The recent devastating earthquake in Haiti has focused attention on many things about that country, including politics, economics, its history and culture, and many other poignant topics, not the least of which is the safety and design of buildings there. When the first photos came onto TV, it was obvious that a lot of buildings were not even close to being able to resist a substantial earthquake.
A number of colleagues in the wall system business called me after the earthquake and asked about EIFS in Haiti. This prompted me to explain to them how EIFS behaves in earthquakes, and I thought readers would like to know. So, this month’s column is a primer on earthquakes and EIFS, using Haiti as an example. The short answer is: EIFS performs quite well, thank you.
Members
of Fairfax County Urban Search and Rescue scale a collapsed section of the
Hotel Montana in Port-au-Prince, Haiti during a search for survivors of a 7.0
magnitude earthquake. The unit was activated by the U.S. Agency for
International Development. Eight people, including 7 Americans, have been
rescued from the rubble of the hotel. (U.S. Navy photo by Mass Communication
Specialist 1st Class Joshua Lee Kelsey/Released)
It’s no secret that Haiti is known as one of the world’s most impoverished and corrupt countries. This terrible situation trickles through the entire economy, including into the construction industry. This leads to poor-quality construction, including bad design, low-grade materials and compromised inspection. When I was doing market research for the Caribbean area, Haiti didn’t even come close to making it onto a list of countries to consider as a place to do business. In essence, Haiti has no economy, a very small class of very wealthy people, a huge class of very poor people, and almost no middle class. Bribes are common and the streets aren’t safe.
Lightweight, modern materials, like EIFS over studs and sheathing, is not that common in the Caribbean. Instead, block and concrete construction is preferred, as it is highly resistant to hurricanes, pests, the corrosive effects of the sea and humidity. For instance, the Atlantis resort in Nassau, which uses EIFS as the cladding, has a concrete and masonry substrate, where a building of this sort in the U.S. or Canada would probably have a stud and sheathing wall system.
A lot of Haiti’s buildings are masonry or concrete or a combination thereof. Generally speaking, strong, limber materials, such as wood and steel, do best in earthquakes. It is not difficult to design buildings that are highly earthquake-resistant using traditional materials like brick, masonry and concrete. The key is in the quality of the block or concrete, the reinforcement and mortar. Older or poorly engineered unreinforced masonry buildings are notorious for fairing poorly in earthquakes. There are countless examples around the world of buildings that were not reinforced masonry, which became a pile of rumble, since there was little holding them together when the shaking started.
There is virtually no EIFS in Haiti, but there is some in the Dominican Republic, which is on the other side of the island of Hispanola, and which, oddly, is a tourist destination and has a decent economy.
STRUCTURAL OR NONSTRUCTURAL
EIFS is a wall cladding. It provides weatherproofing, insulation and aesthetics in a single product but does not provide strength to a wall. EIFS does not support the weight of the building (the supporting wall does that), nor the loads imposed on the building’s structure by its contents. It is only structural in the sense that any exterior wall cladding must be able to resist the forces to which it is exposed, such as wind, and also earthquakes.
The fact that EIFS is nonstructural is misleading, though. Due to the reinforcement in the basecoat, EIFS does stiffen a wall somewhat against forces from the side-like wind and earthquakes. However, the strengthening effect is not taken into account when a designer is doing the structural engineering calculations for an EIFS-clad building.
EARTHQUAKE FORCES
Earthquakes are usually caused by the movement of vast areas of underground rock called plates. Plates can be the size of a continent or bigger, and are moving very slowly in different directions-they sort of “float” over the molten core of the Earth. This movement builds up enormous locked-in stresses at the interfaces of the plates. These interfaces are commonly called a fault (the famous San Andreas Fault, in California, is a familiar example). At some point, the forces become so high that this fault interface snaps, releasing gigantic waves of energy that propagate through the ground, eventually reaching the earth’s surface. The shock waves created by earthquakes can impose both up-and-down, side-to-side forces, and splitting forces-or all three. Clearly, such forces can wreak havoc on a building. If the main structural members of a building are not properly tied together and/or are weak, the building can be twisted to such an extent that it comes apart.
