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The flexural performance of a spliced composite slim beam with a slotted web (SCSB-SW) was assessed and prediction formulae of flexural capacity and initial stiffness for the beam were deduced. Through a four-point bending test, the flexural performance of the SCSB-SW was preliminary studied. The experimental results indicated that the section of the SCSB-SW conformed to the plane section assumption in the elastic stage. The beam failed in a ductile failure mode while there was no obvious relative slip between the steel beam and concrete slab in the failure stage. Finite-element models were developed and validated using the test results. A parametric analysis revealed that even if the cross-sectional dimensions and the position of the neutral axis in the beam are changed, the results predicted by the formulae still matched the numerical results well. The material strength, the thickness of the bottom flange of the steel beam and the concrete slab dimensions were found to play key roles in the flexural capacity of the beam, whereas the compressive strength grade of the concrete, the depth of the steel beam web and the dimensions of the concrete flange have significant effects on the initial stiffness of the beam.

The ‘rope effect’ is a positive effect caused by the failure of fasteners of dowel-type connections. A similar mechanism can be found in connections with screw reinforcement. For self-tapping screws used as reinforcement for connections, bending of the self-tapping screws tends to close developed cracks. Utilising the withdrawal resistance provided by the threads on the pointed end of the screw and the pull-through resistance from the screw head, screw reinforcement enhances the embedment strength and splitting resistance of the wood and increases the ductility of the connection. The influence of different thread lengths and locations on reinforcement effectiveness regarding the embedment strength of the timber was investigated in this study. For cases with threads located only on the pointed end, the splitting resistance increased with longer thread length, indicating that the rope effect was progressively enhanced. It was also found that screws with halved thread length demonstrated similar reinforcement effectiveness to fully threaded screws while the partial threads reduced the risk of damaging the screw during installation. A calculation method to predict the load-carrying capacity of screw-reinforced dowel-type connections was also formulated.

Soils containing organic matter exhibit low shear strength and high compressibility. Lime stabilisation has been shown to improve the engineering properties of clayey soils. An attempt was made to study the effect of organic matter (starch and peat) on the shear strength of lime-stabilised clayey soils subjected to longer curing periods (up to 180 days). Most studies have reported the strength behaviour of lime-stabilised organic soils up to 60 days. Vane shear tests were carried out on artificially prepared organic soil mixtures treated with 6% lime after different curing periods (0, 7, 30, 60, 90 and 180 days). The results indicate that the improving effect of lime is deteriorated in the presence of organic matter as the curing period increases. It was observed that, for lime-stabilised clayey soils containing organic matter, the strength seemed to increase up to 30 days, after which it ceased. The strength reduction in lime-stabilised clayey soils containing organic matter depended on the pH and functional groups present in the soil. Fourier transform infrared spectroscopy of cured samples was also carried out to examine the microstructural changes responsible for the strength change in lime-stabilised clayey soils.

Desiccation cracking in clay soils is a combined mechanical and hydraulic problem and such soils can be improved by various methods including reinforcement with fibres. The relationships between tensile strength, cracking resistance and water-retention properties of fibre-reinforced fine-grained soils lack coverage in the literature to date. In this study, these three properties are evaluated and connected by way of a series of tensile strength and desiccation cracking tests on fibre-reinforced London clay. The results confirm that increased fibre addition delays the occurrence of peak stress and changes failure behaviour from brittle to ductile. The tensile strength increment gets higher as water content decreases, and reaches a maximum value of 460 kPa when the water content is 12%. The crack intensity factor reduces from 7.20% to 0.89% when 12 mm long fibre is used at a ratio of 0.9%. Fibre reinforcement also changes the crack development pattern by reducing the size of large cracks and increasing the proportion of small individual cracks. However, the presence of fibres was not observed to change the water-retention properties of the soil, indicating that the tensile improvement comes from the pull-out resistance of the fibres rather than suction changes.

This paper presents the results of both experimental and numerical investigations on the overall structural performance of two-equal-span reinforced concrete perforated (castellated) beams subjected to external pre-stressing. First, the effects of providing castellated openings along with the application of external pre-stressing on both the ultimate capacity and the percentage of moment redistribution were investigated experimentally. Then, after validation of the numerical modelling, the effects of controlling the parameters on the percentage of moment redistribution were investigated numerically. Experimental results showed that providing castellated openings accelerated the appearance of both flexural and shear cracks, and decreased the ultimate capacity by about 24% compared to that of a solid beam. Moreover, application of external pre-stressing on the castellated beam compensated for the reduction in ultimate capacity and outperformed it by about 9% compared to that of a solid beam. Based on the numerical results, it appears to be better to increase the amount of main tensile steel and strand eccentricity at the hogging moment zone, as well as increase the effective pre-stressing force, to reduce the percentage of moment redistribution at both sagging and hogging moments.

Radiative cooling without energy consumption and environmental pollution holds great promise as the next-generation cooling technology. To date, daytime radiative cooling performance is still slightly low, especially in humid areas. In this work, we demonstrated that nanoporous polyethylene (Nano PE) film can improve solar reflectivity from 96% to 99%, thus boosting radiative cooling performance. Moreover, the experimental results in humid areas indicate that Nano PE films can improve radiative cooling performance by ∼76% in a clear day and 120% in a day with few clouds. Additionally, compared with ordinary PE films, thin Nano PE films have significantly higher weather fastness and mechanical strength. More importantly, nano PE films can scatter part of visible light, thus suppressing the generation of light pollution in practical applications. Lastly, the modeling results reveal that with Nano PE films, more than 95% of China's areas can achieve daytime cooling performance. Our work can boost the development of radiative cooling technology with a very low cost.

