building was tested in the final phase of a Network for Earthquake Engineering Simulation (NEES) project. Specifically, NEESWood Capstone Building was designed to meet four performance expectations: damage limitation, life safety, far-field collapse prevention (CP), and near-fault CP. The performance expectations are defined in terms of combinations of interstory drift limits and prescribed seismic hazard levels associated with predefined nonexceedance probabilities. To verify that design requirements were met, a series of nonlinear time-history analyses (NLTHAs) was performed using suits of both far-field and near-fault ground motion records. The distributions of interstory drifts obtained from the NLTHA confirm that the Capstone Building designed using DDD meets all four target performance expectations, thereby validating the DDD procedure. Additionally, collapse analysis in accordance with the recently proposed Applied Technology Council project 63 (ATC-63) methodology was performed. The results of incremental dynamic analyses confirmed that the Capstone Building designed using the DDD procedure has adequate capacity margin against collapse, as dictated by the ATC-63 methodology.

Nonlinear Earthquake Response Modeling of a Large-Scale Two-Span Concrete Bridge

A quarter scale model of a two-span RC bridge was tested using the Network for Earthquake Engineering Simulation (NEES) multiple shake table system at the University of Nevada, Reno, Nev. The project was funded through a National Science Foundation-NEES demonstration grant. The bridge system was tested from a preyield state until column failure. In depth analytical modeling was conducted to determine the effectiveness of current structural analysis software and methodology in predicting the bridge model response. Both SAP2000 v.9 and Drain-3DX were used for this purpose. Both models produced reasonable results up to column failure, however, the Drain-3DX model was determined to be most effective to predict the nonlinear bridge model response. Parametric studies were conducted to investigate optimal element discretization and integration parameters. Existing equations for pre and postyield column shear stiffness showed good correlation when compared with the measured data.

Comparative Study of Refraction Microtremor (ReMi) and Active Source Methods for Developing Low-Frequency Surface Wave Dispersion Curves

Obtaining high-quality dispersion curves is a critical step in the development of reliable shear wave velocity profiles from surface wave measurements. Because of its limited equipment and space requirements, the refraction microtremor (ReMi) method has become a popular approach for determining surface wave dispersion curves, and is increasingly being used for estimating low-frequency (long wavelength) surface wave velocities that are beyond the range of most active sources. The recent development of a low-frequency field vibrator as part of the Network for Earthquake Engineering Simulation (NEES) program has made it possible to actively generate surface wave energy down to frequencies of less than 1 Hz. This paper presents a comparative study of the ReMi method and the active-source frequency-wavenumber [Formula: see text] method (using the NEES vibrator) for developing low-frequency dispersion curves. Linear arrays of 1-Hz seismometers were deployed at eight deep soil sites in the Mississippi Embayment. Using both ambient and active energy, surface wave dispersion curves were determined to wavelengths of 600 m. The dispersion data from the two methods were in good agreement (within about ±5%) to wavelengths of 100 to 150 m (3 to 4 Hz) at most sites. However, at longer wavelengths the dispersion estimates from the ReMi approach deviated significantly from the active source measurements. The validity of the [Formula: see text] dispersion curve was supported by dispersion data obtained using the SASW method, as well as ambient vibration measurements performed using a circular array at four of the sites. Analyses of ambient vibrations recorded using circular arrays show that the poor performance of the ReMi method at long wavelengths is not because of a lack of ambient surface wave energy at low frequencies, but can be attributed to invalid assumptions about the nature of the ambient wavefield.

Tsunami bore forces on a compliant residential building model

The forces exerted on light-frame wood buildings as a result of surge and waves are not fully understood. With a better understanding of these types of forces, it may eventually be possible to build coastal structures to better withstand the loads. In this paper, a recent two part experimental study that focused on determining the forces induced in a structurally compliant model of a typical Gulf Coast residential building is summarized. The one-sixth scale building was designed to approximately behave as the full scale building would under wave loading using rules of energy-based similitude. The compliant model was subjected to solitary wave loading in the Network for Earthquake Engineering Simulation (NEES) tsunami wave basin (TWB) at Oregon State University with wave heights ranging from 0.1 m to 0.6 m. Then, at Colorado State University, lateral force–deformation tests on a nominally identical model were performed in order to determine the force–deformation relationship for the building. The structural deformation produced by solitary waves in the wave basin was combined with the experimentally measured deformation in the structural laboratory to determine the force induced by the waves between 0.2m and 0.6 m. Finally, a simplified force equation constant similar to the existing design code formats was found to be 0.31.

