Strength Degradation Research Articles

Asymmetric and mechanically enhanced MOF derived magnetic carbon-MXene/cellulose nanofiber films for electromagnetic interference shielding and electrothermal/photothermal conversion

The prosperity of wearable and microelectronic devices tremendously facilitates to exploit thin and flexible composite films with multifunction. Free-standing MXene films have aroused considerable interest in the fields of electromagnetic interference (EMI) shielding and thermal management because of brilliant electrical conductivity, distinctive layered architecture and remarkable localized surface plasmon resonance effect. Nevertheless, the inferior mechanical strength and potential performance degradation in humid environments seriously constrain their practical applications. In this regard, robust and multifunctional CoNi-MOF-74 derived magnetic carbon/cellulose nanofibers (CNF)-MXene/CNF composite films with Janus architecture were successfully constructed via two-step vacuum-assisted filtration technology. The rational arrangement of functional fillers effectively improves the impedance matching, promoting the incident electromagnetic waves to enter the films for consumption. Constructing double-layered structure could induce the generation of “absorption-reflection-reabsorption” dissipation manner, dramatically enhancing EMI shielding performance. The bi-layered magnetic carbon/CNF-MXene/CNF composite membranes (0.1 mm in thickness) realize a fascinating EMI shielding effectiveness of 68.86 dB and a superior absorption efficiency of 58.82 dB. Meanwhile, the brilliant conductivity and significant localized surface plasmon resonance effect of MXene/CNF layer endow the composite films with excellent electrothermal/photothermal conversion capability, greatly broadening application prospects. The steady temperature of the composite films is as high as 112.9 °C within 10 s under the low driven voltage of 3.0 V and the saturation temperature reaches up to 154.2 °C within 15 s at the light intensity of 1500 W/m2, respectively. Moreover, the plentiful hydrogen bonding interaction and compact interfacial combination jointly enable the composite films to possess robust mechanical flexibility, satisfying the demands in practice. This work supplies a prospective guidance for preparing flexible and multifunctional composite films with Janus architecture, revealing great application potential in wearable and microelectronic devices even under harsh conditions.

Review on Constitutive Model for Simulation of Weak Rock Mass

Understanding the behavior of weak rock masses is important for predicting the stability of structures under different loading conditions. Traditional models such as the generalized Hoek–Brown and Coulomb weak plane are widely used; however, they often fail to capture the nonlinear and irreversible behavior of weak rock masses. This study offers a comprehensive overview of a critical analysis of constitutive models’ strengths and limitations for simulating weak rock masses. By comparing traditional and advanced novel approaches such as the strength degradation of rock (SDR) masses and continuous damage mechanics (CDM), this investigation shows that the new advanced methods significantly enhance the quality and accuracy of simulations. Moreover, SDR models address the limitations of classical plasticity models by incorporating nonlinear stress paths and irreversible stress changes, while CDM offers detailed insights into microstructural defect progression. These advancements allow for more accurate and practical predictions of long-term stability in geomechanical engineering tailored to specific requirements of each project.

Evaluation of the long-term performance and durability of basalt fiber reinforced polymer bars in concrete structures

To simulate the internal corrosion process of basalt fiber reinforced polymer (BFRP) bars in an alkaline environment of concrete, a diffusion based model was employed and modified in this study according to Fickian diffusion and diffusion coefficients at 25 ℃, 40 ℃, and 55 ℃ obtained from existing studies. Thus, the long-term corrosion medium concentration diagram, degraded depth, and strength retention of BFRP bars in the concrete environment at any ambient temperature can be predicted. Durability tests of BFRP bars in an alkaline solution at 60 ℃ were conducted to verify that the diffusion based model’s predictions were accurate. Moreover, long-term bonding tests between BFRP bars and concrete were conducted. The results indicate that the predicted results of the degraded depth and strength degradation of BFRP bars corresponded well to the experimental data. Morphology analysis by scanning electron microscopy (SEM) indicates that the alkaline solution intrusion caused the resin matrix to deteriorate, the fibers and the resin to debond, and the reaction between OH- and SiO2 in the fibers to occur, which in turn caused the tensile and bonding strengths of FRP bars to degrade. Moreover, after 63 days of corrosion at 55 ℃, the degraded depth exceeded 7 times that of 25 ℃ and 2 times that of 40 ℃, which implies that the ambient temperature had an obvious influence on the deterioration of BFRPs. The degradation rate was extremely slow at room temperature and rapidly accelerated with the rise in temperature.

