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• Mechanical and thermal properties of straw boards with high densities are studied. • Tensile strength prediction method of straw boards is proposed. • Correlation between thermal conductivity and density of straw boards is revealed. • Feasibility of using straw boards for load bearing and insulation is verified. • Wheat straw strand board is identified as transversely isotropic material. Straw is an environmentally friendly, cost-effective, and abundant raw material for building boards. To assess the feasibility of using straw boards in building envelops, such as being alternative sheathing panels in light-gauge steel-framed members, for instance, walls and floors, both the mechanical and thermal properties of straw boards with high densities were investigated. The straw boards involved in this study include five wheat straw strand boards (WSSB12, WSSB15, WSSB18, WSSB25, and WSSB30) and a paper straw board (PSB58) named with a combination of the respective board type and thickness. Among them, the WSSBs are a type of straw composite, while the PSB is an improved straw bale with sheathing paper, which is mainly for enhancing the board integrality. Moreover, the former is composed of smashed straw fibers and isocyanate resin and has higher densities, while the latter is without using any artificial binders. Mechanical properties, including compression, tension, and bending properties, were investigated by tests and a proposed prediction method of tensile strength. In the experimental studies of compression properties, the failure modes, characteristics of load-deformation curves, and the differences in material directivity were analyzed and discussed. The results show that the WSSBs were considered to be transverse isotropic material with brittle characteristics in the plane. Then, the experimental studies of bending properties were carried out, and the results show that the bending strength is less than the compressive strength for WSSBs, while the bending strength of PSB is greater than its compressive strength. And the bending elastic modulus and the compression elastic modulus are close for either the WSSBs or the PSB. Furthermore, finite element models of the bending test specimens using the user material subroutine UMAT were developed to predict the tensile strength f t , and the constraint checks were conducted. It is verified that the prediction results of f t are believable, and the prediction method proposed is feasible. For the thermal properties of straw boards, tests were performed using the temperature control box - heat flux meter method, and the thermal conductivity λ was mainly focused. It is found that a significant linear correlation exists between the density ρ and λ , and the proposed fitting formula can be used to predict the thermal conductivities of such materials. Finally, brief comparisons of the mechanical and thermal properties between the straw boards and the oriented strand boards (OSBs) were conducted, and the feasibility of applying straw boards in building envelops, such as alternative sheathing panels with load bearing and insulation demands was verified. This study contributes to popularizing the application of straw boards in engineering structures by a compromising consideration of mechanical and thermal properties, which plays a positive role in the development of green buildings. [ABSTRACT FROM AUTHOR]

Ultra-High Performance Concrete Filled Stainless Steel Tubular (UHPCFSST) column is a novel type of composite columns appealing to be adopted in corrosive and marine environment. To explore the axial performance of UHPCFSST columns, this paper initiates an experimental program containing 14 UHPCFSST columns subjected to either monotonic or cyclical axial compressive loading. The test variables in this program mainly include the column dimension, tube thickness and the loading schemes. Based on the test results, the damage evolution process, ultimate failure mode, load-deformation response and the typical mechanical performance indexes inclusive of loading-carrying capacity, stiffness degradation, as well as ductility coefficient are thoroughly examined. After that, theoretical analysis is carried out to explore the interaction behavior between UHPC and stainless-steel tube and hence judge the degree of confinement effect. To assess the applicability of the code equations stipulated in current international design guidelines and the empirical formulas proposed by other researchers, a small-scale dataset containing 41 UHPCFSST columns was compiled to make comparison of axial capacity between test results and analytical predictions. In view of the limited accuracy or the burdensome calculation process, a new formula considering actual loading carrying mechanism was proposed to calculate the axial capacity of UHPCFSST columns, which exhibits enhanced accuracy and efficiency than the current formulas. • 14 UHPCFSST columns were test under monotonic or cyclic axial loading. • The failure mode and performance indexes UHPCFSST columns were analyzed. • The confinement effect of UHPCFSST columns were discussed. • The prediction performance of current design formulas was evaluated. [ABSTRACT FROM AUTHOR]

An innovative anchorage technology named load distributive compression anchor (LDCA) has recently been employed in a multitude of geotechnical engineering. The anchoring structure comprises multiple anchor bodies, thereby overcoming the bearing defects associated with conventional load-concentrated anchors and providing superior bearing performance. The complex structural configuration of LDCA considerably complicates the process of load-transfer theoretical modeling. A lack of relevant studies from theoretical solution perspective is yet evident in previous works. In this paper, a theoretical model was proposed for the load-transfer analyses of LDCA, of which the soil-anchor interface mechanical behavior was specially characterized by a disturbed state concept (DSC)-based nonlinear model. The mechanical simulation for the connections in different anchor bodies was incorporated into the theoretical analysis framework through the utilization of finite difference method. Three groups of 3D finite element (FE) models were established to simulate the load-transfer behaviors of LDCAs with different numbers of anchor bodies. The theoretical calculations agree well with the FE numerical results and the in-situ pullout test data, thereby confirming the applicability of the load-transfer theoretical model. The axial force and interface shear stress distributions, as well as the bearing capacity for LDCAs, were discussed based on theoretical calculations and FE simulations. Sensitivity analysis of several key design parameters was conducted to investigate their effects on the bearing capacity of LDCAs. The findings achieved in this study can provide insights into the understanding of the load-transfer behaviors of LDCA, and contribute to the bearing performance evaluation. • A theoretical model for predicting the load-transfer behaviors of LDCA integrating a DSC-based interface nonlinear model. • Three groups of FE models to simulate the stress distributions of LDCAs with different numbers of anchor bodies. • Sensitivity analysis for investigating the effects of several key design parameters on the bearing capacity of LDCA. [ABSTRACT FROM AUTHOR]

To overcome the poor energy-absorbing efficiency of existing layered panels, three kinds of novel steel-glass fiber reinforced polymer (GFRP)-foam sandwich structures composed of two steel face sheets and GFRP-foam composite cores were proposed in this paper. The effect of the composite core thickness and GFRP lattice configuration on the energy absorption performance for sandwich structures was studied through quasi-static crushing tests. Considering the role of steel face sheets, a theoretical prediction model was derived to calculate the initial absorbed energy for all types of sandwich panels. Parametric studies were carried out to investigate the influence of five different variables (axial compressive load, steel sheet thickness, GFRP web thickness, GFRP and foam compressive modulus) on the overall energy dissipation for each kind of composite panel. Test results indicated that both the thicker core component and double-layered dislocation GFRP layout could effectively promote the energy consumption property of all the steel-GFRP-foam structures, and the steel face sheet played a crucial role in the proposed sandwich panels due to its excellent absorbed-energy capacity per volume and exceptional ductility. Theoretical results demonstrated that the equivalent energy-absorbing formula was desirable to be used to assess the crushing resistant behavior of each sandwich structure. Parametric analysis results showed that a larger axial compressive load was able to improve the structural initial energy absorption, but the increase of four other structural parameters, especially the thickness of the front (rear) steel sheet, could weaken such an identical performance. • Three types of innovative steel-GFRP-foam sandwich structures were proposed to promote the overall energy-absorbing efficiency. • Quasi-static crushing experiments were taken to investigate the energy absorption performance of steel-GFRP-foam structures. • A theoretical model was firstly established to predict the initial absorbed energy of steel-GFRP-foam sandwich panels. • Parametric studies were conducted to discuss the effect of various structural indicators on the energy dissipation of steel-GFRP-foam panels. [ABSTRACT FROM AUTHOR]

The aim of this paper is to numerically investigate the relationship between mechanical strength and microstructural evolution of concrete, firstly, based on the geometrical characteristics of constituents, a multi-scale model of concrete was geometrically reconstructed; Secondly, a stress response equation of composite material at different scale of concrete was presented, and a multiscale model of concrete strength associated with stress response was proposed; Finally, after being verified, this model was utilized to conduct a numerical analysis on the characteristics of stress response and the mechanical strength of concrete in the curing process as well as the effect of microstructural characteristics on the strength of concrete. Results show that, the fact that the compressive strength of concrete is clearly greater than its tensile strength is attributed to the difference in the stress response under uniaxial compressive and tensile loading, while the mechanical strength of concrete is obviously affected by spatial orientation and geometric shape of hydration products in the microstructure. • A multiscale geometrical model of concrete was reconstructed to reflect its heterogeneous features. • A multiscale model for macro-mechanical strength of concrete was proposed based on its constituents. • The stress response characteristics and mechanical strength of concrete were numerically investigated. [ABSTRACT FROM AUTHOR]