Performance of Active and Passive Methods for Measuring Low-Frequency Surface Wave Dispersion Curves

This paper examines the consistency between surface wave dispersion curves measured at wavelengths of up to 600 m using active and passive methods at sites in the Mississippi Embayment. Large-diameter (200 m) circular receiver arrays were deployed at five deep soil sites located in Tennessee, Arkansas, and Missouri to record ambient ground vibrations at low frequencies. Measurements were performed at the same locations using linear receiver arrays and actively generated low-frequency energy using the recently developed Network for Earthquake Engineering Simulation (NEES) field vibrator (termed Liquidator). Characteristics of the ambient wavefield measured at the five sites in the Mississippi Embayment are presented along with comparisons between the surface wave dispersion curves obtained from the active and passive measurements at each site. The ambient wavefield measurements exhibited peak levels in the frequency range of 1–5 Hz. Surface wave dispersion curves developed from frequency-wavenumber (f-k) processing of the active and passive methods were in good agreement at four of the sites, with phase velocities from the passive measurements within 5–10 % of the active-source measurements out to wavelengths of about 550 m. Improved comparisons were obtained at the fifth site by applying high-resolution f-k processing.

Induced Dynamic Nonlinear Ground Response at Garner Valley, California

We present results from a prototype experiment in which we actively induce, observe, and quantify in situ nonlinear sediment response in the near surface. This experiment was part of a suite of experiments conducted during August 2004 in Garner Valley, California, using a large mobile shaker truck from the Network for Earthquake Engineering Simulation (NEES) facility. We deployed a dense accel- erometer array within meters of the mobile shaker truck to replicate a controlled, laboratory-style soil dynamics experiment in order to observe wave-amplitude- dependent sediment properties. Ground motion exceeding 1g acceleration was pro- duced near the shaker truck. Thewave field was dominated by Rayleigh surface waves and ground motions were strong enough to produce observable nonlinear changes in wave velocity. We found that as the force load of the shaker increased, the Rayleigh- wave phase velocity decreased by as much as ∼30% at the highest frequencies used (up to 30 Hz). Phase velocity dispersion curves were inverted for S-wave velocity as a function of depth using a simple isotropic elastic model to estimate the depth depen- dence of changes to the velocity structure. The greatest change in velocity occurred nearest the surface, within the upper 4 m. These estimated S-wave velocity values were used with estimates of surface strain to compare with laboratory-based shear modulus reduction measurements from the same site. Our results suggest that it may be possible to characterize nonlinear soil properties in situ using a noninvasive field technique.

Large-Scale Experimental Verification of Semiactive Control through Real-Time Hybrid Simulation

Magneto-rheological (MR) fluid dampers have been identified as a particularly promising type of semiactive control device for hazard mitigation in civil engineering structures. Large-scale experimental testing is important to verify the performance of MR fluid dampers for seismic protection of civil structures. Real-time hybrid testing, where only the critical components of the system are physically tested while the rest of the structure is simulated, can provide a cost-effective means for large-scale testing of semiactive controlled structures. This paper describes the real-time hybrid simulation experimental setup for multiple large-scale MR fluid dampers and demonstrates the capability at the University of Colorado at Boulder shared-use Fast Hybrid Test facility to conduct real-time hybrid testing within the Network for Earthquake Engineering Simulation.

Seismic Testing of a Two-Span Reinforced Concrete Bridge

A quarter-scale, two-span reinforced concrete bridge was tested using the shake-table system at the University of Nevada, Reno. The shake-table tests were part of a multiuniversity, multidisciplinary project utilizing the network for earthquake engineering simulation, with the objective of investigating the effects of soil-foundation-structure interaction on bridges. This paper discusses the development and testing of the bridge model, and selected experimental results, including those that demonstrate the effects of incoherent motions and stiffness irregularities on the distribution of forces and deformations within the bridge system. Motion incoherency affected the asymmetric bridge response (planar torsion of the superstructure), but had little effect on the symmetric bridge response (center-of-mass displacement of the superstructure). These experimental findings are consistent with conclusions from numerical analyses conducted by other researchers. During a 2.0g PGA earthquake excitation, numerous longitudinal bars buckled and fractured at a drift ratio between 5.5 and 7.9%. Despite the level of damage, detailing of the column transverse reinforcement according to NCHRP 12-49 guidelines provided sufficient column ductility to prevent collapse during a subsequent 1.4g PGA earthquake excitation.

