نشریه مهندسی عمران مدرس
سال بیست و دوم شماره 3 (امرداد و شهریور 1401)

Growing apprehension about the environmental effects of producing Portland cement as the main component of the concrete, has raised widespread concerns in construction industry about the urgency of finding appropriate materials to substitute it. Recently, lime-pozzolan binders that were used before the advent of Portland cement, have been revived and reconsidered in a quite modern way showing reliable properties. In this study, according to past research on lime-pozzolan concrete, with the aim of producing concrete having dominant lime-pozzolan binder with desirable structural properties, different lime-pozzolan concrete mixes with double and triple compounds of hydraulic lime with silica fume, blast furnace slag and zeolite and two mixes with the presence of 30% Portland cement in lime-pozzolan concrete were made and tested. In all mixes, the super-plastisizer admixture was used to improve the concrete workability. To gain the most concrete strength, a constant water to binder ratio of 0.35 was used for manufacturing all concretes specimens except the one containing zeolite in which water to binder ratios lower than 0.45 wasn’t practical. Portland cement binder concrete were manufactured as well for comparing purposes. Slump test was conducted on fresh concrete and compressive strength test on cubic molds (10×10×10 cm) in 7, 28 and 56 days, spilling tensile strength test on cylindrical molds (with a diameter of 10cm and a height of 20cm) in 28 days, flexural strength test on prismatic templates (10×10×35 cm) in 14 and 28 days and elastic modulus test on cylindrical molds (with a diameter of 10cm and a height of 20 cm) in 28 days was conducted on hardened concretes. To analyze pozzolanic activity,the Thermal Gravimetric Analysis (TGA) was performed on concrete samples which showed better strength results than others. Slumpchr('39')s results show that the use of the super-plastisizer in the lime-pozzolan concrete improves their workability; Most slumps were obtained in lime-slag-silica and lime-slag-cement concrete at 22 and 23 mm, respectively. Four mixes of lime-pozzolan concrete (two mixes with 50% natural hydraulic lime (NHL) composition and 30% cement with 25% silica fume (SF) or 25% ground granulated blastfurnace slag (GGBS) and two other triple mixes 50% NHL, 25% SF and 25% GGBS and dual mixes 70% NHL with 30% SF) showed competitive mechanical properties compared to ordinary concrete and their 28-day compressive strength were achieved above 30 MPa (Equivalent to 58.6, 40.2, 40.1 and 33.5 MPa, respectively), which is quite favorable to be used as structural concrete. Concrete containing zeolite had less mechanical strength than others. The results of thermal gravimetric analysis were determined in the lime-pozzolan concrete, more calcium hydroxide is consumed as the amount of pozzolan increases. Silica fume performed more active than blast furnace slag, because it consumed more calcium hydroxide in concrete. Also blast furnace slag was more active than zeolite.

Shallow sediments and large displacement of the fault in bedrock can make the fault activity may appear to be surface faulting. Propagation of the fault rupture through the soil layer is one of the hazards associated with the fault dislocation in bedrock. The ruins from the 1999 earthquakes in Turkey and Taiwan and the 2008 earthquake in Wenchuan of China clarified the effect of fault rupture on the structures located near the fault trace on the ground surface. Also, previous studies have revealed the destructive effects of the impact of surface faulting on a structure. It seems that the alluvium depth can affect the interaction between the structures and faults. Therefore, the present study used a numerical model validated with centrifuge test results to evaluate the effect of alluvium depth on the response of shallow foundation-normal fault interaction. The Mohr-Coulomb constitutive law, with internal friction angle and dilation angle softening behavior, was used to model the interaction. The alluvium depth was considered as 15, 20, 30, and 40 m. The foundation was assumed to be rigid in all cases. It was placed at different positions relative to the free field fault outcrop on the ground surface. Normal faulting also was applied pseudo-statically to the model boundaries at a dip angle of 60°. The rotation of foundation and the vertical displacement profile of the ground surface was investigated to evaluate the effect of alluvium depth on the fault rupture and foundation interaction. The results show that there is no difference between the free-field faulting zones for different alluvium depths of loose soil. A graben is formed for deeper alluvium depths of dense soil in agreement with the analytical models, although the width of faulting zones is the same for different alluvium depths. It should be noted, a graben may form in a low-angle dipping normal fault (i.e. <60°) for loose sand. In interaction models, it has been observed that the interaction mechanism of the foundation and fault remains constant for both dense and loose sands. The footwall, gapping, and hanging wall mechanisms were formed for all alluvium depths related to the position of the foundation. Also, a graben was observed as one of the hazards associated with the normal fault rupture and shallow foundation interaction in the deeper alluvium depth of dense soil. By increasing the weight of the structure, the foundation experienced more rotation for 15 and 20m alluvium depths. The reliable foundation rotation could be estimated by considering alluvium depths of 20 m and more for both dense and loose sands.

