AMIRKABIR JOURNAL OF CIVIL ENGINEERING (AMIRKABIR)
Year:2018 | Volume:50 | Issue:6 |Papers Count:15

As a first endeavor, a mixed power series expansions and Galerkin’ s method in the context of linear buckling and free vibration analyses of non-uniform beams is presented. For this aim, the governing equilibrium and motion equations are first obtained from the stationary condition of the total potential energy. The power series approximation is then applied to solve the fourth order differential equilibrium equation, since in the presence of variable cross-section, geometrical properties are variable. Regarding aforementioned method, the expression of deflected shape of the buckled member is identified. Afterwards, the critical buckling loads can be acquired by imposing the boundary conditions and solving the eigenvalue problem. Note that the buckling mode shapes of an elastic member are similar to the vibrational ones. Therefore, the obtained deformation shape of the considered non-prismatic columns under linear stability analysis can be used as vibrational shape of member. The natural frequencies of beams with varying cross-section can be estimated by adopting Galerkin’ s method based on the energy principle. In order to illustrate the correctness and performance of this method, one comprehensive example of non-uniform beams with various end conditions is presented.

Obtaining physical and mechanical parameters of the soil has always been the primary challenge in the science of soil mechanics. These parameters are mostly obtained in laboratories or by field tests. In the present paper a hammer similar to Schmidt hammer is introduced which can be used to calculate soil parameters by its single impact. Such a novel hammer is termed RH impact hammer. The results of RH test are compared with that of ultrasonic tests. First, using the modified Proctor compaction test introduced in AASHTO standard, the modeling of the materials is done. In the continuation, the materials with known gradation range and based on the quality parameters such as compaction percent and natural and optimum moisture content are directly exposed to pressure waves of ultrasonic device and are simultaneously compact-metered with RH hammer. Without any field or laboratory experiments and only based on velocity and transmission time of waves and also using calibration plots and correlation formulas and base steel specimen. Readings are above 3 of the densities of more than 90% of the soil.

Geopolymers are alumino-silicate polymer that formed by alkali activation of Si and Al rich materials. This paper describes the effects of different alkaline solution types and concentrations, modulus of sodium silicate and sodium silicate to alkaline solution ratio on the flowability and mechanical properties of alkali activated slag and the optimum activator has been determined for the slag-based geopolymers production. Results reveal that adding the sodium silicate largely enhances the workability and compressive strength of slag-based geopolymer paste. The optimum modulus of sodium silicate and sodium silicate to alkaline solution ratio to reach the maximum strength are 2. 33 and 0. 4 respectively. At 91 days of curing, the compressive strength of the optimum mixture of slag-based gepolymer is about 74 % more than the compressive strength of ordinary Portland cement paste.

Stone columns are one of soil improvement methods that helps to increase the bearing capacity of soft soils. Therefore, finding ways to enhance their workability can be considerable. Bulging, known as the most important columns failure, can be dealt with by using suitable encasements. In this paper, single and group of stone columns were studied with and without geotextile encasement. Single stone columns with diameters of 63 and 82 mm and length to diameter ratio of 5 were tested. Results showed that by using geotextile, the bearing capacity of columns increased. Also, stone columns were tested in groups and their bearing capacities are compared.

Progressive collapse occurs when a sudden event such as a blast or an impact load influences a structure. Wherein, loss of continuity and low ductility of the remaining structural members result in total collapse of it. Alternate Path Method (APM) is an efficient method to study progressive collapse that is recommended in common guidelines such as GSA and UFC. APM check outs alternate paths in remained structure to resist progressive collapse due to key elements loss. This research surveys different scenarios of column elimination in planar regular and irregular frames by conducting non-linear dynamic analysis. Verification of the selected methods is conducted via analyzing an experimental model. Generally removal of corner column leads to significant responses compared with other scenarios. Moreover, eliminating a column in irregular frame causes large displacements and beam rotations which could be attributed to uneven distribution of forces in structural members; so regularity is an important factor to resist collapse.

In this paper, the application of Singular Variable Decomposition (SVD)-based principal component analysis (PCA) performed on truncated form of transfer function is demonstrated. Damage scenarios with light severity and distributed locations could be detected, localized and quantified using a one-step model updating. In many cases, it enhances the capability of FRF-based model updating with the presence of high noise levels and much less updating data. A numerical simulation on a truss has been validated to show the ability of this technique for damage detection.