Due to the ongoing disasters caused by local damage to underground pipelines in urban areas, a new method has been proposed for local trenchless rehabilitation of pipelines.This method utilizes the auxetic effect of an auxetic pipe structure to create support brackets inside the pipeline for repairing damaged sections, with the aim of reducing overall repair costs and improving efficiency. The main objectives of this study are to demonstrate the feasibility of using auxetic pipes for pipeline repairs and to enhance key parameters of auxetic support pipes. This paper presents a tube with auxetic support - the Surrounding Auxetic Tubular Structure (SATS). Using 3D printing technology, the preparation of SATS specimens was carried out, and the compressive properties of SATS were studied through finite element analysis and quasi-static compression test. The results show that the proposed SATS has a significant negative Poisson's ratio effect during the compression process and exhibits a high structural rebound rate after the load is removed. The size of the structure's boundary is the most influential factor on the auxetic effect. Additionally, the compression displacement of SATS increases with the increase of the elliptical short axis, and decreases with the increase of the elliptical long axis. The compressive load decreases with the increase of the short axis, and increases with the increase of the long axis. This demonstrates the excellent mechanical performance of the proposed auxetic support structure and lays the foundation for the feasibility of local repair work for trenchless rehabilitation. • The new auxetic cell and auxetic tubular structure was designed. • The new rotational deformation mechanism of the auxetic cell was investigated. • The influence of boundary size on the auxetic effect was investigated. • The structural deformation caused by compression and recovery was investigated. • The influence of geometry on the auxetic effect was investigated. [ABSTRACT FROM AUTHOR]

Fiber-reinforced polymer (FRP) is a practical approach to delay or even suppress the deformation of steel structures. However, their application has been constrained by brittle damage and low strengthening efficiency. This paper presents an investigation of the mechanical behavior of short circular hollow section (CHS) steel columns restrained with hybrid fiber-reinforced polymer (HFRP) composed of carbon fiber-reinforced polymer (CFRP) and glass fiber-reinforced polymer (GFRP) under axial compression. The results show that the restraint effect of HFRP composed of one layer of transverse CFRP as the middle layer and two layers of transverse GFRP as the inner and outer layers is better than two layers of transverse CFRP, with peak load and ductility increased by 7.29 % and 12.36 % over the latter. Then, a simplified method for simulating HFRP and single FRP restrained short CHS steel columns is proposed and verified by experimental results. Moreover, a parametric study is performed to discuss the effect of the diameter-to-thickness ratio on the bearing capacity. Finally, a universal method is proposed to calculate the ultimate bearing capacity of HFRP and single FRP restrained short CHS steel columns, for which the average error and standard deviation from the measured values are 2.27 % and 0.024, respectively. • Studied behaviors of HFRP-restrained short CHS columns composed of GFRP and CFRP. • Explored effects of FRP type, direction, and number of layers on short CHS columns. • Proposed a simplified method for simulating the HFRP-restrained short CHS columns. • Studied effects of diameter-to-thickness ratio on HFRP-restrained CHS columns. • Proposed a method to calculate the bearing capacity of HFRP-restrained CHS columns. [ABSTRACT FROM AUTHOR]

• Experimental study into the load carrying capacity of straw bale wall assemblies. • Characterised and compared the vertical load carrying performance without and with plaster coatings. • Studied the effect of wall height, plaster use, and load eccentricity on compressive resistance. • Results from 29 wall tests presented. To reduce the significant carbon emissions associated with construction materials, there is growing recognition of the potential for bio-based resources, including materials derived from agricultural crops such as straw, hemp and flax. The biogenic carbon stored with plant based materials can significantly reduce carbon emissions compared to other products. Uses of bio-based materials are however generally limited to non-structural, in particular as insulation, but in contrast to many other solutions straw bales can also be used structurally in low-rise construction. Despite the use of straw bales for over 100 years there is still relatively little known about their compression performance, and there are no recognised guides or standards to support structural engineers. This paper describes an experimental study into the load carrying capacity of straw bale wall assemblies. In keeping with practice in the UK, and different to previous North American studies, the wall plates do not directly bear onto the plaster coats. The aim of the paper is to characterise and compare the vertical load carrying performance of straw bale walls without and with plaster coatings, and study the effect of wall height, plaster use, and load eccentricity on compressive resistance. A series of wall assemblies were built from stacking 1 m long wheat straw bales. Wall assembly heights varied with the number of bale courses: one, two, three and four bales high. In total results from 29 tests are presented. Key findings of the study concern the influence of load eccentricity, use of plaster and wall geometry on compression performance. In the absence of national guidance, the results of this experimental study will support structural engineers designing loadbearing straw bale walls. [ABSTRACT FROM AUTHOR]

Earth is a traditional building material used through History in many areas around the world. Nowadays, there is also a significant revival of its use because of its ecological value and architectural performance. However, there is still a lack of knowledge about its actual mechanical behavior. This paper is aimed at providing experimental data for the development of consistent methodologies for the characterization of this building material. Compression tests of prismatic, cubic and cylindrical specimens were carried out. The compressive strength, Young modulus and the stress-strain constitutive law are obtained and analyzed. The paper shows that the Unconfined Compression Strength of the material should not be obtained by applying existing correction factors for other materials. The paper also analyzes the meaning and usefulness of different estimates of the Young modulus. Finally, the paper proposes a simplified method for estimating stress-strain relationships from the compressive strength and its corresponding strain of tested samples by using reference normalized curves. [ABSTRACT FROM AUTHOR]

Reinforcement bars based on glass fibre reinforced polymers (GFRP) show good mechanical properties and advantageous durability properties compared to conventional steel reinforcement. The increasing use of GFRP reinforcement can, therefore, also be seen against the background of an advised resource-efficient adoption of materials in the construction industry. However, the mechanical properties of GFRP reinforcement are still not sufficiently researched, currently leading to regulatory restrictions. More specifically, regarding the compressive material properties of GFRP reinforcement bars under long-term loading, there is a significant lack of information. This paper introduces a novel model for predicting the stress redistribution in GFRP reinforced concrete members subjected to long-term compression. A comprehensive examination of the mechanical background and a brief summary of existing literature on relevant test results form the basis for the initial development of an extensive test program to be applied. In the first part of the experimental investigations, GFRP reinforcement bars are statically loaded for an experimental period of 1000 hours in order to determine creep rates. Subsequently, GFRP reinforced concrete specimens are subjected to compression for 190 days at three different load levels. The results show a significant stress increase in the GFRP reinforcement due to creep and shrinkage. The high ultimate loads of preloaded specimens demonstrate that the long-term loading did not lead to any damage. The proposed analytical model combines the two parts of the experimental program and provides a practical method for determining the load redistribution in GFRP reinforced concrete members under permanent compressive loading. • Experimental determination of GFRP compressive creep behaviour. • Determination of a GFRP compressive creep model. • Investigation of creep induced GFRP load share to compressive capacity. • Assessment of shrinkage induced GFRP load share to compressive capacity. • Model proposal for the load-redistribution in compressed GFRP RC members. [ABSTRACT FROM AUTHOR]

