Texas Tech University National Wind Institute Disaster ......Tornadoes & Hurricanes 3 Investigated...

4/11/2017

1

1

Designing for Disaster

April 11, 2017

Presented by:

Larry Tanner, R.A., P.E.NWI Research Assistant Professor

Texas Tech University National Wind Institute

2

History of National Wind Institute Tornado Research

3Tornadoes & Hurricanes Investigated Since 1970

• 182 Storms Investigated • Includes 2-Mexico, 2-Australia, Puerto Rico, & Guam• Notable tornadoes and hurricanes include:

• Tornadoes – 1970 Lubbock, TX; 1974 Xenia, OH; 1979 Wichita Falls, TX; 1997 Jarrell, TX; 1999 OKC, OK; 2007 Central Florida, 2008 Super Tuesday, 2011 Alabama/Missouri Tornadoes, 2013 Moore Tornadoes

• Hurricanes – 1970 Celia, TX; 1983 Alicia, TX; 1989 Hugo, SC & PR; 1992 Andrew, FL, LA; 2004 Ivan, FL; 2005 Katrina, AL, MS, LA; 2008 Ike, TX, LA

4Significant Contributions in Wind Research

• Overcame myths about wind speeds

• Concluded that max ground-level wind speeds seldom exceed 200 mph

• Concluded that about 90% of all tornadoes have wind speeds less than 150 mph

• Developed knowledge base for tornado resistant design …wind pressures and debris impact resistance

5

• Thunderstorms• Gust Fronts• Downbursts

• Tornadoes

• Tropical Cyclones• Hurricanes• Typhoons• Nor'easters

Types of Wind Hazard6

Tornadoes

• Definition: A rotating column of air characterized by a twisting, funnel-shaped cloud that extends to the ground

• The most violent tornadoes have ground level wind speeds of 200 to 250 mph

• The highest wind speeds may occur at a radius greater than the visible funnel cloud

4/11/2017

2

7

Tornadoes are Complex

• Air rushes inward and rises in the vortex – this creates extremely low pressures near the ground

• Inflow winds can be damaging

• Vortex diameters change with time, and wind speeds vary along the vortex

• Severe tornado winds greatly exceed design wind speeds

8

F-Scale Developed by Dr. Ted Fujita 1971

• Categorized tornadoes by intensity and area (F-1 through F-5)

• Associated wind speed ranges with each category of tornado

• Did not recognize differences in construction

• Based upon worst damage

• Overestimated wind speeds greater than F-3

• Did not recognize weak structures

9

Enhanced Fujita Scale – EF Scale

• Based on proposed 28 damage indicators that consist of buildings, structures, and trees

• For each damage indicator (DI), several degrees of damage (DODs) are identified with expected wind speeds

• Damage ranges from the initiation of visible damage to complete destruction of the particular DI

Developed by Texas Tech with a Consensus Group in 2004

10

Enhanced Fujita Damage Scale

• DI – Residential

• DOD - 9• Roofs and some walls torn

from structures

• Expected Wind Speed - 152 mph

EF-3. Severe Damage

11


• DI – Elementary School

• DOD - 10• Total destruction of all

or a large portion of building

• Expected Wind Speed –176 mph

EF-4. Devastating Damage

12


• DI – Residential

• DOD – 10• Total destruction of well

constructed residential structures

• Expected Wind Speed –200 mph

EF-5. Incredible Damage

4/11/2017

3

13

Tornado Annual Occurrence

• 1000+ Storms

• Approximately 100 deaths

Tornados14

Riot/Civil Disorder1.0%

Explosion/Fire4.5%

Earthquake24.9%

Wind/Hail/Tornado36.5%

Hurricane/Tropical Storm32.7%

Other0.4%

Dollar Losses by Claim

15

Where are the Risks?16

Mitigating the Damage

17

• Professionally designed and engineered structures perform best.

• Non-professionally designed structures do not have the redundancies of engineered safety factors and the attention to connections.

