Iranian Journal of Science and Technology, Transactions of Civil Engineering最新文献

An enhancement of the inherent strength and durability characteristics is required for the effective utilization of fly ash (FA) in geotechnical engineering applications. This study presents a novel technique employing nano-silica (NS) to stabilize FA deposits, focusing on its effects on the unconfined compressive strength (UCS) and durability. The effects of different NS dosages (0.25%, 0.50%, 0.75%, and 1%), curing periods (7, 14, 28, 60, and 90 days), mixing methods (dry and wet), cement (CEM) addition, and cyclic wetting-drying (C-W-D) on the mechanical characteristics of FA-NS composites were studied. The test results revealed that FA-NS composites exhibit superior performance compared to FA in terms of strength and durability. An optimal dosage of 0.50% NS resulted in a substantial increase of 1043% in 28-day UCS, with strength development most pronounced during the early curing stages (7 days). The type of mixing method plays a major role in the assessment of the UCS of FA-NS composites. The addition of CEM, alone or combined with NS in FA, increased the UCS but was less effective than the FA-NS composite. The durability against C-W-D was improved, with 50% and 20% increases in the 28-day UCS after the 1^st and 12^th cycles, respectively, maintaining a higher UCS than the actual 28-day UCS. Scanning electron microscopy images and Fourier transform infrared spectroscopy indicated the formation of primary and secondary pozzolanic compounds, contributing to a cohesive structure and enhancing the UCS and durability of the FA-NS composite. Thus, incorporating a small dosage of NS remarkably improves the inherent strength characteristics of FA and offers substantial benefits for long-term construction and geotechnical engineering applications.

Household and similar wastes are increasingly being produced in public landfills. Their decomposition requires very high energy consumption, releasing harmful carbon dioxide gases that pollute the air. Therefore, it is necessary to take effective measures to ensure their disposal in an environmentally sustainable and economically feasible manner. Incorporating different types of them into cement matrices can be a valuable solution. To achieve this, physical and mechanical characterization and even subjecting them to harsh conditions of use are a crucial step for their use. Such gaps include this study, which aims to characterize the mechanical properties of two types of slurry containing ground coffee waste, using two types of sand: dune and quarry sand. The research is based on how these slurries perform under extreme conditions such as wetting/drying, freezing/thawing, chloride exposure, and temperature changes. Therefore, the mixtures were manufactured by replacing sand with ground coffee in varying proportions (5%, 10%, 15%, and 20%). Mechanical properties were evaluated after seven cycles of each condition. The incorporation of ground coffee significantly affected the physical and mechanical properties of the slurry, especially after extreme conditions cycles. Using analysis of variance (ANOVA), the effect of substituting ground coffee on the slurry under freeze/thaw conditions was evaluated. Response surface methodology and central composite design models indicated significant results for all alternatives with p values less than 5%. Numerical optimization showed that replacing 20% of sand with coffee powder resulted in the best mixture, demonstrating very satisfactory mechanical performance even at freezing temperatures as low as − 4 °C.

Irregularities present in buildings play a crucial role when subjected to earthquake loads. In this study, an existing Reinforced Concrete (RC) structure is considered, which is designed and constructed without considering irregularity and seismic load effect. Due to functional requirements and usage of the floor for other occupancy purposes, columns were removed, which resulted in stiffness irregularity, and the imposed load difference resulted in mass irregularity at the same storey level. Three types of structures were analyzed and compared to understand the seismic effects and collapse probability of induced irregularity in existing RC structures. The main goal of this study is to find out how multiple earthquakes affect the induced irregularity in structures. To assess the performance of the structures, Incremental Dynamic Analysis (IDA) is performed, and fragility relationships are generated with and without irregularities for both single and multiple earthquakes. The results are compared in terms of Inter-storey Drift Ratio (IDR), roof displacement, and probability of collapse for three framed structures. The analytical study identifies that the effect of multiple earthquakes has a crucial impact on irregular structures. The irregular structure’s median storey drift has been observed to have attained the maximum drift threshold of 4% as per FEMA 273.The findings highlight the importance of analyzing the structures subjected to multiple earthquakes. The results indicate that multiple earthquakes are significant and should be considered in the analysis phase to avoid the collapse of regular and irregular structures. Introducing irregularity into structures already constructed should be avoided.

