Search

Three-dimensional (3-D) nonlinear site response analyses are conducted using finite element models of actual soil profiles from ten nuclear power plant (NPP) sites in the United States to investiga...

Over 2000 buildings were surveyed by members of the Colegio de Ingenieros (CICM) and Sociedad Mexicana de Ingenieria Estructural (SMIE) in Mexico City following the Puebla-Morelos Earthquake of 2017. This inventory of surveyed buildings included nearly 40 collapses and over 600 buildings deemed to have structural damage. Correlation of damage with peak ground acceleration (PGA), peak ground velocity (PGV), predominant spectral period, building location, and building properties including height, estimated stiffness, and presence of walls or retrofits was investigated for the surveyed buildings. The evidence available suggests that (1) ground motion intensity (PGV) drove the occurrence of damage and (2) buildings with more infill and stiff retrofit systems did better than other buildings.

Communities need seismic vulnerability indices to identify which buildings are most susceptible to severe damage during earthquakes. To be of greatest value, these indices should be easy to use and should be vetted against data from previous earthquakes. To date, more than 800 reinforced concrete buildings have been surveyed after earthquakes for the purpose of evaluating a seismic vulnerability index proposed by Hassan and Sozen in 1997. This number includes 130 buildings surveyed after the 6 February 2016 earthquake in Taiwan. The data collected during these surveys consist of descriptions and photographs of damage, structural sketches, and measurements. Analyses of the data indicate that probability of severe damage and failure increases with decreasing column index and wall index (normalized measures of column and wall areas). They also suggest that the exact form of the threshold used to distinguish more vulnerable structures from less vulnerable structures is of little consequence in terms of the probable cost and benefits of the strengthening program this threshold may inform.

Cities in seismic regions often have unknown numbers of older buildings vulnerable to strong earthquake ground motion. Simple methods are needed with urgency to screen these buildings. The problem is of immense proportions as it affects some of the largest cities in the world. Seismic vulnerability indices proposed by Hassan and Sozen (ACI Struct J 94(1):31–39, 1997), Islam et al. (Architectural Institute of Japan-Academic Lecture Collection Summary, 2017), NCREE (Chiou et al. in 16th World Conference on Earthquake Engineering, 16WCEE 2017, Santiago, 2017), and Shiga et al. (Proceedings, Tohuku District symposium, Architectural Institute of Japan, 1968) possess the required simplicity. The indices have different forms and have been calibrated through independent activities, but all imply that the key to building survival is in the relative sizes of elements resisting lateral inertial forces. Data collected after the 2016 Meinong, Taiwan, Earthquake were used to evaluate these indices. The evaluation showed that differences among indices did not lead to wide differences in the cost associated with a given benefit especially if they are used to include the effects of all lateral-load resisting elements including masonry infill.

The complex behavior of reinforced concrete frames with infill walls under earthquake loads requires a realistic conceptual model that recognizes changes in strength and stiffness occurring during loading. Accordingly, a new hysteresis model is developed in this article for such reinforced concrete frames to investigate the ultimate damage state given a ground motion. Using this model, the infilled frame can be represented as a single-degree-of-freedom system for computationally efficient dynamic in-plane response analysis. A backbone curve is developed first to provide an envelope within which load–displacement paths occur. Then, the load reversal effects are described and integrated into the backbone curve to obtain the hysteresis model. The hysteresis model developed in this article is checked using data from 11 laboratory experiments carried out by other researchers. The applicability of the hysteresis model is also illustrated on a laboratory specimen that was tested by other researchers under base excitation.

