Stiffness Reduction Research Articles

A Comparative Study of Histotripsy Parameters for the Treatment of Fibrotic ex-vivo Human Benign Prostatic Hyperplasia Tissue.

Histotripsy is a noninvasive focused ultrasound therapy that mechanically fractionates tissue to create well-defined lesions. In a previous clinical pilot trial to treat benign prostatic hyperplasia (BPH), histotripsy did not result in consistent objective improvements in symptoms, potentially because of the fibrotic and mechanically tough nature of this tissue. In this study, we aimed to identify the dosage required to homogenize BPH tissue by different histotripsy modalities, including boiling histotripsy (BH) and cavitation histotripsy (CH). A method for histotripsy lesion quantification via entropy (HLQE) analysis was developed and utilized to quantify lesion area of the respective treatments. These data were correlated to changes in mechanical stiffness measured by ultrasound shear-wave elastography before and after treatment with each parameter set and dose. Time points corresponding to histologically observed complete lesions were qualitatively evaluated and quantitatively measured. For the BH treatment, complete lesions occurred with >=30s treatment time, with a corresponding maximum reduction in stiffness of -90.9±7.2(s.d.)%. High pulse repetition frequency (PRF) CH achieved a similar reduction to that of BH at 288s (-91.6±6.0(s.d.)%), and low-PRF CH achieved a (-82.1±5.1(s.d.)%) reduction in stiffness at dose >=144s. Receiver operating characteristic curve analysis showed that a >~75% reduction in stiffness positively correlated with complete lesions observed histologically, and can provide an alternative metric to track treatment progression.

A Hybrid Approach for Damage Detection and Localization on a Thin Metallic Plate

This paper illustrates a hybrid method for identifying structural damage that includes concepts from Physics-Based approaches within a Data-Driven framework. The lessons learned from the use of damage identification methods based on the analysis of modal curvature allows us to develop effective feature engineering in the development of Machine Learning (ML) algorithms. Moreover, the training of the algorithms exploits data provided from a population of damage cases generated by Finite Element (FE) analysis. The above data-analysis pipeline is applied to the identification of damage in a rectangular metallic plate for which measured modal data are available from a dedicated experimental campaign in CNR-INM laboratory using accelerometers. The damage is modelled as a stiffness reduction over a small area being also representative of material thinning due to corrosion. To have meaningful samples of the training database, the modal convergence of the FE model to the real structure is guaranteed by a structural optimization process. Experimentally identified noise, representative of real-life applications, is then added to the FE results before algorithm training. Damage existence and position are determined by a Novelty Detection approach and a Regression Neural Network, respectively. First, damage is identified on new test cases generated by the same FE procedure used for training. Secondly, the trained algorithms are applied to the experimental dataset. Sensitivity analysis on several parameters (number of samples for training, damage severity and noise levels) is numerically carried out to understand the applicability limits of the present methodology.

A discrete-to-continuum model for the human cornea with application to keratoconus.

We introduce a discrete mathematical model for the mechanical behaviour of a planar slice of human corneal tissue, in equilibrium under the action of physiological intraocular pressure (IOP). The model considers a regular (two-dimensional) network of structural elements mimicking a discrete number of parallel collagen lamellae connected by proteoglycan-based chemical bonds (crosslinks). Since the thickness of each collagen lamella is small compared to the overall corneal thickness, we upscale the discrete force balance into a continuum system of partial differential equations and deduce the corresponding macroscopic stress tensor and strain energy function for the micro-structured corneal tissue. We demonstrate that, for physiological values of the IOP, the predictions of the discrete model converge to those of the continuum model. We use the continuum model to simulate the progression of the degenerative disease known as keratoconus, characterized by a localized bulging of the corneal shell. We assign a spatial distribution of damage (i.e. reduction of the stiffness) to the mechanical properties of the structural elements and predict the resulting macroscopic shape of the cornea, showing that a large reduction in the element stiffness results in substantial corneal thinning and a significant increase in the curvature of both the anterior and posterior surfaces.