Due to the relatively high use of steel buildings in Iran and the importance of rigid steel beam-to-column connections, which are among the vital components in this type of buildings, the need to better understand the behavior of these connections against earthquakes has been noted. Also due to the special characteristics of the near-field earthquakes, which is different than far-field earthquakes and it has its own characteristics; and the fact that some catastrophic earthquakes occurred in Iran, such as the Bam earthquake (2003) and the Tabas earthquake (1978) had the characteristics of the near-field earthquakes, which can show the importance of the near-field ground motions; the purpose of this study was to propose a loading protocol for special steel moment- resisting frames under near-field earthquakes for Iran. Therefore, first, by examining the earthquakes that have occurred in Iran during several years, near-field earthquakes have been selected. Steel buildings of 3, 5, 7, 9, 12 and 20 floors were designed and analyzed according to the rules and regulations of Iran, then for each of the designed steel buildings a critical frame was determined; the values of the scale factors are also specified. After performing nonlinear time‐history analysis and applying the proposed near-field ground motions to all of the critical frames, inter-story drift angles for all frames was obtained and compared. The third floor of the 3-story critical frame was selected as the critical floor; which is a story whose results will be used to construct a loading protocol; The basic rainflow counting and simplified rainflow counting were performed for the critical inter-story drift angles results; The proposed loading protocol are derived based on the MCE-level seismic hazard and 84th percentile values of key seismic demand parameters. These parameters are number of damaging cycles, maximum inter-story drift, sum of inter-story drift range, inter-story drift range and residual inter-story. The rationality of the proposed loading protocol was justified by showing the cumulative distribution function. The proposed loading protocol has 23 damage half-cycles, including 3 pulse half-cycles with inter-story drift ranges of 0.060, 0.100 and 0.078 radians; which are calculated by the basic rainflow counting method. The maximum inter-story drift was obtained 0.065 radians. In the final half cycle, the mean value is the same as the residual inter-story drift of 0.03 radians. Also, the sum of the inter-story drift ranges is equal to 0.684 radians. The proposed loading protocol was compared with the SAC near-field earthquake protocol, the maximum inter-story drifts in the proposed protocol is 0.065 radians and in the SAC protocol is 0.06 radians. Furthermore the pulse cycles in the proposed protocol have inter-story drift ranges equal to 0.060, 0.100 and 0.078 radians; while the three pulse half-cycles at the beginning of the SAC loading protocol have inter-story drifts of 0.08, 0.05 and 0.04; respectively. Therefore, the proposed loading protocol has a higher inter-story drift and stronger pulse cycles than the SAC near-field earthquake protocol; but the total number of cycles defined in the SAC protocol is greater than the proposed protocol.

Beam-column joints are one of the most important members of the reinforced concrete structures that are responsible for transferring existing loads. These joints require some criteria such as the development length of the beam's and column's rebars for proper operation. Lack of sufficient development length reduces the capacity of the structure and thus increases its deformation. In this study, three specimens of external reinforced concrete beam-column joints were tested on a real scale with applying lateral loads. The dimensions of beams and columns are 300 and 300 mm. Samples include a control sample with insufficient development length of longitudinal rebars of the beam (at joint area), a sample with sufficient development length through end mechanical restraint, and another sample with insufficient development length and retrofitting with dowel anchor carbon FRP composites (to improve the beam-Column joint). For making FRP anchors, columns should be pierced and dowels pass through this hole and they connect to concrete elements surface with proper epoxy adhesive. In all samples, lateral displacement load cycle diagrams (hysteresis diagram), failure modes, ductility coefficient, and stiffness were extracted and compared with each other. The results of this study showed that lack of sufficient development length leads to severe damage in the joint and plastic hinge is not formed, and energy dissipation and crack formation is occurring in the joint; while in retrofitted and restrained sample improvement of seismic performance, formation of the plastic joint in the beam and effects of sufficient development length is observed and energy dissipates in that area. Pinching in the hysteresis diagram of the control specimen is observed and maximum load capacity is much less than the others. end restraint of the rebar and reinforcement of the specimen with FRP increases the lateral bearing capacity of the joint by 53% compared to the control specimen. Also, the residual capacity increases by about 84% and 73% respectively at the end of the test (corresponding to 6% drift). The ductility of the sample with end restraint and the sample reinforced with dowel anchor FRP composites are 34% and 19% higher than the control sample, respectively. Insufficient development length also reduces the stiffness of the control sample by up to 45% compared to the restrained and retrofitted sample. Another result of insufficient development length of rebars of the beam is the angle between beam and column. In the fixed connections, this angle should remain constant while in the control specimen, this angle changes dramatically. By retrofitting the connection with FRP composites or restraining the rebars, this angle varies much less. The results of three tested samples showed that strengthening the connection with anchor dowel FRPs can effectively fix the lack of development length of rebars in the beams and increase the load capacity, stiffness, and ductility of the connection.

