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This paper presents the results of cement-based mortars characterizations that were taken from rendered layers of military bunkers in the Rupnik Line. The Rupnik Line was conceived as a part of the fortified defence system protecting the Rapallo Border between the Kingdom of Italy and the Kingdom of Yugoslavia, established in 1920. The bunkers were built between 1938 and 1941, and the renders of various compositions were applied as a camouflage layer that merged the bunkers with the environment. Results of petrographic examination and microstructural and chemical analysis of the samples confirmed that locally available crushed dolomite or limestone sands were used as an aggregate in the mortars. As binders, pure Portland cement or a mixture of cement and ground granulated blast furnace slag were used. The selection of the aggregate and binder type in a particular mortar was based on the colour of the artificial stone produced. All samples with the dolomite aggregate show the presence of alkali-aggregate reactions, dedolomitization of the grains and secondary calcite formation in the cement binder, along with the Mg-Al, Mg-Si and Mg-Al-Si phase formations. In mortar compositions with a high Portland cement content, the presence of delayed ettringite formation was also confirmed.

Maintenance of miter gates in navigation locks is crucial to facilitate water navigation of cargo ships. Scheduled and unscheduled maintenance are the two types of actions performed to keep miter gates continuously operational. In practice, visual inspections and rating systems are used to monitor the current state of miter gate components in order to prioritize maintenance. This paper shows an example of how to find the optimal time to plan for maintenance using deterioration curves obtained from real visual inspection assessments of components in miter gates. Predictive deterioration curves are derived using a Markov Chain approach. In addition, the advantages of implementing Structural Health Monitoring (SHM) are discussed.

This paper presents a collaboratively adaptive vibration monitoring system that captures high-fidelity structural vibration signals induced by pedestrians. These signals can be used for various human activities’ monitoring by inferring information about the impact sources, such as pedestrian footsteps, door opening and closing, and dragging objects. Such applications often require high-fidelity (high resolution and low distortion) signals. Traditionally, expensive high resolution and high dynamic range sensors are adopted to ensure sufficient resolution. However, for sensing systems that use low-cost sensing devices, the resolution and dynamic range are often limited; hence this type of sensing methods is not well explored ubiquitously. We propose a low-cost sensing system that utilizes (1) a heuristic model of the investigating excitations and (2) shared information through networked devices to adapt hardware configurations and obtain high-fidelity structural vibration signals. To further explain the system, we use indoor pedestrian footstep sensing through ambient structural vibration as an example to demonstrate the system performance. We evaluate the application with three metrics that measure the signal quality from different aspects: the sufficient resolution rate to present signal resolution improvement without clipping, the clipping rate to measure the distortion of the footstep signal, and the signal magnitude to quantify the detailed resolution of the detected footstep signal. In experiments conducted in a school building, our system demonstrated up to 2× increase on the sufficient resolution rate and 2× less error rate when used to locate the pedestrians as they walk along the hallway, compared to a fixed sensing setting.

This paper details a programme of centrifuge tests (100g) on the monotonic and cyclic lateral behaviour of large-diameter semi-rigid monopiles in kaolin clay. Piles of different diameters were used, with a maximum prototype value of 5·9 m. The pile–soil interaction was investigated in terms of the overall load–displacement behaviour, distribution of bending moment and pile deflection, p–y curves and excess pore pressure response. For monotonic loading, procedures were developed to fit the monotonic p–y curves obtained from different pile and soil properties using a hyperbolic tangent model. In addition, an explicit model was derived to assess the development of excess pore pressure within the surficial soil, which was found to approach the vertical effective soil stress at large displacement. For cyclic loading, the accumulation of lateral pile displacement could be accompanied by either increase or decrease in soil resistance, which strongly depends on the loading rate. Strong correlation between the development of peak soil resistance and a dimensionless velocity group was obtained, and was supported by the measured excess pore pressure. Under undrained conditions, the peak soil resistance decreases almost linearly with the accumulation of excess pore pressure.

A swelling pressure cell is introduced to measure apparent swelling pressure (ps) and basal spacing of montmorillonite (d001) simultaneously for compacted bentonite during water absorption. Specimens with an initial dry density of up to 1·7 Mg/m3 were prepared with initially oven-dried bentonite powder. Results show that the ps time history curve has four stages: a sharp increase to the peak swelling pressure (pp); a drop to a valley swelling pressure (pv); another increase to the initial swelling pressure for equilibrium (pei); and equilibrium swelling pressure (peq). Meanwhile, d001 changes from 0·98 nm to 1·26 nm, 1·58 nm, 1·90 nm and 4·0 nm gradually during water absorption. Results imply that crystalline swelling of montmorillonite serves an important role for interpretation of ps behaviour of tested specimens. Another testing programme to measure ps compacted bentonite only was conducted using the swelling pressure cell. Results suggest that specimen dry density closely correlates with feature points of ps time history (i.e. pp, pv, pei and peq), which is consistent with results of earlier studies. Importantly, the 2 mm specimen thickness was used, which reduced the test duration to less than 24 h. Evidence from experiments suggests that the swelling pressure cell is a powerful and inexpensive tool for studying the swelling behaviour of compacted bentonite.

Heritage at risk is a terminology used to describe the sites that are highly at risk of being lost as a result of intentional demolition, deterioration, negligence or subject to improper preservation or mistreatment. Iraq is one of the countries that suffered in the last decade from intentional demolition of highly valuable heritage sites and objects. As Iraq gradually recovering from wars and violence with limited resources and budgets, historical and heritage places are still at risk because of neglect, community ignorance, insufficient planning, and military actions. Therefore, in this paper, we propose the idea of using crowdsource drone images and videos which are captured by amateurs for the documentation of heritage sites. Those crowdsource images represent a great source of data that does not require significant financial and hard labor resources. It should be noted that there is no guarantee to have the captured data being sufficient for the 3D documentation and therefore it is proposed to integrate, when possible, multiple captured crowdsource data to ensure complete documentation. In this paper, three Iraqi historical sites are 3D reconstructed using crowdsource drone videos, namely: Rabban Hormizd Monastery (AD 640), Taq Kasra (AD 242 to 272), and the Great Mosque of Samarra (AD 849–851). The experiments showed a successful 3D modeling of the three mentioned heritage objects using the crowdsource drone video images despite being captured for non-3D purposes which require high expertise and planning. With the absence of highly accurate reference data, the overall relative accuracy of the object’s dimensions is found to be less than 1 m.

