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Articles 1 - 14 of 14
Full-Text Articles in Engineering
Effects Of Friction On The Dynamic Behavior Of Flexible Rocking Bodies, S. Mohammadreza Farooghi Mehr, Christine E. Wittich
Effects Of Friction On The Dynamic Behavior Of Flexible Rocking Bodies, S. Mohammadreza Farooghi Mehr, Christine E. Wittich
Department of Civil and Environmental Engineering: Faculty Publications
Flexible rocking bodies are freestanding structures that are free to deform and rock, potentially overturning, when subject to ground excitation. Prior research on the seismic behavior of this type of structure typically assumed sufficient friction at the ground surface to avoid sliding motion. However, experimental observations showed that this assumption was often violated and structures demonstrated non-negligible sliding during their responses. The overarching goal of this study is to evaluate the impact of sliding on the overturning response of flexible rocking bodies. To this end, a two-dimensional analytical model was developed in a Lagrangian formulation, which is presented in this …
Post-Earthquake Assessment And Numerical Modeling Of Freestanding Heritage Structures, M. Khalid Saifullah, Christine E. Wittich
Post-Earthquake Assessment And Numerical Modeling Of Freestanding Heritage Structures, M. Khalid Saifullah, Christine E. Wittich
Department of Civil and Environmental Engineering: Faculty Publications
Historic and heritage structures are particularly vulnerable to earthquakes, where damage or collapse can not only lead to loss of a structure but also the loss of irreplaceable heritage. Many heritage structures can be classified as freestanding (detached) structures, including unreinforced masonry walls, classical multi-drum columns, and statue-pedestal systems. However, the seismic response of freestanding structures (sliding, rocking, rock-slide, overturning) is poorly predicted by existing methods due to geometric non-linearities as well as sensitivity to interface conditions and modeling parameters. Previous studies have focused on analytical modeling of simplified systems and/or experimentation under controlled laboratory conditions. In contrast, this paper …
Damage Assessment Of A Sixteen Story Building Following The 2017 Central Mexico Earthquake, Yijun Liao, Richard L. Wood, M Ebrahim Mohammadi, Kanchan Devkota, Christine E. Wittich
Damage Assessment Of A Sixteen Story Building Following The 2017 Central Mexico Earthquake, Yijun Liao, Richard L. Wood, M Ebrahim Mohammadi, Kanchan Devkota, Christine E. Wittich
Department of Civil and Environmental Engineering: Faculty Publications
The 2017 M7.1 Central Mexico Earthquake caused significant infrastructural damage in the Mexico City area. The earthquake contained a significant pulse in the long period, resulting in numerous buildings severely damaged or collapsed. This paper discusses a reinforced concrete building which was still partially occupied post-earthquake. The building’s interior walls were examined to have substantial damage, including some extensive cracking. In January 2018, the authors visited the structure and collected detailed assessment data. The data collection included ground-based lidar scans and recorded ambient vibrations of the damaged structure using accelerometers. Eleven scans were collected from the four exterior facades to …
Post-Fire Damage Geospatial Assessment Via Point Clouds Of A Highway Bridge Structure, Yijun Liao, M Ebrahim Mohammadi, Richard L. Wood, Christine E. Wittich
Post-Fire Damage Geospatial Assessment Via Point Clouds Of A Highway Bridge Structure, Yijun Liao, M Ebrahim Mohammadi, Richard L. Wood, Christine E. Wittich
Department of Civil and Environmental Engineering: Faculty Publications
This paper discusses the quantitative post-fire damage assessment of a steel girder bridge via point clouds. In this case study, the point cloud was collected using light detection and ranging (lidar) for a detailed geometric and shape analysis. The out-of-plane deformation was analyzed to locate and quantify buckling across the length of the steel girders.