Recoverability degradation of adhesion between soft matters under uniaxial cyclic bonding–debonding: Modified cohesive interface model and numerical implementation

The main objective of this work is to propose a partial recoverable cohesive interface model, coupled with a bi-potential contact algorithm, to simulate the phenomenon of adhesion recoverability degradation under cyclic bonding–debonding between hyperelastic bodies. For this end, the proposed adhesion recoverability degradation model is constructed by defining the recovery of interface damage during the rebonding when two bodies come into contact, and a degradation factor related to the number of bonding–debonding cycles is introduced into the fully recoverable adhesion model to reduce energy dissipation after multiple cycles. Recoverability degradation includes adhesive stiffness and strength degradation, which is physically described as parallel, series and mixed arrays of adhesive bonds. Then, a finite element framework coupling the adhesion recoverability degradation model and the bi-potential contact algorithm is proposed, with Mooney–Rivlin hyperelastic material used to describe the soft matters. This framework is implemented in an in-house finite element code, with numerical examples demonstrating the model’s reliability. The proposed approach could be applied to investigate interfacial adhesion effects in fields such as flexible electronics and intelligent robotics.

Effect of corrosion on bond between reinforcement and concrete-an experimental study

The presence of cracks in concrete structures can lead to corrosion as it exposes the steel reinforcement to environmental factors. When moisture and oxygen reach the steel, corrosion weakens the bond between the steel and the surrounding concrete. This weakening can reduce the load-carrying capacity and, in severe cases, lead to failure. Understanding the relationship between corrosion and bond strength is vital for reinforced concrete structures. This paper investigates the impact of corrosion on bond strength in reinforced concrete structures by examining the bond performance of concrete with both corroded and uncorroded reinforcement bars. The study considers concrete grades M20, M25, and M30, as well as corrosion levels varying from 0 to 20% in intervals of 5%. To conduct the study, cylindrical samples with different levels of corrosion were created using the corrosion acceleration process with the impressed current technique. Pull-out tests were then carried out to determine the bond-slip relationship and the degradation of bond strength due to corrosion. The test results show that lower-grade concrete (M20) experiences a significant decrease in bond strength compared to higher grades (M25 and M30), with M20 showing a 30.7% reduction and M25 showing a 25.8% reduction in bond strength relative to M30 in controlled specimens. The bond stress-slip relationship reveals a non-linear response, with reduced bond stress and slips for all grades of concrete as corrosion levels increase. Additionally, the reduction in bar diameter due to corrosion ranged from 11.3 to 11.6 mm at 5% corrosion and from 9.4 to 9.7 mm at 20% corrosion, significantly impacting the load-carrying capacity of the reinforced concrete structures. These findings underscore the importance of considering concrete grade and corrosion levels when assessing and maintaining bond performance in reinforced concrete structures.

Development of improved finite element formulations for pile group behavior analysis under cyclic loading

AbstractThe effect of cyclic loading is an essential factor leading to progressive soil strength degradation. Therefore, a comprehensive analysis of the pile‐soil system behavior under cyclic loading is required to ensure the stability of pile group. There is room for improvement in the inherent constraint of the conventional numerical model in terms of approximating the soil resistance distribution along the pile by point loads at element nodes, necessitating a specific element that integrates considerations of pile group effect and cyclic loading within a unified framework. This study aims to develop a newly specific type of element for efficiently predicting nonlinear behavior within the pile‐soil system, addressing simulations involving nonlinear pile‐soil interaction, pile group effect, and cyclic loading. Modified element formulations based on soil stiffness matrices and soil resistance vectors specifically address pile group effect and consider parameters that influence pile behavior under cyclic lateral loading. The numerical solution procedure with Newton‐Raphson iteration allows the calculation of pile responses in geometric and material nonlinear analyses. The validation of the proposed method includes several examples, comparing it with existing numerical solutions and experimental tests of single piles and pile groups under cyclic loading. These comparisons further support the consistency of the proposed method with measured data and validate its accuracy in considering group effect and cyclic loading. The parametric study illustrates the ability of the proposed method to capture cyclic loading parameters while considering the influence of the number and magnitude of load cycles, the cyclic load direction, and the installation methods.

