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Results for “Journal of Structural Engineering”

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At least 19 recordsLinked to original sources
USGS2014

Pros and cons of rotating ground motion records to fault-normal/parallel directions for response history analysis of buildings

According to the regulatory building codes in the United States (e.g., 2010 California Building Code), at least two horizontal ground motion components are required for three-dimensional (3D) response history analysis (RHA) of building structures. For sites within 5 km of an active fault, these records should be rotated to fault-normal/fault-parallel (FN/FP) directions, and two RHAs should be performed separately (when FN and then FP are aligned with the transverse direction of the structural axes). It is assumed that this approach will lead to two sets of responses that envelope the range of possible responses over all nonredundant rotation angles. This assumption is examined here, for the first time, using a 3D computer model of a six-story reinforced-concrete instrumented building subjected to an ensemble of bidirectional near-fault ground motions. Peak values of engineering demand parameters (EDPs) were computed for rotation angles ranging from 0 through 180° to quantify the difference between peak values of EDPs over all rotation angles and those due to FN/FP direction rotated motions. It is demonstrated that rotating ground motions to FN/FP directions (1) does not always lead to the maximum responses over all angles, (2) does not always envelope the range of possible responses, and (3) does not provide maximum responses for all EDPs simultaneously even if it provides a maximum response for a specific EDP.

Journal of Structural Engineering↗
USGS1993

Seismic response of eccentrically braced tall buildings

Spectral analysis and system identification techniques are used to analyze a set of acceleration reponse records obtained during the Loma Prieta earthquake from the 47-story, moment-resisting framed and eccentrically braced Embarcadero Building (EMB). The EMB was constructed in 1979 based on the 1976 Uniform Building Code requirements and a design response spectra defined by two levels of earthquake performances. The EMB is in the lower market area of San Francisco, which is of great interest to the engineering community because of the area's soft soil characteristics that amplify ground motions originating at long distances, and because the Embarcadero freeway suffered extensive damage during the earthquake and was razed in 1991. The first modal frequencies of the building at approximately 0.19 Hz (north-south) and 0.16 Hz (east-west) are identified. The torsional response and rocking motions of the building are insignificant. Discontinuity of stiffness and mass at the 40th floor level causes significant response issues above that floor such as excessive drift ratios.

Journal of Structural Engineering↗
USGS2011

Modal-pushover-based ground-motion scaling procedure

Earthquake engineering is increasingly using nonlinear response history analysis (RHA) to demonstrate the performance of structures. This rigorous method of analysis requires selection and scaling of ground motions appropriate to design hazard levels. This paper presents a modal-pushover-based scaling (MPS) procedure to scale ground motions for use in a nonlinear RHA of buildings. In the MPS method, the ground motions are scaled to match to a specified tolerance, a target value of the inelastic deformation of the first-mode inelastic single-degree-of-freedom (SDF) system whose properties are determined by the first-mode pushover analysis. Appropriate for first-mode dominated structures, this approach is extended for structures with significant contributions of higher modes by considering elastic deformation of second-mode SDF systems in selecting a subset of the scaled ground motions. Based on results presented for three actual buildings-4, 6, and 13-story-the accuracy and efficiency of the MPS procedure are established and its superiority over the ASCE/SEI 7-05 scaling procedure is demonstrated.

Journal of Structural Engineering↗
USGS1990

Method to estimate center of rigidity using vibration recordings

A method to estimate the center of rigidity of buildings by using vibration recordings is presented. The method is based on the criterion that the coherence of translational motions with the rotational motion is minimum at the center of rigidity. Since the coherence is a function of frequency, a gross but frequency-independent measure of the coherency is defined as the integral of the coherence function over the frequency. The center of rigidity is determined by minimizing this integral. The formulation is given for two-dimensional motions. Two examples are presented for the method; a rectangular building with ambient-vibration recordings, and a triangular building with earthquake-vibration recordings. Although the examples given are for buildings, the method can be applied to any structure with two-dimensional motions.

