2031 research outputs found
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Finite Element Analysis on Shear Responses of Reinforced Concrete Beams Strengthened with ETS-FRP Bars
No full textThis study conducts a numerical analysis on the shear performance of reinforced concrete beams retrofitted with fiber-reinforced polymer (FRP) bars with embedded through-section (ETS) technique. The study uses 3D nonlinear finite element method (FEM) and evaluates the shear features of ETS-FRP-strengthened beams in failure modes, shear capacity, stiffness, and ductility. The FE analyses consider the effects of key design parameters, including transverse steel stiffness (Eswρsw), ETS-FRP bar stiffness (Efρf), compressive strength of concrete (f’c), beam geometry, and the values of shear span-to-effective depth (a/d) ratio. Consequently, ETS-strengthened beams with higher concrete strength (f’c) or greater total rigidity of ETS and transverse reinforcement (Efρf + Eswρsw) showed notable improvements in stiffness and load-carrying capacity, with average increases exceeding 20%. The enhancement in shear strength from increased shear reinforcement stiffness is less pronounced in specimens with high concrete strength than in those with lower strength. ETS-strengthened beams with T-shaped sections exhibit more effective performance and safer failure modes. An enhancement in the a/d ratio reduces the stress in ETS bars but results in more ductile failures. This study also proposes a new analytical formulation for determining the maximum shear resistance of ETS-intervened beams, accounting for all failure modes. The model achieved an average predicted-to-tested shear maximum force ratio of 0.93 along with a coefficient of variation of 26%, demonstrating improved accuracy compared to existing models
Methodology for Seismic Vulnerability Assessment of Pre-Code Masonry Buildings Using Region-Specific Data
Get PDFThis study presents a comprehensive methodology for evaluating the seismic vulnerability of existing pre-code masonry structures through a multidisciplinary approach that integrates region-specific building typologies with site-specific seismic input. A key gap motivating this work is the absence of fragility curves for masonry structures typical of the region despite their prevalence and high seismic exposure. Recognizing the importance of reliable Seismic Hazard Assessment (SHA) in risk evaluation, a scenario-based Neo-Deterministic Seismic Hazard Assessment (NDSHA) approach was employed. This method incorporates a detailed understanding of the region’s tectonic regime, active fault systems, earth crust structure, and historical seismicity to produce realistic site-specific response spectra for analysis. The seismic capacity of the structures was assessed using multiple iterations of a nonlinear static (pushover) analysis, accounting for uncertainties in the material and geometric input parameters. The structural displacement was used as the primary damage index, and the damage was classified into five discrete damage grades. Consequently, new fragility and reliability curves were developed: (i) a general set for unreinforced masonry (URM) structures, (ii) four regional sets corresponding to distinct zones within the country, and (iii) two sets differentiating between regular and irregular plan configurations. The novelty of this study lies in the development of region-specific fragility curves for URM buildings, providing urgently needed tools for seismic risk assessment and supporting mitigation strategies and decision-making at the local and national levels
Measurement Invariance of Expectations Toward Sustainable Public Transport Service Quality Among Urban and Rural Older Adults
No full textThis study examines measurement invariance of expectations toward sustainable public transport service quality between urban and rural older adults in Thailand. Using second-order confirmatory factor analysis, data were collected from 1,189 elderly respondents across Thailand's four major regions through face-to-face interviews. The measurement framework incorporated eleven service quality dimensions: nine traditional attributes (Vehicle, Bus Stop, Accessibility, Convenience, Information, Staff, Safety and Security, Reliability, and Affordability) and two extended dimensions (Older's Facilities and Post-Pandemic Prevention). Results demonstrated successful measurement invariance, confirming that the eleven-factor structure operates equivalently across urban and rural contexts. Universal priorities emerged for Convenience, Staff quality, and Reliability, while rural elderly showed elevated importance for Safety and Security. The validation of Older's Facilities and Post-Pandemic Prevention as distinct dimensions establishes empirical support for incorporating age-inclusive design and health protection measures as permanent components of sustainable transport planning, justifying unified national standards while accommodating regional variations for Thailand's aging population
Sizing Optimization of Trusses Using Elitist Stepped Distribution Algorithm
