Post-Earthquake Assessment and Numerical Modeling of Freestanding Heritage Structures

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 presents the post-earthquake assessment of multiple statue-pedestal systems following the 2014 South Napa earthquake. The objective is to examine the seismic response of these complex freestanding structural systems, under real-world conditions, to elucidate key characteristics of the response and evaluate the influence of both physical and modeling parameters. In this study, the responses of the selected statues from the Napa area are numerically simulated under original ground motion records. The complex geometries of the statues are represented using meshes generated from lidar-based point clouds obtained during post-earthquake reconnaissance. The responses of the statues are simulated using the Distinct Element Method (DEM) where the statue and pedestal have been modeled as rigid blocks with deformation concentrated at the joints (i.e. interface of statue and pedestal or pedestal and ground). The study analyzes the results of the numerical simulations in comparison to the observed physical response during the earthquake event. Results emphasize the significant impact of ground motion parameters (e.g. directionality), the presence of soil, and modeling parameters such as contact stiffness

Efficient Intensity Measures of Slide-Rocking Structures for Precariously Balanced Rocks

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 their application to PBRs and reliable probabilistic relationships are necessary. Previous probabilistic studies on freestanding structures and PBRs have focused on a single response mode, such as overturning, and utilized a single intensity measure, typically the peak ground acceleration. To this end, this paper aims to identify optimal ground motion intensity measures (IMs) that correlate well with the multiple possible rigid body modes including rocking and sliding. In this study, structural parameters, including geometry and friction, were varied to induce each of the fundamental rigid body modes. The response of each structure was simulated to 3750 analytical pulse motions through numerical integration of the slide-rocking equations of motion within MATLAB. The results of the simulations were statistically analyzed to determine the optimal IMs in terms of both sufficiency and efficiency. A set of viable IMs are presented that have more robust probabilistic relationships with the dynamic response of a sliding or rocking block compared to previous IM studies

Effects of Friction on the Dynamic Behavior of Flexible Rocking Bodies

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 paper. This model was subjected to one-cycle sine pulses of varying amplitude and frequency for several levels of base friction to quantify the impact of sliding on overturning. In general, the results highlight that sliding behavior reduces the overturning demand, however motion-to-motion variability was observed

3-D Reconstructions and Numerical Simulations of Precarious Rocks in Southern California

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 to the Elsinore fault east of San Diego, CA. Each identified PBR is modeled using point clouds derived from ground-based laser scanning and images from an unmanned aerial vehicle. The resultant geometric reconstructions are then used in a probabilistic overturning analysis and compared to the anticipated seismic hazard at the site. Accounting for an estimated age range and 50% probability of overturning for the PBRs, approximately half of the surveyed PBRs indicate a potential overestimation of seismic hazard at the site

Robust nonparametric detection of objects in noisy images

We propose a novel statistical hypothesis testing method for detection of objects in noisy images. The method uses results from percolation theory and random graph theory. We present an algorithm that allows to detect objects of unknown shapes in the presence of nonparametric noise of unknown level and of unknown distribution. No boundary shape constraints are imposed on the object, only a weak bulk condition for the object's interior is required. The algorithm has linear complexity and exponential accuracy and is appropriate for real-time systems. In this paper, we develop further the mathematical formalism of our method and explore important connections to the mathematical theory of percolation and statistical physics. We prove results on consistency and algorithmic complexity of our testing procedure. In addition, we address not only an asymptotic behavior of the method, but also a finite sample performance of our test.Comment: This paper initially appeared in 2010 as EURANDOM Report 2010-049. Link to the abstract at EURANDOM repository: http://www.eurandom.tue.nl/reports/2010/049-abstract.pdf Link to the paper at EURANDOM repository: http://www.eurandom.tue.nl/reports/2010/049-report.pd

Damage Assessment of a Sixteen Story Building Following the 2017 Central Mexico Earthquake

