Revealing Bluff-Body Aerodynamics on Low-Rise Buildings under Tornadic Winds using Numerical Laboratory Tornado Simulator

Tornadoes result in death and property loss in communities around the world. To quantify the actions of tornadoes on civil structures, researchers have built physical laboratory tornado simulators to simulate tornadoes in the lab environment and tested building models in the simulated tornadic wind field, which is similar to wind tunnel testing when quantifying the wind effects induced by straight-line winds. Unfortunately, physical tornado simulators are much less common than straight-line wind tunnels, leading to the lack of research on bluff-body aerodynamics on civil structures under tornadic winds. Considering that it is expensive to conduct experimental testing in physical tornado simulators, numerical models of physical tornado simulator has been developed using computational fluid dynamics (CFD) simulations. However, they have not been validated at the level of pressure distribution on the structural surface of the testing model. In this study, the numerical model developed for the large-scale tornado simulator of the Missouri University of Science and Technology (Missouri S&T), which is based on the numerical simulation of the entire process of the physical testing in tornado simulator, will be validated by the measured data on the building model tested in the physical tornado simulator. Then, through the validated numerical simulation model, the bluff-body aerodynamics of buildings under tornadic winds will be revealed. To be specific, CFD simulation is first applied to model the entire process of experimental testing of a low-rise building model in the physical tornado simulator. Then, the obtained results are compared with laboratory-measured data to evaluate the effects of the building model on the wind field and the surface pressure on the building model. Then, the bluff-body aerodynamics on low-rise buildings under tornadic winds will be revealed based on the data obtained from numerical simulations using the relationship between streamline pattern change and velocity magnitude change (mass continuity theorem) and using the relationship between the velocity magnitude change and the pressure change (Bernoulli\u27s theorem), as well as the flow separation and vortex shedding

Minimum Performance Targets for the Built Environment based on Community-Resilience Objectives

Disrupted critical infrastructure systems following disasters can result in population outmigration which may subsequently negatively impact a communitys indirect socioeconomic losses over time. In this study, a community was modeled with its interconnected physical-socio-economic attributes and population outmigration was used as a basic proxy community resilience metric. The probability of outmigration for each household was assessed based on the probability that the school-age students, household residents, and employees in the household are affected over a prescribed time period from the occurrence of the hazard to the full restoration of the community. Finally, the potential population outmigration for the community was assessed by aggregating the probability for all the households in the community. Additionally, a prediction model for the number of injuries and fatalities was implemented in the analysis to be served as a community-level life-safety metric. Ultimately, these metrics were combined and utilized to propose a framework for disaggregation of a set of community-level objectives into a set of performance targets for the components of the built environment. Such a model is desirable for policymakers and community leaders in order to make long-term decisions for their community

Seismic Performance Comparison of a High-Content SDA Frame and Standard RC Frame

This study presents the method and results of an experiment to study the seismic behavior of a concrete portal frame with fifty percent of its cement content replaced with a spray dryer ash (SDA). Based on multiple-shake-table tests, the high content SDA frame was found to perform as well as the standard concrete frame for two earthquakes exceeding design-level intensity earthquakes. Hence, from a purely seismic/structural standpoint, it may be possible to replace approximately fifty percent of cement in a concrete mix with SDA for the construction of structural members in high seismic zones. This would help significantly redirect spray dryer ash away from landfills, thus, providing a sustainable greener alternative to concrete that uses only Portland cement, or only a small percentage of SDA or fly ash

SEISMIC DESIGN OF CROSS-LAMINATED TIMBER BUILDINGS

The increasing interest in cross-laminated timber (CLT) construction has resulted in multiple international research projects and publications covering the manufacturing and performance of CLT. Multiple regions and countries have adopted provisions for CLT into their engineering design standards and building regulations. Designing and building CLT structures, also in earthquake-prone regions is no longer a domain for early adopters, but is becoming a part of regular timber engineering practice. The increasing interest in CLT construction has resulted in multiple regions and countries adopting provisions for CLT into their engineering design standards. However, given the economic and legal differences between each region, some fundamental issues are treated differently, particularly with respect to seismic design. This article reflects the state-of-the-art on seismic design of CLT buildings including both, the global perspective and regional differences comparing the seismic design practice in Europe, Canada, the United States, New Zealand, Japan, China, and Chile

Computational environment for modeling and enhancing community resilience: Introducing the center for risk-based community resilience planning

The resilience of a community is defined as its ability to prepare for, withstand, recover from and adapt to the effects of natural or human-caused disasters, and depends on the performance of the built environment and on supporting social, economic and public institutions that are essential for immediate response and long-term recovery and adaptation. The performance of the built environment generally is governed by codes, standards, and regulations, which are applicable to individual facilities and residences, are based on different performance criteria, and do not account for the interdependence of buildings, transportation, utilities and other infrastructure sectors. The National Institute of Standards and Technology recently awarded a new Center of Excellence (NIST-CoE) for Risk-Based Community Resilience Planning, which is headquartered at Colorado State University and involves nine additional universities. Research in this Center is focusing on three major research thrusts: (1) developing the NIST-Community Resilience Modeling Environment known as NIST-CORE, thereby enabling alternative strategies to enhance community resilience to be measured quantitatively; (2) developing a standardized data ontology, robust data architecture and data management tools in support of NIST-CORE; and (3) performing a comprehensive set of hindcasts on disasters to validate the data architecture and NIST-CORE

