Assessing Risk – Buildings in Coastal Locations

MAIN ROLE OF BUILDINGS

Given their roles as shelters of life and property and venues for human activity, buildings need to be designed and built to protect human life, and property, and to ensure continuity of function. This means buildings must be designed and built to protect against the elements, and also against the impact of natural hazards that may affect them from time to time during their service life.

DESIGN CRITERIA

Toward that end the design team must establish design criteria based on a projected range of conditions the building may be subjected to due to the characteristics and variability of the natural environment at the specific location. Factors such as range of temperature, sun light, precipitation of all types such as rain, hail or snow, must all be taken into account. Equally important is to ensure these design criteria also take into account the external forces and other consequences the building may be under as a result of the impact of natural hazards such as hurricanes, tornadoes, floods, earthquakes, lightning, landslides, wild fires and others.

METHODOLOGY

An effective methodology to define and apply such design criteria would include the following elements:

a) Vulnerability assessment:

b) Characterization of impact:

c) Risk assessment:

d) Use Accepted design  standards, such as ASCE-7, as baseline:

e) Enhance design criteria based on findings from a, b and c:

THE REALITY OF ACTUAL PRACTICE

The reality of actual building design practice is that the vast majority of, if not all, engineers, architects and other building design professionals are satisfied with merely complying with requirements of applicable building codes. Even in cases when experimental analysis is used, such as the use of wind tunnels or shake tables to test models of projected buildings, to assist in the design process the reality is that such tests are conducted using the minimum design loads stipulated by the building code. So, the accepted practice is to design to comply with the requirements of the building code, nothing else.

Given that building codes represent the minimum standards of building design and construction required by law, this means most and perhaps all of our buildings are built using design criteria that meet the minimum legally required levels of performance, but not potentially higher external loads and conditions that could be encountered in the course of interaction with natural hazards during the useful service life of a building.

Simply put, current approach to building design is to meet a minimum level of performance required by law rather than an anticipated level of performance required to meet recurring actual conditions during the life of the building.

In fairness, it is important to recognize there are exceptional cases where regulations require much higher levels of performance. Nuclear power plants, dams and a variety of buildings and structures designated as critical, are examples of cases where design criteria exceeds the minimum requirements of local building codes.

Sadly this imperfect system, which is the best we’ve got, is mainly in place where building codes have been adopted. There are many countries, and several jurisdictions in the USA, without a building code. One can only imagine what norms and criteria are used for building design and construction in places without a mandatory building code, but if widespread destruction caused by the impact on a natural hazard are any evidence it is clear the results speak for themselves.

What is then, the effect of what has been described above? The net result is that in USA jurisdiction and countries with a mandatory building code, the regulatory process through a mostly arbitrary approach has determined the minimum level of performance to which buildings must be designed for. For example, this system has been used to decide that buildings in some regions of Florida will be designed to perform effectively up to a mid category 3 hurricane, or that buildings and structures in California are designed to withstand the impact of a magnitude 7.5 earthquake. This regardless of the fact that the historical record has shown hurricanes of higher categories [4 and 5] in Florida, and earthquakes of stronger magnitudes [8.0, 8.5 and higher] in California, have stricken in the past and may in the future strike again.

A NEW PARADIGM WOULD BENEFIT ALL

It should be clear to anyone who objectively assesses risk, or damage in the aftermath of disasters, just meeting the requirements of the applicable building code or business as usual will not do when it comes to designing/constructing buildings in vulnerable locations.

Meeting the building code is not an option, it is required by law! So, when a building design professional or a builder highlights that a building “meets the Florida Building Code” as if this were some kind of special achievement, the fact is that all that has been done is to comply with the law.

If we are serious about designing buildings capable of fulfilling their main role, it is clear such buildings must be capable of resisting the impact of natural hazards with minimal damage to their key structural components and building envelope. To achieve this objective the design team must use design criteria above and beyond the minimum requirements of the building code, based on  findings from vulnerability assessment and characterization of impact exercises completed for the project site, which will provide estimates of the external loads and other hazards a building will encounter as it interacts with a natural hazard in the area.

In addition the design team will also need to take into account other factors such as: the shape of the building, continuity of the building envelope, relationship of main structural elements to the overall shape of the building, and surrounding man-made or natural elements or features that may act as impact modifiers.

Through this approach the design team will be able to obtain an accurate description of the environment the building will encounter as it interacts with  natural hazard, assess how it would perform under such impact and, based on this, identify design criteria to ensure the building will effectively resist such impact keeping structural and internal damage to a minimum.

In reference to the need for a new building design paradigm it It should be said that  there are building design professionals who oppose it, mostly based on erroneous assumptions. One argument used against the proposed new design paradigm is that it will make building construction too costly. In response to this I can categorically state that the cost is marginal when the methodology is applied during the design phase of a building , based on experience, and I can also add that when you factor in the damage suffered by buildings when impacted by forces generated by a hurricane, or other natural hazard, that exceed the original design criteria, plus the cost of repairs and consequential damages, it becomes rather simply to show how cost-effective the new paradigm is.

Even in the case of existing buildings that are strengthened by way of retrofit, it is easy to show the benefits to be derived in terms of damages avoided during the useful life of the building, especially for what it means in terms of breaking the cycle of damage, repairs and more damage caused by the impact of natural hazards and the practice of continuing with the business-as-usual approach when it comes to building design and repairs..

In my opinion it is the current approach to building design in vulnerable communities that it is too costly practically from any perspective that is chosen.

THE COASTAL REGIONS OF FLORIDA

Based on the number of hits it has sustained over the years Florida is clearly the most hurricane-vulnerable state in the country. Within Florida the southeastern coastal region is the most at risk from the impact of recurring hurricanes, not only because of the frequency of repeated impacts, but also because of the population and value of the built environment at risk in the four-county area extending from Key West in Monroe County to Palm Beach County, and because some of the damage components of hurricanes such as storm surge are continuously being exacerbated by global warming, creating the potential for progressively worse impacts in the future.

This scenario of vulnerability and high risk forcefully send us the message that it is in these coastal regions, especially in southeast Florida, that this new building design paradigm needs to be urgently adopted into the everyday practice of engineering and architecture. Clearly, the same applies to vulnerable coastal regions in many other states along the Gulf of Mexico and the Atlantic seaboard.

Ideally a design team will have the opportunity of using the methodology described here during the design phase of a building, as it is at that stage that the opportunity for being most effective, both structurally and economically, is greatest.  Using the same approach on existing buildings is still possible through retrofitting measures or remodeling, resulting in higher costs because of the work involved, but even in these instances it is recommendable given that the alternative could be catastrophic damage and economic loss caused by the impact of a hurricane or other natural hazard.

For those who may be wandering how the described approach could be implemented I’d like to offer, by way of illustration, a brief presentation summarizing some of my findings when I was engaged in 2008 to preliminarily assess the vulnerability and characterize the impact of hurricanes on a high rise building, which was in the design phase, proposed for a site on an island in Biscayne Bay. This information can be viewed by clicking of the link that follows [ CONSULTING26 ]. Please note attached presentation has been edited to comply with limitations on the size of attachments.

CONTACT US

To discuss how to incorporate vulnerability assessment and characterization of impact in the design of your new building or facility or the retrofit of an existing building, as well as the benefits to be derived from this, you may contact Ricardo Alvarez at: [305] 931-0871; via FAX: [305] 931-4704, or EMAIL: ricardoalfonso@mitigat.com.


Vulnerability Assessnebt & Mitigation

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