Day 4: Journeying Further South
Journeying Further South
October 31, 2017
Today the team headed further south towards the center of the lake bed area. Yes, as it turns out Mexico City was once a lake in some areas! The surrounding rocky terrain slopes downward towards the city center and there are many subterranean rivers and canals that run in this direction. The neighborhood we visited today had a river flowing nearby and buildings in this area experienced significant structural damage; however, in some cases this damage is simply an indicator of ductile performance – a desired response from a seismic design perspective.
Characteristic Examples of Concrete Damage
A building of particular interest was Tehuantepec 153. In one of his reports from the mid-1990s, Dr. Breña had documented its retrofits which consisted of the addition of an entire new concrete frame system. There were numerous cracks on both faces of most columns along the perimeter of the frame system. Upon further investigation, the cracks on the column faces in the east-west direction were concentrated at column ends to form a hinge-type mechanism. The opposite column faces exhibited uniformly distributed, horizontal flexural cracks which was likely due to the rocking or tilting of the building tower above these first-floor level columns. The photographs below show hinging at the base of the column (left), and distributed cracking along the full length of the column (right).
Tehuantepec 153: variation of column crack patterns based on direction of loading
During the investigation of Tehuantepec 153, we also observed exposed what appears to be a pile cap foundation underneath the previously described first-floor level column.
Tehuantepec 153: First-floor column and underlying exposed foundation system
We were very grateful to the gentleman who gave us a tour of the inside of his own apartment in the building to investigate interior damage(pictured left).
Further down the street, we came upon Manzanillo 114. While this building was not noted as damaged in our database, we happened to look through the window and notice shear cracking on an interior column. We were fortunate to meet with the apartment complex owner. He, along with several other residents, was able to share his account of being in the building during the earthquake. Further investigation of the property indicated that nearly all of the first-floor columns inside the garage had one column face with flexural hinging at both ends (below left), and the other face starting to show signs of shear cracking (below right). Other than crack pattern, an important metric that we collect is crack width using a crack width gage (below center). We also observed pounding damage from interaction with neighboring buildings. Our discussions with building residences led us to conclude that pounding against the adjacent buildings caused the shear cracks in the columns. Unfortunately, the issue of pounding noted at Mazanillo 114 was not an isolated case. In the area we were investigating today, many buildings were constructed on small land parcels and in close proximity to adjacent structures, resulting in structural damage when these buildings impacted each other during ground shaking.
Manzanillo 114: (left) Column hinging at ends, (center) shear cracking, (right) collecting crack width data(0.30mm)
As Día de los Muertos continues, more decorations and costumes appear in the city streets. The photograph below is a mural dedicated to the holiday.
