Scientia Iranica
Volume:28 Issue: 3, May-Jun 2021

The paper presents a numerical analysis of hydrodynamic pressures on rigid structures caused by dynamic base excitation. First, the model for the fluid simulation, based on the numerical approach called the Smoothed Particle Hydrodynamics (SPH) method, is presented. Then, the described model is used to calculate the pressures on rigid structures. In the performed analysis, the structures of various geometries (a rectangular tank with vertical sides, rectangular tanks with one inclined side of constant slope and a cylindrical tank) are exposed to simple harmonic horizontal base excitations. The obtained hydrodynamic pressures on the sides of the tanks are compared with analytical and other numerical solutions.

Currently, there is a clear need for reliable procedures for condition assessment and service-life evaluation of existing infrastructures. Advanced 3D Nonlinear Finite Element (3D NLFE) analysis has proven to be capable of describing the behavior of reinforced concrete provided that detailed and appropriate condition assessment data are available. The present study aims to review and compare different procedures for coupling 3D NLFE analysis with condition assessment data to model corrosion induced cracking, and consequently to find a method with better accuracy, less computational cost, and improved robustness. This paper introduces a new method for adding cracked elements directly to the finite element model, called ReFEM. The force-displacement response, ultimate crack pattern, and failure mode from this model are compared with four other methods for a pull out test case on specimens under accelerated corrosion process. Using this method, the force displacement response for the corroded specimens was overestimated by about 70%. However, the trend was promising and the failure mode and crack pattern were correct. Moreover, the analysis continued after the peak point in the force-displacement curve which makes it possible to monitor the behavior of the specimen in the softening regime.

One of the most imperfections of the steel shear wall is out of plane displacements that cause severe damage in both structural and non-structural elements. In this paper, the effects of shape-memory alloys on steel shear walls are investigated. First, a numerical analysis using the finite element method in ABAQUS software has been carried out according to an experimental test. The results of the numerical analysis have been verified with experimental results. Next, shape-memory alloy fibers have been added vertically and horizontally to various parts of the steel shear wall. The results show that retrofitting with the shape-memory alloy reduces the out-of-plane displacement of the steel shear wall under both cyclic and seismic loadings. Besides, the buckling load in the steel shear wall increases when it is retrofitted with the shape-memory alloy. Also, the total out-of-plane movement (accumulated absolute displacements) of the steel shear wall and non-structural damage are controlled by the characteristic of a shape-memory alloy material called “super-elastic”.

This article presents information on the average speed enforcement system technology used in a university campus on sections with speed limits of 20, 30 and 50 km/h which is determined to be effective for decreasing the speeding behavior of drivers during a certain period of time. Afterwards, a study is presented which puts forth driver characteristics and their opinions. At the end of the application, drivers are subject to surveys within the scope of, “driver’s personal characteristics, driver behaviors known by themselves, opinions on the average speed enforcement in the campus and the applied speed limits as well as other enforcements”. A sample group of 729 drivers who regularly enter-exit the campus are included in the study as a result of which 52.8% of the participants indicated that the speed limits enforced via average speed enforcement technology are low, 42.6% indicated that they are sufficient and 1.6% stated that they are high. Accordingly, it is thought that the speed limits enforced by average speed enforcement are not considered as reasonable by the drivers and that these limits may be neglected frequently in the future. I

This study is focused on the propagation of plane harmonic body waves in a transversely isotropic linear poroelastic fluid-saturated medium, where the material symmetry axes for both solid and fluid are coincide. Simplified formulation is considered as the framework. A set of two scalar potential functions is employed to decouple the coupled fluid continuity equation and equations of motion. The velocities and corresponding attenuation coefficients of both longitudinal and transverse waves are extracted from the presented acoustic equations for the body waves. To show the validity of the analytical solution given in this paper, degeneration to the case of a single phase transversely isotropic and consequently isotropic solid is presented to provide interesting comparisons with the solutions reported in the literatures. The incompressible solid and fluid are degenerated from the general slowness obtained in this study for some special cases. In addition, the effects of mechanical and hydraulic parameters of materials on the velocity of propagation and attenuation coefficient of the waves are investigated in more detail. To this end, various synthetic poroelastic transversely isotropic materials are defined and the dependency of wave motion to these parameters is illustrated by plotting the graphs.