Constraints of local stiffness adaption for reduced-order models of large-scale steel bridges

Large and complex structures, such as bridges, are subjected to a variety of environmental factors and loads over time, leading to evolving structural states. To assess their current condition and plan predictive maintenance, Digital Twins enriched with Structural Health Monitoring (SHM) data are essential. However, for large-scale structures, the creation of physics-based Digital Twins necessitates reduced-order modeling to ensure efficient adaptation to SHM data. Many of these methods for structural damage assessment rely on localized stiffness reduction to characterize discrete damage states. The Static Condensation Reduced Basis Element (SCRBE) method is a promising approach for model order reduction by decomposing the structure into parametric components. However, SCRBE's effectiveness and the accuracy of the Digital Twin depend on an appropriate partitioning of the structure into to components with reduced stiffness. This paper systematically investigates the process and the constraints of component selection for steel bridges with discrete damages, considering factors like numerics, sensor placement and complex geometries. A comprehensive analysis is conducted using a real bridge case study augmented with synthetic measurement data representing damage scenarios. The results reveal both challenges and the potential of the SCRBE method for Digital Twins. A systematic approach for component selection within the SCRBE framework is proposed, specifically tailored for real-world application scenarios. This structured methodology facilitates the efficient and adaptive development of Digital Twins for large, intricate structures, such as steel bridges.

Monitoring Fatigue of Grouted Connections Using Autoencoders and In-Situ Fiber Optical Sensors

This paper investigates a traditional autoencoder trained with time series data for unsupervised damage detection and localization. The results are validated using innovative fiber optical sensory inside the grouted connection of a monopile sub-structure. Sensors are installed due to a limited understanding of the degradation mechanisms in grouted connections under cyclic loading. In most experiments, the grouted connection has only been assessed by destructively examining the grouted connection after the appearance of a complete crack pattern. To address these limitations, the signals of the innovative fiber optical sensory are used to gain insight into the crack development inside the grout. Further, the dynamic response of the structure is evaluated using an autoencoder to monitor the changes linked to the degradation process. The fiber sensors are placed within the grout between the diagonal shear keys, which has been identified as the compression strut failure from previous experiments. The cyclic load was repetitively increased to simulate the degradation process and induce structural change inside the grouted connection. After each testing phase, the structure was excited using a shaker, and the acceleration sensors were evaluated using the autoencoder. The results of the study show a high sensitivity of the residuals to minor structural changes that can be explained using the sensors within the grout. Additionally, the local stiffness reduction can be localized evaluating the autoencoder residuals. The study presents the innovative sensory to follow the crack opening of the grout due to cyclic loading. Further, these local changes are detected and localized using an autoencoder with time series data in vibration-based SHM.

Damaged mortise–tenon joint strengthened using an assembled spring–steel hoop based on a design of similar rotational stiffness

The excessive enhancement of rotational stiffness leads to an uneven distribution of rotational stiffness across the entire timber frame. This uneven distribution concentrates the load effect on the strengthened mortise–tenon joints (MJs), causing localized failure in advance. To address this issue, a reversible and non-destructive strengthening method for the damaged MJs is devised, involving the utilization of an assembled spring-steel hoop. The rotational stiffness of a strengthened MJ is derived from the springs that link the steel hoop of the beam and column, resembling the rotational stiffness of an intact MJ. A comparison of the measured moment-rotation curves of various types of MJ reveals that the rotational stiffness similarity necessitates the strengthened MJ's yield moment and ultimate moment, along with the associated rotation angles, to closely resemble those of the intact MJ. Secondly, a design methodology is developed for the assembled spring-steel hoop, which involves determining the parameters of the connecting spring. The comparative analysis of the hysteretic test results on multiple strengthened and intact MJs indicates that the strengthened MJs exhibit rotational stiffness deviations of less than 12.2 % during the elasticity stage and 6.6 % during the plasticity stage, in comparison to the intact MJs. A spring exhibits a lower ultimate extension compared to timber, leading to a maximum discrepancy of 37.5 % in the ductility coefficients between the strengthened MJs and intact MJs. The strengthened and intact MJs display similar patterns of stiffness reduction and energy dissipation progression.