This study deals with the behaviour of duplex stainless steel bolted connections. The aim of the study is to respond to the question if the current stainless steel design specifications are able to predict the behaviour of such connections. Firstly, the net cross-section capacity of duplex stainless steel plates subjected to tensile loading are presented. They were conducted to obtain the stress–strain curves and tensile fracture behaviour used to support the finite element (FE) fracture simulations. Secondly, nonlinear FE models are developed for duplex stainless steel bolted connections subjected to tensile loading. The FE models are validated against experimental data in terms of load–displacement curves, failure modes and ultimate loads. Then, a numerical parametric study that consists of 133 duplex stainless steel grade EN 1.4162 bolted connection specimens is carried out. The failure modes of bolted connections are carefully examined, including combined tear out and bearing, bearing and net section, looking at the influence of parameters such as end distance, edge distance and spacing between the bolts in the connections. The results are compared to the design rules prescribed in the current stainless steel design specifications. Generally, it is found that the Australian/New Zealand (AS/NZS), American (SEI/ASCE) Specification and European codes conservatively predict the ultimate strengths of the bolted connections, whereas the strengths predicted by the AS/NZS and SEI/ASCE specifications are overall more accurate and less scattered.

This paper studies the buckling behaviour and design of welded I-section stainless steel columns. Experimental and numerical structural performance data together with the design methods for stainless steel welded I-section columns available in the literature have been collated and reviewed. A numerical modelling programme including validation and parametric studies has been carried out to supplement the literature experimental and numerical data for the assessment of the existing codified and literature proposed flexural buckling design formulations for stainless steel welded I-section columns. Columns of austenitic, duplex and ferritic stainless steel grades undergoing major axis and minor axis flexural buckling have been investigated. From comparisons with the EN 1993–1-4 (EC3) flexural buckling capacity predictions, it was found that (1) for the austenitic welded I-section columns, the EC3 buckling curve (α = 0.76 and λ¯ 0 = 0.2) is suitable for both axes, (2) for the duplex and ferritic grades, the EC3 buckling curve (α = 0.76 and λ¯ 0 = 0.2) is conservative, and a higher buckling curve with (i) α = 0.49 and λ¯ 0 = 0.2 for both axes or (ii) α = 0.49 and λ¯ 0 = 0.2 for minor axis and α = 0.34 and λ¯ 0 = 0.2 for major axis may be adopted. In addition, comparisons with the recently proposed Continuous Strength Method showed marginally improved strength predictions but with slightly higher scatter.

Light-gauge Steel Framed (LSF) floor panels are commonly employed in conventional and modular building constructions on the basis of their lightweight nature. Previous research studies on the fire performance of LSF floor panels have been limited to Cold-Formed Steel (CFS) lipped channel and hollow flange joists. Therefore, there is a need for research on the fire performance of the LSF floor panels designed with optimised CFS joists in conventional floor panels and modular floor panels. This paper focuses on the fire performance of LSF conventional and modular floor panels made of optimised CFS joists found in the literature, using Finite Element (FE) analyses. Heat transfer FE models of LSF floor panels were developed and validated against the data available in the literature. Subsequently, the validated FE models were extended to investigate the LSF conventional and modular floor panels made of optimised CFS joists. In total 32 different LSF modular and conventional panels were analysed. A load ratio-critical average joist temperature relationship was derived based on the past test results and extensive FE results. The established relationship in conjunction with time-temperature profiles from the FE analysis was used to predict the Fire Resistance Rating (FRR) of the LSF conventional and modular floor panels made of optimised CFS joists. The results showed that modular floor panels withstand significant standard fire loading compared to the conventional floor panels while optimised CFS joists can also be used to enhance the fire performance.

A dynamic stiffness element for flexural vibration analysis of delaminated multilayer beams is developed and subsequently used to investigate the natural frequencies and modes of two-layer beam configurations. Using the Euler-Bernoulli bending beam theory, the governing differential equations are exploited and representative, frequency-dependent, field variables are chosen based on the closed form solution to these equations. The boundary conditions are then imposed to formulate the dynamic stiffness matrix (DSM), which relates harmonically varying loads to harmonically varying displacements at the beam ends. The bending vibration of an illustrative example problem, characterized by delamination zone of variable length, is investigated. Two computer codes, based on the conventional Finite Element Method (FEM) and the analytical solutions reported in the literature, are also developed and used for comparison. The intact and defective beam natural frequencies and modes obtained from the proposed DSM method are presented along with the FEM and analytical results and those available in the literature.

High-belite cement (HBC) is increasingly used in hydraulic concrete, of which the frost resistance is an important index in cold climatic areas. In the present study, the mass loss, dynamic modulus, cube compressive strength, micro-morphology and pore characteristic parameters of HBC concrete and reference specimens were investigated under freezing and thawing, and their internal frost damages were quantified by micro-Vickers hardness and ultrasonic theory. Test results showed that the frost resistance of HBC concrete was similar to that of ordinary Portland cement (OPC) concrete under the same proportioning, and that their freeze–thaw failure was a continuous and asynchronous process of both surface-to-interior damage and overall deterioration caused by the test mechanism and specimen size. Service life of concrete could be calculated through the thickness of the damaged layer obtained by ultrasonic theory, and models of Vickers hardness distribution and compressive strength prediction based on equivalent Vickers hardness were proposed to evaluate the performance of frozen concrete with high accuracy. This potentially provides a better understanding of freeze–thaw damage and a reference for the popularisation and application of HBC concrete.

