Publications

BEHAVIORS OF NEW GENERATION OF FRP BRIDGE DECK WITH OUTSIDE FILAMENT-WOUND REINFORCEMENT

OFR (outside filament-wound reinforcement) is an effective configuration to improve the performance of FRP bridge decks. It can enhance the transverse stiffness of FRP decks and restrict the swelling and dispreading trends of the FRP components to increase the ultimate load and deformation capacity of FRP decks. The new generation of FRP bridge deck with OFR, named HD deck, was designed. Four HD decks were manufactured and tested in static and fatigue loads. The results show that the HD decks satisfy the demands of China Bridge Design Codes. The efficiency of OFR was verified. Based on the results, the reinforcement mechanism was analyzed.

Buckling behavior analysis of prestressed CFRP-reinforced steel columns via FEM and ANN

Prestressed (PS) carbon fiber reinforced polymer (CFRP)-reinforced steel columns are novel multiparameter systems exhibiting complex nonlinear buckling behavior. In this study, this behavior was investigated with the finite element method (FEM) and an artificial neural network (ANN). First, FEM models of the columns under axial and eccentric compression were built. The numerical and experimental force–displacement curves, failure modes, and CFRP stress–displacement curves were in good agreement. Moreover, the influencing rules of 9 key parameters (i.e., CFRP initial prestressing force, supporting length, eccentricity, steel yield strength, slenderness, CFRP elastic modulus, initial imperfection and boundary conditions) on the buckling capacity and reinforcing efficiency of the reinforced columns were determined. Afterward, 312 datasets from the validated finite element model covering 8 input parameters were generated via the ANSYS parametric design language (APDL). Finally, as ANNs can manage highly complex and computationally intensive nonlinear problems, a practical ANN tool was developed to predict the buckling capacity of PS CFRP-reinforced steel columns.

Lactate Metabolism in the Intervertebral Disc: Mechanistic Insights and Pathological Implications

Intervertebral disc (IVD), the largest avascular structure in the human body, contains nucleus pulposus (NP) cells that generate an abundant quantity of lactate from anaerobic glycolysis as an adaptation to hypoxia. Historically, IVD lactate was viewed as a metabolic toxic byproduct necessitating clearance to maintain IVD health. This is because accumulation of lactic acid, the protonated form of lactate, acidifies the IVD microenvironment, impairs cell viability, disrupts extracellular matrix integrity, and promotes degeneration. However, recent studies discovered that lactate serves as an important IVD biofuel in a process known as lactate-dependent metabolic symbiosis in which lactate produced by NP is shuttled into cells of the neighboring annulus fibrosus (AF), and cartilage endplate (CEP) to be metabolized via the tricarboxylic acid cycle and oxidative phosphorylation to generate ATP and amino acids to maintain IVD matrix homeostasis. Additionally, lactate is found to function as a signaling molecule and epigenetic regulator in IVD: it regulates transcription via histone lactylation that modulates ferroptosis and other cell fate decisions. Lactate also modulates senescence, apoptosis, and inflammatory responses through pathways such as Phosphatidylinositol 3-kinase/Protein kinase B (PI3K/Akt) in IVD and other organs. This review synthesizes current knowledge on lactate production, transport, and clearance in the IVD along with the emerging roles of lactate in IVD health and pathophysiology. The review also provides research perspectives and directions aimed at advancing our understanding of lactate biology and evaluating its potential as a therapeutic target for treating intervertebral disc degeneration.

Development and behavior of novel FRP-UHPC tubular members

In this short communication, a series of novel forms of tubular members made of fiber-reinforced polymer (FRP) grid reinforced ultra-high-performance concrete (UHPC) (referred to as “FRP-UHPC tubular members”) are developed. FRP-UHPC tubular members have excellent mechanical properties, and their excellent performances are demonstrated through three preliminary studies: i) behavior of FRP-UHPC tubular beams under bending; ii) behavior of FRP-UHPC tubular columns under axial compression; and iii) behavior of FRP-UHPC plates with a novel grouting sleeve connection system under bending. The experimental programs and results are briefed in the paper. The proposed FRP-UHPC tubular members are attractive in various structural applications such as pipelines, bridge box girders, permanent formwork of beams/columns, especially in marine environments (e.g., floating structures).