Experimental study on the small strain stiffness-strength of a fully weathered red mudstone

Assessing the stability of embankments during railway operation is paramount for ensuring safety of railway. However, directly measuring the strength of fill materials can be challenging when the railway is in use. A strong correlation has been observed between soil shear strength and small strain stiffness. By establishing a robust correlation between shear strength and small-strain stiffness in the laboratory, considering various of factors, and combining it with field measurement of in-situ soil small stiffness might be an effective way to this problem. This study focuses on a type of filling materials commonly used in southwestern parts of China for railway construction: fully weathered red mudstone (FWRM) and its lime-treated counterpart (LFWRM), as the objects. A series of triaxial and unconfined compression tests were conducted to examine the effects of water content, confined pressure, and lime treatment on the shear strength and small strain stiffness of FWRM and LFWRM. The results show that the strength and stiffness of FWRM significantly decrease with increasing water content, while LFWRM specimens demonstrate good resistance. All LFWRM specimens displayed a brittle shear behavior. Empirical correlation was established for FWRM and LFWRM. The relationship for LFWRM is water content independent, meanwhile for FWRM is strongly dependent upon whether soil is saturated or not. The ratio of small strain stiffness to strength (Emax /qmax) for FWRM decreases substantially after saturation, whereas it remains almost constant for LFWRM. The reduction in strength and stiffness can be attributed to the degradation of the soil fabric due to increasing water content, where the pore size distribution (PSD) of FWRM changes significantly with increasing water content due to aggregate swelling. However, for LFWRM, the PSD remains bi-modal, which is due to the cementation bonding observed between lime-treated aggregates that explains the stable structure and improved performance of LFWRM.

Aramchol improves hepatic fibrosis in metabolic dysfunction-associated steatohepatitis: Results of multimodality assessment using both conventional and digital pathology.

Antifibrotic trials rely on conventional pathology despite recognized limitations. We compared single-fiber digital image analysis with conventional pathology to quantify the antifibrotic effect of Aramchol, a stearoyl-CoA desaturase 1 inhibitor in development for metabolic dysfunction-associated steatohepatitis. Fifty-one patients with metabolic dysfunction-associated steatohepatitis enrolled in the open-label part of the ARMOR trial received Aramchol 300mg BID and had paired pre-post treatment liver biopsies scored by consensus among 3 hepatopathologists, and separately assessed by a digital image analysis platform (PharmaNest) that generates a continuous phenotypic Fibrosis Composite Severity (Ph-FCS) score. Fibrosis improvement was defined as: ≥1 NASH Clinical Research Network (NASH-CRN) stage reduction; "improved" by ranked pair assessment; reduction in Ph-FCS ("any" for ≥0.3 absolute reduction and "substantial" for ≥25% relative reduction). Fibrosis improved in 31% of patients (NASH-CRN), 51% (ranked pair assessment), 74.5% (any Ph-FCS reduction), and 41% (substantial Ph-FCS reduction). Most patients with stable fibrosis by NASH-CRN or ranked pair assessment had a Ph-FCS reduction (a third with substantial reduction). Fibrosis improvement increased with treatment duration: 25% for <48 weeks versus 39% for ≥48 weeks by NASH-CRN; 43% versus 61% by ranked pair assessment, mean Ph-FCS reduction -0.54 (SD: 1.22) versus -1.72 (SD: 1.02); Ph-FCS reduction (any in 54% vs. 100%, substantial in 21% vs. 65%). The antifibrotic effect of Aramchol was corroborated by reductions in liver stiffness, Pro-C3, and enhanced liver fibrosis. Changes in Ph-FCS were positively correlated with changes in liver stiffness. Continuous fibrosis scores generated in antifibrotic trials by digital image analysis quantify antifibrotic effects with greater sensitivity and a larger dynamic range than conventional pathology.