Concept of Community Fragilities for Tsunami Coastal Inundation Studies

Tsunamis have devastated coastal regions worldwide, with the most recent being the result of the Great Tohoku Japan earthquake and tsunami, which was a M9.0 undersea megathrust earthquake that occurred off the east coast of Japan on March 11, 2011. In this study, a fragility formulation is utilized to develop and illustrate the concept of community fragilities for a community subjected to a wave of a particular height because fragilities are independent of occurrence rate. The fragility formulation for single structures is explained and then extended to the community scale by assigning one of eight archetype structural models and corresponding fragility to each of the buildings in a community. One key feature of the approach is that both the earthquake and tsunami are considered in succession. Three wave forces, i.e., hydrostatic, hydrodynamic, and impulsive wave forces, and the successive hazard loadings, i.e., earthquakes and tsunamis, were considered during the analysis. While debris loading is often critical during inundation, it is not assessed here but should be eventually considered. The tsunami fragility methodology is briefly demonstrated on a single building and then extended to Cannon Beach, Oregon, as an illustrative example. The fragility approach shows that community fragilities follow a similar trend with single structure fragilities and can help with decision making for retrofit and land-use planning. The concept proposed herein can provide a framework regardless of the structural or hydrodynamic model used, provided information on the community is available and a basic understanding of the structure types can be developed

Tsunami bore forces on a compliant residential building model

The forces exerted on light-frame wood buildings as a result of surge and waves are not fully understood. With a better understanding of these types of forces, it may eventually be possible to build coastal structures to better withstand the loads. In this paper, a recent two part experimental study that focused on determining the forces induced in a structurally compliant model of a typical Gulf Coast residential building is summarized. The one-sixth scale building was designed to approximately behave as the full scale building would under wave loading using rules of energy-based similitude. The compliant model was subjected to solitary wave loading in the Network for Earthquake Engineering Simulation (NEES) tsunami wave basin (TWB) at Oregon State University with wave heights ranging from 0.1 m to 0.6 m. Then, at Colorado State University, lateral force–deformation tests on a nominally identical model were performed in order to determine the force–deformation relationship for the building. The structural deformation produced by solitary waves in the wave basin was combined with the experimentally measured deformation in the structural laboratory to determine the force induced by the waves between 0.2m and 0.6 m. Finally, a simplified force equation constant similar to the existing design code formats was found to be 0.31

Effectiveness of Small Onshore Seawall in Reducing Forces Induced by Tsunami Bore: Large Scale Experimental Study

Tsunami force and pressure distributions on a rigid wall fronted by a small seawall were determined experimentally in a large-scale wave flume. Six different seawall heights were examined, two of which were exposed to a range of solitary wave heights. The same experiment was done without a seawall for comparison. The measured wave profile contained incident offshore, incident broken, reflected broken, and transmitted wave heights measured using wire resistance and ultrasonic wave gauges. Small individual seawalls increased reflection of the incoming broken bore front and reduced force on the rigid landward wall. These findings agree well with published field reconnaissance on small seawalls in Thailand that showed a correlation between seawalls and reduced damage on landward structures.This is the publisher’s final pdf. The published article is copyrighted by the author(s) and published by Fuji Technology Press. The published article can be found at: http://www.fujipress.jp/JDR/.Keywords: tsunami inundation, tsunami defense strategy, tsunami hazard mitigation, tsunami risk reduction, wave force

Risk analysis procedure for woodframe roof sheathing panel debris impact to windows in hurricanes

The assessment of losses during extreme events such as hurricanes is important for performance-based design of residential buildings. In this paper, a methodology for estimating the risk of debris impact, specifically roof sheathing panels, to windows as a result of hurricanes is introduced and applied to an illustrative example. The method is a combination of approaches on flat plate trajectories, numerical hurricane modeling, and statistical analysis of structural capacity. Within this methodology, one can estimate the risk of impact for one or more windows in a certain house group as a hurricane approaches and passes on a deterministic track as defined by the center of its eye. The impact risk is analyzed for the each hour making up the full hurricane duration rather than a single analysis using the blended (total) hurricane statistics. An illustration of the method is presented through a risk assessment of windborne debris impacts to windows in a house group located near the U.S. Gulf coast using a hurricane having the same track as hurricane Katrina in 2005. As a result, the probability of each window being hit by a roof sheathing panel (RSP) during each hour of the hurricane as well as during each hurricane is presented. The results quantify the risk from hour to hour during a hurricane and may serve to better orient houses in planned communities in hurricane prone regions as well as provide a better understanding of the interaction of hurricanes and structures.KEYWORDS: fragility, wind force, windborne debris, light-frame wood, hurrican

Wave Impact Study on a Residential Building

Recent natural disasters around the world including both tsunamis and hurricanes, have highlighted the inability of wood buildings to withstand wave and surge loading during these extreme events. Little is known about the interaction between coastal residential light-frame wood buildings and wave and surge loading because often little is left of the buildings. This leaves minimal opportunity for forensic investigations. This paper summarizes the results of a study whose objective was to begin to better understand the interaction between North American style residential structures and wave loading. To do this, one-sixth scale residential building models typical of North American coastal construction, were subjected to tsunami wave bores generated from waves of heights varying from 10 cm to 60 cm. The lateral force produced by the wave bores were, as expected, found to vary nonlinearly with parent wave height.This is the publisher’s final pdf. The published article is copyrighted by the author(s) and published by Fuji Technology Press. The published article can be found at: http://www.fujipress.jp/JDR/.Keywords: hurricane, residential building, light-frame wood, tsunami, bore, wav