Roberto Meli

Criteria and Experiences on Structural Rehabilitation of Stone Masonry Buildings in Mexico City

Structural safety of colonial stone masonry buildings is severely jeopardized in most parts of Mexico by earthquakes and by ground subsidence. The situation is particularly severe in Mexico City where subsidence has been aggravated by excessive extraction of underground water. Despite of frequent rehabilitations, cumulative damage caused by differential settlements through the centuries has led many of these structures to a critical condition. This article provides a general description of the causes of differential settlements and their effects, reviews the new techniques developed and validated in Mexico City for correcting historic trends of differential settlements, and comments on the methods for improving structural behavior. Recent rehabilitations performed in two buildings are briefly described, emphasizing the criteria and techniques adopted and the underlying studies and analyses. The complexity of the actions to be taken and the basis of the supporting studies are outlined, with the conclusion that adequate performance of these buildings in the long term can only be achieved if the rate of regional settlement is significantly reduced by diminishing extraction of underground water.

Failure of a drainage tunnel caused by an entrapped air pocket

A severe storm event occurred over the western area of Mexico City causing the rupture of a drainage tunnel, resulting in surface flooding, severe infrastructure damage and three deaths. This paper describes the methodology followed in order to validate the diagnostic of the event. The detailed investigation comprised in situ observation of the system, as well as hydraulic and structural analyses. In this case, severe pressure oscillations inside the tunnel caused by rapid filling and sudden air leakage through a large orifice (manhole) were recognized as the direct cause of the conduit burst. Further, the low strength of the concrete pipes of the tunnel, constructed without reinforced steel, and the low confinement by the dead load due to the soil above the tunnel also contributed to the rupture. The numerical results show a very unfavorable stress distribution along the tunnel stretch where the accident occurred, sufficient to cause the rupture.

Structural Monitoring of the Mexico City Cathedral (1990–2014)

ABSTRACT The Mexico City Cathedral underwent major rehabilitation during the 1990s to mitigate the effect of extreme differential settlement. As part of a comprehensive program, the project undertook a partial correction of existing differential settlements and remedial interventions to prevent additional settlement and improve the structural safety of the building. Monitoring the response of the structure during and after the rehabilitation was an essential component of the program because it enabled adjustments to the actions that were being undertaken in the subsoil and the foundation. Subsequently, this assessment was the basis for the detection of any sign of inappropriate structural performance. This article provides a brief description of the entire project and the effect of the various stages of rehabilitation on the patterns of differential settlement and the structural response of the building. It also describes the monitoring systems and evaluates their results, especially the results obtained 14 years after the completion of the rehabilitation program. Particular emphasis is placed on the results of the seismic network, which has provided a substantial amount of valuable information about the peculiar characteristics of the seismic input and the dynamic response of the structure. The findings conclude that the mitigating measures have significantly prolonged the life expectancy of the building and achieved a significant reduction of the growth rate of its differential settlements. However, continuous monitoring is essential for the detection of early signs of changes in the patterns of subsidence or the structural response to the building.

Shaking Table Tests of a Typical Mexican Colonial Temple: Evaluation of Two Retrofitting Techniques

This paper reports the results of the second phase of a research program that carried out shaking table tests on a scale model of a typical stone masonry temple. This second phase evaluates the efficacy of two different retrofitting techniques by comparing the response of the retrofitted models with that of the original unreinforced model. It was found that both retrofitting schemes substantially enhanced the performance of the model temple. The maximum intensity of the base motion for which damage was considered to be still repairable increased by 80% and 120% for the first and the second levels of retrofitting, respectively. In terms of displacement capacity, the response of the model with the second level of retrofit reached a maximum drift of 0.4%. The initial damping ratios were found to be in the range of 7% to 9%, both in the original and the retrofitted models. These ratios constitute a significant source of energy dissipation for this kind of structure.

Correction of Pattern of Subsidence and Structural Rehabilitation of the Old San Agustín Temple in Mexico City

This paper deals with the major rehabilitation of an important historic building, which had suffered heavy damage due to the great subsidence it had experienced since its origin to the present day. The first phase of the rehabilitation consisted in several campaigns of selective stiffening of the most deformable layers of the subsoil in order to decrease and, above all, to make more uniform, the subsidence of both the main temple and its adjacent chapel. Subsequently, the structure and its foundations were retrofitted to correct the damages and restore the integrity of the original building, as well as to make it less sensitive to future subsidence. To do this, the two bodies of the building were separated by creating a construction joint between them, because the sinking patterns of the two parts were incompatible. In the paper, emphasis is placed on the interpretation of the results of monitoring the behavior of the two buildings throughout the different phases of the intervention, as well as after its completion, especially concerning the correction of their sinking patterns.

Protection and Monitoring of Three Temples Close to the Excavation of a Tunnel in Guadalajara, Mexico

Because of the threat that the excavation of the tunnel would damage adjacent buildings, soil stabilization works were carried out in the areas adjacent to the tunnel. Moreover, three important historic temples were retrofitted to reduce their vulnerability, and a network of automatic sensors was installed and operated to monitor their structural behavior. The paper describes the structural engineering studies carried out for the diagnosis as well as those related to the design of the retrofitting of the three buildings. The behavior of the three temples during the stabilization works of the subsoil and during the passage of the tunneling machine is discussed. In general terms, the performance of the three temples was satisfactory; the only damage consisted in the reopening of some preexisting cracks, which were repaired soon after the passage of the boring machine. The case of the temple of San Francisco required some additional studies: environmental vibration measurements were performed to determine the dynamic properties of the structure before and after the passage of tunneling machine in order to detect possible damage, as well as to determine the effect of the changes in the soil properties in the seismic response of the temple.

Earthquake-Resilient Communities Resilient communities Resilient communities Resilient communities Resilient communities : A Look from Mexico

It is the aim of this chapter to assess the general situation of earthquake resilience in communities in Mexico. This evaluation is performed from a public policy point of view. From the diagnosis presented, challenges and areas of opportunity for implementing programs aimed at reducing risk and attaining more resilience are discussed. It is conjectured that some conclusions and recommendations aimed at achieving resilient communities in the developing countries are also applicable to the developed world.