Suction caisson foundations provide options for new foundation systems for offshore structures, particularly for wind turbine applications. During the foundation design process, it is necessary to make reliable predictions of the stiffness of the foundation, since this has an important influence on the dynamic performance of the overall support structure. The dynamic characteristics of the structure, in turn, influence its fatigue life. This paper describes a thermodynamically consistent Winkler model, called OxCaisson, that delivers computationally efficient estimates of foundation stiffness for caissons installed in homogeneous and non-homogeneous linear elastic soil, for general six degrees-of-freedom loading. OxCaisson is capable of delivering stiffness predictions that are comparable to those computed with three-dimensional finite-element analysis, but at a much lower computational cost. Therefore, the proposed model is suited to design applications where both speed and accuracy are essential, such as large-scale fatigue assessments of offshore wind farm structures. The paper demonstrates that the OxCaisson model can also be applied to short, rigid monopile foundations.

In the present work, cohesive and overlapping crack models are integrated in a comprehensive numerical algorithm in order to investigate both tensile and compressive failures in plain or steel-bar reinforced concrete (RC) structural elements. These two fracture mechanics models offer a high capability in the investigation of non-linear phenomena occurring in the loading process of plain concrete or RC beams subjected to bending. Based on the crack-length control scheme, these non-linear models are able to describe snap-back and snap-through instabilities, crack formation/propagation, steel yielding/slippage, concrete crushing and scale effects on the structural brittleness. In the present work, some parametric studies are carried out on plain concrete or RC beams in order to highlight how the abovementioned structural phenomena, which are observed in engineering practice, can be effectively captured by means of a non-linear fracture mechanics approach. Moreover, dimensional analysis is adopted to confirm how the behaviour of lightly reinforced concrete beams can be effectively described by means of two non-dimensional brittleness numbers, leading to a scale effect on the minimum reinforcement percentage, ρmin, proportional to beam depth raised to −0.15.

This study models the flexural strength of concrete modified with cashew nutshell ash (CNA) using reactivity index concepts. Cashew nutshell was valorised and its ash was used at 5, 10, 15 and 20 wt.% of cement via mix proportions of concrete grades C 25–40 targeted at 25–40 MPa at 28 days. The reactivity indexes (RIs) were evaluated based on the oxide compositions and chemical moduli of both the cement and CNA. The design mix parameters, water/binder and binder/aggregate ratios, and RIs were applied to model the flexural strength at 7–90 days’ curing. The results revealed that, at 28 and 90 days’ curing, the developed models yielded high precisions at 91 and 84% R2, respectively, hence indicating a good agreement. Moreover, there was a good relationship between these developed models and previous studies. Therefore, the flexural strength of concrete incorporating supplementary cementitious materials (SCMs) can be efficiently predicted via these developed models; this would save both time and money when carrying out the experimental works.

The combined use of coal bottom ash (CBA) and ground CBA (GCBA) as partial replacement of fine natural aggregate (FNA) and Portland cement, respectively, was investigated for the production of concrete mixtures. Five concrete mixtures incorporating GCBA at 20 wt% replacement of binder and CBA at 0, 25, 50, 75 and 100 wt% replacement of FNA were produced and tested for strength, microstructural characteristics and carbonation resistance. A base concrete mixture made of conventional concrete was also produced as a reference concrete mixture. Test results showed that the combined use of GCBA and CBA in concrete mixtures results in enhancement of the microstructure, carbonation resistance and compressive strength of the resulting concrete mixtures. Scanning electron microscopy and X-ray diffraction analyses pointed at the occurrence of pozzolanic reaction and pore-filling effect of GCBA and CBA in the resulting concrete mixtures. It was observed that 25 wt% replacement of FNA with CBA is an optimum dosage considering its effects on the later age strength and durability characteristics of the resulting concrete mixtures.

Both obsidian and perlite belong to acid volcanic rock and have a similar structure and chemical composition, but the insulation material prepared from expanded obsidian cannot reach the performance level of that prepared from expanded perlite. To date, obsidian cannot be used in large quantities, although its resource is abundant. In order to comprehensively utilise this resource, in the present work the authors developed a new type of lightweight thermal insulation material by using obsidian as a main raw material which is energy-efficient and environmentally friendly. The effects of raw materials such as obsidian, sodium silicate, hydrogen peroxide and cetyltrimethylammonium bromide on physical properties including thermal conductivity, porosity, density and compressive strength were studied in detail. The optimised thermal insulation material exhibits low thermal conductivity (0.051–0.86 W m−1 K−1), low density (0.1–0.24 g/cm3) and adjustable compressive strength (0.09–1.52 MPa). Compared to other inorganic insulation materials, this new thermal insulation material is very light and has a better thermal insulation performance. Therefore, this work proposes a new energy-efficient way to prepare a promising noncombustible thermal insulation material, and also provides a way to use obsidian resources in large quantities.

Modelling the expansion and damage generated by alkali–aggregate reaction (AAR) in reinforced concrete structures is quite complex, yet necessary to obtain accurate predictions of the structural response of distressed members. Several AAR models have been developed to predict expansion and damage at the material (microscopic) or the structural (macroscopic) scales. However, those models tend to either neglect or overemphasise the critical physicochemical parameters of the reaction, which limits their applicability. Therefore, a new simple yet reliable finite-element approach is proposed to fill this gap. It accounts for the most important parameters affecting AAR through an engineering approach, without the need for non-technical guesses or to ‘fit’ model parameters. The proposed model is validated through the computational simulation of reinforced concrete specimens cast and monitored in the laboratory. Results show that AAR expansion was accurately simulated by accounting for the anisotropic (stress state dependent) nature of the reaction, mechanical properties deterioration and an analytical equation capable of representing AAR's free expansion. Next steps include validating the approach by simulating real structures and incorporating phenomena like leaching and combined distress mechanisms.

Besides strength and elastic modulus properties of concrete, creep and shrinkage are also important in designing structures as they can affect seriously their integrity in the long term. It is shown that design codes internationally, as well as researchers in general, have omitted to consider the influence of aggregate, in particular its stiffness, in the models developed for estimating creep and shrinkage of concrete. This paper shows that the American ACI, Australian AS 3600, European Eurocode 2, Japanese JSCE and B4 models are mostly found to estimate creep coefficient and shrinkage strain of concrete inaccurately, irrespective of the type of aggregate used – natural, recycled or secondary. It is proposed that the stiffness of aggregate can be represented reasonably by its pore structure and in turn, for ease of measurement, by its water absorption. Two empirical models are proposed for estimating creep coefficient and shrinkage strain of concrete covering a wide range of natural, recycled and secondary aggregates alone or in any combination of these, as well as the cement effect and its proportion effect in the form of aggregate/cement ratio.