Impact of a 5-min massage session on the gastrocnemius contractile and passive mechanical properties in young adults - A randomized controlled trial

The analysis of the impact of a 5-min massage session on the gastrocnemius contractile and passive mechanical properties in young adults - a randomized controlled trial. BackgroundThe effect of massage therapy on the muscle properties is unclear. New technologies make investigation more in-depth and reliable. ObjectivesThis study examined the effects of a 5-min massage session on the muscle stiffness and tone reduction in healthy young adults. Materials and methodsParticipants aged between 19 and 24 were randomly assigned to an intervention group (IG) (n = 40) or a control group (CG) (n = 40). The IG participated in a 5-min massage session of the lateral and medial gastrocnemius muscle (LGCM and MGCM respectively). The muscle contractile properties were assessed by tensiomyography (TMG). It measured maximal displacement (Dm), delay time (Td) and contraction time (Tc). Oscillation frequency (F) and stiffness (S) were used to assess muscle passive mechanical properties. These measurements were collected by MytonPro. ResultsThere were no differences between the groups in the pre-test measurements. The results of mixed-model ANOVA showed significant (p < 0.05) time × group interactions, with greater alteration in the IG compared to the CG in the LGCM for Dm (%diff = 22.5, ƞp2 = 0.41), Td (%diff = 3.63, ƞp2 = 0.02), Tc (%diff = 13.38, ƞp2 = 0.1), F (%diff = 5.55, ƞp2 = 0.07) and in the MGCM for Dm (%diff = −14.34, ƞp2 = 0.06), F (%diff = −7.53, ƞp2 = 0.12). No difference (p > 0.05) was noticed in other variables. ConclusionsA 5-min massage session impacts the contractile and passive mechanical properties of the LGCM and MGCM. The size and direction of changes may depend on the muscle type, its geometry as well as other factors.

Experimental investigation of welded steel T-stub components under high loading rates

The equivalent steel T-stub approach is widely used in practice to analyse and design bolted steel joints that are otherwise complex to study. The available analytical and empirical models for characterizing the response of T-stub components are based on numerous experimental and numerical research studies. This research is mostly concerned with the pseudo-static response of the T-stub. However, natural and man-made hazards (such as earthquakes and impacts) are dynamic. Considering the strain-rate sensitivity of steel, dynamic effects may have a notable effect on structural behaviour. A limited number of studies investigated the response of steel components/joints at high loading rates with inconclusive, and sometimes conflicting, observations. Accordingly, an experimental study is undertaken to address the data shortage. A total of 57 welded steel T-stubs were tested under monotonic tension. The main test parameters included the T-stub flange plate thickness, the loading rate, and the bolt preload condition. The test data underscored the influence of the loading rate and bolt preload. Notably, at a loading rate of 50 mm/s, an average of 35% reduction in the elastic stiffness, a 5% amplification of strength, and a 22% reduction in ductility is observed compared to the reference pseudo-static loading rate. The paper discusses the test observations in detail, evaluates the findings considering past research, and assesses potential implications on design.

Unsupervised autoencoders with features in the electromechanical impedance domain for early damage assessment in FRP-strengthened concrete elements

This paper presents the development of a robust automatic diagnosis technique that uses raw Electro-Mechanical Impedance (EMI) signals and deep autoencoder models to detect damage in fiber-reinforced-polymers (FRP) strengthened reinforced concrete (RC) elements, for which the most common failure modes occur in a sudden and brittle way by debonding. The contribution of this work is threefold: First, for the first time, two autoencoder models, convolutional and fully connected, based on an unsupervised learning framework supplemented by appropriate pre-processing techniques, are proposed for effective tracking of FRP-strengthened RC elements from raw EMI response variations in different locations of the auscultated structure; their implementation is also extensively investigated. The proposed framework consists of two main components, namely, dimensionality reduction and relationship learning. The first component is to reduce the dimensionality of the raw EMI signal while preserving the necessary information required, and the second component is to perform the relationship learning between the features with the reduced dimensionality and the stiffness reduction parameters of the structure. The approach is beneficial as only the EMI spectrum from the healthy structure state is considered for the training of the autoencoders. Second, the superior performance of the proposed framework is demonstrated. The results show that the proposed technique can accurately detect minor damage in its earliest stages for this kind of strengthened structures, while removing the need for manual or signal processing-based damage sensitive feature extraction from EMI signals for damage diagnosis. Finally, research presented in this work can potentially open up new opportunities for successful condition monitoring of this type of strengthened structures.

