International Concrete Abstracts Portal

Structural health monitoring and sensing are rapidly developing fields of study that have been successfully applied to engineered structures, such as aircraft frames. The implementation in concrete structures, however, is neither common nor currently accepted. ACI Committees 236, Materials Science of Concrete, and 444, Analysis for Concrete Structures, undertook an effort to organize a technical session and special publication that recognize new achievements in this promising field of research. The objective of this effort is to increase awareness of leading research that applies this technology to concrete structures, and thus to promote interest in the field. Many quality papers were submitted in response to the original call for papers for this session; regrettably, several worthy papers could not be included. The subject matter of the selected papers represents a broad range of topics, from the development of specific types of embedded sensors for concrete to the implementation of wireless sensor networks to managing infrastructure systems. This volume will be of interest to engineers, researchers, and students who wish to learn more about this important, dynamic, and developing topic.

A new method is proposed for updating the nonlinear finite element (FE) model of a structural system. It has been recognized that in some classes of structures, the degradation of the capacity of the structure occurs with a change in the zero-crossing stiffness. A relationship is obtained between the damage parameters used in a numerical simulation and the FE model stiffness at the zero-load crossings. This relationship is used to update the state of the FE model to reflect the damage that is associated with dynamic parameters. The modal characteristics are identified using ambient vibration data. The approach has been applied to a numerical model of a RC beam-column building subassemblage under quasi-static loading to demonstrate the proposed method. For simulation purposes, a one-dimensional hysteretic load-deformation material model is used in the FE model to represent the nonlinear moment-rotation behavior of RC beam-column joints. A modal flexibility-based model updating procedure is performed to update the damage parameters based on the change in the dynamic characteristics at each zero-load crossing. Good agreement between the updating and simulated stiffness demonstrates the efficacy of the proposed method.

In this research, a series of innovative optically-based sensors, which were designed, fabricated and characterized were created for potential evaluation for applications in determining moisture ingress in a range of concrete materials subjected to various environmental conditions. The approach taken to the creation of these novel humidity sensors is using long period grating (LPG) technology in an optical fibre. Several sensor configurations are fabricated by coating LPGs and then characterizing and cross-comparing and evaluating the resulting sensor performance. The thin layer of polyvinyl alcohol (PVA), whose refractive index varies as a function of humidity level when coated onto a LPG written into an optical fibre, provides a means to change the optical propagation in the fibre and thus to induce the a wavelength shift in the attenuation bands of its transmission spectrum, which then is calibrated against the measurand, humidity. When compared to the more familiar optical fibre-based humidity sensors, using Fibre Bragg gratings (FBGs), the LPG-based devices show a much higher measurement sensitivity, with more relaxed requirements for coating thickness and uniformity.

This paper provides an overview of three different instrumentation schemes used to monitor long term performance of FRP repaired piles in tidal waters. These schemes were evaluated in four demonstration projects extending nearly five years. Two of these used linear polarization to estimate the corrosion rate while the third focused on the variation in the corrosion current. Problems associated with selection, installation and monitoring are described and representative results presented from all three systems. The results suggest data from linear polarization is more consistent. Findings indicate FRP wrapping lowers the prevailing corrosion rate.

Routine management and maintenance of civil infrastructure is undertaken based on structural health indicators from qualitative information gathered during inspections. The need to measure and collect data reflective of the true state of the infrastructure is crucial for proper management of the system. Presented in this paper are methods for incorporating field measurements for improved condition assessment. A full scale field deployment of a wireless, lowcost and automatic system for structural health management and condition assessment of highway structures is shown to demonstrate the ability of obtaining the necessary behavior characteristics. A short-span integral-abutment bridge was instrumented with a developed wireless sensor system measuring strain, in real time through a single network, monitoring the behavior of the structure under various loading conditions. Measurements validated the performance characteristics of the bridge, including transverse moment distribution, end fixity, and composite action of the girders and bridge deck.