Efficient Intensity Measures Of Slide-Rocking Structures For Precariously Balanced Rocks, Taylor J. Knickerbocker, Christine E. Wittich
Efficient Intensity Measures Of Slide-Rocking Structures For Precariously Balanced Rocks, Taylor J. Knickerbocker, Christine E. Wittich
Department of Civil and Environmental Engineering: Faculty Publications
Precariously balanced rocks (PBRs) and other fragile geologic features are important in both the engineering and seismological communities since they are indicative of the maximum ground motion at a site over the rock’s lifetime. Precariously balanced rocks are individual or stacks of freestanding rocks that tend to respond in rigid body modes when subject to seismic excitation – namely, rocking, sliding, slide-rocking, and free-flight, which can lead to overturning. The seismic response of freestanding structures, such as PBRs, is known to be extremely sensitive to small changes in geometry, position, and earthquake excitation. As such, deterministic methods are limited in …
3-D Reconstructions And Numerical Simulations Of Precarious Rocks In Southern California, Christine E. Wittich, Tara C. Hutchinson, J. Desanto, D. Sandwell
3-D Reconstructions And Numerical Simulations Of Precarious Rocks In Southern California, Christine E. Wittich, Tara C. Hutchinson, J. Desanto, D. Sandwell
Department of Civil and Environmental Engineering: Faculty Publications
Reliable estimates of seismic hazard are essential for the development of resilient communities; however, estimates of rare, yet high intensity earthquakes are highly uncertain due to a lack of observations and recordings. Lacking this data, seismic hazard analyses may be based on extrapolations from earthquakes with more moderate return periods, which can lead to physically unrealistic earthquake scenarios. However, the existence of certain precariously balanced rocks (PBRs) has been identified as an indicator of an upper bound ground motion, which precludes toppling of the balanced rock, over its lifetime. To this end, a survey of PBRs was conducted in proximity …
Mechanical Characterization Of Polysilicon Mems: A Hybrid Tmcmc/Pod-Kriging Approach, Ramin Mirzazadeh, Saeed Eftekhar Azam, Stefano Mariani
Mechanical Characterization Of Polysilicon Mems: A Hybrid Tmcmc/Pod-Kriging Approach, Ramin Mirzazadeh, Saeed Eftekhar Azam, Stefano Mariani
Department of Civil and Environmental Engineering: Faculty Publications
Microscale uncertainties related to the geometry and morphology of polycrystalline silicon films, constituting the movable structures of micro electro-mechanical systems (MEMS), were investigated through a joint numerical/experimental approach. An on-chip testing device was designed and fabricated to deform a compliant polysilicon beam. In previous studies, we showed that the scattering in the input–output characteristics of the device can be properly described only if statistical features related to the morphology of the columnar polysilicon film and to the etching process adopted to release the movable structure are taken into account. In this work, a high fidelity finite element model of the …
Investigation Of Rapid Remote Sensing Techniques For Forensic Wind Analyses, Yijun Liao, Richard L. Wood, Mohammad Ebrahim Mohammadi, Peter J. Hughes, J. Arn Womble
Investigation Of Rapid Remote Sensing Techniques For Forensic Wind Analyses, Yijun Liao, Richard L. Wood, Mohammad Ebrahim Mohammadi, Peter J. Hughes, J. Arn Womble
Department of Civil and Environmental Engineering: Faculty Publications
Perishable damage data resulting from severe windstorms require efficient and rapid field collection techniques. Such datasets permit forensic damage investigations and characterization of civil infrastructure. Ultimately, observed structural damage serves as a proxy approach to estimate wind speeds for storms that include hurricanes, tornadoes, straight-line winds, etc. One of the more common methods to collect, preserve, and reconstruct three-dimensional damage scenes is the use of an unmanned aerial system (UAS), commonly known as a drone. Onboard photographic payloads permit scene reconstruction via structure-from-motion; however, such approaches often require direct site access and survey points for accurate results, which limit its …
Behavior Of Cold-Formed Steel Metal Industrial Buildings, Adrianna M. Early, Mohammad Ebrahim Mohammadi, Richard L. Wood, Kara D. Peterma
Behavior Of Cold-Formed Steel Metal Industrial Buildings, Adrianna M. Early, Mohammad Ebrahim Mohammadi, Richard L. Wood, Kara D. Peterma
Department of Civil and Environmental Engineering: Faculty Publications
This paper presents research focused on understanding the observed behavior of cold-formed steel (CFS) metal buildings during Hurricane Harvey, which made landfall Friday, August 25, 2017 between Port Aransas and Port O’Connor, Texas. Through the Geotechnical Extreme Event Reconnaissance (GEER) association (funded by the National Science Foundation) a team of structural engineers and researchers performed rapid and detailed assessments of structural damage caused by the hurricane. The National Science Foundation gathered photographs, damage assessments sheets, and three-dimensional laser point cloud data of severely damaged cold-formed steel industrial buildings. The Port Aransas County Airport experienced severe damage to several cold-formed steel …
