The corrosion of steel reinforcement in concrete structures due to chloride exposure poses significant financial and environmental risks. An accurate assessment of chloride diffusion is essential for predicting the service life of steel-reinforced concrete. This article develops six models for estimating the chloride diffusion coefficient (CDC) in concrete, considering various exposure conditions like tidal, splash, atmospheric, and submerged environments. The models utilize a hybrid approach combining the adaptive neuro-fuzzy inference system (ANFIS) and least square support vector regression (LSSVR), enhanced by an improved arithmetic optimization algorithm (IAA). The IAA merges the arithmetic optimization algorithm (AOA) with the Aquila optimizer (AO) to address AOA's limitations. The models undergo sensitivity analysis using the Fourier Amplitude Sensitivity Test (FAST), revealing that the curing mechanism (CM) is the most influential factor, with a sensitivity value of 0.993. The study demonstrates that LSSVR and ANFIS-based methods are highly effective in predicting CDC. Among them, the ANFIS combined with IAA outperforms others regarding reliability and accuracy, making it a superior choice for CDC estimation. This robust model could lead to better management and longevity of concrete structures exposed to chloride, mitigating potential risks. The main application of this research is to enhance the durability management and service life prediction of steel-reinforced concrete structures exposed to chloride-laden environments. Engineers and infrastructure managers can better assess the risk and timing of corrosion onset by accurately estimating the CDC, which is crucial for preventive maintenance and cost-effective design.

In this study, the finite element method is applied to study the vibration characteristics of the Euler-Bernoulli beam. The theory is employed to derive partial differential equation of pipes carrying hot fluid flow. The numerical investigations have considered some geometrical and physical parameters to evaluate the effects on the vibration behavior of the pipe structure such as the fluid velocity, mass ratio, and thermal loads. The present analysis is validated by comparing the results with those available in literature, which has a good consistency. The study showed that an increase in temperature negatively affected the stability region and instabilities of the system, as the critical velocity approaches the instability of the fluid decreased regularly and corresponded to the decrease in the frequencies.

The seismic behavior of a concrete dam depends mainly upon its connection joints to foundation rock. The paper present aims to show the effect of dam-foundation interface behavior on the earthquake response of Oued Fodda concrete gravity dam, situated in high seismic activity zone of Algeria, considering bonded contact and friction contact. The latter is represented using contact elements based on Coulomb's friction law. To this end, a three-dimensional discretization of dam-foundation system using finite elements is used in different analyses. The hydrodynamic interaction between the reservoir water and dam-foundation system is implicitly taken into consideration by Westergaard approach using surface finite elements added to dam-fluid and foundation-fluid interfaces. The concrete material model is used to present the seismic cracking of dam concrete using Willam and Warnke failure criterion. Material and contact nonlinearity are considered in this numerical investigation. Drucker-Prager model is utilized in nonlinear analyses for dam concrete and foundation rock. The displacement response, principal stress and strain components as well as cracking response of the dam are investigated considering contact conditions along dam-foundation interface. The results obtained from bonded and friction contacts are compared to each other.

The durability failure of marine concrete is primarily induced by the erosive effect of seawater, exacerbated by freeze-thaw and wet-dry cycles. Reactive powder concrete (RPC) renowned for its high strength and durability, undergoes further enhancement when reinforced with fibers. In structures the fiber RPC is commonly reinforced with rebars. This study aims to investigate the seawater erosion resistance of rapid-strength RPC with fibers and rebar, five groups of reinforced RPC specimens with steel fibers, basalt fibers, and hybrid fibers were fabricated, and the erosion solutions were prepared with reference to the seawater composition of a specific region. Then freeze-thaw cycle and wet-dry cycle tests were carried out. The mass loss rate and electrochemical parameters according to Tafel curve were conducted. The result reveals that: the mass loss rate, resistivity, corrosion current density and corrosion rate of each group of reinforcing RPC gradually increase with the increase of cycles of freeze-thaw or wet-dry. With the influence of rebar and fiber, the mass losses of the specimen increase at low cycle times. Under the same times of freeze-thaw cycles or wet-dry cycles, the resistivity, corrosion current density and corrosion rate of the reinforcing RPC specimens with hybrid fibers of steel and basalt are all smaller. Compared with the Tafel curve after 300 freeze-thaw cycles, the voltage value corresponding to the extreme point after 40 cycles of dry-wet cycles is smaller, indicating that the corrosion of steel bars is more severe under the action of dry-wet cycles. The RPC mixed with 0.5% basalt fiber +1.5% steel fiber shows the best performance to resist salt freezing and wet-dry cycle performance.

Ultra-high-performance fiber-reinforced concrete (UHPFRC) is characterized by its exceptional flowability, achieved through the absence of coarse aggregate. However, this characteristic causes the fibers in UHPFRC to change direction depending on the initial pouring direction or structure shape, making it anisotropic and influencing its mechanical performance. This study adopts an innovative approach for predicting fiber orientation based on tensor analysis by simulating the casting process of cementitious materials. Understanding these changes can help optimize the structural performance of UHPFRC by leveraging its anisotropy and minimizing performance variability caused by uncontrolled fiber orientation. To generate the steady simple shear flow, fresh UHPFRC was poured from one end of the mould, allowing it to flow and distribute evenly. Different dosages of Water-Reducing Agent (WRA) were used to study their effects on fiber orientation and mechanical properties. The UHPFRC mixes were prepared with 2% steel fiber by volume of concrete (% vol.) and varying WRA dosages (1.2% to 3% of binder mass). The results revealed that optimal compressive and flexural tensile strengths were achieved at 1.2% and 1.8% WRA, while higher dosages (2.4% and 3%) led to a reduction in strength. Fiber orientation distribution was examined through image analysis at four distinct sections (35 mm, 110 mm, 220 mm, and 270 mm) from the flow-generating end. Additionally, an analytical modelling framework was developed using MATLAB to quantify fiber orientation through orientation tensors, fiber spacing (a_c), and interaction coefficient (C_l) by selecting suitable values for the proportionality constant (K₁). A strong correlation was observed between experimental and analytical results, with K₁ values ranging from 0.013 to 0.015 and C_l values between 0.107 and 0.123, demonstrating the model's predictive accuracy. Overall, this research establishes a quantitative framework for fiber orientation prediction, enabling performance optimization through controlled casting techniques.