Photochromic webbing structures for monitoring UV-induced mechanical strength degradation

Abstract Webbing structures are critical load-bearing components in a wide array of applications from structural restraint layers in inflatable space habitats to safety harness belts used by construction workers. In the field, webbings are subjected to ultraviolet (UV) irradiation from sunlight, leading to material degradation and a loss of mechanical strength. To date, health monitoring of webbings has relied on empirically correlating UV-induced strength loss with variations in their inherent color, which often yields inconsistent and imprecise results. To fill this gap, we propose a novel class of photochromic webbing structures that afford noninvasive monitoring of UV-induced degradation of their mechanical strength. The webbings’ sensing capabilities are achieved by integrating a class of photochromic yarns, fabricated through a pressurized coating process. Under continuous UV irradiation, the proposed photochromic webbings exhibit a substantial color change, demonstrating a sensing lifetime equivalent to several months in field conditions. We establish a strong correlation between the webbings’ photochromic response and their strength loss, supporting the feasibility of the proposed webbings in monitoring their mechanical integrity. To elucidate the sensing mechanism, we propose a physics-based mathematical model that describes the underlying photochemical reactions. Through an asymptotic analysis, we demonstrate that the model accurately predicts the webbing’s long-term photochromic responses under extended UV irradiation. The proposed photochromic webbing structures and the predictive mathematical model could enhance the safety and integrity of webbing-based engineering systems.

Experimental Study on the Properties of Basalt Fiber–Cement-Stabilized Expansive Soil

Expansive soil is prone to rapid strength degradation caused by repeated volume swelling and shrinkage under alternating dry–wet conditions. Basalt fiber (BF) and cement are utilized to stabilize expansive soil, aiming to curb its swelling and shrinkage, enhance its strength, and ensure its durability in dry–wet cycles. This study examines the impact of varying content (0–1%) of BF on the physical and mechanical characteristics of expansive soil stabilized with a 6% cement content. We investigated these effects through a series of experiments including compaction, swelling and shrinkage, unconfined compressive strength (UCS), undrained and consolidation shear, dry–wet cycles, and scanning electron microscope (SEM) analyses. The experiments yielded the following conclusions: Combining cement and BF to stabilize expansive soil leverages cement’s chemical curing ability and BF’s reinforcing effect. Incorporating 0.4% BFs significantly improves the swelling and shrinkage characteristics of cement-stabilized expansive soils, reducing expansion by 36.17% and contraction by 28.4%. Furthermore, it enhances both the initial strength and durability of these soils under dry–wet cycles. Without dry–wet cycles, the addition of 0.4% BFs increased UCS by 24.8% and shear strength by 24.6% to 40%. After 16 dry–wet cycles, the UCS improved by 38.87% compared to cement-stabilized expansive soil alone. Both the content of BF and the number of dry–wet cycles significantly influenced the UCS of cement-stabilized expansive soils. Multivariate nonlinear equations were used to model the UCS, offering a predictive framework for assessing the strength of these soils under varying BF contents and dry–wet cycles. The cement hydrate adheres to the fiber surface, increasing adhesion and friction between the fibers and soil particles. Additionally, the fibers form a network structure within the soil. These factors collectively enhance the strength, deformation resistance, and durability of cement-stabilized expansive soils. These findings offer valuable insights into combining traditional cementitious materials with basalt fiber to manage expansive soil hazards, reduce resource consumption, and mitigate environmental impacts, thereby contributing to sustainable development.

