Earthquake Engineering Laboratory Research Articles

The 2022 Seismic Hazard Model for Costa Rica

AB4STRACTCosta Rica is located at the boundary of four tectonic plates where the regularity of destructive earthquakes highlights the necessity of seismic hazard estimations. This study contains the most recent Probabilistic Seismic Hazard Assessment (PSHA) for Costa Rica, calculated with the largest and the most updated earthquake database from both—the Earthquake Engineering Laboratory and the National Seismological Network of the University of Costa Rica. For the PSHA, we updated the seismicity parameters for the upper plate, subduction interplate, and intraslab tectonic domains, characterized the upper-plate zones by percentages of fault types, and used weighted ground-motion models for each of the tectonic domains. The resulted maps of peak ground acceleration (PGA) at return periods of 475 yr (PGA-475) and 2475 yr, as well as the spectral accelerations, show geographic trends that allow for the division of the country in four seismic hazard levels: (1) extremely high for the Nicoya, Osa, and Burica peninsulas, situated directly above the subduction interplate, where the PGA-475 could be 0.55–1.20g; (2) very high for most of the Guanacaste Province, where the PGA-475 may be 0.55–0.70g; (3) high for most of the country (∼41%) with PGA-475 values of 0.40–0.55g, including Central Costa Rica and the capital city of San Jose; and (4) moderate for the Talamanca Cordillera and Northern Costa Rica, with PGA-475 up to 0.40g. These ground-motion values are 0.1–0.6g higher than the previous PSHA for the Pacific peninsulas, Guanacaste, and the southeastern Caribbean. Further, hazard curves, uniform hazard spectra, and a hazard disaggregation indicate that the seismic hazard is lower but more complex in San Jose than in Liberia—the largest city in Guanacaste.

Sustainable Earthquake Resilience with the Versatile Shape Memory Alloy (SMA)-Based Superelasticity-Assisted Slider.

Earthquakes threaten humanity globally in complex ways that mainly include various socioeconomic consequences of life and property losses. Resilience against seismic risks is of high importance in the modern world and needs to be sustainable. Sustainable earthquake resilience (SER) from the perspective of structural engineering means equipping the built environment with appropriate aseismic systems. Shape memory alloys (SMAs) are a class of advanced materials well suited for fulfilling the SER demand of the built environment. This article explores how this capability can be realized by the innovative SMA-based superelasticity-assisted slider (SSS), recently proposed for next-generation seismic protection of structures. The versatility of SSS is first discussed as a critical advantage for an effective SER. Alternative configurations and implementation styles of the system are presented, and other advantageous features of this high-tech isolation system (IS) are studied. Results of shaking table experiments, focused on investigating the expected usefulness of SSS for seismic protection in hospitals and conducted at the structural earthquake engineering laboratory of the University of Bonab, are then reported. SSS is compared with currently used ISs, and it is shown that SSS provides the required SER for the built environments and outperforms other ISs by benefitting from the pioneered utilization of SMAs in a novel approach.

30 años después, ¿Qué aprendimos con el terremoto de Limón 1991 en el diseño de edificios y viviendas?

On April 22, 1991, an earthquake of magnitude 7.7Mw generated a great amount of damage in the structures located in the Caribbean zone of Costa Rica. The follow-up of the earthquake-resistant design code available at that time (Costa Rican Seismic Code 1986), as well as the recommendations given in the current regulations (Costa Rican Seismic Code 2010/14), are used to assess the observed damage in some structures, to identify if they were caused by a breach of the regulations of that date or due to lack of development in the regulations. In this document, three structural typologies are evaluated through representative cases: reinforced concrete buildings, concrete masonry structures, and elevated structures to be flood resistant. For this evaluation, a photographic record available in the Earthquake Engineering Laboratory was analyzed. All photographs were taken by members of the Laboratory during inspection campaigns carried out days after the main event.

