Ertugrul Taciroglu

Validated Simulation Models for Lateral Response of Bridge Abutments with Typical Backfills

Abutment-backfill soil interaction can significantly influence the seismic response of bridges. In the present study, we provide numerical simulation models that are validated using data from recent experiments on the lateral response of typical abutment systems. Those tests involve well-compacted clayey silt and silty sand backfill materials. The simulation methods considered include a method of slices approach for the backfill materials with an assumed log-spiral failure surface coupled with hyperbolic soil stress-strain relationships [referred to as “log-spiral hyperbolic (LSH) model”] as well as detailed finite-element models, both of which were found to compare well with test data. Through parametric studies on the validated LSH model, we develop equations for the lateral load-displacement backbone curves for abutments of varying height for the two aforementioned backfill types. The equations describe a hyperbolic relationship between lateral load per unit width of the abutment wall and the wall defl...

Ambient and Forced Vibration Testing of a Reinforced Concrete Building before and after Its Seismic Retrofitting

AbstractThis paper investigates the effects of seismic retrofitting on the modal characteristics of a 6-story RC building located in Istanbul, Turkey. Ambient vibration surveys were carried out before, during, and after the retrofitting work, which took place between June and December 2010. The building was retrofitted via jacketing of columns, addition of structural walls, and construction of a mat foundation. These studies were complemented with data from forced vibration tests performed with an eccentric-mass shaker after the retrofitting work was completed. During retrofitting, partitions were demolished; as a result, the first modal frequency of the building decreased by 11%, based on the results of the ambient vibration survey. The ambient vibration survey also showed that the modal frequencies after the seismic retrofitting increased by almost 96%. During the forced vibration tests, the building was excited around its modal frequencies using an eccentric-mass shaker. It was found that the modal dam...

Parametric Identification of Nondegrading Hysteresis in a Laterally and Torsionally Coupled Building Using an Unscented Kalman Filter

AbstractA parametric approach is proposed for identifying the inelastic response of individual elements, which provide resistance against lateral loads in torsionally coupled buildings. Depending on the severity of the ground shaking in each lateral direction and the amount of eccentricity, different lateral load resisting elements (LLREs) will experience different levels of permanent deformation and energy dissipation based on their location and orientation. The proposed method utilizes the well-known Bouc-Wen model for representing the hysteretic response of each LLRE. An unscented Kalman filtering approach is implemented for identifying the Bouc-Wen model parameters, and for direct estimation of the force-displacement loops experienced by each LLRE during damaging seismic events. The simulated response of a single-story building to ground motion is used for demonstrating the utility of the proposed method, which may also be applied to multistory frames in a straightforward fashion, if certain instrumen...

Blind Modal Identification of Non-Classically Damped Systems from Free or Ambient Vibration Records

A significant segment of system identification literature on civil structures is devoted to response-only identification, simply because lack of measurements of input excitations for civil structures is a fairly common scenario. In recent years, several researchers have successfully adapted a second-order blind identification (SOBI) technique—a method originally developed for “blind source separation” of audio signals—to response-only identification of mechanical and civil structures. However, this development had been confined to fully instrumented classically damped systems. While several approaches have been proposed recently for extending SOBI to non-classically damped systems, they all require additional data such as velocity or analytic signals. Herein, we present a version of SOBI that requires only acceleration signals recorded during free or ambient vibration tests, and yields the systems complex mode shapes, natural frequencies, and damping ratios. Performance of the proposed technique is demonstrated through two synthetic examples: a ten-story structure possessing a passive control system, and a soil-structure system with seven degrees of freedom (seven-DOF).

Responses of Two Tall Buildings in Tokyo, Japan, Before, During, and After the M9.0 Tohoku Earthquake of 11 March 2011

The 11 March 2011 M 9.0 Tohoku earthquake generated significant long duration shaking that propagated hundreds of kilometers from the epicenter and affected urban areas throughout much of Honshu. Recorded responses of tall buildings at several hundred km from the epicenter of the main shock and other events show tall buildings were affected by long-period motions of events at distant sources. This study presents behavioral aspects of 29-story and 30-story neighboring buildings in the Shinjuku area of Tokyo, Japan, as inferred from records retrieved from a sparse array of accelerometers deployed in the superstructures, at ground and 100 m below the ground level over a time interval covering before, during, and after the main shock. Such long-period effects are common in several regions of Japan as well as in the United States and in other seismically active countries. Permanent shifts in fundamental frequencies are observed. Drift ratios indicate possible structural nonlinear behavior occurred during the main shock. The need to consider risks to built environments from distant sources, including those in neighboring countries, is emphasized.

