Masonry Resiliency Protects Occupants & Buildings

Building Beyond Building Codes

David Biggs, PE, SE

Masonry Resiliency Protects Occupants & Buildings

David Biggs

Figure 1 - Emerging Megaregions

Building Beyond Building Codes

The English term resilience originated between 1620 and 1630. Derived from the Latin word resili(ēns), which is the present participle of resilīre, meaning to spring back or rebound.1 While first applied to describe a property of materials, now resilience is used in regard to nearly every aspect of our society. Resiliency describes the response to events of adversity, misfortune, threat or even disasters.

Masonry is the only structural system that has millennia of survivability

For architects and engineers, resiliency describes the ability to quickly return a damaged building or facility to productive use following a major event or disaster. The repaired building thereby springs back, or rebounds, from a devastating event.

Why do we need resiliency?

There are two primary reasons for resiliency. The growing population and the projections that this growth will result in megaregions. According to the Regional Plan Association, US metropolitan regions have grown since the mid 20th century such that boundaries are blending and developing into megaregions.2 Figure 1 shows 11 projected megaregions for 2050. These megaregions share many characteristics in addition to concentration of population. These characteristics include some or all environmental systems and topography, infrastructure systems, economic linkages, settlement patterns and land use, shared culture and history. Every disastrous event will impact the lives of many.

A second reason for resiliency is the occurrence of natural and man-made disasters. The Federal Emergency Management Agency (FEMA) maintains records for federal natural disaster declarations since 1953.3 Beginning in 1996, yearly declarations have generally doubled over previous years. Extreme natural events appear to be increasing. Since the 1990s, fear of man-made disasters has increased as well.

In 2014, Core Logic ranked the continental states and the District of Columbia for natural hazard risk. Florida rated number 1 and Michigan number 49. Alaska and Hawaii were not included. Ranking is based upon data representing nine natural hazards: flood, wildfire, tornado, storm surge, earthquake, straight-line wind, hurricane wind, hail and sinkhole. For those living in northern climates, snow and ice storms appear to be underrepresented.4 Figure 2 shows Core Logic ranking in graphical form.

Figure 2 - Map illustrating natural hazard risks with areas of high risk in red and low risk in green

Although this ranking system is just one company’s attempt to qualitatively assess risk, results are useful for this discussion.

What constitutes building resiliency?

Two key ingredients for a resilient building to accommodate an extreme event are safety and durability. From a safety perspective, it’s desirable for the building to survive with no loss of life to the occupants. Regarding durability, the building should remain intact and capable of being repaired. Realistically, economics must always be considered for commercial properties. It may be possible to repair the building, however, the completed structure must be capable of generating sufficient cash flow to support ongoing operations and maintenance.

Resiliency requires both materials and systems to be resilient. Optimally, there would also be redundancy to serve multiple functions.

Figure 3 Masonry is an ideal solution. Materials are durable, sustainable and reusable after many extreme events. Masonry is the only structural system that has millennia of survivability. World monuments (pyramids, ancient cities, Great Wall of China and countless more) are uniquely masonry. No material or system has survived the ages like masonry. Masonry construction also provides multi-functional redundancy for acoustics, fire resistance, structure, finish and more.

Figure 3 – Resiliency happens when both systems and materials are resilient and ideally redundant, serving multiple functions

Challenges of designing for resilience

Architects and engineers wanting to design buildings for resilience must anticipate extreme events and determine appropriate loads to minimize potential destruction. Traditionally, building codes are the source of loads on a structure by reference to ASCE 7, Minimum Design Loads and Associated Criteria for Buildings and Other Structures for structural loadings. This standard is intended to provide minimum load requirements to protect the life, health and safety of occupants. The standard does not specifically address resiliency, but it does include design loadings for some events such as flood, wind, seismic and atmospheric ice. In the 2016 edition of ASCE 7, tsunami design was added. As of the 2015 International Building Code (IBC), storm shelters are now required in tornado regions for specific facilities.

The resiliency of masonry is essential for residential and commercial buildings in high winds regions

Codes also have risk categories for flood, wind, snow, earthquake and ice loads with loadings. To some degree, this provides resiliency for specific events. However, safety is still the key component to design. Durability is not addressed.