The problem of determining the prestressing force in the tendons of prestressed concrete structures and monitoring the non-exceedance of prestressing drops is an issue that has been addressed by many researchers over the past decades and has provided methods in this field. Today, pre-installation sensors are installed in important prestressed concrete structures to monitor prestressing loss. However, due to the unpredictability of such equipment in older structures, monitoring of these forces requires destructive or non-destructive testing but is inaccurate. Therefore, in this paper, a method is presented that without the need for these sensors and destructive tests, only by measuring static displacement, is able to detect the amount of prestressing loss in the cross-sectional tendons of a prestressed concrete beam. In this regard, an algorithm in the Python program environment based on genetic algorithm as well as modeling in the finite element analysis program is provided. The numerical example presented in this research shows that the proposed algorithm detects the values ​​of prestressing loss with good accuracy even in spite of 10% of the intentional error due to measurement. In recent years, the use of prestressing methods has become much simpler and more effective, and its materials have been optimized. Today, a high percentage of structures under construction worldwide are built using this technology, and the advance has found wide applications in the construction of office buildings, residential, commercial, parking lots, sports stadiums, concrete tanks and special structures such as piers. Therefore, in recent years, for long-term monitoring of prefabricated structures, equipment and sensors sensitive to force drop, such as fiber optic sensors and FBG sensors in the construction phase are predicted and installed in the desired locations. [13] However, since the above equipment requires a lot of money and it is not possible to use them in old structures, the need for a technique that shows the amount and location of force reduction in all tendons without using them remains. Therefore, in this paper, a method is presented that, while using the simplest tools, provides the most accurate results only by measuring static displacements under the effect of various loading scenarios and using an artificial intelligence algorithm based on genetic algorithm. The proposed method is based on computer analysis and comparison of the results of two prestressed concrete beams with the same geometry, loading and arrangement of tendons. First, a specific prestressing beam is modeled in the SAP2000 analysis program and the desired prestressing forces are applied to it, and then these forces are reduced in some of the studied tendons. This deliberate change in prestressing values ​​is considered as failure and the technique presented in this mapping tries to discover the extent and location of failure of this beam. In other words, this paper is the determination of the amount of prestressing force in prestressed concrete beams in which force measuring sensors are not predicted without the need for destructive testing and only by measuring the static displacement under load. In the form of a numerical example on a prestressed concrete beam consisting of 6 steel tendons and using a genetic algorithm, it was shown that the displacement is a function of the amount of prestressing and its location and amount of reduction by the technique used. It was correctly detected with 93% accuracy when 10% of the deliberate error due to displacement field measurement was applied. As a suggestion for future work, this research will be able to be developed in the simultaneous diagnosis of prestressing reduction and beam concrete failure.

Deep foundations are often used in a typical engineering project to transfer loads from heavy superstructures (bridges, highways, embankments and high-rise buildings) to the subsoil safely without subsidence or instability problems. In order to achieve an accurate and economical design in each of these projects, we must have a good understanding of how deep foundations behave, which can be done through analytical methods, numerical methods and experiments or experimental observations. Since a series of simplifications are usually performed in numerical and analytical methods, the use of experimental methods is selected to achieve a more desirable result. Experimental methods can be done by examining real models on site or performing experiments on a small-scale model in the laboratory (physical modeling), which due to lower cost, simplicity and reproducibility, usually physical modeling compared to Real on-site models are preferred. For physical modeling, various devices such as Simple Chamber (1 g), Calibration Chamber (CC) and centrifuge device can be used. The limitations and difficulties of these devices led to the recent introduction of a device called the Frustum Confining Vessel (FCV) for the physical modeling of deep foundations. In this device, which is in the form of an incomplete cone, by applying pressure to the bottom of the device, a linear stress gradient can be created along the central axis to be consistent with what is actually happening. Despite the many advantages that this device , it does not have a system for measuring the matric suction in unsaturated soils. Therefore, in this article, by embedding precision instruments in the sample made of this device in Amirkabir University of Technology (FCV-AUT) and implementing and loading of a pile in the soil inside it, It is possible to study the behavior of piles in unsaturated soil and the effect of moisture and matric suction on the load-displacement curve. The pile used in this research is an open-end pile which was implemented by driving method in Firoozkooh silty sand with gravimetric moisture contents of 0, 5, 10, 15 and 20% and in each case a load-displacement curve was drawn. The floor pressure applied in this research is equal to 100 kPa, Which was determined by placing several stress sensors at different soil depths and measuring the stress changes in depth. The following results were obtained after experiments: In the tested soil, up to 5% moisture content, no significant lateral friction is observed between the pile and the soil, and the end resistance, which is the result of plugging the soil inside the pile, provides most of the bearing capacity of the pile. From 5 to 15% moisture content, the lateral friction between the pile and the soil is gradually mobilized and while creating an initial jump in the curve of load-displacement, it increases the bearing capacity of the pile exponentially. But from 15% moisture content onwards, the initial slope decreases again due to the reduction of lateral friction. Considering the final bearing capacity of the pile as the load corresponding to 10% of the displacement of the pile head, the effect of matric suction on the changes of final bearing capacity was investigated. It was found that By increasing the amount of matric suction, first the final bearing capacity of the pile increases and after reaching a certain value, it decreases. The cause of this phenomenon is changes in wet soil behavior in different areas of the soil-water characteristic curve (SWCC) and is affected by various factors such as grain size, initial moisture content and soil density percentage.

