The research in this paper focuses on detection and quantification of subsurface damage in reinforced concrete (RC) structures by the analysis of infrared images. Experimental investigations were performed on RC slabs with embedded reinforcing bars (rebars). The corrosion mechanism in rebars was accelerated using an electrical circuit setup. The initial temperature of the slabs was adjusted in the environmental chamber and IR images were taken at regular intervals while they were exchanging heat to laboratory air through convection. Records of IR images were post-processed using an objective thresholding method proposed based on unsupervised k-means clustering. The results were discussed in context and with respect to the ASTM D 4788-03 recommendation for minimum detectable thermal contrast (0.5 degrees C) from delamination in bridge concrete by infrared thermography (IRT). The conclusions lead to recommendations for improved practical implementation of IRT that contribute to the broader prospects of structural health monitoring (SHM).

Experimental and numerical analyses of eight in-plane restrained slabs (1425 mm (length) × 475 mm (width) × 150 mm (thickness)) reinforced with glass fiber-reinforced polymer (GFRP) bars are reported in this paper. The test slabs were installed into a rig, that provided 855 kN/mm in-plane stiffness and rotational stiffness. The effective depths of the reinforcement in the slabs varied from 75 mm to 150 mm, and the amount of reinforcement changed from 0 to 1.2% with 8, 12, and 16 mm bar diameters. A comparison of the service and ultimate limit state behavior of the tested one-way spanning slabs shows that a different design approach is necessary for GFRP-reinforced in-plane restrained slabs that demonstrate compressive membrane action behavior. Design codes based on yield line theory, which considers simply supported and rotationally restrained slabs, are not sufficient to predict the ultimate limit state behavior of restrained GFRP-reinforced slabs. Tests reported a higher failure load for GFRP-reinforced slabs by a factor of 2, which was further validated by numerical models. The experimental investigation was validated by a numerical analysis, and the acceptability of the model was further confirmed by consistent results obtained by analyzing in-plane restrained slab data from the literature.

This paper presents segmentation analysis of Infrared (IR images of reinforced concrete (RC blocks for characterisation and quantification of corrosion defects using unsupervised clustering. The IR images used in this study were collected during cool down process of RC slabs to laboratory environment temperature through convection heat exchange. The RC slabs were cast from a normal strength mix, typical for bridge construction in the UK and Ireland. The slabs had two steel rebars with protruding ends that were used for accelerated corrosion setups. Unsupervised clustering was conducted on IR images by applying k-means clustering method on normalised temperature readings in a region of interest. In this paper, the performance of clustering method to distinguish between environmental or surface effects and true bridge anomalies is studied, and the corrosion-affected concrete is quantified. Variation of thermal contrast and quantity of defective concrete during the experiments as well as discussion of the results in context provides a basis for improved implementation of IRT for RC structures and contributes to wider objectives of structural health monitoring (SHM).

This paper presents observations from an active infrared thermography (IRT) experiment about structural monitoring by taking advantage from solar irradiance as a clean and renewable source of energy for thermal excitation. This contributes to reduction of carbon emissions associated with maintenance of existing concrete infrastructure and ensuring their extended life, and safe operation. The models in these observations were five concrete slabs made from a typical mix used for bridge construction in the UK, with simulated subsurface void (representing the defect) at depths of 5 to 25 mm (5mm increment) at the centre of slabs, and one slab without simulated defect. This study was conducted during a sunny afternoon. A sequence of IR images was collected for each slab (six sequences in total), and these sequences were used to calculate the average thermal contrast on surface of the slabs and evaluate its variation with depth of subsurface defect. Finally, the trend of thermal contrast is compared with the trend of thermal contrast from excitation by IR heater to highlight the limitations and future research needs for subsurface damage detection using solar irradiance.