This paper investigates the buckling of screws loaded in compression inserted into timber members. Screws are often used as a reinforcement in timber structures. However, under compression forces, they are prone to axial buckling. The current model for the screw buckling, enclosed in the EC5 proposal, is based on the general framework of EC3 for the instability of compressed steel members. The main shortcomings of the current formulation for the buckling of screws are the following. (1) The analytical expression for calculating the theoretical buckling load does not follow the observed modes. (2) Due to the need for dedicated studies, the value of the imperfection coefficient is arbitrarily chosen. This paper fills the above gaps. Firstly, a simple analytical expression for predicting the buckling of screws is proposed and validated against experimental and finite element (FE) findings. Furthermore, the formulation adopts a more accurate expression for lateral deformation based on experimental observation. Secondly, a FE model calibrated on experimental tests is used to estimate the defect coefficients of the instability curves as a function of the amplitude of the geometric defects of the screw, expressed as a fraction of its length. Finally, a Markov chain Monte Carlo analysis is carried out to simulate the capacity of screws with different sizes, assuming the uncertainty of all input parameters sampled from suitable probability distributions. The results are used to validate the proposed deterministic capacity model and estimate the uncertainty factors of the design equation. • Buckling model for compressed timber screws. • Analytical model for the theoretical buckling load. • Numerical validation of the analytical model. • Experimental tests and numerical model calibration. • Calibration of the imperfection coefficients from Monte Carlo analysis. [ABSTRACT FROM AUTHOR]

Fiber-reinforced polymer (FRP) jacketing has become an attractive strengthening technique for concrete columns. Existing research has demonstrated that FRP confinement is effective for circular columns, whereas it is less effective for square columns. The lower FRP confinement effectiveness in a square column is predominantly attributed to the non-uniform FRP confinement in the column, while the concrete in an FRP-confined circular column is uniformly confined. Although rounding the corners of a square column can enhance the effectiveness of FRP confinement, its benefit is still not satisfactory as the radius of rounded corners is usually limited owing to the presence of internal steel reinforcement. An appropriate approach to enhancing the confinement effectiveness of FRP strengthening technique for square columns is to circularize a square column before FRP jacketing. This paper aims to study the compressive behavior of circularized square columns (CSCs). A total of 33 column specimens were prepared and tested under axial compression in this paper. The column parameters include FRP wrapping schemes (including fully wrapped and partially wrapped), FRP volumetric ratio, sectional shapes and unconfined concrete strength. The test results have indicated that the section circularization of square columns can significantly improve the effectiveness of FRP confinement, and strengthening square columns using section circularization in combination with partial FRP confinement is a promising and economical alternative to the fully FRP strengthening technique. Comparisons between the theoretical predictions and the test results were conducted, and the accuracy of existing partially FRP-confined concrete models were also examined. [ABSTRACT FROM AUTHOR]

The present paper investigates the load-bearing properties of composite laminates featuring filled circular-frustum-shaped countersunk holes under compression loads. A sophisticated three-dimensional model based on the continuum damage mechanism (CDM) is employed in finite element analysis (FEA). This model integrates both the fiber-kinking and modified characteristic length sub-models and is implemented through a user subroutine. The FEA results exhibit a strong correlation with experimental findings, highlighting that delamination tends to occur before other failure modes such as fiber breakage and matrix cracking. Following validation, the FEM is utilized to explore the relationships between the bevel depths of countersunk holes and the strength of laminates. Regarding the effects of hole configurations, when the bevel depths are below 1.25 mm, composite laminates demonstrate a converging load-bearing capability with increasing bevel depth. However, for bevel depths ranging from 1.25 to 2.75 mm and exceeding 2.75 mm, the load-bearing capacities exhibit fluctuating decline and a monotonic decreasing trend, respectively, as the bevel depth increases. The developed model, coupled with the obtained results, can serve as a valuable tool for guiding the design and optimization of connection mechanisms in composite structures across various sectors, including constructions and buildings. • The developed model can capture the damage modes, with the deviations of predicted failure stress and strain within 3%. • The ± 45° layers are able to inhibit the damage propagation, and leads to a higher failure strain of FHC laminates. • With the increased bevel depth of countersunk hole, the load-bearing capacity decline with three distinct stages. [ABSTRACT FROM AUTHOR]

In practical engineering, chloride ions often attack concrete structures through non-uniform small regions, whose microstructure and stress forms are very complex and are usually influenced by the water-to-binder (W/B) ratio. In this paper, the chloride diffusion in concrete with three different W/B ratios under biaxial compression was tested, and the microstructure characterization and property analysis were carried out using digital image correlation (DIC), mercury intrusion method (MIP), and nanoindentation test. It was found that the chloride diffusion coefficient showed a trend of first decreasing and then increasing with the increase of biaxial compressive load, regardless of W/B ratios. A larger W/B ratio resulted in a larger porosity of concrete, poorer micromechanical properties of the interface transition zone, and a greater sensitivity to microcracks under load, thereby accelerating the chloride diffusion. Finally, a theoretical model considering the biaxial compressive stress level and W/B ratios was developed and effectively validated by the experimental results. [Display omitted] • Chloride ion diffusion in concrete is affected by compressive load and water-cement ratio. • An increase in thickness of nanoindentation ITZ accelerates the chloride ion diffusion. • A theoretical model for chloride ion diffusion is proposed considering the influence of multiple factors. [ABSTRACT FROM AUTHOR]

Sustained load is a common type of load for concrete structures during service. It may affect the pore structure of mortar, thereby affecting the transmission characteristics of water and the durability of concrete. In this paper, the pore structure and transport properties of mortars at low- stress levels were investigated. Non-destructive axial tensile and compressive loads were applied to the mortar to study the permeability and water absorption of the mortar under different loads. In addition, the mortar's pore structure was analyzed under varying sustained loads using the RapidAir 457 pore structure analyzer and micro-CT scans. Results show that within the stress levels of the experimental design, compressive loads tend to reduce the water transmission rate in mortar, whereas tensile loads have a positive effect on water transmission. The pore-size distribution of mortars with different water-cement ratios is affected differently by load. Finally, seepage simulation was carried out using the three-dimensional model established by CT scanning. The results show that the simulated values and experimental test values were consistent with the changing trend of the load. With increasing compressive load, the water seepage path is obstructed, resulting in decreased permeability. Conversely, under tensile loads, the number and density of streamlines increase, facilitating water penetration. • The effect of sustained loading on the pore structure was studied. • The effect of sustained loading on the permeability of mortar was studied. • Three-dimensional pore models of mortar was established based on CT scan results. • Seepage simulation was performed using a three-dimensional model. [ABSTRACT FROM AUTHOR]

Masonry walls are typically subjected to eccentric compressive loadings in common buildings. However, the design of walls towards this type of solicitation remains very empirical, often leading to oversizing the structure. This is especially true for natural stone masonry, for which experimental data are quite scarce. This paper presents an experimental campaign on 15 natural stone masonry wallettes subjected to centred and eccentric compression until failure. Different values of the eccentricity of the load, ranging from h /12 to h /4 (where h is the thickness of the wallette) were investigated, highlighting the noticeable effect of such a value on the compressive failure load. During the tests, the displacements were recorded by a Digital Image Correlation system, providing insights into the different failure mechanisms that depend on the value of the eccentricity. The so-obtained experimental failure loads are then compared to the predictions of Eurocode 6. Finally, a finite-element yield-design analysis of these tests is proposed which shows that this modelling framework is suitable to find the ultimate bearing capacity of a masonry wallette. • The greater the eccentricity of a compressive load, the lower the failure load. • Two types of failure mechanisms were identified depending on the eccentricity value. • Eurocode 6 underestimates the compressive strength of the wallettes by a 3.4 factor. • Experimental results corroborate the eccentricity correction factor from Eurocode 6. • 3D yield design provides accurate predictive results. [ABSTRACT FROM AUTHOR]

Automated crack segmentation from digital imagery is crucial for infrastructure health monitoring via non-destructive evaluation techniques. However, accurately capturing complex, multi-branch crack patterns remains challenging. This paper presents a comparative study of four state-of-the-art deep learning models – UNet, FPN, PSPNet, and DeepLabV3 – for crack segmentation from video data. Various encoder backbones, including ResNet, ResNeXt, SENet, and DPN are examined under manual and automatic compression loading conditions. Cracks were induced in cement-based materials via a uniaxial compression loading system equipped with synchronized imaging, containing diverse crack phenomena ranging from single, discrete cracks to complex crack networks with branches and intersections. Segmentation datasets were manually labeled for model training and testing. Experiments were conducted to evaluate crack segmentation performance using four widely-used metrics: Intersection over Union (IoU), F1-score, Recall, and Precision. Results showed that UNet paired with SENet as the encoder backbone achieved the best overall performance by IoU, F1-score, and Precision for manual loading, while FPN leveraging a DPN68 encoder achieved the most balanced and robust tracking of intricate crack propagations. This work benchmarks state-of-the-art solutions and analyzes failure cases, guiding model design and continued research priorities for persistent challenges in crack monitoring tasks. • Captured large-scale crack propagation dataset containing diverse crack morphologies. • Comprehensively evaluated four SOTA models and encodes for crack segmentation. • Identified key factors influencing crack segmentation accuracy. [ABSTRACT FROM AUTHOR]

