Elia A. Tantele

Integration of Probabilistic Effectiveness with a Two-stage Genetic Algorithm Methodology to Develop Optimum Maintenance Strategies for Bridges

Preventative Maintenance (PM) measures can be used to postpone/delay the initiation of corrosion from chlo- ride attack in reinforced concrete bridges. However there are a lot of uncertainties that influence their degree of effective- ness. Also the time-application of these measures can raise a conflict between safety requirements and budgets. This paper presents a stochastic approach for estimating the effectiveness of different PM measures. Additionally a two-stage optimi- sation methodology using the principles of Genetic Algorithms (GA) is developed to address the problem of the time- application by linking the effectiveness with the cost to produce optimum PM strategies. Futhermore, the role of the pre- sented time-dependent probabilistic approach in the proposed two-stage GA methodology for obtaining optimum PM strategies is demonstrated.

Effect of environmental deterioration on buildings: a condition assessment case study

The deterioration of structures due to corrosion is probably the most significant factor for their damaging condition and the need for maintenance. Corrosion mechanisms depend on the environmental conditions and the geographic characteristics of the area. In this paper a condition assessment methodology is presented through an application on a deteriorated building in Cyprus. The methodologys starting point is the collection of information through Google Earth for classification of buildings in regions based on their environmental and geographic characteristics. Through this screening process, buildings in each defined region are selected for evaluation. The following steps of the methodology include testing on selected structural members for the estimation of the compression strength and the depth of carbonation. The results of the case study, are used from the responsible engineer to evaluate the current condition of the building regarding its structural integrity and the effect of corrosion. The testing data showed that the current building strength is lower than the codes requirements and that carbonation induced corrosion must be addressed to prevent further damage.

Mapping the variability of carbonation progress using GIS techniques and field data: a case study of the Limassol district

Carbonation-induced corrosion of the steel reinforcement is the major deterioration factor of the RC infrastructures in urban areas. Carbonation progress in concrete is influenced by the exposure and environmental conditions prevailing at each area. Therefore, the rate of deterioration due to carbonation varies at different areas. Field measurements can quantify this carbonation progress for specific structures and areas. However, the scattered nature of individual field data offers little information to be considered for the assessment of existing structures or the design of new structures. This study aims to bridge this gap and shows that individual field data can be combined to characterise an area using GIS mapping tools. A generated map can depict the variability of carbonation progress with the geographical location. Measurements of the carbonation depth of several buildings at different locations in the Limassol district have been provided by a construction laboratory. Such information can be used to depict the carbonation progress on each structure through the calculation of the carbonation factor and then portray its value using mapping techniques. The result is a corrosion risk map of the Limassol district depicting the variability of carbonation progress with geographical locations. This can be used by engineers and managing authorities as a prediction tool for the initiation of carbonation-induced corrosion in existing structures and also at design stage to set the durability requirements of the concrete cover depth.

Classification of corrosion risk zones using GIS

Corrosion of steel reinforcement is the major deterioration factor of the RC infrastructures. Several factors are contributing towards increasing the corrosion risk like the exposure and environmental conditions which are a function of the geographical location of the infrastructure. Information for these conditions and their affected areas can be proved valuable at design stage and/or during maintenance planning. This study aims to relate corrosion risk of RC infrastructures with their geographical location. The corrosion risk is quantified through data from NDT methods and subsequently correlated with its location. Therefore high risk areas with structures prone to corrosion deterioration are identified. The latter is implemented via GIS tools in order to create maps that describe how corrosion risk is related to the location of each structure. Two GIS methods are suggested, the grid system and the use of classified areas. Corrosion data has been collected from labs about various constructions in Cyprus and used in conjunction with GIS tools to provide useful information on corrosion identification. The outcome is a digitized map of the Limassol area which indicates the risks levels associated with corrosion of the steel reinforcement.

Evaluation of Seismic Demand for Substandard Reinforced Concrete Structures

Background: Reinforced Concrete (RC) buildings with no seismic design exhibit degrading behaviour under severe seismic loading due to non-ductile brittle failure modes. The seismic performance of such substandard structures can be predicted using existing capacity demand diagram methods through the idealization of the non-linear capacity curve of the degrading system, and its comparison with a reduced earthquake demand spectrum. Objective: Modern non-linear static methods for derivation of capacity curves incorporate idealization assumptions that are too simplistic and do not apply for sub-standard buildings. The conventional idealisation procedures cannot maintain the true strength degradation behaviour of such structures in the post-peak part, and thus may lead to significant errors in seismic performance prediction especially in the cases of brittle failure modes dominating the response. Method: In order to increase the accuracy of the prediction, an alternative idealisation procedure using equivalent elastic perfectly plastic systems is proposed herein that can be used in conjunction with any capacity demand diagram method. Results: Moreover, the performance of this improved equivalent linearization procedure in predicting the response of an RC frame is assessed herein. Conclusion: This improved idealization procedure has been proven to reduce the error in the seismic performance prediction as compared to seismic shaking table test results [1] and will be further investigated probabilistically herein.

