Network For Earthquake Engineering Simulation Research Articles

NHERI@UC San Diego 6-DOF Large High-Performance Outdoor Shake Table Facility

Since its commissioning in 2004, the UC San Diego Large High-Performance Outdoor Shake Table (LHPOST) has enabled the seismic testing of large structural, geostructural and soil-foundation-structural systems, with its ability to accurately reproduce far- and near-field ground motions. Thirty-four (34) landmark projects were conducted on the LHPOST as a national shared-use equipment facility part of the National Science Foundation (NSF) Network for Earthquake Engineering Simulation (NEES) and currently Natural Hazards Engineering Research Infrastructure (NHERI) programs, and an ISO/IEC Standard 17025:2005 accredited facility. The tallest structures ever tested on a shake table were conducted on the LHPOST, free from height restrictions. Experiments using the LHPOST generate essential knowledge that has greatly advanced seismic design practice and response predictive capabilities for structural, geostructural, and non-structural systems, leading to improved earthquake safety in the community overall. Indeed, the ability to test full-size structures has made it possible to physically validate the seismic performance of various systems that previously could only be studied at reduced scale or with computer models. However, the LHPOST's limitation of 1-DOF (uni-directional) input motion prevented the investigation of important aspects of the seismic response of 3-D structural systems. The LHPOST was originally conceived as a six degrees-of-freedom (6-DOF) shake table but built as a single degree-of-freedom (1-DOF) system due to budget limitations. The LHPOST is currently being upgraded to 6-DOF capabilities. The 6-DOF upgraded LHPOST (LHPOST6) will create a unique, large-scale, high-performance, experimental research facility that will enable research for the advancement of the science, technology, and practice in earthquake engineering. Testing of infrastructure at large scale under realistic multi-DOF seismic excitation is essential to fully understand the seismic response behavior of civil infrastructure systems. The upgraded 6-DOF capabilities will enable the development, calibration, and validation of predictive high-fidelity mathematical/computational models, and verifying effective methods for earthquake disaster mitigation and prevention. Research conducted using the LHPOST6 will improve design codes and construction standards and develop accurate decision-making tools necessary to build and maintain sustainable and disaster-resilient communities. Moreover, it will support the advancement of new and innovative materials, manufacturing methods, detailing, earthquake protective systems, seismic retrofit methods, and construction methods. This paper will provide a brief overview of the 1-DOF LHPOST and the impact of some past landmark projects. It will also describe the upgrade to 6-DOF and the new seismic research and testing that the LHPOST6 facility will enable.

Incremental dynamic analysis and FEMA P695 seismic performance evaluation of a cold‐formed steel–framed building with gravity framing and architectural sheathing

SummaryThe objective of this paper is to present incremental dynamic analysis (IDA) and seismic performance evaluation results for a two‐story cold‐formed steel (CFS)–framed building. The archetype building was designed to current U.S. standards and then subjected to full‐scale shake table tests under the U.S. National Science Foundation Network for Earthquake Engineering Simulation (NEES) program. Test results showed that the building's stiffness and capacity were considerably higher than expected and the building suffered only nonstructural damage even at excitations in excess of Maximum Considered Earthquake levels for a high seismic zone. For the archetype building, three‐dimensional finite element models at different modeling fidelity levels were created using OpenSees. The models are subjected to IDA using the far‐field ground motion records prescribed in Federal Emergency Management Agency (FEMA) P695. Seismic performance quantification following the FEMA P695 procedure shows that if the modeling fidelity only follows the state‐of‐the‐practice, ie, only includes shear walls, unsafe collapse margin ratios are predicted. State‐of‐the‐art models that account for participation from CFS gravity walls and architectural sheathing have overall performance that are consistent with testing, and IDA results indicate acceptable collapse margin ratios, predicated primarily on large system overstrength. Neglecting the lateral force resistance of the gravity system and nonstructural components, as done in current design, renders a safe design in the studied archetype, but largely divorced from actual system behavior. The modeling protocols established here provide a means to analyze a future suite of CFS‐framed archetype buildings for developing further insight on the seismic response modification coefficients for CFS‐framed buildings.

