Erica Fischer reports on construction challenges facing post-earthquake Haiti
The earthquake that hit Haiti on January 12th was described as a “middle-class disaster.” I was not sure what that meant until I arrived in Port-au-Prince on March 20th and began doing building assessments with the ATC-20 guidelines. Those who could afford proper building materials, a structural engineer to design their house, and a skilled mason to build the house, had homes which were in pristine condition. These people are considered the upper class.
Those who could not afford proper building materials, and either built the house themselves, or had a mason who did not know proper construction methods, were left with collapses and damages beyond repair. This group was the middle class.
During my time in Haiti, I saw three different types of houses:
1. Multiple story concrete frame with masonry infill and cast-in-place concrete roof.
2. One story concrete columns with masonry walls and light-gauge metal deck roof.
3. Timber frame with stone infill and wood roof.
Each type of construction had houses that had collapsed and houses that are still standing.
Haitians build their houses in stages: what they can afford at first and then add on floors and additions as they make and save more money. Unlike Americans, no one in Haiti has a mortgage. Those who do not rent own their houses, which made the destruction that more difficult to bear. Unfortunately, in many cases, the original portion of the house was not designed for additional floors to be put on top. Nor was the house, on the whole, designed to withstand an earthquake—let alone one with a magnitude of 7.0.
Multiple story concrete frame with masonry infill and cast-in-place concrete roofs
Houses that are concrete frame with masonry infill were constructed in two different ways:
1. Place the concrete for the columns and beams and then infill the openings with masonry.
2. Build the masonry walls and then place the concrete for the beams and columns.
When the beams and the columns are placed first, there is no connection between the masonry and the concrete frame, and thus the building does not perform compositely. I found, in this instance, that there were cracks along where the ceiling meets the walls and where the walls intersect. This was a result of the plaster coating the masonry and the columns cracking because there was no connection between the two.
On the other hand, when the CMU walls were built first, and then the concrete placed for the beams and columns, the concrete was able to fill the voids of the masonry, thereby making a connection between the columns, beams, and the masonry walls. This allowed the building to work compositely. In these buildings I did not see cracks at the corners, nor where the slab met the walls. In all, these buildings performed much better than those built using the first method.
Especially with this type of construction, it is crucial to have a skilled mason or a structural engineer involved. The majority of those who could not afford a structural engineer, or did not use a skilled mason, found their homes in shambles after the earthquake. Nevertheless, structural engineers and skilled masons are expensive, and when money is not available to hire them, Haitians will build homes themselves. When this happens, the concrete is usually poorly mixed and will crumble easily.
There are many different factors that go into the construction of a concrete and masonry building. The type of aggregate used in the concrete, the amount of water added to the concrete, the size of the mortar joints in the masonry walls, how the concrete is mixed, and many others. In the United States, there are strict rules for the design-mix used in concrete buildings. Laboratories must submit mix designs to the structural engineer far in advance of placing the concrete itself. In New York, for example, concrete contractors and laboratories are required to sign off on each mix design with the Department of Buildings. In Haiti, there is little-to-no quality control on concrete mixes or designs.
One story concrete columns with masonry walls and light-gauge metal deck roof
The second type of building I saw was made of concrete columns, masonry infill, and then a wood framed metal corrugated deck roof. These buildings were built in two ways, just as the concrete frame with masonry infill buildings were built: columns first and then masonry infill wall; or walls first and then concrete columns. In these types of buildings, there are no beams on the top of the walls and, therefore, most of the walls collapsed. These walls were not confined masonry walls, but cantilevered walls that were not braced on the top. The metal roofs were tied into the structure by taking the rebar in the columns, if there was any, and wrapping it around the wood framing for the roof. In most cases, the roofs were not tied into the structure, which resulted in partial or full collapses.
|House in Delmas 95: concrete columns with masonry infill. There are no concrete beams on top to confine the masonry.|
|Typical connection from concrete columns to wood framed metal deck roof.|
In an earthquake it is important to have a light-weight structure. Earthquakes are attracted to mass, so the more your structure weighs, the more force an earthquake will exert on it. A metal corrugated deck roof with wood framing is a great way to reduce the mass of your structure. However, when the roof is not properly tied in, it won’t act to brace the top of the walls. When the walls are not braced on the top, the walls act as a vertical cantilevered beam instead of properly supporting the structure.
Timber frame with stone infill and wood roof
The third type of building structure—which I saw more frequently outside of Port-au-Prince—was timber framed with stone infill. These buildings were very interesting because, as I approached the structure for an inspection, I would notice the building was leaning. I soon learned that the wood used for the timber construction was not straight, and instead of straightening the wood, the builders constructed the house to the shape of the wood: on a slant. After a timber frame was erected, stones were stacked for infill, and then everything was plastered over. These structures were very lightweight, and since earthquakes are attracted to mass, these buildings, on the whole, fared very well.
However, being lightweight isn’t always enough to save a structure, and houses which were not built with skilled labor, or with a proper grade lumber, sustained significant damage.
Wood construction has its pros and cons, yet one of the advantages is that less quality control is required. A skilled laborer is not necessarily required when building a wood home, which, for those who cannot afford a skilled laborer, allows people to build their own homes. This is important to keep in mind when it comes to rebuilding the country.
A major disadvantage to wood construction is, of course, deforestation. This is especially true in Haiti, where the country is already 98% deforested. Current rebuilding efforts involving wood construction are importing wood from the United States to Port-au-Prince. With the various taxes and fees imposed at the port, this is not a sustainable method for low income housing. Future rebuilding efforts will have to use products produced or grown within the country itself. Many different organizations have begun to look into light gauge steel as a source of material. Light gauge steel has the same advantages as wood: easy for people to build with themselves, and low quality control.
No matter what the future building material of Haiti is, it will need to be something that is lightweight, easy for people to build with themselves, and produced in Haiti itself.
Despite any damage that had occurred, all the residents I encountered were very proud of their homes. I felt honored that the Haitian people invited me into their homes and private spaces to look around. I would say that the most rewarding part of the trip was being able to tell a family that their house was safe and they no longer had to sleep outside.
Born and raised in Pound Ridge, NY, Erica grew up a Yankees and Giants fan. Not wanting to venture far from her New York roots, she attended Cornell University, graduating with a Bachelor of Science in Civil Engineering. After moving to New York City, her work has focused on high-end cultural renovations and new residential buildings.
Erica’s renovation experience concentrates on residential and theater renovations. In addition to working on the structural design of the David H. Koch Theater at Lincoln Center, Erica has worked on a variety of residential and mixed-use, high-rise buildings throughout New York.
Erica is currently chair of several committees for the Structural Engineers Association of New York (SEAoNY) including the Programs Committee Co-Chair, University Outreach Committee Chair, and the Sponsorship Committee Chair. Through these roles she helps plan the SEAoNY monthly lecture series at the Center for Architecture in New York as well as full day seminars for SEAoNY. She also plans SEAoNY university lectures in New York, where young members speak to students about current significant projects under construction.
Erica will be attending Purdue University this fall for her Masters of Science in Civil Engineering.