Gokhan Pekcan

The Seismic Response of a 1:3 Scale Model R.C. Structure with Elastomeric Spring Dampers

In this experimental study, elastomeric spring dampers, which have a distinct re-centering characteristic, are used to retrofit a non-ductile, previously damaged 1/3 scale model reinforced concrete building frame structure which is subjected to a variety of ground motions in shaking table tests. A velocity dependent analytical model is developed and verified for the elastomeric spring dampers. This model is implemented in the widely available non-linear dynamic time history analysis computer program DRAIN-2DX to produce response predictions which are in good agreement with experimental observations. The elastomeric spring damper devices significantly attenuate the seismic response of the structure and provide a considerable amount of energy dissipation while the main non-ductile reinforced concrete structural load carrying elements remain elastic. The effect of varying the damper configuration on the structural response was also investigated.

Assessment of seismic performance of skew reinforced concrete box girder bridges

The seismic vulnerability of highway bridges remains an important problem and has received increased attention as a consequence of unprecedented damage observed during several major earthquakes. A significant number of research studies have examined the performance of skew bridges under service and seismic loads. The results of these studies are particularly sensitive to modeling assumptions in view of the interacting parameters. In the present study, three-dimensional improved beam-stick models of two-span highway bridges with skew angles varying from 0° to 60° are developed to investigate the seismic response characteristics of skew box girder bridges. The relative accuracy of beam-stick models is verified against counterpart finite element models. The effect of various parameters and conditions on the overall seismic response was examined such as skew angle, ground motion intensity, soil condition, abutment support conditions, bridge aspect ratio, and foundation-base conditions. The study shows that the improved beam-stick models can be used to conduct accurate nonlinear time history analysis of skew bridges. Skew angle and interacting parameters were found to have significant effect on the behavior of skewed highway bridges. Furthermore, the performance of shear keys may have a predominant effect on the overall seismic response of the skew bridges.

Floor Accelerations in Yielding Special Moment Resisting Frame Structures

Severe damage to acceleration sensitive nonstructural components in recent earthquakes has resulted in unprecedented losses. Recent research has been aimed at increasing the understanding of acceleration demands on nonstructural components in buildings. This investigation subjects a set of four special moment resisting frame (SMRF) building models to a suite of 21 far-field ground motions using the incremental dynamic analysis procedure. Full three-dimensional models including floor slabs are used to extract both the horizontal and vertical responses. Floor acceleration response spectra are generated to assess the acceleration demands on elastic nonstructural components. Changes to the current code provisions that include the influence of structural period are proposed. An alternative design approach that directly amplifies the ground acceleration spectrum to achieve the desired floor acceleration spectrum is presented.

Analytical Fragility Functions for Horizontally Curved Steel I-Girder Highway Bridges

Horizontally curved bridges were investigated following a statistical evaluation of typical details commonly used in the United States. Both seismically and non-seismically designed bridges are considered where the primary differences are in column confinement, type of bearings and abutment support length. Columns and bearings were found to be the most seismically vulnerable components for both categories. Central angle was identified as an important factor that increases the demand on various components, particularly columns. Furthermore, larger angles lead to increased deformations at the supports which adversely affect the seismic vulnerability. Consistent with the fragility curves that account for the central angle explicitly, a second set of system fragility curves were introduced for cases when central angle is not specified such as the case in the National Bridge Inventory. Comparison of fragility parameters to those suggested by HAZUS-MH highlighted the need for revisions to account for current design practices and central angle.

Response of a 2-story test-bed structure for the seismic evaluation of nonstructural systems

A full-scale, two-story, two-by-one bay, steel braced-frame was subjected to a number of unidirectional ground motions using three shake tables at the UNR-NEES site. The test-bed frame was designed to study the seismic performance of nonstructural systems including steel-framed gypsum partition walls, suspended ceilings and fire sprinkler systems. The frame can be configured to perform as an elastic or inelastic system to generate large floor accelerations or large inter story drift, respectively. In this study, the dynamic performance of the linear and nonlinear test-beds was comprehensively studied. The seismic performance of nonstructural systems installed in the linear and nonlinear test-beds were assessed during extreme excitations. In addition, the dynamic interactions of the test-bed and installed nonstructural systems are investigated.

