This study evaluated the effectiveness of carbon fiber-reinforced polymer (CFRP) composites in strengthening RC beams for a simple span overhanging from both ends and subjected to equal concentrated forces at each end. This innovative loading configuration allows for investigating the performance of CFRP composites under pure moment within the middle span and ensuring continuity of the moment over the supports, which cannot be captured using the classical simple span with four-point loading configuration. A nonlinear finite-element analysis (NLFEA) using Abaqus software was carried out to accomplish the objectives of this study. The NLFEA models were verified initially based on independent experimental results from the literature to calibrate the NLFEA models in terms of the material constitutive models, boundary conditions, and meshing. Then 12 NLFEA models were created with different strengthening schemes of CFRP strips, varying in terms of length and number of layers, in addition to a control beam. All the evaluated RC beams were similar in terms of length and cross-sectional dimensions, material properties, and steel reinforcement. The results revealed that the developed NLFEA models can reasonably simulate the flexural behavior and failure mode of the studied RC beams, which are significantly affected by the configuration and length of the CFRP strips. The results also indicated that it is essential to extend the CFRP strips from the middle span toward the overhanging span to provide continuity and allow the CFRP strips to contribute effectively to the flexural strength.
In response to the global shift toward renewable energy, wind energy is a pivotal player in sustainability. Floating offshore wind turbines (FOWTs) emerge as a promising solution for expanding wind energy into economically challenging deep waters. Despite their potential, challenges persist, necessitating a thorough understanding of the complex coupling effects between wind turbine aerodynamics and hydrodynamics, particularly during the design phase. This study highlights this critical need and extends its scope to review the relevant existing literature. The paper provides insights into the design considerations and assessment methodologies crucial for both new structures and the evaluation of existing ones. Through modeling in the Ashes wind turbine software, the study reveals that platform surge motion significantly impacts rotor performance, causing rotor power and thrust fluctuations. By comparing various wind and sea states with baseline testing, the study underscores the necessity of coupling aerodynamic and hydrodynamic forces for accurate performance predictions. Besides, the paper offers actionable recommendations for designing and optimizing FOWTs, and sheds light on the challenges and opportunities within offshore wind energy, offering valuable guidance for engineers working toward sustainable energy solutions.
Reinforced concrete (RC) construction stands as one of the most prevalent engineering endeavors, underscoring the importance of routine structural health assessments. Numerous factors, including overloading, design deficiencies, and fatigue, pose risks to RC structures by inducing cracks in various components. These damages significantly compromise the strength of RC constructions, necessitating vigilant monitoring to avert catastrophic structural failures. Structural health monitoring (SHM) techniques primarily aim to detect such damages. Leveraging piezoelectric (PZT) principles, the electromechanical impedance (EMI) methodology emerges as a promising SHM approach. EMI relies on variations in responses recorded through the electromechanical interaction between PZT and the structure to identify structural damages. Admittance signatures, comprising conductance (G) and susceptance (B), serve as indicators of structural condition, with deviations in the plot of G across a frequency range signaling structural deterioration. PZT transducers, either embedded within the structure or surface bonded, facilitate damage monitoring. This study aims to assess the damage detection capabilities of surface bonded PZT and embedded concrete vibrational sensors (CVS) in grade M25 RC beams. The root mean square deviation (RMSD) serves as the damage index, derived from variations in signatures recorded at different load levels. Experimental testing, conducted on nine RC beam specimens using a universal testing machine (UTM), yielded reliable results for comparison. Comparative analysis between surface bonded PZT and embedded CVS evaluated their performance in detecting structural anomalies under various load levels using RMSD values. Baseline conductance signatures revealed a lower amplitude for CVS due to inherent damping effects within the concrete material. Additionally, CVS consistently displayed lower RMSD values than PZT across different load levels, indicating lesser sensitivity to surface cracks and defects owing to its embedded position within the concrete.
Iran is located in a seismically active region, which poses a significant threat of destructive earthquakes. Given the dense populations they support and their structural importance, schools demand resilience across various dimensions. In this study, we aimed to evaluate the seismic performance of schools in Khorramabad, Lorestan, Iran, by obtaining resilience curves. The research involved a thorough analysis of retrofitting options for a specific school, identified through a review of data from Lorestan province. Three retrofitting options were considered: (1) bracing, (2) friction dampers, and (3) utilization of fiber-reinforced polymers (FRP) in the columns. The structure was modeled and designed using suitable software before and after implementing the retrofitting options. Incremental dynamic analysis (IDA) was conducted using recommended ground motions (including 10 ground motions for near and far fields). Subsequently, a risk analysis of the study area was performed, and a comparison was made between damage and fragility curves under different conditions; this included an assessment of potential damage in future earthquakes. The results demonstrated the efficacy of the analysis method in evaluating the seismic performance of buildings. Last, the study highlighted the building's response under different earthquake intensities and confirmed that the maximum capacity determined closely corresponded to findings from other nonlinear analyses. This approach was proven to be highly effective in assessing a building's behavior and ultimate capacity in the face of earthquakes.
Double-skin tubular columns (DSTCs) are promising modern columns with concrete sandwiched between fiber-reinforced polymer (FRP) and steel skins. Typical concentrated and localized failure modes in DSTCs can be constrained or delayed when stiffened inner steel tubes are used. DSTCs with circular cross sections are better investigated in the literature than scarcely studied square shapes, especially with variations of stiffened inner steel tubes. This study examined the nonlinear confined concrete behavior in stiffened DSTCs with square-shaped glass FRP as outer skins and stiffened steel tube as inner skins. The documented test results on 26 DSTCs were used to formulate a new analysis-oriented, axial stress-strain model for confined concrete. Primary model-formulation parameters were evaluated using a genetic algorithm (GA)-driven error minimization. A detailed parametric study was then performed on square DSTCs by incorporating the proposed stress-strain constitutive relationship for confined concrete in nonlinear finite-element analysis. The variations used in the parametric study included the shape of the inner steel tube (circular versus square), unconfined concrete strength, and flat-stiffener geometry characteristics (i.e., quantity, configuration in terms of thickness versus the number of stiffeners for similar total cross-sectional area, and its cross-sectional dimensions). Analytical results were finally used to propose a new load-bearing equation for estimating the axial load capacity of square DSTCs having stiffened inner steel skins of circular or square shapes. The proposed formulation showed better accuracy (about 2% on average and 14% maximum disparity with refined ultimate axial load capacities of DSTCs used in this study) than the existing prediction models.