Applications of thermal imaging camera for assessing structural integrity

The ongoing degradation of structures is associated with expensive maintenance and the resulting decline in safety, force the engineer to search for structural health monitoring tools that will be fast, effective, cover large areas and cost as minimum as possible. In this context the thermal imaging cameras are an ideal monitoring tool; with the radical development of higher resolution thermal imaging, the decreasing cost of the camera and its portable size makes this technology promising to accomplish the requirements of modern structural monitoring. Thermal imaging camera uses algorithms to interpret visual displays of the amount of infrared energy emitted, transmitted and reflected by an object and form images that are invisible to the human eye. Therefore, the thermal imaging technology can be used as a tool to help the engineer gain better insight and viable information and thus enabling the structure to retain/sustain its function, form and strength within acceptable limits under operational loading. This paper presents applications of this technology for assessing the integrity of structures along with possible trends and gains on different areas of structural integrity, such as the detection of corrosion in steel rebars embedded in RC structures and the chloride contents on concrete surface.

Framework for an integrated system for enhancing the energy efficiency and structural performance of buildings

The building stock should be in operational and reliable state in order to ensure primarily the safety of the users. In addition to safety, nowadays the comfort of the users is of prime importance. To satisfy the required comfort levels the user should consume energy, in the form of heating, cooling etc. Therefore this ongoing trend to satisfy these conditions, results in buildings which are safer, more economic to operate and more sustainable. Taking into account economic, technical, durability and environmental factors there is the need for a holistic approach for the optimum performance of buildings for structural integrity and energy efficiency. Current practice evolves around building solutions that isolate each deficiency and proposes solutions to enhance each of the two separately. In the last few years, from a sustainability perspective, emphasis is placed on developing an integrated system for buildings that will improve simultaneously both the structural integrity and the energy performance and should be preferred over individual actions. This study investigates independent building and/or retrofit actions applied for structural strengthening and energy performance improvements that have the potential to be combined into an integrated system to enhance the overall performance of buildings. Such multidisciplinary approach will ensure that new and existing buildings satisfy both structural safety and energy efficiency targets in a more economic and effective manner. Furthermore, as first step in this direction, an experimental test program was conducted in the laboratory to examine the benefit of applying thermal insulation in the form of polystyrene on the durability context by reducing the building’s material deterioration due to environmental effects.

Remote monitoring as a tool in condition assessment of a highway bridge

The deterioration of civil infrastructure and their subsequent maintenance is a significant problem for the responsible managing authorities. The ideal scenario is to detect deterioration and/or structural problems at early stages so that the maintenance cost is kept low and the safety of the infrastructure remains undisputed. The current inspection regimes implemented mostly via visual inspection are planned at specific intervals but are not always executed on time due to shortcomings in expert personnel and finance. However the introduction of technological advances in the assessment of infrastructures provides the tools to alleviate this problem. This study describes the assessment of a highway RC bridges structural condition using remote structural health monitoring. A monitoring plan is implemented focusing on strain measurements; as strain is a parameter influenced by the environmental conditions supplementary data are provided from temperature and wind sensors. The data are acquired using wired sensors (deployed at specific locations) which are connected to a wireless sensor unit installed at the bridge. This WSN application enables the transmission of the raw data from the field to the office for processing and evaluation. The processed data are then used to assess the condition of the bridge. This case study, which is part of an undergoing RPF research project, illustrates that remote monitoring can alleviate the problem of missing structural inspections. Additionally, shows its potential to be the main part of a fully automated smart procedure of obtaining structural data, processed them and trigger an alarm when certain undesirable conditions are met.

Field dynamic testing on a Cyprus concrete highway bridge using Wireless Sensor Network (WSN)

The aims of the bridge management authorities are to ensure that bridges fulfil their purpose and functionality during their design life. So, it is important to identify and quantify the deterioration of the structural condition early so that a timely application of an intervention will avoid more serious problems and increased costs at a later stage. A measure to enhance the effectiveness of the existing structural evaluation by visual inspection is instrumental monitoring using sensors. The activities performed in this process belong to the field of Structural Health Monitoring (SHM). The SHM offers opportunities for continuous or periodic monitoring on bridges and technological advances allow nowadays the employment of wireless sensors networks (WSN) for this task. A SHM application using WSN was implemented on a multi-span reinforced concrete (RC) highway bridge in Limassol with the objective to study its dynamic characteristics and performance. Part of the specific bridge will be replaced and this offered a unique opportunity for measurements before and after construction so that apparent changes in the dynamic characteristics of the bridge will be identified after the repairing work. The measurements provided indications on the frequencies and mode shapes of the bridge and the response amplitude during the passing of traffic. The latter enabled the investigation of the dependency of the bridge’s structural damping to the amplitude of vibration induced by the passing of traffic. The results showed that as the excitation increases the magnitude of modal damping increases as well.

Effect of Damage on the Dynamic Characteristics of St. Nicholas Cathedral in CYPRUS

The protection of monuments from aging and natural hazards, such as earthquakes, is very important since such structures are part of the cultural heritage of many countries around the world. In order to protect them from earthquakes, their structural system has to be identified and their capacity to withstand dynamic loads has to be clearly understood. Due to the large size of such structures and the limitations imposed by antiquities departments on the methods that can be used to obtain the properties of the materials of these structures and their dynamic characteristics, the ambient vibration survey method seems to be the most appropriate one to be used. Once the dynamic characteristics are identified, they will form a bench mark and any deviation in these parameters will be used for the identification and localization of damage caused to the structure, either due to environmental factors and aging, or due to an earthquake. In this work the dynamic characteristics of St. Nicholas Cathedral obtained through ambient vibration survey and the subsequent calibrated FE model are presented. Then a numerical sensitivity analysis is performed, in which damage is inflicted at vulnerable sections of the structure and the effects of this damage on the dynamic characteristics of the structure are recorded. Finally, conclusions are drawn on the type of sensors and locations they should be placed, as well as on the effectiveness of a monitoring system in identifying and localizing damage on the structure.