EXPERIMENTAL STUDY ON SEISMIC STRENGTHENING OF RC COLUMNS WITH WRAPPED CFRP SHEETS

The paper describes the testing of eight specimens under constant axial load and lateral cyclic load to investigate seismic performance of RC (reinforced concrete) columns strengthened with carbon fiber reinforced polymer (CFRP) sheet. The eight specimens included two strengthened after yielding to imitate strengthening with some damage and one strengthened under a sustained axial load to imitate strengthening under service. Studied is the ductility increment with the confinement of CFRP sheet. An effective confinement factor of CFRP was suggested based on the experimental results. The paper concludes that the seismic design method of current seismic design code can be directly used in determining seismic strengthening amount of CFRP sheet for RC column.

EXPERIMENTAL STUDY ON BUCKLING RESISTANCE TECHNIQUE OF STEEL MEMBERS STRENGTHENED USING FRP

Fiber-reinforced polymer (FRP) strengthening technique to improve buckling resistance of steel members is presented in concept and experimental demonstration. The conceptual design of this method is introduced through the preliminary experiments on three specimens. Then, another 14 specimens are tested under axially compressive loading, by which the compressive behavior and the strengthening effects are investigated considering different design parameters and configuration, including the slenderness ratio, the confinement detail, the filled materials and the end connection. The strengthening effects are analyzed by the comparison of both theoretical and test results, which show that the overall buckling failure of steel members can be prevented by FRP strengthening and the ultimate loading capacity and deformation capacity of steel members are enhanced considerably. The maximum load-bearing capacity of strengthened members is 2.86 times of the nonstrengthened ones, and the failure maintains a ductile behavior. In addition, the load-bearing capacity of the members strengthened in this way is compared with the Euler loads of the original steel member and the composite member.

Fatigue life prediction for design of steel beams strengthened with CFRP

No abstract is provided for this article.

Axial compressive performance of concrete-filled steel tube stub columns with high-strength spiral confined concrete core

Concrete-filled steel tubes (CFSTs) are widely used as hybrid columns. However, rectangular/square CFST columns are less ductile and have lower strength than circular CFST columns. To solve this problem, a novel hybrid column, namely, a high-strength steel (HSS) spiral confined CFST (HSSS-CCFST or CCFST) column, was recently proposed and investigated in this study. The spiral confinement can enhance the axial compressive performance of concrete, including load capacity, deformability and especially secondary stiffness. Monotonic axial compressive tests were conducted on 12 CCFFT columns, a steel concrete FRP concrete (SCFC) column and a CFST column. The failure modes, failure processes and mechanical behaviour of the CCFFT columns were compared with those of the SCFC and CFST columns. The relationships between the states of the columns and the materials were analysed. In addition, 3D laser scanning was performed to obtain the deformation modes. Finite element (FE) analysis of the CCFST column was conducted using commercial finite element software (Abaqus). To improve the accuracy of the simulation, the constitutive models of spirals with different strength grades were modified using the section strip method and considering the residual stress from manufacturing; the constitutive model of concrete was also improved. The results of the FE analysis agreed well with the failure modes of the components in the CCFST and the stress–strain behaviours. A parametric analysis was conducted to determine the influence of the strength and dimension parameters, and finally, the design method of the axial load capacity of the CCFST was obtained by fitting the results from the experiments and the parametric analysis.

Cyclic loading behaviors of novel RC beams with kinked rebar configuration

Lateral collapses due to earthquakes and progressive collapses due to the sudden destruction of columns are two of the most commonly encountered failure mechanisms for buildings. In a previous study, a novel kinked rebar (KB) configuration was proposed by the authors to simultaneously improve the seismic performance and the progressive collapse resistance of reinforced concrete (RC) frame structures. This configuration works because KB has a weaker initial yielding capacity and larger tensile deformability, and almost the same ultimate tensile capacity compared to ordinary steel rebar. This paper aims to provide further experimental validation and enhance the understanding of the seismic performance of RC beams with KB configurations. First, to overcome the disadvantages of the application of KB found in a previous study, the middle longitudinal bars in an RC beam were proposed to further improve the KB configuration. Second, cyclic loading tests of bare KB specimens were conducted to investigate the hysteresis equivalent stress-equivalent strain curves and failure modes of KB. Third, a cyclic loading test of RC beams with KB was performed. The test results showed that the application of KB could help relocate the plastic hinges to protect the RC column and joint, weaken the yielding loading capacity of the beams to increase the strong column-weak beam (SCWB) ratio, and increase the loading capacity of the beam again at large rotations to maintain a certain lateral load resistance at large deformation of the frame structure. An interesting “two-hinge” behavior was also found in the tests for RC beams with the KB configuration.