A new constitutive model for sand is formulated by incorporating two new constitutive ingredients into the platform of a reference critical state compatible bounding surface plasticity model with kinematic hardening, in order to address primarily the undrained cyclic response. The first ingredient is a memory surface for more precisely controlling stiffness affecting the plastic deviatoric and volumetric strains and ensuing excess pore pressure development in the pre-liquefaction stage. The second ingredient is the concept of a semifluidised state and the related formulation of stiffness and dilatancy degradation, aiming at modelling large shear strain development in the post-liquefaction stage. In parallel, a modified flow rule aimed at providing a better description of non-proportional monotonic and cyclic loading is introduced. With a single set of constants, for which a detailed calibration procedure is provided, this new model successfully simulates undrained cyclic torsional and triaxial tests with different cyclic stress ratios, separately for the pre- and post-liquefaction stages, as well as liquefaction strength curves based on [Formula: see text] and shear strain criteria for initial liquefaction. The successful reproduction of the sand element response under undrained cyclic shearing contributes to future applications in realistic and thorough seismic site response analysis.

This paper deals with an evaluation of the generalised partial safety factor for resistance properties by using a statistical determination of a resistance model for predicting the punching capacity. The factor takes the material, model and geometric uncertainties into account. The Eurocode 2 design model for the assessment of the punching resistance without shear reinforcement was statistically analysed using an extensive database of experimental tests. The correction factor b of the model and the coefficient of variation of the model errors were evaluated according to Annex D of EN 1990. The statistical parameters of the basic variables in the resistance functions were assumed according to the recommendations of the Joint Committee on Structural Safety Probabilistic Model Code. The comparison of the safety factors obtained with the material safety factor currently used reveals that the current factor 1.50 underestimates the values obtained for the design model analysed.

Heritage masonry structures require detailed monitoring during nearby underground construction, to address the concerns of building owners and mitigate uncertainties relating to the soil–structure system. This paper discusses innovative displacement and strain monitoring of a listed masonry church undergoing ground movements due to nearby tunnelling in London Clay. In addition to conventional surveying and tilt monitoring, laser scan displacement monitoring and fibre optic strain sensing was conducted. Prior to construction, point clouds of the structure were used to map pre-existing geometric distortions in the structure. During construction, detailed monitoring of displacements and strains was conducted across the building facades and the tower. The same techniques were also used to monitor the painted dome of the church where conventional displacement monitoring was not feasible. With a focus on the new engineering insight provided by the innovative monitoring techniques, the impact of the underground construction activities on the church is discussed in this paper. The proposed sensing techniques provide new data on the influence of pre-existing damage and tunnel advance on soil–structure interaction.

Seismic assessment of reinforced concrete (RC) buildings heavily relies on the deformation capacity predictions of members. Similarly, the prediction of the deformation capacity of retrofitted RC columns has the utmost importance for seismic retrofit design. In this paper, a new unified drift model is proposed in order to estimate the rotation capacity of RC columns retrofitted with concrete jacketing, steel jacketing and fibre-reinforced polymer (FRP) wrapping. In order to generate the model, an extensive database was compiled consisting of 269 columns composed of 39 concrete-jacketed, 91 steel-jacketed and 139 FRP-wrapped RC columns failing in flexure mode. In the proposed drift model, the key model parameters are the confinement stress ratio, the axial load ratio and the lap splice length. The accuracy and scatter of the estimations with regard to the previous models were studied. For all of the column retrofitting options, the proposed unified model was observed to have rotation predictions better than the previous models in terms of the mean of the predicted to experimental rotation capacity ratios and with a reduced standard deviation.

This article studies the formation tracking control problem for a group of underactuated surface vehicles with guaranteed transient properties, including connectivity maintenance, collision avoidance, and tracking performance specifications. The formation is within the leader-follower control framework, in which every follower is controlled to track its leader and maintain a desired relative distance and bearing angle with respect to its leader such that the prescribed formation geometry is achieved based on local sensing capability. The onboard sensor systems are of limited range and angle of view, thus defining a cone of detectable region for every follower. Each follower can detect its leader, if and only if the relative distance and bearing angle keep always inside the predefined detectable region such that the connectivity between the follower and its leader is maintained over time. In addition to the consideration of connectivity maintenance, no collision between the follower and its leader is also considered. A transverse function control approach is introduced to overcome the difficulties caused by the off-diagonal system matrix and underactuation. The barrier Lyapunov function and adaptive backstepping procedure are incorporated into the formation control design to achieve the boundedness of the closed-loop systems with guaranteed transient performance. Collision avoidance and connectivity maintenance between every follower and its leader are also proven mathematically. Simulation studies are performed to show the effectiveness of the proposed control design technique.

The durability of ultra-high-performance concrete (UHPC) exposed to freezing–thawing (F–T) is closely associated with its micromechanical properties. In this study, the nanoindentation technique is employed to characterise the micromechanical properties of UHPC at different F–T cycles. It is observed that the indentation moduli of low-density calcium silicate hydrate, high-density calcium silicate hydrate, and calcium hydroxide in the studied UHPC decrease moderately with the decreasing ranges of 11.58, 14.56 and 3.3%, respectively, after undergoing 1500 F–T cycles. More micropores gradually form, converge and connect, and the volume fraction of micropores increases up to about 120%. The interfacial transition zone (ITZ) between steel fibre and cement paste is more prone to act as the weakest zone than that between fine sand and cement paste. The thickness of ITZ enlarges from 22 μm of the unconditioned stage to 60 μm at 1500 F–T cycles. Based on the micromechanical properties obtained from the nanoindentation test, the modulus of elasticity values of UHPC under different F–T cycles are predicted using the multiscale homogenisation model. It is proved that the combined micromechanical characterisation and multiscale homogenisation technique is capable of predicting the macromechanical properties of UHPC and their changes under F–T action.