Fatigue performance analysis of fine aggregate matrix using a newly designed experimental strategy and viscoelastic continuum damage theory

Fine aggregate matrix (FAM), as the matrix phase in asphalt concrete (AC), significantly affects the fatigue behavior of AC. To accurately assess the mechanical properties of FAM, a newly designed experimental strategy for FAM testing was developed, and the viscoelastic continuum damage theory (VECD) theory was applied to analyze FAM’s fatigue cracking characteristics. In this study, a dumbbell-shaped geometry for dynamic shear rheometer testing was designed and verified through the FE-aided method. Subsequently, three AC mixtures’ FAM specimens with this special geometry were fabricated for the frequency sweep and linear amplitude sweep tests. Results showed that the specially designed specimens effectively capture the viscoelastic and fatigue properties of FAM with high replicability. Analyses based on the VECD theory indicated that FAM of porous asphalt (FAM(PA13)), featuring a higher asphalt content, exhibits a significant reduction in pseudo stiffness with increasing damage at the initial stage, but the reduction rate diminishes as damage progresses when compared to the other two FAMs. It was speculated that the higher aggregate content in FAM of dense-graded AC mixture (FAM(AC20) induces stress concentrations in the asphalt mastic near the protrusion areas of aggregates, thereby rendering the sample more susceptible to damage. The proposed methods will be readily extended to characterize other mechanical properties of FAM.

A mussel-inspired, antibacterial, antioxidant, injectable composite hydrogel for the sustain delivery of salvianolic acid B for the treatment of frozen shoulder

Frozen shoulder (FS) manifests as progressively worsening pain and a reduction in shoulder range of motion (ROM). Salvianolic acid B (SaB) is recently expected to be used in the treatment of fibrosis diseases including FS. We firstly demonstrate that SaB can effectively hinder the progression of oxidative stress, inflammation, and pathological fibrosis within the synovial tissue in FS, potentially leading to the reduction or reversal of capsule fibrosis and joint stiffness. For further clinical application, we design and synthesize a novel, superior, antioxidant and antibacterial CSMA-PBA/OD-DA (CPDA) hydrogel for the delivery of SaB. In vitro experiments demonstrate that the CPDA hydrogel exhibits excellent biocompatibility and rheological properties, rendering it suitable for intra-articular injections. Upon injection into the contracted joint cavity of FS model rat, the SaB-CPDA hydrogel accelerate the recovery of ROM and exhibit superior anti-fibrosis effect, presenting the promise for the treatment of FS in vivo.

Influence of Reinforcement Architecture on Behavior of Flax/PLA Green Composites under Low-Velocity Impact.

The main goal of this study is the comparison of different reinforcement architectures on the low-velocity impact behavior of green composites. The study includes the comparison of unidirectional, basket weave, and twill weave flax/PLA composites, they are subjected to unidirectional tensile tests, drop-weight impact tests, and after-impact compression tests. Results show that the unidirectional composite demonstrates superior tensile strength and initial modulus due to reduced fiber crimp, while basket weave exhibits the highest energy absorption capability and strain capacity attributed to its higher fiber-weight ratio and fiber crimp. Unidirectional composite also shows a larger impacted damage area compared to basket weave and twill weave, attributed to its internal architecture. Residual compressive strength across all composites decreased by 40% compared to the reference sample. However, the reduction in stiffness after impact was different, UD/PLA composite stiffness was reduced by 30% while the reduction in BW/PLA and T/PLA composites was about 20%.

