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Concrete disaster resistance
Masonry Safe Room
Concrete is resistant to wind, hurricanes, floods, and fire. Concrete, as a structural material and as the building exterior skin, has the ability to withstand nature’s normal deteriorating mechanisms as well as natural disasters. Properly designed, reinforced concrete is resistant to earthquakes and provides blast protection for occupants. Concrete safe rooms help provide protection from earthquakes, tornadoes, hurricanes, fires, and other disasters.

how

 

Fire Remains
Image After a fire, concrete and masonry may be all that remains. (PCA)
Fire Resistance

Concrete offers noncombustible construction that helps contain a fire within boundaries.
 
 
  • As a separation wall, concrete helps to prevent a fire from spreading throughout a building.  
  • As an exterior wall or roof, concrete helps to prevent a fire from jumping from building to building.  
  • During wild fires, concrete walls and roofs help provide protection to human life and the occupants’ possessions within a building.  
  • Concrete helps contain a fire even if no water supply is available, whereas sprinklers rely on a water source.   
  • Concrete that endures a fire can often be reused when the building is rebuilt.
     

The American Society for Testing and Materials (ASTM) E119, “Standard Test Methods for Fire Tests of Building Construction and Materials,” describes test procedures for determining fire endurance of building materials. In fire endurance tests, concrete generally fails by heat transmission long before structural failure, whereas other construction materials fail by heat transmission when collapse is imminent. A 2-hr fire endurance for a concrete wall will most likely mean the wall gets hot (experiences an average temperature rise of 250 °F for all points or 325 °F at any one point.) The fire endurance of concrete can be determined by its thickness and type of aggregate using ACI procedures.

Fire Remains
Stucco is fire-resistant, which is one of the main reasons this home was the only house left standing on this California hillside after the wild fire. (PCA No. 13560)

Concrete has also performed well during the Urban-Wildland Interface fires that have destroyed billions of dollars of property in Southern California and other parts of the western U.S. Hilly terrain, hot dry winds, combustible vegetation, and closely spaced dwellings create favorable conditions for these types of fire. This trend is expected to continue as populations continue to expand into wildland areas. Data collected after these fires shows a correlation between fire damage and the exterior surfaces of buildings, including:
 
 
  • Concrete or clay tile roofs performed much better than wood shake or shingle roofs.  
  • Buildings having noncombustible exterior wall surfaces, such as masonry or stucco, achieved a higher level of survival.  
  • Double-pane windows are needed to minimize heat transfer to the building interior.  
  • Minimal roof projections or the use of non-combustible materials to protect combustible eaves and projections plus the elimination of soffit vents will also increase a structure's chances of surviving a wildland fire.  
Tornado, Hurricane, and Wind Resistance
Concrete is resistant to tornadoes, hurricanes, and wind. Following Hurricane Katrina, a concrete house was the sole house left standing in a Pass Christian, MS, neighborhood.

Fire Remains
The Sundbergs' home, in the Pass Christian, MS, area affected by Hurricane Katrina, is shown in the yellow circle and is a prime example of the durability of concrete homes. (PCA photo from FEMA)

Investigators have learned from previous hurricanes that:
 
 
  • Asphalt shingles often failed due to holes created by staple guns. Nails held better than staples if they were properly placed.
  • Clay roof tiles resisted wind forces better than asphalt shingles but were apt to shatter if hit by flying debris.
  • Concrete roof tiles suffered similar damage as clay roof tiles from debris, but were more resistant to shattering than clay tiles.
  • Asphalt gravel roofs, if not well maintained, were flaked off in layers by the wind, exposing sub-layers.
  • Plywood sheathing failures were due to inadequate nailing.
  • Particle board does not provide a good base for the attachment of surface roofing materials.
  • Gables were more prone to failure than hip roofs. Gables constructed of concrete masonry faired much better than frame construction. Inadequate attachment to walls and inadequate lateral support caused many failures of gables, particularly wood frame gables.
  • Concrete block walls performed well. Concrete masonry construction was more forgiving of poor craftsmanship than wood frame construction. Compliance with the SSTD 10-93, Standard for Hurricane Resistant Residential Construction or the provisions of ACI 530/ASCE 5/TMS402-95 would have probably reduced the amount of damage observed in these structures.
  • Masonry veneer also performed well when properly constructed and connected to the structure. Damaged veneers were invariably a result of corroded, inadequate, or improperly embedded ties. Masonry veneer structures subjected to storm surges were able in many cases to withstand the storm surge better than wood frame houses without veneer.
  • Wood frame walls performed poorly unless well designed and constructed.
  • Loads on building components and connections are significantly increased when the envelope is breached by high wind or flying debris. Masonry systems appeared to resist breaching as well, if not better, than other wall systems.
  • Windows and doors need to be carefully installed. Windows must be protected with hurricane shutters.