The most important danger that threatens a petrochemical refinery is an explosion, which is followed by a fire or vice versa. In fact, the occurrence of initial events such as explosions and fires spread from one part to another like the domino effect if the distance between the storage tanks is not sufficiently considered. Therefore, the distance and arrangement of petrochemical storage tank can play an important role in reducing the damage of initial accidents. So far, due to the explosion uncertainties, no definitive solution has been offered, but a combination of active and passive techniques such as the efficient use of intelligence and security organizations, increasing the scaled distance between the detonation point and the target buildings or providing physical barriers, the use of deformable materials to absorb energy, and the use of appropriate retrofit structural techniques can reduce the effects of explosions. As it turns out, it is virtually impossible to study the propagation of blast waves experimentally on a large scale due to financial constraints and potential hazards. Therefore, to solve this problem, two solutions are proposed: the use of small-scale laboratory methods and the use of numerical methods. Three-dimensional numerical analysis is an efficient method for investigating structural weaknesses, hazard risk analysis, and evaluating of explosion hazard points. In this study, with the help of explosion simulation by Eulerian-Lagrangian coupling method, the research has been surveyed in two parts. In the first part, petrochemical tanks in different arrangements, and,at  different distances from each other are modeled in 3D on Autodyn software on the scale of  and the propagation of explosion waves and the confinement of 8g of TNT pressure in the environment between the tanks are investigated. In the second part, the effect of barrier shape on reducing the blast pressure of 1000 kg of TNT on a real scale has been investigated. The results show that the use of semi-empirical relation in UFC-0-340-02 to determine the blast pressure is applicable only to open environments, and it is not precise in closed environments due to the confinement of the blast pressure.  Moreover, the results show that it is not conservative to use the required distance between tanks considering the amounts proposed by the regulations. As a result, increasing the distance up to twice the amount proposed by the regulations, the effect of explosion pressure confinement is eliminated. The best way to position the tanks in this study is a zigzag pattern with a distance equal to twice the safe distance between the tanks in accordance with NFPA-30. In addition, the results show that by creating a barrier against the explosion, the explosion over-pressure can be greatly reduced, but the shape of the barrier does not have much effect. Although, using the Eulerian-Lagrangian coupling method requires considerable time and appropriate software to perform the calculations, it provides a comprehensive understanding of the blast wave interaction with structures. With the advancement of technology and the use of parallel processing in the cloud space, and the mapping technology it is possible to evaluate the different structures on a real scale against the explosion.

In this paper, a finite element analysis of the behavior of embedded CFST columns to the foundation under axial-lateral combined loading. First, the proposed finite element model is compared and analyzed by the experimental results of previous research, which showed that the local damage, failure patterns and hysteresis curves were consistent. A detailed parametric study to evaluate the cyclic behavior of embedded CFST columns to the foundation with the characteristics, the ration diameter to thickness, embedded length, compressive strength and connection conditions CFST column to the foundation. Based on the parametric study, the values of stiffness, strength, ductility and energy for the studied specimen have been calculated. The results showed that using the proposed finite element model, weak cyclic behavior for CFST connection to the foundation in the conditions of connection with the base plate and better cyclic behavior for the CFST column and its connection to the foundation in the embedded conditions is obtained. In addition, the hysteresis behavior of the CFST column connection with the embedded stiffener plate is much better than the embedded connection without the stiffener. The rings stiffener of the hysteresis diagram changes compact condition with increasing concrete strength. In addition, lateral strength, lateral stiffness, ductility performance and cumulative energy dissipation also increased in compact specimens with increasing confine concrete. The failure modes of the CFST connection to the foundation with the base plate are the same as the embedded connection mode without the stiffener and with the ring stiffener. The failure modes in these three modes are from the connection as a tearing steel pipe at the end of the column. In the case of an embedded connection with a longitudinal stiffener, it is a diagonal crack of the concrete on the foundation. Lateral strength, lateral stiffness, ductility performance, and cumulative energy also increase with increasing steel pipe thickness. CFST column burial conditions with hardeners have a positive effect on the hysteresis rings of CFST connection to the foundation, and this type of connection has been able to significantly improve lateral strength, lateral stiffness, ductility and dissipative cumulative dissipation energy.