Post-Earthquake Structural Damage Assessment Through Point Cloud Data, Mohammad Ebrahim Mohammadi, Richard L. Wood
Post-Earthquake Structural Damage Assessment Through Point Cloud Data, Mohammad Ebrahim Mohammadi, Richard L. Wood
Department of Civil and Environmental Engineering: Faculty Publications
Structural damage assessment following an extreme event can provide valuable information and insight into unanticipated damage and failure modes to improve design philosophies and design codes as well as reduce vulnerability. Oftentimes, structural engineers create finite element models (FEM) of the structure in which numerous model parameters require calibration to simulate the current state. This information may include structural plan details (geometry), material characteristics (strength and stiffness parameters), as well as observed damage patterns (cracks, spalling, etc.). Ground-based lidar (GBL) scans and Structure-from-Motion (SfM) can rapidly capture dimensionally accurate point clouds of the structure or facility of interest. Furthermore, point …
Damage Assessment Of Built-Up Areas Via Uas-Sfm Derived Point Cloud Data, Mohammad Ebrahim Mohammadi, Richard L. Wood
Damage Assessment Of Built-Up Areas Via Uas-Sfm Derived Point Cloud Data, Mohammad Ebrahim Mohammadi, Richard L. Wood
Department of Civil and Environmental Engineering: Faculty Publications
In the aftermath of extreme events (e.g., earthquakes, tsunami, tornados, etc.), rapid and reliable identification of the damage in a built-up area are crucial in to rescue, recovery, and reconstruction operations. While it is critical to conduct efficient emergency response management, lack of classified or tagged damaged regions due to communications and accessibility limitations can further delay recovery operations, rescue efforts, and resource management. Furthermore, critical and perishable damage scenes can also be lost during recovery and cleanup operations immediately following the event. In recent decades, advances in remote sensing technologies demonstrate a great potential to perform rapid reconnaissance and …
Experimental Modal Analysis And Seismic Mitigation Of Statue-Pedestal Systems, Christine E. Wittich, Tara C. Hutchinson
Experimental Modal Analysis And Seismic Mitigation Of Statue-Pedestal Systems, Christine E. Wittich, Tara C. Hutchinson
Department of Civil and Environmental Engineering: Faculty Publications
The seismic protection of cultural heritage, particularly statues, is a critical issue due to its high cultural significance, difficulty to repair or replace artifacts, and observed poor behavior during past earthquakes. Recent research has explored analysis techniques and methodologies for predicting the seismic response of statues; however, these studies typically assume the statue to be either freestanding or rigidly attached. The seismic response of statues with these different boundary conditions varies widely and therefore accurate characterization is critical. While modern mounting techniques aim to rigidly attach a statue to the floor or to a pedestal, the degree of rigidity of …
Lidar Scanning With Supplementary Uav Captured Images For Structural Inspections, Richard L. Wood, Mohammad Ebrahim Mohammadi
Lidar Scanning With Supplementary Uav Captured Images For Structural Inspections, Richard L. Wood, Mohammad Ebrahim Mohammadi
Department of Civil and Environmental Engineering: Faculty Publications
Structural assessment using remote sensing technologies can be performed efficiently and effectively using such technologies as LiDAR (light detection and ranging). LiDAR can be employed for various structural assessments, such as as-built conditions for a newly constructed facility, routine inspection during its service life, or structural collapse evaluation after a natural hazard or extreme event. However, the main disadvantage of LiDAR is that it is a line-of-sight technology that can result in significant occlusions. Architectural or structural components can be partially or fully occluded by another object with respect to the location of the laser scanner. Supplemental photogrammetry techniques, such …
Equipment Fragility Due To Shock Response, Christopher Y. Tuan
Equipment Fragility Due To Shock Response, Christopher Y. Tuan
Department of Civil and Environmental Engineering: Faculty Publications
Because of its simplicity, the shock response spectrum has become widely used as a means of describing the shock responses and fragilities of structures and equipment. This paper focuses on the drawbacks of using the shock response spectrum for defining equipment shock tolerance. A cantilever beam with a tip mass was used to model a hypothetical piece of equipment subjected to strong ground motion such as that caused by an explosion. The exact solution from a detailed modal analysis shows that multiple modes of response were excited. Contributions from higher modes can be more predominant than that from the fundamental …