Infrared thermography (IRT) is a non-destructive technique capable of detection and localisation of hidden subsurface defects in components of transportation infrastructure, such as concrete bridges, thereby contributing to structural health monitoring (SHM). Addressing the lack of research on subsurface defect detection in concretes by convection heat exchange, and regarding the importance of laboratory studies for proper implementation of IRT, this paper presents results from recent laboratory investigations of IRT on concrete slabs with simulated hidden defects using a convective thermal excitation mechanism. The concrete slabs in this study had simulated defects ranging 5–25 mm in depth from the surface. These studies show the effect of initial temperature, heating/cooling process, temperature range and defect depth on thermal contrast in the concrete slabs. Furthermore, this paper compares the performance of the IRT as a non-contact sensor and thermocouples attached to the surface, in the evaluation of the thermal contrast on slabs with various defect depth. The dependence of maximum thermal contrast on the initial temperature and defect depth is explored using multivariate linear regression.

Concrete is a highly consumed construction material used in the built environment and civil infrastructure. Therefore, condition monitoring using non-destructive techniques such as infrared thermography (IRT) should be optimised to extend the safe and continuous operation of existing structural asset and to reduce the requirement for new construction, which is more carbon intensive. The objective of this paper is to present an in-depth understanding of the heat flow mechanism in concrete slabs with hidden subsurface defects using IRT experi-ments. The experiments were performed on six concrete slabs with dimensions of 250 x 250 x 100 mm. Five of these slabs had 5 to 25 mm concrete cover over the simulated subsurface defect, and the sixth slab was plain concrete with no defect, used as control sample. Two sets of experiments using step heating thermography (SHT) technique were conducted using an IR heater as the excitation mechanism. By thermography of slabs, several sequences of IR images were recorded during both heating and cooling phases. Subsequently, the sequences of IR images were post-processed using a routine developed in MATLAB to achieve the evolution of temperature on surface of the samples. The temperature records from the tests during both heating and cooling phases were used to calculate thermal contrast, as well as first and second time derivatives of thermal contrast. By close exami-nation of the sequences of IR images as well as sign analysis of the thermal contrast and its time derivatives, the mechanism of heat transition in defective concretes was characterised and interpreted in three stages during both heating and cooling phases. The three stages of heating phase are named as simultaneous heat-up, lateral heat flow and maximum thermal contrast. The formation of the lateral heat flow that corresponds to the transition from stage one to two causes the thermal gradient on the surface observable by the thermal camera. Likewise, three stages of cooling phase are simultaneous cool down, lateral heat diffusion from void cover to sound concrete and inverse thermal contrast. The conclusions of this study increase the basic understanding about mechanism of heat transfer in defective concrete and put forward new directions toward optimised imple-mentation of IRT for the detection of hidden defects in concrete bridges.

This paper presents the work carried out on a collaborative tripartite project between the USA, Republic of Ireland and Northern Ireland to create and investigate the design, development and testing of a new class of intermeshed steel connections (ISCs) that do not rely on field welding and minimise bolting, thus targeting the facilitation of fast disassembly of steel structures and material reuse. This research took advantage of fully automated, precise, advanced manufacturing cutting technologies (e.g. laser, waterjet and high-definition plasma cutting) to achieve a connection method in steel that previously was only possible in materials such as timber, with the potential to revolutionise the steel construction industry. The paper outlines the ongoing research work by the collaborative team, focusing on the design, fabrication, finite-element analysis (FEA) and scaled experimental testing of side ISCs for the flanges of open sections, which included the use of state-of-the-art digital image correlation technology for non-contact measurements. A simplified connection design procedure is presented based on yielding of the side plates. This design procedure is refined based on the results of experimental testing and FEA of the local axial behaviour of the flange connection, addressing stress concentrations in the flange, fabrication tolerances and material overstrength.