A Strong-Motion Database of Costa Rica: 20 Yr of Digital Records

AbstractIn this article, we present a strong-motion database from earthquakes recorded by the Earthquake Engineering Laboratory at the University of Costa Rica. The database consists of 2471 three-component accelerograms from 155 digitally recorded events. It covers the last 20 yr of measurements, including records from the 5 September 2012 Mw 7.6 Nicoya earthquake. The engineering and seismological communities can use this data either to conduct new research or to improve seismic hazard studies in the region. A catalog is also available with metadata of each record containing several intensity measures from the ground-motion time histories.

Seismic performance of slender RC U-shaped walls with a single-layer of reinforcement

Reinforced concrete walls are commonly used to resist the lateral loading induced by wind and earthquake actions. While most walls include two vertical reinforcement layers, some regions of the world construct slender, non-rectangular concrete walls with a single vertical layer of reinforcement. The seismic performance of such elements is largely unknown given the paucity of experimental research. This paper presents the results of two slender reinforced concrete U-shaped walls tested at the Earthquake Engineering and Structural Dynamics Laboratory (EESD Lab), École Polytechnique Fédérale de Lausanne (EPFL) in Switzerland. Both wall specimens, designed similar to construction practice in Colombia, were tested using quasi-static cyclic loading to observe if out-of-plane instability would develop when deformations were limited to prevent the flange boundary ends crushing. Initial failure of both wall specimens corresponded with local out-of-plane buckling in the boundary ends of the flanges occurring on load reversal. The buckling lengths were approximately 700–800 mm, which corresponded to 44–50 bar diameters. The crack patterns were observed to be steepest in the web of the walls, demonstrating the increased shear demand in comparison to that of a rectangular wall. Both wall specimens reached ultimate drifts larger than 2.5–3.0% before global failure occurring in the web-flange intersection due to crushing. A small twist was subjected to one of the walls when centered and loaded diagonally, which showed that the decay in torsional stiffness is proportional to the decay in translational stiffness.

Feed-Forward Controlling of Servo-Hydraulic Actuators Utilizing a Least-Squares Support-Vector Machine

Feed-forward control of hysteretic systems is a challenging task due to the hysteresis nonlinearity. Hysteresis models are utilized not only for identification, but also for hysteresis control. The feed-forward control, which is not an error-based (feedback-based) algorithm, plays a significant role in hysteresis control problems. Instead, it works based on knowledge about the process in the form of a mathematical model of the process. In feed-forward control problems, it is important to identify the inverse relationship of the output and input of the system, i.e., determining the mapping of the output and input of the system plays a key role in feed-forward controlling. This paper presents a new feed-forward controller model to control an actuator in a laboratory to tackle the restrictions of feedback control systems. For this purpose, first, a numerical model of a Proportional-Integral-Derivative (PID)-controlled actuator was created, and sets of numerical data of inputs and outputs of the plant were generated. Then, a least-squares support-vector machine (LS-SVM) hysteresis model was trained inversely on the generated data sets of the numerical modeling. Afterwards, to examine the efficacy of the proposed method for real-world hydraulic actuators in the presence of experimental errors and noise, sets of experimental data were obtained from physical modeling at KNTU’s Structural and Earthquake Engineering Laboratory (KSEEL). The results indicate the high performance of the proposed model.

Seismic performance analysis and assessment of a precast bridge computational model

A large-scale, two-span bridge model constructed by assembling precast elements was tested under a series of bi-axial ground motionssimulated on a shake table at the Earthquake Engineering Laboratory at the University of Nevada, Reno. The response of the bridge wasestimated before the tests using a three-dimensional computational model developed in OpenSees software. After the tests, key measuredseismic responses were compared to those predicted by the computational model to assess the modeling assumptions. Relatively largeerrors for the displacements, base shears, and hysteretic response of the bridge were observed. The influence of the earthquake loading,materials, connectivity of the precast elements, and boundary conditions in the computational model on the errors are discussed in thispaper. Future modeling directions are proposed to reduce these errors.

