09
Jul

4 Ways Structurally Engineered Buildings Hold Up Better in Natural Disasters

Most structures in the United States have been influenced by a structural engineer (SE) in some way. The development of commercial buildings is mostly required, by code, to involve an SE working in tandem with the building’s architect. And for home builders, the final step in blueprint development usually involves an SE reviewing plans and making final calculations to ensure the final construction maintains the integrity and can handle the loads and forces it will encounter, such as weight loads as well as wind, thermal, and seismic activity.

While new buildings almost universally cross the desk of an SE, we are reminded by a recent event that some buildings predate current coding and may even have been built without the help of an SE. On September 20, 2017, an earthquake of 7.1 magnitude struck Mexico’s capital city resulting in roughly 230 deaths. The irony is that most of the casualties were not from the quake itself, but from the structural failure of mostly older buildings that had not been designed to withstand such extreme forces.

It’s easy to assume the role of the SE, but in areas of the U.S. where natural disasters are more likely, the need for more deliberate structural engineering becomes not only necessary but also lifesaving. Earthquake and fire prone areas such as California; hurricane zones in the Carolinas, Florida, and Georgia; tornado alleys of the midwest; and flood plains along the coast and major rivers need to consider the specialized skill sets of SE in incorporating disaster preparedness in new construction and in retrofitting existing structures.

What Structural Engineers Can Do

The basic job of the SE is to consider the integrity and functionality of a building. SEs take into consideration bracing and load-bearing walls, for example, to prevent structural and foundational failures. They also examine exterior cladding to be sure that doors, windows, and siding can withstand the local elements. However, in disaster zones, SEs may be called upon to consider the extremes of wind, water, seismic, and thermal forces to design buildings that can resist destruction.

  1.  Wind forces: Because skyscrapers must withstand high wind forces, SEs have long focused on how to prevent wind damage and catastrophic failure. Much work, for example, has been put into construction methods that allow structures to bend or sway without causing damage, particularly to joints that would set off major problems. Pendulums installed in the highest floors of buildings counteract sway and allow buildings to right themselves. In residential construction, SEs recommend non-gabled roofs, strong exterior doors and windows, and eaves less than 20 inches as means of counteracting strong wind forces.
  2. Seismic activity: Earthquakes can have far reaching and devastating impacts on an area’s structures, which has required SEs to reconsider the way buildings are constructed. To maintain integrity under earthquake conditions, buildings must be made of materials that are both strong and flexible. New materials such as structural steel offer durability while allowing flexibility under strain. Wood, too, has proven to be light enough to reduce the load on a structure while providing significant strength. Some of the most fascinating structural engineering feats have come in the form of vibration damping systems. Base isolation is a technique by which the foundations of a building are placed upon rubbery bases that do not as readily transmit ground vibrations to the structure. Another innovative method has been to essentially place shock absorbers at each level between column and beam. The oil-filled cylinder translates seismic force into heat energy which dissipates vibration.
  3. Flooding: Water damage caused by hurricanes and by rivers overflowing their banks has driven SEs to focus on prevention and on material formats. Basic changes such as constructing buildings on raised foundations of erosion resistant concrete have given way to considerations of sealants, coatings, and equipment that render subfloors and lower floors of buildings effectively dry proof. SEs have also had to take into account the post flood impact on materials, so they have worked toward mold resistant structural elements and coatings that are less likely to collapse after lengthy submersion.
  4. Thermal forces: Disasters such as the London tenement that burned down because of faulty fireproof tiling have not only led to a deeper consideration of basic fireproof materials and prevention systems, but also to design elements that limit thermal damage. Sprinkler systems, for example, are now being designed as “clean agent” systems that won’t damage sensitive electronics if set off. SEs design buildings with compartmentalization features that use fireproof materials to prevent fire spread and with pressurized stairwells so that smoke is forced out of an escape space rather than gathering there.
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What Structural Engineers Could Do

The future of structural engineering is promising and fascinating. Seismic specialists, for example, are experimenting with a new system of concentric plastic rings that are installed beneath the foundations of a building to redirect earthquake forces around the building rendering it essentially invisible to seismic activity. Material specialists are testing an ultra high performance concrete that is six times stronger than ordinary concrete, but bendable. Some structural specialists are developing memory materials that would allow buildings to essentially right themselves after being displaced by exterior forces, while others are actually developing self healing materials.
As SEs make our future brighter and safer, we need to consider the areas in which we live and the destructive forces that act on them. While retrofitting buildings is sometimes more expensive than new construction, it is well worth the peace of mind it provides that your building won’t become an insurance casualty, but, more important, that the lives inside will be protected against harm.