This study presents the decays of three components of velocity for a ship twin-propeller jet associated with turbulence intensities using the Acoustic Doppler Velocimetry (ADV) measurement and computational fluid dynamics (CFD) methods. Previous research has shown that a single-propeller jet consists of a zone of flow establishment and a zone of established flow. Twin-propeller jets are more complex than single-propeller jets, and can be divided into zones with four peaks, two peaks, and one peak. The axial velocity distribution is the main contributor and can be predicted using the Gaussian normal distribution. The axial velocity decay is described by linear equations using the maximum axial velocity in the efflux plane. The tangential and radial velocity decays show linear and nonlinear distributions in different zones. The turbulence intensity increases locally in the critical position of the noninterference zone and the interference zone. The current research converts the axial momentum theory of a single propeller into twin-propeller jet theory with a series of equations used to predict the overall twin-propeller jet structure.

Scour mechanism caused by the external and internal rotating twin-propellers, and a single propeller is investigated using an experimental method. Powertrain system, twin-propeller, tank, sand, and scour measurement were designed and built enabling two counter-rotating jets to cause scour in a water tank that the scour depths are measured using Acoustic Doppler Velocimetry (ADV). Temporal study found that the counter-rotating twin-propeller scour consists of three stages, which are the initial stage, developing stage and equilibrium stage. Two independent scour holes were found in the initial stage within the first 10 min. Two holes merged to be a connecting hole to reach the developing stage. The maximum scour depth, and the scour area continued to expand up to 2 h to reach the established stage. The established stage shows the equilibrium condition without excessive changes in scour depth and area. The experimental results showed that the maximum scour from an external rotating twin-propeller occurred along the rotational axis of each propeller, whereas the internal rotating propeller scour occurred along the central axis in-between two propellers. The jets from external rotating and internal rotating systems have different flow characteristics leading to different scour patterns. Proportional factors were proposed to relate the scour generated by external-rotating twin-propeller, internal-rotating twinpropeller, and a single propeller.

Experiments were conducted to investigate the seabed scour holes due to the interaction between the twin-propeller jet and quay wall. Vertical quay wall was modelled by using a polyvinyl chloride (PVC) plastic plate in a water tank. The relationship between the positions of the propeller and the vertical quay wall was designed according to the actual working conditions of a ship entering and leaving a port. Propeller-to-wall distance and rotational speed were changed to observe the various scour conditions. The scour depth was measured by using an Acoustic Doppler Velocimeter (ADV). Primary scour hole was found within the jet downstream and secondary scour hole occurred beneath of the propeller. Third scour hole was found close to the quay wall due to horseshoe vortices. The maximum scour position of this third scour hole was found at the jet centre near the quay wall. Temporal formation of scour holes can be divided into three stages: axial scour formation, obstructed scour expansion and equilibrium stages. The quantitative relationships for six characteristic parameters of the scour pit were established including the maximum scour depth (εmax,q), maximum scour depth position (Xm，q), maximum scour width (Wm，q), length of main scour pit (XS，q), maximum deposition height (ZD，q), and location of maximum deposition height (XD，q).

The Road authority specifications for unbound granular materials (UGMs) do not typically include a direct measure of resistance to rutting caused by repeated loading yet. These specifications can preclude the use of locally available aggregates or recycled materials that may provide adequate performance (resistance to rutting). As an alternative or compliment to current UGM assessment methods via specifications, a serviceability design method is proposed that utilises results from tests in the repeated load tri-axial (RLT) apparatus. Permanent strain behaviour at a range of stress conditions of four unbound granular materials (UGM) were assessed in the RLT apparatus. Behaviour was categorised into 3 possible ranges A, B or C, where A is a stable response and C is incremental collapse while B is intermediate. From this data, test stresses near or at the boundary of range A and B were determined to define a serviceability limit line stress boundary in p (mean normal stress)-q (principle stress difference) stress space. The serviceability limit line was applied as a yield criteria in a finite element model of a pavement to predict whether or not stable (Range A) behaviour occurs in the UGM for a range of asphalt cover thicknesses.