Extended Blind Modal Identification Technique for Nonstationary Excitations and Its Verification and Validation

AbstractRecently the authors developed an output-only (or blind) identification technique for the modal identification of structures under ambient/free vibrations. In the present study, this method is extended to incorporate nonstationary unknown inputs—a feature that existing output-only methods are unable to replicate. The method employs a so-called PARAllel FACtor technique to decompose the third-order tensor that is built using the spatial time–frequency matrices of the response signals in order to find the mode shapes and modal coordinates’ auto time–frequency distribution (TFD). The proposed method is first verified using a synthetic data set and then used to extract the modal parameters from vibration data recorded during shaking table tests on the International Institute of Earthquake Engineering and Seismology (IIEES) test structure. The accuracy of the blind identification results is assessed through comparisons with a well-established input–output identification method, namely, a well-known com...

Responses of a tall building with U.S. code-type instrumentation in Tokyo, Japan, to events before, during and after the Tohoku earthquake of 11 March 2011

The 11 March 2011 M 9.0 Tohoku earthquake generated long-duration shaking that propagated hundreds of kilometers from the epicenter and affected tall buildings in urban areas several hundred kilometers from the epicenter of the main shock. Recorded responses show that tall buildings were affected by long-period motions. This study presents the behavior and performance of a 37-story building in the Tsukuda area of Tokyo, Japan, as inferred from modal analyses of records retrieved for a time interval covering a few days before, during, and for several months after the main shock. The U.S. “code-type” array comprises three triaxial accelerometers deployed at three levels in the superstructure. Such a sparse array in a tall structure limits a reliable assessment, because its performance must be based on only the average drift ratios. Based on the inferred values of this parameter, the subject building was not structurally damaged.

Nonlinear Efficiency of Bored Pile Group under Lateral Loading

A 3×3 bored pile group consisting of nine cast-in-drilled-hole reinforced concrete shafts and a comparable single-shaft were subjected to reversed cyclic, lateral head loading to investigate group interaction effects across a wide range of lateral displacements. The piles had the same diameter of d=0.61 m and similar soil conditions; however, various equipment constraints led to two differences: (1) a fixed head (zero rotation) boundary condition for the single pile versus minor pile cap rotation in the vertical plane for the group and (2) shaft longitudinal reinforcement ratios of 1.8% for the single pile and 1% for the group piles. To enable comparisons between the test results, a calibrated model of the single pile (1.8% reinforcement) was developed and used to simulate the response of a single shaft with 1% reinforcement. Additional simulations of the pile group were performed to evaluate the effects of cap rotation on group response. By comparing the simulated responses for common conditions, i.e., 1...

Analysis and design of multimodal piezoelectric layered tubular sensors and actuators

A semi-analytic method is proposed for analyzing layered, tubular piezoelectric cylinders under axisymmetric mechanical and electric loads. Discretization occurs in the radial direction, and axial and circumferential behaviors are obtained analytically. Mechanical loads include axial forces, torque, longitudinal and circumferential surface shears, and arbitrary pressure distributions. Electric loads include voltage and charge distributions along the axis of the cylinder that may be applied on any layers surface. In the present approach, electro-mechanical loads are represented by power series in the axial coordinate. The veracity of this semi-analytic method and its implementation are demonstrated by comparing the solutions for various problems with those obtained via fully discrete finite element analyses. The analysis of a two-layered, tubular bimodal actuator that can simultaneously provide any desired pattern of axial displacement and twist at its tip-end is performed to demonstrate the utility of the present technique.

Nonlinear Load-Deflection Behavior of Reinforced Concrete Drilled Piles in Stiff Clay

AbstractThe results of three full-scale lateral load tests of cast-in-drilled-hole RC piles are evaluated to provide insights into the soil-pile interaction behavior as represented by p-y curves (p = soil reaction/length; y = lateral pile deflection) spanning from elastic conditions to mobilization of the soil capacity. The test sequence enables evaluation of the diameter effects on the p-y behavior as a result of testing two otherwise similar specimens, but with different diameters (0.6 and 1.8 m), and evaluation of the head-fixity effects as a result of testing similar specimens (with a 0.6 m diameter) under flagpole and fixed-head conditions. A constrained exhaustive search procedure that facilitates data interpretation even in the presence of severe shaft nonlinearity is introduced, which was needed because the testing was performed to full structural failure conditions. The p-y curves obtained with the present test data differ from the predictions of a standard (American Petroleum Institute) model, i...