Another standard, ASCE/SEI 41-17, Seismic Evaluation and Retrofit of Existing Buildings, allows engineers and owners to assess and retrofit existing structures for seismic loads based upon desired performance. This standard has aspects of resiliency embedded within. It considers various building performance levels with key levels being :

  • collapse prevention
  • life safety
  • immediate occupancy.

Recent code changes have resulted in less safe buildings that should be corrected through the use of passive systems such as compartmentalization and non-combustible construction

Life safety performance is closest to new building design where occupant injuries are expected to be less than life-threatening. However, building damage may be more extensive than expected in a new building for the same seismic event. In both the new building and retrofitted building, damage may be so extensive that repairs might not be economically feasible. Retrofitted buildings with immediate occupancy level performance are expected to have minimal or minor structural damage and very low risk of life safety. Codes and standards have aspects of resiliency but not enough.

Where are codes going?

The future of building codes is tending toward performance-based design.

Performance-based has the potential to incorporate resiliency by setting building performance levels to address risks associated with a region similar to what ASCE 41 does for seismic assessment of existing buildings. Code efforts are underway, but it could be decades before new standards become code. Until then, it falls to architects and engineers to work with owners and local building officials to address resiliency on a project basis or even a community basis.

Pushing codes forward are various government efforts, including the National Mitigation Framework from FEMA.5 In the next decade, we can expect resiliency to equal sustainability as top priorities for construction.

What buildings and facilities require greatest resilience?

On a personal level, people want their homes to be safe and resilient. From a community perspective, essential facilities such as emergency response (fire, police, EMT and ambulance), hospitals, schools, community shelters are the high priority. In the business field, many industries such as insurance, banking, water, power facilities and others require resiliency for continuity of service.

Resiliency guidelines

In the absence of building code direction, architects and engineers need guidelines to assist in resiliency decision making. Advice is available from such organizations as:

  • FEMA: Risk Management Series (26), 2013.

Pre-Disaster Recovery Planning Guide for Local Governments, February 2017.

Design Guide for Improving Critical Facility Safety from Flooding and High Winds, FEMA 543, January 2007.

Safe Rooms for Tornadoes and Hurricanes Guidance for Community and Residential Safe Rooms FEMA P-361, Third Edition, March 2015.

Flood Damage-Resistant Materials Requirements for Buildings Located in Special Flood Hazard Areas in accordance with the National Flood Insurance Program Technical Bulletin 2, August 2008.

  • US Department of Homeland Security: Resilience.
  • National Institute of Building Sciences and Sustainable Building Industries Council: Whole Building Design Guidelines.
  • Institute for Business and Home Safety (IBHS): FORTIFIED HOME.
  • Brick Industry Association (BIA): Technical Notes.
  • National Concrete Masonry Association (NCMA): Tech Notes
  • United States Resiliency Council: http://usrc.org/about-us

Masonry Resiliency Examples

Figure 4 – For buildings where combustible materials are acceptable, there is no assurance they will survive a fire.

Fire - Building fires can be devastating. Figure 4 Building codes expect that in the event of a fire, occupants will have time to safely exit. However, codes do not expect that there will be a building left after a fire.

Masonry buildings can be designed for resiliency by using a balanced design of passive and active systems including noncombustible materials, compartmentalization of the space and an active fire suppression system of sprinklers.

Since clay masonry is created in a kiln at high temperature, it is non-combustible. What material could be better to resist fire? Compartmentalization of the space limits spread of fire and minimizes damage to contents. Sprinklers actively work to extinguish fire before it spreads. The fire in Figure 5 was limited to room of fire origination.

Figure 5 - Masonry’s ability to compartmentalize fire may prevent it’s spread beyond the room of origin.