This paper presents the results of a study that was carried out to investigate the use of small-diameter CFRP strands for strengthening steel plates subjected to uniaxial compression. This study is part of a comprehensive research program to evaluate the use of the small-diameter CFRP strands for shear strengthening of steel girders. The research in this paper was undertaken to examine the bond characteristics of the proposed material which is expected to eliminate the debonding failure observed for CFRP laminates strengthening system and to resist the compressive stresses induced in high shear zones. The small-diameter CFRP strands are stitched together with a gap between the strands to allow each strand to be completely covered by the adhesive material. The effectiveness of the strengthening system was investigated by varying various parameters believed to affect the overall behavior including the slenderness ratio of the steel plates as well as mechanical properties and reinforcement ratios of the CFRP strands. Strengthened plates exhibited higher buckling capacity in comparison to similar plates without CFRP strands. In addition, the small-diameter CFRP strands did not show any signs of debonding at large lateral deformation associated with elastic buckling. [ABSTRACT FROM AUTHOR]

The potential applications of fiber reinforced polymer (FRP) composites as concrete confinement in retrofitting existing concrete columns and in the construction of new high-performance composite columns have received significant research attention. In practical applications, the ages of concrete in retrofitted columns are significantly different from those of newly constructed columns. Without a full understanding on the influence of concrete age on their compressive behaviors, the validity of existing experimental findings, which are based the age of concrete at the time of testing, remains ambiguous when the design application lapses in time. This paper presents the results of an experimental study on the influence of concrete age on the compressive behavior of FRP-confined normal-strength (NSC) and high-strength concrete (HSC). The first part of the paper presents the results of 18 FRP-confined and 18 unconfined concrete specimens tested at 7 and 28 days. To extend the investigation with specimens with concrete ages up to 900 days, existing test results of FRP-confined concrete was assembled from the review of the literature. Based on observations from both short- and long-term influences of concrete age on compressive behavior of FRP-confined concrete, a number of important findings were drawn and are presented in the second part of the paper. It was observed that, at a same level of FRP confinement and unconfined concrete strength, the stress–strain behavior of FRP-confined concrete changes with concrete age. This difference is particularly pronounced at the transition zone of the stress–strain curves. It is found that, in the short-term, the ultimate condition of FRP-confined concrete is not significantly affected by the age of concrete. However, in the long-term, slight decreases in the compressive strength and the ultimate axial strain are observed with an increase in concrete age. [ABSTRACT FROM AUTHOR]

This paper discusses an affordable and effective lateral confinement technique to enhance concrete’s compressive strength and ductility – the steel strapping tensioning technique (SSTT). Considerable studies have been done on the characteristics of SSTT-confined concrete under uniaxial monotonic compression loading, but none has addressed its uniaxial cyclic response. In this paper, 21 high-strength concrete specimens having diameter of 150 mm and height of 300 mm had been cast, laterally pre-tensioned with steel straps in different confining ratios, and tested to failure under uniaxial cyclic and monotonic compression loadings. Results indicated that the basic hypothesis of envelope curve is valid for SSTT-confined high-strength concrete specimens for uniaxial monotonic and cyclic loadings. The development of plastic strain is independent of the confining ratio when the envelope unloading strain exceeds 0.0025. Moreover, SSTT-confinement has the lowest plastic strain compared to several related existing plastic strain models. The stress deterioration ratio is independent of confining ratio and loading patterns. Lastly, the concept which neglects the effect of loading history on the permanent axial strain of the unloading and reloading paths of concrete is invalid because repeated unloading/reloading cycles have demonstrated a cumulative effect on the permanent strain and stress deterioration. [ABSTRACT FROM AUTHOR]

• Experimental investigations of shear behavior of inclined cross screws. • Testing various screw arrangements of the screw connections. • Deriving models for predicting strength and stiffness of inclined cross screws. The mechanical performance of shear connectors has an important effect on the load bearing capacity and the bending stiffness of timer-concrete composite (TCC) beams. Most studies reported so far have focused on the shear behavior of the single inclined screw working only under shear–tension stress. However, there are few researches on the shear behavior of inclined cross screws. In this paper, a total of thirty-six push-out tests were conducted to investigate the shear behavior of the inclined cross lag screws for glulam-concrete composite beams. Based on the push-out test results, the influences of concrete strength, screw diameter, penetration length of screw into timber, screw inclination angle and screw arrangement with respect to the shear plane on the shear bearing capacity and slip modulus were investigated in detail. Two types of failure mechanisms of inclined cross lag screws were observed from the push-out tests: cone expulsion of concrete ahead of the shear-compression loaded screw and the shear-tensile loaded screw withdrawn from timber. When the inclined screws worked only under shear-compression load, the screw connectors were in the worst stress state. Since the direction of interface shear force in timber-concrete composite beams changed constantly under seismic load, the optimal screw arrangement was the crossed screws working simultaneously under shear-compression and shear–tension load. In addition, the analytical models were proposed to predict the shear bearing capacity and slip modulus of the inclined cross screws, and the calculated results were in good agreement with the test results. [ABSTRACT FROM AUTHOR]

• The shear-compression failure modes confined UHPC were explained, and the effects of parameters on the axial stress–strain curves of confined UHPC were analyzed. • The prediction models for the axial stress–strain curves of confined UHPC were established. • The prediction models for the peak stress and peak strain curves of confined UHPC were developed. The axial stress–strain models of confined ultra-high performance concrete (UHPC) were important key inputs for analytical programs to predict the full-range loading deformation of confined UHPC. The concrete columns confined with stirrups under axial compression tended to be a failure in shear-compression failure. However, the existing models for evaluating the axial stress–strain models of confined UHPC did not consider the shear-compression failure. In this paper, an experiment on the axial stress–strain behaviour of confined UHPC was presented. The specimens consisted of 75 UHPC with compressive strength up to 155.45 MPa were confined by spiral stirrups. According to test results, a theoretical model for axial stress–strain curves of confined UHPC by considering the shear-compression mechanism of UHPC was developed. In the proposed models, the real lateral stress of stirrups was adopted to calculate the lateral confinement of stirrups, rather than assumed that the stirrups reached the yield strength. In addition, the effects of dowel action of stirrups and longitudinal reinforcement were considered. Furthermore, the prediction models for the compression behaviour indicators of confined UHPC included peak stress, peak strain, initial tangent modulus, residual stress, and residual strain were proposed. By comparing with existing models, the proposed analytical models of axial stress–strain curves of confined UHPC had high accuracy and high stability. [ABSTRACT FROM AUTHOR]

• Prediction equations for compressive stress/ elastic modulus and S-N curve were established. • The macro-microscopic morphology of PU grouting materials was characterized. • Mechanical degradation and failure mechanisms under static-dynamic conditions were analyzed. • Density and size effects were due to the combined effects of relative skin thickness, cell structure, and matrix content. Foamed polyurethane (PU) grouting materials are widely used for road trenchless rehabilitation. However, the density and size effects on their mechanical properties and the microscopic mechanisms under quasi-static and cyclic compression are still unclear. In this paper, the degradation mechanisms of PU grouting materials with different densities and specimen sizes were studied by quasi-static compression, cyclic compression, and macro–micro morphological characterization. As the specimen diameter increased, the compressive strength decreased and the elastic modulus increased. As the diameter-to-height ratio increased, the compressive strength increased and the elastic modulus decreased. The compressive strength/elastic modulus increased as a power function with density. When the stress levels were above the fatigue threshold, cyclic failure occurred. When the stress level reached the fatigue threshold, the loading rate, elastic strain, and loss factor were concentrated at 0.25 s−1, 0.013, and 0.023, respectively. The initial dynamic stiffness increased by 55.94 % compared to the quasi-static stiffness. The fatigue threshold tended to decrease with the increasing specimen diameter and diameter-to-height ratio. For specimens with D20H20, the density effect on the fatigue threshold was not significant. For specimens with D40H80 and D40H40, the fatigue threshold decreased with increasing density. Density and size effects were due to the combined effects of relative skin thickness, cell structure, and matrix content. Moreover, the S-N curve was established. [ABSTRACT FROM AUTHOR]

