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Papers by Kasun Kariyawasam

Journal of Civil Structural Health Monitoring, 2020

One of the most prevalent causes of bridge failure around the world is “scour” – the gradual eros... more One of the most prevalent causes of bridge failure around the world is “scour” – the gradual erosion of soil around a bridge foundation due to fast-flowing water. A reliable technique for monitoring scour would help bridge engineers take timely countermeasures to safeguard against failure. Although vibration-based techniques for monitoring structural damage have had limited success, primarily due to insufficient sensitivity, these have tended to focus on the detection of local damage. High natural frequency sensitivity has recently been reported for scour damage. Previous experiments to investigate this have been limited as a result of the cost of full-scale testing and the fact that scaled-down soil-structure models tested outside a centrifuge do not adequately simulate full-scale behaviour. This paper describes the development of what is believed to be the first-ever centrifuge-testing programme to establish the sensitivity of bridge natural frequency to scour. A 1/60 scale model of a two-span integral bridge with 15 m spans was tested at varying levels of scour. For the fundamental mode of vibration, these tests found up to a 40% variation in natural frequency for 30% loss of embedment. Models of three other types of foundation, which represent a shallow pad foundation, a deep pile bent and a deep monopile, were also tested in the centrifuge at different scour levels. The shallow foundation model showed lower frequency sensitivity to scour than the deep foundation models. Another important finding is that the frequency sensitivity to “global scour” is slightly higher than the sensitivity to “local scour”, for all foundation types. The level of frequency sensitivity (3.1–44% per scour depth equivalent to 30% of embedment of scour) detected in this experiment demonstrates the potential for using natural frequency as an indicator of both local and global scour of bridges, particularly those with deep foundations.

Structural Health Monitoring 2019, 2019

Scour is the main cause of bridge failure in the United States and around the world. It involves ... more Scour is the main cause of bridge failure in the United States and around the world. It involves the loss of soil from around bridge foundations due to fast flowing water. Monitoring bridge scour is challenging as it occurs underwater. A scour monitoring technique that uses accelerometers on the bridge piers and deck to provide real-time measurements of ambient vibration, from which scour-induced changes in the natural frequencies of the bridge may be monitored, has recently emerged. However, field validation of this method is difficult as scour is hard to predict-a monitoring system would need to be installed on a candidate bridge with no guarantee that natural scouring would occur within the trial monitoring period. Previous research on vibration-based scour monitoring has therefore been limited to laboratory-based experiments and numerical simulations. This paper presents a field study in which a bridge with pre-existing scour was monitored throughout a repair program, which involved the controlled raising of the riverbed level (i.e. scour in reverse). Ambient vibration due to vehicle traffic over the bridge was monitored before, during and after the repair, using eight high-sensitivity accelerometers and a remote data acquisition system. The riverbed profile was measured with sonar scanning before and after the repair. Numerical modeling predicted a 3-5% change in the first two natural frequencies of the bridge due to the scour repair. However, the actual frequencies measured on site, derived using operational modal analysis (in this case, Frequency Domain Decomposition), showed a high degree of variation. Alternative structural response parameters (mean power spectral density at the modal peaks and the modal amplitude) were found to capture the change in behavior resulting from scour. The opportunities for using these alternative parameters as a measure of scour, and the challenges involved in using operational modal analysis for scour monitoring on a real bridge, are discussed in detail. _____________

THE 7TH INTERNATIONAL CONFERENCE ON SUSTAINABLE BUILT ENVIRONMENT, 2016

Over usage of natural resources for construction of buildings has caused many environmental probl... more Over usage of natural resources for construction of buildings has caused many environmental problems. Hence mainstream requirements of building projects such as cost effectiveness and rapid construction should be achieved while ensuring that the impact on the environment is also minimum. In this context, it is beneficial to use recyclable or renewable materials as building elements. This paper describes a successful adoption of the combination of such systems in a rapid building construction project in Sri Lanka. The building envelope consists of two and three storey steel portal frames, walling system based on compressed straw panels, upper floor with precast concrete slab panels supported on a steel framework, and ceiling made from compressed straw panels. The successful application of these systems indicates the possibility to adopt them in the future for rapid, cost effective and sustainable building construction.