Get PDFThis study investigates the efficiency of the recently developed Elitist Stepped Distribution Algorithm (ESDA) as a metaheuristic framework for truss sizing optimization. ESDA builds upon the Cross-Entropy Method by introducing an elitist stepped sampling strategy that improves the balance between exploration and exploitation during the search process. To evaluate its effectiveness, ESDA is applied to a comprehensive test suite comprising seven benchmark truss optimization problems that cover a wide range of sizes, design variables, loading conditions, and constraint types. In all cases, the objective is to minimize structural weight while satisfying stress, displacement, and stability requirements. Numerical experiments are conducted with the proposed method, and the results are compared with those algorithms reported in the literature. The findings show that ESDA attains new best or near-best solutions for large-scale problems such as the 117-bar cantilever, 130-bar transmission tower, 354-bar dome, and 942-bar tower trusses, while also producing competitive results for the 25-bar, 72-bar, and 200-bar structures with relatively modest computational effort. The novelty of this work lies in demonstrating the robustness, efficiency, and scalability of ESDA across diverse benchmarks, highlighting its potential for future structural optimization applications
Numerical Investigation for Selection the Optimal Flexural Strengthening Strategy of Reinforced Concrete Beams
No full textReinforced concrete is the most widespread material that is used in structural applications. In structural systems, concrete beams can become damaged due to aging and increased design loads. Furthermore, for architectural purposes, specific dimensions may be imposed on concrete beams. For these reasons, it always needed to strengthen these beams. In this study, a numerical study was conducted to simulate the strengthening and improving of the flexural strength of reinforced concrete beams using three techniques: carbon fiber (CFRP sheets), steel plate, and external bars. The numerical analysis was verified with previous experimental studies. For the parametric study, the thickness, number of layers, and tensile strength were adopted for the CFRP strengthening technique. For the steel plates, the effect of changing the thickness and number of layers and yield stress was studied. Finally, for the additional external bars, different ratios of longitudinal reinforcement were investigated. After conducting numerical analysis of the studied models, the results showed a clear increase in the ultimate load and stiffness of the beams when strengthened with carbon fiber and steel plate, especially when increasing the tensile strength and yield strength, which was the most influential parameter, compared to a very limited effect of the number of layers due to the separation between the layers, especially for CFRP. However, both strategies showed brittle failure without clear ductility. Using additional external bars or increasing the ratio of longitudinal reinforcement was the most influential strengthening strategy in terms of increasing the beams’ capacity for bending and ductility
Clay Crack Initiation and Propagation Resistance Mechanism Using Municipal Solid Waste
Get PDFThis study investigates the potential of black seed flour (Nigella sativa) as an additive to enhance the crack resistance of clay-based landfill liners, aiming to mitigate gas transfer and leachate formation in landfill environments. Two distinct clay types were mixed with varying proportions of black seed flour (10%, 20%, and 30% by weight). The crack propagation resistance was assessed through desiccation tests over short (24 hours) and medium (72 hours) durations. Parameters such as crack morphology, fracture toughness, and crack propagation time were analyzed using image analysis and mechanical testing. The addition of black seed flour significantly influenced the crack morphology and propagation characteristics. Clay type 2 exhibited optimal fracture toughness at 10% and 30% black seed flour concentrations. The presence of black seed flour delayed crack initiation and reduced crack width, indicating improved crack resistance. Comparative analysis with existing literature suggests that the incorporation of natural additives like black seed flour can enhance the structural integrity of landfill liners. This research introduces black seed flour as a sustainable, cost-effective additive to improve the mechanical properties of clay-based landfill liners. The study provides new insights into utilizing natural materials for environmental engineering applications, contributing to the development of more resilient and eco-friendly landfill liner systems
The Influence of Nanodiamonds and Aluminum Oxide Nanoparticles on the Structure and Properties of High-Strength Concrete
Get PDFHigh-performance concrete (HPC) is an important construction material that can be improved with nano-additives. In this study, the modification of HPC with KHA-HC nanodiamond and nano aluminum oxide (NA) admixtures was investigated; the admixture rate was applied in the range of 0-1.4% in 0.2% increments. The rheology, density, compressive and flexural strength, water absorption, and microstructure properties were investigated; the results showed that the KHA-HC nanodiamond showed higher efficiency than NA. Compared with HPC without nano-additives, the strength properties of HPC with the most optimal content of nano-additives, 0.6% KHA-HC and 1.0% NA, were improved by 47.1% and 17.0% for compressive strength and by 44.9% and 16.3% for flexural strength. Water absorption decreased by 33.0% and 26.0%, respectively. Also, with optimal dosages of nano-additives, an improvement in the rheology of the HPC mixture was recorded. The complex modification of HPC 0.6% KHA-HC and 1.0% NA provides a synergistic effect and maximum improvements in properties: the increase in compressive strength was 58.2%; flexural strength - 54.1%; decrease in water absorption - 49.1%. HPC modified by nano-additives has an improved macro- and microstructure. The two types of nano-additives’ effectiveness, KHA-HC and NA, both separately and together in HPC technology for additional improvement of their operational properties, has been proven
