Ferdowsi Civil Engineering
Year:2024 | Volume:37 | Issue:1|Papers Count:6

Several numerical methods, such as finite difference, finite volume, finite element, and so on, have been utilized to solve the problem of the free surface seepage in one-dimensional and two-dimensional domains. The governing equation of the seepage problem in porous media is the well-known Laplace equation. The finite difference and finite element methods are based on meshing the desired surface and obtaining the head values at this level; and repeating this process until convergence is reached. In this paper, a new method is proposed to solve the one-dimensional free-surface seepage problem in one-dimensional water column based on the Taylor-series expansion, entitled Differential Transform Method (DTM). It should be mentioned, up to now, DTM is employed to solve the various form of differential equations, but it has not been used in seepage problems. For some verification purposes, the obtained results are compared with the well-known finite difference method, and the good agreement is observed. Moreover, the analytical solution of the problem is attained by the use of mathematical techniques and it is reported in the paper as an appendix.

The observed damage during the past earthquakes shows that the damage of the masonry infill in the in-plane and the reduction of the contact surface between the masonry infill and the surrounding frame led to an increase in the vulnerability out-of-plane. Considering the different contact conditions of the masonry infill with the surrounding concrete frame, the interaction, and influence of the out-of-plane on the in-plane behavior of the masonry infills, which is a new topic in the field of seismic performance of the masonry infills. In this paper, the effect of different boundary conditions the masonry infill and the reinforced concrete frame, which include four edges supported by the frame, three edges supported by the frame, two horizontal edges supported by the frame, and one edge supported by the frame, by analyzing three types of loading, which are: 1-out-of-plane loading only, 2-the out-of-plane loading after in-plane loading, 3-the in-plane loading after out-of-plane loading, have been evaluated by using the finite element software ABAQUS. The results demonstrated that the absence of proper connection between the frame structure and the infill increases the Out-of-plane direction vulnerability, and does not prevent their collapse. Previous damage due to in-plane loading, which reached a maximum drift of 3%, can reduce about 70% of the out-of-plane capacity of the infill frame and consequently, the strength and stiffness were affected by the boundary conditions and type loading.

Bridges play a vital role in transportation, traffic management, and providing access to strategic locations, especially during crises. Earthquakes are unpredictable events that disrupt critical transportation routes and damage important structures. Innovative technologies, such as Ultra High-Performance Concrete (UHPC), offer hope for enhancing structural flexibility and reducing damage. UHPC, known for its uniformity, low permeability, and durability, increases the resistance of bridges to seismic forces and limits the spread of damage. One of the most effective methods for assessing seismic vulnerability is Fragility Analysis. This study evaluates urban bridges with UHPC concrete columns supporting cast-in-place concrete T-beam superstructures. The analysis was conducted using CSI Bridge software, and appropriate ground motion records were selected for Incremental Dynamic Analysis (IDA) and damage level calculations. The results indicate that the probability of damage exceeding a certain threshold in UHPC concrete piers is lower compared to those made of ordinary concrete. Examining damage intensity levels reveals that high-performance concrete improves performance by 7% in the worst-case scenario and up to 26% in the best-case scenario compared to ordinary concrete.

In this research, the seismic behavior of the back-to-back MSE walls has been assessed in a probabilistic approach using the fragility curves and the effect of the overlapping length of the metal strips on the vulnerability of this type of walls has been investigated. To this end, the back-to-back MSE walls are simulated using FLAC2D finite difference program, and validated with a shaking table physical model test. So, using the results of nonlinear incremental analysis, fragility curves are analytically extracted based on PGA and PGV intensity measures under far-field and near-fault earthquakes. The obtained results, in addition to providing the possibility of predicting the vulnerability of the wall in different seismic intensities, indicate that increasing the length of the metal strips from 0.65 to 0.85 of the wall height (increasing the overlapping length from 0.3 to 0.7wall height), reduces the probability of seismic damage up to 35% in the far-field and by about 50% in the near-fault earthquakes, respectively.

The use of roller-compacted concrete in construction projects, such as road paving, parking lots, dam construction, and industrial pavement, is attributed to its quick implementation, relatively low cost, and sufficient strength without the need for steel bar. However, the brittle nature of roller-compacted concrete prompted an investigation into how steel fibers could improve its mechanical behavior. This research focused on the effect of steel fibers on fracture strength, compressive strength, and tensile strength of roller-compacted concrete. The study involved testing semicircular samples with edge cracks under three-point bending loading to simulate pure tension, pure shear, and their combination. Additionally, the compressive and tensile strength of roller-compacted concrete samples with steel fibers were evaluated at 7 and 28 days. The laboratory results showed that adding 0.1%, 0.3%, and 0.5% steel fibers improved the 28-day compressive strength by 12%, 15%, and 36%, respectively, and the tensile strength by 14%, 21%, and 39%, respectively. Moreover, the failure load of all samples increased in all loading modes with higher percentages of steel fibers, leading to greater resistance to crack growth. The study identified 0.3% of steel fibers as the most effective amount for improving the fracture resistance of roller-compacted concrete in different loading modes, while the optimal percentage for enhancing the compressive and tensile strength was determined to be 0.5%.

The present study has investigated the effect of vinyl acrylic polymer emulsion (VA) on the shear strength of aeolian sands in the Khuzestan plain. For this purpose, after sampling the aeolian sands of the mentioned area, a standard compaction test was performed and the optimum water content and maximum dry density of the aeolian sand were determined. Then, solutions with percentages of 10, 20 and 30% of polymer material were made and added to the aeolian sand in such a way that it reached the optimum water content. The prepared soil with maximum dry density was placed in square metal molds kept in the laboratory for 1, 7, 14 and 21 days and then subjected to direct shear test. The results of the direct shear test on the stabilized samples showed that by increasing the curing time and the concentration of the polymer solution, cohesion and the shear strength increase and the angle of internal friction decreases. So the polymer solution with a concentration of 30% has caused a 146% increase in shear strength aeolian sand. Electron microscope images (SEM) show the creation of bridges between sand grains in the stabilized samples, which is the reason for the increased cohesion and shear strength of the samples.