Real-Time Monitoring of Drift for Occupancy Resumption

At selected locations of instrumented structures, real-time displacements are acquired by either double integration of accelerometer time-series data, or differential global positioning system (GPS) with high sampling ratios deployed at roofs of tall buildings. Thus, sensor data is related to performance level and health of a building. Drift ratios are computed as the parametric indicator of damage condition of a structure. Several levels of threshold drift ratios can be postulated in order to make decisions for inspections and/or occupancy. Drift ratio is computed using relative displacement between two floors computed from accelerometers strategically deployed at select number of pairs of consecutive floors. However, GPS-measured relative displacements are limited to being acquired only at the roof with respect to its reference base - yielding only average drift ratio for a building. Until recently, GPS systems available were limited to 10-20 sps capability – limiting their use only to long-period structures (T>1s). Most recently, up to 50 sps differential GPS systems readily available are successfully used. Thus enabling future usefulness of GPS to all types of structures. Experience with data acquired from both accelerometers and GPS deployments indicates that they are reliable and provide pragmatic alternatives to alert the owners and other authorized parties to make informed decisions and select choices for pre-defined actions following significant events. Furthermore, recent adoption of such methods by financial and industrial enterprises is testimony to their viability