Effects of joint persistence and testing conditions on cyclic shear behavior of en-echelon joints under CNS conditions

Cyclic shear tests on rock joints serve as a practical strategy for understanding the shear behavior of jointed rock masses under seismic conditions. We explored the cyclic shear behavior of en-echelon and how joint persistence and test conditions (initial normal stress, normal stiffness, shear velocity, and cyclic distance) influence it through cyclic shear tests under CNS conditions. The results revealed a through-going shear zone induced by cyclic loads, characterized by abrasive rupture surfaces and brecciated material. Key findings included that increased joint persistence enlarged and smoothened the shear zone, while increased initial normal stress and cyclic distance, and decreased normal stiffness and shear velocity, diminished and roughened the brecciated material. Shear strength decreased across shear cycles, with the most significant reduction in the initial shear cycle. After ten cycles, the shear strength damage factor D varied from 0.785 to 0.909. Shear strength degradation was particularly sensitive to normal stiffness and cyclic distance. Low joint persistence, high initial normal stress, high normal stiffness, slow shear velocity, and large cyclic distance were the most destabilizing combinations. Cyclic loads significantly compressed en-echelon joints, with compressibility highly dependent on normal stress and stiffness. The frictional coefficient initially declined and then increased under a rising cycle number. This work provides crucial insights for understanding and predicting the mechanical response of en-echelon joints under seismic conditions.

FTIR and GC-MS analyses of raw materials produced from food wastes used in synthesis of biofilms

The present study carried out the GC-MS and FTIR analyses of raw materials (ripe plantain peel powder, cassava starch, glycerol, acetic acid (vinegar) and eggshell powder) produced from food wastes that are used in production of biofilm. The GC-MS results revealed the presence of pentadecane, bis (2-methylpropyl) ester and benzoic acid, 3-(2-Hydroxy-6-methylphenyl)-4(3H)-quinazolinone). The FTIR analysis revealed 17 peaks for glycerol, 16 peaks for vinegar, 15 peaks for cassava starch, 16 peaks for eggshell; representing the functional groups of ether, ethene, amine, carboxylic acid, nitriles, methylene cyclic ester, primary, secondary and tertiary alcohols common to hydrocarbons. The presence of carboxylic acid was important for enhancing the mechanical and chemical properties of biofilms thereby making them viable alternatives to petroleum-based plastics. Amines contributed to the flexibility, strength, and thermal degradation resistance of biofilms, thus aiding in their biodegradability. In conclusion, the study showed that the raw materials possessed biological activities and their functional groups indicated that the raw materials are safe to humans and the environment.

Bending strength degradation of a cantilever plate with surface energy due to partial debonding at the clamped boundary

Bending strength degradation of a cantilever plate with surface energy due to partial debonding at the clamped boundary

Cyclic loading experiments on seismic performance of precast concrete superposed shear walls with CFST end columns

The seismic performance of precast concrete shear walls is a major concern when considering their application in earthquake-prone regions. To improve the seismic performance and constructability of conventional precast concrete superposed shear walls, an innovative design, termed Precast Concrete Superposed Shear Walls with CFST End Columns (PCSSWEC), has been proposed. Given the limited research on the seismic performance of PCSSWECs, cyclic loading experiments were conducted on three full-scale PCSSWEC specimens and one monolithic RC shear wall specimen. The design axial compression ratio (ACR) and the thickness of the steel tube were employed as research variables. Experimental observations and results gave a comprehensive view of the hysteretic behavior of PCSSWECs, reflecting a favorable seismic performance (in terms of failure modes, global and local damage, force-displacement responses, load-bearing capacity, stiffness and strength degradation, deformability, ductility, and energy dissipation capacity). The experiment also revealed significant differences between PCSSWECs and monolithic RC shear walls in concrete crack development and deformation characteristics, confirming that the CFST columns and the wall panel could work together until the failure phase. Moderately increasing the ACR (0.3–0.5) was beneficial for PCSSWECs. However, increasing the steel tube thickness (3.5 mm–5.0 mm) could lead to unfavorable degradation in strength and stiffness and weaken ductility. In addition, a simplified method was proposed to evaluate the flexural strength of PCSSWECs.