2x4
This wood 2x4 impaled a wood frame home due to a tornado spawned by Hurricane Katrina (http://www.noaa.gov/)

Debris driven by high winds presents the greatest hazard to homeowners and their homes during hurricanes and tornados. Tests show that concrete wall systems suffer no structural damage when impacted by debris carried by hurricane and tornado-force winds.
 
As another example, in 1967, a series of deadly tornadoes hit northern Illinois, killing 57 people and destroying 484 homes. Damages at the time were estimated at $50 million. Two prestressed concrete structures, a grocery store and a high school, were in the direct path of two tornadoes that struck almost simultaneously. Repairs to the structural system of the grocery store were less than $200. In the high school, structural damage was also limited.

Flood Resistance
Concrete is not damaged by water; concrete that does not dry out continues to gain strength in the presence of moisture. Concrete submerged in water absorbs very small amounts of water over long periods of time, and the concrete is not damaged. In flood-damaged areas, concrete buildings are often salvageable. Concrete dams and levees are used for long-lasting flood control.

In the rebuilding of New Orleans after Hurricane Katrina, architects and engineers are looking at structures that will keep water out and not shift or float away when submersed in floodwaters. One solution is reinforced concrete walls to the roof height with a 12-in. thick concrete slab. In one example, the slab will be kept in place with 8-in. helical anchors drilled 10 to 13 feet into the ground (Architect Hank Browne and engineers DMK Group, April 2006 Building Design and Construction).

Concrete will only contribute to moisture problems in buildings if it is enclosed in a system that traps moisture between the concrete and other building materials. For instance, a vinyl wall covering in hot and humid climates will act as a vapor retarder and moisture can get trapped between the concrete and the wall covering. For this reason, impermeable wall coverings (such as vinyl wallpaper) should not be used on concrete walls.

High Humidity and Wind-Driven Rain
Concrete is not affected by wind-driven rain and moist outdoor air in hot and humid climates because it is impermeable to air infiltration and wind-driven rain. Moisture that enters a building must come through joints between concrete elements. Annual inspection and repair of joints will minimize this potential. More importantly, if moisture does enter through joints, it will not damage the concrete. Good practice for all types of wall construction is to have permeable materials that breathe (are allowed to dry) on at least one surface and to not encapsulate concrete between two impermeable surfaces. Concrete will dry out if not covered by impermeable treatments.

Earthquake Resistance
northridge
The L.A. Metro Blue Line Bridge was designed to sustain no functional damage from the worst earthquake expected in the next 75 years, and only minimal damage from an earthquake 10 times stronger than the 1995 Northridge quake. (PCA No. 10037)
Concrete is resistant to earthquakes. Earthquakes in Guam, the United States (Richter scale 8.1); Manila, the Philippines (Richter scale 7.2); and Kobe, Japan (Richter scale 6.9) have subjected concrete buildings to some of nature’s deadliest forces. Concrete framing systems have a proven capacity to withstand these major earthquakes. Another pertinent example is the 1994 Northridge, CA, earthquake (Richter scale 6.8). It was one of the costliest natural disasters in U.S. history, with total damages estimated at $20 billion. Most engineered structures within the affected region performed well, including structures with concrete components. It should be noted that parking structures with large plan areas—regardless of structural system—did not perform as well as other types of buildings.

Built according to good practices, concrete homes can be among the safest and most durable types of structures during an earthquake. Homes built with reinforced concrete walls have a record of surviving earthquakes intact, structurally sound and largely unblemished. In reinforced concrete construction, the combination of concrete and steel provides the three most important properties for earthquake resistance: stiffness, strength, and ductility.

Anchor
Properly anchored walls are key to earthquake resistance in low rise buildings (http://www.cement.org/)

Studies of earthquake damage consistently show well-anchored shear walls are the key to earthquake resistance in low-rise buildings. Optimal design conditions include shear walls that extend the entire height and are located on all four sides of a building. Long walls are stronger than short walls, and solid walls are better than ones with a lot of openings for windows and doors. These elements are designed to survive severe sideways (in-plane) forces, called racking and shear, without being damaged or bent far out of position. Shear walls also must be well anchored to the foundation structure to work effectively. Properly installed steel reinforcing bars extend across the joint between the walls and the foundation to provide secure anchorage to the foundation.
 