Mitigating the Damage

Non-Professionally Designed Structure

Professionally designed Structured

18

Perils of Wind Pressure

• Roof suction (uplift)• Suction on side and back walls• Positive (above atmospheric) pressure on windward walls• Airflows around sharp edges and corners create turbulence

and localize pressure extremes• Wind pressures are generally greater on the building envelope

(C&C) than on the structure (MWFRS)

Pressure distributionFlow pattern

18

4/11/2017

4

19

Roof Slope

19

For a 3-second gust design wind speed of 120 mph (Exposure C)

4-19

Roof pressures for different roof pitches

20

Roof Uplift and Bldg. Sliding

21

Racking and Overturning22

Keep the Load Path Connected

23

Residential Loss of Load Path24

Commercial Loss of Load Path

4/11/2017

5

25

Commercial Loss of Load Path26

“Exploding” Phenomenon

• Windward wall breach is primary cause

• Rapid drop in atmospheric pressures is a secondary effect (particularly with safe rooms)

• Do not open windows

27

Debris Impacts – The Other Peril28

Debris Impacts – The Other Peril

29

Debris Impacts – The Other Peril30

Debris Impacts – The Other Peril

4/11/2017

6

31

So what have we learned?

• Buildings are subject to failure, unless they are specifically designed to withstand tornado wind pressures.

• Building envelopes are perforated by storm debris impacts, thereby allowing internal pressures to add to the existing external forces.

• Tested storm shelters, community shelters, and components are the best line of defense.

32

Residential Shelters

33

Residential Shelters

Below Ground Cellars and Shelters have been around since

“Man invented the shovel”.

34

New Concept – In-garage Floor Shelter

35

Above Ground Shelters Do Work36

Above Ground Shelters Do Work

4/11/2017

7

37

Site Constructed Concrete Shelter with Tested Door

Above Ground Shelters Do Work38

Building Code and Standards Updates

39

• FEMA P-361 2015

• FEMA P-320 2014

• ICC-500 2014

• ASCE 7-10

• I-Codes 2015

Reference Materials40

ASCE 7-10 Updates

• Most Significant Update since 1995 Edition

• Strength Design (LRFD) Wind Speeds [previously Allowable Stress

Design (ASD) ]

• 3 Maps ( No Importance Factor, I = 1 for all Categories of Risk)

• Wind-borne Debris Region More Conservative for Some Critical

Facilities

• Exposure D at Hurricane Coast added

41Comparison ASCE-7 to ASCE 10, Category II Risk Map

7-05 7-10, Risk Cat. II7% Exceed. 50 yrs. (MRI=700 yrs.)

42Comparison ASCE-7 to ASCE 10, Category III & IV Risk Map

7-05 7-10, Risk Cat. III & IV3% Exceed. 50 yrs. (MRI 1700 yrs.)

4/11/2017

8

43Comparison of Hurricane Debris Zones

44FEMA Tornado Safe Room Design Wind Speed Map

45

• IBC 2015 Section 423 requires Safe Rooms for Critical Emergency Facilities and E (schools) Occupancies

• Applies to the above categories in the 250 mph high wind zone

• Construction in accordance to ICC-500

• Other loads and considerations, i.e., flood hazards and falling structure protection

Wind Effects on Buildings IBC 2015 Code Changes

46

Wind Effects on Buildings

• General effects:• Building geometry• Building orientation to wind• Building envelop integrity

• Localized effects:• Edges and corners• Affects C&C and (in some cases) MWFRS design

• Safe room design• I = 1.00 Safe rooms are critical but since we are already

designing for an extreme high wind event, no need to increase loads more

• Exposure C: (Use for safe room design)

47

Wind Pressures

Wind pressures increase with the square of wind speed ( q = 0.00256 K V2)

Where:

q = velocity pressure

K = combination of coefficients quantifying a wind pressure factor such as directionality or topographic effects

V = velocity

Wind Speeds

100 mph

125 mph

150 mph

200 mph

250 mph

350 mph

Pressure Magnification

1.0

1.56

2.25

4.0

6.25

12.25

48

Wind Varies With Elevation

Higher portions of buildingsexposed to higher winds

4/11/2017

9

49

Wind Effects on Buildings

Wind pressures are affected by the building shape and roof pitch

50

Non-Structural Vulnerable Elements

• Parapets, chimneys, canopies, ornamentation

• Cladding and glazing

• Partitions

• Roof-mounted equipment

• Portable buildings

51Community Safe Room Design Considerations

• Safe room must not overturn, slide, lift, or be torn apart

• Debris must not penetrate the safe room

• Safe room must not flood

52

Other Design Considerations

• Proximity of adjacent buildings• Possibility of adjacent building failure loading the safe room

• Non-structural components• Utilities, ceilings, shelves, etc.

