Resilient architecture: consider building shape

There was a time long ago when you could determine the function, location and even the prevailing climate at the location, just by looking at a building. Those were the now mostly gone days when most buildings were good examples of the form-follows-function dictum.

One can still see examples of buildings with thick tall walls, with very few small window openings, sited on high ground or on the side of a mountain, clearly designed and built for protection against human and natural foes. Or buildings elevated above ground in regions subjected to regular flooding. Buildings with thick walls and windows protected by screens to guard against hot climates. Or buildings with steep sloping roofs in areas of copious rains or heavy snowfalls, and I could go on with others examples, but I am sure we all know what I am talking about.

It is possible for one to compare images of the building types mentioned above with buildings actually seen in hotel strips at international tourism destinations, in waterfront districts and downtown business districts, in places as diverse as Miami, Cancun, Dubai, Johannesburg, Sao Paulo, Moscow, London or Shanghai and come to one conclusion, these modern buildings are so similar and look so much the same in terms of materials and shapes, that they could be anywhere, they are truly interchangeable. Granted that air conditioning has pretty much taken climate out of the equation, and methods and materials of modern construction are quite universal around the world, but this is no reason for not designing for place, local climate, and vulnerability to natural hazards. It is clear there is a homogeneous character to modern architecture worldwide. See the photographs that follow from four big cities (Chicago, Miami, Singapore and Moscow), in four corners of the world far away from each other and draw your own conclusions about the homogeneity of the architecture.

Chicago
FIGURE 1: Chicago waterfront skyline
FIGURE 2: Miami waterfront skyline
FIGURE 3: Moscow business district
FIGURE 4: Singapore waterfront

So, how did we get to this point? Upon careful consideration of multiple factors it could be argued that it all started with migration of rural populations to urban centers, many of which were already crowded with empty land in short supply. With cities’ population continued growth demand for residential and commercial built-environment soon exceeded existing availability, leaving higher high-rise construction as the only available option to keep pace in fully built-up urban centers. The structure made of steel, or reinforced concrete, and more recently even heavy timber, the skeleton, of these new buildings became the focal point of the design while the building envelope, the skin, depended on glass, masonry, precast concrete, and a variety of aluminum or synthetic panels to clad the exterior. Architects used the colors of various materials, or discontinuities, recesses, projecting elements and changes in the direction of the envelope to create texture, or the shape of the building itself to make a statement that distinguished a project from others around it. The end results of these movements were jungles of structurally similar buildings with a menagerie of looks, crowding urban centers. This has happened around the world, and continues to happen although in some cases for totally different reasons than those mentioned above.

Let us for a moment consider our theory of how this kind of architecture came about, and at the same time let us consider natural hazard vulnerability and climatic differences between the four cities depicted in the photos above. Singapore is barely 140 kilometers north of the equator, it has a tropical and rather warm climate, and it is vulnerable to tropical cyclones, extreme rain events, and flooding. Miami, has a subtropical climate and is located 2700 kilometers farther north from the equator than Singapore. The city is vulnerable to tropical cyclones, extreme rain events and coastal flooding. Chicago is located 4500 kilometers farther north than Singapore, enjoys a temperate climate, and it is vulnerable to windstorms and lake-effect winter storms, snow and icy conditions, as well as tornadoes. And then we have Moscow more than 6000 kilometers farther north than Singapore, with a subartic climate, subjected to winter storms, snow and ice storms, extreme rain and other cold weather extremes. I believe it would be safe to say we all agree there are vast differences in climate and vulnerability to natural hazards between these four cities, because of their individual locations around the globe. This being so, a valid question is: how come the buildings in these photos look pretty much the same despite being located in widely diverse climates, and being vulnerable to different types of natural hazards? Or could we just chalk-off these similarities in design and construction in the face of such climatic and vulnerability differences to the wise use of heating, ventilation, air conditioning and insulating materials?

Perhaps a rather more relevant question would be to ask how each of the types of buildings shown in these photos would perform, when interacting with different types of natural hazards? Answering this question requires visualizing buildings interacting with the damaging components of specific hazards, as well as what happens when the hazard interacts with a conglomerate of buildings in close proximity to one another. What effect do the height, shape, and proportions of the building – the profile it presents to the hazard – as well as the shape and characteristics of the building envelope have, and how these factors affect its performance under a hazard impact?