Dynamic response of structures is a complex process that is not well-understood. Seismic design codes allow structural systems of buildings to behave inelastically during strong ground shaking. While hysteretic energy dissipation due to inelastic behavior is rather well-understood, there exist other energy dissipation mechanisms which are not as well-understood. Energy dissipation due to mechanisms other than material non-linearity are often modeled in the form of a single, velocity proportional damping mechanism with an equivalent viscous damping ratio. In seismic design and dynamic analysis of structures, this equivalent viscous damping ratio is generally taken to be constant (e.g., 2 or 5% of the critical) regardless the response is elastic or inelastic. Instead of making such a strong assumption about the viscous damping ratio, which may have large influence on the peak response levels, it is advisable to use an effective viscous damping estimate based on studying the actual response of real structures responding to dynamic loads. Use of such obtained viscous damping will allow extraction of restoring forces from dynamic force estimates. At low strain-rate levels, such as those observed during seismic response, restoring forces match the resistance that develops during quasi-static loading, a method to estimate effective viscous damping and restoring force empirically from dynamic response of a structure is presented. The method considers inelastic response explicitly, i.e., no linearization assumptions are made for the load-deformation behavior of the structure. The presented method is tested on several computational simulation models with various hysteretic behaviors and a preset constant viscous damping ratio to verify that the algorithm (1) estimates a damping ratio close to the value used in the simulations, and accordingly, (2) captures the hysteretic behavior accurately. The method is illustrated using data obtained from reinforced concrete test specimens subjected to design-level base excitations on an earthquake simulator.

A method is presented for extracting empirical capacity curves from building earthquake response data. The method can be applied to buildings with acceleration response records from each floor to develop story empirical capacity curves assuming the building has flexible columns and rigid floors. The method can also be applied to buildings with acceleration response records from the roof and ground to develop a fundamental mode empirical capacity curve. The method relies on extracting the restoring force and relative displacement of the system by removing damping force, considered as equivalent viscous damping, from the inertial response, using a proposed viscous damping identification procedure. The method is demonstrated using data from a small-scale, three-story experimental model subjected to strong base motion.

Wireless sensor networks (WSNs) have emerged as a novel solution to many of the challenges of structural health monitoring (SHM) in civil engineering structures. While research projects using WSNs are ongoing worldwide, implementations of WSNs on full-scale structures are limited. In this study, a WSN is deployed on a full-scale 17.3m-long, 11-bay highway sign support structure to investigate the ability to use vibration response data to detect damage induced in the structure. A multi-level damage detection strategy is employed for this structure: the Angle-between-String-and-Horizon (ASH) flexibility-based algorithm as the Level I and the Axial Strain (AS) flexibility-based algorithm as the Level II. For the proposed multi-level damage detection strategy, a coarse resolution Level I damage detection will be conducted first to detect the damaged region(s). Subsequently, a fine resolution Level II damage detection will be conducted in the damaged region(s) to locate the damaged element(s). Several damage cases are created on the full-scale highway sign support structure to validate the multi-level detection strategy. The multi-level damage detection strategy is shown to be successful in detecting damage in the structure in these cases.

Highway sign support structures enhance traffic safety by allowing messages to be delivered to motorists related to directions and warning of hazards ahead, and facilitating the monitoring of traffic speed and flow. These structures are exposed to adverse environmental conditions while in service. Strong wind and vibration accelerate their deterioration. Typical damage to this type of structure includes local fatigue fractures and partial loosening of bolted connections. The occurrence of these types of damage can lead to a failure in large portions of the structure, jeopardizing the safety of passing traffic. Therefore, it is important to have effective damage detection approaches to ensure the integrity of these structures. In this study, an extension of the Angle-between-String-and-Horizon (ASH) flexibility-based approach [32] is applied to locate damage in sign support truss structures at bay level. Ambient excitations (e.g. wind) can be considered as a significant source of vibration in these structures. Considering that ambient excitation is immeasurable, a pseudo ASH flexibility matrix constructed from output-only derived operational deflection shapes is proposed. A damage detection method based on the use of pseudo flexibility matrices is proposed to address several of the challenges posed in real-world applications. Tests are conducted on a 17.5-m long full-scale sign support truss structure to validate the effectiveness of the proposed method. Damage cases associated with loosened bolts and weld failures are considered. These cases are realistic for this type of structure. The results successfully demonstrate the efficacy of the proposed method to locate the two common forms of damage on sign support truss structures instrumented with a few accelerometers.

