نشریه مهندسی عمران
سال پنجاه و پنجم شماره 8 (آبان 1402)

In the present paper, the effect of the sediment level of the dam reservoir on the nonlinear dynamic response of a concrete gravity dam under TNT explosion has been studied in a three-dimensional numerical model. For this purpose, assuming two different levels of sediments in the dam reservoir, the effect of its level on the dynamic behavior and the amount of damage on the concrete gravity dam has been investigated. The concrete damaged plasticity model (CDP), which includes the strain hardening/softening behavior of concrete, is applied in the modeling. In the analysis, the nonlinear dynamics of the dam-reservoir-foundation system utilizing ABAQUS software and finite element method have been used. CONWEP theory was used to apply the explosion load. As a case study, the failure analysis of the Koyna concrete gravity dam located in India under the TNT explosion has been evaluated. Analyzes were performed for three different blast points and two different amounts of explosives. The results obtained from the analysis show that the farther the blast location is from the sediments, the greater the displacement in the crown of the dam. Increasing the depth of sediment in the dam reservoir will cause stress and energy consumption and ultimately reduce the damage and displacement of the dam crown.

The mechanical behavior of cemented sand is different from that of uncemented sand because of the presence of bonds between particles. In this study, the effect of bond strength on the mechanical behavior of cemented sand under isotropic compression test is investigated by using a numerical method called as Discrete Element Method (DEM) in a two-dimensional space. DEM is a powerful numerical tool by which, each particle is considered as a rigid body, and the equilibrium condition is satisfied by applying accelerations and displacement along with applied forces from adjacent particles. The novelty of this study in comparison to similar works is to consider the angular geometry of particle shape rather than supposing circular. The particles are connected to each other To simulate the cementation agent. For the simulation of bonds, a bond contact model is defined by considering tension, compression, and shear strengths; the tension and shear resistance of bonds are assumed to be equal. In this model, it is essential for particles to have physical contact and overlap to consider that they are bonded to each other. For the simulation of isotropic compression tests, the samples are loaded isotropically up to 60 MPa under different stress levels. The results indicate that with an increase in the bond strength, the sample resists higher against volume reduction, and also, primary and gross yield stresses increase. Results show that when a cemented sample reaches the primary yield point, the rate of broken bonds increases. The pressure that is carried out by bonds increases as the volumetric strain augments. In this research, the results are validated by existing experiments in the literature.

Process towers or vertical vessels are among the industrial structures that play a key role in the production process of petroleum products and their derivatives in refineries and oil and gas industries. Due to the vulnerability of these structures in past earthquakes, and the lack of valid regulations and methods for seismic analysis and design of these structures, a case study on a designed and constructed process tower 26.5 meters high, located in Qeshm Island Refinery, has been conducted in this research. Since considering a rigid foundation, without the interaction of soil and structure, may lead to wrong results, in this study, the tower has been modeled in Abaqus finite element software considering soil behavior. The Winkler model used for soil modeling and the seismic behavior of the tower was investigated using pushover and incremental dynamic analysis, and finally, the resulting fragility curve is presented to show the structure's vulnerability at different levels of seismic intensities. In this investigation, the probable failures, including the failure of the body and the skirt, as well as the overturning of the structure, have been investigated. According to the incremental dynamic analysis results, no buckling was observed in the body and the tower's skirt before the tower overturned. The results show that overturning was the predominant failure mode and the probability of this failure mode until PGA=0.1g is approximately equal to zero, and for PGA= 0.35g, this probability is less than 20%. But for rare seismic intensities, the overturning probability is considerable.

Stabilizing weak and poorly graded soils in engineering projects is commonly achieved using lime and cement. However, the cement production process requires significant energy and generates a substantial volume of carbon dioxide, which presents considerable environmental risks. As an alternative to cement and lime, alkali-activated aluminosilicates have gained recognition due to their cost-effectiveness and environmental compatibility. This study aims to investigate the feasibility of utilizing metakaolin as a stabilizing agent for sandy soil, with Calcium carbide residue (CCR) serving as an alkaline activator. To this end, factors such as the concentration of alkaline activator, metakaolin content, curing time, and temperature of treated soil samples were examined through unconfined compressive strength (UCS) and California Bearing Ratio (CBR) tests. The results were then compared to those of sand stabilized with Portland cement. Furthermore, scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDX) were used to analyze the microstructures formed during the soil stabilization process. The findings indicate a significant increase in the stabilized soil samples' compressive strength and ductile behavior. Moreover, the analysis of the developed microstructures in the stabilized soil samples demonstrates a noticeable bond between the binding gel and sand particles and the filling of intergranular space with alkali-activated binding gel. Overall, the findings of the present study suggest that the introduced binding gel has the potential to be an environmentally compatible stabilizing agent for stabilizing sandy soils.