Experimental studies have demonstrated that the elastic moduli of concrete, specifically Young’s modulus and Poisson’s ratio, undergo changes during compressive loading. Despite the fact that variations in Young’s modulus are frequently considered in nonlinear analyses, Poisson’s ratio is typically assumed to be constant, which has a direct impact on confinement modeling. In this research project, an attempt was made to enhance the accuracy of predicting the behavior of concrete columns confined by AFRP and CFRP by considering the variation of elastic moduli of concrete during loading. To account for the changes of Poisson’s ratio, an approximate method was proposed that involves assembling a three-part stress–strain curve. The first and last parts of the curve coincide with the stress–strain curves obtained by the limit Poisson’s ratio of 0.2 and 0.5, respectively, while a linear function serves as the transition curve in the middle region. The parameters of the middle zone were calculated using two different approaches: the first involved data fitting and optimization, while the second entailed using a proposed closed-form equation. The finite element program ABAQUS was employed to conduct incremental plastic analyses within the Concrete Damage Plasticity framework. The proposed model is capable of predicting the complete axial compressive stress–strain curve of concrete columns confined by AFRP and CFRP under monotonic compressive loading. A corroboration study was conducted using an experimental dataset from 24 concrete short column test specimens confined by AFRP and CFRP with a wide range of properties. The results showed that the average errors of both the proposed methods are nearly 3%. It means that both the numerical methods generally have a similar and acceptable precision.

In this research, the performance of plates installment in the type VI fishway has been numerically investigated using Ansys-Fluent software and the RNG k-ε turbulence model. The effects of the longitudinal plate position from the upstream partition wall (first scheme), the plate angle at the pool inlet (second scheme), and the transversal plate position (third scheme) have been assessed. The results indicate that for different designs in the first, second, and third schemes, the maximum average velocity reductions are 13.40, 19.39, and 11.35%, respectively. These reductions were observed when the plate was positioned near the upstream partition wall, when the plate angle was 45° relative to the side of the pool, and when the plate was situated at the farthest spanwise distance from the right side wall of the pool in the first, second, and third schemes, respectively. Furthermore, the highest reductions in the turbulent kinetic energy for the first, second, and third schemes are 49.61, 51.11, and 41.48%, respectively. The quadruple zones analysis of velocity, vorticity, and turbulence criteria revealed that all schemes create improved flow conditions for fish and enlarge the fish's desired zone. Specifically, the most suitable zones are 48.56, 48.93, and 53.68% of the pool in schemes 1 to 3, larger than the desired zone in the standard base design. Thus, the plate may improve the performance of fishways and can be used in practical problems.

Rayleigh damping is usually adopted in seismic analysis of steel buildings to develop the damping matrix (C^R), where the initial stiffness (K_i) and the lumped mass (M_L) matrices, and the first two lateral vibration modes are often used. Additionally, it is a widespread practice to use M_L in the nonlinear dynamic equilibrium equation. Similarly, the contributions to the response of higher modes related to rotations and vertical displacement of joints (JR-VD) are generally ignored. In this study, some issues related to these practices are addressed, contrasting the results obtained through the use of C^R with those of a damping matrix (C^M) obtained with a more accurate model as that of modal damping matrix superposition (MDMS) procedure, and by comparing the responses derived from M_L with those of the consistent mass matrix (M_C). Three steel building models are used, which are considered low, medium and high height. If C^R is adopted, axial loads, bending moments, drifts, and interstory shears are underestimated, on average, by up to 42%, 23%, 22% and 20%, respectively, compared to the results obtained with the MDMS procedure; the horizontal damping forces are overestimated by up to 232%. The contribution of the JR-VD modes can be up 41% for axial loads and up to 20% for bending moments, interstory shears and drifts. If M_L and K_i are used, average overestimations of up to 80% are observed for axial loads with respect to those of M_C and the tangent stiffness matrix (K_t); bending moments and interstory shears, in contrast, can be underestimated by up to 24% and 16%, respectively. Hence, the C^M, K_t and M_C matrices should be used; the contributions of the JR-VD modes should not be overlooked; and if C^R is used, to increase the accuracy, mode 1 and a mode greater than the second must be considered to obtain the Rayleigh damping matrix. Failure to do so may result in non-conservative designs.