In practical engineering, natural soil deposits often sustain an initial driving force prior to cyclic shear, owing to earthquakes, traffic and waves; such asymmetrical loading conditions may significantly affect the liquefaction susceptibility and failure mechanism of sand. To understand the typical cyclic liquefaction responses, comprehensive asymmetrical cyclic loading tests were conducted on sand samples subjected to either compressional or extensional static stress. The results indicated that different stress conditions can result in three distinct failure mechanisms: flow liquefaction, cyclic mobility and residual deformation accumulation. According to the experimental observations, an anisotropic sand model was developed within the framework of the anisotropic critical state theory. The model employed a fabric-dependent dilatancy, and accounted for the effects of the fabric evolution and accumulated loading index on the plastic hardening, in order to better reflect the cyclic degradation of the plastic modulus. The predictive capacity of the model was confirmed through undrained monotonic test results for samples with different densities. Comparisons between the model responses and experimental results indicated the excellent capabilities of the developed model in terms of capturing the typical deformation, strength and fabric characteristics of different cyclic failure mechanisms of sand under either symmetrical or asymmetrical loading conditions.

Concern has been expressed in the recent decades about the corrosion prediction of concrete structures in a chloride environment. This paper summarises the corrosion prediction models developed for chloride-contaminated concrete, including both the empirical and electrochemical corrosion models. The definition methods of the steel de-passivation process for electrochemical models, such as anode–cathode ratio (Aa/Ac), critical chloride concentration (CCl,crit), modification of anodic Tafel slope (βa) or passive film resistance (Rf), are considered essential and discussed in detail. Furthermore, electrochemical parameters regarding the definition and selection in electrochemical models and experimental measurements are discussed. This study confirms that Aa/Ac and CCl,crit have been generally used in recent years, and that the modifications of βa and Rf related to free chloride concentration are technically feasible. In addition, the discreteness of electrochemical parameters in electrochemical models and experimental measurements are observed, and time-dependent characteristics of electrochemical parameters are scarcely presented in the existing literature.

This paper presents the results of an experimental evaluation of masonry grout made with lime-activated slag–glass powder blend as a binder. The purpose of this study is to develop a grout mixture that is low-carbon dioxide (‘low-carbon’) and has the potential to replace the traditional grout material used in load-bearing concrete block masonry construction. Traditional grout material uses Portland cement, production of which is responsible for a large proportion of carbon dioxide emissions. Thus, elimination or even reduction in the use of Portland cement will minimise environmental impacts. Three grout mixtures incorporating different proportions of glass powder as a partial replacement of slag as an aluminosilicate precursor were investigated to determine the optimum mix proportion that yields the desired properties of the grout material used in concrete block masonry construction. The workability, compressive strength and permeability properties of the mixtures were evaluated. Results from this study show that the use of glass powder at 25% replacement of slag as a precursor in the binder system provides the best performance, and that this mixture can be successfully used as an alternative and low-carbon grout material for concrete block masonry construction.

The potential of utilising alkaline industrial waste with weak or no cementitious properties for carbon dioxide (CO2) capture and for new binders by accelerated carbonation was studied; steel slag (SS), calcium carbide residue (CCR) and waste hydrated cement (WHC) were compared. The carbon dioxide uptake and strength development of SS, CCR and WHC were studied and the relationship of strength development with carbon dioxide uptake and characteristics of carbonation products was analysed. The results indicate that carbon dioxide uptake of SS, CCR and WHC strongly depends on the mineral composition: calcium hydroxide (Ca(OH)2) and calcium silicate hydrate (C–S–H) show relatively higher carbonation activity; dicalcium silicate (Ca2SiO4) absorbs less carbon dioxide than calcium hydroxide and C–S–H. The carbon dioxide uptake of SS, CCR and WHC are 6.1, 23.2 and 17.9%, respectively, after 2 h carbonation curing. Compacted SS, CCR and WHC specimens displayed a compressive strength of 74.9, 20.5 and 28.6 MPa after carbonation for 2 h. Compressive strength development depends on carbon dioxide uptake and mechanical properties of raw materials and carbonation products. Calcium carbonate (CaCO3) and amorphous products fill the pore structure, making the matrix denser; improvement of pore structure relates positively to carbon dioxide uptake. The highest compressive strength of compacted SS is mainly caused by the high elastic modulus of SS and formation of C–S–H gel in the carbonation process.

Prestressed hollowcore slabs are potentially critical segments in the construction sequence of a precast concrete structure, in which very early age strength is vital for ensuring factory productivity. Importantly, the construction industry is striving to reduce concrete's carbon footprint by using Portland cement substitutes, particularly using ground granulated blastfurnace slag (GGBS) in Ireland. This paper investigates the early age strength enhancement methods for slag-concrete mixes, in order to address the well-known retarding effects arising from slag's inclusion. The strength enhancement methods, including temperature curing and a novel accelerating admixture, are used to activate the slag in the concrete mixes, with replacement rates up to 50% GGBS. The efficacy of these methods is investigated in relation to establishing the development of compressive strength and modulus of elasticity over time (being relevant to stress transfer), particularly at very early and at later ages for strength compliance. The study demonstrates the potential for using up to 50% GGBS mixes for slab production while still maintaining the strengths sufficient to achieve existing productivity targets in precast concrete production.

In this study, shear resistance of ultra-high-performance fibre-reinforced concrete (UHPFRCs) containing different types (smooth, hooked and twisted fibre), fibre aspect ratios (l/d = 100, 95 and 65) and volume contents (0.0, 0.5 and 1.5 vol.%) of steel fibre was investigated using a new shear test method. Shear resistance of UHPFRCs strongly depended on the fibre type, fibre aspect ratio and fibre volume content. The twisted fibre exhibited the highest resistance in terms of shear strength, shear strain capacity and shear peak toughness, the smooth was the next and the hooked fibres produced the lowest response. The bigger the aspect ratio of fibre added to the mixture, the higher the shear resistance of UHPFRCs can be observed. Besides, the shear resistance of UHPFRCs was significantly enhanced with the increase of fibre volume content. The compressive strength and flowability of all mixtures were also checked. The compressive strength increased from 184 MPa for ultra-high-performance concrete to 210 MPa for UHPFRCs, whereas the flowability of mixtures varied from 203 mm to 250 mm. Finally, a theoretical model to predict the shear resistance of UHPFRC beams without the stirrup bar was proposed and verified.