Inelastic behavior and seismic design of multistory chevron-braced frames with yielding beams

Chevron or inverted V-braced frames offer numerous architectural and structural advantages, but the current special concentrically braced frame (SCBF) seismic-design requirements in the American Institute of Steel Construction (AISC) Seismic Provisions for Structural Steel Buildings lead to deep, heavy chevron beams; as a result, few chevron SCBFs are built today. Recent research on single-story chevron SCBFs demonstrated that beam yielding can be advantageous at higher demand levels, and design for large, inelastic unbalanced brace-force demands may still result in acceptable seismic performance. However, this prior research did not consider the response of multistory frames. In particular, questions remain as to the potential for concentration of damage, the impacts of composite slabs, and the effects of different beam-to-column connections; these issues can only be investigated using multistory frames. A companion research program was conducted to investigate multistory systems with chevron SCBFs using experimental and computational simulation methods. In the first phase of the research, a three-story chevron SCBF designed to permit beam yielding was tested at the National Center for Research on Earthquake Engineering (NCREE) Laboratory in Taipei, Taiwan. The test results were then used to validate a nonlinear, continuum finite-element model. A limited parametric study was conducted to build upon and further the experiments, specifically to evaluate different beam strengths and stiffnesses. These results were combined to develop design recommendations for chevron SCBFs with yielding beams.

System Identification of Large-Scale Bridges Using Target-Tracking Digital Image Correlation

This paper characterizes the extensive research activities conducted in the Earthquake Engineering Laboratory of University of Nevada, Reno, in the field of dynamic monitoring and system identification of three 1/3-scale two-span bridges. The first part of the study briefly presents the verification of target-tracking Digital Image Correlation (DIC) results as compared to conventional sensors, e.g. string potentiometers and triaxial accelerometers from one of the three bridge tests. Structural system identification is presented in the second part for the other two bridges with focus on determining structural model parameters based on the DIC measured response data. All bridges were tested under bidirectional earthquake loading using the multiple shake table array. However, the system identification used data collected from the white noise runs before and after the seismic tests. A quasi-linear response of the system was assumed because of the low intensity white noise base excitation, and the modal parameters were estimated accordingly. Using the structural vibration data recorded by target-tracking DIC at various locations on the bridges, five system identification methods were applied to analyze the modal parameters of the tested bridges. The results were used to estimate the frequency, damping ratio, and mode shapes, of the bridges in two states. The initial state is before seismic testing and the end state is the damaged state after the completion of the seismic tests. The results show that the applied methods provide a reasonable estimate of the natural frequency and damping ratio of the bridge systems in the original and damaged states.

01.24: Moment‐resisting beam‐to‐column connections of corrugated web I sections

ABSTRACTThin sinusoidal corrugated web I‐sections have been utilizing commonly in recent years. Though, there are scarce number of studies about their connections.The moment‐resisting extended end plate type beam‐to‐column connections of sinusoidal corrugated web I sections are assessed by means of experimental studies to reveal the important response characteristics. Three full scale beam‐to‐column connections were tested in the Structural and Earthquake Engineering Laboratory of Istanbul Technical University. Although two of the specimens have corrugated‐web panel zone, the third one has relatively thicker flat plate in the panel zone and its near‐vicinity. Double diagonal stiffeners are used in the sinusoidal panel zone of one specimen.It is obtained that two distinct specimens exhibit the comparable responses in terms of the stiffness and strength properties.

