Preservation and rehabilitation of valuable historic heritage buildings require effective and efficient monitoring systems to ensure proper maintenance of durability and functionality of the building structures and materials. Moisture transport and retention in building infrastructure are some of the most common problems, often inducing structural damage and resulting in harmful microbial growth affecting human health. This work presents an evaluation of measurement techniques for moisture content (MC) in three types of building stone specimens. Moisture measurements, using weight, relative humidity (RH), electrical resistance, capacitance and inductance–capacitance (LC) resonant sensors, were carried out to evaluate moisture measurements in stone. The measurement techniques were evaluated through moisture saturation and drying cycles by partially submerging the stones in water and drying them in air. The results of the MC measurements demonstrate that: (1) RH moisture sensor is not fully capable of measuring the MC in the specimens due to sensor saturation; (2) electrical resistance is nonlinear traversing a large dynamic range from GΩ to kΩ and encounters ion accumulation and polarization problems; and (3) the capacitance and the LC resonant moisture-sensing techniques have a much better signal response to the variation of the moisture content, since both are directly related to the changing dielectric constant in relation to the moisture content. In addition, the LC resonant-sensing technique has an advantage in wireless sensing over other moisture measurement methods. Also, weight measurement results reveal that the moisture behavior in the stone specimens is dominated with capillary transport providing a better understanding of the MC behavior in these three types of building stones. These results lead to the conclusion that the MHz frequency dielectric properties of stone (capacitance) provide better estimates of moisture content than the RH of closed cavities within the stone or DC resistance of the stone.

As the design and construction of civil structures continue to evolve, it is becoming imperative that these structures be monitored for their health. To meet this need, the discipline of civionics has emerged. It involves the application of electronics to civil structures and aims to assist engineers in realizing the full benefits of structural health monitoring (SHM). Therefore, the goal of the civionics specifications outlined in this work is to ensure that the installation and operation of fibre optic sensors are successful. This paper will discuss several lessons learned during the implementation of health monitoring systems for civil structures. The monitoring of these structures primarily motivated the writing of these specifications. Creating a standard procedure for SHM eliminated several ambiguities, such as fibre sensor specifications and the types of cables required. As a result, it is expected that these specifications will help ensure that the sensors will survive the installation process and eventually prove their value over years of structural health monitoring. The civionics fibre optic sensor specifications include the requirements for fibre sensors and their corresponding readout units. They also include specifications for the cables, conduits, junction boxes, termination, and environmental protection.

Fiber Bragg grating (FBG) sensors are one of many fiber optic sensor technologies that are currently being used in structural health monitoring systems. The sensors operate by detecting a shift in the wavelength of the reflected maxima due to applied strain. This paper studies a new fiber Bragg interrogation method that combines a swept wavelength laser in combination with wavelength references. These include a gas cell which is used as the long term wavelength standard and an etalon used for accurate interpolation of peak wavelengths. An etalon is essentially a filter that has a periodic response over a broad wavelength range. Since its wavelength response spacing is smaller than the gas cell, it can be used to determine the intermediate wavelengths between two gas cell absorption lines. Peak location is a key element of this interrogation method and several detection algorithms are investigated. It was determined that polynomial peak fitting is the most computationally efficient method and yields a resolution of better than 0.5 pm with signal to noise ratios of 30:1 or better. With higher signal to noise ratios, polynomial peak fitting can yield a resolution of better than 0.25 pm. Using a tunable laser, a hydrogen cyanide (HCN) gas cell and an etalon with maxima every 140 pm, static load tests have demonstrated a resolution of 1 pm and an accuracy of less than 5 pm. Also, this accuracy will be maintained over a long period of time as it is based on absorption lines in the gas cell. The results of this study demonstrate that absolute accurate strain measurements can be obtained with the use of wavelength references in conjunction with a suitable peak location algorithm.