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This paper proposes a Deep Learning Enhanced Principal Component Analysis (PCA) approach for outlier detection to assess the structural condition of bridges. We employ partially explainable autoencoder architecture to replicate and enhance the data compression and reconstruction ability of PCA. The particularity of the method lies in the addition of residual connections to account for nonlinearities. We apply the proposed method to monitoring data obtained from two bridges under real operation conditions and compare the results before and after adding the residual connections. Results show that the addition of residual connections enhances the outlier detection ability of the network, allowing to detect lighter damages.

Seismic isolation systems exposed to far-fault earthquakes can reduce floor accelerations and story drift ratios to acceptable levels. However, they exhibit different structural performances in each earthquake due to different excitation frequency contents. By optimizing the isolation system parameters, their performance may be maintained at the best level under different far-fault earthquakes. In this study, the optimization of the parameters of the nonlinear isolation system of a 5-story benchmark building is performed by Teaching-Learning Based Optimization (TLBO) algorithm to minimize peak floor accelerations under historical far-fault earthquakes with and without exceeding a specified base displacement limit. According to the results of the analyses, it can be said that TLBO algorithm is a robust algorithm with low standard deviations for determining optimum nonlinear isolation system parameters.

A modified design method of a novel large-span floor system called an open-web sandwich slab (OWSS) is discussed. By considering some crucial parameters ignored in current design procedures, a new design procedure based on experiments and simulations is proposed. Considering the dimensions of the shear keys, the linear stiffness of the chords and the linear stiffness ratio between the chords and the shear keys, four specimens were tested and the failure modes and plastic behaviour of the specimens were studied. Based on the experimental results, a series of finite-element simulations was conducted and a crucial integrality coefficient was proposed. Based on the tests and simulations, a modified design procedure was then developed, with recommended values of some crucial coefficients. Finally, a case study was examined to show the efficiency of the new design procedure and the advantage of the OWSS; the results showed that the newly designed OWSS had advantages compared with a traditional solid beam.

A ‘locking-bolt’ demountable shear connector (LBDSC) is proposed to facilitate the deconstruction and reuse of steel-concrete composite structures, in line with achieving a more sustainable construction design paradigm. The LBDSC is comprised of a grout-filled steel tube and a geometrically compatible partially threaded bolt. The latter has a geometry that ‘locks’ the bolt in compatible holes predrilled on the steel flange and eliminates initial slip and construction tolerance issues. The structural behaviour of the LBDSC is evaluated through nine pushout tests using a horizontal test setup. The effects of the tube thickness, strength of concrete slab, and strength of infilled grout on the shear resistance, initial stiffness, and ductility of the LBDSC are assessed. The experimental results show that the LBDSC can achieve higher shear resistance and similar initial stiffness as compared to traditional welded studs. In addition, all tested LBDSCs exhibited slip capacities ranging from 14 to 32 mm and can be classified as ductile shear connectors according to Eurocode 4. A detailed finite element model was also created and found to be reliable to reproduce the experimental behaviour. Parametric studies were subsequently conducted using the validated model to study further parameters and generalise the experimental results. Due to the specific test setup, non-negligible uplift forces were generated in the connector and the potential implications are discussed.

In order to improve the performance of wet joints in prefabricated ultra-high-performance concrete (UHPC) bridges, a comparative study was conducted to investigate the flexural behaviour of UHPC joint beams. Experimental tests were implemented on a complete beam and on five further specimens with, respectively, vertical joint, rhombus joint, vertical joint with strips, tied rhombus joint with strips, and welded rhombus joint with strips. The specimens’ failure modes, ultimate flexural capacities, strain distributions and load–deflection curves were investigated. The test results show that the flexural capacity of the joint beams is lower than that of the complete beam. Among the five specimens with wet joints, the welded rhombus joint with top and bottom strips had the greatest stiffness, the highest cracking resistance capacity, and the best flexural performance. From the best to the worst performing, the remainder of the wet joint specimens took the following order: the unwelded rhombus joint with strips, the vertical joint with strips, the rhombus joint and the vertical joint. In accordance with the test results and the related theoretical analysis, this paper proposes formulas to calculate the flexural capacity of the beam with UHPC joints.

Civil infrastructures are vulnerable to catastrophic failures when exceeding the limit loading, requiring a reliable structural control mechanism, such as bracing systems, to enhance the integrity and stability of the structure. Bracing systems improve the performance of the structures by increasing the stiffness/strength of structures, the damping coefficient, and/or the energy absorption capacity. However, the functionality of these bracing systems is not controllable and may be altered after strong seismic events. Recently, the smart bracing systems based on multifunctional materials, particularly the shape memory alloy (SMA) and the magnetorheological fluid (MRF) have been developed. The superelasticity properties of SMA give the capability of recovering the original state after remarkable deformation. Furthermore, the SMA dissipates the energy of the applied load in the loading-unloading mechanism. The viscosity of MRF is variable and depends on the intensity of the applied magnetic fields. In the present study, a state-of-art hybrid SMA-MRF-based core bracing system is designed and in-house fabricated to enhance the structural behavior of the bracing system, including energy dissipation capacity and equivalent damping coefficient. Experimental tests have been conducted to illustrate the functionality of the system and the benefits of the SMA and the MRF systems. Finally, the seismic performance of the three-, six- and nine-story buildings equipped with the proposed SMA-MRF damping system is numerically assessed using nonlinear response history analyses. The results reveal that the proposed damping system significantly improves the seismic performance of the archetype buildings.