In recent years, the use of nano-materials in different engineering and science projects has increased. The study of the impact of nano-materials in combination with other civil engineering constituents in different geotechnical and geo-environmental engineering projects is very common. This study is aimed to investigate the mechanism of cadmium retention in the process of cement based solidification/stabilization of cadmium contaminated bentonite in the presence of nano-silica. The mechanism of contaminant retention is investigated with the evaluation of cadmium and nano-silica behaviour with change in pH of the environment, adsorption, TCLP results, and evaluation of XRD experimental achievements. The bentonite sample for this research is taken from Iran-Barit Company. To establish the availability of silica ions for interaction with cement and bentonite at different pH, a series of solubility experiments of nano-silica at different pH levels were performed. The results of solubility experiments show that as the pH increases to the alkaline range, the solubility of nano-silica noticeably increases. This fact proves that at the high range of pH due to the use of cement, the required pH conditions for solubility of nano-silica will be provided. Therefore, there will be more possibility for the formation of CSH component. Cadmium nitrate was used to contaminate the bentonite sample for the experimental part. For this purpose, bentonite samples were mixed with 10, 30, and 50 cmol/kg-soil of cadmium nitrate in the electrolyte soil ratio of 20:1. Then, these samples were shaken for two hours in every 24 hours. This process was repeated for 96 hours. After this equilibrium step, the soil suspension was centrifuged. After drying these laboratory contaminated samples, they were solidified/stabilized with different percentages of cement and nano-silica. The results of this paper indicate that the contaminant adsorption and retention of cadmium by bentonite is less than that of adsorption for zinc and lead. The achieved results of TCLP experiments for solidified/stabilized samples with different percentages of cement indicate that the EPA criteria for TCLP experiment which emphasizes for test performance after 28 days, is not suitable for solidification and stabilization of cadmium. In fact, a longer period is necessary to achieve equilibrium and stable results. Furthermore, the results show that due to the low adsorption of cadmium by bentonite and due to the noticeable reduction of pH at the presence of cadmium ions, the required percentages of cement for solidification/stabilization of cadmium contaminated bentonite is much more than the required quantity of cement for other heavy metal contaminated bentonite samples. In addition, the results of XRD experiments show that the pozzolanic interaction process is more efficient in the presence of nano-silica. Furthermore, based on the results of TCLP experiments, the formation of CSH in the presence of nano-silica contributes to the contaminant retention by solidification/stabilization of cement based cadmium contaminated bentonite. Finally, according to the results of this study, in solidified/stabilized samples by mixtures of cement and nano-silica, it is shown that due to the contribution of silica ions in pozzolanic interactions, the solidification is the governing phenomenon for the prevention of heavy metal leachate from solidified/stabilized samples.

Numerical models are cost-effective solutions compared to field and laboratory tests that have the ability to predict the behavior of materials with acceptable accuracy if the exact properties of the material are taken into account. Another advantage of numerical models on the meso-scale is the ability to provide the interaction behavior of different components of inhomogeneous materials such as concrete, which is highly effective in predicting the behavior of concrete against dynamic loads. In order to model concrete at the meso-scale, a platform was created to create concrete samples considering aggregates, mortars, and fibers. The platform created in this research can produce elliptical aggregates according to the desired granulation curve in a completely random manner. By controlling the non-interference of aggregates next to each other stochastically placed within the mold boundaries and after determining the sample geometry and grid, The constructed model is converted into input text of numerical analysis programs. Compression and tensile loading are performed on it. Using numerical models, the effect of changes in these parameters was investigated: the volume ratio of aggregates in the sample, the allowable elongation of elliptical aggregates, whether or not to consider the ITZ element, and the use of fibers. In the performed analyzes, the maximum compressive strength and ductility of concrete and, in some cases, the crack propagation path have been investigated. Results show that considering both the maximum strength and the area under the stress-strain diagram; it can be concluded that among the percentages of aggregate volume ratios to the sample equal to 65, 70, 75, and 80%, the volume ratio of 75% to the optimal ratio to achieve the best compressive performance Concrete is closer. Comparison of the shape of the elliptical aggregates in the modeling showed that the closer the aggregate form is to the sphere, the maximum resistance increases, but the strength of the concrete decreases with a steeper slope after the peak.although the analysis of concrete samples at the meso-scale requires much higher computational costs than the macro analysis, this analysis can provide diagrams of tensile and compressive strength of concrete more accurately and also to test new samples with changes in the main parameters acceptable estimation of behavior. Provide concrete without the need to build a physical sample. Studies have shown that unstructured tetrahedron meshing provides graphs closer to empirical results. In analyses with unstructured mesh, mesh size has minimal effect on the results; In the case of models with a structured cubic mesh, the mesh size severely overshadows the analysis results. Suppose the appropriate size for uniform meshing is calibrated using the results of non-structured mesh samples. In that case, results close to the meshes of non-structured samples can be obtained with much less computational time and cost. Although considering the ITZ helps the stress-strain curve at the front of the peak to be closer to the laboratory graphs and also to predict the location of the crack more accurately than without modeling without ITZ, it causes a decrease in resistance at the rear of the peak and is predicted. This can be partially controlled by calibrating the ITZ resistance reduction value.