The occurrence of ice lenses and the subsequent melting of the ice causes a lot of damage to the beds consisting of fine sand soils every year. Volumetric changes of soil during freezing-thawing is a factor that reduces soil strength and increases deformations. In this study, several laboratory measurements are presented to investigate the effects of freeze-thaw cycles on the behavior of cylindrical sand-cement-fiber specimens. Fine-grained sand has been chosen to investigate the effects of freeze-thaw. At the same time, chemical stabilization methods of soil by mixing with cement with amounts of 2, 4, and 6% by weight of dry soil and mechanical reinforcement by adding 0, 0.5, and 1% by weight of recycled nylon fibers have been used. This study shows that the presence of fibers next to cement causes obvious changes in the stiffness, strength, and durability characteristics of the samples under the effect of freeze-thaw cycles. From the findings of this study, it can be concluded that in samples without fibers, distinct and wide cracks are observed. While, in samples armed with fibers, the cracks are smaller and distributed in a wider width. The results related to the behavior of the samples during loading showed that in the samples reinforced with fibers, failure occurred due to the pull-out of the fibers. In 7-day dry samples (without the freezing-thawing cycle effect), the compressive strength of the samples increases with the addition of fibers. In the 28-day samples, with an increase of only 0.5% of fibers with a length of 0.5cm, the unconfined compressive strength increased , and its decrease was observed after that. In all 7d and 28d dry samples, with the increase of fiber size from 0.5cm to 1 and 1.5cm, the compressive strength of the samples has a decreasing trend. Also, by adding the percentage of fibers from 0.5 to 1%, the trend of decreasing strength of the specimens can be seen.

Fracture toughness is one of the most important properties of concrete that controls the conditions for crack propagation and ultimately concrete failure. This research uses the Brazilian disk test to prediction of crack propagation and fracture toughness in ordinary concrete samples without micro-silica and lime powder and ordinary concrete samples containing micro-silica and lime powder has been investigated. Micro-silica replaces 10% by weight of cement and limestone powder replaces 5% by weight of cement. The crack propagation process was investigated from pre-existing cracks in the specimens as well as fracture toughness in modes I, II and hybrid mode I-II. Fracture toughness tests have been performed on Brazilian disk specimens at angles of 0, 15, 28.83, 45, 60, 75 and 90 degrees relative to the pre-existing crack direction. After laboratory studies, it was found that the onset of fin cracks at angles less than 60 degrees (0 <α <60) occurs from the pre-existing crack tip and approaches the loading direction by continuing to load and propagate the crack path. However, for angles of 60 degrees or greater, the crack starts at a distance d from the tip of the crack. This distance is more in ordinary concrete samples without micro-silica and limestone powder than in ordinary concrete samples containing micro-silica and limestone powder. Samples containing micro-silica and limestone powder have higher fracture toughness of modes I, II and mixed state (I-II) than samples without micro-silica and limestone powder.

Some natural clay-rich soils are highly erodible by flowing water both at and below the land surface. These soils contain an abundance of clay particles that disperse (slake) and deflocculate when relatively pure water is added. Dispersive soils can cause great damage to various structures, so geotechnical engineers propose different methods to modify and stabilize these types of soils. Chemical stabilization with cement or lime is the most common method to improve the properties of dispersivity and swelling soils. Word environmental problems such as producing large amounts of heat-trapping greenhouse gases for the production of cement or lime made engineers replace them. This paper investigated the effect of replacing part of cement with zeolite (as an environmentally friendly additive) to stabilize a type of clay and the change in dispersivity potential has been evaluated. The results of this study showed that by replacing a part of cement with zeolite, the maximum dry density increases and the optimum moisture decreases, which is a different process compared to cement stabilization. The behavior of the sample in the uniaxial test was influenced by the percentage of replacement of cement with zeolite. The results of the double hydrometer test also showed that the combination of cement and zeolite reduces the potential of soil dispersion. It also observed in the sedimentation experiments that increase in the zeolite ratio, the sedimentation rate increases, which can be justified by the decrease in the thickness of the double layer of clay so confirming decrease the dispersion potential. SEM microstructural analysis also indicated the formation of hydrated calcium silicate gel in the mixture, which improved the mechanical and resistance characteristics and reduced the swelling clay dispersivity potential.