One of the key elements in a structural health monitoring system is the sensing element and data acquisition system. One type of fiber optic sensor used to measure strain is the fiber Bragg grating. Bragg gratings are fabricated using different methods. One method involves placing a mask pattern over the optical fiber and projecting UV light through it to change the refractive index of the core. However, before the grating is written into the core of the fibre, the outer fibre coatings must be stripped away either mechanically or chemically. Fibre Bragg gratings are then recoated after the grating has been written to maintain the strength and flexibility of the fibre by protecting the exposed glass from damage. Acrylate and polyimide are two types of recoat material typically used on fibre Bragg grating sensors. This work is a controlled comparison of polyimide and acrylate recoated fibres for Bragg grating strain sensors. The comparison was carried out using a tension test coupon with recoated FBG and electrical strain gauges bonded to its surface. The tension test specimen was made of cold rolled steel and was designed according to ASTM A30-97a standard. The dimensions were chosen such that three fibre optic sensors and a strain gauge can be attached on each side. The load was applied in 40 mu epsilon steps until the strain reached approximately 200 mu epsilon. The load was then incrementally decreased back to zero. FBG sensors from 2 manufacturers were compared. For the first manufacturer the Acrylate coated sensors required a gauge factor is 0.75 in order for electrical and FBG strain readings to agree. For Polyimide coated sensors, the appropriate gauge factor was very close to the theoretically predicted value of 0.8. Using these gauge factors, the error between the first manufacturers sensor readings and the strain gauges was well within +/- 5 mu epsilon. On the other hand, the second manufacturers sensors did not perform nearly as well. Their readings were substantially lower than the corresponding electrical strain gauges readings and varied from 7% to 13% below expected strain readings. This study demonstrates that bonded FBG sensors can reliably measure strain, but that not all manufacturers are producing recoated FBG sensors to the standard required for strain sensing in civil structures.

As the design and construction of civil structures continue to evolve, it is becoming imperative that these structures be monitored for their health. In order to meet this need, the discipline of Civionics has emerged. Civionics is a new term coined from Civil-Electronics, which is derived from the application of electronics to civil structures. It is similar to the term Avionics, which is used in the aerospace industry. If structural health monitoring is to become part of civil structural engineering, it should include Civionics. It involves the application of electronics to civil structures and aims to assist engineers in realizing the full benefits of structural health monitoring (SHM). In past SHM field applications, the main reason for the failure of a sensor was not the installation of the sensor itself but the egress of the sensor cables. Often, the cables were not handled and protected correctly. For SHM to be successful, specifications must be written on the entire process, beginning with system design and concluding with data collection, interpretation, and management. Civionics specifications include the technical requirements for a SHM system which encompasses fibre optic sensors, cables, conduits, junction boxes and the control room. A specification for data collection and storage is currently being developed as well. In the spring of 2004 research engineers at the University of Manitoba constructed a full-scale second generation steel free bridge deck. The bridge deck is the first of its kind to fully incorporate a complete civionics structural health monitoring system to monitor the deck's behaviour during destructive testing. Throughout the construction of the bridge deck, the entire installation of the civionics system was carried out by research engineers simulating an actual implementation of such a system in a large scale construction environment. One major concern that consulting engineers have raised is the impact that a civionics system that uses conduit, junction boxes, and other electrical ancillary protection, will have when embedded and installed externally on full-scale infrastructure. The full-scale destructive testing of a second generation steel-free bridge deck using a civionics system designed and implemented following guidelines in a civioncs specification manual at the University of Manitoba will provide engineers with the information necessary to address the constructability and structural integrity issues. Civioncs combined with structural health monitoring will provide engineers with feedback necessary to aid in optimizing design techniques and understanding our infrastructures performance, behaviour and state of condition.

As the design and construction of civil structures continue to evolve, it is becoming imperative that these structures be monitored for their health. In order to meet this need, the discipline of Civionics has emerged. It involves the applications to civil structures and aims to assist engineers in realizing the full benefits of structural health monitoring (SHM). Therefore, the goal of the specification outlined in this work is to ensure that correct installation and operating of fiber optic sensors, such as bridges, will be discussed that motivated the writing of these specifications. The main reason for the failure of FOS based monitoring systems can be traced directly to the installation of the fiber sensor itself. Therefore, by creating a standard procedure for SHM, several ambiguities are eliminated such as fiber sensor specifications and the types of cables required. As a result, these specifications will help ensure that the sensors will survive the installation process and eventually prove their value over years of monitoring the health of the structure. The Civionics FOS specifications include the requirements for fiber sensors, specifically Bragg grating sensors, and their corresponding readout unit. It also includes specifications on the cables, conduits, junction boxes, cable termination and the environmental.

The development of a fiber optic sensor system for the long-term monitoring of composite glass fiber-reinforced polymer (GFRP) poles is presented Due to aging and substantial usage of these structures, there is a growing interest in developing techniques which evaluate and monitor structural integrity. In the past few years, fiber optic sensor technology has emerged as a promising alternative to conventional methods. Fiber optic sensors can be attached to or embedded in civil structures such as bridges, dams and buildings. They operate by responding to changes in temperature and strain on the structure. One type is called a long gauge fiber optic sensor and it measures the average strain between two points on a structure. Long gauges are interferometric sensors which involve phase matching two optical paths to create a maximum interference pattern at the photodetector. The strain is calculated using the distance in which the reference arm of the interferometer is moved in order to match the optical path lengths.