Impact of column-to-beam strength ratio on the seismic response of steel MRFs

The strong-column/weak-beam seismic design concept in moment resisting frames is perhaps one of the least well-understood design provisions. This study is aimed at improving the understanding of the effect of column-to-beam strength ratio (CBSR) on several seismic performance measures. Through nonlinear analyses of 3-, 9-, and 20-story moment resisting frame, the impacts of CBSR on member ductility demands, maximum inter-story drifts, and floor acceleration amplifications are investigated. For each frame, the value of CBSR is varied by changing the yield strength of the material and/or by altering sizes of the columns. The probabilities of exceeding certain performance limits are investigated through fragility analyses. The single curvature bending of the columns within a story is found to be inevitable due to the participation of higher modes of vibration. Consequently, under large ground motions, the yielding of the columns is expected even for CBSRs larger than 2.0. The fragility relationships were used to calculate the design force modification factors needed for achieving a comparable probability of column yielding for different values of CBSR. The values of the yield base shear and the inter-story drifts were found to depend more on the strength of the beams than the value of CBSR. The floor acceleration amplification was found to be the least sensitive demand parameter to the CBSR.

Design of a Test-Bed Structure for Shake Table Simulation of the Seismic Performance of Nonstructural Systems

As part of the project entitled “NEESR-GC: Simulation of the Seismic Performance of Nonstructural System,” a series of system-level full-scale experiments of ceilings-piping-partition systems will be conducted at the University of Nevada, Reno NEES Site. This project is aimed at understanding the seismic response of these systems and their interaction with each other and the parent structure. A two-story, two-bay steel braced frame spanning across three biaxial shake tables was designed as a Test-Bed structure to simulate a variety of dynamic environments. After introducing the design considerations of the Test-Bed structure within this paper, the method proposed to develop the shake table drive motions is explained. To obtain the drive motion, a transfer function (TF) was formulated for a multi-support dynamic system under differential support excitation and combined with a TF previously developed for target floor acceleration of a generic structure. A suitable high-pass filter was suggested to limit exerted demands on the shake tables. 1191 Structures Congress 2011

A self-sensing magnetorheological elastomer-based adaptive bridge bearing with a wireless data monitoring system

This study presents an adaptive bridge bearing that can sense structural loads and tune its properties to mitigate structural vibrations. The bearing utilizes magnetorheological elastomer (MRE) layers which allow for an increased stiffness induced with a magnetic field. The system also features a MRE-based sensing system for sensing the structural wind and traffic load. The sensing system is capable of transmitting data wirelessly to a central logging computer for monitoring bridge performance and sending alerts in the case of a major event. The capability of the MRE-based sensing system for sensing structural loads and wireless transmission of data were investigated. The adaptive bridge bearing incorporates a closed-loop magnetic circuit that results in an enhanced magnetic field in the MRE layers. Results show the sensitivity of the MRE-based sensors and the performance of the wireless system, as well as the design and analysis of the tunable bridge bearing.

Analytical Modeling of Horizontally Curved Steel Girder Highway Bridges for Seismic Analysis

This article introduces a generic modeling approach that is suitable for static and dynamic analysis, and response assessment of highway bridges with varying levels of irregularities. The proposed approach and modeling recommendations are based on grillage modeling rules that allows explicit representation of various types of details and components. The validity and accuracy of the proposed approach is demonstrated against three-dimensional finite element models as well as experimentally recorded response various benchmark bridges. While achieving remarkable accuracy, the required analysis time was also reduced up to 80%, making the proposed approach suitable for computationally intensive studies.

Analytical Fragility Curves for a Class of Horizontally Curved Box-Girder Bridges

ABSTRACT Analytical fragility curves were developed for curved single-frame concrete box-girder bridges with seat-type abutments. The bridges incorporated the current seismic design considerations and modern details that were recently adopted by CALTRANS. Fragility curves demonstrated that columns were the most vulnerable components, while the modern seismic details successfully protected the abutment piles from damage during large earthquakes. Increasing the subtended angle affected the seismic vulnerability at both the component and system levels. Functional relationships were proposed to evaluate the seismic vulnerability of curved bridges. Moreover, fragility curve parameters were shown to depend on soil condition and spectral characteristics of ground motions.