Computational framework for remotely operable laboratories

Decision-makers envision a significant role for remotely operable laboratories in advancing research in structural engineering, as seen from the tremendous support for the network for earthquake engineering simulation (NEES) framework. This paper proposes a computational framework that uses LabVIEW and web technologies to enable observation and control of laboratory experiments via the internet. The framework, which is illustrated for a shaketable experiment, consists of two key hardware components: (1) a local network that has an NI-PXI with hardware for measurement acquisition and shaketable control along with a Windows-based PC that acquires images from a high-speed camera for video, and (2) a proxy server that controls access to the local network. The software for shaketable control and data/video acquisition are developed in the form of virtual instruments (VI) using LabVIEW development system. The proxy server employs a user-based authentication protocol to provide security to the experiment. The user can run perl-based CGI scripts on the proxy server for scheduling to control or observe the experiment in a future timeslot as well as gain access to control or observe the experiment during that timeslot. The proxy server implements single-controller multiple-observer architecture so that many users can simultaneously observe and download measurements as a single controller decides the waveform input into the shaketable. A provision is also created for users to simultaneously view the real-time video of the experiment. Two different methods to communicate the video are studied. It is concluded that a JPEG compression of the images acquired from the camera offers the best performance over a wide range of networks. The framework is accessible by a remote user with a computer that has access to a high-speed internet connection and has the LabVIEW runtime engine that is available at no cost to the user. Care is taken to ensure that the implementation of the LabVIEW applications and the perl scripts have little dependency for ease of portability to other experiments.

Data Model for Large-Scale Structural Experiments

Large-scale laboratory experiments are carried out to evaluate and improve the performance of structural members, connections, and assemblies. The information related to these large-scale structural laboratory experiments, such as pseudo-dynamic tests and hybrid pseudo-dynamic tests, is often complicated and stored in various documents, drawings, photos, and other computer-based files. A data model is needed to organize this information and the related data from the structural experiments, so that this information and data can be accessed, shared, and used efficiently. This paper describes a data model for large-scale structural laboratory experiments developed at the Real-Time Multi-Directional (RTMD) testing facility at the ATLSS Center at Lehigh University. The RTMD facility is an equipment site within the George E. Brown, Jr. Network for Earthquake Engineering Simulation (NEES). The data model is called the Lehigh Model. For typical structural experiments, the Lehigh Model has a class hierarchy consisting of the project, experimental task, test condition, and test classes to organize and represent information about structural laboratory experiments. For hybrid pseudo-dynamic tests, the model also has the hybrid experimental task class and related classes to represent the communications among the simulation coordinator at a site, the analytical substructures at one or more sites, and the physical substructures at one or more sites. The test condition class provides more detailed information on the setup of a structural experiment including the geometries, materials, and locations of the components of the specimen. An application of the classes of the Lehigh Model is presented using steel moment connection tests as an example.

Integration of the NEES T-Rex Vibrator and PASSCAL Texan Recorders for Seismic Profiling of Shallow and Deep Crustal Targets

In September 2004, Stanford University and the University of Texas (UT) at Austin collected crustal reflection and refraction data with the Network for Earthquake Engineering Simulation (NEES) tri-axial (T-Rex) vibrator in two separate surveys: (1) a 40-km “crustal-scale” profile in the Black Rock Desert and Black Rock Range, NV; and (2) a 16-km “high-resolution” basin imaging profile in Surprise Valley, CA (figure 1). Both experiments were completed at the northwestern margin of the Basin and Range Province, embedded in a larger, 300-km wide-angle refraction line recorded by an Incorporated Research Institutions for Seismology (IRIS) PASSCAL transportable array (Lerch et al. 2007). Our broad goals were to test the feasibility of the T-Rex in crustal-scale applications with existing IRIS-PASSCAL equipment and to augment our refraction data with structural information. T-Rex (figure 1, inset A), acquired by NEES-UT Austin in 2002, is a 29,000-kg buggy-mounted vibrator with a tri-axial mass, capable of generating P , SV , and SH waves (for details on T-Rex, see Stokoe et al. 2004). Given its relatively large mass, and hence its high peak force output of 267 kN for frequencies between 12 and 180 Hz, T-Rex is a potentially viable source for single-vibrator crustal profiling compared to COCORP (Consortium for Continental Reflection Profiling) profiling with five vibrators, each producing ≤ 120 kN (Allmendinger et al. 1987). Additionally, T-Rex's ability to produce shear waves may open the door to a variety of exciting research avenues, from Vs velocity modeling of basin sediments for earthquake hazard analysis to the ability to record mid- and lower-crustal shear-wave anisotropy resulting from regional tectonic deformation. The integration of T-Rex into our crustal-scale and high-res profiles revealed its strengths and limitations as well as the logistic and quality-control problems associated with recording continuous vibrator data with PASSCAL's transportable instrumentation. Our attempts …