• Wind often controls in large community shelters over debris impacts

53

General Design and Drawings

• Type of Tornado or Hurricane

• Design Standards (FEMA 361 and ICC-500)

• Design Wind Speed

• Structural & Envelope Parameters

• Safe Room Location

• Safe Room Supplies

54

Designer Checklists

Available from FEMA Region VII

4/11/2017

10

55

Walls/Opening

• Vulnerability Identification and Criteria• Walls• Roof systems• Openings• Glazing• Doors• Windows• Vital outdoor equipment, i.e., generators, HVAC equipment

56

Other Hazards

• Flood Hazard

• Structural Collapse• Adjoining Buildings• Adjacent Taller Buildings or Towers

• Seismic

57

• Passive (P)

• Community Safe Rooms are large and incapable of comfortably handling the Atmospheric Pressure Change (APC), the designer must use a Gust Effect Internal Pressure Coefficient (GCpi) = +/- 0.55 and consider the shelter partially enclosed (door open during the event)

• Mechanical (IMC) per IBC• Required for Hurricane Safe Rooms >50 occupants

• Air exchanges /hour per IMC, minimum 15 cu.ft/person

• Openings protection• General• Wind• Impact

Ventilation58

Ventilation - Passive

* Refer to ICC‐500 for allowable locations. Increase to 4 sq. in. for all upper room half venting

Tornado Safe Room Venting Area (per Occupant)

Residential 2 square inches*

Community (<= 50 occupants)

5 square inches

Community (> 50 occupants)

6 square inches

59Recommended Square Footage (RSF) Calculations

• Number of standing and seated occupants – 5 sf/per

• Number of wheelchair-bound occupants – 10 sf/per

• Number of bedridden occupants – 30 sf/per

Total square footage (RSF) based on total number and type of occupants

60

Square Foot/Occupancy

• Maximum expected occupancy

• Net available square footage (ASF) – Open areas

• Net available square footage (ASF) – Less restrooms, kitchens, equipment rooms, seating & storage areas

• Total usable square footage

4/11/2017

11

61

Alternative Area Calculation Method

• Increase Gross SF (GSF) 50% for safe room with fixed seating or concentrated furnishings

• Increase GSF 35% for safe room with un-concentrated furnishings and no fixed seating

• Increase GSF 15% for safe room with open plan furnishings and no fixed seating

62

• Accessibility – ADA Requirements

• Assume power-off condition unless backup power source is used

• Toilets per Building Code

• Number of Toilets

• Location

• Special Requirements

• Special Inspection Program per IBC

• Quality Assurance/Quality Control (QA/QC) Plan per FEMA 361

• Peer Review per FEMA 361 for Safe Rooms > 50 occupants

Other Considerations

63

Special Inspections

• Roof cladding and framing connections

• Wall-roof and wall-floor connections

• Roof and floor diaphragm systems

• MWFRS and connections to foundation

Per IBC Section 1704, 1705, 1706, inspect:

64

Special Inspections

• All prefabricated elements and connections

• All components for missile impact resistance

• Corrosion resistance or protection of metal connectors

• Recommendations for critical support systems and debris impact protection of the components and connections

Per IBC Section 1704, 1705, 1706, inspect:

65

Code Compliance and Permitting

• Safe room design addressed in 2009 IBC and updated in 2015 IBC

• A/E must work with local building officials to establish acceptable requirements where AHJ has not adopted ICC-500

• FEMA 361 safe rooms inherently satisfy structural criteria

• Egress and fire generally designed for maximum safe room occupancy

(normal)

