The Economy of Preventive Maintenance of Concrete Bridges Due to Corrosion

The current practice for physical evaluation and delayed maintenance of deteriorated concrete bridge is fundamentally wrong. This research presents a new approach for the evaluation of the condition states of steel reinforced concrete bridge members, which is based on their chemical conditions instead of the physical deficiencies such as cracks and delamination. Using the proposed chemical based inspection approach, a more effective and economic preventive maintenance plan could be achieved. The available non-destructive evaluation (NDE) methods and preventive maintenance measure are identified. Since the chloride induced corrosion is the major factor that dictates the service life of the steel reinforced bridge element, a refined equation for estimation of the diffusion coefficient of chloride ions into concrete is proposed. A Finite Element Analysis (FEA) model that accounts for time-dependent and temperature-dependent diffusion coefficient was developed and verified against experimental data produced by several researchers. The results of the numerical analysis showed good agreement with experimental data. After validation against experimental data, the FEA model was used to evaluate the effectiveness of the preventive maintenance measures, such as surface sealers and overlays. The chloride profiles derived from the FEA model was then used as an indicator to select appropriate preventive maintenance measures at the right time based on the chloride concentration at the surface of the steel. A simplified concrete bridge deck element is selected to compare the life-cycle cost of a bridge deck with different concrete mix design and different maintenance strategies under various exposure conditions. For cost-effective management of concrete highway bridges, the following measures should be taken, depending on the exposure conditions: 1. For severe exposure conditions, such as coastal area or cold regions that require a large amount of deicing salt, carbon steel reinforced bridge decks have a short service life. Therefore, a well-planned preventive maintenance strategy needs to be implemented in order to postpone or eliminate the needs of major rehabilitation and replacement. In such case, the use of stainless steel could be the most economical solution for the long run. In addition, the use of integrated overlay made of high performance concrete or cathodic protection systems may reduce the life-cycle cost based on a 75-year expected service life. 2. For moderate exposures, the use of overlays and surface sealers has been deemed cost-effective. However, the life-cycle cost is very sensitive for sealer application since it needs to be reapplied frequently. Thus, the effectiveness of the sealer should be closely monitored by the Non-destructive Evaluation (NDE) methods. 3. For mild exposures, the corrosion may not be the most critical deterioration mechanism for the bridge deck element. The riding surface of the bridge deck needs to be replaced periodically due to other deterioration mechanisms such as erosion, fatigue cracks, etc. In conclusion, this research shows that it is not only economical, but also necessary to allocate more funds to perform in-depth, chemical oriented non-destructive tests and active preventive maintenance

A Study of the Allan Variance for Constant-Mean Non-Stationary Processes

The Allan Variance (AV) is a widely used quantity in areas focusing on error measurement as well as in the general analysis of variance for autocorrelated processes in domains such as engineering and, more specifically, metrology. The form of this quantity is widely used to detect noise patterns and indications of stability within signals. However, the properties of this quantity are not known for commonly occurring processes whose covariance structure is non-stationary and, in these cases, an erroneous interpretation of the AV could lead to misleading conclusions. This paper generalizes the theoretical form of the AV to some non-stationary processes while at the same time being valid also for weakly stationary processes. Some simulation examples show how this new form can help to understand the processes for which the AV is able to distinguish these from the stationary cases and hence allow for a better interpretation of this quantity in applied cases

Consensus of Multi-Agent Networks in the Presence of Adversaries Using Only Local Information

This paper addresses the problem of resilient consensus in the presence of misbehaving nodes. Although it is typical to assume knowledge of at least some nonlocal information when studying secure and fault-tolerant consensus algorithms, this assumption is not suitable for large-scale dynamic networks. To remedy this, we emphasize the use of local strategies to deal with resilience to security breaches. We study a consensus protocol that uses only local information and we consider worst-case security breaches, where the compromised nodes have full knowledge of the network and the intentions of the other nodes. We provide necessary and sufficient conditions for the normal nodes to reach consensus despite the influence of the malicious nodes under different threat assumptions. These conditions are stated in terms of a novel graph-theoretic property referred to as network robustness.Comment: This report contains the proofs of the results presented at HiCoNS 201

Tensor Computation: A New Framework for High-Dimensional Problems in EDA

Many critical EDA problems suffer from the curse of dimensionality, i.e. the very fast-scaling computational burden produced by large number of parameters and/or unknown variables. This phenomenon may be caused by multiple spatial or temporal factors (e.g. 3-D field solvers discretizations and multi-rate circuit simulation), nonlinearity of devices and circuits, large number of design or optimization parameters (e.g. full-chip routing/placement and circuit sizing), or extensive process variations (e.g. variability/reliability analysis and design for manufacturability). The computational challenges generated by such high dimensional problems are generally hard to handle efficiently with traditional EDA core algorithms that are based on matrix and vector computation. This paper presents "tensor computation" as an alternative general framework for the development of efficient EDA algorithms and tools. A tensor is a high-dimensional generalization of a matrix and a vector, and is a natural choice for both storing and solving efficiently high-dimensional EDA problems. This paper gives a basic tutorial on tensors, demonstrates some recent examples of EDA applications (e.g., nonlinear circuit modeling and high-dimensional uncertainty quantification), and suggests further open EDA problems where the use of tensor computation could be of advantage.Comment: 14 figures. Accepted by IEEE Trans. CAD of Integrated Circuits and System