Timothy P. Ambrose

Performance and health monitoring of the Stafford Medical Building using embedded sensors

The University of Vermont is in the process of constructing a new major facility to house various biotechnology research laboratories and offices. This five-storey, 65000 square foot concrete structure, named the Stafford Building, is being equipped with fiber optic and conventional sensors embedded into the concrete superstructure. These sensors will allow monitoring of stresses incurred during the construction phase and monitoring of concrete curing as well as vibration sensing and internal crack sensing. Longitudinal studies of the buildings in-service performance and overall health will also be carried out. A description of the sensor choices, physical placements, use and review of relevant construction practices are presented in this paper.

Remote Monitoring of Instrumented Structures Using the INTERNET Information Superhighway

The requirements of sensor monitoring associated with instrumented civil structures poses potential logistical constraints on manpower, training, and costs. The need for frequent or even continuous data monitoring places potentially severe constraints on overall system performance given real-world factors such as available manpower, geographic separation of the instrumented structures, and data archiving as well as the training and cost issues. While the pool of available low wage, moderate skill workers available to the authors is sizable (undergraduate engineering students), the level of performance of such workers is quite variable leading to data acquisition integrity and continuity issues - matters that are not acceptable in the practical field implementation of such developed systems. In the case of acquiring data from the numerous sensors within the civil structures which the authors have instrumented (e.g., a multistory building, roadway/railway bridges, and a hydroelectric dam), we have found that many of these concerns may be alleviated through the use of an automated data acquisition system which archives the acquired information in an electronic location remotely accessible through the Internet global computer network. It is therefore a possible for the data monitoring to be performed at a remote location with the only requirements for data acquisition being Internet accessibility. A description of the developed scheme is presented as well as guiding philosophies.

Embedded sensors results from the Winooski One Hydroelectric Dam

Fiber optic sensors were embedded into a 7.5 MW hydroelectric dam during its construction phase. Power generation began at the facility during the spring of 1993 as did initial verification of the on-line use of certain key embedded sensors. Reliability information, as well as structural vibration signatures for the dam, has been obtained under various operational regimes. This information as well as the initial perspectives from builders, owners, users, and regulatory officials regarding embedded sensors is presented.

Lessons learned in embedding fiber sensors into large civil structures

Fiber optic cables have long since held the promise of providing low cost, widespread sensing capabilities. The use of fiber optic sensors within a large civil structure could allow for multiple sensing capabilities providing information as to the health of a structure. The Stafford Emerging Technologies Research Complex is a five-story, 65,000 square foot building currently under the final phases of construction on the campus of the University of Vermont. Over the course of the eight months approximately seventy fiber optic sensors have been installed within the concrete frame work of the building. The intrinsic and extrinsic fiber sensors are comprised of various types of singlemode and multimode cables. Since this project is the first major installation of its kind, very little was known as to what techniques should be implemented to maximize fiber survivability. While installing the sensor network at the Stafford building site many lessons have been learned that would aid in future fiber installations. The techniques developed while installing fiber optic sensors are presented.

Shoring systems for construction load monitoring

Over the past 25 years in the US there have been more than 85 collapses of structures under construction that have been directly attributable to formwork failure. We have investigated sensing systems and techniques applicable to the monitoring of construction-site shoring and scaffolding with preliminary systems being used in the field and in the laboratory. Such a sensor network may provide significant information about the load distribution on shoring systems-information that is currently not available. This information will allow dangerous situations to be quickly identified so that corrective action can then be taken. Thus the risk of injury or loss of life at a construction site should be reduced, possibly leading to lower liability insurance costs. Furthermore, this information may also be used to formulate new construction codes that will further enhance construction work safety. Laboratory proof-of-concept experiments as well as actual field-site measurements presenting the in-service use and capabilities of an intelligent shoring system are described in this paper.

Prefabricated sensor panels for smart-civil-structures instrumentation

Installation of fiber optic sensors into large civil structures entails either embedding or attaching the sensors to some structural member. While we have performed sensor installations on numerous types and sizes of civil structures, this process is frequently quite labor- and time-intensive -- both of which can potentially conflict with construction site practices. In instances where it is desirable to install many sensors in close proximity, it may prove very beneficial to prefabricate panels of sensors and then install the panel into the structure. However, issues such as the effect of the panels on the structural integrity of the building may arise. In this paper we discuss this matter as well as the panel interconnect and sensor interrogation issues. Examples of prefabricated sensor panels designed for installation into a new wing of the Medical Center Hospital of Vermont are then presented.

Internet monitoring of an instrumented civil structure

Routine acquisition of data from instrumented civil structures need not require onsite presence. We have developed a sensor interrogation method which utilizes the Internet global computer network as the information conduit from sensor(s) to user. It is therefore possible for the data monitoring to be performed at a remote location with the only requirements for data acquisition being Internet accessibility. Such a system may prove quite advantageous when a single user, or small group, is required to acquire and analyze data from several instrumented structures which are geographically very separated. In this developed system, it is possible to remotely acquire raw sensor data as well as realtime video/audio images of the current status at the instrumented structure.

Large deflection measurements in structures using diffraction gratings

An optical technique has been developed whereby two angles and linear displacement can be simultaneously measured in a non-contact manner. The method depends upon the usage of a diffraction grating with linear variation of period along its length. The grating is attached to a structure at a point of interest while all other system components are placed at a remote location. Evaluation of this measurement technique has been demonstrated on a laboratory- based structure which simulated conditions found at deep trench (or tunnel) walls or bracing systems. In a construction site configuration, this sensor allows the user to determine if the walls are undergoing structural deformation. In addition, the magnitude of deformation may be measured and alarm conditions may be monitored. Experimental results obtained using this technique are presented and compared with theory.

Machine Guarding by Electromagnetic Field Distortion

The effective guarding of machines against human injury is an enormous problem already with many available solutions. Guarding procedures generally fall into one of three classes: (1) Physical guards which prevent the placing of limbs and personnel in potential crush points. (2) Those devices which require the removal of the human from the device so that they can be activated, e.g. switches for activation. (3) Sensor, such as light sheets which shut down the machinery when the presence of an object, such as a hand, is detected in a hazardous position. We have developed a novel machine guarding technique based on the measurement of electromagnetic field distortion. There are no physical connections between the operator and the machine. The machine guarding is accomplished by merely sensing operator presence/absence through the capacitance change caused by the operator themself. As such we see few easy ways in which such a machine guard may be deactivated.

Polymer Optical Fiber Sensors for Structural Sensing Applications

The research area of “Smart Materials and Structures” represents one of the blossoming stars in multi/cross-disciplinary applied and fundamental research. Activities abound both in the fundamental area of investigation into new “smart or intelligent” materials as well as the application of existing materials into structural elements and systems.