• This paper is focused on the true triaxial mechanical behavior of steel fiber recycled aggregate concrete. • True triaxial experiments were conducted considering three variables - the volume fraction of steel fiber V f , the replacement ratio of recycled coarse aggregate RAR , and the stress ratio α. • Failure modes, complete stress-strain curves and the Bresler-Pister failure criterion under true triaxial compression are well addressed. This paper presents an experimental research on the triaxial behavior of 270 steel fiber recycled aggregate concrete (SFRAC) specimens under true triaxial compression (σ 1 ≠ σ 2 ≠ σ 3). By using a servo-hydraulic closed loop testing system, triaxial loading experiments were conducted considering three variables - the volume fraction of steel fiber (V f), the replacement ratio of recycled coarse aggregate (RAR), and the stress ratio (α). The influences of these parameters on the failure modes, the stress–strain curves and the peak triaxial strength are analyzed. The experimental results indicated: (i) the stress ratio had the most significant effect on the failure mode of SFRAC specimens, where four modes were observed; (ii) the peak triaxial strength of specimens was sensitive to V f , and a value between 0.6% and 1.2% was found to be optimum; (iii) the minimum stress ratio σ 1 / σ 3 and the second stress ratio σ 2 / σ 3 exhibited opposite effects on the peak triaxial strength of specimens, while RAR showed the least effect. Finally, a three-parameter failure criterion for SFRAC under true triaxial compression was proposed. The experimental results will provide SFRAC triaxial mechanical behavior for future engineering design and applications. [ABSTRACT FROM AUTHOR]

Abstract: The present paper deals with the in situ mechanical characterization of 2000years old adobe bricks from the archaeological site of Nisa Partica in Turkmenistan. For this purpose, a portable instrument was designed to perform compression, three point bending, and ‘Brazilian’ tests. This simple instrument allowed in situ measurement of compressive and tensile strengths of the material, providing stress–strain curves that have been used to calibrate simple constitutive relationships. Finally, bricks were mineralogically and petrographically characterized. The paper shows that with simple tools it is possible to measure the main mechanical properties of adobe bricks even in critical in situ conditions. [Copyright &y& Elsevier]

• Review of numerical models for concrete fatigue under compressive loading. • Distinction of three classes of fatigue damage hypothesis for concrete compression. • Stress driven formulation of damage-plasticity model for fatigue simulation. • Comparison of selected modeling approaches to fatigue considering the sequence effect. In this paper an evaluation of existing numerical models for concrete fatigue behavior subjected to compressive loading is presented. The brief review of available modeling approaches is accompanied with their classification based on the postulated fatigue damage hypothesis and on the modeling scale at which the damage is introduced. Based on the review, three numerical models for concrete fatigue that are considered to be relevant for the simulation of high cycle fatigue are selected as representatives of different fatigue modeling hypotheses and evaluated in view of heir ability to reproduce several aspects of concrete fatigue behavior. The strengths and weaknesses of the studied numerical models are illustrated and discussed. Each model is presented by explaining its calibration procedure and showing its ability to reproduce the Wöhler curves, fatigue creep curves, energy dissipation, effect of loading sequence and computational efficiency. The discussion of the models includes also conclusions and suggestions for possible improvements of approaches to high cycle fatigue modeling. [ABSTRACT FROM AUTHOR]

• Large-scale phased cyclic loading of asphaltic railway tracks. • Investigation of asphalt railroad performance at a subgrade transition zone. • Asphaltic track shown to outperform ballast track in terms of settlement and subgrade pressure reduction. The use of structural asphalt layers inside ballasted railway tracks is attractive because it can increase track bending stiffness. Therefore, for the first time, this paper investigates the long-term settlement characteristics of asphaltic track in the presence of a subgrade stiffness transition zone. Phased load cyclic compression laboratory tests are performed on a large-scale hybrid asphalt-ballast track, supported by subgrade with varying stiffness. It is found that an asphaltic layer acts as a bridge to shield the subgrade from high stresses. It is also found that the asphalt reduces track settlement, and is particularly effective when subgrade stiffness is low. [ABSTRACT FROM AUTHOR]

Highlights • A multiscale model is adopted to compute the buckling capacity of CLT walls. • The homogenization is sequentially carried out from nano to structural scale. • Experimental tests are conducted to determine buckling critical load of CLT walls. • The influence of openings on CLT wall buckling capacity is investigated. Abstract The recent trend towards the use of Cross-Laminated Timber (CLT) as a novel construction material in mid- and high-rise buildings has steered the research efforts into this subject over the last few years. Despite the considerable progress made on the structural response of CLT, there are still several unresolved issues related to the analysis and design of CLT. This is of great interest for engineers and designers working on the mass timber construction sector. In particular, the buckling behaviour of CLT walls is a problem not fully understood to date. Therefore, in this paper we investigate the buckling capacity of CLT subject to compressive loads. In order to capture the heterogeneities present in wood, a multi-scale modelling strategy is adopted. To improve the numerical predictions, an optimisation-based parameter identification procedure is performed to calibrate the micromechanical parameters of wood. The numerical predictions are compared with experimental results and are validated successfully. The numerical model is then used to study the influence of the number of layers and wall openings on the buckling capacity of CLT walls. [ABSTRACT FROM AUTHOR]

Highlights • Discussing the limitations of Werkmeister's criteria and the simplification adopted in European Standard. • Defining a "representative cycle number" to distinguish the post-compaction and second cyclic compression periods. • Proposing more reasonable and versatile new criteria to characterize the shakedown ranges of granular materials. Abstract The Werkmeister's criteria are widely utilized for characterizing the permanent axial strain behaviour of granular materials. These criteria are based on shakedown theory and are adopted in the European Standards. In this paper, the limitations of Werkmeister's criteria and the simplification adopted in European Standard are discussed. To overcome these shortcomings, new criteria on characterizing the shakedown ranges of granular materials are proposed. The mathematical expression and physical meanings of the proposed criteria are presented and discussed in detail. It is noteworthy mentioning that, based on the new criteria, the characterizing of shakedown range only assesses the whole development trend of permanent axial strain occurred during the secondary cyclic compression period. Firstly, the performances of the new criteria and Werkmeister's criteria are compared using the test data from existing literature. It can be concluded that the new criteria are capable of giving quite satisfactory prediction. Furthermore, in this study, several cyclic triaxial tests with step-wisely increasing cyclic deviatoric stress were conducted to verify the new criteria. The test results show a transitional range, which indicates the onset of the disruption of external loading to the original stable structure of granular materials. [ABSTRACT FROM AUTHOR]

Highlights • P-M interaction behavior of severely damaged and repaired RC columns is studied. • The columns were damaged under different compression to bending load ratios. • Efficiency of hybrid FRP repair using NSM laminates and external confinement is studied. • P-M interaction curves were developed from test results and analytical calculations. • Hybrid FRP technique effectively restored the original capacity of damaged RC columns. Abstract This paper investigates the axial compression and bending interaction behavior of reinforced concrete (RC) columns repaired and strengthened with different FRP (Fiber Reinforced Polymer) techniques after severe damage. The columns were initially damaged under different axial compression to bending load ratios. The loads were applied at different eccentricity (e) to depth (h) ratios to have (i) pure compression (e/h = 0), (ii) eccentric compression (e/h = 0.63) and (iii) pure flexure (e/h = ∞). After initial damage, the specimens underwent severe concrete core degradation with the main steel reinforcement reaching its yield strain. Later, the specimens were repaired using high strength cement grout (HSCG) and further strengthened using (i) near surface mounting (NSM) of carbon FRP (CFRP) laminates and (ii) hybrid FRP technique with a combination of NSM laminates and external bonded (EB) fabrics. After that, the columns were loaded again until failure. An axial compression (P) – bending moment (M) interaction diagram was developed experimentally for the severely damaged columns. Also, the interaction curves were developed analytically using strain compatibility procedure with the modified constitutive models. Experimental results reveal that the specimens repaired and strengthened using hybrid FRP technique can effectively restore the original capacity under different eccentric load levels. The analytical predictions showed a close match when compared to the experimental observations. [ABSTRACT FROM AUTHOR]