In cold regions, concrete practitioners face challenges when trying to achieve quality results with concrete produced under low temperatures. The addition of nano-silica, which has vigorous reactivity, to concrete can produce mixtures with a dense microstructure and improved hardened properties under cold temperatures. Thus, this research focused on gaining a fundamental understanding of the performance of nano-modified concrete which was mixed, cast and cured at a temperature of −5°C, without any method of heating or insulation. This study adopted the response surface method as a statistical modelling approach to assess the effect of different parameters on the performance of 28 mixtures. Four factors were implemented in this model – water/binder ratio, fly ash content (0–25%), nano-silica dosage (0–4%) and type of antifreeze admixtures – followed by optimisation scenarios. The mixtures’ performance was assessed based on multiple responses: initial and final setting times, early- and late-age compressive strengths and resistance to freezing–thawing cycles. In addition, mercury intrusion porosimetry, thermogravimetry and backscattered scanning electron microscopy were conducted to capture the microstructural evolution of the mixtures. Nano-modified mixtures with and without fly ash, especially with a low water/binder ratio (0·32) and high calcium nitrite content, showed promising performance when cast under cold weather conditions without any protection method.

The corrosion resistance of concrete strengthened with three types of fibre-reinforced polymer (FRP) sheets (unidirectional carbon-FRP (CFRP), unidirectional basalt-FRP (BFRP) and bidirectional BFRP) was evaluated under chloride attack and the combined attack of chloride and ultraviolet radiation. After different corrosion durations, powder samples were collected from various depths of the concrete specimens to measure the total chloride ion concentrations (CICs). Scanning electron microscopy (SEM) was conducted to analyse the microscale morphology changes of the concrete surface layer, FRP fibre layer and resin matrix layer before and after combined attack. The results showed that all three types of FRP sheet provided significant chloride ion resistance, with the barrier effect of CFRP being better than that of BFRP under the same conditions. The total CIC of the FRP-strengthened concretes was higher under the combined attack than under chloride attack alone. The SEM observations showed that the resin matrix and fibre filaments of the FRP layer under combined attack were damaged, resulting in an increase in the permeability of the FRP-strengthened concretes. Finally, a time-varying model of CIC inside the FRP-strengthened concrete under chloride attack was established.

Geotechnical methods, such as cone penetration tests (CPTs), standard penetration tests (SPTs) and seismic cone penetration tests (sCPTs), are widely used to characterise the in situ properties of soil. In studies where more than one in situ method in close spacing is used, it is important for geotechnical engineers to balance between soil heterogeneity and the artefacts of disturbed testing zones. The same applies if detailed information about the subsoil is required and one in situ method is used in close spacing. There is no consensus on how to define the minimum spacing between testing zones and no study on the effect of disturbance caused by in situ tests. In this study, 33 CPTs were performed in natural sediments in northern Germany and a spacing threshold was defined at which cone resistance is affected by soil disturbance from previously performed CPTs. The CPTs were performed sequentially by successively refining the grid spacing, starting with a spacing of 119 cone diameters between CPTs, to a fine grid spacing of seven cone diameters. The cone resistance is affected by previous CPT measurements below a spacing threshold of 24 cone diameters in medium-dense sands. Silt and clay layers showed no reduction in the cone resistance for the minimum grid spacing of seven cone diameters.

Based on the structural characteristics of pervious concrete, an improved mix design method for pervious concrete was developed based on permeability, compressive strength and slurry layer thickness relationships. The results of validation experiments showed that when the slurry layer thickness of the pervious concrete is about 0.35–0.55 mm, the effective porosity is about 22–36%, the permeability coefficient is about 4.88–8.90 mm/s and the compressive strength is about 5.9–18.5 MPa. With an increase in the slurry layer thickness of the pervious concrete, the compressive strength increased, but the effective porosity and permeability coefficient decreased, and vice versa. The results of this study proved that pervious concrete can be formulated to satisfy permeability and compressive strength requirements by using the improved mix design method.

This paper analyses experimental data on sediment incipient motion with varying sediment bed thickness (of d50, 5, 10 and 24 mm). Sediment particles (with sizes ranging from 0.5 mm to 4.78 mm) were used to evaluate the effect of deposited bed. Variation of shear velocity estimation was investigated where the critical Shields parameter was expressed using bed-slope product u∗cb, log-law u∗cl and was extended in terms of critical mean velocity. The critical Shields parameters obtained were significantly lower than the traditional Shields curve when u∗cl was used compared to u∗cb. Higher critical mean velocity is needed for shallower deposits.

Pre-compacted MX80 bentonite/Callovo-Oxfordian (COx) claystone mixture has been considered as a promising sealing/backfilling material in deep geological repository for high-level radioactive waste in France. When the pre-compacted blocks are emplaced in the gallery, technological voids can remain. After the infiltration of groundwater from the host rock, they will swell freely, filling the technological voids, and then undergo further hydration under constant-volume conditions. From the perspective of the storage safety, it is essential to understand the effects of technological voids and hydration time on the hydro-mechanical behaviour of such pre-compacted blocks. In this work, a series of infiltration tests at various hydration times was carried out on compacted MX80 bentonite/COx claystone mixture with different technological voids. The evolutions of the swelling pressures in axial and radial directions as well as the hydraulic conductivity were monitored while wetting. After the predetermined hydration times, the dry density, water content and suction at different positions were determined, together with the microstructure investigation using mercury intrusion porosimetry. It was observed that the soils close to initial voids swelled and filled the initial voids upon contact with water, with significant increases in large-pore and medium-pore void ratios. From the variation of dry density profile with time, compression and swelling zones could be identified: in the compression zone, the soils corresponding to the initial soils were subjected to compression, with decrease in large-pore and medium-pore void ratios over time, whereas in the swelling zone, the soils with a higher dry density than the expected final one underwent further swelling, with large-pore void ratio increasing until saturation and then a slight decrease due to water redistribution in the soil. Owing to the soil density heterogeneity, the axial swelling pressure and hydraulic conductivity of samples with voids were slightly larger than those of samples without voids; contrarily, the radial swelling pressure was lower than that of the samples without voids.