• Must follow all other state and local requirements for code compliance and permitting

• FEMA 361 and ICC-500 peer review and special inspections begin at 50 + persons

66

Quality Assurance

• Standards should exceed levels for typical building construction

• Specify• Components to be inspected• Frequency and method• Structural observations

4/11/2017

12

67

Tornado Community Safe Room Costs

• Safe Room costs vary with use, size, & materials used

• New, tornado community safe room projects have revealed (> 5,000 square feet):

• Protection level of 250 mph vs. 90 mph IBC 2009 vs 115 mph IBC 2015

• Minimal openings (typically just doors)

Costs 15%-20% more than conventional construction projects when incorporated as a portion of a new project (250 mph vs 115 mph design wind speed)

68

Community Shelter Examples

691974 Hereford Elementary

Hereford, Texas

BGR Architects, Lubbock, TX

701982 Jr/Sr High SchoolSudan, Texas


71Jr/Sr High School

Sudan, Texas


721990 Primary School

Littlefield, Texas


4/11/2017

13

73Primary SchoolLittlefield, Texas


74Jefferson Elementary, Wichita, KS

Multi-Purpose Bldg. / FEMA 361 Shelter

PBA Architects, Wichita, KS

75Jefferson Elementary, Wichita, KS

Multi-Purpose Bldg. / FEMA 361 Shelter


76Coffeyville Elementary School

Coffeyville, KS


77Kansas City Elementary

Prototype Buildings


78


Kansas City Elementary Prototype Buildings

4/11/2017

14

79


Kansas City Elementary Prototype Buildings

80Seneca Middle School

Seneca, MO

81Western Texas College Shelter

Snyder, Texas

Randall Scott Architects, Dallas, TX

82Community Shelters and Safe Rooms

Amory, MS

82

83

Community Shelters and Safe Rooms

Similar single “tube” used in Phil Campbell, AL

FEMA Safe Room – Brookwood, AL

84

Storm Debris

4/11/2017

15

85Debris Is Abundant

Walls , roofs, doors, windows, and openings are vulnerable

OKC, 1999

Hurricane Katrina, 2005

86

Safe Room Wall Test

87

American Association for Laboratory Accreditation

Laboratory Testing

ISO/TEC 17025:2005 Accredited LaboratoryTesting TechnologyTornado and Hurricane Large Impacts

Performance of Exterior Windows, Curtain Walls, Doors, and Impact Protective Systems Impacted by Missiles and Exposed to Cyclic Pressure Differentials

ICC/NSSA Standard for the Design and Construction of Storm Shelters

Natural Phenomena Hazards Design and Evaluation Criteria for Department of Energy Facilities

Uniform Static Air Pressure Difference using Air Bladders

ASTM E1886 (Except Small Missiles and Cyclic Pressure Differentials)

ICC-500

DOE-STD-1020-2002 (Superseded by DOE-STD-1020-2012)1

NWI DIF Air Bladder Standard 1.1.2016

88

Recent Missile Tests

• Many tests have been conducted since the 1999 & 2008 FEMA 361 publications

• TTU NWI website, http://www.depts.ttu.edu/nwi/research/DebrisImpact/

• contains information on products that have passed FEMA 361/320 missile tests

• Others laboratories are conducting similar tests

89

Windborne Debris – Tornado Missiles

• Building components are physically tested to determine their debris resistance

• For 250 mph ground speed tornado – the test “missile” is:• A 15-pound 2x4• Shot from a cannon at 100 mph horizontally, 67 mph vertically

Safe Room Design Wind SpeedMissile Speed (of 15 lb 2x4 board member) and

Safe Room Impact Surface

250 mphVertical Surfaces: 100 mph

Horizontal Surfaces: 67 mph

200mphVertical Surfaces: 90 mph






90Windborne Debris –Tornado and Hurricane Missiles

• Testing for missile impacts: Use ICC-500, Section 305

• Wall and roof assemblies: Use ICC-500, Section 306

• Openings and opening protective's in tornado safe rooms: Use ICC-500, Section 306

• Soil-covered portions of safe rooms: Safe rooms with minimum 12-inch horizontal soil cover or 36-inch vertical soil cover protecting do not need to be tested

FEMA 361 guidance on debris impacts refers to ICC-500

4/11/2017

16

91

ICC-500

• Section 806.4.1 Window assemblies and other glazed openings in tornado shelters. Window assemblies and other glazed openings for tornado shelters shall be static pressure tested away from stops following procedures detailed in ASTM E330 to at least 1.2 times the pressures specified in Section 304. Pressure tests are allowed to be conducted separately from debris impacts tests.