Regarding visualization, let me digress a bit before discussing this topic. During the seventeen years I taught graduate courses at Florida International University (FIU) and Florida Atlantic University (FAU) on these subjects of hazards, vulnerability, mitigation and risk management most of my students were already practicing design professionals, engineers and architects. Despite their academic backgrounds and professional experience most of my students, especially those with degrees in architecture, expressed surprise that the topics we were discussing in class, which they found highly relevant and critically important to their practices, had not been introduced or discussed while they were pursuing their undergraduate degrees. Furthermore, class discussions revealed most of these professionals had neither been exposed to undergraduate courses discussing impacts of natural hazards on buildings, nor had they been taught or asked to visualize what happens when a building interacts with a hazard, or consider the role of building shape in influencing the performance of a building under hazard impact. Related to this, surveys of educational curricula throughout the country over the years continue to show that most architectural students graduate with a five-year bachelor degree without taking a class on building codes, and the same applies to civil engineering students, but these at least learn about standards for design such as the American Society of Civil Engineers (ASCE) Standard 7 focusing on external environmental loads acting on buildings, and to some degree how building height and shape, as well as the character of the vicinity to a building influence the impacts of such external loads.

In summary our higher education system, save some notable exceptions, has been forming design professionals without equipping them with some critically important tools for their practices, which translates into adverse consequences and higher risk for the way we design and build in vulnerable communities.

With the above in mind let us get back to the topic of visualization. It is clear that various aspects of the building shape can influence the effects of external loads generated by a hazard’s damaging components as it interacts with the hazard itself. Design professionals must be capable of visualizing and recognizing such effects in order to assess the potential for damage and adopt design criteria to protect the structural integrity and functionality of the building.

Let us for example consider wind, the movement of air, as a damaging component of tropical cyclones, tornadoes, and storms. Wind is a fluid in motion that will flow over and around buildings in its path. Therefore a first step in the process of visualization is to determine how aerodynamic the overall shape of the building is; is it a blunt object or a streamlined one? The image below illustrates the basic effects as wind flow around a blunt or a streamlined shape:

FIGURE 5: Wind flow around blunt and streamlined objects

From the illustration we can see how the wind stream separates at it flows around a blunt shape (a) creating a wake and various effects, such as eddies, vortices and turbulence on the leeward side of the object. But when the flow is around a streamlined shape (b) the separation of flow is minimal on the leeward side of the shape. What the design professional must do is visualize what kind of profile the building presents to the flow of wind and what kind of effects will take place from that interaction with the wind, keeping in mind of course that the direction of wind flow may change rapidly or more slowly over time during a hazard event. So the design professional will need to consider what happens when the direction of windflow changes, and determine which may be the worst case scenario.

Once the interaction between the overall shape of the building and wind flow is well understood, we will need to zoom-in and consider more specific details such as the shape of the building envelope. Does the building envelope consists of flat planes with abrupt changes in direction, vertically or horizontally creating 90 degrees or lower-angle corners between adjacent walls or between walls and roof? Or, is the building envelope mainly formed by curving planes? Are there recesses and/or projecting elements, such as balconies, parapets or overhangs, in the envelope? Is the roof flat, or flat with some projecting elements, or is it a sloping roof such as a gable-end or hip roof? Are the exterior walls formed by continuous flat or curved planes, or do they incorporate discontinuities in isolated areas or throughout the entire wall? Does the building have an open-side? How tall and slender is the building? I believe it is clear what the intent is here, we are gathering as much detail as possible about the characteristics of the building envelope, in order to visualize what the actual flow and resulting effects will look like as the building interacts with the wind of a hazard, for example a hurricane.

FIGURE 6: Example of a continuous curving building envelope. There are no recesses, or projecting elements, nor discontinuities
FIGURE 7: Example of a building envelope with major discontinuties, changes in direction of the planes of exterior walls, recesses, and projecting elements.

Figures 6 and 7 above illustrate two quite contrasting types of building envelopes. I believe we would all agree that the building in Figure 6 looks much more like a streamlined object, while that in Figure 7 is definitely a collection of blunt objects. Can you visualize, or imagine, how the wind will flow around each of these buildings during a hurricane? Which will be the more turbulent or the most streamlined flow?

While we engage is this visualization exercise it is critically important that we focus on the fact that we are studying a fluid, the wind, that is applying external loads by way of wind pressure to the building with which it is interacting. This wind pressure can be positive when it pushes against the building envelope, or negative when it suctions on the envelope. Also, the tendency of the wind flow is to remain attached to the surface of the planes of the building envelope, but to separate when it finds a change in direction such as a corner of a wall or the place where exterior walls meets the roof of the building. This attached flow is what we call the boundary layer and a rather important component of wind flow, because it is the behavior of the boundary layer that we are trying to visualize to understand what happens during the wind-building interaction. In doing this the ultimate objective if to characterize the actual impact on wind on a building in terms of actual forces acting on various areas of the building. The direction, magnitude, and complex interaction of these forces with the building envelope and the building structure determine the results of interaction between building and wind. When we understand such results and the potential for damage, we will be in a position to identify alternatives for hazard mitigation solutions for the protection of the building itself, its interiors and contents, and the human life and function that it shelters.