Seismic performance of helical piles in dry sand from large-scale shaking table tests

Recent earthquakes have highlighted the need for safe and efficient construction of earthquake-resilient structures. Meanwhile, helical piles are gaining popularity as a foundation not only for new construction, but also retrofitted structures, owing to their advantages over conventional driven pile alternatives. In addition, several structures supported by helical piles in New Zealand sustained minimal damage during the Christchurch earthquake, proving that helical piles can be a suitable foundation option in highly seismic areas. However, there is a knowledge gap concerning their seismic performance. Therefore, the current study investigates the performance of helical piles through a full-scale shaking table test programme – the inaugural large-scale seismic testing programme performed on helical piles. The experimental set-up involved installing ten steel piles with different configurations and pile head masses in dry sand enclosed in a laminar shear box mounted on the Network for Earthquake Engineering Simulation at University of California, San Diego (NEES/UCSD) large high-performance outdoor shaking table (LHPOST). The loading scheme consisted of white noise and two earthquake time histories with varying intensity and frequency content. The experimental results are presented in terms of the natural frequency and response of test piles (peak deflections). The effects of loading frequency and intensity and the pile's geometrical configuration and installation method were evaluated.

Multidimensional Fragility Analysis for a NEES Frame Structure by Integrating a New Energy Damage Index: Cumulative Plastic Strain

Cumulative plastic strain (CPS) damage index is proposed in this study for seismic fragility analysis by integrating the force analogy method into the energy balance equation, and CPS can be defined as the ratio of the demand of plastic dissipation energy to its capacity. The cumulative plastic strain can indicate the structural damage cumulative effect under earthquakes, which makes it especially suitable to be selected as the damage index for the structural component. Threshold values of cumulative plastic strain for different performance limit state (PLS) levels are obtained through the degree of consistency of interstory drift-based fragility curves and CPS-based fragility curves. Regarding the multidimensional fragility evaluation, CPS and the floor acceleration will be selected as the quantification indices for performance limit state of the structural component and nonstructural component, respectively. The probabilistic seismic demand model (PSDM) following multivariate logarithmic normal distribution will be developed, and taking PLS uncertainty and correlation into consideration, multidimensional PLS function is constructed to identify the structural failure domain. A full-scale 2-bay 2-story frame structure for the Network for Earthquake Engineering Simulation (NEES) project is employed as the case study structure to demonstrate the proposed theory. Nonlinear dynamic time-history analysis is carried out for the structure to obtain its maximum responses under earthquakes. Consequently, the multidimensional fragility curves can be derived on the basis of CPS. Besides, the influence of PLS threshold value, engineering demand parameter (EDP) correlation, and PLS correlation on the multidimensional fragility is investigated. Results show that (1) CPS damage index can fully consider the cumulative effect of damage under earthquakes, which makes up for the deficiency of the interstory drift damage index in this aspect, (2) the multidimensional fragility framework can deal with the PLS correlation and EDP correlation simultaneously, which will generate a more precise seismic damage assessment result, and (3) multidimensional fragility is sensitive to PLS threshold values and PLS correlation parameters.

Pretest Nonlinear Finite-Element Modeling and Response Simulation of a Full-Scale 5-Story Reinforced Concrete Building Tested on the NEES-UCSD Shake Table

A full-scale five-story reinforced concrete building specimen, outfitted with a variety of nonstructural components and systems (NCSs), was built and tested on the Network for Earthquake Engineering Simulation at the University of California, San Diego (NEES–UCSD) large outdoor shake table in the period March 2011–June 2012. The building specimen was subjected to a sequence of dynamic tests including scaled and unscaled earthquake motions. A detailed three-dimensional nonlinear finite-element (FE) model of the structure was developed and used for pretest response simulations to predict the seismic response of the test specimen and for decision support in defining the seismic test protocol and selecting the instrumentation layout for both the structure and NCSs. This paper introduces the building specimen and the shake table test protocol and describes the techniques used for the nonlinear FE modeling and response simulation. Utilized as blind prediction, the pretest simulation results at different scales (global structural level and local member/section/fiber levels) are compared with their experimental counterparts for seismic input (base excitation) of increasing intensity from serviceability to design levels. The predictive capabilities of the used FE modeling techniques are evaluated and possible sources of discrepancies between the FE predictions and experimental measurements are investigated and discussed.