Highlights • Kaiser and Felicity effect are demonstrated in masonry under compression. • AE Load-Calm ratios indicate progressive damage in masonry for the first time. • AE-based damage limits are validated with full-field deformation measurements. Abstract Determining the mechanical behaviour of masonry under compression remains challenging, as masonry is anisotropic and heterogeneous in nature. This paper focuses on an Acoustic Emission (AE)-based method to quantify the progressive damage in masonry under cyclic compressive loads. In this study, eight masonry walls were built in combination with four different mortar types. Results indicated that critical limits applied for AE-based damage quantification in concrete were too conservative for masonry under axial loading. However, it is the first time that these AE indices are investigated in masonry. Nevertheless, a good agreement was found between the progressive damage quantification with AE-based methods and through deformation analysis from Digital Image Correlation (DIC) and Linear Variable Differential Transformers (LVDTs). [ABSTRACT FROM AUTHOR]

Highlights • Compression tests on two different standard masonry specimens yielded similar results. • Tests provided new data on clay brick and lime mortar masonry under cyclic loading. • Cyclic tests allowed characterizing the stiffness degradation for increasing strains. • Available analytical and empirical models fit the experimental results satisfactorily. Abstract This research presents an experimental programme on the mechanical characterization of masonry under monotonic and cyclic uniaxial compression. Two different types of standard specimens, running bond walls and stack bond prisms, were built using handmade clay bricks and hydraulic lime mortar. The experimental results are compared and discussed in terms of strength, stiffness and deformability. It was observed that the two specimen types provided very similar results on both strength and stiffness. Cyclic loading tests carried out on a set of samples provided new experimental evidence on the stiffness degradation, loss of load carrying capacity for increasing irreversible compressive strains and energy dissipation. The paper presents eventually a thorough discussion about the comparison between the obtained experimental results with available predictive models for strength, stiffness and fracture energy of masonry under monotonic and cyclic compression loading. [ABSTRACT FROM AUTHOR]

Highlights • The behaviour of rammed earth was investigated under compression and shear loading. • The repair effectiveness of clay- and lime-based grouts was compared. • The clay- and lime-based grouts present similar repair performance. • The injection repair was unable to recover the interlocking of the coarse particles. • Sonic tests were not sufficiently sensitive to evaluate the repair effectiveness of injection. Abstract Earth constructions constitute an important part of the built heritage and are spread worldwide. Rammed earth is among the most used earth construction techniques, though it exhibits a high seismic vulnerability. Nevertheless, the structural behaviour of rammed earth structures is still insufficiently comprehended. Thus, the preservation of this built heritage requires exhaustive characterisation of its mechanical and structural behaviours, as well as the development and validation of adequate intervention solutions. In this context, this paper presents an experimental program aimed at evaluating the effectiveness of grout injection to repair cracks and at further characterising the in-plane shear behaviour of rammed earth walls. The experimental program included the testing of rammed earth wallets under diagonal compression, which were subsequently repaired with injection of a clay-based or a hydraulic lime-based grout, and retested. Furthermore, sonic tests were conducted on the wallets before the destructive tests. The obtained results allowed to highlight that both grouts led to similar repairing performances, though the interlocking contribution promoted by the coarse particles of the rammed earth to the shear behaviour was found to be irrecoverable. [ABSTRACT FROM AUTHOR]

Highlights • A comprehensive review of strain-rate sensitivity of SFRC is conducted. • Existing DIF formulas for SFRC in both tension and compression are evaluated. • A unified DIF model is proposed with the consideration of various effects. • The new model is employed in the numerical analysis of SFRC plates under impact. Abstract The use of steel fibre reinforced concrete (SFRC) in protective structures against extreme loading conditions (e.g. high-velocity impact and blast) has gained worldwide interest in recent years, which is attributed to its advantages of higher tensile strength and better energy absorption capability compared to normal concrete. This paper presents a comprehensive review of the dynamic increase factors (DIF) for both compressive strength and tensile strength of SFRC reported in the literature. In particular, the influences of matrix strength, fibre shape and fibre volume fraction on the rate sensitivity of SFRC are investigated. A versatile DIF formula is then proposed based on the reported data for describing the dynamic material strength of SFRC, which considers the effects of various parameters in one unified formulation for the first time. To demonstrate the effectiveness and feasibility of the proposed DIF formula, a 3D finite element model is established, and the proposed DIF formula is employed to simulate the dynamic responses of SFRC plates under impact. The developed finite element model is validated by comparing the predicted results with experimental data. [ABSTRACT FROM AUTHOR]

Highlights • The critical stress level of AAS under compressive load is in the range of 80%–90%. • Water glass activated slag are compacted considerably by compressive load. • There is no significant compacting effect in compression of NaOH activated slag. • Closure of pores takes predominant in water glass activated slag under compression. Abstract It would make sense to detect the rules and mechanisms of degradation and mass transport of alkali-activated slag concrete (AASC) in actual service environment. In this paper, hydration products characterization implies higher crystallinity degree of C-S-H activated by NaOH and higher polymerization of the one activated by water glass. During compressive loading, Poisson's ratio of AASC keeps constant at the stress level ranging from 0 to 0.5, with an uprush takes place at stress level of 0.8–0.9. For slag concrete activated by NaOH, volume increases with stress level, while the volume of slag concrete activated by water glass decreases first and then increase with stress level. The apparent chloride diffusion coefficient of specimens activated by NaOH is 4–7 times smaller than the ones activated by water glass, which is verified by the results that volume of pores above 10 μm of water glass activated sample is nearly 20 times more than that of NaOH activated one. Slag concrete activated by water glass is compacted considerably by compressive loading contributing to the decrease in chloride diffusivity, while no significant compacting phenomenon is observed in slag concrete activated by NaOH. However, there is no significant compacting effect on capillary absorption for both specimens activated by two activators. [ABSTRACT FROM AUTHOR]

Highlights • Unreinforced masonry (URM) under multiaxial loading examined. • In-plane and out-of-plane loading combined with precompression considered. • Three edges supported URM walls analysed and interaction curves established. • Interaction curves are affected by the type of support condition. • In-plane resistance increases with increase in precompression. • In-plane resistance sharply reduces with the increase in out-of-plane loading. Abstract Interaction curves for masonry walls supported on all four edges subject to multi-directional loading has recently been reported by the authors (Noor-E-Khuda et al., 2018). Load bearing URM walls are generally detailed with vertical control joints (which are structural end where the normal stress vanishes), and non-load bearing walls are likely to have unsupported top horizontal edge. Therefore, three sides supported URM walls are examined in this study. An explicit finite element macro model based on a layered shell element is used in the investigation. A series of interaction curves approximately resembling bilinear domain is developed to represent the response of the one vertical edge unsupported URM walls under multi-directional loading. The interaction curves for the top horizontal edge free walls showed a trilinear approximation. Influence of the boundary conditions and the level of out-of-plane loading to the shape of the interaction curve have been examined. It is shown that the in-plane capacity reduces rapidly beyond a critical out-of-plane load level; therefore, disregarding the multi-directional loading interaction could be unsafe. A simplified non-dimensional expression proposed by the authors for the interaction curves of four sides supported walls is extended for the three sides supported walls in this paper. [ABSTRACT FROM AUTHOR]