FIGURE 8: This ilustrates the effects of windflow on a building. Red arrows illustrate the direction of the wind flow. Black arrows illustrate the direction of wind-pressure.
FIGURE 9: This illustrates that when wind strikes a particular corner of a building at certain angles vortices are generated that travel along the edges of the roof generating damaging forces
FIGURE 10: Building depicted here has a recessed portion in its building envelope. Red arows illustrate how wind gets “caught’ when flowing into the recess, which causes a momentary “stagnation’ of flow until the ‘push’ of additional wind allows the flow to continue. This phenomenon generates extreme damaging loads in this area of the building.

Two rather important factors to consider during the visualization process are building heigth and tall building slenderness. Main reasons for this are that wind-velocity increases with elevation above ground due to reduced friction to counteract wind flow. The faster flowing wind generates higher wind-pressure in direct proportion to the square of the increase in velocity. From this it follows that high-rise buildings will sustain higher external wind forces on its higher floors and roof than at ground level or lower elevation floors. Also, the proportions of the building in terms of horizontal (plan view) cross section versus the height of the building determine how slender the building is. More slender buildings have lower capacity to resist overturning, drift, and flexure loads, and are therefore subject to a higher potential for damage as they interact with wind. Figures that follow illustrate this.

FIGURE 11: This illustrates how wind flows over and around a tall building in its path resulting in various loadinf effects, such as overturning, uplift, drift, and torsion (not shown here).
FIGURE 12: This basically illustrates the same effects as Figure 11, but adds the torsion effect which happens when you have a non-centric asymetrical structure. The torsion effect is accentuated in slender high-rise buildings.

So, I am sure we all get the idea on what is involved in visualizing the interaction of wind with a building, and how such visualization helps the design professional characterize and quantify the external forces acting on the building envelope, as well as the forces transferred to the building structure. This in turn helps in determining the building’s capability to sustain such forces, and what the potential for damage is based on specific as-built or as-designed design criteria.

We can apply the same visualization methodology to assessing what happens when the building interacts with water, another major damaging component of hurricanes. In the case of water there are others factors to take into account, such as: a) Is it rushing water, such as storm surge or a flash flood? b) Waves, which result from the transfer of wind energy to the water and ride above the mean level of storm surge; c) Effects of the ground such as erosion, undermining, or waterlogging, which generate additional external loads acting on the building.

The same methodology applies to understanding what happens when a particular building shape interacts with other natural hazards including earthquake, floods, tornadoes and others. The overall shape of the building as well as that of the building envelope are key factors in what results from such interactions.

Design professionals, architects in particular, need to pay more attention and understand that when building shape or the building envelope are used to make an architectural statement, something that differentiates this one building from all others around it, this shape and building envelope are also critical factors that determine how the building will perform during a hazard event, and what the potential for damage is.

The higher education sector must also understand the importance of shape in determining building integrity and capability to sustain external loads generated by natural hazards, and introduce this critical topic early in the curriculum allowing students to incorporate it as they complete design projects or participate in research initiatives. By the same token, professional licensing boards must also require that professionals applying for licenses demonstrate a clear understanding of the concept of shape and its importance in influencing building performance during hazard events.

It will truly take educators, regulators, and building design practicioners working together to achieve a paradigm change in building design approach, for the benefit of vulnerable communities everywhere.

When aiming for resilience always consider building shape!

Posted in Characterization of Impacts, Earthquakes, Education, Flooding, Hazard Assessment, Hazard Mitigation, Hazards, Hurricanes, Resilience, Storm Surge, Tornado, Tropical Cyclones, Vulnerability Assessment | Tagged , , , , , , , | Leave a comment

RESILIENCE: A NEW FRAMEWORK IS NEEDED

During my college years, in California, as I pursued studies in environmental design, architecture and urban planning, I became interested in finding out what happens when a building interacts with a natural hazard. What external forces are applied to the building by the hazard? What are the effects from such interaction? How does a building manage to remain standing after being hit by an earthquake, or a hurricane, or by flooding? How does damage happens, what are the main causes of damage?

