Pentagon (Project Phoenix), Arlington, VA
In late September 2001, after
the Army and the FBI had completed their crime scene investigation, ECS was
called upon to complete two major tasks. The first was to assist the Structural
Engineer of Record in determining how much of the fire-damaged concrete
structure required demolition. The second was to determine if additional piles
were required to support the replacement structure, or demonstrate that the
existing foundations could support the higher loads of the replacement
structure. ECS, Ltd. was later retained to perform concrete quality control
testing during replacement of the concrete structure. The
· ECS performed concrete coring operations to obtain samples of damaged and undamaged concrete to provide a comparison for evaluation. Tests were performed on the concrete including compressive strength testing of the cores as well as Petrographic analysis. The reinforcing steel was subjected to metallurgical and tensile strength testing. Utilizing the data developed by ECS, Ltd., the Structural Engineer of Record defined the limits of demolition required. The data was also useful in the design of structural upgrades to beams and columns subjected to high heat stress to limit the amount of demolition required.
· ECS performed soil load testing designed to account for the replacement structure for the damaged portion being able to resist various internal and external forces; one that would be heavier than the original structure. Having to perform the foundation load test with the damaged structure overhead presented several major challenges.
· Additional vibration could not be induced which may further compromise the integrity of the structure.
· Due to low overhead clearances within the structure, the use of driven reaction piles or dead weight reactions was unfeasible.
· Columns and the 2nd floor above were continuously monitored for settlement and distress during the loading test procedures.
· ECS monitored concrete placement, tracked curing conditions, and sampled and tested more than 5,000 concrete cylinders using an on-site laboratory. Due to the accelerated construction schedule, three full-time ECS technicians monitored concrete operations during extended construction shifts.
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