• Low temperature improves tensile and compressive strengths of GFRP bar. • Reinforcements can further improve compressive behaviours of RCFFT. • Low temperature greatly increases the ultimate compressive strength of RCFFTs. • Proposed formulae predict well low-temperature compression behaviours of RCFFT. A series of low-temperature tests on axial compression behaviours of 18 stub columns were presented in this paper, which included eight unconfined reinforced concrete columns (URCC) and ten reinforced concrete-filled GFRP tubes (RCFFTs). Regarding the compression tests on RCFFTs, axial compression load was applied to both inside confined reinforced concrete column (CRCC) and GFRP tube. The studied parameters of this paper included low temperatures of 20, −30, −60, and −80 ℃, diameter-to-thickness ratios of 20, 21, 30, 40, and 50, reinforcement ratio of 2.18% and 3.84%, and reinforcement type of steel reinforcement and GFRP bar. The failure modes, axial compression load–strain curves, and compressive stress–strain curves of RCFFTs at low temperatures have been revealed. Meanwhile, the influences of different parameters on the ultimate compression resistance, ultimate compression strength, stiffness, ultimate axial strain, and ultimate hoop rupture strain of RCFFTs at low temperatures were detailly discussed. These results indicated that low temperature generally improved the axial compression behaviours of RCFFTs. According to the test results, prediction formulae have been proposed to determine the ultimate compression resistance and ultimate axial strain of RCFFTs reasonably but conservatively at low temperatures, which considered the influence of longitudinal reinforcements and ties. [ABSTRACT FROM AUTHOR]

• Developed a FEA model for six-phase MRCAC. • Studied the influence of MRCA replacement rate and residual mortar thickness on compressive performance of recycled concrete. • Clarified coverage and adhesion amount of old cement mortar by statistical methods and analysis results. Based on the typical morphology of recycled coarse aggregate in reality and the ontological relationship of the existing recycled aggregate concrete (RAC) mesoscopic constituent materials, a finite element analysis model of recycled coarse aggregate that can take into account the factors of the amount and location of attachment of the residual mortar was developed to establish the Modeled Recycled Coarse Aggregate Concrete (MRCAC). Combined with the mesoscopic mechanical properties of MRCAC, a plastic damage intrinsic model was used in the numerical analysis of MRCAC under uniaxial compressive loading to study the damage characteristics and stress–strain relationships of MRCAC. In this paper, the Modeled Recycled Coarse Aggregate (MRCA) is established in the ABAQUS numerical analysis software by self-compiled Python script, and the uniaxial compression simulation of MRCAC is carried out. Compared with the existing idealized model recycled concrete and other forms of digital recycled concrete model, The results show that, on the premise of meeting the general law of existing research results, the development of cracks in MRCAC under load is directly related to the shape of residual mortar wrapping. The strength of MRCAC is minimally influenced by residual mortar adhesion amount; however, the coverage of residual mortar has a significant impact on its strength. The arrangement of MRCA may also play a role in the stress–strain relationship of MRCAC. Additionally, it should be noted that residual mortar adhesion amount and coverage are distinct concepts that affect the strength and strain of MRCAC independently. These findings highlight the need to differentiate between these two factors in further research. [ABSTRACT FROM AUTHOR]

Highlights • A region where the actual density is lower than the control density is presented. • Rubber-sand mixtures are categorized into low, medium and high compressible materials. • A good linear relationship is proposed between B r and RV. • Three force transmission ways are proposed to interpret the force micro-mechanics. Abstract The waste materials of scrap tires are becoming more prevalent in geotechnical engineering. While adding scrap tires particles into sand particles as a filling material can reduce the stockpiles of scrap tires and minimize the environmental pollution. Therefore, investigating the effect of scrap tires-sand particle mixtures on compression properties is in urgent demand. In this study, the effect of the rubber particle content and vertical stress on the actual density, void ratio, coefficient of compressibility, modulus of compression, rebound and grain breakage is investigated systematically by a serious of laboratory tests. The test results reveal that when rubber content RV exceeds 50% (or less than 50%), the three-stage change trend of void ratio is proposed: accelerating reduction, deceleration stage and slow reduction (or accelerating reduction, slow reduction and stable stage). A region where the actual density is lower than the control density is given under different vertical stress and RV. In accordance with the coefficient of compressibility, the rubber-sand mixtures used in this paper is categorized into three groups: (1) Low compressive materials (RV = 0–10%); (2) Medium compressive materials (RV = 20–30%); (3) High compressible materials (RV > 50%). The addition of rubber particles to sand particles generates a significant reduction in modulus of compression, and the modulus of compression at the same rage of vertical stress decays exponentially with increasing RV. In addition, the plastic strain of specimens is greater than the elastic strain, and the gap between elastic strain and plastic strain is increasing with the increase of RV. A good linear relationship is derived between grain breakage B r and RV. Obviously, the particle breakage decreases with the increase of RV at different vertical stress levels. Based on the analysis of SEM, three force transmission ways with different RV are proposed to describe the compression micro-mechanic of rubber-sand particle mixtures. [ABSTRACT FROM AUTHOR]

Highlights • This study examines the cyclic behavior of superelastic SMA bars with BRDs under tension–compression cycles. • The material properties of typical interest in seismic applications are evaluated. • The reversed compression loading benefitted SMA behavior in the cyclic tension–compression tests. Abstract Shape memory alloys (SMAs) show great potential in seismic applications because of their appealing superelastic feature and good energy dissipation capacity. The tensile behavior of SMA wires and bars has been extensively studied over the past decades. However, little attention has been paid to their compressive properties under cyclic loading. Thus, this paper presents a systematic experimental study on the cyclic behavior of superelastic SMA bars with buckling-restrained devices (BRDs) when subjected to tension–compression cycles. The detailed design of BRD is described first. The material properties such as “yield-like” strength, peak strength, self-centering capability, and energy dissipation of typical interest in seismic applications are evaluated with varying strain amplitudes, strain rates, and loading protocols. Test results show that satisfactory and stable flag-shaped hysteretic loops without any strength degradation are obtained in multiple loading cycles under cyclic tension–compression loading. Moreover, the SMA bars exhibit remarkable self-centering capability that is nearly independent of strain rate and loading protocol. [ABSTRACT FROM AUTHOR]

The properties relating to the compressive stress-strain curve of self-compacting steel fiber reinforced concrete (SFRC) were experimentally studied in this paper. Type of steel fiber, volume fraction of steel fiber and water-binder ratio were considered as the influence parameters. Test results showed that regardless of fiber type, self-compacting SFRC had greater compression toughness due to the better sustainability of descending portion of stress-strain curve, and the compression toughness ratio, axial compressive strength, peak-strain of self-compacting SFRC increased with the volume fraction of steel fiber. The influence of water-binder ratio was reflected by the strength of self-compacting SFRC. Based on the experimental data, the predictive models are proposed for the prediction of compressive stress-strain relationship of self-compacting SFRC. [ABSTRACT FROM AUTHOR]

Recent years have seen valuable research work on using glass-fiber-reinforced-polymer (GFRP) bars in reinforced-concrete (RC) members under compression. Nonetheless, lap splicing of GFRP bars under compression has not yet been explored with due consideration of its components. To address this knowledge gap, this paper comparatively demonstrates the results of an experimental investigation pertaining to the effect of splice length on the compression lap splicing of GFRP bars in concrete columns. The experiment comprised 11 large-scale circular columns measuring 300 mm in diameter and 1600 mm in height: seven specimens reinforced with GFRP bars, three specimens with steel bars for comparison purposes, and one specimen without reinforcement (plain concrete). All columns were tested under a monotonically increasing concentric load. The test variables included the reinforcement type (GFRP versus steel) and splice length. The results were compared in terms of the stress–strain curves, ultimate loading, displacement capacity, and splice strength. The test results indicate that the required compression splice length for GFRP bars is less than that required for steel. As the strength of a compression splice consists of end-bearing and bond components, the contribution of each part was scrutinized in detail using measured strain values. The required splice length for GFRP bars was considerably based on the end-bearing component. Based on the experimental results, a length of 8 d b can reliably be considered as the required splice length for No. 5 GFRP bars in compression. [ABSTRACT FROM AUTHOR]