Journal of Structural Engineering↗
USGS1991

Torsional response of unique building

Acceleration response records obtained during the October 1, 1987 Whittier‐Narrows earthquake ( M s = 5.6 ) "> ( M s = 5.6 ) from the 32‐story, vertically irregular 1100 Wilshire Finance Building, of which the cross section changes from a nominally rectangular shape to a triangular one, are analyzed. The building was instrumented with 21 channels of synchronized sensors, consisting of 12 uniaxial accelerometers deployed throughout the superstructure and connected to a central recording system and three triaxial strong‐motion accelerographs in the basement. At each of the four levels of the superstructure, three uniaxial accelerometers were deployed, two parallel and at a distance apart, and the third one orthogonal to the parallel pair. The records permit the identification of the predominantly coupled torsional‐translational response of the building and the associated frequency at approximately 0.7–0.8 Hz from the difference between accelerations recorded by the parallel pairs of accelerometers at different levels. This mode corresponds to the second torsional mode. A translational mode at 0.3 Hz is also identified from the records. The center of rigidity of any instrumented level is identified by minimizing the coherence between the relative accelerations and the translational acceleration. Employing system identification techniques provides the modal damping percentage for the second torsional mode as 6–7%.

California↗
USGS1991

Seismic response of transamerical building. I. Data and preliminary analysis

The objective of this paper is to present preliminary analyses of a set of acceleration response records obtained during the October 17, 1989 Loma Prieta earthquake (Ms = 7.1) from the 60-story vertically tapered, pyramid-shaped Trans-america Building-a landmark of San Francisco. The building was instrumented in 1985 with 22 channels of synchronized sensors consisting of 13 uniaxial accelerometers deployed throughout the structure and connected to a central recording system and three triaxial strong-motion accelerographs at three different levels of the structure. No free-field accelerographs are at the site. The acceleration records permit the study of the behavior of this unique structure. The predominant translational response of the building and the associated frequency at approximately 0.28 Hz are identified from the records and their Fourier amplitude spectra. The records do not indicate any significant torsional motion. However, there is rocking type soil-structure interaction, and an associated frequency of approximately 2.0 Hz is identified from the Fourier amplitude spectra of the differential motions between the ground level and that at the basement. In addition, the response spectra for the basement motions indicate significant resonance in both directions at a period of approximately 0.5 seconds.

Journal of Structural Engineering↗
USGS1991

Seismic response of transamerica building. II. System identification

A detailed analysis of the recorded seismic response of the Transamerica Building during the October 17, 1989 Loma Prieta earthquake is presented. The system identification algorithm used for the analysis is based on the discrete-time linear filtering approach with least-squares approximation, and assumes a multi-input, single-output model for the building. Fifteen modes in the north-south direction, and 18 modes in the east-west direction are identified from the records. The analysis shows that the building's response to the earthquake was dominated by a coupled mode of vibration at 0.28 Hz in the southwest-northeast direction, which is almost parallel to one of the diagonals in the building's square cross section. The reason for this behavior is the symmetry of the building's structural characteristics, as well as the strong polarization of the S-waves of the earthquake. Several higher modes of the building were excited during the strong-motion part of the earthquake. The results also show a significant amount of rocking in the building at a frequency of 2.15 Hz.

Journal of Structural Engineering↗
USGS1992

Seismic response of Pacific Park Plaza. I. Data and preliminary analysis

The objective of this paper is to present analyses of a set of acceleration response records obtained during the October 17, 1989 Loma Prieta earthquake (Ms = 7.1) from the 30-story, three-winged, ductile moment-resistant reinforced-concrete-framed Pacific Park Plaza Building, located in Emeryville, east of San Francisco, Calif. The building was constructed in 1983, and instrumented in 1985 with 21 channels of synchronized uniaxial accelerometers deployed throughout the structure, and three channels of accelerometers located at free-field outside on the north side of the building, all connected to a central recording system. In addition, a triaxial strong-motion accelerograph is deployed at free-field on the south side of the building. The predominant response modes of the building and the associated frequencies at approximately 0.4 Hz and 1.0 Hz are identified visually from the unprocessed records, and also from Fourier amplitude spectra of the processed records, which, as expected, reveal significant torsional motion. In addition, the response spectra of the free-field and basement motions are very similar. These spectra show that significant structural resonances at higher modes influence both the ground level and the free-field motions, thus rising the question as to the definition of free-field motion, at least at this site. This part of the paper includes the preliminary analyses of the data acquired from this building. Part 2 of the paper provides detailed analyses of the data using system identification techniques.

Journal of Structural Engineering↗
USGS1993

Seismic responses of two adjacent buildings. I. Data and analyses

In this two-part paper, responses of two, adjacent, seven-story buildings in Norwalk, California, to the Whittier-Narrows, Calif, earthquake of Oct. 1, 1987 are studied. Building A, instrumented according to code recommendations, and building B, extensively instrumented, are offset by 16.3 m from one another. The data set includes motions from the superstructure of both buildings, from a downhole below the foundation of building B, and from three free-field sites. Part I of the paper includes descriptions of the buildings, site, instrumentation, and analysis of the data of each building. System identification and spectral analysis techniques are employed in part I. Building A has identical first-mode frequencies of 0.65 Hz for both building axes. The strong-motion response characteristics of building A are considerably different than those determined from low-amplitude tests. Building B has fundamental modes at 0.76 Hz and 0.83 Hz in the major and minor axes, respectively. Torsional and diaphragm effects in building B are negligible.