The effects of high-strength steel (HSS) on the damage indices (DIs) of four special moment frames and three beam–column connection (BCC) specimens under cyclical loading were experimentally studied. The specimens with HSS rebars (with yield strengths of 500 MPa and 580 MPa) were designed and constructed based on the special seismic provisions of ACI 318-19. Several types of DIs (from single DIs to combined DIs based on parameters such as displacement, absorbed energy and stiffness) were calculated according to the experimental results. The results showed that the application of the higher strength steel expedited the failure process of the specimens. Moreover, the DIs indicated that the specimen fitted with HSS for both the longitudinal and transverse rebars had the greatest damage propagation speed of the frames. For the BCCs, the specimen with HSS as just the longitudinal rebars showed the greatest damage propagation speed. The results also showed that the displacement-based DIs were less accurate than the other types of DIs for studying the damage behaviour of both the frame and the BCC specimens. The combined DIs were found to be more accurate than the other DIs.

This study analyses the effectiveness of the biopolymer xanthan gum (XG) to improve the mechanical properties of silty sand. The study focuses on the effects of the curing time and the content of XG on the unconfined and confined behaviour of soil treated with this biopolymer. The study was carried out with specimens cured under high-humidity conditions, through the comparison of the unconfined compressive strength (UCS), stiffness, compressibility and vertical yield stress of non-stabilised and biostabilised specimens, obtained from UCS and oedometer tests. Additionally, the pH value and results of scanning electron microscopy (SEM)/ energy-dispersive X-ray analysis (EDX) tests are presented and discussed. The biostabilisation of this soil with XG induces a more ductile stress–strain behaviour, a moderate increase in UCS and stiffness, and in the increase of the one-dimensional compressibility, with a greater effect for higher XG contents. The SEM/EDX tests show that the biopolymer induces a random biopolymer network in the biostabilised specimens that is related to the strengthening obtained.

Steel plate shear wall (SPSWs) have good ductility, high strength and stiffness, and considerable energy absorption capability. These advantages have been confirmed in experimental and numerical studies. However, despite these advantages, the need for huge columns surrounding the infill plates is the main limitation of SPSWs. Although the high-performance steel plate shear wall (HPSPSW) has solved this shortcoming, there are still some unknowns about this high-performance system. The HPSPSW system is expected to be more economical than other resisting systems due to ease of fabrication, the elimination of complete joint penetration field welds, the elimination of stress transfer from infill plates to main columns, the higher modification factor and no need for huge main columns. A comparison of analysis results of HPSPSW and SPSW systems revealed that the HPSPSW has desirable stiffness, ductility and energy absorption when its length to height ratio is greater than 1.5. In addition, the HPSPSW system had an ultimate lateral strength only 2–5% lower than that of the SPSW. Modification factors were calculated and average values of 6.67 and 8.64 were obtained for the SPSW and HPSPSW systems, respectively. Therefore, a modification factor of 8.5 is suggested for the HPSPSW.

Basalt fibres and biocement were used to improve the mechanical properties of calcareous sand. The biocement was produced through a microbial-induced calcium carbonate precipitation (MICP) process. The unconfined compressive strength (UCS), tensile strength and permeability of the biocemented and fibre-reinforced calcareous sand were evaluated. The calcium carbonate content of each sample was also measured. The microstructure of the biocemented calcareous sand was observed using scanning electron microscopy (SEM). The SEM results indicated that the fibre facilitated the MICP process by bridging the pores in the calcareous sand. As a result, the fibre reduced the brittleness and increased the failure strains of the biocemented calcareous sand. Compared with biocemented calcareous sand without fibre, for all fibre lengths except 4 mm, the UCS, tensile strength and calcium carbonate content of the biocemented calcareous sand increased gradually with an increase in fibre content up to a fibre content of 1%; the optimum fibre content and fibre length were found to be 1% and 8 mm, respectively. The UCS and tensile strength of the biocemented calcareous sand at the optimum fibre content and fibre length increased by 717% and 115%, respectively.

The influence of additives on the structural behaviour of cement-stabilised rammed earth was investigated through an experimental programme based on 13 different mixes with varying cement contents (6, 8 and 10% by earth weight) and three different types of additives (superplasticiser, air-entraining agent (AEA) and hardening accelerator). In total, 156 specimens were fabricated and tested at 7 and 28 days in order to compare their compressive strength and other properties such as stress–strain relationships, shrinkage and workability. The results highlighted the essential role of cement in increasing the compressive strength of the material. Specifically, cement contents of 6%, 8% and 10% corresponded, respectively, to strength increases of 41%, 80% and 92% compared with the reference mix with a mean compressive strength of 1.15 MPa. The AEA was found to be the most effective additive for increasing the compressive strength, with obtained strengths of up to 2.93 MPa (an increase of 155% compared with the reference mix). The efficiency of each mix was evaluated through a strength/cost ratio. In addition, an overall comparison of compressive strength, shrinkage, deformation, cost and workability was performed using an analytic hierarchy process. Finally, the experimental results were compared with the mechanical requirements of various codes.

Welded hollow spherical joints are commonly used in reticulated shell structures. Corrosion on the surface of the joints can significantly reduce their compression capacity. Pitting corrosion is a typical corrosion type on steel structures. A corrosion pit forms at random locations and has a random size. Its random size is indicated by random planar size and thickness – that is, multiple-random pitting corrosion. In this work, a series of non-linear numerical analyses was conducted to investigate the influences of these parameters on the mass loss and compression capacity of welded hollow spherical joints. The aim of this work was to construct a probabilistic distribution model of the compression capacity of the joints with multiple-random pitting corrosion and establish the relationship of the probabilistic distribution model with the specified corrosion and geometric parameters. The work also provided a method for determining the probabilistic model of the joints under actual conditions. This work could serve as a basis for the stochastic analysis of integral structures connected by welded hollow spherical joints with random pitting corrosion.