There are lots of examples in Haiti where rows of buildings fell over onto each other, creating a domino-like collapse, because the walls were not anchored sufficiently to the floor and roof slabs, or were too brittle and weak.
Part of the trick in earthquake engineering is to control the behavior of the structure once it starts moving. There are many ways of doing this, including isolating the building from the ground; using heavy objects suspended in the building to dampen the movement, and; allowing slippage between building elements.
For example, vinyl siding, with miles of horizontal seams between the siding pieces, can slip past adjacent siding pieces as the wall racks out of square. On the other hand, EIFS has few joints and is firmly bonded to the substrate, and thus must be able to “go along for the ride” as the building moves.
Light materials, such as studs and sheathing, are easier to prevent uncontrollable motion than heavy dense materials. Heavy rigid materials, like concrete, once they get moving in an earthquake, require substantial reinforcement to keep them from oscillating too much and pulling themselves apart.
Ground
Motion in Earthquakes: Side-to-Side; Up-and-Down; Split Open
The foam insulation in EIFS is soft and springy. This is good in earthquakes, as it allows the insulation to “give” without breaking when subjected to force. The EIFS lamina is reinforced with strong materials (glass) and is made of flexible materials (resins), and thus can withstand a lot of pushing, pulling and bending without cracking. The light weight of EIFS is also helpful in earthquakes, as there is less mass on the wall to keep in control as the building shakes. Normally being fully bonded to the substrate, EIFS is unlikely to come loose from its substrate, so the chance of someone getting hit with loose EIFS is unlikely, unless the whole supporting wall gives way.
Most of an earthquake’s effect on an EIFS wall is in the plane of the wall. With walls of studs and sheathing, the sheathing acts as a diaphragm, stiffening the wall in the plane. Thus, the EIFS does not so much have a tendency to be pulled off the wall-as occurs due to wind-but rather to be sheared off due to the racking of the wall as the building “goes out of square” due to the lateral force of the seismic movement.
Mechanically fastened EIFS tends to stiffen the wall less than adhesively attached EIFS, as the fasteners hold the foam in place by a clamping action, which allows for some slip between the foam and the substrate surface.
If the behavior of the wall supporting the EIFS is such that it cracks the substrate, the chances that the EIFS will crack is high, as the EIFS can only withstand limited movement of the substrate without the forces being transmitted through the foam insulation to the EIFS lamina and cracking it.
EIFS WITH DRAINAGE
With EIFS with drainage, special conditions occur if a trowel-applied water resistive barrier is used between the foam and the substrate. When applied onto the substrate surface, the WRB is intimately bonded to the surface and thus is subjected to the same forces as the sheathing during an earthquake (this effect also occurs due to wind, if the wall is parallel to the direction of the wind). This is not a problem in the field of the sheathing, but shearing forces do build up where the sheathing board’s edges meet. This could crack the WRB coating, thereby making the WRB ineffective at that point.
When EIFS producers obtain technical reports for their EIFS with drainage products from the building code agencies, like the International Code Council, one of the things that need to be tested is the ability of the WRB to remain crack-free despite racking forces. This is determined by testing full-size wall mockups and applying a force parallel to the plane of the wall to force the wall out of square. The WRB needs to remain crack-free despite the movement.
When Direct-Applied Coating Systems are applied directly to sheathing, the same thing occurs, only more so. Since the DAFS is the outermost layer, it must remain crack-free, lest water get directly into the wall. With EIFS, the soft foam insulation and the lamina provide extra layers of water penetration resistance.
OFF TO HAITI?
Right after the Haiti earthquake, I was contacted by several federal agencies about going down to Haiti to help to assess the condition of buildings. Somehow, my name had gotten onto a list of people with the right kind of background, and they were checking to see who was available. Their contacting me was probably due to my work after Katrina in assessing buildings, and with my work on building code seismic issues. In the end, they didn’t call back, and I do not know who actually went there to help. I was both excited about the possibility of the experience and doing some good, but also nervous about health and safety issues. It looks like Haiti is slowly rebuilding itself. However, “normal” for the poor Haitian people is now even worse than before the earthquake. W&C
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