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

Modeling System Effects and Structural Load Paths in a Wood-Framed Structure

The objective of this project was to evaluate system effects and further define load paths within a light-frame wood structure under extreme wind events. The three-dimensional 30- by 40-ft (9.1- by 12.2-m) building, designed to be representative of typical light-frame wood construction in the southeastern coastal region of the United States, was modeled using SAP2000. Wall and roof sheathing was modeled using SAP’s built-in thick shell element. The effect of edge nail spacing of the wall sheathing was incorporated by way of a novel correlation procedure, which eliminated the need to represent each nail individually. The computer model was validated against both two- and three-dimensional experimental studies (in plane and out of plane). Uniform uplift pressure, worst-case simulated hurricane, and ASCE 7-05 pres-sures were applied to the roof, and vertical foundation reactions were evaluated. The ASCE 7-05 uplift pressures were found to adequately encompass the range of uplift reactions that can be expected from a severe wind event such as a hurricane. Consequently, it was observed that ASCE 7-05 “component and cladding” pressures satisfactorily captured the building’s uplift response at the foundation level without the use of “main wind force-resisting system” loads. Additionally, the manner in which the walls of the structure distribute roof-level loads to the foun-dation depends on the edge nailing of the wall sheathing. It was also revealed that an opening in any wall results in a loss of load-carrying capacity for the entire wall. Moreover, the wall opposite the one with the opening can also be significantly affected depending on the orientation of the trusses. In general, it was determined that complex, three-dimensional building responses can be adequately characterized using the practical and effective modeling procedures developed in this study. The same modeling process can be readily applied in industry for similar light-framed wood structures

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 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 non-engineered 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 EF4 tornado devastated a 0.8 km (1/2 mile) wide path almost 10 km (5.9 miles) long through the city of Tuscaloosa, Alabama continuing on the ground for 130 km (80 miles). 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 windspeeds 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 focused at separate tornado intensity levels.Keywords: Residential building, Design method, Natural hazard, TornadoKeywords: Residential building, Design method, Natural hazard, Tornad

MANTA: A Negative-Triangularity NASEM-Compliant Fusion Pilot Plant

The MANTA (Modular Adjustable Negative Triangularity ARC-class) design study investigated how negative-triangularity (NT) may be leveraged in a compact, fusion pilot plant (FPP) to take a ``power-handling first" approach. The result is a pulsed, radiative, ELM-free tokamak that satisfies and exceeds the FPP requirements described in the 2021 National Academies of Sciences, Engineering, and Medicine report ``Bringing Fusion to the U.S. Grid". A self-consistent integrated modeling workflow predicts a fusion power of 450 MW and a plasma gain of 11.5 with only 23.5 MW of power to the scrape-off layer (SOL). This low $P_\text{SOL}$ together with impurity seeding and high density at the separatrix results in a peak heat flux of just 2.8 MW/m$^{2}$. MANTA's high aspect ratio provides space for a large central solenoid (CS), resulting in ${\sim}$15 minute inductive pulses. In spite of the high B fields on the CS and the other REBCO-based magnets, the electromagnetic stresses remain below structural and critical current density limits. Iterative optimization of neutron shielding and tritium breeding blanket yield tritium self-sufficiency with a breeding ratio of 1.15, a blanket power multiplication factor of 1.11, toroidal field coil lifetimes of $3100 \pm 400$ MW-yr, and poloidal field coil lifetimes of at least $890 \pm 40$ MW-yr. Following balance of plant modeling, MANTA is projected to generate 90 MW of net electricity at an electricity gain factor of ${\sim}2.4$. Systems-level economic analysis estimates an overnight cost of US\$3.4 billion, meeting the NASEM FPP requirement that this first-of-a-kind be less than US\$5 billion. The toroidal field coil cost and replacement time are the most critical upfront and lifetime cost drivers, respectively