The leachate may cause negative effects on the mechanical behavior of contaminated soil. The objective of this research was to study this effect through performing consolidation and shearing experiments. The samples with different pollution contents underwent direct shear and consolidation tests in bot long-term short-term conditions. The shear strength and oedometric behavior of contaminated specimens was compared with non-contaminated specimens. In order to study the effect of pollution duration, and the length of soil exposure to leachate, the experiments were conducted at certain time intervals after contaminations of specimens. The samples were kept at barred packages and then tested at the required time. The result show that permeation of leachate into the soil pores leads to decrease in shear strength and increase in settlement. The result also shows that long term exposure of specimens by leachate with low concentration shows the same results observed for specimens exposed to high concentrated leachate in a short period of time. In other words, leachate even in small concentrations have major long-term drawbacks on shear strength and compressibility of soil. Therefore, the leachate will affect the performance of structures relied on such soils.

The researches show that the buckling of braced frame, remarkably decrease the ductility and energy absorption of the system which lead to use an innovative system called “ Drawer Bracing System (DBS)” . This innovative system improve the seismic performance of the system through buckling elimination. The Drawer Bracing System (DBS) is a passive energy dissipation device made up of three parallel plates that are connected by some plates which are located at a right angle to the parallel plates and undergo minor axis bending. Energy dissipated through the inelastic behavior of these plates. The parallel plates are designed to remain elastic and to prepare the required strength and stiffness to transfer the load to the energy dissipating component of the system. In contrast to other bracing systems, removing destructive effects of buckling phenomenon is the main advantage of this system. The energy is dissipated with the use of sliding movement of its components. In this paper, the tests are carried out by the authors explain. Besides this, analytical investigation is made and the parameters which affect the buckling behavior of the system are evaluated. The results show that the buckling strength of the system is 3 percent higher and 17 percent lower than the ultimate strength of DBS in tests 1 and 2, respectively. Thus, to prevent the occurrence of buckling in the system, the buckling strength of the parallel plates should be selected larger than the ultimate strength of the system with keeping it safe margin.

Biological methods (adding bacteria to mixing water) is a one way to increase durability of concrete and repairing the cracks. Studies show that concrete contains bacteria has harsh environment, i. e. very high pH, small pore size and dry conditions, hence bacteria should be protected from this circumstances. In this study, for the first time, air entrained concrete is used for protecting the bacteria in the harsh condition of concrete. The effect of using sporosarcina pasteurii, which is a calcium carbonate-producing bacteria, on the performance of air entrained concrete has been studied in the carbonation depth; to do so, 24 concrete prisms were made using bacterial strains accompanied with mixing water. The results indicated that bacteria incorporation in air entrained concrete, near the source of calcium, reduces carbonation depth.

During an earthquake event, the adjacent buildings that lack a sufficient gap from one another may experience a severe structural damage as a result of structural pounding. The effects of structural pounding specially gained more attention after the historic earthquakes of Mexico City (1985) and Loma Prieta (1989) where, a significant number of buildings were damaged due to pounding. In this paper, the analytical models that are reported in the literature to simulate the pounding forces were reviewed. These include linear elastic, linear viscoelastic, modified linear viscoelastic, Hertz non-linear elastic, Hertz-damp non-linear viscoelastic, and non-linear viscoelastic models. The accuracy of these methods has been examined and compared in this paper. Additionally, current strategies for mitigating the pounding effects in adjacent building structures are reviewed. The last component of this paper includes a case study wherein the pounding effects are mitigated via improving the effective lateral stiffness and/or effective damping ratio in the building structure of interest. Results of the case study indicate that the application of supplemental energy dissipation devices is effective in the mitigation of pounding effects in those buildings that lack any seismic gap with their neighboring structures.

The vast use of chemical productions and the large amount of leachate which produced by human, lead to the pollution of the soil and groundwater supplies. Acidic contamination is one of the most common contaminations that goes to the nature by different ways such as leachate of factories, industry and acidic rains. These contaminants which cause environmental hazards, are also important in geotechnical perspectives and need more investigations. In this paper, the effects of sulfuric acid contamination on the shear strength and consolidation parameters of a clay soil is studied. Unconfined compression strength and one-dimensional consolidation test conducted on the soil under specific conditions. The soil itself was clean at first, and it was contaminated by adding sulfuric acid in three different pH values (5, 3 and 1). Also in order to compare the test results, one test conducted with drinking water (pH=7. 8). The results showed that acidic contamination and pH reduction, decreases the shear strength of clay. Also, by reducing the pH values, the coefficients of compression and swelling increased under the influence of the contaminant. The presence of the acid, increases the coefficient of consolidation and the rate of consolidation.