In this study, an innovative thermal energy storage design method was developed by adding the combination of metal foam and fin to phase change materials (PCMs). A numerical model was built and verified based on the comparison among the present model prediction, experimental measurements, and numerical results in open literature. To highlight the novel design method, four cases including fin-PCM, foam-PCM, fin-foam-PCM, and PCM unit were compared by means of solidification features. The temperature distribution, solidification front propagation, and buoyancy-induced convection in the liquid PCM were accounted for. Numerical results demonstrated that metal foam outperformed fin regarding the improvement on solidification phase change. The combination of foam and fin achieved the best performance, leading to a 90.5% reduction in complete energy release time in comparison with the PCM unit. The proposed design method provided reference potentials for advancing energy storage engineering. However, buoyancy-induced convection in the liquid PCM before solidification was harmful to the formation of solidification front and its movement. A maximal 11.5% prolonging time for the complete solidification was found.

This paper reports on a numerical study into the crack-dependent behaviour of a steel-plate girder bridge strengthened with carbon-fibre-reinforced polymer sheets. Progressive cracking, which represented fatigue-induced damage, was simulated from up to 10% of the girder depth. Finite-element analysis was used to evaluate the performance of the control, damaged and strengthened cases subject to standard US highway fatigue loading. The efficacy of polymer strengthening was also examined from a strength perspective, using the load factor rating method and the load and resistance factor rating method. Localised fatigue cracking caused a stress concentration along the girder and its progression rate was related to the degree of web fracture. The damage of the tensile flange was more influential in reducing the flexural capacity of the girder relative to damage of the web. The strengthening decreased the stress ranges, thereby increasing the fatigue life of the girder, and enhanced the maximum average daily traffic capacity. Reliability modelling indicated a transition in failure rates before and after 3% cracking in the girder, supporting the extended functional time resulting from strengthening.

To resolve the problem of ductile fracturing of beam flanges in traditional connections with concrete-filled steel tube columns using site-welded side plates, an alternative connection design requiring minimal site welding was designed and studied. An explicit analysis method, considering the fracture strain criterion developed by the stress triaxiality path, was adopted to study the seismic performance and fracture resistance of the proposed connection. The results of a verified finite-element model indicated that the steel beam flange in the connection never fractured. The connection exhibited a notably higher maximum bending moment and ductility than the traditional connection. The side plates in the proposed connection were tension-bending or compression-bending elements, unlike in the traditional connection. The failure modes, maximum bending moment, ductility and stress distribution of the side plates were compared and analysed parametrically. Based on the stress distribution of the side plates according to the finite-element results, a fitting formula related to the width and thickness of the side plates was obtained. A formula to calculate the flexural capacity was also developed according to the force model of the proposed connection. The calculations and finite-element results were in good agreement.

The objective of this study was to evaluate the bond behaviour of concrete-filled steel tubes (CFSTs) where waste chipped rubber, sourced from scrap tyres, partially replaces natural coarse aggregate. A series of push-out tests on 112 circular and square CFST specimens were investigated with the main parameters considered in the tests being: (a) cross-sectional type (circular and square); (b) cross-sectional dimensions; (c) concrete type (normal and rubberised concretes); (d) replacement ratio of recycled chipped rubber; and (e) concrete age (28–365 days). Four rubber chip replacement ratios (0, 10, 20 and 30%) by volume of coarse aggregate were used. The experimental results indicated that cross-sectional type and dimensions have a high impact on the interfacial bond strength. The bond strength in larger circular tubes was about 60% more than the bond strength in smaller circular tubes, and about 127% and 42% more than the bond strength in large and small square tubes, respectively. It was also found that CFSTs incorporating chipped rubber shared a generally similar interface bond behaviour between the concrete core and steel tubes with conventional CFSTs. Moreover, the bond strength decreased remarkably with the increase of concrete age.

Molten salt has been widely used in latent heat thermal energy storage (LHTES) system, which can be incorporated into hybrid photovoltaic/thermal solar system to accommodate the built environment. Solar salt (60 wt.% NaNO3 and 40 wt.% KNO3) was employed as the phase change materials (PCMs) in this study, and both aluminum oxide (Al2O3) nanopowder and metal foam were used to improve the properties of pure solar salt. The synthesis of the salt/metal foam composites seeded with Al2O3 nanopowder were performed with the two-step and impregnation methods, and the composite PCMs were characterized morphologically and thermally. Then pure solar salt, the salt/2 wt.% Al2O3 nanopowder and salt/copper foam composite seeded with 2 wt.% Al2O3 nanopowder were encapsulated in a pilot test rig, respectively, where a heater of 380.0 W was located in the center of the LHTES unit. The charging and discharging processes of the LHTES unit were conducted extensively, whereas the heating temperatures were controlled at 240 °C, 260 °C and 280 °C respectively. Temperature evolutions at radial, angular and axial positions were recorded, and the time-durations and volumetric mean powers during the charging and discharging processes were obtained and calculated subsequently. The results show that physical bonding between Al2O3 nanopowder and nitrate molecule has been formed from the morphological pictures together with XRD and FTIR curves. Slight changes are found between the melting/freezing phase change temperatures of the salt/metal foam composites seeded with Al2O3 nanopowder and those of pure solar salt, and the specific heats of the salt/Al2O3 nanopowder composite slightly increase with the addition of Al2O3 nanopowder. The time-duration of the charging process for the salt/copper foam composite seeded with Al2O3 nanopowder at the heating temperature of 240 °C can be reduced by about 74.0%, compared to that of pure solar salt, indicating that the heat transfer characteristics of the LHTES unit encapsulated with the salt/copper foam composite seeded with Al2O3 nanopowder can be enhanced significantly. Consequently, the mean volumetric powers of the charging process were distinctly enhanced, e.g., the volumetric mean power of heat storage can reach 110.76 kW/m3, compared to 31.94 kW/m3 of pure solar salt. However, the additive has little effect on the volumetric mean power of heat retrieval because of the domination of natural air cooling.