This paper aims to propose an adaptive control approach for the PID controller known as ANN-OPID controller with simultaneous use of the advantages of the classical PID controller and neural networks so that it can provide better seismic performance than the optimal PID controller tuned by the teaching–learning-based optimization (TLBO) algorithm. In this approach, the structural dynamic is estimated using a neural network block and hence the parameters of the PID controller are adjusted adaptively. The seismic performance evaluation of the proposed controller is compared with the conventional optimal PID controller for an 8-story smart base-isolated structure subjected to various near-field and far-field earthquakes. Overall, the results obtained for the studied structure subjected to six earthquakes show that the TLBO-PID controller leads to a reduction of 24% and 25% in the maximum base displacement and its root mean square (RMS), an increase of 24% and 11% in the maximum acceleration and its RMS of superstructure floors and an increase of 6% and 6% in the maximum drift and its RMS of superstructure floors. However, the proposed ANN-OPID controller approach causes a reduction of 35% and 33% in the maximum base displacement and its RMS, a reduction of 9% and 7% in the maximum superstructure acceleration and its RMS, and a reduction of 5% and 6% in the maximum drift and its RMS of superstructure floors. Consequently, the proposed ANN-OPID controller can give a simultaneous reduction of the base displacement, acceleration, and drift of superstructure floors, while the TLBO-PID controller reduces the base displacement at the cost of an increase in acceleration and drift of superstructure floors.

In the recent past, the application of various types of passive dampers (e.g., yielding metallic dampers) has become a common practice for improving seismic performance of the under-construction buildings and rehabilitation of existing constructions. In this study, a new elliptical metallic damper was introduced to improve the seismic behavior of existing steel structures. Among other parameters, geometrical characteristics are known to affect the seismic performance of the constructions rehabilitated with the proposed elliptical damper. Accordingly, the performance of the proposed damper was investigated through accurate numerical studies on various types of dampers considering various damper dimensions, ellipse major and minor axes length-to-plate thickness ratios, and placements of elliptical shear diaphragm. To study the proposed elliptical damper in terms of its effect on the seismic behavior of rehabilitated buildings, three benchmark structures with 3, 9, and 20 stories were used. Further, far-field and near-field earthquake records were used to undertake nonlinear dynamic analyses. In this work, the proposed elliptical damper was verified by the Abaqus finite-element software, and nonlinear time-history analyses were conducted in the SAP2000 software to check for seismic performance of rehabilitated structural frames with the considered damper. Results of the nonlinear dynamic analyses indicated the appropriate performance of the proposed elliptical damper in terms of reducing the seismic responses of the rehabilitated structures and suitable behavior of the proposed elliptical damper in dissipating the imposed earthquake energy to the structures. Based on these results, upon rehabilitation with the proposed damper, the 3-, 9-, and 20-story structures exhibited smaller maximum lateral roof displacements by 66, 64, and 31%, respectively.

The traffic noise pollution measurement has always been considered by urban transportation system managers. Sound and noise definitions, evaluation of their differences, production and propagation factors of traffic noise pollution, various laboratory and field sound energy measurement methods, noise maps, and investigation of the methods of sound energy reduction are the most important topics studied in this research. Tire-pavement interaction noise (TPIN) is known as the most important source of traffic noise pollution at speeds above 40 km/h for passenger cars and 70 km/h for trucks. Using the appropriate air void content in asphalt surfaces has reduced the noise pollution caused by TPIN up to 10 dB. Porous asphalt with more than 20% air void content has shown good performance in reducing traffic noise pollution. The severity of traffic noise pollution has been measured using laboratory and field methods. Laboratory methods can be performed in a laboratory environment and under controlled conditions. Laboratory test results are more accurate and this method has been widely used in TPIN measurements. Field methods measure the tire-pavement interaction noise (TPIN) more realistically despite ambient noise pollution.