Due to the production and extensive use of oil and its derivatives, soil pollution with oil compounds is a challenging subject in todaychr('39')s world. In Iran and many other countries, the soil around oil exploration reservoirs, refineries, etc., has been polluted by oil pollution and may also pollute groundwater. The greatest concern and danger are when the oil contaminant reaches the groundwater aquifer, its solvent dissolves in the water and contaminates the environment with groundwater. Therefore, the importance of studying how the contamination moves and spreads in the soil is clear and valuable. The purpose of this study is to investigate the effect of an organic amendment such as municipal waste compost on behavior and emission of diesel as a light non-aqueous phase liquid (LNAPL) in the sand and to use an efficient model to predict the distribution of pollutants in mixed sand with compost. Also, the effect of grain parameters and rainfall intensity on the way of diesel emission into the sand without compost and the sand mixed with compost was investigated. In this regard, in this study, 30 cm long columns with a diameter of 2.4 cm made of Plexiglas were used to simulate a one-dimensional environment of transmission. Three types of sand with the particle size of 0.1-0.25mm (fine-grained sand), 0.2-0.5mm (medium-grained sand), and 0.5-1.0mm (coarse-grained sand), prepared and after decontamination was entered into columns. The columns were filled to a height of 24 cm with sand, and the top layer to a height of 4 cm was filled with a mixture of sand and compost with specified ratios. Then, half a layer of mixed sand and compost in each column was soaked in diesel at a concentration of 20 mg per 1 gr of the sand. The distilled water was entered into the column at three flow rates of 1, 0.5, and 0.25 mL/min (equal to the intensity of 13.27, 6.33, and 3.31 cm/h, respectively) to simulate the process of transfer of diesel into the columns. Laboratory data have been simulated using a UTCHEM numerical model. UTCHEM is a three-dimensional and multi-phase model that simulates the process of flow and chemical transfer in homogeneous and heterogeneous porous media. Increasing rainfall intensity and particle diameter have led to an increase in the flow rate of contamination within the sand and reduced contamination time. There are no significant changes were observed in the parameter of the dispersion coefficient by increasing the amount of compost. As the amount of compost in the sand has increased, the soil distribution coefficient and the retardation factor, which are the two effective parameters on the absorption of pollutants, have increased. As an example, by doubling the amount of compost at flow rates of 0.25, 0.5, and 1 mL/min, the retardation factor increased by 78, 100, and 80 percent, respectively. These values ​​for the mixture of medium sand and compost were 70, 79, and 71 percent, respectively, and in the mixture of coarse sand with compost were 76, 82, and 73 percent respectively. The amount of distribution coefficient has increased by 110% with doubling the amount of compost in all three types of sand. There is an exponential relationship between the intensity of the rainfall and the distribution coefficient in the mixture of fine-grained sand, medium-grained sand, and coarse-grained sand and three amounts of 5, 10, and 15 grams of compost. There is an exponential relationship between flow intensity and retardation factor for sand without compost and sand mixture and 5 grams of compost in a mixture of the three types of sand. In the case of mixing all three types of sand with 10 grams and 15 grams of compost, the linear relationship is the most accurate mathematical equation between flow intensity and retardation factor.