Thin-walled shell structures are characterised by a lightweight structural form with high strength. The importance of using cylinders and cones has long been known to engineers and designers in various engineering disciplines and they are widely used in shell form. In this work, the buckling and post-buckling behaviour of thin-walled cylindrical shells with geometric imperfections was investigated under vacuum-type pressure loads. Ten shell models with dents of two depths and lengths were designed for experimental tests: the dents were the thickness or twice the thickness of the shell, while their lengths were half or one-third of the height of the model. Carbon-fibre-reinforced polymer (CFRP) was used to retrofit some of the dented models. Test results from the CFRP specimens and the non-CFRP specimens were then compared with each other and with theoretical calculations.

In order to promote the application and development of steel–concrete composite beams in bridges, the fatigue performance of corroded studs was investigated. Based on fatigue crack propagation theory and the fatigue failure mechanism of corroded studs, a fatigue life prediction model for corroded studs was proposed. The values of key parameters in the fatigue life prediction model of corroded studs were obtained. Moreover, the fatigue life of corroded studs was analysed. Results show that the error between the calculated value and the test value of the fatigue life of corroded studs is less than 10%, and the fatigue life prediction model for corroded studs is sufficiently accurate. As the corrosion rate of a stud increases, its fatigue life rapidly decreases. When the corrosion rate of the stud increases from 5 to 50%, the fatigue life of the stud decreases from 20 to 90%, respectively; thus corrosion greatly reduces the fatigue life of the stud.

Although research has shown a considerable influence of the pre-cracking phenomenon on steel-congested concrete members, only normal concrete (NC) has been considered in the literature. The intention in this paper is thus to study the effect of the pre-cracking phenomenon on the bond response of pre-cracked NC with different slump flow values and self-consolidating concrete (SCC). Initial crack widths ranging from 0.0 to 0.5 mm are studied. Results show that initial crack widths larger than 0.10 mm have a significant influence on bond properties, such that reduction factors greater than 30% and 50% are obtained for the maximum bond strength of concrete specimens exposed to initial crack widths of 0.2 mm and 0.4 mm, respectively. Results show that concrete mixtures with higher workability are less sensitive to the pre-cracking phenomenon as compared to NC mixtures. The average bond stress of steel rebar in the pre-cracked SCC is found to be similar to that of the NC with a slump flow of 200 mm, which is considerably better than for NC with a slump flow of 97 mm. Moreover, results show that 65.8, 80.6, 88.5 and 93.1% fracture energy reductions are obtained for crack widths of 0.20, 0.30, 0.40 and 0.50 mm, respectively, as compared to the small crack width of 0.15 mm.

In mechanised tunnelling, the filling of the annular gap behind the precast concrete segments is one of the essential operations. The main goal of filling this space is to reduce surface settlements and limit movements due to tunnel excavation in the soil mass. To achieve this aim, a two-component grout is often used to fill the annular gap. Determination of the amounts of ingredients in the two-component grout should be carried out in such a way that the injection materials will be able to fulfil the required performance and technical properties. In this study, laboratory tests were carried out to investigate two-component grout properties, such as flowability, bleeding, gelling time and uniaxial compressive strength. The effect of lateral pressure on grout resistance was studied according to real excavation situations. The influences of the grout ingredients and effective parameters such as bentonite and cement contents, water–cement ratio and the dosage of accelerator (sodium silicate) and accelerator ratio were also investigated.

A preliminary experimental investigation of box-section reinforced concrete (RC) beams strengthened with carbon-fibre-reinforced polymer (CFRP) under shear and torsion was carried out. Based on different torque-to-shear ratios (TSRs) (0.958, 1.597, and 2.556), 12 box-section specimens were divided into three groups. In each group, one beam was a non-strengthened control while the other three beams were strengthened with CFRP U-jackets or CFRP U-jackets and longitudinal strips. Tests on the beams showed that the average cracking angle at the ultimate state was inversely proportional to the TSR. Two failure patterns were observed: debonding in the beams strengthened with U-jackets and fracture in the beams strengthened with both U-jackets with longitudinal strips. At the ultimate state, the best improvement in torsional capacity was achieved in the specimens retrofitted with longitudinal strips bonded on the U-wrapping strips. Equations using a modified effective strain expression were developed to compute the ultimate torque of all the specimens, the results of which were in good agreement to existing experimental data.

Cold-formed steel members are usually used as purlins in buildings to support roof cladding and thus they can be treated as beams restrained fully or partially in the lateral and torsional directions. However, when these beams are subjected to wind suction loading, their free flange is in compression, which may cause web–flange distortional buckling (WFDB). This paper presents an analytical study on the WFDB of zed-section purlins when subjected to uplift bending. A simplified model is proposed to describe the WFDB of partially restrained purlins, from which the formula for calculating the critical stress of the WFDB is derived. The present model is validated by the results obtained from the finite strip analysis.

Reliable column–column connection contributes to a reduction in waste materials and enables structures to be demountable after their service life. This paper demonstrates the feasibility of using a bolted-flange connection with concrete-filled steel tube (CFST) columns subjected to axial compression load. Compression capacity, ductility, axial stiffness and toughness, as well as failure modes are discussed. The specimens are grouped into two categories: group I—connection without stiffeners and group II—connections supported by stiffeners. Three thicknesses of 2, 4 and 6 mm were used to manufacture the bolted flanges and stiffeners. The results showed that the proposed connection was effective to avoid a reduction in compression capacity. The various thicknesses of bolted flanges in group I specimens had a slight influence on the axial stiffness value and that influence was doubled in group II specimens. The stiffeners played a significant role in the toughness value and this was reduced with a reduction in the thickness of the stiffeners. In addition, an improvement in ductility was noticeable in stiffened specimens. Consequently, it can be inferred that bolted-flange joints have the potential to produce reliable and economical designs for CFST columns.