This paper aims to analyze the elastic buckling of porous orthotropic two-layered cylindrical panels based on the trigonometric shear deformation theory. In the porous two-layered cylindrical panel model, porosities are dispersed by uniform and non-uniform distribution patterns. The porosity-dependent material properties of a two-layered cylindrical panel are assumed to vary along the layer’s thickness direction. First, the Virtual work principle is applied to derive governing equations. Then, the critical buckling loads of the porous orthotropic two-layered cylindrical panels are obtained using Galerkin’s solution procedure. Furthermore, the reliability of the current formulation is validated by several examples. Finally, the influence of porosity coefficients, porosity distribution patterns, geometrical parameters, and lamination sequences of the panel on the critical buckling load are investigated in detail.

The gravity recovery and climate experiment (GRACE) satellite mission, which was active between March 2002 and June 2017 and its successor, the GRACE follow-on (GRACE-FO), which has been in operation since May 2018, marked the pioneering remote sensing missions to track changes in terrestrial water storage (TWS) across time. TWS encompasses the cumulative water masses found in the Earth’s soil column, including elements like surface water, soil moisture, snow water equivalent and groundwater (GW). Over the course of the last 20 years, there has been extensive research conducted on fluctuations in the mass of different Elements of the Earth's system, such as the hydrosphere, seas, cryosphere, and solid Earth, utilizing time-varying gravity measurements from the GRACE/GRACE-FO missions. This technology can be utilised to improve monitoring results of large-scale spatial and temporal variations in the water cycle patterns. A review of recent GRACE data used for monitoring terrestrial hydrology over India is provided in this work. The primary applications of GRACE data in the context of large-scale terrestrial hydrological monitoring, such as assessing alterations in terrestrial water storage, involve: retrieving the hydrological components of GW, analysing droughts, floods, land subsidence and determining how glaciers are responding to climate change, have recently been described. India has the tenth position globally in the utilization of GRACE data. Therefore, more investigation is required to completely understand the potential of GRACE data. It was found through a review of the literature that several hydrological models have not yet been thoroughly examined with GRACE data. Furthermore, small river basins can be analysed at a fine scale with downscale GRACE data using machine learning/artificial intelligence. In the Indian context, no research has been conducted to estimate river discharge by using GRACE data.

A novel hybrid buckling-restrained brace (HBRB) configuration is introduced in this study to address the inherent limitations of conventional buckling-restrained braced frames (BRBFs). The HBRB comprised parallel steel plates with different yield strengths, featuring a low yield point (LYP160) and high strength (SA440B). A staged yielding mechanism is intended to be achieved, whereby the LYP160 cores yield initially during minor seismic excitations while the SA440B core remains elastic, providing requisite re-centering force. The hysteretic behavior of the proposed brace was scrutinized through cyclic loading. Subsequently, pushover and incremental dynamic analyses were conducted on two- and three-story frame models incorporating various bracing configurations to assess seismic performance factors. Furthermore, Nonlinear time history analysis was employed to evaluate the efficacy of HBRBs in mitigating residual displacements. Results indicate that the HBRB exhibits enhanced post-yield stiffness and partial re-centering capacity due to its staged yielding behavior. Comparative pushover and incremental dynamic analysis revealed lower average overstrength and response modification factors for HBRB models obtained from pushover analysis (3.4 and 9.3, respectively) than the incremental dynamic analysis (4.9 and 12.1, respectively). Conversely, a slightly higher ductility reduction factor was observed in the pushover analysis (2.8) relative to incremental dynamic analysis (2.5). Eventually, nonlinear time history analysis demonstrated an average reduction of 18% and 43% in maximum and residual drift ratios for HBRB models compared to BRB models.