Correlating damage level and changes in dynamic characteristics of a structure forms the basis for damage detection techniques in structural health monitoring. In reinforced concrete building structures such correlation is not well established. A damage detection technique capable of identifying the structural condition of the system based on its small amplitude vibration response is desirable because such response is easier to obtain. It is a common practice in engineering applications to estimate dynamic parameters from small-amplitude vibrations assuming a linear behavior of the structure. This simplification causes inaccurate estimation of the dynamic properties in reinforced concrete structures due to the presence of nonlinear elastic behavior. In this study no such assumption is made and a linear model is only used for sets of data corresponding to the same displacement amplitude of a nonlinear elastic system. The trends found between small-amplitude vibration dynamic properties and past levels of maximum displacement in various reinforced concrete structures are reported. In addition to analytical and numerical studies, results from a series of laboratory tests are reported to demonstrate the use of the approach. One full-scale three-story reinforced concrete flat-plate building and six small-scale reinforced concrete beams were examined. In this study, small displacements are defined as displacements below an overall drift ratio of 0.03%. The displacement dependence of the dynamic properties is considered explicitly. It was found that while fundamental frequencies of the examined reinforced concrete specimens were found to decrease uniformly as past peak displacement level increased, the equivalent viscous damping ratio was found to increase until the past peak displacement reached the neighborhood of nominal yield displacement and then observed to decrease when the specimens are pushed beyond the nominal yield displacement level, which has not been reported in literature before. Recommendations are provided as to how small amplitude vibration tests should be set up to avoid misleading observations due to nonlinear response at small amplitude response, observations that could lead to erroneous conclusions regarding the damage state of a structure.

The civil engineering capstone senior design course at Purdue University involves all seniors in their last semester before graduation and is titled “Civil Engineering Design Project.” The course catalog describes it as “Planning, design, and analysis of a civil project; an integrated and realistic group project involving as much as possible all major aspects of the civil engineering profession.” This high-enrollment course (30–120 students per semester) has been team taught since the early 1960s and many approaches to teaching it have been utilized. Since 2001, the version of the course discussed in this paper has been taught in the spring semester with the student teams responding to a request for proposals (RFP) for local projects following the design-build method of project delivery. The proposals are submitted in two phases: (1) conceptual designs and alternatives analyses; and (2) design-build project proposal with approximately 30% complete design, total construction cost, and scheduling. The desig...

Following the 12 January 2010 Haiti earthquake, teams of students and faculty members from the United States and Haiti surveyed 170 reinforced concrete (RC) buildings in Port-au-Prince and Léogâne. This paper summarizes the survey results and compares them with results from a similar survey done after the 1999 earthquakes near Düzce, Turkey. The survey results demonstrate that the frequency of damage in RC buildings was higher in Haiti than in Turkey. This increased level of damage is consistent with practical screening criteria based on cross-sectional areas of building columns and walls. Based on these criteria, 90% of the structures surveyed in Haiti would have been classified as seismically vulnerable before the earthquake. Damage was more frequent in structures with captive columns. A two-tiered screening process is suggested to rapidly assess the vulnerability of scores of poorly built low-rise RC buildings in future earthquakes.

In this study, a solution model is proposed to obtain input ground motion datasets compatible with given design spectra based on meta-heuristic harmony search algorithm. The utility of the solution model is demonstrated by generating ground motion datasets matching the Eurocode-8 design spectra for different soil types out of an extensive database of recorded motions. A total of 352 records are selected from the Pacific Earthquake Engineering Center (PEER) Strong Motion Database based on magnitude, distance, and site conditions to form the original ground motion domain. Then, the proposed harmony search based solution algorithm is applied on the pre-selected 352 time-series to obtain the ground motion record sets compatible with design spectra. The results demonstrate that the proposed HS based solution model provides an efficient way to develop input ground motion record sets that are consistent with code-based design spectra. (C) 2011 Elsevier Ltd. All rights reserved.

