Finite Element Analysis of Saferooms Subjected to Tornado Impact Loads YEVGENIY PARFILKO Fernando Amaral de Arruda Benjamin Varela Dept. of Mechanical Engineering, Rochester Institute of Technology, Rochester, NY, USA 3rd International Conference "Innovative Materials, Structures and Technologies"

Introduction Tornadoes are high speed windstorms that occur multiple times per year in regions of the US. Tornado saferooms are designed to protect occupants from high winds and windborne projectiles that occur during severe storms (EF4 and EF5 tornadoes). A projectile may be construction material, debris, trees, vehicles, ice, power lines, and so on. Vehicle impacts are of special concern since they are usually present near a saferoom, are heavy, and can roll easily. Our team conducted a study of vehicle impacts into a monolithic concrete saferoom, since this work had not been done before. 3rd International Conference "Innovative Materials, Structures and Technologies"

Introduction Shelters designed to comply with NSSA Code must be able to withstand projectile impact as well as wind loads. 3rd International Conference "Innovative Materials, Structures and Technologies"

Methodology We define the problem: complex interaction of vehicle, structure, and soil Saferoom-soil component Identify material model, appropriate mesh, rebar interaction Define soil contact and boundary conditions on soil only Vehicle component Identify vehicle, mass, velocity range, contact surfaces Determine the vehicle orientation and impact location Concrete material models, vehicle models, projectile speeds, boundary conditions Simulation parameters Control over initial velocity parameter Select termination time, time step, stability controls Material-specific damage variable tracking enabled Contact forces from vehicle Internal forces from rebar Reaction forces from soil 3rd International Conference "Innovative Materials, Structures and Technologies"

Model Parameters Concrete material properties: 35.4 MPa compressive strength, 16.0 MPa shear Reidel-Hermaier-Thoma (RHT) material model Elastic steel material model for rebar Coupled via Constrained-in-Lagrange formulation Finite element simulation properties: 30-50 mm element size; 210k-470k elements Simplified explicit dynamics solid elements (Puso) for concrete Shell and beam elements for vehicle and rebar steels RHT Damage variable defined for all concrete elements 0.200 s of impact simulated at internal time step of 9.00E-07 s Car model properties: NCAC Chevrolet C2500 Pickup; 2000 kg at 15.6 m/s (56.3 km/h) 3rd International Conference "Innovative Materials, Structures and Technologies"

Animation: Frontal wall impact 3rd International Conference "Innovative Materials, Structures and Technologies"

Results: Frontal impact into wall Results show measureable and reasonable deflection 1.65 mm total dynamic displacement 1.13 max. structure displacement 0.68 max. wall deflection relative to structure Clear indication of elastic response of structure Plate-like vibrational mode can be extracted Damping properties can be approximately extracted Identifiable damage pattern Zones of compaction for chassis rails, engine block Similar results expected with other vehicle models 3rd International Conference "Innovative Materials, Structures and Technologies"

Animation : Frontal impact into roof 3rd International Conference "Innovative Materials, Structures and Technologies"

Results: Frontal impact into roof Displacements are less due to dampening mass 1.03 mm max. dynamic displacement 0.26 mm max. structure displacement 0.77 mm max. relative displacement History variable tracks significant surface damage in impact zone. 40% damage averaged between affected elements Interpretation: elastic yield exceeded, with 40% of element considered to reach fracture. 3rd International Conference "Innovative Materials, Structures and Technologies"

Animation: Side impact into door 3rd International Conference "Innovative Materials, Structures and Technologies"

Results: Side impact into door Results show evidence of damage and plastic deformation Nonzero relative displacement after transient “Messy” power spectrum – change in domain properties High relative deflection (1.98 mm), similar global displacement 3rd International Conference "Innovative Materials, Structures and Technologies"

Conclusions Three distinct crash scenarios identified: frontal, side, and top impacts. The damage pattern is unique for each case. Distributed damage pattern along a side wall, plate-like deflection. Less severe damage in roof due to dissipation, lowest displacement of all three. Possible cracking along free surface of doorway, with higher displacements. Protective specification of saferooms can be validated by simulation. Stability of saferoom in soil can also be validated. Saferoom design proved to withstand impact from all sides, with varying levels of damage. Highest damage and deflections observed in front doorway. Soil and concrete displacements are comparably scaled. Along free surfaces, cracks develop readily. At the centers of faces, internal damage often develops in reinforced concretes before external cracks appear. 3rd International Conference "Innovative Materials, Structures and Technologies"

Further work: Simulation Comparative analysis on other saferoom designs: ensure comparable performance Integration of impact analysis into codes and certifications: prolong life cycle of saferooms Extend analysis method to schools, roadside buildings, hospitals, and other buildings 3rd International Conference "Innovative Materials, Structures and Technologies"

Further work: Testing Real-world validation of safety and impact resistance Integration of accelerometers and force gauges into structural surfaces Assessment of damage by nondestructive means such as a rebound hammer or ultrasonic transducer 3rd International Conference "Innovative Materials, Structures and Technologies"

References United States. Federal Emergency Management Agency., National Association of Home Builders of the United States., and Texas Tech University., Taking shelter from the storm: building a safe room for your home or small business, 4th ed. Washington, DC: FEMA, 2014. S. P. Center, "U.S. TORNADOES* (1950-2015) ", ed. Online.:http://www.spc.noaa.gov/wcm/#data, 2016. United States Federal Emergency Management Agency, "Design and Construction Guidance for Community Saferooms", FEMA P-361, Second Edition, August 2008. Y. Parfilko and B. Varela, "Simulating Debris Impacts Into Tornado Saferooms with LS-DYNA," Canadian Congress on Applied Mechanics, London, On. Canada, 2015, pp. 339-341. T. Borrvall and W. Riedel, "The RHT Concrete Model in LS-DYNA," LS-DYNA Users Conference, 2011. US Department of Transportation. "Users Manual for LS-DYNA Concrete Material Model 159". Federal Highway Administration FHWA-HRT-05-062. May 2007. "LS-DYNA Keyword User's Manual," R7.1 ed: Livermore Software Technology Corp., 2014. NCAC. Finite Element Model of C2500 Pickup Truck. Model Year 1994, Version 7; October 2008. http://www.ncac.gwu.edu/vml/models.html 3rd International Conference "Innovative Materials, Structures and Technologies"

Thank you for your attention! Correspond with us: Geopolymer Research Lab Benjamin Varela, Ph.D. Rochester Institute of Technology Rochester, NY, USA Special thanks to OZ Saferooms for financial support of this project. 3rd International Conference "Innovative Materials, Structures and Technologies"