Vibration properties of civil structures, which are commonly analysed for damage detection, are affected by changing environmental and operational conditions, and most notably are subjected to bilinear effects from changing ambient temperature conditions. Therefore, damage detection in structures during the past decade has focused on eliminating the effects of these changing environments that affect the vibration properties of the structures. Several methods have been proposed in the literature to tackle the non-linear effects from changing environments. However, these methods can only analyse systems (e.g. natural frequency–environmental and operational system) that have an incremental change in relationship; they cannot model the bilinear effects from the changing temperature conditions, which may lead to false alerts. Hence, a damage detection method is proposed in this paper to tackle the piecewise effects from changing temperature conditions. The method makes use of a Gaussian mixture model to separate the different effects acting on the structures and uses principal component analysis for data processing. The method is applied to the Z24 Bridge, in Switzerland, which was subjected to bilinear effects from changing temperature conditions. The results obtained demonstrate that the proposed method successfully takes into account the piecewise effects to indicate the presence of damage.

To design a steel shear wall, dynamics of stress concentration on the columns and beam under lateral loads is essential. Therefore, it has been suggested that the thickness of plates should be reduced as much as possible. In cases where a plate with low thickness is not available, this is compensated by using either low-yield-stress plate or by preparing some holes in the structure. Two objectives are pursued in this study, namely, the formulation of a new time integration method for evaluating structural seismic behaviour, and to discover the influences of the yield strength of the steel plate and openings on the wall. The results obtained indicate that the proposed scheme can accurately assess the seismic performance of structures. In addition, in the shear wall with low yield stress, where the steel plate has 5% and 10% openings, there are no significant differences between the outputs of widespread and concentrated openings. The behaviours of these two kinds of shear walls are approximately the same.

Fibre-reinforced polymer bars are rapidly becoming an approved alternative to conventional reinforcing steel bars, especially for severely exposed structures such as bridges. This paper reports on an experimental study on the bond characteristics of both sand-coated and ribbed-surface glass-fibre-reinforced polymer bars embedded in high-strength concrete (HSC). A total of 145 pull-out tests were conducted to examine the effect of varying parameters on the bond characteristics, namely embedment length, bar diameter, surface treatment and concrete cover. In addition, 45 pull-out tests were conducted to investigate the effect of providing headed-end anchorage for the sand-coated bars. The experimental results showed that the sand-coated bars exhibited better bond strength than the ribbed-surface bars, which entailed lower development lengths. Thus, based on the experimental results, expressions for the development length of both sand-coated and ribbed-surface bars embedded in HSC were developed and compared against the results of formulae in available design standards. The comparison revealed that ACI 440-1R-06 produced lower conservative results than CAN/CSA S806-12.

The design and construction of mechanically stabilised earth (MSE) walls is widespread and stiffness-based MSE wall designs are becoming popular. In MSE wall design, the pullout resistance of reinforcement plays a major role. For various field conditions, properties such as the normal stress and stiffness of reinforcement are hard to determine in the laboratory. In this study, a numerical model, developed using finite-element software, was used to assess pullout behaviour by varying other parameters such as normal stress, soil friction angle and, especially, the stiffness of reinforcements. Pullout resistance factors (F*) were developed based on the stiffness of the reinforcements considered in this study, which were in the range 100−10 000 kN/m for normal stresses of 10–300 kPa (equivalent to a maximum MSE wall height of 17 m). The developed design chart can be used for the optimistic design of MSE walls.

The influence of polyacrylamide (PAM) on the mechanical and physical characteristics of two kinds of soft soils was investigated laboratory tests including consistency, standard Proctor compaction, incremental loading consolidation and desiccation tests were conducted on the untreated and treated soils. Based on results, addition of PAM caused a reduction in the soils' plasticity indices. Although adding PAM slightly increased the maximum dry density, it had a negligible impact on the optimum moisture content. An increase in PAM content reduced compressibility, initial void ratio, compression and swelling indices, coefficient of consolidation and permeability. Adding PAM caused the cracking potential of soils to decrease. Moreover, to have a better interpretation of the stabilisation mechanism as well as the microstructural changes induced by PAM, the field emission scanning electron microscopy and X-ray diffraction analyses were conducted on the soils. The results demonstrated that the PAM additive enables physical bonding between soil particles rather than chemical reactions. In other words, PAM does not change the soil in terms of the atomic structure of clay particles, rather it alters the whole structure of the clay mass by accumulating particles and creating a strong connection network between them by flocculating the aggregates.

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The structural behaviour of concrete-filled steel tubular columns subjected to full and local compression loads was investigated. Experiments were performed on 18 columns with different cross-sectional slenderness ratios. The experimental parameters were the local compression area ratio and the slenderness ratio. The strength index, stiffness and ductility index of the columns were obtained through experimental tests. The results revealed that the local compression area ratio and slenderness ratio are key parameters that considerably affect the strength capacity of columns subjected to full and local compression loads. Design models provided in various international codes and various studies were used to validate the experimental results. Furthermore, the suitability of these design models for predicting the strength capacity of columns subjected to full and local compression loads was examined. Finally, through regression analysis, a simplified design model was developed for predicting the strength capacity of columns under full and local compression loads.

Background: The fiber-loop ring-down spectroscopy technique has the benefits of optical fiber sensors and also has many unique advantages. Combined with various sensor structures, the FLRD system can achieve different physical, chemical, and biological sensors. Objective: To find a way to solve the problems of light fluctuation and low sensitivity, high sensitivity, and reliability torsion relative angle measurement system is necessary. Methods: The torsion relative angle measurement is achieved by using the fiber loop ring-down intra- cavity amplification. The sensitivity, correlation coefficient, and repeatability are analyzed with the experiment. Results: The sensitivity and correlation coefficient of the proposed system are 4.05 μs/° and 0.9996, respectively. The repeated experiments show that the standard deviation is 9.592×10-4. Conclusion: The proposed measurement method provides a way to solve the problems of light fluctuation and low sensitivity and has promising applications in the optically active solutions, fiber radial stress birefringence and polarization state measurement of fiber lasers.

Since its first use several decades ago, scanning electron microscopy has been used in numerous investigations dedicated to biological systems. This contribution focuses on observations on pathological calcifications in order to review several major applications of primary importance to the clinician. Among these, we highlight such observations as medical diagnostic tools in pathologies arising from primary hyperoxaluria and urinary infections.