I began building models of my designs, seeking answers to these questions, to test their performance under simulated external loads while looking for solutions to reduce adverse effects. This process helped me focus on the cause and effect triggered by external loads acting on a building, the resulting effects, and how design criteria could counteract the same.

These early concerns led me to the practice of forensic architecture early in my career, as I had opportunities to conduct damage assessment and both building repair and reconstruction, as well as some demolition, in the aftermath of major earthquakes in Central America. What I learned during that period served me well when I conducted damage assessment in Cancun, Mexico and the Maya Riviera following major hurricane Gilbert in 1988. Building upon invaluable empirical knowledge acquired during these events, I was ready when the Florida Department of Community Affairs (DCA) retained my services to help with damage assessment in Miami-Dade County, Florida during the response and initial recovery phase after the disaster caused by Category 5 Hurricane Andrew in 1992.

At that time in 1992 the practice of emergency management was based on a simple three-phase framework, often referred to as a “three-legged-stool”. This framework is illustrated in the figure below:

Early in 1993 the federal Emergency Management Agency (FEMA) engaged my services to support their hazard mitigation program for the Hurricane Andrew major disaster declaration. This was something new in my career and yet quite familiar as it related to the questions I had been asking when I was a college student. The focus of this program was the identification and implementation of cost-effective measures to reduce the potential for damage to the built environment from future disasters. When I started managing this program FEMA’s policies were heavy on rules and regulations from Title 44 of the Code of Federal Regulations (44 CFR), and quite light when it came to actual field experience and implementation of structural “brick-and-mortar” or other engineering solutions. I designed a program where my team and I started with some inhouse training focusing on issues of project eligibility, eligible costs, benefit-cost analysis, and on how to go from 44 CFR regulations on paper to actual implementation of engineering measures in the field, to then apply a “learn-by-doing” process where we learned empirically in the field on a project by project basis. Soon our methodical approach started showing practical results in the form of hundreds of funded and completed projects using a wide range of effective and often imaginative engineering solutions.

Over time as our method proven successful, FEMA asked me to do the same and take charge of hazard mitigation programs for three other declared major disasters, including one that may be familiar to some in South Florida: the “No-name storm of March 1993”! Also, and for the first time ever, FEMA requested both their hazard mitigation programs, under Section 404 and Section 406 of the Stafford Act, be managed by the same manager, which I did for the next three years. By early 1996 we had processed, funded, and partially implemented some 700 projects worth hundreds of million of dollars throughout Florida, having learned quite a bit in the process.

Three of the most important things we learned while managing hazard mitigation programs were the following: a) Assessing the vulnerability of a facility on a site-specific basis is a required foundation for an effective hazard mitigation project; b) Above all hazard mitigation is about the reduction of potential damage, meaning damage before it happens; and c) Hazard mitigation is the foundation of emergency management. This acquired foundational knowledge lead to FEMA launching a “National Mitigation Startegy” and soon therafter a program known as “Project Impact” under which several communities were selected in different regions of the country to pursue initiatives with the objective on involving entire communities in being educated in and in practicing preparedness and hazard mitigation. One of the first Project Impact communities was Deerfield Beach, Florida, right in our neighborhood. A citically important byproduct of Project Impact was a pilot project funded by FEMA in Miami-Dade County, in which I am honored to have participated, and in which I continue to participate as member of the Steering Committee, this important project is known as the “Local Mitigation Strategy” which became a national example and the foundation for a federal law modifying the Stafford Act in 2000 to require all states and their jurisdictions to practice “Mitigation Planning”. Under these requirements states must draft and implement a “State Hazard Mitigation Plan”, which involves a process of periodic review and approval by FEMA, and a state-wide risk assessment to be completed every three years. In support of this plan the state requires all counties to have their own Hazard Mitigation Plan and to organize and manage a “Local Mitigation Strategy” (LMS) involving all county departments, all municipalities, and other critical participants such as representtaives from FEMA, the Red Cross, the U.S. Army Corps of Engineers, the State Division of Emergency Management, other state institutions, local universities, major healthcare facilities and others.

As a result of all of the above actions and events, and of the acquired knowledge associated with the same, it became clear that a new framerwork was needed to more accurately reflect the reality of the practice of emergency management. The following figure ilustrates this change:

In my opinion this new framework, illustrated above, is right on target. So much so, that as my team worked on identifying mitigation solutions for various projects the real test of whether a proposed mitigation alternative would be effective came down to the answer when asking the following question: “will this reduce potential damage”? In other words, hazard mitigation, read “damage reduction”, was at the core of emergency management.