Seismic performance of the ST-RC columns to RC beams exterior joint with assembled connection details

An innovative composite column type, the steel tube-reinforced concrete column (ST-RC), consists of a core of concrete-filled steel tube (CFST) and reinforced concrete (RC) encasement. This study aims to validate the reliability of two convenient and rapid assembly methods between RC beams and ST-RC columns. Four full-scale beam-column joint specimens were tested, comprising two prefabricated assembly joints of ST-RC column-RC beam frames, one integrally cast joint of ST-RC column-RC beam frames, and one traditional integrally cast joint of RC column-RC beam frames for comparison. The experiments were conducted based on the principles of a self-balanced system, and quasi-static tests under constant axial compression on the ST-RC columns were performed. Hysteresis curves, skeleton curves, failure modes, strength degradation, energy dissipation capacity, stiffness degradation, deformation capacity and the influence of connection method and joint form on mechanical performance were analyzed and obtained based on the test results. The results indicate that, compared to integral casting, the assembly surrounding method with steel sleeves reduces specimen energy dissipation by 19.8 % and damping ratio by 21 % at 4 % drift, with minimal impact on other mechanical properties. In contrast, reinforcement surrounded and connected by steel plates reduces initial stiffness and peak load-carrying capacity by 1.0 %, along with decreasing negative ductility. It also lowers total energy dissipation by 37.4 % and damping ratio by 45.4 % due to compressive effects from bottom steel plate connections. Despite these effects, its impact on negative ductility and load-carrying capacity remains minimal. Additionally, experimental observations and rebar strain data indicate higher stress on rebars at the base of steel plate connection beams, suggesting a need to strengthen transverse rebars at the beam’s base. The study confirms the feasibility of two convenient and rapid assembly methods for the joints of ST-RC column. Both methods meet current Chinese standards for MCE, with failure modes characterized by “strong columns and weak beams” in both cases.

Multi-response optimization of thermally efficient RC-based geopolymer binder using response surface methodology approach

This research addresses the persistent challenge of strength degradation in geopolymer-based materials incorporating rubber crumb (RC). An optimization model was developed, focusing on critical variables such as RC grade (particle size), percentage incorporation, and the molarity of NaOH, using slags as alumina-silicate precursors. Response surface methodology (RSM) was employed for experimental design and statistical modelling to predict the strengths and thermal conductivity of the resulting geopolymer. The study meticulously analyzed the influence of each parameter on the performance of RC-based geopolymers to understand their practical implications. The models generated were highly significant, demonstrating high practicability and minimal errors. The optimization revealed that a geopolymer with the highest strength (41.91 MPa) and lowest thermal conductivity (0.504 W/mK) can be achieved using a molarity of 10, grade 20 RC, and 18.5% RC content. This study highlights the potential of optimizing RC-based geopolymer mixes to enhance material performance, promoting the sustainable use of waste tires and advancing the development of high-performance construction materials.

Degradation mechanism of cement–sodium silicate hardened grout bodies under ion erosion

Cement-sodium silicate (C-S) grout is extensively employed as a grouting material in shield tunnel synchronous grouting projects. However, in water-rich areas, its hardened grout bodies are vulnerable to erosion damage caused by various ions. In order to elucidate the degradation mechanism of C-S hardened grout bodies' strength under salt ion erosion. This study analyzed the influence of SO42- ions, Cl- ions, and SO42- and Cl- mixed ions at different concentrations on the compressive strength of C-S hardened grout bodies through laboratory experiments. Moreover, microscopic techniques (XRD, SEM-EDS) were employed to illustrate the phase characteristics and microstructure of ion-eroded C-S hardened grout bodies, and the distribution of surface calcium elements. Molecular dynamics (MD) simulation investigated the adsorption, diffusion degree, and energy change of erosive ions in C-S-H gel. The results show that the higher the concentration of erosion ions, the faster the erosion rate. A nonlinear spatiotemporal strength degradation prediction model was developed, assessing the deterioration degree of hardened grout bodies due to ions: SO42- > SO42-and Cl- mixture > Cl- > water. Additionally, microscopic observations reveal a tight correlation between the degradation level of C-S hardened grout bodies and the loss of Ca2+ ions inside. The more significant the loss of Ca2+ ions from hydration products, the more evident the strength degradation of C-S hardened grout bodies. MD simulations demonstrate that SO42- ions and Cl- ions occupy adsorption sites like SiOCa+ and SiOH, altering interatomic Coulomb forces and intermolecular van der Waals forces, changing system energy, thereby influencing the structure of C-S-H gel, leading to strength degradation in C-S hardened grout bodies.