Background: Crystal violet dye is stable and difficult to be biodegraded owing to the existence of the multiple aromatic rings of the crystal violet molecules. Removing crystal violet dye from the wastewater is a major challenge. Objective: The aim of the research is to synthesize barium carbonate/tin dioxide nanoparticles and investigate the photocatalytic performance for the degradation of crystal violet. Methods: Barium carbonate/tin dioxide nanoparticles were synthesized via a facile hydrothermal route without any surfactants. The crystal structure, micro-morphology, size and optical performance of the barium carbonate/tin dioxide nanoparticles were investigated by powder X-ray diffraction, scanning electron microscopy, transmission electron microscopy and solid ultraviolet-visible diffuse reflectance spectrum. Results : The size of the barium carbonate/tin dioxide nanoparticles is 20 nm to 200 nm with the band gap of 3.71 eV. The photocatalytic activity of the barium carbonate/tin dioxide nanoparticles was measured by the photocatalytic degradation of crystal violet. The crystal violet degradation efficiency reaches 92.1% with the ultraviolet-visible irradiation time of 8 h using 10 mg barium carbonate/tin dioxide nanoparticles. The crystal violet degradation ratio increases to 96.1% when the dosage of the barium carbonate/tin dioxide nanoparticles increases to 20 mg/10 mL crystal violet dye solution. Active species capture photocatalytic experiments showed that the holes, hydroxyl radicals and superoxide ion radicals are the main active species. Reusability experiments displayed that the barium carbonate/tin dioxide nanoparticles are stable for the crystal violet dye degradation. Conclusion: The barium carbonate/tin dioxide nanoparticles show good photocatalytic performance toward crystal violet under ultraviolet light irradiation.

Background: Al is the promising candidate for deep UV and longer wavelength range plasmonic applications. But it is difficult to have the pure aluminium nanostructure as it is easily oxidized, forming a thin layer of Al2O3. In this paper, we have evaluated the field enhancement of oxide layer on metallic shell (Al-Al2O3 and Au-Al2O3) for single and dimer core-shell configuration and showed potential of the oxide layer in SERS. Methods: The Finite Difference Time Domain (FDTD) has been used to evaluate the LSPR and field enhancement of single and dimer Al-Al2O3 and Au- Al2O3 nanostructure. Results: The results exhibit the tunable plasmon resonance on varying the inner and outer radii of the Al2O3 shell. A redshift and decrease in enhancement were observed as shell thickness increases, whereas on increasing the core size, the enhancement increases in the case of Au-Al2O3 and decreases in Al- Al2O3 due to quadrupole contribution. But on comparing the Au-Al2O3 with Al-Al2O3 for the same particle size, Al-Al2O3 shows larger enhancement because Au has to compete with its interband transition. Conclusion: By optimizing the thickness of the shell and core size, it can be concluded that an ultrathin shell of Al2O3 can give higher enhancement. With Al as a core metal, the enhancement increases as compared to Au-Al2O3. Since a single Al-Al2O3 nanoshell has shown a huge enhancement we have considered the multimer configuration of two identical nanoshells. Due to coupling between two nanoshells a huge increase in enhancement factor ~1012 was observed for Al-Al2O3 dimer nanoshell in the UV region.

To study the effect of steel corrosion on the shear resistance of new shear connectors, push-out tests were carried out on three groups of six discontinuous perfobond rib shear connectors with different corrosion ratios. After testing, the displacement, strain distribution, crack development and relative slip between concrete and steel were assessed. Based on the experimental work, the effects of corrosion of perfobond ribs and transverse rebars on the shear resistance of the connectors were studied using finite-element models. The results showed that when the corrosion ratio was low, the corrosion of the perfobond rib increased the cohesion between the steel and the concrete, thereby improving the initial stiffness and ultimate bearing capacity (UBC) of the structure. With an increase in the corrosion ratio, expansion cracks on the joint surface led to bonding failure between the steel and concrete and the shear resistance of the structure was greatly reduced. When the corrosion ratio of the transverse rebars was 10%, the UBC of the connection decreased by only 5% and the initial stiffness hardly changed.

Background: The utilization of high-performance Phase Change Materials (PCMs) that can reversibly store thermal energy is of immense interest and strategy for effective energy conservation and management. Methods: In this work, a new PCM nanocomposite, consisting of a eutectic mixture of stearic acid and n-nonadecane as core and SiO2 as shell, was prepared by direct impregnation method. Additionally, a laboratory scaled test room was designed to investigate the intelligent temperature control function of the nanocomposite in building materials. Results: The optimized nanocomposite was characterized using Fourier Transform Infrared (FTIR) spectroscopy, Differential Scanning Calorimetry (DSC), X-Ray Diffraction (XRD), and Scanning Electron Microscopy (SEM) techniques. The DSC data demonstrated that the PCMs eutectic mixture content in the stearic acid- n-nonadecane–SiO2 nanocomposite was 52.8 wt.% and the melting temperatures and latent heats of stearic acid - n-nonadecane eutectic mixture and optimized nanocomposite were 45.1 and 44.0 °C, and 163.7 and 86.5 J/g, respectively. Furthermore, the accelerated thermal cycling test confirmed the excellent thermal cycling stability of the nanocomposite after 500 heating-cooling cycles. Moreover, the laboratory scaled test room results showed that the incorporation of the resulting nanocomposite in the gypsum could reduce indoor temperature fluctuation, and the performance was improved with the increase in the mass percentage of the nanocomposite in the gypsum composite. Conclusion: The obtained nanocomposite had good thermal reliability and temperature control performance and thus can be a promising candidate for hi-tech applications in intelligent temperature control and precise thermal management.