Beam-column connection is one of the most important parts of steel ductile flexural frames, as the performance of frame is depending on connection’ s flexibility. The rigid steel connections with cover plate are one of the most common connections in Iran. Due to the importance of seismic resistant design, it is necessary to investigate their seismic performance. In this experimental research, three steel connection specimens with 1/2 scale with introduction of new T-shape plate were built based on Iran steel code to evaluate their seismic performance and the specimens were subjected to cyclic loading. The results indicated that specimen designed based on Iran steel code cannot satisfy all of rigid connection criteria, and also, the strength was increased up to 10% and ductility was decreased up to 18% by adding the plates. Plastic hinges were transmitted to flange of beams, and the collapse mechanism of connections were changed due to deleting groove welding, strength and ductility were decreased respectively.

Zinc is an impure element in acidic solutions obtained from gallium sources; therefore, the selective separation of gallium from zinc using sodium dodecyl sulfate as an anionic collector was investigated by flotation. The effect of the collector concentration on the selective separation of Ga(III) from Zn(II) were studied at pH=2. The results indicated that the size of Ga(III)-cupferron complexes formed in aqueous solution were significantly affected on the selective separation of gallium from zinc. Also, the results indicated that the optimum selective separation of gallium at an equimolar solution of Ga(III) and Al(III) (1. 5 ×10-4 M) obtained after the addition of 4. 5×10-4 M sodium dodecyl sulfate to solution. The separation mechanism of flotation and the Ga(III)-cupferron complexes formed was studied using UV-visible spectroscopy, conductimetric analyze, dynamic light scattering and scanning electron microscopy (SEM).

The large volume of unrecoverable waste glass has recently been considered as an alternative to some concrete components. In the previous studies, the replacement of sand with crumb glass at high ratios resulted in a significant reduction in the mechanical properties of concrete. In this research, the sand was replaced with waste fractures with ratios of 5%, 8% and 12%, and 3 mixing designs were cast. Three mixes were also made by replacing glass powder with cement at 4%, 8% and 12%. Combined designs with a constant replacement of 8% glass crumbs with sand and cement with glass powder in ratios of 4%, 8% and 12% were also prepared. A total of 230 sampling was done. The compressive strength of samples at the age of 7, 28, 56 and 91 days, and tensile strength at 28 days were also measured. Static modulus test was performed on cylindrical specimens. Experiments results in fresh and hardened concretes compounds decreased compared to mixed glass containing glass powder, which is indicative of the undesirable use of glass as a crumbly and increased alkali-silica activity. The undesirable performance of glass jar on the mechanical properties of concrete through the replacement of cement with glass powder has been greatly improved. The results showed that simultaneous replacement of cement with glass powder in low proportions in designs containing 8% permanent sand replacement with glass jar, resulted in a significant reduction in the workability and improvement of mechanical properties of concrete compared to the reference design.

Rehabilitation (improvement) is a process and repairing method or modifying one structure in order to achieve the new operating conditions or increasing the useful life operation. In fact, in designing and implementation the retrofit, we are looking to achieve the new condition for concrete structure in terms of operating or loading. Retrofit operations can be necessity for design errors and problem causes, administrative problems and errors, changes in standards and regulations, increasing the useful life of the operation, changing the structure, increasing the classes and imposed load. Also, damaging in reinforced concrete columns can be cause the irreparable and strong damages. So, study the retrofitting the reinforced concrete columns by polymer fibers and with different layouts of polymer fibers. Improvements with polymer fibers and proper laboratory study have been used in order to validation exam for modeling. Then, proper retrofit layout of polymer fibers is discussed in Abaqus finite element software with simulation with several various models. After studying the hysteresis-bar curves transformation, load-displacement curve cover-transformation, ultimate load and the contribution of polymer fibers of models was found that samples those have polymer fibers have a greater ability to more loading bearing and also, have more absorb property and more energy amortization (82 percentage of increasing the capacity) than samples without fiber.