Experimental and numerical study of corrugated anchors for CFRP plates

Carbon fibre-reinforced polymer (CFRP) plates are promising materials for cables and prestress tendons in structural engineering for the excellent tensile performance, light in weight and anti-corrosion character. Anchoring has always been the main challenge of this high-performance material due to its anisotropy and brittleness. Corrugated anchors are high-efficiency clamping-type anchorage devices. Nevertheless, premature failure of the CFRP plates can still be observed with this type of anchors, and the anchor efficiency for the corrugated anchors needs further improvement. This paper proposes a novel configuration of corrugated anchors. Experimental tests are then carried out to investigate the influence of the pre-tensioning bolt load and adhesive layer. Consequently, numerical analysis is conducted to reveal the anchoring mechanism. The results indicate the traditional corrugated anchors lead to non-uniform stress distribution in the CFRP plate, and with the proposed configuration the anchor efficiency can be increased up to 100 %.

Epoxy Enhanced by Recycled Milled Carbon Fibres in Adhesively-Bonded CFRP for Structural Strengthening

This paper investigates the mechanical performance and electrical resistivity of a structural adhesive epoxy enhanced using milled carbon fibre (MCF) as well as the bond performance of carbon fibre reinforced polymers (CFRP) and steel adhesively bonded joints using the enhanced epoxy. The epoxy was enhanced using such MCFs with different weight ratios of 1.5%, 3% and 5%. Tensile experiments were performed on the original and enhanced epoxy specimens according to ASTM D638. More ductile process failure was found for the epoxy after modification and significant improvements of E-modulus and tensile strength were evidenced when the MCF weight ratio was larger than 1.5%. Scanning electron microscopy (SEM) revealed that the failure mechanism of short MCFs pulled out from the epoxy matrix contributed to the enhancement of the mechanical performance of the epoxy. The electrical resistivity of the epoxy with MCF weight ratio of 5% was reduced by at least four orders of magnitude compared to the original epoxy, due to the conductive network formed by MCFs. Steel/CFRP double strap joints (with either CFRP sheets or CFRP laminates) were prepared using the enhanced epoxy and then tested in tension, however no obvious increase in joint stiffness or strength was observed.

A novel rigidizable inflatable lunar habitation system: Design concept and material characterization

Constructing lunar bases is crucial as lunar missions progress towards utilization and exploitation. The challenging lunar environment, with its unique characteristics and limited resources, requires special materials, structures, and construction methods. Inflatable structures offer great potential for lunar construction due to their advantages in transportation, stowage, construction, and reliability. This paper proposes a rigidizable inflatable lunar habitat that maintains its shape even after air leakage, enhancing safety, durability, and fixability. The membrane material adapts to different requirements during transportation, construction, and service, achieved through solid-state actuation of shape memory polymer (SMP) for stiffness variation, allowing multiple moves and ground tests. This work comprises three parts: 1) system: design concept and construction processes, 2) material: design and characterization of restraint and rigidization materials, and 3) structure: numerical validation of structural properties. Finite element analysis, based on material models obtained through dynamic mechanical analysis (DMA) and tensile tests, demonstrates the effectiveness of including an SMP rigidizable layer in collapse prevention and improving dynamic performance. This paper proposes a new system, provides material design methods and requirements, and structure validation methods. Findings validate the feasibility of rigidizable inflatable lunar habitats, applicable in extreme environments, also in temporary buildings, space structures, and soft robotics.

Spatio-temporal characteristics and influencing factors of the coupling coordination of the water-energy-food nexus in Northeast China

As critical components for sustainable development, water, energy, and food resources form an interdependent system that supports regional socioeconomic progress. To alleviate resource constraints and advance sustainability in Northeast China, this study constructs a multidimensional assessment framework for the water-energy-food (WEF) nexus by integrating methodologies including composite index evaluation, coupled coordination modeling (CCDM), spatial autocorrelation analysis (ESDA), and spatiotemporal regression (GTWR). Our analytical framework systematically investigates the evolutionary patterns and driving mechanisms of inter-resource coordination. Key findings reveal a phase-fluctuating yet progressive enhancement in the composite development index, ascending from 0.41 (2003) to 0.49 (2021), with energy subsystems demonstrating predominant influence. Coupling coordination levels (0.62-0.69) currently reside in the elementary harmonization phase but are projected to attain intermediate coordination by 2028. Spatial analysis uncovers heterogeneous regulatory effects across urban centers, particularly noting population density's dual-directional impacts on system coordination among the studied 40 cities. These empirical insights culminate in evidence-based policy recommendations for optimizing WEF synergistic governance, presenting a replicable analytical paradigm for regional resource management studies.