An approach for shake table performance evaluation during repair and retrofit actions

SummaryLarge‐scale, servo‐hydraulic shake tables are a central fixture of many earthquake engineering and structural dynamics laboratories. Wear and component failure from frequent use may lead to control problems resulting in reduced motion fidelity, necessitating repairs and replacement of major components. This paper presents a methodology to evaluate shake table performance pre‐ and post‐repair, including the definition of important performance metrics. The strategy suggested is presented in the context of the rebuilding of a 4.9 × 3.1 m, 350‐kN‐capacity uniaxial shake table. In this case, the rebuild consisted of characterization of wear to table components, replacement of worn bearing surfaces, and replacement of hydraulic accumulators. To assess the effectiveness of the repair actions, sinusoidal and triangular waves, white noise, and earthquake histories were run on the table before and after the rebuild. The repair actions were successful in reducing the position and velocity dependence of friction, improving the ability of control algorithms to accurately reproduce earthquake motions. The maximum and average response spectral misfits in the period range of 0.1–2 seconds were reduced from approximately 50% to 15%, and from 5% to less than 2.5%, respectively.

Experimental and numerical investigation of lead-rubber dampers in chevron concentrically braced frames

This paper presents a theoretical and experimental evaluation of the application of lead rubber dampers (LRD) in the chevron bracing of structures. This device consists of a circular lead core with several layers of steel and rubber plates that are sandwiched together. This damper was manufactured at the earthquake engineering laboratory of Urmia University and installed inside a SDOF steel frame. The frame was placed on a shaking table, and its responses under several earthquake excitations were recorded. A 3D finite element model was created for the device, and hyper-elastic properties were determined for the rubber layers. To check the effectiveness of the device in mitigating the responses of multi-story frames, several nonlinear time history analyses were conducted on the structures using three earthquake excitations. The results indicate that significant reductions in the stories’ drift can be achieved by installing lead-rubber dampers in the chevron bracing.

Spring tube braces for seismic isolation of buildings

A new low-cost seismic isolation system based on spring tube bracings has been proposed and studied at the Structural and Earthquake Engineering Laboratory of Istanbul Technical University. Multiple compression-type springs are positioned in a special cylindrical tube to obtain a symmetrical response in tension and compression-type axial loading. An isolation floor, which consists of pin-ended steel columns and spring tube bracings, is constructed at the foundation level or any intermediate level of the building. An experimental campaign with three stages was completed to evaluate the capability of the system. First, the behavior of the spring tubes subjected to axial displacement reversals with varying frequencies was determined. In the second phase, the isolation floor was assessed in the quasi-static tests. Finally, a ¼ scaled 3D steel frame was tested on the shake table using actual acceleration records. The transmitted acceleration to the floor levels is greatly diminished because of the isolation story, which effects longer period and higher damping. There are no stability and self-centering problems in the isolation floor.

Cyclic behaviour of diagonally-stiffened beam-to-column connections of corrugated-web I sections

Corrugated web profiles are generally used in single story long span structures though there exists limited number of researches about the performance of the connections. Besides there is a rising demand for utilization of corrugated web profiles in construction of low-rise moment resisting frames. This paper aims to evaluate the behaviours of two distinct types of beam-to-column connections namely; i. Conventional types: thick flat plate is used in the panel zone and its near-vicinity, ii. Alternative types: single or double stiffeners are used at both faces in the corrugated-web panel zone. The latter provides key advantages particularly for fabrication. The full scale beam-to-column connections were tested in the Structural and Earthquake Engineering Laboratory of Istanbul Technical University (ITU). In comparing the stiffness and strength characteristics of the tested connections, single and double diagonally-stiffened connections exhibited comparable behaviour to the specimens with flat plate panel zones. The finite element models of all the tested connections were produced with ABAQUS. The analytical results are in good agreement up to an inter-story drift angle of 0.04rad with the experimental ones.

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...