Predicting the velocity distribution of double horizontal axis tidal turbines (DHATTs) is significant for the effective development of tidal streams. This current research gives an account on double turbine wake theory and flow structure of DHATT connected to single support by using the joint axial momentum theory and computational fluid dynamics (CFD) method. Characteristics of single turbine wake were previously studied with two theoretical equations predicting the initial upstream velocity closer to the turbine, and it’s lateral distributions along the downstream of the turbine. This current works agreed with the previous wake equations, which was used for predicting the velocity region along the downstream of the turbines. Flow field separating the two turbines is complicated in nature due to the indirect disturbance of turbines and no report was found on this central region. The Central region in the downstream flow is initially suppressed due to the blockage effects with a high velocity close to the free stream. Lateral expansion of two turbine wakes penetrated the central region with velocity reduction and followed by the flow recovery further downstream. This work provides more understandings of the wake and its central mixing region for double turbines with a proposed theoretical model.

This research paper proposes the use of empirical equations to estimate the temporal maximum scour that is induced by twin-propeller ( ε t w i n = Ω t [ l n ( t ) ] Γ t ) when acting over non-cohesive bed materials. A purpose built experimental apparatus is used to obtain the measurement data required for the calculation of the empirical constants. The output from rigorous experimental investigations demonstrates that the maximum scour depth produced from the operation of twin-propeller ( ε t w i n ), within the confines of a harbour basin, varies as a logarithmic function of time. A dimensional analysis of the standard single propeller configuration is used as the foundation upon which the scour equation is postulated. This is extended to include the influence of the operating distance between the twin-propeller configurations for the first time. The division of scours by twin-propeller and single-propeller ( ε twin / ε m ) enables the establishment of mathematical relation to calculate C1, C2, A, and B. The constants are C 1 = 366.11, C 2 = 0.3376, A = 0.859, and B = 0.1571. The proposed scour equation is more reliable within the time zone up to two hours based on the experimental data.

This paper outlines basalt fibre reinforced polymer (BFRP) and carbon fibre reinforced polymer (CFRP) strengthening of laterally restrained concrete floor slabs. In-plane restraint has previously been shown to enhance slab capacity due to the development of internal compressive membrane action (CMA), which is not generally included in codified strength assessments. By installing fibre reinforced polymers (FRPs) using the near surface mounted (NSM) technique, disturbance to the existing structure can be minimised. The span-to-depth ratios of test slabs were 20 and 15 and these were constructed with normal strength concrete (similar to 40 N/mm(2)) with 0.15% steel reinforcement. 0.10% FRP (either BFRP or CFRP), was used to strengthen samples which were then compared with control samples. Investigations showed that FRP strengthening and CMA are generally separate, with limited overlap in terms of their contribution to capacity increase. Recommendations are then made for designers to better determine the capacity of FRP strengthened restrained slabs.

Today's urban environment and transportation networks rely heavily on the use of steel load carrying structures. Despite the two main steel connection methods, welding and bolting, being slow and/or expensive field activities, a new universally applicable, structural steel connection mechanism has not been introduced in more than a century, regardless of the new manufacturing capabilities available. It is clear that by improving and refining these features of multi-storey steel buildings, considerable savings in both weight and cost could be achieved. To achieve these savings, improved construction efficiency and heightened material reuse, a new class of interlocking steel connections using computer-controlled, advanced manufacturing techniques in laser cutting has been developed that rely on neither bolting nor welding. This paper presents the experimental testing and numerical modelling of the flange of the new interlocking steel connection in direct tension. A series of experimental tests were performed to capture the behaviour and failure modes of the new steel connection under tension. A simplified two-dimensional (2D) finite element (FE) model has been created using the ABAQUS software. The connection model accounts for material and geometric non-linearity, large deformation and contact behaviour. Contact is critical to model the tensile behaviour of the joint and was modelled using a surface to surface contact interaction taking into consideration friction between the surfaces. The model has been analysed through the elastic and plastic ranges up to failure and predicts the failure mode of the connection well. The comparison with the experimental data shows that the 2D model has a very good level of accuracy and the highest effectiveness in terms of computational time and memory usage.