A series of numerical aircraft crash simulations and thermal behavior analyses were made at Purdue University to study the response of the World Trade Center Tower 1 (WTC-1) on September 11, 2001. The process included accuracy verification for the computational tools using available experiment data. Numerical models for the Boeing 767–200ER aircraft and the structural system for the top 20 stories of WTC-1 were developed for the simulations. A second aircraft model, simpler yet comparable in effect, was developed and used for a parametric sensitivity analysis. Results from these simulations and published by other researchers indicate that while the observed impact damage to tower exterior framing can be estimated accurately, the unseen impact damage to the core structure of the tower could not be estimated with high confidence. Although the computational tools helped in developing an understanding as to what might have happened as the aircraft penetrated and disintegrated into the structure, they were not able to reduce the uncertainty in the core damage estimate. However, reflecting insight from the behavior of the Pentagon building under the impact loads it received on the same day and studying the effects of elevated temperature on mechanical properties of steel in light of experimental data, the uncertainty in the core structural damage estimate was found to be of negligible importance with regards to the ultimate fate of the tower. It is demonstrated that through use of numerical simulations and engineering reasoning, a dominant factor in the collapse of the tower could be proposed with confidence. It was the loss of fire-proofing in the tower core during aircraft impact that left the core vulnerable to ensuing thermal loads and resulted in the eventual collapse of the tower.

The behavior of the World Trade Center Tower 1 on September 11, 2001 is studied in light of experimental data on the effect of elevated temperature on mechanical properties of structural steel. It is concluded that the damage inflicted by aircraft impact on the insulation of the core framing was the dominant factor in the collapse of the structure.

Several school buildings were surveyed in the disaster areas of the Marmara (17 August 1999, [Formula: see text]), Düzce (12 November 1999, [Formula: see text]), and Bingöl (1 May 2003, [Formula: see text]) earthquakes in Turkey. Among them, 21 reinforced concrete buildings were found to have an identical floor plan. Lateral load resisting structural system consisted of reinforced concrete frames (moment-resisting frame) in 16 of the buildings and structural concrete walls integrated with the moment-resisting frame (dual system) in the remaining five buildings. The number of stories above ground in these buildings ranged from two to four. These school buildings provide a nearly ideal test of the effect of a single important structural characteristic on the performance of buildings with structural designs that are uniform in all other respects. Our observation is that the presence of structural walls improves the behavior of reinforced concrete systems drastically.

Most of the public school buildings in Turkey and Peru are built according to a small number of template plans. Over the years, these template plans are kept the same while the structural designs are varied with the seismic design codes in force. During recent strong earthquakes in Turkey and Peru, the design concepts and construction styles for these template school buildings have been put to test. In this paper, observed earthquake performances of template reinforced concrete school buildings with moment-frames or moment-frames and shear walls are compared. The comparison reveals choices in design that were successful as well as those that were not. The disastrous results of “captive columns” are demonstrated in illustrations from what has been observed in recent earthquakes in these seismically active countries. It is shown that since 1997 the Peruvian practice has been producing school buildings that perform well during strong earthquakes.

The writers report on a simulation study of the performance of the North Tower (WTC-I) of the World Trade Center complex during the impact of American Airlines Flight 11 on September 11, 2001. We discuss impact damage that the structural core might have sustained and its possible behavior under structural and thermal loading. Our simulations indicate that the worst damage to the core structure was in stories 95 through 97 of the tower. We estimate that a core collapse mechanism could be initiated if the tower core column temperatures were elevated to about 700°C.

In seismic design, buildings are designed to respond to strong earthquake ground motions inelastically. The engineering norm followed in design and analysis is to use constant modal viscous damping ratios to account for all energy dissipation aside from that arising from material nonlinearity. In general, equivalent linear models, which aim to capture primarily the peak response with typically 2–5 % of critical damping are employed. In this paper, we show that the effective viscous damping ratio can be estimated from the dynamic response of actual building structural systems without linearization of the load-deformation characteristics. The empirical method we present, which estimates the effective viscous damping ratios of buildings, has been applied to several laboratory specimens and actual buildings. We show that the effective viscous damping ratio in a low to mid-rise reinforced concrete (RC) building responding at its dominant mode (equivalent of fundamental mode in linear elastic systems) varies linearly with the effective period of its dominant mode. The practical use of the method is demonstrated using acceleration records obtained in two 9-story small-scale RC laboratory test specimens during a series of strong base motions. Fundamental mode envelopes of hysteretic responses, that is, the backbone curves for both structures are estimated by excluding higher mode effects from the measured responses.

