Yazar "Shamsi, Mohammad" seçeneğine göre listele

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    Analytical model of isolated bridges considering soil-pile-structure interaction for moderate earthquakes
    (Techno-Press, 2023) Shamsi, Mohammad; Moshtagh, Ehsan; Vakili, Amir H.
    The coupled soil-pile-structure seismic response is recently in the spotlight of researchers because of its extensive applications in the different fields of engineering such as bridges, offshore platforms, wind turbines, and buildings. In this paper, a simple analytical model is developed to evaluate the dynamic performance of seismically isolated bridges considering triple interactions of soil, piles, and bridges simultaneously. Novel expressions are proposed to present the dynamic behavior of pile groups in inhomogeneous soils with various shear modulus along with depth. Both cohesive and cohesionless soil deposits can be simulated by this analytical model with a generalized function of varied shear modulus along the soil depth belonging to an inhomogeneous stratum. The methodology is discussed in detail and validated by rigorous dynamic solution of 3D continuum modeling, and time history analysis of centrifuge tests. The proposed analytical model accuracy is guaranteed by the acceptable agreement between the experimental/numerical and analytical results. A comparison of the proposed linear model results with nonlinear centrifuge tests showed that during moderate (frequent) earthquakes the relative differences in responses of the superstructure and the pile cap can be ignored. However, during strong excitations, the response calculated in the linear time history analysis is always lower than the real conditions with the nonlinear behavior of the soil-pile-bridge system. The current simple and efficient method provides the accuracy and the least computational costs in comparison to the full three-dimensional analyses.
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    Effects of polyvinyl acetate content on contact erosion parameters of pavement embankment constructed by dispersive soils
    (Springer Heidelberg, 2023) Vakili, Amir Hossein; Salimi, Mahdi; Keskin, Inan; Abujazar, Mohammed Shadi S.; Shamsi, Mohammad
    This study deals with the contact erosion investigation and mechanical properties of both the un-stabilized and polyvinyl acetate (PVAc)-stabilized dispersive embankment layer. To this end, in addition to performing the specific dispersivity identification tests, i.e. pinhole and double hydrometer tests and contact erosion test for measuring the contact erosion parameters, a series of basic geotechnical tests was carried out. The microstructural changes with the aid of scanning electron microscopy (SEM) test and financial analysis were studied respectively to understand underlying mechanisms of stabilization and to estimate the economic benefits owing to PVAc addition. The results indicated that 2% PVAc content was the most effective proportion such that it decreased the dispersion potential, mass loss, and settlement of the dispersive soil by 69.6%, 70.5%, and 68.5% respectively, and at the same time, the strength of the samples increased by 107.4% only after 7 days of curing. The reaction between the polarity carboxyl hydrophilic group of PVAc and the hydroxyl group of the soil led to form the strong hydrogen bonds, and therefore, the structure stability and strength of the soil were enhanced. The formation of reticulated membrane structures and stronger bonds between soil particles, as documented by SEM images, testified to the excellent efficiency of PVAc in dispersive soil stabilization. Finally, the accuracy of available correlations between soil dispersivity and contact erosion parameters was examined, and then, the correlations were developed to cover a broad range of soils by using the results of this study.
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    Slope topographic effects on the nonlinear seismic behavior of groups of similar buildings
    (Wiley, 2022) Shamsi, Mohammad; Shabani, Mohammad Javad; Zakerinejad, Mohammad; Vakili, Amir Hossein
    The occurrence of vibrational energy exchange between neighboring buildings via soil is a well-known issue today as structure-soil-structure interaction (SSSI) problems. Furthermore, the seismic performance of buildings near the slopes considering seismic topography-soil-structure interaction (TSSI) is entirely different from their performance on the flat grounds considering seismic soil-structure interaction (SSI). Therefore, this study evaluates the seismic response of three moments resistant frame steel buildings with 15, 10, and 5 stories using three dimensional numerical analysis as a new topography-structure-soil-structure interaction (TSSSI) problem. This issue has not been investigated in previous studies to the best of the authors' knowledge. In each case of TSSSI, two, three, and four buildings with similar dynamic properties were simulated simultaneously. The effects of foundation's rocking, numbers of buildings, and the 2D and 3D arrangements of buildings were investigated, and the results of TSSSI cases were compared with the corresponding SSSI cases. The inelastic behavior for both building components and soil was considered in the simulations. Analyzes are performed based on seven earthquake records from which the average value was taken as final results. Results show that it is essential to consider the TSSSI effect, and it can completely change the seismic performance of buildings near the slopes. Although the effects of TSSI and SSSI on the seismic responses of the low-rise similar structures are negligible relative to the SSI cases, the results show that the nonlinear TSSSI effects of adjacent buildings should be fully considered even for 5-story low-rise structures.
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    Strength and post-freeze-thaw behavior of a marl soil modified by lignosulfonate and polypropylene fiber: An environmentally friendly approach
    (Elsevier Sci Ltd, 2022) Vakili, Amir Hossein; Salimi, Mahdi; Lu, Yang; Shamsi, Mohammad; Nazari, Zeynab
    Lignosulfonate is one of the by-products in the paper and pulp industry that is widely produced around the world and its improper disposal or storage can pose irreparable risks to human health and the environment. Sustainable reuse of this industrial waste as a stabilizing agent not only provides a novel approach in the construction industry, but also prevents the loss of natural resources. In this study, an environmentally friendly strategy involving lignosulfonate as a binder along with the polypropylene (PP) fiber as a reinforcing material was adopted to enhance the characteristics of marl soils from detrimental impacts of freeze-thaw (F-T) cycles. To this end, the pure marl specimens were improved by various contents of lignosulfonate and polypropylene fiber solely and simultaneously and cured for different time intervals. The variables assessed in this study were lignosulfonate content, polypropylene fiber content, curing period as well as the number of F-T cycles. The results showed that the greatest improvement was observed in the samples containing 1.5% lignosulfonate and 0.6% PP fibers, showing the least amplitude of fluctuations in MR reduction upon the F-T cycles. Moreover, freeze-thaw weathering transformed the stress-strain pattern of the samples from strain-softening to hardening behavior as well as increased the ductility behavior. It was observed that the simultaneous application of lignosulfonate and PP fibers led to the complete bonding of soil particles and the formation of interlocking zones around the fiber strands, leading to stronger particle bonding. The results of the Fourier transform infrared (FTIR) test also verified the formation of ionic bonds owing to the inclusion of lignosulfonate in the marl soil and the presence of lignosulfonate in the distance between the mineral layers of the soil. Overall, the reuse of lignosulfonate as a nontraditional alternative to marl soil modification can play an effective role in enhancing the durability and mechanical characteristics as well as sustainable development.