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

Probabilistic procedure for wood-frame 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 probability of debris impact, specifically roof sheathing panels, to windows as a result of hurricanes is introduced and applied to a series of illustrative examples. The methodology 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 probability 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 probability is analyzed for 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 an assessment of windborne debris impacts to windows in a house group located near the US 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 of the example hurricanes is presented. The results quantify the probability from hour to hour during a hurricane and will provide a more accurate estimate of the probability and timing of pressurization of buildings for total loss estimation including rainwater intrusion volumes

Database-assisted design methodology to predict wind-induced structural behavior of a light-framed wood building

This study investigates the applicability of the database-assisted design (DAD) methodology to predict structural reactions in a light-framed wood structure subjected to fluctuating wind pressures. Structural influence functions were determined on a 1/3-scale light-frame wood structure, which was then subjected to a wind flow, while the surface pressures and structural reactions at roof-to-wall and wall-to-foundation connections were simultaneously recorded. There was a good agreement between the DAD-predicted structural reactions and experimentally measured reactions, confirming that the DAD method is suitable for predicting the structural reactions in light-frame wood buildings. Subsequently structural reaction time histories at several connections within the building were generated using a 1:50 scale wind tunnel model of the structure and the peak structural reactions determined using the DAD method and previously obtained influence functions. When the DAD-estimated reactions were compared with reactions predicted by the ASCE 7-05 main wind force resisting system (MWFRS) method, they showed the ASCE 7 reactions were highly non-conservative(i.e. smaller than the DAD method predictions), by as much as 39% at the gable end truss. The components and cladding method showed reasonable agreement with the DAD method for the gable end and first interior truss reactions but it too underestimated the reaction loads at the second and third interior trusses by 30% and 12% respectively

Dual-Objective-Based Tornado Design Philosophy

Tornadoes represent a unique natural hazard because of the very low probability of occurrence, short warning times (on the order of only a few minutes), and the intense and destructive forces imposed on engineered and nonengineered buildings. The very low-probability/very high-consequence nature of a tornado strike makes designing for survival and reducing damage under typical financial constraints a substantial challenge. On April 27, 2011, an enhanced Fujita (EF) 4 (EF4) tornado devastated an almost 10-km (5.9-mi) long, 0.8-km-wide (1/2-mi-wide) path, through the city of Tuscaloosa, Alabama, and continued on the ground for 130 km (80 mi). This paper presents the design concept that resulted following a week-long data reconnaissance deployment throughout the city of Tuscaloosa by the authors. The dual-objective philosophy proposed herein is intended to focus on both building damage and loss reduction in low-to-moderate tornado wind speeds and building occupant life safety in more damaging wind-speed events such as EF4 and EF5 tornadoes. The philosophy articulates a design methodology that is the basis upon which structural engineering was formed—namely, provide life safety and control damage—but the new philosophy is focused at separate tornado intensity levels

A vulnerability assessment tool for residential structures and extreme wind events

Studies of hurricane damage to residential buildings confirm that the risk of wind and/or water damage related losses can be mitigated via retrofit solutions. However, adoption of appropriate retrofits by homeowners has been limited despite its obvious benefits. For several reasons, including high cost of retrofitting, the practical difficulty of implementing upgrades, and other homeowner priorities, the level of structural retrofits remain low. This paper proposes a performance-based design approach to retrofitting, targeted for residential homeowners (and their construction team) to advise on incremental retrofits that ultimately result in desired performance targets for wind-resistant houses. To specifically engage the homeowner, a user-friendly smartphone application is developed that evaluates the wind resistance and vulnerability of existing homes. The app provides each homeowner an individualized vulnerability assessment, while engaging and educating them on the effects of structural systems and building characteristics on damage and on the options for retrofits and costs associated with the work. The vulnerability assessment is determined using a database of fragility curves, developed originally for the FEMA's HAZUS-MH program, and adapted for this use. The analysis yields the top three recommended retrofits for each house as-is, and its expected hurricane-induced economic losses compared against the predicted loss if all the retrofits were conducted. Beta trials of the mobile app will be conducted in at-risk coastal communities in Florida, USA. The authors suggest that direct engagement of homeowners in identifying wind mitigation techniques and solutions may yield more positive outcomes than traditional communication approach and it may eventually increase the number of building retrofits

Tornado damage and impacts on nuclear facilities in the United States

This report provides an overview of the tornado impact on the safe operation and shutdown of nuclear power plants in the United States. The motivation for this review stems from the damage and failure of the Fukushima nuclear power plant on March 11, 2011. That disaster warrants comparison of the safety measures in place within the global nuclear power industry

Wind load determination using field data and wind tunnel studies on residential buildings

Abstract The Caribbean islands from Grenada through Cuba continued to suffer wind damage during the 2004 and 2005 hurricanes seasons. Engineering research is urgently needed to minimize the damaging effects of these winds on residential buildings. The House Instrumentation System of the Florida Coastal Monitoring Program successfully recorded high-resolution wind pressure on a single family house from within Tropical Storm Isidore (2002) and Hurricane Ivan (2004). This paper briefly reviews the process of full-scale tests and presents the wind pressure data collected in two extreme wind events. The corresponding wind tunnel model studies were conducted in the Boundary Layer Wind Tunnel at Clemson University, and these results were compared with field measurement data to validate the current wind tunnel testing techniques. The comparison of full-scale and wind tunnel tests showed that the wind tunnel simulation results generally agree with the hurricane wind loads observed in two extreme wind events, through the peak negative pressure coefficients were insufficient to be reproduced at several test locations