The increasing number of natural disasters affecting communities worldwide is pushing the limits of existing residential and infrastructure resiliency during storm events. The New York City Build It Back program, administered by the Mayor's Office of Housing Recovery Operations, was created to assist homeowners, landlords, renters and tenants affected by Hurricane Sandy within the five boroughs. The primary goal of the program is to make Sandy-affected New Yorkers and communities safer and more resilient. In the hardest hit waterfront communities, Build It Back is rebuilding and elevating almost 1,400 homes to today’s stringent regulations for flood compliance.
This paper presents the construction challenges encountered in lifting hundreds of existing houses to a required flood protection elevation in New York City and in anchoring those structures to a different foundation system. The paper discusses some of the major construction considerations addressed in this program; property or lot logistic constraints, soil quality, proximity to water bodies, elevation differences between adjacent structures, condition and nature of the structure - both vertical and lateral load supporting systems.
The initial process of lifting a house was to inspect the underbelly structure, verify the base framing and anchorage to the existing foundation. Based on this data and on the new foundation design, the lifting engineer provided the contractor plans indicating the crib stack location, dimensions and grid of the supporting beams. Field Inspections were then performed to verify appropriate execution and pro-actively updated the lifting plan. This paper presents case studies showing different framing systems encountered and describes the path taken to address them.
One of the most challenging problems encountered during this house lifting process was the pile installation within a set range of tolerance, accounting for variables such as water tide, water table and property constraints. Interferences encountered during pile installations required in many cases foundation modifications. This was recurring issue in this program that was addressed by setting a set of standard protocols to avoid design and construction fragmentation.
The suggested approach consisted of setting locations and elevations of shoring crib stacks in reference to the new foundations, preparing a set of structural design alternatives to mitigate interferences or soil excavation issues, performing post-lift inspections to evaluate the existing structural system and to update the design accordingly.
The paper shows that on a large-scale project the use of a set of engineering and construction parameters, protocols and corrective procedures, can minimize construction difficulties and delays while preventing design fragmentation. The large amount of construction data and field design changes collected over time provided the design and field teams a streamlined approach in facing large-scale resiliency project. This paper aims at sharing the knowledge gained in this program so it can benefit other programs addressing similar resiliency issues.