Development of a Risk Framework for Forecasting Earthquake Losses in Port Systems

Ports play a critical role in transportation infrastructure but are vulnerable to seismic hazards. Downtime and reduced throughput from seismic damage in ports results in significant business interruption losses for port stakeholders. Managing risks from systemwide disruptions resulting from earthquake damage has been studied as a central element of a project sponsored by the National Science Foundation Network for Earthquake Engineering Simulation (NEES) program. Presented are the concepts and methods developed for the seismic risk management of a portwide system of berths. The framework used to calculate port losses is discussed, particularly the use of spatially correlated ground motion intensity measures that estimate damage to pile-supported wharves and container cranes, the repair costs and downtimes subsequently determined via repair models for both types of structures, and the impact on cargo handling operations calculated via logistical models of the port system. Results, expressed in the form of loss exceedance curves, are calculated.

Shaking Table Performance of a New Bridge System with Pretensioned Rocking Columns

AbstractA new bridge bent system has been developed to reduce on-site construction time, minimize residual displacements even after a large earthquake, and reduce seismic damage in comparison with conventional cast-in-place construction. Accelerated construction is achieved through the use of precast columns and cap beams that can be assembled quickly. Postearthquake residual displacements are reduced by pretensioning the columns with partially unbonded tendons. Damage in the columns is nearly eliminated by concentrating flexural deformations to specially detailed regions at the top and bottom of the columns. In this study, the seismic performance of the new system was evaluated with a multi-shaking table test of a quarter scale, two-span bridge at the Network for Earthquake Engineering Simulation (NEES) Earthquake Engineering Laboratory at the University of Nevada, Reno. The maximum displacements of the bents were similar to those expected for a conventional bridge through the 100% design-level event [pe...

Experimental Seismic Collapse Study of a Full-Scale, 4-Story, Soft-Story, Wood-Frame Building

AbstractIn the San Francisco Bay Area and throughout much of California, there are a large number of wood-frame buildings with garage space at ground level, resulting in open fronts on one or two sides. This type of geometry results in a soft and weak first story, and buildings of this archetype are generally referred to as soft-story buildings. During an earthquake, these buildings are susceptible to severe damage and collapse and have been recognized as a disaster-preparedness problem. The five-university Network for Earthquake Engineering Simulation (NEES)-Soft project culminated in a series of full-scale soft-story wood-frame building tests to validate two different retrofit philosophies and included a 2-month test program encompassing four different retrofits. The building had 370 m2 of living space and was designed to be generally representative of older San Francisco Marina and Mission District construction, circa 1950s. Following the retrofit testing, which only moderately damaged the test buildin...

A New Data Set for Full-Scale Reinforced Concrete Columns under Collapse-Consistent Loading Protocols

A series of eight full-scale reinforced concrete column tests was recently carried out at the NEES (Network for Earthquake Engineering Simulation) Multi-Axial Subassemblage Testing (MAST) site at the University of Minnesota as part of a National Science Foundation (NSF) NEES research program. The tests were conducted to address the shortcomings in the available database of reinforced concrete (RC) columns tested with large drift ratios under monotonic and cyclic loading protocols. The specimens were designed based on ACI 318-11 and featured two different cross-sectional dimensions, both larger than nearly all of the columns tested previously. They were subjected to several large displacement loading protocols, including a monotonic and a cyclic biaxial loading protocol. Also, to investigate the effectiveness of novel materials, one specimen was constructed with ultra-high-performance fiber-reinforced concrete (UHP-FRC). This paper presents a description of and potential uses for the data set that is made accessible via a digital object identifier (DOI) (data set DOIs: 10.4231/D33T9D65T, 10.4231/D3028PD2G, 10.4231/D3V97ZR8Z, 10.4231/D3QN5ZB62, 10.4231/D3KW57J3S, 10.4231/D3G44HQ9B, 10.4231/D3BC3SX4Q, and 10.4231/D36M3340C).