National Association of State Fire Marshals issued a press release on December 13, 2017, “Project FAIL-SAFE finds sprinkler trade-offs lead to drop in overall fire safety scores”.While strongly supporting sprinklers and other fire suppression systems, the press release states, However, if sprinkler systems do not function as designed, results can be devastating. Modern buildings, especially those built since the creation of the I-Codes, often have reduced passive fire safety features. This means fire can spread more rapidly, leading to a heightened potential for a catastrophic collapse or failure. Their conclusion is that recent code changes have resulted in less safe buildings that should be corrected through the use of passive systems such as compartmentalization and non-combustible construction. Masonry provides the needed protection.

Wildfires illustrate that not all fires emanate from inside a building. Non-combustible masonry exterior walls are essential to resiliency against wild fires. The weakness is often with roofing and roof structure. Masonry tiles can be part of a resilient solution.

Figure 6 –Wind Speed Areas in the Continental United States taken from the IBC

High Winds – Tornadoes and hurricanes account for the majority of damage and deaths from natural disasters in the US in recent years. Figure 6 is taken from the International Building Code to show high wind areas in the US.

The United States Geological Survey, Figure 7, has mapped tornado risk areas within the high wind zones identified in the IBC, Figure 6. In comparing Figures 6 and 7 with the megaregions of Figure 1, high wind risks are clear.

Figure 7 – Map illustrates high and highest areas of risk for tornadoes in the US.

Thus, the resiliency of masonry is essential for residential and commercial buildings in high wind regions. FEMA Independent Study course IS-394.A: Protecting Your Home or Small Business from Disaster actually recommends to engineer and construct masonry walls to support specific building architecture (ie, exterior wall panels, parapets and decorative finishes). Diaphragm action to resist wind-generated shear forces must be maintained and reinforcement must be properly placed in concrete and masonry walls to reduce the possibility of collapse during high wind storms.

Figure 8 - Continuos Load Path

In recent years, the National Science Foundation has expanded its wind research initiatives in its multiple natural hazards program which already includes earthquake and water hazards. Figure 8 is taken from FEMA P-691 Disaster Assistance Programs, Figure B3-6 and highlights reinforced masonry as a design choice. It illustrates the ability to create a continuous load path from foundation to roof.

See SMART| dynamics of masonry (Resilience issue v2.6, 2016 p21-28) for Corey Schultz’s article about high wind storm shelters for communities or residences using reinforced masonry. Storm shelters use design techniques common to reinforced masonry in building codes, but with special design loads for wind and debris impact. One of the various masonry industry documents for high wind design is NCMA TEK 5-11, Residential Details for High Wind Areas.

The masonry industry takes resiliency very seriously. The International Masonry Institute (IMI) offers a seminar/webinar titled Tornado Shelter Design with Masonryfor designers and contractors. In addition, the Masonry Contractors Association of America (MCAA) offers a Storm Shelter Construction Education and Credentialing Program of five courses specifically designed for the masonry installer, it covers critical facets of successful installation of a storm shelter. Masons who complete this program earn the designation Credentialed Storm Shelter Installer. Owners and designers can specify that masons have this credential for their projects.

Components used in storm shelters are addressed by the National Storm Shelter Association. They include structural clay brick and concrete masonry.6

Floods - Flooding can affect any region due to coastal effects, rivers and streams. Figure 9 FEMA states, masonry construction is the most suited to wet floodproofing in terms of damage resistance. In addition, FEMA recommends solid-grouted masonry construction within the flood depth because it resists water damage to walls, resists mold development and protects against contamination.

Figure 9 –Many New Jersey apartments had water several feet high in and around them after the storm surge from Hurricane Sandy, 2012.

Masonry cavity walls present specific challenges. Backup must be waterproofed, Figure 10, and strong enough to resist the hydrostatic pressure of the rising flood waters. Using grouted concrete masonry as backup provides both structural strength and a solid base for waterproofing.

Backup of the cavity wall can be waterproofed, but flood waters that enter the cavity bring contamination and require partial demolition to implement repair.

For existing buildings, Protecting Your Property from Floodingby FEMA suggests adding a waterproof membrane to existing framing and protecting it with a masonry veneer. Figure 10

Figure 10 - FEMA suggests adding a waterproof membrane to existing framing and protecting it with a masonry veneer.

Masonry construction is a logical choice for new buildings that could be subjected to flooding.