Journal of Structural Engineering↗
USGS1994

Structural response to 3D simulated earthquake motions in San Bernardino Valley

Structural repsonse to one- and three-dimensional (3D) simulated motions in San Bernardino Valley from a hypothetical earthquake along the San Andreas fault with moment magnitude 6.5 and rupture length of 30km is investigated. The results show that the ground motions and the structural response vary dramatically with the type of simulation and the location. -from Authors

Journal of Structural Engineering↗
USGS1999

Wave-propagation formulation of seismic response of multistory buildings

This paper presents a discrete-time wave-propagation method to calculate the seismic response of multistory buildings, founded on layered soil media and subjected to vertically propagating shear waves. Buildings are modeled as an extension of the layered soil media by considering each story as another layer in the wave-propagation path. The seismic response is expressed in terms of wave travel times between the layers and wave reflection and transmission coefficients at layer interfaces. The method accounts for the filtering effects of the concentrated foundation and floor masses. Compared with commonly used vibration formulation, the wave-propagation formulation provides several advantages, including simplicity, improved accuracy, better representation of damping, the ability to incorporate the soil layers under the foundation, and providing better tools for identification and damage detection from seismic records. Examples are presented to show the versatility and the superiority of the method.

Journal of Structural Engineering↗
USGS2011

Scaling earthquake ground motions for performance-based assessment of buildings

The impact of alternate ground-motion scaling procedures on the distribution of displacement responses in simplified structural systems is investigated. Recommendations are provided for selecting and scaling ground motions for performance-based assessment of buildings. Four scaling methods are studied, namely, (1) geometric-mean scaling of pairs of ground motions, (2) spectrum matching of ground motions, (3) first-mode-period scaling to a target spectral acceleration, and (4) scaling of ground motions per the distribution of spectral demands. Data were developed by nonlinear response-history analysis of a large family of nonlinear single degree-of-freedom (SDOF) oscillators that could represent fixed-base and base-isolated structures. The advantages and disadvantages of each scaling method are discussed. The relationship between spectral shape and a ground-motion randomness parameter, ε, is presented. A scaling procedure that explicitly considers spectral shape is proposed.

Journal of Structural Engineering↗
USGS2021

Seismic response of a typical shear-wall dominated high-rise condominium building during the January 7, 2020 Mw6.4 Indios, Puerto Rico earthquake

Seismic response records were retrieved from the monitored 21-story (53.26-m-tall) typical Puerto Rican reinforced-concrete shear-wall dominated El Castillo Building in Mayaguez, 50 km from the mainshock epicenter of the January 7, 2020, M w 6.4 offshore Indios, Puerto Rico earthquake. The shear-wall-to-floor areas of the building are 0.97 and 3.49 in the longitudinal and transverse directions, respectively, and have a slenderness ratio of 3.0 in the transverse direction. Basement and top-floor peak accelerations were 5% g and 12.8% g, respectively. Additionally, records from a nearby free-field station indicate a site period of 0.16 s. No visible damage was observed in the building after the earthquake. Spectral ratios and system identification allow identification of the transverse, longitudinal, and torsional fundamental periods as 0.97, 0.88, and 0.81 s, respectively, and are consistent with ASCE/SEI 7-16 (2017) formula. Damping percentages are 4.5%, 3.4%, and 2.2%, respectively. The maximum drift ratios are 0.20% and 0.12% in the longitudinal and transverse directions, well below the damage threshold for structural elements of ∼0.5%.