• Section 805.3 – 806.4.1 Window and skylight assemblies for tornado shelters.

• Section 805.4 – 805.4.2 Window and skylight assemblies for hurricane shelters.

92Windborne Debris –Tornado and Hurricane Missiles

FEMA 361 & ICC-500 provides guidance for the following:

• Alcove or baffled entry systems: Meet windborne debris criteria, Section 3.3.2

• Other debris hazards: Lay down, rollover, and collapse hazards should be considered by design professional

92

93Glazing is Extremely Vulnerable to Debris Impacts

94Glazing is Extremely Vulnerable to Debris Impacts

95Doors are Extremely Vulnerable to Debris Impacts


4/11/2017

17


98

Door, Hardware & Glazing Testing

99

FEMA 320 Residential Doors

• 14 gage hollow metal door and frame specially constructed.

• Three hinges & 3 deadbolts.

• Can swing in either direction.

• Pressure and impacts away from door stops

• Hold pressure x 1.2 factor for 10 seconds.

• Resist missile perforation w/ 2 locks remaining engaged.

• Door deflection not to exceed 3-in.

100

FEMA 361 Community Shelter Doors

• 14 gage hollow metal door & frame specially constructed.

• Egress hardware – panic bar activation of three-point latching system.

• Classroom function hardware allowed to be installed in a Tornado Rated Door for classroom shelters or entrance into a hall shelter from the classroom

• Hold pressure x 1.2 factor x 10 secs.• Pressure away from stops & missile

impacts into stops.• Resist missile perforation with deflections

less than 3-in. & 2 locks remain engaged.

101

Above Ground Shelter Door Failure

April 24, 2014, One Death, Mayflower, Arkansas

102Non-Complying Above Ground Tornado Shelter Doors

NSSA/NWI DIF Sponsored Project

• The failure of the Mayflower shelter door emphasized the fact that non-tested tornado doors were being installed in site constructed shelters.

• The Sponsored Project pressured and impacted tested six common types of doors thought to be installed in many shelters.

• Goal 1 of the test was to identify the strongest of these doors and develop mitigation measures to pass the tests.

• Goal 2 was to demonstrate the performance of a Tornado Rated Door Assembly as compared to the six doors previously tested.

4/11/2017

18

103

1) 26 ga. metal clad wood frame door with Styrofoam core and residential hardware

2) 6 Panel Hurricane Resistant (Dade Co. 201/203) door in 18 ga HM frame and residential hardware

3) 18 ga. HM Door/Frame with Styrofoam core with residential grade hardware

4) 16 ga. HM Door and 18 ga. Frame steel stiffened core with residential Grade 1 hardware

5) Similar to Door 3 with steel stiffeners and with mitigations – 3/16-in. HSS bars and shear pins

6) Same as Door 4 with mitigations - ¼-in. HSS bars, shear and safety pins

7) Tornado Door – 14 ga. HM with 18 ga. frame, reinforced lock boxes and strike boxes, hinge reinforcements, Com. Grade 1 HDW

Doors Tested:

Non-Complying Above Ground Tornado Shelter Doors


104

• Doors 1 & 2 failed the pressure and impact tests.

• Doors 3 & 4 passed pressure, but failed the impact tests.

• Doors 5 & 6 (3 & 4) had already passed the pressure tests, but failed impact tests, though mitigated.

• The Tornado Doors passed both pressure and impact tests.