Data from the Network for Earthquake Engineering Simulation/E-Defense Collaborative Test Program on Innovative Isolation Systems and Nonstructural Components

The data sets generated from E-Defense shake table experiments of a full-scale, five-story building tested with two innovative isolation systems and in the fixed-base configuration are available in the Network for Earthquake Engineering Simulation (NEES) Project Warehouse. The experiments included an integrated subassemblage of partition walls, suspended ceilings, and sprinkler piping on the fourth and fifth floors of the building; a full-story precast concrete cladding column cover; and enclosed areas staged with building contents. Totaling approximately 211 GB between three experiments, the data set includes isolator forces and displacements, floor accelerations, and story drifts, local accelerations, and relative displacements at strategic locations on the nonstructural components, as well as extensive videos and inspection photos. The project was a collaboration between U.S. researchers of the NEES Tools for Isolation and Protective Systems (TIPS) and NEES Nonstructural Grand Challenge projects and Japanese researchers from the National Research Institute of Earth Science and Disaster Prevention. Data set DOIs are 10.4231/D3X34MR7R, 10.4231/D3SB3WZ43, and 10.4231/D3NP1WJ3P.

In SituAssessment of theG–γCurve for Characterizing the Nonlinear Response of Soil: Application to the Garner Valley Downhole Array and the Wildlife Liquefaction Array

Abstract We analyze the nonlinear and near‐surface geological effects of two Network for Earthquake Engineering Simulation at University of California, Santa Barbara (NEES@UCSB) instrumented sites: the Garner Valley Downhole Array (GVDA) and the Wildlife Liquefaction Array (WLA). The seismic interferometry by deconvolution method is applied to earthquake data recorded by the multisensor vertical array between January 2005 and September 2013. Along the cross section, local shear‐wave velocity is extracted by estimating travel time between sensors. The S ‐wave velocity profiles are constructed and compared with classical in situ geophysical surveys. We show that velocity values change according to the amplitude of the ground motion, and we find anisotropy between east–west and north–south directions at the GVDA site. The ratio between average peak particle velocity v * and local S ‐wave velocity between two boreholes is tested as a deformation proxy. Using average peak particle acceleration a * , the a * versus curve is used to represent the stress–strain curve for observing the site’s nonlinear responses under different levels of excitation. Nonlinearity is observed from quite low shear‐strain levels (∼1×10 −5 ) and a classic hyperbolic model is derived. proves to be a good deformation proxy. Finally, the shear modulus degradation curves are constructed for each depth and test site, and they are similar to previous laboratory measurements or in situ geophysical surveys. A simple comparison regarding nonlinear behavior between GVDA and WLA is performed.

Shake Table Test of Large-Scale Bridge Columns Supported on Rocking Shallow Foundations

AbstractThis paper presents the results of a series of shake table tests of two 460-mm-diameter columns supported on 1.5-meter-square shallow rocking foundations. The tests were conducted using the Large Outdoor High-Performance Shake Table of the Network for Earthquake Engineering Simulation at the University of California at San Diego. The first specimen was aligned with the uniaxial direction of shaking, and the second was positioned in a skew configuration. The specimens were placed inside a soil-confining box 10.1 m long and 4.6 m wide with a 3.4-m height of clean sand compacted at 90% relative density. Three series of tests were performed; each had different groundwater and backfill conditions. The test protocols included up to six historical ground motions and resulted in peak drift ratios up to 13.8%. For peak drift ratios up to 6.9%, the rocking foundations performed very well, with residual drift ratios between 0.5 and 0.9% depending on the backfill conditions and with minimal settlements and no...

Building Infrastructure for Preservation and Publication of Earthquake Engineering Research Data

The objective of this paper is to showcase the progress of the earthquake engineering community during a decade-long effort supported by the National Science Foundation in the George E. Brown Jr., Network for Earthquake Engineering Simulation (NEES). During the four years that NEES network operations have been headquartered at Purdue University, the NEEScomm management team has facilitated an unprecedented cultural change in the ways research is performed in earthquake engineering. NEES has not only played a major role in advancing the cyberinfrastructure required for transformative engineering research, but NEES research outcomes are making an impact by contributing to safer structures throughout the USA and abroad. This paper reflects on some of the developments and initiatives that helped instil change in the ways that the earthquake engineering and tsunami community share and reuse data and collaborate in general.