During the past years, researchers have developed ideas to thoroughly investigated into the behavior of structural bracing systems. Accordingly, one of these emerging systems is the Strong Back Bracing System (SBBS) by which the inter-storey drifts are maintained constant to prevent occurrence of failure. This system is comprised of the components of conventional concentrically braced frames together with a strong truss whose presence is aimed at uniform distribution of drifts along height of the building. This truss precludes concentration of damages in one or several stories in the concentrically braced frames. On the other hand, the near-filed earthquakes differ from the far-field ones in terms of both amplitude and frequency content. Thus, it is required to study the effects of such earthquakes on behavior of the SBBS. In addition to earthquake, the soil underlying the structure can affect the structural responses especially in cases when structure rests on soft soils. This system is comprised of the components of conventional concentrically braced frames together with a strong truss whose presence is aimed at uniform distribution of drifts along height of the building. This truss precludes concentration of damages in one or several stories in the concentrically braced frames. On the other hand, the near-filed earthquakes differ from the far-field ones in terms of both amplitude and frequency content. Thus, it is required to study the effects of such earthquakes on behavior of the SBBS. In addition to earthquake, the soil underlying the structure can affect the structural responses especially in cases when structure rests on soft soils. Typically, the codes provide methods for structural analysis assuming that the structure is located on a rigid base whereas in reality, this assumption does not always hold true highlighting the need for inclusion of soil-structure interaction into the analyses. Accordingly, this paper deals with seismic behavior of the structures equipped with the SBBS considering the soil-structure interaction under near and far-field earthquakes. In this respect, 3, 6 and 12-storey structures resting on stiff and loose soil (soil type II and IV according to classification of Standard 2800) have been analyzed. To this end, nonlinear time-history analyses using seven far and near-field earthquakes for both cases of rigid and flexible base, have been carried out. The results indicate that maximum roof displacement of 3, 6 and 12-storey structures founded on stiff soils (soil type II) vary insignificantly under the far and near-field earthquakes. Conversely, in the case of soft soils (soil type IV), displacements have increased by 2.93 to 18.22%. Moreover, it was found that drift ratios for the structures on stiff soil, in the case of 3 and 6-storey structures, increases slightly and reduced by 6.75% for the 12-storey structure. In the case of soft soil, all structures under the near-field motion, incurred increase in drift ratios by 11.67% and in the case of far-field, 3 and 6-storey structures experienced 4.86% decrease and conversely, the 12-storey structure encountered 7.7% increase. In addition, ratio of residual drift of the 3, 6 and 12-storey structures under average of near-field earthquakes, has decreased and increased by 8.52 and 36.02 in the case of stiff and soft soils, respectively.

A significant number of engineering structures around the world are exposed to fire on a daily basis. The most important effect of fire on the structure is elevated temperatures, which may reach more than 1000 degrees Celsius and cause not only thermal stresses and deformations but also diminished mechanical properties of materials comprising the structure. Fire-related collapses have been observed in numerous structural fires. However, many reinforced concrete structures exposed to fire do not demonstrate notable apparent damage and survive despite having experienced elevated temperatures before the fire is put out. Estimating the residual strength of such structures is of critical importance when deciding whether such structures can be safely used after fire. Moreover, in many industrial applications, there is a need to concrete that can withstand repeated long-term cycles of elevated temperatures without diminished mechanical properties. The objective of this paper is to investigate the effects of silica fume and fly ash as two widely used supplementary cementitious materials on the residual strength of concrete exposed to elevated temperatures and evaluate while such materials can be of benefit in improving the strength retention in case of heat exposure. Using 19 mix designs, a series of 570 concrete cylinders was fabricated using different water to cement ratios (0.35, 0.5, and 0.65), silica fume replacement ratios (0, 10, and 15 percent), and fly ash replacement ratios (0, 10, 20, and 30 percent). The specimens were cured in water for 56 days, after which they were placed in a rate-controlled large-scale electrical furnace, and their residual compressive and tensile strengths were measured before heat, and after heat exposure for 2-, 12-, and 24-hour heating cycles with temperatures reaching 200, 400, and 600 degrees Celsius. To eliminate the risk of explosive spalling, all specimens were preheated at a temperature of 100 degrees for 24 hours before the main heating cycle. Results showed that the compressive and tensile strengths did not reduce noticeably after exposure to 200 degrees but demonstrated a significant drop after exposure to 400- and 600-degree cycles. In many cases, the residual compressive and tensile strengths of specimens were found to be smaller than those predicted in previous studies. The square root equation widely used in the literature was found to provide a reasonable lower-bound estimate of the residual splitting tensile strength of concrete from the residual compressive strength; however, a linear trend was identified to provide a more accurate estimate for the results of this study. Moreover, due to less scatter, the splitting tensile strength was found to be a better indicator of heat damage in the structure than the compressive strength. The use of silica fume did not result in a meaningful trend in the residual compressive strength but reduced the residual tensile strength of specimens. Fly ash, on the other hand, could increase the residual compressive strength of the specimens but reduces the residual tensile strength. The results suggest that generally, and with few exceptions, these two supplementary cementitious materials are not recommendable choices for improving the strength retention of concrete in case of heat exposure.