Ilizarov technique for treating elbow stiffness caused by myositis ossificans: A case report

BACKGROUND Myositis ossificans (MO) is a rare disease involving the formation of bone outside the musculoskeletal system. While surgical intervention is the main treatment approach, preventing recurrence and standardized rehabilitation are also crucial. Here, we present a surgical strategy to prevent the recurrence of MO. CASE SUMMARY A 28-year-old female patient was admitted for the first time for a comminuted fracture of the left olecranon. However, incorrect postoperative rehabilitation resulted in the development of elbow joint stiffness with ectopic ossification, causing a loss of normal range of motion. The patient was diagnosed with MO based on physical examination, X-ray findings, and clinical presentation. We devised a surgical strategy to remove MO, followed by fixation with an Ilizarov frame, and implemented a scientifically reasonable rehabilitation plan. The surgery lasted for 3 h with an estimated blood loss of 45 mL. A drainage tube was placed after surgery, and fluid was aspirated through ultrasound-guided puncture. The patient experienced a significant reduction in joint stiffness after surgery. In the final follow-up at 9 mouths, there was evident improvement in the range of motion of the elbow joint, and no other symptoms were reported. CONCLUSION The Ilizarov frame is an advantageous surgical technique for facilitating rehabilitation after MO removal. It offers benefits such as passive recovery, individualized treatment, and prompt recovery.

Analysis of viscoelastic behaviour in asphalt pavement through four-point beam bending tests

This study, conducted in accordance with ASTM T321-14 standards, offers crucial insights into the behaviour of asphalt materials subjected to cyclic loading. For proper maintenance and pavement design, it is essential to understand the material response under different loading conditions. This study focuses on the four-point beam bending test to investigate the viscoelastic behaviour of asphalt pavement. The four-point beam bending test is a useful method for determining the material's ability to withstand cyclic loading and deformation, which the material experiences during field traffic conditions. The experimental setup involves subjecting asphalt samples to cyclic loading using a four-point bending apparatus. The imposed load causes the specimen to experience bending strains, representing the actual loading conditions that pavements endure. The data gathered during testing include stress, strain, and deformation properties under various loading conditions. The stress-strain response demonstrates the material's resilience to fatigue, with a gradual decrease in stiffness beyond 10,300 cycles. Fatigue failure criteria include a 50% reduction in initial stiffness for strain-controlled fatigue tests and cracking in stress-controlled tests. The dynamic modulus in a compressive-type, repeated load test follows a three-phase pattern, highlighting the impact of temperature and binder characterization methods on sample performance. The results provide information about the material's resilience to rutting and fatigue cracking, the most significant distresses indicated in asphalt pavements. The findings from this study contribute to an in-depth understanding of the viscoelastic behaviour of asphalt pavement and can aid in the development of improved design guidelines and maintenance strategies characterizing the material response to cyclic loading. Engineers and researchers can make better decisions on the durability and performance of asphalt pavements, resulting in more cost-effective and sustainable road infrastructure.

Acute Whole-Body Vibration Does Not Alter Passive Muscle Stiffness in Physically Active Males

Whole-body vibration (WBV) is a widely used training method to increase muscle strength and power. However, its working mechanisms are still poorly understood, and studies investigating the effects of WBV on muscle stiffness are scant. Therefore, the aim of this study is to investigate the acute effects of WBV on stiffness and countermovement jump (CMJ). Twenty-four recreationally active males, on separate days and in random order, performed a static squat under two different conditions: with WBV (WBV) or without vibration (CC). Muscle stiffness was assessed through the Wartenberg pendulum test, and CMJ was recorded. RM-ANOVA was employed to test differences between conditions in the above-mentioned variables. In the CC condition, stiffness was significantly lower after the exposure to the static squat (p = 0.006), whereas no difference was observed after the exposure to WBV. WBV and CC did not affect CMJ. No significant correlation was observed between changes in CMJ and changes in stiffness. Our results show that WBV may mitigate the reduction in muscle stiffness observed after static squats. However, current results do not support the notion that WBV exposure may account for an increase in CMJ performance.