Clasificación de suelos de 15 estaciones acelerográficas, mediante el uso de métodos basados en vibraciones ambientales y del parámetro Vs30

The H/V, FK and SPAC techniques were applied , all based on the measurement of ambient vibrations generated by surface waves for the characterization of soils beneath 15 selected sites, 12 of them corresponding to accelerographic stations of the Earthquake Engineering Laboratory of the University of Costa Rica. To achieve this, sensors (triaxial geophones) were placed in circular arrays and spectral ratios (from H/V) dispersion curves (from FK) and autocorrelation curves (from SPAC) for each site were obtained. Based on the above, the soil type was determined according to the characteristic site period (T0) read from H/V and criteria according to Zhao et al. (2006). Each site was also classified according to the Seismic Code of Costa Rica (2010) and Vs30 parameter calculated from the inversion of dispersion and autocorrelation curves. T0 values from 0.3 s to 1.5 s and Vs30 between 244 m/s to 379 m/s were obtained, indicating that soils correspond to S3 (soft soil, 67% of all cases). No site whose classification corresponds to S1 (rock) or S4 (very soft soil) was found

In-plane behaviour of beam-to-column connections of corrugated web I-sections

This paper presents the results of an experimental study to examine the in-plane behaviour of the moment-resisting beam-to-column connections of thin-walled sinusoidally-corrugated web I-sections. A group of specimens of nearly full-sized beam–column assemblies made of sinusoidal corrugated web I-sections were tested under cyclic loading in the Structural and Earthquake Engineering Laboratory of Istanbul Technical University (ITU). Whereas two of the specimens have corrugated panel zones, the others have flat plate panel zones, according to an existing practice. The results of the experimental works are evaluated in terms of the general behaviour of the specimens and the regional behaviour of the panel zones. Three-dimensional nonlinear finite element analysis (FEA) models are developed in ABAQUS, including nonlinear interaction along with the contacting parts. The analytical results show a satisfactory convergence with the experimental results. The specimens that had relatively thicker flat plate webs in the panel zone were more stable than those which had corrugated web panels.

The Behavior of a Steel Connection Equipped with the Lead Extrusion Damper

The seismic behavior of the steel connection equipped with the lead extrusion damper (LED) is examined through the experimental and analytical studies. The LED implemented has spherical type bulge and does not consist any lubricant layer. The experimental study is performed in Structural and Earthquake Engineering Laboratory of Istanbul Technical University (STEELAB). In the experimental part, force-displacement relations of the connections with and without LED are achieved for the reversal displacement cycles. The measures of the dissipated energy, the equivalent damping ratio and the effective stiffness are obtained from the experimental study and compared for the connections. The total energy dissipated by the connection with the LED is approximately 175% greater than the total energy dissipated by the bare connection. In the analytical part of the study, nonlinear dynamic time history analyses are performed for the selected earthquakes and mass condition using the analytical models for the connections with and without LED. The maximum top displacement decreases approximately 50% for the connection equipped with the LED respect to the bare connection for the considered earthquakes. The maximum value of restoring force for the connection equipped with LED is approximately 25% greater than the bare connection for the accomplished analyses. Finally, the LED responses obtained in the nonlinear time history analyses are compared with the isolated LED test results.

Process and Future of Data Integration within the European Earthquake Engineering Laboratories

AbstractIn common with many scientific disciplines, earthquake engineering research is increasingly focusing on large international collaborations to address complex problems. Data integration is a...

Virtual Earthquake Engineering Laboratory Capturing Nonlinear Shear, Localized Damage and Progressive Buckling of Bar

We embarked upon developing a novel parallel simulation platform that is rooted in microphysical mechanisms. Primarily aiming at large-scale reinforced-concrete structures exposed to cyclic loading, we sought to settle the question as to how to capture nonlinear shear, localized damage and progressive buckling of reinforcing bar. We proposed a tribology-inspired three-dimensional (3-D) interlocking mechanism in the well-established framework of multidirec-tional smeared crack models. Strong correlation between random material property and localized damage has been shown, notably at the global system level. An automated platform has been suggested to capture progressive buckling phenomena. Validation and applications straddle a wide range, from small laboratory tests to large-scale 3-D experiments, successfully offering a clear causal pathway between underlying physical mechanisms and the unresolved issues addressed above.