Porous breakwater structures are widely used as protection against waves for ports and harbors as well as for general coastal protection. Often the breakwater structure is designed as a porous structure that allows water to flow through the structure while the wave energy is removed. These structures prevent coastal erosion and ensure safe and functioning harbors. As such, it is of high importance that these structures remain stable under extreme wave action. On the other hand, regarding the high complexity of wave interaction with porous structures, it is required to provide a rich understanding and conduct fundamental studies on the mechanism of rubble mound breakwaters subjected to incident waves. The existing literature review on wave interaction with rubble mound breakwaters reveals two mechanisms inside the porous media of such structures and outside the structure on the armor layer. Both could make destructive forces affecting the structure’s stability. In the present study, the stability of the multi-layer berm breakwater has been studied by considering the effect of run-up/run-down flow on the armor layer of a breakwater and, consequently, the flow inside the porous media as it gets filled and empty during wave run-up and run-down. Both numerical and experimental methods are used to investigate the flow inside and outside the multi-layer berm breakwater. Validation of numerical results is conducted through the use of experimental results, including the water level fluctuation outside the structure and also the water pressure variations inside the breakwater. The Flow-3D software has been used to simulate and solve the governing equations on the flow. FLOW-3D numerically integrates RANS (Reynolds Average Navier-Stokes) equations using the Volume of- Fluid (VOF) method to track the free surface. It has been thoroughly tested for coastal hydrodynamics problems. Various turbulence models are available, and the results presented here are based on the RNG turbulence model. The time series of pressure variation in the porous media indicates that as the flow infiltrates, the created pressure damping and also its variation at a constant elevation have been significantly decreased due to energy dissipation during the infiltration. Moreover, at the maximum run-down and exfiltration process, the created flow from inside to outside would be approximately perpendicular to the structure’s slope at about the maximum run-down elevation. Results reveal that the pressure gradient due to changes in the flow field of porous media would lead to a pressure force toward the outside during the run-down and a pressure force toward the inside during the run-up. It has been found that the positive pressure gradient force toward outside during the run-down and also the perpendicular force of flow during the exfiltration occurred simultaneously and acted as an active force to destabilize the stones. More to the destabilizing mechanism of stones, the effect of flows occurred during the run-up, and run-down on the armor layer have been investigated using the recorded images during the experimental tests.

Nowadays, performance evaluation of buildings against earthquakes is one of the common debates among researchers. Old buildings designed on the basis of previous versions of seismic codes are exposed to more damages in earthquakes. To evaluate vulnerability of existing buildings for earthquakes, Instruction on Rapid Earthquake Evaluation of the Existing Buildings (Code No. 364) has been proposed. By this code, a building can be rapidly evaluated by easily available data such as structural type, designing and construction date, appearance, etc., with very low cost. One of important parameters for such evaluation is the version of the seismic code (Standard 2800) which had been applied in the designing process of inspected building; later version has greater score.  However, the rapid evaluation code (Code No. 364) has been prepared before releasing version 4 of Standard-2800 and therefore do not have the score of designing with this version. Therefore, this paper is focused on comparing version-3 and vetsion-4 of Standard 2800 in designing buildings. For this, three buildings, having 3, 5 or 7 story, with regular plane is considered. Each is designed twice, based on the version-3 and vetsion-4  and then their fragility curves are calculated. The obtained fragility curves are compared in two levels of earthquakes having return period of 475 years and 2475 years (PGA of these earthquakes are assumed as 0.35g and 0.5g, respectively). To achieve the fragility curves, 50 earthquake records, recommended by FEMA-P695, are considered. They include 22 far field ones, 14 near field ones having pulse and 14 near field records without pulse. To consider nonlinear behavior of the structural elements, concentrated plasticity is assumed at two ends of each element by Opensees software. Properties of the plastic hinges are introduced in the software based on Lignos model. The obtained results show that in IO performance level, there is no meaningful difference between the structures designed on the basis of version 3 and version 4 of Standard-2800. However, in Life Safety (LS) and Collapse Prevention (CP) performance levels, version 4 leads to much better structure. Furthermore, the difference between these two versions of standard is greater for 475 year earthquakes, in comparison with 2475 year earthquakes, and also for LS rather than CP performance level.

Graphic Statics is a visual analysis and calculation method to find the type and amount of internal forces in structures, which achieves this importance away from computational difficulties and only with a geometric approach focused on two reciprocal diagrams of form and force. In this paper, arched trusses based on Warren type are analyzed using graphic statics. For this purpose, the parametric model of form and force diagrams were programmed in the Grasshopper parametric plugin. Parametrization has also provided the ability to find and analyze any different types of free-form trusses based on the type of warren truss. To measure the validity of the method and the accuracy of the algorithm written in the Grasshopper add-on, the numerical results obtained from several samples of arched trusses under different loads have been compared with the finite element computational method. The results of the validation simulations indicate the high accuracy and speed of the proposed algorithm.