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Seismic Evaluation and Retrofit of Haitian Masonry Construction
Day 1 – Tuesday June 14, 2011I worked with Mark Sinclair and Elizabeth Hausler from Build Change during the months of March and April to help develop a retrofit procedure for Haitian buildings. The procedure is based on an ASCE-31 style checklist to identify major structural deficiencies. As one checklist item, field engineers calculate the wall area percentage in each primary direction (capacity), and compare that value to the required wall area percentage (demand). The required wall area percentage is a function of the number of the seismicity, the number of stories, the type of construction, and several modification factors.During the development, we talked about the opportunity for me to get to Haiti to see understand the buildings and test the procedure. That opportunity came last week. I left Monday night (6/13) and arrived in Haiti Tuesday morning. Staff from Build Change greeted me at the airport and we got in the truck to drive back to the BC office. I met Matthew Hockley from Build Change who is leading the engineering effort in Haiti. We left in the afternoon to the pilot retrofit project that Build Change is performing for UNOPS. The site is in a neighborhood called Bristout Boba. We weave through PV and turn off the main road onto a dirt road requiring 4wd. We wind back into the hills while passing street vendors, small stores, and piles of trash being picked through by pigs and goats. The road becomes paved in a small neighborhood, and then goes back to eroded dirt. We arrive at the material drop area where there are piles of sand, gravel, a water tanks, and a guy hired by UNOPS to watch the materials. I had seen pictures of this jobsite prior to leaving. Mark and I provided input to the retrofit design. We walked from the drop area down a narrow path between the buildings. The paths form a labyrinth between the poorly built masonry and concrete buildings. Stairs connect the buildings like an Escher drawings. It’s difficult to determine where one building stops and the other starts. There are kids and mothers sitting at the doors on the sides of the path. The kids point at me and Matthew and say “Blanc” in Creole. I didn’t take it to be derogatory, just pointing out the difference.The building we’ve been assigned for retrofit is a one story unreinforced masonry building with a sheet metal roof. The front corner collapsed in the earthquake, and the building was red tagged by the Ministry as not safe to occupy, although the family never left. There is a 1.2 m stone retaining wall directly below the front wall, which partially collapsed, although it’s not clear whether the masonry caused the retaining wall to collapse, or vice versa. The retaining wall could have failed due to rain before or after the earthquake. The retrofit plan provides a concrete skin over the retaining wall to contain the stones. The bottom has an embedded footing and the top will be connected to the existing slab with embedded rebar. The wall will be rebuilt and the top of all the walls will receive a new “ring” beam or “cap” beam to provide strength for the wall between perpendicular walls for out-of-plane loads. The first thing I realize is how difficult it is to get materials to the site. Porters were hired to haul materials from the drop area at the top of the hill. The concrete is mixed in small batches on the roof of the adjacent downhill building and dropped into the hole for the footing. Apparently this is a problem in getting the material to the drop area, and then the porters are slow to bring materials down the hill. The word is that the porters are paid by UNOPS per day, and have no incentive to work harder or move more material. They will rotate to a new site next week to spread out the jobs, so they don’t have any long term commitment to the project.There are 4 porters, 4 builders, and 4 “engineers” hired by the MTPTC to oversee the construction. With Matthew and myself, there are at least 6 people watching the builders. Seems like an inefficient process. Progress is slow, they overdug the hole for the footing and are filling up the bottom with rocks and concrete. Every cubic foot of concrete is very labor intensive.Adjacent to our project site, Miyamoto International was overseeing construction of their own pilot project. They were encountering similar procurement problems in their effort to pour a new slab and build a new wall. It felt like a small world to have engineers from Degenkolb and Miyamoto discussing side by side retrofit projects on hillside in Haiti.http://youtu.be/X688fIIDvlU
Filed Under: Community, Degenkolb, Earthquake, Engineering, Seismic
Posted by noblestudios on June 21, 2011 11:04 AM
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