Proceedings of the International Conference on Smart Infrastructure and Construction, 2019

Scour, the loss of material around bridge foundations due to hydraulic action, is the main cause ... more Scour, the loss of material around bridge foundations due to hydraulic action, is the main cause of bridge failures in the United Kingdom and in many other parts of the world. Various techniques have been used to monitor bridge scour, ranging from scuba divers using crude depth measuring instrumentation to high-tech sonar and radar-based systems. In contrast to most other techniques, vibration-based scour monitoring uses accelerometers to provide real-time monitoring whilst also being robust and relatively simple to install. This is an indirect technique that aims to measure changes in the dynamic response of the structure due to the effects of scour, rather than attempting to measure scour directly. To date, research on vibration-based scour monitoring has been limited to laboratory-based experiments and numerical simulations, both of which have indicated that the natural frequencies of bridges should indeed be sensitive to scour. Due to pre-existing scouring, and planned repair work, Baildon Bridge in Shipley, Yorkshire provided a rare opportunity to validate vibration-based scour monitoring in both a scoured and a repaired state. A sensor system was deployed with 10 Epson low-noise, high-sensitivity accelerometers to measure the ambient vibration of the bridge before, during, and after the repair. This paper describes the installation of the accelerometer-based system, the numerical modelling of the bridge and the model updating carried out with the initial findings. Initial operational modal analysis has found two consistent vibration modes of the bridge that were scour sensitive according to the updated numerical model. But the variability of the measured frequencies, compared to the expected scour induced change in frequency, indicates a potential challenge for monitoring scour of small span bridges with vibration-based methods.

Journal of Green Building, 2018

Increased demand for affordable housing and the limited availability of flat terrain for its cons... more Increased demand for affordable housing and the limited availability of flat terrain for its construction are two major problems facing the provision of houses of acceptable quality in many countries around the world. There is limited research integrating the utilization of a stepped approach to sloping terrain with appropriate housing models to minimize slope instability potential. This paper introduces a new semi-tiered housing model where the footprint of the house is located on tiers prepared with short vertical cuts of 1.5-2m. Such vertical cuts are found to be stable with laterite soil which is a commonly available type of soil in the tropics. The excess soil generated from cut material was transformed into cement stabilized rammed earth, which is a cost effective material with low embodied energy. This is an ideal candidate for the construction of retaining walls and foundations, and such applications are demonstrated with adequate details. Further, many other types of sustainable building materials are highlighted with a case study of this housing model in a scheme of 13 housing units in Sri Lanka. The attention to detail required in construction and the applicability of alternative building materials and methods to improve the sustainability of such houses have been discussed in detail. These semi-tiered houses have the potential to address many of the current construction challenges.

Low cycle fatigue is an important design consideration for large steel structures and metallic ma... more Low cycle fatigue is an important design consideration for large steel structures and metallic machine components. Accurate prediction of fatigue endurance is essential to design the elements subjected to fatigue. The design guidelines given in codes of practices are applicable only to simple shapes and laboratory experimental verification is costly. Therefore simulation using finite element software is becoming popular. This paper demonstrate successful coupling of Abaqus/FEA and fe-safe software in predicting the uni-axial fatigue behaviour of a stainless steel specimen. The simulated results are verified against experimental results available in literature. Sensitivity to surface roughness and material model were examined.

Thesis Chapters by Kasun Kariyawasam

Research Thesis, 2015

Fatigue is an important design consideration for tall steel structures. Accurate prediction of fa... more Fatigue is an important design consideration for tall steel structures. Accurate prediction of fatigue endurance is essential to design the elements subjected to wind and earthquake induced fatigue. The design guidelines given in codes of practices are applicable only to simple shapes and laboratory experimental verification is costly. Therefore, simulation using finite element software is becoming popular. An attempt is made to couple Abaqus finite element analysis software and fe-safe software to estimate the fatigue life of a structure. First, the accuracy of the techniques and idealizations used in simulations validated by simulating experiments available in the literature. Standard Uni-Axialfatigue experiments which were conducted at several strain amplitudes showed a closer relationship to simulation results. Moreoversensitivity of fatigue life to surface finish and stress strain dataset importing method in fe-safe software were evaluated. It was found that the surface finish is a highly sensitive parameter and it should be estimated accurately. Elastic plastic block method gave good results while elastic block method with Neuter’s rule gave poor results. This indicates the importance of using elastic plastic block method for low cycle fatigue especially when stress redistribution is high. Simulation result of multi-axial fatigue experiment showed similar results to the results obtained from the physical experiments. The verified technique was then applied to estimate the fatigue life of a 64m tall steel mast with an opening located at the top of a 285m tall concrete tower. The sensitivity of the plate thickness and shape of the opening of the mast were studied. It was found that a small increase in plate thickness rapidly increases the fatigue endurance. This shows the importance of using stiffeners in fatigue prone areas. Comparison of the shape of the opening showed that square shape would have higher endurance thana circular shape* of the same opening area. However only monolithic sections were studied here and effects on welds and bolted connections are beyond the scope of this research. *Follow-up note: further research with finer FE mesh found that circular shapes have higher endurance than rectangular shapes. See Kariyawasam K. and Mallikarachchi C. Estimation of fatigue lives of steel masts using Finite Element Modelling. Int. Conf. Struct. Eng., SSESL; 2015, doi:10.13140/RG.2.1.2992.5208