The stress–strain behaviour of concrete confined by fibre-reinforced polymer (FRP) is an important part of studying the seismic rehabilitation of concrete structures. Most previous studies have investigated the stress–strain behaviour of concrete prisms confined by polymer composites without preloading, but concrete columns are under various loading conditions before being retrofitted with polymer confinement. Therefore, in this study, FRP-confined concrete cylinders with different preloading ratios were prepared to examine the effect of preloading on the behaviour of retrofitted concrete columns. The results indicated that preloading affects important points of stress–strain curve. Preloading up to 75% of the unconfined concrete strength had a positive effect on the stress–strain behaviour, but 90% preloading reduced the strength of the FRP-confined concrete. A modification for the stress–strain models of preloaded FRP-confined concrete is thus suggested.

Background: Since (1-x)[Pb(Mg1/3Nb2/3)O3]-(x)PbTiO3 (PMN-PT) ceramic has a high dielectric constant and piezoelectric coefficient, it has been widely investigated for profound applications in electro-optical devices, sensors, multilayer capacitors and actuators. Objectives: The objective of this paper is to study the structural and electrical properties of 0.7Pb(Mg1/3Nb2/3)O3-0.3PbTiO3 (0.7PMN-0.3PT) ceramic to understand the biphasic structural nature using Rietveld Refinement. Also, it characterises the type of conduction process as well as the role of grain and grain boundary resistance in the material on the basis of electrical properties such as impedance and modulus to understand the relaxation process. Methods: 0.7PMN-0.3PT is synthesised by mixed oxide method using PbO, MgO, Nb2O5 and TiO2 as precursor materials. Results: The XRD data reveals the biphasic structure of the tetragonal phase with the space group of P4mm and the monoclinic phase with the space group of Pm. The complex impedance analysis clearly represents the effect of grain on the overall resistance and departs from normal Debye-type behaviour. Also, the resistance is found to decrease with temperature, thereby confirming the semiconducting nature of the sample. The presence of long as well as short-range mobility of charge carriers is confirmed from the modulus and impedance analysis. The influence of long-range motion is observed at high temperatures and of short-range motion at low temperatures. Conclusion: XRD analysis confirmed the biphasic structure of the M+T phase. The frequencydependent modulus and impedance spectroscopy show the presence of a relaxation effect in the ceramic which is found to increase with temperature. The Nyquist plot shows that the resistance is decreased with temperature, thereby confirming the NTCR behaviour in the studied sample.

The effects of different dosages and lengths of carbon fibre (CF), sisal fibre (SF) and polypropylene fibre (PPF) on the microstructure and mechanical properties of mortar and concrete made with coral sand were studied through mechanical tests and scanning electron microscopy. In total, 37 groups of coral mortar and concrete specimens with the addition of CF, SF and PPF in four different dosages and three different lengths were tested. Based on mechanical tests and microstructure analysis, the strengthening effect and strengthening mechanism of fibre in coral mortar and concrete, and the mechanical properties of coral mortar and concrete were investigated. It was found that – compared with normal mortar and concrete – the workability of the coral mortar and concrete was poor due to its light weight, high porosity and rough surface. The strengthening effect of the fibres was reduced due to difficulty in dispersing the fibres evenly in the mortar and concrete. The addition of fibres significantly enhanced the flexural strength and toughness of the coral mortar and concrete, but an excessively high fibre dosage and the use of extra-long fibres significantly reduced its working performance due to the fibre curling and clustering, especially for CF. The optimal length and content of the different fibres were also investigated. The addition of SF was found to have the best strengthening effect.

The effectiveness of some of the most commonly used models for predicting the bond strength of steel and glass-fibre-reinforced polymer reinforcing bars in normal-strength concrete (NSC) and high-strength concrete (HSC) was examined. To this end, a comprehensive database of published results on pullout specimens was collected. A non-linear least-squares fitting method was used to formulate simple and accurate models with a unified structure for both steel- and fibreglass-reinforced specimens. To investigate the efficiency of the proposed model for NSC, the results of specimens in the literature, which were not included in the model construction, were used. However, due to the scarcity of HSC bond specimens compared with NSC specimens, an experimental programme was conducted for model verification. The final results revealed that the simple equations developed in this study were capable of accurately predicting the bond strength of steel and polymer rebars in both NSC and HSC.

Cross-sectional analyses of circular and square reinforced concrete (RC) columns strengthened with reactive powder concrete jacketing and fibre-reinforced polymer (FRP) wrapping were undertaken. The stress block method was used to determine theoretical axial load–bending moment (AL–BM) interactions of the columns. These were then compared with experimental results and found to be in very good agreement. A parametric study was also undertaken to investigate the most important factors that influence the AL–BM capacity of circular and square strengthened columns. Finally, a group of theoretical AL–BM interactions for circular and square strengthened columns was produced. These can be used in a wide range of applications for strengthening RC columns with high-performance concrete jackets and FRP wraps.

This paper presents a study on the punching shear strength and behaviour of ultra-high-performance fibre concrete interior slab–column connections. An experimental programme was performed on ten simply supported slabs subjected to an increasing concentrated load at the slabs’ centre. The main studied variables were concrete strength (56 and 123 N/mm2), fibre content (0, 1, 2, and 3%), fibre shape (end-hooked or corrugated), fibre size with the same aspect ratio, fibre type and material (steel, polypropylene or fibreglass). The test results indicated the efficiency of using steel fibres in ultra-high-performance concrete slabs to enhance their punching shear strength. The test results were used to evaluate existing empirical equations estimating the punching shear strength of ultra-high-performance concrete slabs with fibres. The evaluation indicated that the equations proposed by the Association Française de Génie Civil (AFGC) in 2013, the fib Model Code for Concrete Structures 2010 and by Higashiyama and co-workers in 2011 provided the most accurate estimation when compared with test results.