Rock anchor testing on sandstone from the Botucatu Formation, Paraná River Basin, Brazil: Insights for climbing safety procedures at the Corumbataí Geopark Project

The Corumbataí Geopark Project, located in São Paulo state, southeast Brazil, features valuable geosites that represent Earth's heritage and attract visitors with geoturism activities such as climbing. Rock anchors are crucial for ensuring climbers' safety in case of falls. This study reveals that the load capacity performance of expansion rock anchors is influenced by the applied torque, the physical-mechanical properties of the rock, and the weathering-induced strength degradation over time. The sandstone of Botucatu Formation, the predominant lithotype at these geosites, was assessed through petrographic analysis, non-destructive testing, physical and mechanical assessments, and pull-out tests of the anchors. Our findings indicate that the sandstone generally meets the geotechnical properties requirements for load capacities outlined in international climbing guidelines, a threshold of 80 MPa is recommended for effective rock anchor performance. However, prolonged exposure leads to rock degradation, compromising safety. Consequently, anchors should not be used in weathered rock and regular maintenance is strong recommended for climbing safety, approximately every 6 six years. This study provides a novel approach to characterizing rock-anchor interactions, supporting the development of effective management plans for outdoor activities.

Seismic performance of an innovative self-centering and repairable connection with SMA bolts in modular steel construction

Modular steel construction (MSC) is widely noticed and adopted in the building industry for its benefits of short construction period, low carbon emission, and great flexibility. The performance of inter-module connections, including the strength, toughness and ductility, is the focus of maintaining the load transfer mechanism and overall stability of modular structures. The structure with favorably designed connections can dissipate expected energy under cyclic loading with reduced structural damage. A self-centering and repairable connection (SRC) is herein proposed, with the benefits of a distinct load transmission path and easy assembly. Four full-size specimens were fabricated and tested under low-cycle loading, and the tested specimens were subsequently repaired by replacing angle cleats. The failure mode and bearing capacity of both SRC and repaired SRC specimens were investigated. Several seismic performance indices of the specimens, including hysteresis curves, strength and stiffness degradation, energy dissipation capacity, self-centering and repairable ability, were obtained. Furthermore, the performance of the SRC was comprehensively assessed according to Eurocode 3 Part 1–8, Chinese code GB 50011-2010, and American code AISC 341-16. In addition, an accurate finite element model (FEM) of the SRC was created and verified using experimental results. The developed FEM was used to investigate the effects of critical parameters, including angle cleat thickness and grade, vertical bolt diameter, and SMA bolt number and diameter, on the seismic performance of SRCs. Both experimental and FEM results show that only the replaceable angle cleats experienced the noticed plastic deformation for SRC specimens under cyclic loading, and SMA bolts provided the required self-centering force. It can be hence concluded that the proposed SRC can achieve the expected self-centering and recovery function.

Unraveling time-dependent roof stability dynamics in Iran's coal mines through laboratory-based rock displacement testing

Roof stability is a critical concern in coal mines, as the potential for roof collapse poses a significant risk to miners' safety and productivity. Roof stability is heavily influenced by the time-dependent properties of the rock mass above the workings. This study uses rock displacement testing to examine the effect of time-dependent properties on roof stability and resistance reduction in coal mines in Iran. The study employed laboratory-based rock displacement tests on samples collected from coal mines in Iran, subjected to varying stress levels over time, to simulate the gradual deterioration of rock mass strength in underground mining conditions. The samples were monitored for displacement under these conditions to quantify the reduction in roof resistance over time and assess its effect on roof stability. The study found that areas with high stress at equilibrium gradually fail with time, and the stress transfers from the failure zone into deeper solid rock. The results demonstrate that varying viscous parameters can lead to different relaxation behaviors and stress distribution. Furthermore, incorporating strength degradation into numerical simulation can capture the failure under creep conditions and improve the accuracy of predicting time-dependent roof failure. This research aims to enhance safety measures and reduce the risk of collapses by investigating the time-dependent properties of roof stability through rock displacement testing in Iran's coal mines. The study's innovative approach uses numerical simulation based on the viscoelastic-plastic model to simulate the time-dependent behavior of the rock and incorporate strength degradation into the simulation. The results provide valuable insights into the time-dependent behavior of rock mass in coal mines in Iran and contribute to developing strategies for improving roof stability and lessening the chance of roof collapses. The instantaneous elastic strain was 4.35 × 10–4, and creep simulation was activated to run for a time equivalent to 2 × 106 s.