Low-rise buildings most vulnerable to earthquakes do not have the necessary stiffness, strength, and ductility to resist the forces of an earthquake or have walls that are not well anchored to a solid foundation, or both. Three types of buildings sustain the most significant damage:
 
 
  • Multi-story buildings with a ground floor consisting only of columns;
  • Wood-frame houses with weak connections between the walls and foundation;
  • Unreinforced masonry or concrete buildings
Reinforced concrete walls work well because of the composite system: Concrete resists compression forces, and reinforcing steel resists tensile forces produced by an earthquake. Even a lightly reinforced concrete shear wall has over six times the racking load resistance as framed wall construction.

Fortified…for safer living ®
Extreme weather events (http://www.ibhs.org/)
The Fortified…for safer living ® program an initiative of the Institute for Business & Home Safety, provides design, construction, and landscaping guidelines to increase a new home's resistance to natural disaster. “Fortified” techniques and construction materials raise a home’s overall disaster-resistance above the minimum requirement of local building codes. Extra attention is given to areas especially vulnerable to harsh elements, including doors and windows, roof construction and the foundation.

Homes are exposed to one or more extreme weather events, such as high wind, wildfire, flood, hail and earthquake. The website (http://www.ibhs.org/) indicates major threats depending on the region of the country.
Precast concrete “Fortified” home under construction in Illinois (PCA website, DuKane Precast)
A “Fortified” home under construction in Illinois will have added protection against tornadoes, hail and severe winter weather – three of the state’s most destructive natural elements. “Fortified” construction features in this home will include:
 
 
  • Connections that securely tie the house together from roof to foundation, protecting the structure from winds with speeds up to 130 mph
  • Impact-resistant roof materials that better withstand high winds and are fire resistant.
  • Windows and doors with higher wind and water design pressure ratings and a garage door capable of withstanding impact from large objects.
  • Construction materials and siting work that eliminate the threat of flood or wildfire.
     
Blast resistance
 
ICF reaction boxes prior to blast test (http://www.cement.org/)
An ICF wall after a 50 lb. TNT detonation from 10 feet away. (http://www.cement.org/ )
Concrete has demonstrated blast resistance through tests. The Insulating Concrete Form Association (ICFA) and the Northern Virginia Concrete Advisory Council successfully demonstrated the blast-resistant properties of ICF building systems during the Force Protection Equipment Demonstration (FPED V) April 26–28, 2005, at Quantico Marine Corps Base in Northern Virginia. During the blast demonstrations, eleven separate ICF reaction boxes, weighing 13 tons apiece and with walls measuring 8 feet tall and 6 inches thick were subjected to explosion from 50 lbs of TNT at differing distances (3.5 feet to 10 feet) and to pressures from 300 pounds per square inch (psi) to over 7,000 psi. Known for decades for its impact resistant properties, expanded polystyrene (psi), the primary material in ICFs, has recently shown great potential as a blast-resistant product. In each instance during six different blast demonstrations, EPS compressed against the face of the concrete wall and reduced the pressure of the blast.

In addition, high performance concrete can be designed to have improved blast resistant properties. These concretes often have a compressive strength exceeding 14,500 psi and contain steel fibers. These blast-resistant structures are often used in bank vaults and military applications.
Concrete planters in Washington DC (National Precast Concrete Association)

Building Protection
Ubiquitous precast concrete planters provide protection to federal buildings, museums, and national landmarks. These barriers are attractive yet are a deterrent to wayward vehicles. Attractive concrete barriers that also provide seating are becoming commonplace.

September 11, 2001 World Trade Center
Comparing the present with the past in the world around us can be an important learning experience. Such was the case for the Federal Emergency Management Agency (FEMA) and the American Society of Civil Engineers (ASCE), in the difficult task of conducting an evaluation of the World Trade Center (WTC) and surrounding buildings.
 
On September 11, 2001, airplanes struck two 110-story office towers in New York and the Pentagon in Washington, D.C. The towers (WTC 1 and WTC 2) collapsed in less than two hours, and another building in the complex (WTC 7) collapsed later in the afternoon. These buildings had few or no masonry components. All of the surrounding buildings suffered damage from falling debris, wreckage, and fire from the towers. While the impact of portions of the collapsing buildings did the majority of harm, there was also damage from flying debris to the masonry used in their construction.
WTC
Buildings surrounding World Trade Center collapse Sept. 29, 2001 (FEMA Photo 5695, http://www.fema.gov/ )

Examples demonstrate how masonry helped prevent greater destruction during the World Trade Center disaster. Some of the lessons learned:
 
 
  • Older framed buildings with masonry components performed generally better than newer buildings with lightweight curtain wall construction.
  • Masonry (walls, beams, partitions, infill) served as fireproofing and provided significant structural redundancy.
  • Masonry infill absorbed impact energy to minimize damage locally.
  • Masonry veneers and panelized systems are readily repaired.
Masonry proved in this event that it does more than simply enclose space; it provides fire protection, structural capacity, and even structural redundancy. It can provide safer enclosures for stairways or other exit routes, affording egress in high-rise buildings during emergencies.