Numerical simulations of a highway bridge structure employing passive negative stiffness device for seismic protection

SummaryA new passive seismic response control device has been developed, fabricated, and tested by the authors and shown to be capable of producing negative stiffness via a purely mechanical mechanism, thus representing a new generation of seismic protection devices. Although the concept of negative stiffness may appear to be a reversal on the desired relationship between the force and displacement in structures (the desired relationship being that the product of restoring force and displacement is nonnegative), when implemented in parallel with a structure having positive stiffness, the combined system appears to have substantially reduced stiffness while remaining stable. Thus, there is an ‘apparent weakening and softening’ of the structure that results in reduced forces and increased displacements (where the weakening and softening is of a non‐damaging nature in that it occurs in a seismic protection device rather than within the structural framing system). Any excessive displacement response can then be limited by incorporating a damping device in parallel with the negative stiffness device. The combination of negative stiffness and passive damping provides a large degree of control over the expected performance of the structure. In this paper, a numerical study is presented on the performance of a seismically isolated highway bridge model that is subjected to various strong earthquake ground motions. The Negative Stiffness Devices (NSDs) are described along with their hysteretic behavior as obtained from a series of cyclic tests wherein the tests were conducted using a modified design of the NSDs (modified for testing within the bridge model). Using the results from the cyclic tests, numerical simulations of the seismic response of the isolated bridge model were conducted for various configurations (with/without negative stiffness devices and/or viscous dampers). The results demonstrate that the addition of negative stiffness devices reduces the base shear substantially, while the deck displacement is limited to acceptable values. This assessment was conducted as part of a NEES (Network for Earthquake Engineering Simulation) project which included shaking table tests of a quarter‐scale highway bridge model. Copyright © 2014 John Wiley & Sons, Ltd.

Special Issue on Field Testing of Bridges and Buildings

Understanding the behavior of structures subjected to complex environmental and mechanical loading is essential for their design, safety, and reliability. In many instances, behavioral understanding is developed using laboratory tests of structural components and systems that are at or close to full scale. As a result, a relatively recent trend in experimental structural engineering research has centered on building larger and more complex testing laboratories. Example facilities include those affiliated with the Network for Earthquake Engineering Simulation (NEES) in the United States (NEES 2014) and E-Defense Shake Table in Japan (NIED 2014). Several successful research projects have been executed at these facilities, with results being published in special issues of the ASCE’s Journal of Structural Engineering (Vol. 139, Issues 7 and 8) and elsewhere (e.g., Lignos et al. 2011; Kawashima et al. 2012; Lowes et al. 2012). Despite offering several advantages, which can include better control of loads during testing and dense instrumentation, there are also limitations to experiments conducted in a laboratory setting. These limitations can include costs associated with completing tests, correct simulation of realistic loading, boundary and environmental conditions, adequate reproduction of size effects, and ensuring that material properties and construction techniques used in the lab are representative of actual properties, techniques, and age. As our infrastructure ages, the cost to maintain and replace it continues to rise. The ASCE’s 2013 Report Card for America’s Infrastructure states that 24.9% of the nation’s bridges are either functionally obsolete or structurally deficient, with the total price tag for repair or replacement estimated at $76 billion (ASCE 2013). Therefore, the need to better understand the performance and current health of actual structures in situ is becoming of paramount importance. As a result, structural health monitoring and structural field testing have emerged as important components of structural engineering and prominent research areas. Recent research efforts related to real-world applications of structural identification and health monitoring were documented in the October 2013 Special Issue of the ASCE’s Journal of Structural Engineering (Vol. 139, Issue 10). A similar effort related to documenting the state of the art on field testing and evaluation of large-scale, in situ structural components and systems has not been undertaken by the ASCE for some time. This special issue is intended to fill this knowledge gap by documenting research results on large-scale field testing of structures and contains manuscripts that focus on in situ destructive testing of decommissioned and large-amplitude forced testing of in-service bridges and buildings as well as monitoring under ambient vibration conditions or during construction. A total of 13 papers are included, 7 of which are related to bridges and 6 to buildings. Researchers and engineering practitioners from seven countries located on four continents contributed to this special issue. Brief summaries of the published manuscripts, in the order in which they are published, are provided in what follows.