This paper presents the test results of an experimental program to investigate the structural performance of short and slender concrete-filled fiber-reinforced polymer (FRP)-tubes (CFFTs) columns under pure axial compression load. The test parameters include: transverse reinforcement type (steel spirals versus glass-FRP (GFRP-tube), type of longitudinal reinforcement (steel and carbon-FRP (CFRP) bars), GFRP tube thickness, and slenderness ratio. Comparisons between the experimental test results and the theoretical design equations are performed in terms of ultimate load carrying capacity. The design equation is modified to accurately predict the ultimate load capacities of CFFT columns reinforced with FRP bars. Furthermore, the experimental results showed that the axial compressive strength of CFRP-reinforced CFFT columns was reduced by 22% with increasing the slenderness ratio from 8 to 20. In general, the use of the FRP tube induces a confinement effect for concrete columns which enhances the strength and ductility of such column’s section. This enhancement resulted in a slender section which increased the possibility of buckling instability of the CFFT columns. Thus, a theoretical model was conducted to develop a simplified formula for critical slenderness limit of FRP-reinforced CFFT columns to control the buckling instability mode of failure. Results indicated that the slenderness limit of 14 was suggested as a safe value for the design purposes. A parametric study was conducted which showed the significant effect of the concrete compressive strength and hoop stiffness of FRP tube on the critical slenderness ratio of FRP-reinforced CFFT columns. [ABSTRACT FROM AUTHOR]

This paper presented an experimental study on the failure mode, ultimate bearing capacity and ductility capacity of PVC-CFRP confined reinforced concrete columns subject to low cyclic loading. Several parameters, such as the axial compression ratio, shear span ratio, and hoop spacing of CFRP strips were considered in the analysis. The results showed that all columns at low axial compression ratio failed by bending. The long and short columns with large hoop spacing at high axial compression ratio failed by flexural shear while the short columns with small hoop spacing at high axial compression ratio failed by shear. The ultimate bearing capacity increased as the axial compression ratio increased or the shear span ratio decreased while the ultimate bearing capacity decreased as the hoop spacing of CFRP strips increased. The ultimate strains located at the bottom of the column increased as the axial compression ratio increased while the ultimate strains decreased as the shear span ratio increased. The confining effect of CFRP strips increased gradually as the hoop spacing of CFRP strips decreased. The ductility capacity decreases as the axial compression ratio or the shear span ratio increased while the ductility capacity increases as the hoop spacing of CFRP strips increased. [ABSTRACT FROM AUTHOR]

The properties of axially loaded sea sand recycled aggregate concrete (SSRAC) were experimentally and theoretically investigated in this paper. The main parameters in the test are the sea sand chloride ions (Cl − ) content and the recycled coarse aggregate (RCA) replacement percentage. The influences of sea sand Cl − and RCA content on the compressive strength, stress-strain relation and failure pattern of SSRAC were studied. Test results showed that both the strength and deformation of specimen changed with the variation of sea sand Cl − content and RCA replacement percentage. The compressive strength of SSRAC was higher than that of ordinary concrete. The elastic modulus increased, while the peak strain decreased due to the effect of sea sand. It was also indicated that the influence of recycled coarse aggregate replacement percentage on the properties of SSRAC decreased with increasing sea sand Cl − content. The Poisson's ratio and stress-strain curve of SSRAC were similar to those of ordinary concrete. Finally, a numerical expression for the stress-strain curves of SSRAC under axial loading was presented, which could be used in the theoretical and practical studies. [ABSTRACT FROM AUTHOR]

In this paper, conventional cyclic tension-compression tests and dynamic measurements have been applied to three cylindrical specimens of asphalt mixes. The results of the two tests have been compared. For the tension-compression tests, the complex modulus was obtained from the measurements of the axial stress and axial strain. For the dynamic testing, an instrumented impact hammer and an accelerometer have been used to obtain the frequency response functions of the specimens at different temperatures. The dynamic complex modulus was then back calculated by optimizing finite element calculated frequency response functions to match the measured frequency response functions. The 2S2P1D linear viscoelastic model was used to estimate master curves of the complex modulus for the two test methods. The two tests give similar results. However, the dynamic measurements give a higher value of the norm of the complex modulus and a lower value of the phase angle compared to the tension–compression results. This result is probably explained by the nonlinearity of asphalt mixes as dynamic tests are performed at a much smaller strain level than the tension-compression tests. [ABSTRACT FROM AUTHOR]

High performance cementitious composites have made possible the manufacturing of thin cementitious shell structures which are prone to buckling. Perhaps the most comprehensive design procedure for such shells is provided by the design recommendations issued by the International Association for Shells and Spatial Structures (IASS) which, however, are inconsistent with the modern European design framework. The scope of this paper is to contribute to the development of a design methodology similar to the one recommended by Eurocode 3 part 1–6, which is based on a capacity curve that represents all the possible failure states. In this respect, the capacity curve of an axially compressed cylinder is produced by geometrically and materially nonlinear analyses for different fabrication quality classes, which are in the sequel approximated by parametric capacity curves based on parameters determined following the concept of Eurocode 3. [ABSTRACT FROM AUTHOR]

This paper presents the capacity and structural behaviour of hardwood veneer-based circular hollow sections (CHS) tested in bending, shear and compression. The sections were manufactured from early to mid-rotation (juvenile) Gympie messmate ( Eucalyptus cloeziana ) plantation thinned logs. In total twenty-one 167 mm Outside Diameter (OD) × 1.2 m long CHS were manufactured in seven sets of three nominally identical sections. Two different wall thicknesses were investigated to produce nine compact and twelve more slender cross-sections. The sections were also manufactured in three different structural grades. A sudden failure mode was observed in the compression zone of the slender sections tested in bending. In compression, the compact sections showed a ductile behaviour, while the slender sections showed a more brittle behaviour, with the sections bursting into longitudinal strips. While a relationship was observed between the bending and compressive capacities, and the structural grade, no such relationship was noticed for the shear capacity. Comparison to steel and concrete sections of similar outside diameter proved that the timber sections are the most efficient in terms of bending and compressive capacity to linear weight ratio. The timber sections fall behind their steel and concrete counterparts in terms of shear efficiency, however they still have enough shear capacity for representative structural applications. [ABSTRACT FROM AUTHOR]

Composites made of bio-aggregate particles and lime based binder can be used as a low embodied energy alternative to traditional walling systems and can provide several performance advantages. As the ratio and nature of constituents used in bio-aggregate composites will have bearing on the properties, it is necessary for these to be capable of being optimised to meet specific design requirements. In addition, as these materials are known to be anisotropic, it is required that any impact of constituents is assessed with respect to orientation. In this paper, the influence of the binder to aggregate ratio and aggregate particle size distribution on the compressive strength, flexural strength and thermal conductivity of hemp-lime composites in two directions of loading have been assessed. A newly developed image analysis method was also employed to study the topology of the internal structure. The results show that the material is anisotropic in both behaviour and internal structure and that both binder/aggregate ratio and aggregate particle size distribution affect composite properties. In the case of binder to aggregate ratio, the impact is shown to be directionally dependent and indicative of differing governing factors controlling the failure mode in opposing loading directions. [ABSTRACT FROM AUTHOR]

The demand for building materials and techniques with reduced environmental impact has been increasing in the last few years. Thus, efforts have been taken to include alternative raw materials with reduced extraction impacts and low embodied energy in their production, namely natural materials and industrial by-products with low or no processing needs. Nevertheless, the lack of technical knowledge about this type of materials leads to issues related with its safety, quality and durability. The work presented in this paper intends to be a contribution on this topic. Thus, an experimental program was carried out to evaluate the mechanical performance of interlocking compressed earth blocks (ICEBs) stabilised with activated alkali fly ash. The main objective of the experimental program was to assess the possibility of further exploiting the mechanical performance of the original dry-stack masonry system, by means of the use of mortared joints. Two alkali-activated binder based earth mortars were used for this purpose, and the results showed that a substantial mechanical improvement is obtained in terms of compression and shear behaviour of the respective masonry. [ABSTRACT FROM AUTHOR]