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 create a three-dimensional point cloud of the building. The collected point cloud data were used to measure and quantify the permanent deformation of the structure at three corners as well as to generate depth maps of two parallel exterior walls. The measurements based on the lidar point cloud data are accurate with an error of 2 mm at 10 meters, enabling high resolute and accurate assessments. As for the accelerometers, one setup with sixty minutes of ambient vibrations data collection was performed. Twenty unidirectional accelerometers were installed on the basement, ground, second, fourth, eighth, tenth and roof floors at southwest and northeast corners to capture the torsional and translational acceleration structural response. The collected data can be used to perform system identification throughout operational modal analysis to demonstrate the dynamic and modal properties of the structures. Both the lidar and system identification sensing techniques provide essential input to establish and calibrate a detailed finite element model. The outputs are used to validate through the comparison of modal frequencies obtained in operational modal analysis method. Besides, the finite element model also provides a detailed response and insight to understand performance under future earthquakes

Commissioning of the CMS High Level Trigger

The CMS experiment will collect data from the proton-proton collisions delivered by the Large Hadron Collider (LHC) at a centre-of-mass energy up to 14 TeV. The CMS trigger system is designed to cope with unprecedented luminosities and LHC bunch-crossing rates up to 40 MHz. The unique CMS trigger architecture only employs two trigger levels. The Level-1 trigger is implemented using custom electronics, while the High Level Trigger (HLT) is based on software algorithms running on a large cluster of commercial processors, the Event Filter Farm. We present the major functionalities of the CMS High Level Trigger system as of the starting of LHC beams operations in September 2008. The validation of the HLT system in the online environment with Monte Carlo simulated data and its commissioning during cosmic rays data taking campaigns are discussed in detail. We conclude with the description of the HLT operations with the first circulating LHC beams before the incident occurred the 19th September 2008

The Apollo ATCA Platform

We have developed a novel and generic open-source platform - Apollo - which simplifies the design of custom Advanced Telecommunications Computing Architecture (ATCA) blades by factoring the design into generic infrastructure and application-specific parts. The Apollo "Service Module" provides the required ATCA Intelligent Platform Management Controller, power entry and conditioning, a powerful system-on-module (SoM) computer, and flexible clock and communications infrastructure. The Apollo "Command Module" is customized for each application and typically includes two large field-programmable gate arrays, several hundred optical fiber interfaces operating at speeds up to 28 Gbps, memories, and other supporting infrastructure. The command and service module boards can be operated together or independently on the bench without need for an ATCA shelf.Comment: Submitted to the Proceedings for TWEPP 201

Electron Antineutrino Search at the Sudbury Neutrino Observatory

Upper limits on the \nuebar flux at the Sudbury Neutrino Observatory have been set based on the \nuebar charged-current reaction on deuterium. The reaction produces a positron and two neutrons in coincidence. This distinctive signature allows a search with very low background for \nuebar's from the Sun and other potential sources. Both differential and integral limits on the \nuebar flux have been placed in the energy range from 4 -- 14.8 MeV. For an energy-independent \nu_e --> \nuebar conversion mechanism, the integral limit on the flux of solar \nuebar's in the energy range from 4 -- 14.8 MeV is found to be \Phi_\nuebar <= 3.4 x 10^4 cm^{-2} s^{-1} (90% C.L.), which corresponds to 0.81% of the standard solar model 8B \nu_e flux of 5.05 x 10^6 cm^{-2} s^{-1}, and is consistent with the more sensitive limit from KamLAND in the 8.3 -- 14.8 MeV range of 3.7 x 10^2 cm^{-2} s^{-1} (90% C.L.). In the energy range from 4 -- 8 MeV, a search for \nuebar's is conducted using coincidences in which only the two neutrons are detected. Assuming a \nuebar spectrum for the neutron induced fission of naturally occurring elements, a flux limit of Phi_\nuebar <= 2.0 x 10^6 cm^{-2} s^{-1}(90% C.L.) is obtained.Comment: submitted to Phys. Rev.