A phased approach to enable hybrid simulation of complex structures

Hybrid simulation has been shown to be a cost-effective approach for assessing the seismic performance of structures. In hybrid simulation, critical parts of a structure are physically tested, while the remaining portions of the system are concurrently simulated computationally, typically using a finite element model. This combination is realized through a numerical time-integration scheme, which allows for investigation of full system-level responses of a structure in a cost-effective manner. However, conducting hybrid simulation of complex structures within large-scale testing facilities presents significant challenges. For example, the chosen modeling scheme may create numerical inaccuracies or even result in unstable simulations; the displacement and force capacity of the experimental system can be exceeded; and a hybrid test may be terminated due to poor communication between modules (e.g., loading controllers, data acquisition systems, simulation coordinator). These problems can cause the simulation to stop suddenly, and in some cases can even result in damage to the experimental specimens; the end result can be failure of the entire experiment. This study proposes a phased approach to hybrid simulation that can validate all of the hybrid simulation components and ensure the integrity large-scale hybrid simulation. In this approach, a series of hybrid simulations employing numerical components and small-scale experimental components are examined to establish this preparedness for the large-scale experiment. This validation program is incorporated into an existing, mature hybrid simulation framework, which is currently utilized in the Multi-Axial Full-Scale Sub-Structuring Testing and Simulation (MUST-SIM) facility of the George E. Brown Network for Earthquake Engineering Simulation (NEES) equipment site at the University of Illinois at Urbana-Champaign. A hybrid simulation of a four-span curved bridge is presented as an example, in which three piers are experimentally controlled in a total of 18 degrees of freedom (DOFs). This simulation illustrates the effectiveness of the phased approach presented in this paper.

Impact of construction details on OSB-sheathed cold-formed steel framed shear walls

The objective of this paper is to explore and characterize the impact of practical construction details on the cyclic performance of cold-formed steel framed shear walls sheathed with Oriented Strand Board. The specific construction details explored are motivated from a two-story, ledger-framed, cold-formed steel archetype building that is the focus of a larger effort to advance seismic performance-design for light steel frame construction. This larger effort in cold-formed steel (CFS) research is funded primarily by the National Science Foundation — Network for Earthquake Engineering Simulation (NSF—NEES) effort and is known as the CFS—NEES project. The archetype structure is known as the CFS—NEES building. Shear walls in real construction, such as the CFS—NEES building, have details that differ from shear walls tested and provided for strength prediction in standards such as AISI-S213. Key differences include: (a) ledger (rim track) members attached across the interior face of the studs; (b) OSB panel seams, both horizontal and vertical, may not be aligned with the chord studs or only blocked with strap; (c) interior gypsum board is in place; (d) field studs may have a different thickness or grade from the chord studs; and other differences. In this work, these highlighted differences (a–d) are specifically explored in a series of shear wall tests loaded via cyclic (CUREE) protocols to determine their hysteretic performance. The test results are compared with AISI-S213 and hysteretic material characterizations utilizing an elastic–plastic model and a model capable of exhibiting pinching in the hysteretic loops.

Seismic Behavior of a Modern Concrete Coupled Wall

AbstractRC core walls are used commonly in modern building construction as the primary lateral load–resisting system. To meet architectural constraints, including elevator, stair, and doorway openings, common configurations include walls coupled together with heavily reinforced, low-aspect-ratio coupling beams. Numerous studies have focused on coupling beams and improved seismic performance and design of coupling beams. However, far fewer research programs have studied the seismic behavior of the coupled wall system. Coupled walls are typically used in mid- to high-rise construction, and understanding their seismic response requires simulation beyond the coupling beam and must include all important yielding components of the system. A research project was undertaken to investigate the response of a midrise coupled wall designed to meet current codes. The advanced testing capabilities of the University of Illinois at Urbana-Champaign George E. Brown, Jr. Network for Earthquake Engineering Simulation (NEES)...

Advancing Earthquake Engineering Research through Cyberinfrastructure

AbstractThis paper describes the cyberinfrastructure (CI) of the George E. Brown, Jr. Network for Earthquake Engineering Simulation (NEES) and examines the evidence that this infrastructure is facilitating earthquake engineering research. Among the key features of the CI are the NEES Project Warehouse (PW), which is a data repository for earthquake engineering, an environment that supports the use of tools for web-based data analysis and simulation, and tools that support research collaboration. The value that such CI offers to the user community is discussed. The CI also gathers a myriad of usage statistics, some of which are presented in this paper. Among them are the number of users, pageviews, recorded NEES projects, and other stored resources. This information demonstrates that the CI is used significantly and increasingly so.

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.