Mayaguez, San Juan↗
USGS2023

The new Self Anchored Suspension (SAS) Bridge of the San Francisco Bay Bridge System: A preliminary study of its response and behavior during a small earthquake

Seismic behavior and performance of the new Self- Anchored Suspension (SAS) Bridge of the San Francisco Bay Bridge System is studied using response data recorded during the October 14, 2019, 𝑀𝑤⁢4.6 Pleasant Hill earthquake. The new bridge went into service within the last decade as a replacement for the older truss bridge that spanned between Yerba Buena Island and East Bay. During the October 19, 1989, M6.9 Loma Prieta earthquake, which occurred ∼100 km away from the Bay Bridge, a section of the upper deck of the old truss bridge fell onto the lower deck—thus closing this important lifeline between San Francisco and East Bay. The new SAS Bridge (as well as the rest of the Bay Bridge) is instrumented by the California Strong Motion Instrumentation Program (CSMIP). The unique SAS Bridge is suspended by a single tower that is pivotal in trafficking the cable and hanger system to support the eastbound (E) and westbound (W) decks. At both the west and east ends of the SAS, there is a hinge system that connects the W and E decks to the skyways leading to highways. For the west side, the SAS is led to a tunnel at Yerba Buena Island. The response data analyses highlight the complex and yet identifiable coupled response of the deck, tower, and cable system. Using system identification methods including spectral analyses of both acceleration and displacement time history data, the fundamental frequencies (periods) and critical damping percentages are extracted for the main components (tower, deck, and cables) of the bridge where the sensors are deployed. Frequencies (periods) are then compared with the values computed during the design and analysis process of the bridge. The analyses in this paper showed that there is strong evidence of a beating effect attributed to low critical damping percentages and coupled modes. A possible correlation of fundamental periods of such suspension bridges with their span lengths is discussed. The beating effect and period versus span length can be significant topics for further research.

California↗
USGS1989

Adaptive modeling, identification, and control of dynamic structural systems. I. Theory

A concise review of the fheory of adaptive modeling, identification, and control of dynamic structural systems based on discrete‐time recordings is presented. Adaptive methods have four major advantages over the classical methods: (1) Removal of the noise from the signal is done over the whole frequency band; (2) time‐varying characteristics of systems can be tracked; (3) systems with unknown characteristics can be controlled; and (4) a small segment of the data is needed during the computations. Included in the paper are the discrete‐time representation of single‐input single‐output (SISO) systems, models for SISO systems with noise, the concept of stochastic approximation, recursive prediction error method (RPEM) for system identification, and the adaptive control. Guidelines for model selection and model validation and the computational aspects of the method are also discussed in the paper. The present paper is the first of two companion papers. The theory given in the paper is limited to that which is necessary to follow the examples for applications in structural dynamics presented in the second paper.

Journal of Engineering Mechanics↗
USGS1987

Seismic response of dam with soil‐structure interaction

An analytical solution to the response of a long trapezoidal‐section dam on a foundation consisting of an elastic half‐space and subjected to simulated earthquake morion is developed. An optimum seismic design is achieved when the cross section of the dam is triangular. The effect of soil structure interaction is to lower the strain occurring in the dam.

Journal of Engineering Mechanics↗
USGS2004

Microforms in gravel bed rivers: Formation, disintegration, and effects on bedload transport

This research aims to advance current knowledge on cluster formation and evolution by tackling some of the aspects associated with cluster microtopography and the effects of clusters on bedload transport. The specific objectives of the study are (1) to identify the bed shear stress range in which clusters form and disintegrate, (2) to quantitatively describe the spacing characteristics and orientation of clusters with respect to flow characteristics, (3) to quantify the effects clusters have on the mean bedload rate, and (4) to assess the effects of clusters on the pulsating nature of bedload. In order to meet the objectives of this study, two main experimental scenarios, namely, Test Series A and B (20 experiments overall) are considered in a laboratory flume under well-controlled conditions. Series A tests are performed to address objectives (1) and (2) while Series B is designed to meet objectives (3) and (4). Results show that cluster microforms develop in uniform sediment at 1.25 to 2 times the Shields parameter of an individual particle and start disintegrating at about 2.25 times the Shields parameter. It is found that during an unsteady flow event, effects of clusters on bedload transport rate can be classified in three different phases: a sink phase where clusters absorb incoming sediment, a neutral phase where clusters do not affect bedload, and a source phase where clusters release particles. Clusters also increase the magnitude of the fluctuations in bedload transport rate, showing that clusters amplify the unsteady nature of bedload transport. A fourth-order autoregressive, autoregressive integrated moving average model is employed to describe the time series of bedload and provide a predictive formula for predicting bedload at different periods. Finally, a change-point analysis enhanced with a binary segmentation procedure is performed to identify the abrupt changes in the bedload statistic characteristics due to the effects of clusters and detect the different phases in bedload time series using probability theory. The analysis verifies the experimental findings that three phases are detected in the bedload rate time series structure, namely, sink, neutral, and source. ?? ASCE / JUNE 2004.

Journal of Hydraulic Engineering↗