Tsunami Scour and Forces at Onshore Structures

Tsunami induced scour at onshore coastal structures can cause exposure of the foundations and lead to failure. This paper presents experimental observations of a 147 s crest-led wave inundation, causing scouring and loading on 0.2 m wide square and 0.4 m wide rectangular onshore structures. At 1:50 Froude scale these equate to a 17.3 min inundation at 10 and 20 m wide structures. Scour development is measured using GoPro cameras situated inside the Perspex structures. The hydrostatic load is calculated from the integration of pressure readings along the front face of the structures, and the hydrodynamic loading is estimated from the approach flow velocity, as measured by a Vectrino II profiler. The results show that the maximum scour depth occurs during the inundation before significant slumping decreases the end scour depth. Both the in-test and final scour depths for the 0.4 m structure are greater, due to the larger blockage causing greater acceleration of the flow around the structure. For both structures, the hydrostatic loading is dominant over hydrodynamic load

Geometric depolarization in patterns formed by backscattered light

We formulate a framework for the depolarization of linearly polarized backscattered light based on the concept of geometric phase, {\it i.e} Berry's phase. The predictions of this theory are applied to the patterns formed by backscattered light between crossed or parallel polarizers. This theory should be particularly adapted to the situation in which polarized light is scattered many times but predominantly in the forward direction. We apply these ideas to the patterns which we obtained experimentally with backscattered polarized light from a colloidal suspension.Comment: 3 pages and 3 figure

Experimental study of the runup of tsunami waves on a smooth sloping beach

A series of large-scale laboratory flume experiments are performed using a pneumatic long-wave generator to simulate tsunami-length trough-led waves. The periods generated are from approximately 6.5 – 37, 40, 72 and 230 s. The runup of these waves is measured on a 1:20 sloping beach. Preliminary results from these tests are presented. The reflections of long waves is discussed. Runup of the 230 s waves is found to be lower than the waves with periods of less than 72 s and previously published data in the literature. Plots of various wave parameters against runup show the strongest positive correlations to be with the crest amplitude and the total potential energy for all wave periods presented. The shorter period data shows a reasonably good fit to available runup relationships, with the longer 40, 72 and 230 s waves showing a poorer fit, suggesting another relationship. Outlines of extensive further work is also given

Large-Scale Experiments On Tsunami Inundation And Overtopping Forces At Vertical Sea Walls

Tsunami are very long gravity waves that may cause significant damage to coastal sea walls. The majority of relevant design codes and research papers that describe methods for predicting tsunami loads on coastal walls consider the scenario of transitory force from a bore-led wave. This does not relate to tsunami that do not form bore waves. Bore fronts generally cause short term spikes in force, which may have little effect on the vulnerability of massive structures. Post disaster accounts suggest that most coastal walls show damage that implies failure modes that occur over moderate to long durations. Therefore it is likely that the bore front assumption gives an overly conservative prediction of maximum force, and may not capture the full timescale of tsunami loading. This paper uses a pneumatic tsunami generation facility to determine the force loading on two vertical coastal sea walls during tsunami inundation. Two sea-wall models, 0.15 and 0.25 m high, with crown widths of 0.1 m (7.5 and 12.5 m at a nominal prototype scale of 1:50) are tested. It is shown that bore fronts only occur for short period waves over the bathymetry tested. Bore fronts cause a very short period spike in force, which is followed by a transitory force approximated by the hydrostatic pressure equation. The loading of tsunami length waves of periods $\geq$ 40 s (280 s prototype at 1:50 scale), which do not break is not greater than 1.2 times the hydrostatic force. Overtopping volume is positively correlated to the time duration of positive upstream head over the crest, rather than its maximum value. Overtopping causes a small increase in the horizontal load due to the addition of a drag and momentum load. The magnitude and time of these effects are small and short-lived in comparison to the hydrostatic load. The results compare well with available equations based on hydrostatic force and the engineer may apply a desired multiplying coefficient of a factor of at least 1.2 to account for any added pressure and momentum, and the factor of safety intended

Uncertainty and Quality rating in Analytical Vulnerability Assessment

Fragility curves represent a major component of seismic risk and vulnerability assessment of buildings and infrastructure facilities. A recently conducted extensive literature review under the framework of developing the “GEM Guide for Selecting of Existing Analytical Fragility Curves and Compilation of the Database”, shows that there is a wealth of existing analytically derived fragility curves that can be used for future applications. However, the main challenge in using these curves is how to identify and, if necessary, combine suitable fragility curves from a pool of curves with different characteristics and, often unknown, reliability. The present article introduces a rating system that has been developed following detail review and critique of the various methodologies on the derivation of analytical fragility curves that have been generated in the past two decades. The main scope is to provide guidance, either in choosing suitable and robust existing fragility curves or in generating new fragility curves. The quality rating system rates the quality of a curve according to the effect that various parameters, simulation procedures and assumptions on the reliability of fragility curve. It also assists and steers potential analysts towards a better identification and quantification of expected uncertainties throughout the process