There is no convincing evidence indicating that future ground motion in at least two-thirds of Istanbul, Turkey, shall be less demanding than the ground motions that devastated the city of Duzce, Turkey, in 1999. Comparison of vulnerability indices calibrated for Turkish construction indicates that the structures of the buildings in Istanbul are no better than the structures of buildings in Duzce. On the basis of these arguments, we project that a future earthquake near Istanbul may cause severe damage or collapse approximately quarter of a million buildings. Leaving the vulnerable buildings as they are and organizing for emergency response is not an option for Istanbul. DOI: 10.1193/1.2424988

In this special issues, authors discuss issues in earthquake and tsunami research, as well as in the computational and data infrastructure.

The peak inelastic displacement of a building during a strong ground motion correlates with the elastic period of the structure. Algan (1976) observed this while subjecting laboratory scale reinforced concrete building structures to dynamic base excitations. Later, Lepage (1996) expressed the relationship in a simple form after carrying out regression analysis on dynamic response data from a wide range of buildings. Both Algan and Lepage focused on reinforced concrete buildings. In this study, the presence of a similar correlation between peak inelastic displacement and initial, elastic period in steel special moment resisting frame (SMRF) type building structures is investigated. Two sets of GMs are used in response simulation of 3-story and 9-story SMRFs using OpenSEES. The uniaxial Giuffre-Menegotto-Pinto model with isotropic strain hardening and uniaxial bilinear behaviors are considered as the two steel material properties of the structures. The structures are subjected to a series of ground motions with ascending peak ground accelerations. The results are compared with the corresponding responses from non-deteriorated (pristine) structural systems subjected to the highest intensity ground motion from the mentioned ground motion series. Each ground motion is scaled to a target spectral acceleration with respect to the first period of the structure. It is found that a simple empirical expression could be used to estimate the peak inelastic displacement. The source of this rather unexpected behavior is investigated through extensive high-performance computational simulations of how fundamental dynamic characteristics relate to damage and/or softening in a building structural system, including damage accumulation.

A general framework for multi-criteria optimal design is presented which is well suited for performance-based design of structural systems operating in an uncertain dynamic environment. A decision theoretic approach is used which is based on aggregation of preference functions for the multiple, possibly conflicting, design criteria. This allows the designer to trade off these criteria in a controlled manner during the optimization. Reliability-based design criteria are used to maintain user-specified levels of structural safety by properly taking into account the uncertainties in the modeling and seismic loads that a structure may experience during its lifetime. Code-based requirements are also easily incorporated into this optimal design process. The methodology is demonstrated with a simple example involving the design of a three-story steel-frame building for which the ground motion uncertainty is characterized by a probabilistic response spectrum which is developed from available attenuation formulas and seismic hazard models.

In this paper two modal identification approaches appropriate for use in a distributed computing environment are applied to a full-scale, complex structure. The natural excitation technique (NExT) is used in conjunction with a condensed eigensystem realization algorithm (ERA), and the frequency domain decomposition with peak-picking (FDD-PP) are both applied to sensor data acquired from a 57.5-ft, 10 bay highway sign truss structure. Monte-Carlo simulations are performed on a numerical example to investigate the statistical properties and sensitivity to noise of the two distributed algorithms. Experimental results are provided and discussed.

Izmir, the third largest city and a major economic center in Turkey, has more than three million residents and half million buildings. In this study, the seismic risk in reinforced concrete buildings that dominate the building inventory in Izmir is investigated through multiple approaches. Five typical reinforced concrete buildings were designed, modeled and assessed for seismic vulnerability. The sample structures represent typical existing reinforced concrete hospital, school, public, and residential buildings in Izmir. The seismic assessments of the considered structures indicate that they are vulnerable to damage during expected future earthquakes. © 2009 Springer Science+Business Media B.V.