Bond line shear strength of structural wood adhesives at high temperatures up to wood carbonization – A classification approach

The European timber fire design code EN 1995-1-2 presently specifies that adhesives for timber construction products shall provide integrity throughout the intended fire exposure time, yet no test or requirement specifications are given. Contrary, in North America elevated temperature tests are mandatory and product standards for glued and cross laminated timber demand sufficient bond line shear strength up to 220 °C. This paper deals with block shear compression tests at ambient and elevated temperatures for development of a high temperature resistance classification system for structural wood adhesives. The investigations comprised 1200 specimens made from Norway spruce bonded with twelve brands from five adhesive families. Polycondensation (pcon) resins encompassed phenolic resorcinol formaldehyde, melamine urea formaldehyde and melamine formaldehyde adhesives. Polyaddition (padd) adhesives comprised five one-component polyurethanes and an emulsion polymer isocyanate. The focus was on the strength-temperature (fv-T) relationship of bonded and solid wood reference specimens at 180–270 °C. The pcon adhesives showed almost throughout a fv-T relationship close to solid wood up to 270 °C. Contrary, the padd adhesives revealed massive strength degradations vs. solid wood from 180 °C onwards. An adhesive test, evaluation and classification procedure with four classes T270 to T200 was derived. It is based on a comparison of the temperature-dependent shear strength decline in bonded samples vs. solid wood reference samples beyond 180 °C. Class T270 adhesives are proposed being suited for the linear charring model of EN 1995-1-2 as PRF adhesives without additional fire resistance testing of components deemed necessary today.

New OpenSees material model for simulating reinforced concrete shear walls subjected to coupled axial tension and cyclic lateral loads

In high-rise buildings, reinforced concrete (RC) shear walls, particularly those forming part of coupled wall systems or core wall systems, may be subjected to coupled axial tension and cyclic lateral loads during strong seismic events. A new two-dimensional material model named the “Fixed Angle Model Considering Crack Sliding” (FAM-CS) was proposed for simulating the nonlinear behavior of RC walls subjected to axial tension and cyclic lateral loads. The proposed model was implemented in the OpenSees platform. Nonlinear constitutive models for shear aggregate interlock effects of concrete and dowel action of rebars were incorporated into the proposed model to represent the shear transfer mechanisms along concrete cracks. The proposed model was validated against the test data of six wall specimens subjected to coupled axial tension and cyclic lateral loads. The results indicated that the proposed model reasonably predicted the lateral strength capacity (an average error of 6.2 %) and the residual strength at the maximum drift loading (an average error of 12.3 %) of the specimens. For comparison, three other commonly used models, the Shear-Flexure Interaction Multiple-Vertical-Line-Element-Model, the multi-layer shell element model and the Cyclic Softened Membrane Model were adopted for the simulation of the specimens. Compared with the three existing OpenSees models, the newly implemented material model provided improved predictions of the wall hysteretic behavior with respect to lateral strength capacity, lateral strength degradation, pinching characteristics and cyclic stiffness degradation. In addition, the proposed model reasonably captured the localized failure pattern as well as the energy dissipation characteristics of the test specimens. Finally, a mesh sensitivity study was conducted to assess the robustness of the proposed model. The results revealed that the proposed model was robust regarding the lateral load-drift responses of RC walls, with a mesh size ranging from approximately one to three times the average crack spacing.