An experimental investigation was carried out on a novel type of concrete-filled tube column, which used geopolymer concrete and basalt-fibre-reinforced-polymer reinforcing bars and confinement tube. Geopolymer concrete was used in place of ordinary Portland cement concrete to counter the sustainability challenges of conventional cement manufacture. Longitudinal basalt-fibre-reinforced-polymer bars were used to replace steel reinforcement to avoid corrosion, while basalt-fibre-reinforced-polymer tube confinement was used to replace the conventionally used steel helix to enhance strength and ductility. Compressive load–deformation behaviour of 200 mm dia., 800 mm high specimens under concentric, 25 mm eccentric, 50 mm eccentric and four-point bending loads was experimentally investigated. Experimental axial load–bending moment diagrams were then produced. Although geopolymer concrete is normally considered to be more brittle than Portland cement concrete, the test results showed that the specimens with geopolymer concrete were more ductile compared to those with Portland cement concrete. It was also found that increased load eccentricity resulted in ductility enhancement in specimens with both types of concrete with basalt-fibre-reinforced-polymer bars and tubes, while steel-reinforced specimens suffered loss of ductility with increased load eccentricity.

Fire throttling is the increase in flow resistance due to a large fire in a longitudinally ventilated tunnel. Although the fire throttling effect has been been known and studied for tunnels over the last 40 years, there is not yet a consistent one-dimensional (1D) model that can describe this behaviour or a framework suitable for practical application. We propose a semi-empirical model, based upon pipe flow engineering principles, to describe this effect by separating the resistance to flow, or pressure loses in three parts: upstream of the fire, locally at the fire, and downstream of the fire. The proposed 1D model called TE1D is derived from a simple steady one-dimensional momentum balance in which a semi-empirical mean temperature distribution is assumed across the tunnel. We verify the model by comparing the pressures losses it predicts with those calculated in CFD simulations based on OpenFOAM and Fire Dynamics Simulator. The comparison shows good agreement between the CFD codes for the range of fires sizes considered from 5 to 50 MW and good agreement between TE1D and the CFD results with the proposed 1D model for fire sizes below 30 MW. However, for values above there are large discrepancies between the results obtained by the TE1D and CFD. We posit as a potential explanation that these differences are due to flow and temperature stratification which is not accounted for in the 1D model. The model using pipe flow principles allows engineers to adopt this model for design, together with other pressure losses considered in tunnel ventilation.

Tests have shown that providing passive confinement to concrete, either through the use of internal stirrups, external fibre-reinforced polymer (FRP) wraps, FRP tubes or steel tubes, can increase the concrete strength and, in particular, the concrete ductility, thereby allowing greater absorption of energy and consequently ductile failure. The problem of including the benefits of passive confinement in design is in generalising the effect of passive confinement because it varies with the member size, the configuration of the confining reinforcement and material properties. In this paper, all aspects of the complex fundamental mechanics of passive concrete confinement are explained both qualitatively and quantitatively through the use of shear–friction and bond–slip mechanics. The mechanics model was found to have a good correlation with test results. An analysis-oriented procedure is described for quantifying the passive stress–strain of concrete for rectangular sections and it is envisaged that this can be used to develop simplified rules for design, in particular for new types of members and those with new materials.

Concrete-filled double-skin tubular beams consist of two tubes, placed eccentrically or concentrically, with the hollow space between the two tubes filled with concrete. This type of construction can thus combine the properties of steel and concrete to provide the advantage of increased strength, ductility, stiffness and economy of the section. This paper reports on a study into the flexural properties of beams made of square hollow section steel for the both inner and outer tube, connected with steel strips. In total, 12 specimens were tested under monotonic and cyclic loading. The effects of the concrete infill, the eccentricity of the inner tube, the provision of minimum steel reinforcement and slip control due to the attachment of steel strips at the end of the beams were studied. Beams with an eccentric inner tube showed better flexural response and were also more economical due to the reduced concrete volume; their load-carrying capacity under cyclic loading was less than that under monotonic loading. Compared with beams without longitudinal reinforcement, the beams with longitudinal reinforcement showed improved flexural strength when subjected to cyclic loading.

In engineering materials, defects, such as cracks, may occur during production and/or owing to various reasons. One of the aims of fracture mechanics is to determine the fracture toughness-based residual strength of structural members with cracks. A quasi-brittle material, such as concrete or rock, may include certain defects, such as voids and cracks, even before being exposed to loads. Experimental analyses on concrete members indicated that specimens’ nominal strength values decreased as their sizes increased while specimen geometry remained the same. In fracture mechanics, this condition is defined as the ‘size effect’ in both concrete and reinforced concrete units. In the literature, numerous theoretical and experimental studies have been conducted on beams, while compact split-tension specimens, particularly notched ones, are limited. In this study, six series of notched beams with three different sizes and notched square prismatic specimens with four different sizes were tested. According to the test results, the peak loads were analysed by using the fundamental theorem of the modified size effect law. In conclusion, two formulae were proposed to predict the flexural strength and the splitting strength of quasi-brittle bodies with cracks.

Photovoltaic (PV) system's performance is significantly affected by its orientation and tilt angle. Experimental investigation (indoor and outdoor) has been carried out to trace the variation in PV performance and electrical parameters at varying tilt angles in Malaysian conditions. There were two experimental modus: 1) varying module tilt under constant irradiation level, 2) varying irradiation intensity at the optimum tilt set up. For the former scheme, the irradiation level was maintained at 750 W/m2, and for the later arrangement, the module tilt angle was varied from 0o to 80o by means of a single-axis tracker. Results show that under constant irradiation of 750 W/m2, every 5o increase in tilt angle causes a power drop of 2.09 W at indoor and 3.45 W at outdoor. In contrast, for the same condition, efficiency decreases by 0.54% for indoor case and by 0.76% at outdoor. On the other hand, for every 100 W/m2 increase in irradiation, solar cell temperature rises by 7.52°C at indoor and by 5.67°C at outdoor. As of module electrical parameters, open-circuit voltage, short-circuit current, maximum power point voltage and maximum power point current drops substantially with increasing tilt angle, whereas fill factor drops rather gradually. Outdoor experimental investigation confirms that the optimum tilt angle at Malaysian conditions is 15o and orienting a PV module this angle will maximize the sun's energy captured and thereby enhance its performance.