While engaged in these endeavours, in 1994 I started teaching graduate courses in ‘Vulnerability Assessment’ and in ‘Hazard Mitigation’ for the Department of Construction Management, College of Engineering and Computing at Florida International University (FIU), where in the absence of a textbook I had the privilege of showing my students what hazard mitigation was about by visiting some of my projects throughout South Florida. In 1995 I became involved with the International Hurricane Center (IHC) where a group of academics, mainly from the social sciences, were beginning to chart the waters to develop an agenda of “hurricane research”. In the Fall of 1997 the IHC hosted the “Hemispheric Congress on Disaster Reduction and Sustainable Development”, which I managed, under the umbrella of the “United Nations International Decade of Natural Disaster Reduction ” (UNIDNDR). I still remember some of the presentations and panel discussions focusing on the definition of ‘sustainable development’, which brings me to the topic of the terms we use in our discussions and their definitions.

I recently participated as a speaker and subject matter expert in a webinar on “Designing and Building for Coastal Resiliency” hosted by Half Moon Education, Inc. (Miami, 3 April 2020), where the central theme was ‘Resilience”. I find a distinct common thread between those discussions on sustainable development in 1997 and these on resilience in 2020, which goes through other terms such as sustainability, preparedness, mitigation, and adaptation which at one time or another each became the preferred term over the 24 year span. It is as if we yearn to have a ‘term du jour’ to guide our conversation without really changing the subject matter. In the case of resilience my opinion is that the term is being used as a “catch-all” that is lacking a generally accepted definition and a much needed contextual framework. If we want resilience to become an effective practice we must adopt a clear and specific definition and stablish a well structured framework that truly reflects what the practice of resilience is about. In support of this argument I would like to offer the following ideas regarding what this needed new framework looks like:

I propose a multi-step approach, which I will describe below, with the objective of establishing the needed “New Framewrok for Resilience”. Folowing are the steps I propose:

1. Start by abandoning all preconceptions.

2. Accept the practice of vulnerability assessment as the required starting point and true foundation of resilience. We need to know and understand what can harm our communities before we can protect against such threats.

3. Address natural hazards in terms of their damaging components.

4. Consider the built-environment in terms of its functionality as shelter for human activity.

5. Visualize the interaction of the built-environment with a hazard. Understand the effects of such interaction, and the consequences of such effects on the performance of a building during the hazard event and on its functionality.

6. Always consider the role of building shape and the profile a building presents to external forces generated by a hazard.

7. Understand and consider the continuity of the building envelope as it relates to the performance of a building under impact of a hazard.

8. Always consider the character of the vicinity surrounding the building under study.

9. Identify and consider the effects of impact modifiers, which may exacerbate the impact and potential for damage to a building during a hazard event.

10. Understand and consider hidden threats and unintended consequences. Vulnerability is dynamic and changes over time in response to changes in hazards or the community.

11. Understand and consider interconnections and dependencies. A building may depend of external sources for critical services, or could iteself be a source of services to others.

12. Understand and always consider the climate factor as an exacerbator of existing hazards. For example: global warming leading to higher moisture retention in the atmosphere and extreme rain events, or sea level rise leading to higher faster flowing waves and storm surge and exponentially higher more damaging impacts.

13. Be forward looking. Consider expected impacts (future) during the service life of a building. But look back at the historical record to establish benchmarks for damage and damage functions for buildings.

14. Use previous steps and acquired data to develop scenarios of expected impacts from future hazard events over time.

15. Assess potential damage to a building per hazard event. Consider the full range of potential damage: loss of life, injury, physical, structural, interior, contents, functionality, environmental etc.

16. Assess risk for each hazard event scenario.

17. Consider damage reduction as central toward the goal of resilience.

18. Identify a range of effective hazard mitigation solutions and calculate the cost-effectiveness of each.

19. Develop design criteria for the design of new buildings or retrofitting of existing buildings.

20. Beyond the building by building approach, always consider the possibility of community-wide or regional solutions.

21. Implement

The following diagram illustrates how all of the above identified steps configure the new proposed framework for resilience:

This framework needs to be reviewed, calibrated, modified and enhanced periodically. certainly after each new hazard impact, before designing a new building or retrofitting an existing one, and periodically on a fixed schedule to account for changes in population density, demographics, and in the built-environment.

Posted in Adaptation, Climate Change, Emergency Management, Global Warming, Hazard Assessment, Hazard Mitigation, Hazards, Resilience, Sustainability, Vulnerability Assessment | Tagged , , , , , , | Leave a comment