Influence of Polypropylene Fiber on Mechanical and Shrinkage Behavior of Porcelain Based Geopolymer
Get PDFThis study examines the effects of polypropylene (PP) fiber content and initial curing temperature on shrinkages, mechanical properties, and microstructural characteristics of porcelain-based geopolymers. Geopolymer mixes were prepared with PP fiber dosages of 0.5%, 1.0%, 1.5%, and 2.0% by weight and initially cured at 60 °C, 75 °C, 90 °C, and 105 °C. Autogenous and drying shrinkage were monitored at 24 h, 72 h and 3, 7, 14, 21, 28, 60, 90, and 120 days, while compressive and splitting tensile strengths were tested at 3, 7, 14, 21, and 28 days. The results demonstrated that the incorporation of PP fiber not only shortened the setting time but also significantly reduced both autogenous and drying shrinkage of the geopolymer mortar. The most favorable performance was observed in specimens containing 2.0% PP fiber cured at 105 °C, which exhibited the lowest shrinkage values. Autogenous shrinkage was 439 μɛ at 24 h and 392 μɛ at 120 days, while drying shrinkage was 544 μɛ at 24 h and 194 μɛ at 120 days. Increasing fiber content decreased porosity, producing a more compact, homogeneous matrix and improving mechanical performance of concrete specimens, particularly splitting tensile strength; the optimal dosage was 2%, yielding 28‑day compressive strength of 41.03 N/mm² and splitting tensile strength of 7.65 N/mm²
Fragility Assessment of Cable-Stayed Bridge Towers Under Scaled Earthquakes
Get PDFCable-stayed bridges exhibit exceptional vulnerability to seismic excitation, particularly under combined vertical and horizontal ground motions in tectonically active regions. This study characterizes the seismic fragility of cable-stayed bridge towers using comprehensive probabilistic assessment methodologies. The framework integrates fragility curve development and Monte Carlo simulation, employing 30 earthquake ground motion records to construct robust statistical models of structural response. Fragility functions quantify the probability of exceeding predefined damage states across varying seismic intensity measures, while Monte Carlo analyses capture the stochastic nature of behavior and highlight response clustering around mean performance levels for distinct classifications. The findings reveal pronounced structural vulnerabilities within cable-stayed bridge systems, shaped by both epistemic and aleatory uncertainties that may lead to progressive collapse under extreme seismic events. Computational results indicate that although responses converge statistically around expected values, considerable scatter persists across limit states. For instance, at Sa(T1) = 1.0 g, exceedance probabilities diverge significantly: OP is almost certain (>99.9%), IO reaches 86.5%, DC 46.9%, and CP only 10.9%. Under more severe shaking (2.0 g), DC exceedance exceeds 98%, while CP remains 31%, illustrating substantial variability in fragility across thresholds. These results underscore the urgent need for improved seismic design philosophies in cable-stayed infrastructure within hazardous environments. The research advances bridge engineering practice by clarifying fundamental vulnerability mechanisms and guiding the development of innovative material systems, retrofit strategies, and structural health monitoring protocols aimed at enhancing seismic resilience
Evaluating Rock Mass Quality and Critical Depth for Rockburst Hazard in Deep Mines
No full textThis study investigates the geomechanical behavior of the rock mass at the Zhayssan mine in Kazakhstan, focusing on improving the safety of deep mining operations. The objective is to forecast the working strength of rock masses and assess the associated rockburst risks, especially given the limited existing data on the mechanical properties of the site’s rocks. To achieve this, we conducted comprehensive laboratory tests to determine rock strength characteristics, brittleness, and elastic energy accumulation capacity. We analyzed these data using the Rock Quality Designation (RQD) indicator and constructed a simplified geomechanical model of the deposit. Our findings reveal that rock mass quality improves with depth, as indicated by higher RQD values and reduced fracturing intensity; however, this improvement coincides with an increased risk of dynamic rock pressure events, particularly beyond the analytically estimated critical depth of approximately 400 meters. The study’s novelty lies in its integration of local testing data with comparative regional data, allowing for a more robust preliminary risk assessment despite limited local measurements. As promising directions, the paper suggests further laboratory and field research to refine methods for forecasting the strength and stability of mine workings