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Resources
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Located at Bookstore2009 International Wildland-Urban Interface Code™ (2009)
International Code Council
Price: $42.75 (Member Price: $32.00) Contains provisions addressing fire spread, accessibility, defensible space, water supply and more for buildings constructed near wildland areas.
Located at BookstoreConcrete Homes: Built-in Safety (2005)
Portland Cement Association, Item Code DVD511; 8 minutes
Available for $7.95. Reformatted from VHS to DVD, this 8-minute video documents the results of tests comparing the tornado and hurricane resistance of concrete walls to wood- and steel- frame walls. Wall panels were subjected to the impact of a 15-pound wood stud "missile" traveling at 109 miles per hour. The frame walls failed to stop the airborne hazards. The concrete walls successfully resisted the impact. This DVD also includes the Built-in Safety Technology Brief (IS306) and Investigation of Wind Projectile Resistance of Insulating Concrete Form Homes research report (RP122), both in PDF format.
Located at BookstoreInvestigation of Wind Projectile Resistance of Insulating Concrete Form Homes (1998)
Portland Cement Association. Item Code: RP122
Available for $10. This report presents in-depth results of laboratory testing comparing the impact resistance of residential concrete wall construction to conventionally framed walls. The damage inflicted on ten wall specimens subjected to the impact of a 15-pound wood stud "missile" traveling at up to 109 miles per hour is described. The study compares the differences in inherent resistance to debris driven by high winds, between concrete wall systems and standard residential construction.
Located at BookstoreManual on Design for Fire Resistance of Precast, Prestressed Concrete
Precast/Prestresssed Concrete Insitute No. MNL 124-89, Softcover 96pp
Non-member price $20, member price $10. This design manual presents data on properties of materials at high temperatures, and procedures whereby floors, roofs, and walls can be analyzed for their fire endurance. Design information is augmented with extensive examples and design aids in the form of charts, graphs, or tables. Procedures are also given for redesigning structural assemblies for improved fire endurance. Whereas before, the only means of predicting fire endurance of structural assemblies was by standard fire tests, this manual provides an analytical and proven method of evaluating fire endurance of structures made of precast and prestressed concrete.
Located at BookstoreRebuilding After Katrina (2005)
Lstiburek, J., ASHRAE Journal, Vol. 47, No. 11, Nov. 2005, pp 12-19
Available for $8, free to ASHRAE members. We learn our lessons from disaster. Hurricane Andrew (1992) taught us about wind. Hurricanes Charley, Frances and Jeanne (2004) taught us about rain. The Red River of the North Basin taught us about floods (1997). Hurricane Katrina had it all: wind, rain and flood.
Located at BookstoreReview of Masonry Aspects of the World Trade Center Disaster (2001)
David T. Biggs, P.E., LT277
Available for $45. This report describes an investigation of the World Trade Center and surrounding buildings in New York City following the events of September 11, 2001. Based on the personal observations of a member of one of the investigative teams, which included people from the Federal Emergency Management Agency (FEMA) and the American Society of Civil Engineers (ASCE), masonry clad buildings appear to have performed extremely well. Published by The Masonry Society.
Located at BookstoreSSTD 10-99 Standard for Hurricane Resistant Construction
Building Officials Association of Florida
Available for $34 from the ICC
Located at BookstoreStandard Method for Determining Fire Resistance of Concrete and Masonry Construction Assemblies (1997)
American Concrete Institute Committee, 216.1, 24 pp
Nonmember Price: $70.50; ACI Member Price: $42.00 Fire resistance of building elements is an important consideration in building design. While structural design considerations for concrete and masonry at ambient temperature conditions are addressed by ACI 318 and ACI 530/ASCE 5/TMS 402, respectively, these codes do not consider the impact of fire on concrete and masonry construction. The standard portion for determining the fire resistance of concrete and masonry members and building assemblies. Where differences occur in specific design requirements between this standard and the above referenced codes, as in the case of cover protection of steel reinforcement, the more stringent of the requirements shall apply.
Download DocumentAn Engineers Guide to: Concrete Buildings and Progressive Collapse Resistance (2005)
Portland Cement Assocation, Item Code:IS545