Slope stability is generally analyzed by a two-dimensional (2D) method, ignoring the spatial effect (SE), which no longer meets the evaluation accuracy requirement. This problem is particularly prominent for embankments built on double V-shaped gullies (E-DVSG), which is a typical but unique topography in mountainous areas. Moreover, the technical requirements for engineers will increase sharply if a three-dimensional (3D) slope stability calculation method is adopted. To tackle this issue, pragmatically, a dimension-reduced slope stability analysis method (DR-SSAM) considering the SE of the E-DVSG was proposed and verified by a case study. Specifically, the DR-SSAM obtained the 3D safety factor of the E-DVSG by using the spatial effect curves and the safety factor from the 2D model. The results showed that this method was rational and efficient for engineering applications. In addition, the SE generation mechanism and condition, along with the influences resulting from the major factors, were addressed thoroughly.

This study proposes an innovative carbon fibre reinforced polymer composite-geopolymer concrete (CFRP-GPC) system to improve the durability and structural performance of existing deteriorated reinforced concrete (RC) bridges. A rigorous experimental program is designed to investigate the transport mechanism of corrosive agents such as acids and chloride in the constituents via mechanical and microstructural analysis and to develop diffusion models for CFRP-GPC systems considering synergistic effects of temperature and pH fluctuations. Experimental results show that tensile strength of CFRP and epoxy resin reduces by up to 25% and the failure of composite mainly occurs at the fibre-epoxy interface after exposure to acid. The compressive strength of geopolymer concrete decreases by 66% and 61.3% while the mass loss reduces by 5.3% and 3.7% for samples after exposure to the 10% and 32% hydrochloric acid solution, respectively. The diffusion coefficients of the constituent materials vary from 10-8 to 10-6 mm2/s whilst the diffusion rate within the CFRP is the lowest due to the presence of carbon fibres. Furthermore, a computational model is established to evaluate the performance of the proposed hybrid system in improving long term durability performance of a roadway geopolymer concrete bridge in Australia. The numerical results indicate that the proposed CFRP-confined GPC can substantially impede the acid diffusion into the bridge column, and reduce the level of diffusion and thereby improve the service-life. Parametric study shows that the diffusion rate in CFRP-GPC columns increases up to 58% and 394% for epoxy and CFRP when temperature elevates from 23 °C to 80 °C. In addition, elevation in the exposure temperature from 23 °C to 80 °C increases the mass loss to 22% and 25% under pH = 1 and 7. The findings of this research provide a framework for durability design of hybrid CFRP-GPC systems.

This study investigated the effect of silicate modulus (M = silicon dioxide (SiO2)/sodium oxide (Na2O) by mass) and activator content S (mass proportion of sodium oxide and silicon dioxide to ground granulated blast-furnace slag (GGBS)) of sodium silicate (SS) solution on the compressive strength of alkali-activated GGBS (AAS) mortars. At a given solid content, the specimens activated by SS with modulus of 1.0 and 1.5 had the highest compressive strength. In the case of the same modulus of SS, the compressive strength of the AAS mortars rose linearly and then remained unchanged or declined slightly with the increase in S. The mechanism of the action of SS on AAS was studied using backscattered electron (BSE) and energy-dispersive spectroscopy (EDS). The BSE image of AAS shows that GGBS particles are tightly bonded to the surrounding hardened, jelly-like slurry, and that the structure of the GGBS particles in the AAS slurry is intact without an apparent hydrating layer around it. EDS analysis revealed that only active materials in the GGBS, mainly calcium, are dissolved to participate in reaction, and that dissolving these materials does not damage the GGBS structure. S is solidified by these active materials, which embed the GGBS particles therein to form a whole.

This paper proposes a novel damage detection and localization method of civil structures using a windowed Long Short-Term Memory (LSTM) network. A sequence of windowed samples are extracted from acceleration responses in a novel data pre-processing pipeline, and an LSTM network is developed to classify the signals into multiple classes. Predicted classification of a signal by the LSTM network into one of the damage levels indicates the presence of damage. Furthermore, multiple structural responses obtained from the vibration sensors placed on a structure are provided as input to the LSTM model, and the resulting predicted class probabilities are used to identify the locations with a high probability of damage. The proposed method is validated on the experimental benchmark data of the Qatar University Grandstand Simulator (QUGS) for binary classification, as well as the Z24 bridge benchmark data for multiclass damage classification associated with different levels of pier settlement and the numbers of ruptured tendons. The results show that the proposed LSTM-based method performs on par with the one dimensional convolutional neural network (1D CNN) on the QUGS dataset and outperforms 1D CNN on the Z24 bridge dataset. The novelty of this paper lies in the use of recurrent neural network-based windowed LSTM for multiclass damage identification and localization using vibration response of the structure.

In this work, the influence of the geometry of lightweight perforated breakwaters on their performance against green water impact loads is investigated systematically through a series of numerical simulations. For this purpose, a fully Lagrangian meshfree particle-based method is adopted to model transient and impulsive hydrodynamic phenomenon with free surface and complex geometry. The green water flow is represented by a dam-break problem; the breakwater is modeled as a perforated plate and the protected installation as a vertical wall. Computed impact force, moment, and impulse on the breakwater and protected wall show nonlinear effects, and the main geometric parameter is the open-area ratio. In addition, the increase in the breakwater height is effective only for low open-area ratios. The influence of the arrangement of the holes are also investigated. Different flow patterns are obtained for small and large gaps between the breakwater and the wall. The relation between the loads on the breakwater and the wall also provides the basis for the optimal design of the breakwater, considering the tolerant hydrodynamic loads of protected structures., Comment: 37 pages, 27 figures

© 2018 Earthquake Engineering Research Institute. Damage-induced changes in structure dynamic properties are commonly tracked with time-frequency representations (TFRs). One of the most widely accepted tools for determining a TFR is the continuous wavelet transform (CWT). The success of CWT analysis is highly dependent on selecting the most appropriate values for the parameters that define the mother wavelet. This article presents a detailed analytical and numerical study to select optimal wavelet parameters using the complex Morlet wavelet (CMOR) and the Gabor wavelet. The results obtained suggest that it is possible to define optimal parameter values based on identification target, instantaneous frequency, or average damping ratio. This reduces the computational cost of a reliable CWT analysis when compared with currently employed iterative methodologies based on minimal Shannon entropy criteria. https://doi.org/10.1193/092016EQS154M