Earthquakes – FEMA forecasts the frequency of earthquake damage in the US. Figure 11 shows the affected states. Engineers design using building codes that are derived from FEMA seismic hazard maps. Figure 12

Figure 11 – Forecasted frequency of earthquake shaking capable of causing damage within the united states
Figure 12 – US Geological Survey and FEMA Seismic Hazards Map illustrating US seismic zones.

Design codes are intended to result in buildings that protect life safety. Part of the design process includes assigning risk categories based upon occupant use and greater loads for high risk categories such as essential facilities or buildings. Effectively, this is a partial attempt at resilience.

US Resiliency Council Rating System

Engineers understand limitations within the codes, but many owners are under the mistaken impression their seismically-designed building would survive an earthquake with minimal damage and be back in operation the next day. This is not accurate. An attempt to address these misperceptions led to the development of a rating system and introduction to US Resiliency Council (USRC). The Council formed mostly by structural engineers is implementing and disseminating rating systems that describe performance of buildings during earthquakes and other natural hazard events. Initial efforts are geared to earthquakes, but the Council intends to address other hazards in coming years.

The Council rates buildings on performance, safety, damage and recovery. Figure 13 shows the rating system and general correlation with a code-based design.

Figure 13 – US Resiliency Council (USRC). The Council formed mostly by structural engineers is implementing and disseminating rating systems that describe performance of buildings during earthquakes and other natural hazard events.

Structural reinforced masonry has a proven record of good performance by buildings designed to current codes during recent earthquakes, both internationally and domestically. A Review on Seismic Performance of Reinforced Masonry Structures provides one reference.8 Unfortunately following a major earthquake, the news always shows the disastrous results from many older unreinforced masonry buildings, Figure 14

Figure 14 – After a 6.3 magnitude earthquake in Christchurch, New Zealand 2011

Masonry design has evolved to prevent these failures with new buildings through significant research such as the large-scale masonry testing at the University of California-San Diego and other institutions.

Blast, Impact Accident – Man-made events, whether accidental or intentional, present a real concern in recent decades. The 1993 World Trade Center attack, the 1995 bombing of the Murrah Federal Office building in Oklahoma City Figure 15 and the 9- 11-2001 attacks on the World Trade Center and Pentagon have created a serious concern for our safety.

Figure 15 – A domestic terrorist bombing destroyed the Murrah Federal Office Building and destroyed or damaged 324 buildings in the surrounding area of Oklahoma City, OK, 1995

Following the 2001 World Trade Center attack, masonry buildings surrounding the towers were evaluated and found to be far more resilient than steel-framed structures. Many modern buildings had to be demolished.9 Resiliency of these masonry buildings was documented in 2014 (From Disaster to Present Day: The Resiliency of Masonry Following September 11, 2001, Mauerwerk Magazine, Germany).

Beyond the Code

Resilience has joined sustainability as essential characteristics of new construction. Masonry offers both. Building codes are progressing but they currently do not assure resiliency. Until codes require resiliency, designers must advocate for designing beyond the codes for their clients’ benefit. What designers can be sure of is that masonry construction can provide the resiliency that is needed.

David T Biggs

David T Biggs, PE, SE, DIST M ASCE, HTMS, FSEI, is principal of Biggs Consulting Engineering in Saratoga Springs NY and the Program Coordinator for the BIM-M Initiative. He specializes in structural forensic engineering, masonry design and historic restoration. He lectures, is involved with research projects and provides consulting for the development of new masonry products. He is a Distinguished Member of ASCE, an Honorary Member of The Masonry Society, and a member of the TMS 402/602 Main Committee. Biggs is also an Editorial Advisory Board GREAT MIND of SMART | dynamics of masonry and a partner of Constructive LLC, prefabricated masonry wall system. biggsconsulting@att.net | 518.495.5739

LEARNING OBJECTIVES

Upon reading the article you will be able to:

1 Identify properties of masonry wall systems that produce structures resilient to natural disasters.

2 Explain where code is sufficient and where designers should go beyond code.

3 Name codes, standards and specifications that establish structural load requirements for various natural weather events.

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