Linear and Nonlinear Formulation of Phase Field Model with Generalized Polynomial Degradation Functions for Brittle Fractures

The classical phase field model has wide applications for brittle materials, but nonlinearity and inelasticity are found in its stress–strain curve. The degradation function in the classical phase field model makes it a linear formulation of phase field and computationally attractive, but stiffness reduction happens even at low strain. In this paper, generalized polynomial degradation functions are investigated to solve this problem. The first derivative of degradation function at zero phase is added as an extra constraint, which renders higher-order polynomial degradation function and nonlinear formulation of phase field. Compared with other degradation functions (like algebraic fraction function, exponential function, and trigonometric function), this polynomial degradation function enables phase in [0, 1] (should still avoid the first derivative of degradation function at zero phase to be 0), so there is no Γ\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\Gamma $$\\end{document} convergence problem. The good and meaningful finding is that, under the same fracture strength, the proposed phase field model has a larger length scale, which means larger element size and better computational efficiency. This proposed phase field model is implemented in LS-DYNA user-defined element and user-defined material and solved by the Newton–Raphson method. A tensile test shows that the first derivative of degradation function at zero phase does impact stress–strain curve. Mode I, mode II, and mixed-mode examples show the feasibility of the proposed phase field model in simulating brittle fracture.

Shear performance and durability of adhesively bonded spruce wood-concrete composite joints: Effects of indoor and outdoor environmental conditions, mechanical load, and their coupled effect

A long-term study was conducted on double-lap spruce wood-concrete joints to investigate their shear strength and stiffness over a 12-month period. These joints were manufactured using both wet and dry processes, each incorporating two adhesive types for bonding the wood to the concrete: a brittle epoxy and a ductile polyurethane (PUR). The experimental design exposed the joints to three specific long-term environments: (1) outdoor exposure, (2) indoor conditions with applied load, and (3) outdoor conditions with applied load. The wood-concrete joints exposed to outdoor conditions were subjected to destructive shear testing at intervals of 0 (serving as the reference sample), 2, 4, 6, and 12 months, respectively. For joints subjected to both indoor and outdoor conditions with shear loading, the shear deformation of joints was monitored continuously over the 12 months before performing the destructive tests. A gradual reduction in the shear stiffness and strength of dry joints (produced using the dry bond method) exposed to outdoor conditions was observed over a 12-month period, primarily due to bond failure at the concrete-adhesive interface. The wet joints exhibited no degradation in shear stiffness and strength across long-term conditions over the same period. The bond failure observed in dry joints was predominantly associated with stresses arising from dimensional changes in the wood. No degradation was found in the cross-linking density of the adhesive or in the concrete's compressive stiffness and strength.

Comparative Analysis of Measurement Points for Structural Damage Identification in Free-Free Aluminium Beam using Response Surface Methodology and FRF Curvature

This research paper presents a comprehensive comparative analysis of measurement points for structural damage identification in free-free aluminium beams using Response Surface Methodology (RSM) and Frequency Response Function (FRF) curvature. The primary objective is to determine the optimal measurement points for establishing a relationship between the input parameters and response features, thus forming a surrogate model. The investigation focuses on analyzing the influence of the number of measurement points on RSM's capability to identify structural damage. Three distinct Design of Experiment (DOE) techniques are explored: central composite design (CCD), Box-Behnken design (BBD), and D-optimal design, each incorporating different numbers of measurement points (10 elements, 15 elements, and 20 elements). The study's results highlight BBD's strong capability in detecting damage with fewer measurement points, while CCD design accurately identifies damage in finer measurement points. The findings reveal a clear trend: as the number of measurement points increases, the model becomes more refined, yielding higher stiffness reduction factor (SRF) values. The results underscore the significance of selecting an appropriate number of measurement points to enhance RSM's efficiency in identifying structural damage, thereby optimizing damage identification processes. This study contributes valuable insights into the selection of measurement points for effective structural damage identification, offering practical implications for engineering applications.