Available for free download. This 8-page bulletin discusses the progressive collapse concept. The definitions of progressive collapse as introduced in the ASCE7-02, U.S. General Services Administration, and DoD literature are discussed. The response of reinforced concrete buildings to blast load is discussed. The U.S. General Services Administration (GSA) progressive collapse analysis and guidelines are introduced. The results of a PCA study on applying the GSA method of analysis to concrete moment resisting frame buildings located in different seismic zones is presented. The publication also includes a brief introduction to blast load.
Download DocumentAssessing the Condition and Repair Alternatives of Fire-Exposed Concrete and Masonry Members (1994)
PCA #SR322, 15 pages
Available for free. This guide provides information on assessing the severity of a fire, determining the fire's effects on the load-carrying capacity of fire-exposed members, and repair options.
Download DocumentBuilt-In Safety with Concrete Homes (2005)
Portland Cement Association. Item Code IS306.
Available for free. This document summarizes the results of laboratory testing to compare the impact resistance of residential concrete wall construction to conventionally framed walls.
Download DocumentNew Standard for Calculating Fire Resistance (1998)
Masonry Today, Vol. 7, No. 2. Portland Cement Association. Item Code: PL373
Available for free. Fire Resistant Walls - Beyond the Ratings discusses fire resistance performance of masonry walls, highlighting the fact that masonry walls often out perform other wall systems having equivalent fire resistance ratings. "New Standard for Calculating Fire Resistance" describes provisions of the new joint ACI and TMS standard, ACI 216.1-97/TMS 0216.1-97.
Download DocumentResidential Safe Rooms: Background and Research (2003)
FEMA, 11 pgs (3.7 MB)
A residential safe room is a small, specially designed (“hardened”) room, such as a bathroom or closet, or other space within the house that is intended to provide a place of refuge only for the people who live in the house. In areas subject to extreme-wind events, homeowners should consider building a residential safe room. Wind hazards, such as those associated with tornadoes and hurricanes, vary throughout the United States. The decision to build a safe room will be based largely on the magnitude of the wind hazard in a given area and on the level of risk considered acceptable.
Download DocumentTrial by Earthquake, Fire, and Wind (1996)
Masonry Today, Vol. 6, No. 1
Free to download. This issue focuses on masonry performance in natural disasters starting with an introductory article titled, "Trial by Earthquake, Fire, and investigations. "Standing Up to the Storm Requires Taking It from The Top Down" examines lessons from hurricanes Andrew and Opal. California urban-wildland fires are reviewed in "Urban-Wind." "Hurricane Opal's Impact on Masonry Structures" summarizes the TMS Disaster Investigation Team findings and "TMS Disaster Investigation Teams Stand Ready" explains how teams are sponsored, selected, and trained for Wildland Fires - the Case for Non-Combustible Construction." In addition, a case study of an award-winning residential project titled "Safe and Sound Home" and an article on "New ASTM Standards for Cements for Masonry and Plaster" are included.
Located at External Web SiteConcrete's Contrubition to Sustainable Development
Concrete is the most widely used building material on earth. It has a 2, 000 year track record ofhelping build the Roman Empire to building today's modern societies. As a result ofits versatility, beauty, strength,·and durability, concrete is used in most types ofconstruction, including homes, buildings, roads, bridges, airports, subways, and water resource structures. And with today's heightened awareness and demandfor sustainable construction, concrete performs well when compared to other building materials. Concrete is a sustainable building material due to its many eco{riendly features. The production ofconcrete is resource efficient and the ingredients require little processing. Most materials for concrete are acquired and manufactured locally which minimizes transportation energy. Concrete building systems combine insulation with high thermal mass and low air infiltration to make homes and buildings more energy efficient. Concrete has a long service life for buildings and transportation infrastructure, thereby increasing the period between reconstruction, repair, and maintenance and the associated environmental impact. Concrete, when used as pavement or exterior cladding, helps minimize the urban heat island effect, thus reducing the energy required to heat and cool our homes and buildings. Concrete incorporates recycled industrial byproducts such as fly ash, slag, and silica fume that helps reduce embodied energy, carbon footprint, and waste.
Located at External Web SiteFederal Emergency Management Agency Safe Building Resources
Listing of FEMA publications and resources
Located at External Web SiteFortified... for Safer Living, Institute of Home and Business Safety
The Fortified...for safer living ® program specifies construction, design and landscaping guidelines to increase a new home's resistance to natural disaster from the ground up. All regions of the country are exposed to one or more extreme weather events, such as high wind, wildfire, flood, hail and earthquake.