Day 5: Damage Everywhere
Pounding Structural Damage and Dia de Los Muertos
november 1, 2017
Today was a bit of a transition day for our reconnaissance team. Joining our team was Professor Mike Kreger from the University of Alabama and his graduate student Shane. Also, it was the last full day with Cal Poly alum Garrett Haggen from Degenkolb. We decided to revisit the Condesa neighborhood, the location of one of the main concentrations of building damage in the city, to show the new team members previous structures we had visited from my first day of reconnaissance work. Along the way we encountered buildings we had not investigated before, and were able to make new observations related to pounding between adjacent structures.
Lessons Learned about Pounding between Buildings
Pounding damage results from interaction between two more buildings located next to one another. These can be buildings of the same or uneven heights where they tilt into or impact each other during the earthquake ground motion. For buildings of uneven heights, we noted instances of pounding damage to the shorter structure, and more extreme cases where the taller slender structure collapsed due to a strong force applied repeatedly at or below its mid-height. To understand this failure scenario, consider the analogy where you are standing and a sharp force hits your legs over and over; eventually your upper body becomes unstable and you collapse.
A few, varied examples of pounding are shown in the photographs below. On the left image, there are two buildings of the same height separated by notable gap due to residual lean of one of the buildings after being displaced by pounding. In the center image, a short residential structure adjacent to a 10-story apartment complex experienced shear cracking through its masonry infill due to pounding, the taller building did not have notable structural damage. On the right image, the corner of a mid-rise building is making contact with a taller building. Fortunately based on the aspect ratio and relative heights of the buildings as well as duration and spectral content of the ground motion, there was limited damage from pounding between the structures.
observations of pounding between buildings
Our investigations led me to conclude that relative displacements between buildings, and the gap provided to allow for these movements, are critical design considerations necessary to avoid pounding. Mexico City, like many metropolitan areas, has issues with structural pounding since property is valuable, land space is limited, and buildings are constructed in close proximity to one another. Through questioning the reconnaissance team leaders, I learned from Dr. Breña that pounding is not normally accounted for in design of buildings for dense, urban environments despite its potential to cause significant damage. Garrett also pointed out that when conducting post-earthquake investigation many teams only look for cracks and note the patterns/widths, but do not seek out the causes – such as the interaction between buildings that we saw yesterday which resulted in shear cracking in the columns.
Both Dr. Breña’s and Garrett’s commentaries tell me there is much to be done with transferring lessons learned about pounding from the field into codified seismic practice. I believe that this knowledge transfer is particularly important in conducting building retrofits since developing approaches to better predict and dampen the building interaction could help prevent pounding damage occurring in closely constructed buildings.
Tomorrow we head about an hour further south to the center of the lake bed area. This area experienced heavy damage due to its soil density and type. I look forward to investigating that area and hopefully learning some more about the city.
Cultural Reflections
Though I have been reporting signs of the Día de los Muertos holiday during the week, today officially begins the first day of the two day remembrance. We saw many altars dedicated to those who have passed on. One little girl came up to the group and invited us to look at her family's altar she helped create in the converted front room of their pool supplies shop. You could tell her deep pride in the altar when she broke out in a huge smile when we asked to take a picture of it.
Dia de los muertos artwork and altars