Experimental observations of tsunami induced scour at onshore structures

Tsunami inundation of the coastal environment can induce scour at structure foundations leading to failure. A series of experiments are made using a unique Pneumatic Long Wave Generator to generate tsunami wave periods of 25 - 147 s equating to 3 - 17.3 mins at 1:50 Froude scale. The waves propagate over a sloping bathymetry and impinge upon a square structure founded onshore in a flat sediment bed. Flow velocity, height and scour are recorded as a function of time during tsunami inundation. The rate of scour is observed to be time dependent. Equilibrium, which is not attained, is argued to be an inappropriate measure for time-dependent transient flows such as tsunami in which the flow velocity, depth and direction are variable. The maximum scour depth is recorded and critically is observed not to be equal to the final depth due to significant sediment slumping when flow velocities reduce in the latter stages of inundation. Current and wave scour predictor equations over predict the scour, while the ASCE 7-16 method under predicts. Comparisons with available data in the literature show longer inundation durations increase the amount of scour

A realistic full CFRP retrofit of RC beam-column joints compared to seismically designed specimen

The brittle collapse of reinforced concrete (RC) structures built before the introduction of detailed seismic design codes (pre- 1970’s) in recent earthquakes, has underlined the need for significant upgrades to the existing RC building stock. In particular, the observation of weak-column/strong-beam mechanisms has potentially catastrophic impacts that could be addressed by retrofit solutions. Retrofits with fibre reinforced polymers (FRP) have become increasingly popular and experimental evidence for their effectiveness can be found in the literature. The lack of tests on full-scale specimens with slabs and transverse beams in many studies may however lead to an unrealistic assessment of FRP retrofit schemes. In this study, three realistic full-scale interior beam-column joints with slab and transverse beams are tested under cyclic loading in order to propose and assess practical FRP retrofit solutions. A complete Carbon FRP (CFRP) retrofit strategy aiming to obtain a similar performance to a specimen designed to modern European design guidelines (Eurocode 8) is presented. The retrofit scheme is composed of selective strengthening and weakening components to ensure ductile failure of the specimen according to capacity design principles. Results from full-scale cyclic tests on the CFRP retrofitted specimen are compared to the behaviour of a deficient, pre-1970’s design specimen and a specimen designed to modern guidelines. The observed failure mechanisms and global lateral capacities for the Eurocode 8 and retrofitted specimen show that the CFRP retrofit is effective in improving seismic behaviour. By means of a combined selective weakening and strengthening scheme, a change in hierarchy of strengths can be achieved, which leads to an improved ductile behaviour with significant strength enhancement. The results suggest that a CFRP retrofit scheme can be devised for realistic, significantly under-designed structures in order to achieve a similar performance to modern RC structures designed to sophisticated seismic guidelines

Effect of slab and transverse beam on the FRP retrofit effectiveness for existing reinforced concrete structures under seismic loading

The seismic behaviour of reinforced concrete (RC) structures is critically influenced by the complex mechanical interactions at beam-column joints. To ensure the desired hierarchy of failure is achieved when retrofitting existing structures, numerical and experimental assessments need to represent realistic structures. A review of published literature indicates that most experimental work on the seismic behaviour pre-1970′s RC beam-column connections considers sub-assemblies without slabs or transverse beams, which are unrepresentative of reality. To evaluate the effect of these elements on the failure mechanism, retrofit need and retrofit effectiveness, experiments on four full-scale beam-column joints are carried out. Two specimens with and without slab and transverse beams, are tested in their as-built and FRP strengthened configurations. As expected, the experimental results demonstrate that the progression of damage and failure mechanisms differ significantly when slabs and transverse beams are present, confirming previous numerical and experimental evidence on the strong contribution of these elements on the overall joint behaviour. Moreover, a significantly higher retrofit effectiveness is observed for the specimen without slab and transverse beam. This implies that experiments on retrofitted joints without slab and transverse beam can lead to a focus on joint shear strengthening alone as they inadequately represent the hierarchy of strengths of the framing members. They can also lead to an overestimation of retrofit effectiveness. These observations have implications when considering common simplifying assumptions made in the numerical modelling of RC moment resisting frames when assessing their seismic performance

Gate stability of GaN-Based HEMTs with P-Type Gate

status: publishe

Influence of Fines Content on Liquefaction from a Critical State Framework: the Christchurch Earthquake Case Study

In earthquake engineering practice, the liquefaction potential of soils is commonly evaluated through simplified procedures. These approaches are suitable for sands with very low to no fines content, which have been traditionally thought to be the only liquefiable materials. However, field observations and experimental research have extensively demonstrated that low plasticity silty sands can also be highly liquefiable. Thus, this paper investigates the effect of nonplastic fines contents on the liquefaction potential of soils, taking the 2010–2011 Canterbury Earthquake Sequence as a case study. The validity of standard simplified procedures for high fines content soils is critically evaluated and compared with a finite element model based on a full solid–fluid coupled formulation. The model includes a state parameter-based constitutive law within the generalised plasticity theory, which allows the fines content to be taken into account explicitly. The standard simplified procedures are shown to be less effective in the evaluation of liquefaction potential in soils with high fines content but are still indispensable tools for evaluating the performance of soils over large urban areas. As the main conclusion, it is recommended that empirical models are complemented with an advanced numerical analysis in those cases where silty sands with high fines content are identified, as its outcomes can more realistically represent the soil behaviour during a seismic event