The fiber-reinforced inorganic matrix (FRIM) composite is a new type of composite, which has many economical and performance advantages. Beside the direct shear and bending tests, the tensile tests form an integral part in determining the mechanical properties of these composites. In this paper, to understand the tensile behavior of the FRIM composites, some strip specimens of the composites were tested which were clamped at the both ends, and the strains were measured using the extensometers installed at the middle of each strip. The inorganic matrix composites studied in this paper were constructed using two types of steel and glass fibers together with two different types of inorganic lime and geopolymer mortars. The results of direct tensile tests showed that the inorganic geopolymer mortars had the higher potential to increase the tensile load bearing of the specimens compared with the lime mortars. In addition, in most cases, the maximum values of stress, strain and the stiffness at the final stage of response in the tensile tests of composites were consistent with the results reported from the tensile test of textile fibers without the mortar. Moreover, clamping specimens by applying sufficient compressive force prevents slipping of fibers within the surrounding mortar.

This paper aims at investigating the seismic behavior of strengthened reinforced concrete (RC) shear walls using a 3D finite element analysis. A series of four different configurations of carbon fiber reinforced polymer (CFRP) composites and four different schemes of steel elements are utilized to compare the two methods of retrofitting RC shear walls with similar dimensions and reinforcement ratios. Nonlinear simulations of the RC shear walls are conducted under the action of lateral cyclic loading in ABAQUS Explicit software. In addition, the numerical modeling for RC walls strengthened by CFRP composites as well as steel elements are validated according to the previous experimental studies. The numerical results reveal that both types of strengthening methods have desirable performance in terms of the ultimate load capacity, failure displacement, energy absorption, and ductility in comparison with the control shear wall (CSW). Furthermore, evaluation of the response parameters including secant stiffness and dissipated energy demonstrate that utilizing steel elements is more advantageous compared to CFRP composites.

The main objective of this research was to study the impact of zeolite on mineralogical changes led to the development of compressive strength of cemented-sand mixtures. The mixtures consisted of Portland cement type II, natural zeolite (Clinoptilolite) and Babolsar sand. The cement content was chosen to be 8% based on the dry weight of the sand. The experimental program consists of a cement substitute with 0, 35, 60 and 90 percent zeolite along with the amount of the optimal water content obtained from the standard compaction test. The samples were made by an under-compaction process and cured at room temperature for various periods of time (7, 28, 90 days). The microstructural properties were analyzed using X-Ray Diffractometer (XRD) tests and Scanning Electron Microscope (SEM) tests equipped with an Energy Dispersive X-ray analysis system (EDX). In addition, an unconfined compression test was carried out for various zeolite percentages in the same curing time. Strong adhesion in the Interface Transition Zone (ITZ) resulted in densely compacted mineralogy in the presence of 35% zeolite, which promoted the Unconfined Compressive Strength (UCS). The connection between microstructure and macrostructure was clearly shown suitable relations between compressive strength and the intensity of the C-S-H phase.

The use of the concept of earthquake input energy under far-filed earthquakes and types of internal energy in structures has recently been mentioned to develop the performance-based design method. However, the extension of these studies to near-fault pulse-like earthquakes has been less considered. This paper calculates the applied ratios of energy types in the E-SDOF and MDOF systems and identifies the relationship between them. For this purpose, five steel frames (4, 10, 15, 20, and 30 story steel MRFs with 3-span) were designed, and obtained the E-SDOF structure equivalent to the first mode, using modal pushover analysis (MPA) method. All models were analyzed under 10 near-fault pulse-like earthquake records using nonlinear time history analysis. The results show that the total dissipated energy of the structure (TDE) depends on its nonlinear degree and period. The TDE of the MDOF and E-SDOF systems is equal for long periods, and its size is independent of the design resistance (R) and the degree of nonlinearity. However, in short periods, this ratio is close to the effective modal mass coefficient corresponding to the first mode. The story normalized hysteretic energy ratio is also a function of the height, nonlinear degree and period of the structure.

A series of triaxial compression tests were performed to evaluate the benefits of plastic wastes and investigate the engineering properties of sand reinforced with these materials. In this research, the effects of plastic waste contents (0, 0.25, 0.5, 0.75, and 1% by dry weight of sand), types of plastic wastes -polyethylene terephthalate (PET) and polypropylene (PP) fibers- and confining pressures (50, 100 and 200 kPa) on the behavior of Babolsar sand were investigated. The values of deformation modulus (up to 84%), peak (up to 7 times of the unreinforced sand) and steady state shear strength increased with reinforcement. Also, axial strain at failure for fiber-reinforced sand increased up to 1.5 times of unreinforced one (from 3.36% to 8.53% for 1% PP usage at 50 kPa confining pressure). Therefore, it can be generally stated that the use of plastic wastes in the sand leads to low cost soil reinforcement and also lessens the disposal problem of these kinds of wastes.