Non-Complying Above Ground Tornado Shelter Doors


Results:

105

Door 1: Metal Clad Wood Frame106

Door 1: Metal Clad Wood Frame

107

Door 2: Hurricane Door 3: 18 ga. HM108

Door 4: 16 ga. HM

4/11/2017

19

109

Door 4 & 5: Typical Mitigations110

Door 4: 16 ga. HM - Mitigated

110

111Door 7: 14 ga. HM FEMA 320 Tornado Door

112Door 7: 14 ga. HM FEMA 320 Tornado Door

112

113

Glass Testing114

Glass Testing

4/11/2017

20

115

Closing Summary

116

So, what have we learned?

Mitigation Measures by:1. …keeping the load path connected to achieve better wind

resistance of our homes and other structures.2. …installation of double pane insulating glass provides some

impact resistance.3. …properly attaching components and cladding to wind standards

keeps shingles and siding attached.4. …utilizing stiffened hurricane rated garage doors to help prevent

garage failuresSaving lives by the proper design and construction of Safe Rooms and Community Shelters by addressing:

1. Perils of Wind Pressuring2. Perils of Debris Impacts

117

Incentivizing Codes & Beyond-Code Mitigation• Code+ Concepts• Listing Code Enhancements in MLS Listing and posting List of

Enhancements on a label installed on the home electrical panel cover

Certification, Designation, and Education Programs• Blueprint for Safety• Fortifies for Safer Living• Resilience STAR• South Carolina Safe Home• Federal Alliance for Safe Homes(FLASH)

Other Ideas?

Damaged Fortified HomesHurricane Ike 2008

118

Design methodology with structural engineering as the basis to provide life safety and control damage with a philosophy using the separate tornado intensity levels as defined by the EF-Scale.

• EF-0 & EF-1 damage is addressed at the Component (C) level, i.e., connectors, load path, and horizontal load distribution.

• EF-2 & 3 damage is addressed at the (C) level and the System (S) level which addresses load vertical and lateral load sharing to deal with wind pressures and debris impacts.

• EF-4 & EF-5 intensities require (S) improvements, Life Safety (LS), and Alternative (A) construction, namely shelters.

A Better Idea

Dual-Objective-Based Tornado Design Philosophyvan de Lindt, John; et. al.(2013). Dual-Objective-Based Tornado Design Philosophy. Structural Engineering(139), 251-263

119

Actual Storm Path & Desired Modification

2011 Tuscaloosa, AL Storm Path

Dual Design Objective and Philosophy –Path Modification

120

Modifications based DOD Examples

Table 2. Dual Design Objectives, Philosophy, and Examples of Engineering/Construction Improvements

Proposed Design Objective Philosophy DOD* Damage DescriptionExample Engineering

and/or Construction Improvements

Damage Mitigation Component

2

Loss of roof covering Use manufacturer recommended number and placement of fasteners for high-wind shingles.

Damage Mitigation Component

4

Uplift of roof deck and loss of significant roof covering material

Use hurricane clips on both sides of truss. 2 X 6 trusses, heavier nail schedule on roof sheathing, add blocking for short edge nailing of roof sheathing.

Damage Mitigation System

6

Large sections of roof structure removed

Ensure connection between trusses/rafters to wall top plates. Space trusses at 16 in. o.c. and line them up with vertical wall studs.

Life Safety Alternative

8

Most walls collapsed Safe room or shelter.

4/11/2017

21

121

DOD Damage Examples

DOD 2 – EF-1. 86-110 mph, Loss of Roof Covering DOD 6 – EF-6, 136-165 mph, Loss of Walls and Roof

DOD 4 – EF-4, 111-135 mph, Significant Roof Damage DOD 8 – EF-4, 166-200 mph, Walls Collapsed

122

Questions?

“All Things Wind”

123

Larry J. Tanner, P.E., R.A.

NWI Research Assistant Professor

www.nwi.ttu.edu/research/DebrisImpact

[email protected]

806.834.2320

Thank You!

Texas Tech University National Wind Institute Disaster ......Tornadoes & Hurricanes 3 Investigated...

Documents

Transcript of Texas Tech University National Wind Institute Disaster ......Tornadoes & Hurricanes 3 Investigated...