Rigidization capacity and folding behavior of variable stiffness composite skin for inflatable lunar habitats

Experimental study on loading-induced power generation decline of component-level flexible solar cells

Flexible solar cells have a promising future to be intergraded with building systems, but the practical potential has been limited by the macroscopic mechanical properties that directly relate to power generation efficiency. In this study, the mechanical–photovoltaic properties of two commercialized flexible solar cells (amorphous silicon and dye-sensitized) were experimentally investigated under standard tensile test and cyclic test. Guided by the mechanical tests and the scanning electronic microanalysis, we found that both amorphous silicon and dye sensitized solar cells showed high strain to initiate the power generation decline in terms of mechanical properties and voltage output, while much lower strain, less than 1.0% strain, in terms of fill factor (FF). In addition, variation on geometry and reinforcing materials in the protection layer might improve stiffness but did not prevent the early initiation of FF decline. Identifying the limitation in flexible solar cells is a critical step for the development of multifunctional structural components, in which flexible solar cells are embedded into curved surfaces of buildings and bridges.

Moisture Diffusion in Multi-Layered Materials: The Role of Layer Stacking and Composition

Multi-layered materials are everywhere, from fiber-reinforced polymer composites (FRPCs) to plywood sheets to layered rocks. When in service, these materials are often exposed to long-term environmental factors, like moisture, temperature, salinity, etc. Moisture, in particular, is known to cause significant degradation of materials like polymers, often resulting in loss of material durability. Hence, it is critical to determine the total diffusion coefficient of multi-layered materials given the coefficients of individual layers. However, the relationship between a multi-layered material's total diffusion coefficient and the individual layers' diffusion coefficients is not well established. Existing parallel and series models to determine the total diffusion coefficient do not account for the order of layer stacking. In this paper, we introduce three parameters influencing the diffusion behavior of multi-layered materials: the ratio of diffusion coefficients of individual layers, the volume fraction of individual layers, and the stacking order of individual layers. Computational models are developed within a finite element method framework to conduct parametric analysis considering the proposed parameters. We propose a new model to calculate the total diffusion coefficient of multi-layered materials more accurately than current models. We verify this parametric study by performing moisture immersion experiments on multi-layered materials. Finally, we propose a methodology for designing and optimizing the cross-section of multi-layered materials considering long-term moisture resistance. This study gives new insights into the diffusion behavior of multi-layered materials, focusing on polymer composites.

Long-term performance prediction framework based on XGBoost decision tree for pultruded FRP composites exposed to water, humidity and alkaline solution

Fiber reinforced polymer (FRP) composites are susceptible to material degradation when exposed to environmental effects. To predict the residual tensile strength and modulus of pultruded FRP composites, an XGBoost decision tree model was developed in this work. XGBoost decision tree, as a machine learning technique, is able to provide accurate predictions for tabular dataset with a good prediction interpretability. In this work, the methodology of XGBoost decision tree was presented in detail. Datasets for training and testing included a total of 746 data points which were collected from an existing database. XGBoost decision tree model predictions were cross-validated with 149 test data, and an excellent agreement was observed, showing R2 values of 0.93 and 0.85 for tensile strength and modulus, respectively. In addition, attribute importance analysis was conducted to quantitatively evaluate the attributes pertaining to FRP degradations, including exposure time, exposure temperature, pH value of environment, fiber volume fraction, plate thickness, fiber type and matrix type. Exposure time and temperature were observed to have the greatest impacts on residual tensile properties. The proposed XGBoost decision tree model provides a new approach for predicting the long-term degradations of FRP composites subjected to environmental effects.

Joint capacity of bonded sleeve connections for tubular fibre reinforced polymer members

Bonded sleeve joints formed by telescoping a steel tube connector for bolt-fastening are effective means for assembling tubular fibre reinforced polymer (FRP) members into more complex structures such as planar or space frames. A theoretical formulation is developed in this paper to estimate the capacity of such joints in axial loading and the predictions are validated by experimental results covering various section geometries and bond lengths. The formulation is based on the bilinear bond-slip constitutive relationship considering elastic, softening and debonding behaviour at the adhesive bonding region. Finite element (FE) analysis is also conducted to estimate the joint capacity and to describe shear stress distribution in the adhesive layer, validating the reliability of the theoretic results. The theoretical formulation is therefore further used to study the effects of design parameters including bond length and adherend stiffness ratio, again validated by FE results. An effective bond length can be accurately predicted by the theoretical formulation for the joint capacity at both the elastic limit and the ultimate state. Given a bond length, an optimal adherend stiffness ratio can be identified to achieve the maximum joint capacity at the elastic limit or the ultimate state.