Modares Civil Engineering journal
Year:2018 | Volume:19 | Issue:1 |Papers Count:18

Morning glory spillway is one of the most susceptible cases for the occurrence of the cavitation phenomena. At the entrance of the spillway, the junction location of the funnel entrance, the vertical shaft and within the elbow, cavitation is expected. In the present study, the flow characteristics included the inlet and outlet discharge and the velocity and pressure close to the elbow walls were calculated for Alborz dam spillway by using of Flow3D software and the results were compared with the experimental data. The experimental data has been presented by water research institude. The VOF method was used to simulate the flow surface and the RNG turbulence model was used for flow turbulence simulation. The comparison of the numerical model results and the experimental data showed the good agreement between them. Also, the occurrence probability of the cavitation in various parts of the morning glory spillway was investigated using of the cavitation index. The results showed, the maximum pressure head in different discharges and for different elbow radius, have been located in median of piezometer in the bottem of elbow. Therefore, the cavitation index for these areas is more than the other points. The points of the entry to the elbow and the end points are the most probable points for the probability of the occurrence of the cavitation due to geometric changes that cause the change of direction to flow. As a result, it is suggested that, if possible, the curvature changes in the entrance area from the vertical shaft to the elbow and also from the elbow to the horizontal tunnel gradually. In different discharge and different radius of the elbow, the cavitation index for bottem of the elbow will increase as a result of dynamic impacts on the bottem of the elbow, but the cavitation index, toward to the end of the curvature, will be lower due to the contraction end of the cross section. The results showed that radius change of the elbow due to considerable effect on the flow field, has the significant effect on the occurrence probability of the cavitation. The radius change of the elbow has the different results for the submerged flow and free surface regimes. In the free flow regime, by increasing the radius of the elbow, the occurrence probability of the cavitation will increase, and in the submerged flow regime, by increasing the radius of the elbow, the occurrence probability of the cavitation will decrease. It was also determined that in the free flow regime, the momentum is the dominant mechanism and in the submerged flow regime, the energy parameter is the dominant mechanism. Also, increasing the radius of the elbow will improve the performance of the elbow roof in terms of the cavitation phenomenon. Consequently, it is suggested, as usually morning glory spillway is designed for the free flow regime, this spillway to be designed with a smaller radius. Also, by increasing of the discharge in these spillways, the cavitation index increases and the occurrence probability of the cavitation decreases.

Today, most seismic design codes reduce the lateral elastic force by the behavior factor to design structures, so that by designing a structure based on elastic analysis, the effects of non-elastic behavior of the structure are applied. To obtain a behavior factor of structures, a nonlinear analysis is necessary. Research has shown that the nonlinear behavior of RC members depends on factors such as the effect of varying axial load, the effect of shear failure of the members and the effect of the buckling of the longitudinal bars. It is now generally accepted that axial load plays a dominant role in evaluating the seismic behavior of reinforced concrete columns. However columns, especially the exterior ones, can be subjected to varying axial loads depending on the lateral loads. Also the effects of shear on beams and columns are usually neglected in nonlinear analysis, which is carried out based on the flexural behavior of each element. In this research, the behavior factor of 2, 4, and 8 story reinforced concrete frames with intermediate and special ductility based on the proposed nonlinear analysis is considered. Initially, for verification, the proposed nonlinear analysis model was compared with existing experimental models. The verification results show that the proposed model has a very high accuracy. Designing and detailing of the 2, 4 and 8 story reinforced concrete structures are on the basis of the regulation of the Standard 2800 and the National building regulation chapter 9. In order to obtain the behavior of the 2, 4, and 8 story reinforced concrete frames, the effect of varying axial load, shear failure of the members and the buckling of the longitudinal bars are considered in nonlinear analysis. The behavior factor is mostly effected by ductility factor and over strength factor. The ductility factor has dependence with ductility of the reinforced concrete frames. To obtain ductility of reinforced concrete frames, ultimate deformation is needed. To calculate the frames' behavior factor, various criteria are used to calculate the ultimate deformation of frames. One of the criteria is the deformation correspond to the 0. 75 percent of ultimate rotation in critical structure member. The other criteria is the deformation correspond to ultimate rotation of critical structure member. The results of the study and comparison of the obtained behavior factor with the proposed behavior factor of the reinforced concrete structures of Standard 2800 with intermediate and special ductility have shown that the calculated behavior factor for 2, 4 and 8 story reinforced concrete frames is bigger than the behavior factor in Standard 2800. Also the results indicate that the calculated behavior factor with the ultimate deformation correspond to the 75 percent of ultimate rotation in critical structure member is close to the proposed value of Standard 2800. In intermediate reinforced concrete frames, the amount of ductility factor and over strength factor decreased when the height of the reinforced concrete frames raised, which is not seen in concrete frames with special ductility.

Background and Purpose: Instability of slopes leading to roads in steep mountainous areas is a major problem in the development of roads worldwide, causing excessive human as well as financial losses. Soil nailing is one way of in-situ soil reinforcement. The behavior of a reinforced soil system depends on different parameters including geometry of the structure, mechanical characteristics of the soil, density of the reinforcing material, and length of the soil reinforcing material as well as the angle it makes with the failure plane. Though much research has been conducted on earth slope stability, few studies have examined the effect on slope stability of the soil nailing angle and tensile force distribution along the nail. In spite of the extensive studies conducted on slope stability, no specific insight has been obtained so far on the effect of the failure plane or soil nailing angle on the tensile force distribution along the nails. In view of these facts, this study aims to examine the effect of nail angle as well as nail length on the nail safety factor with due consideration of the effect of shear strain distribution on slope stability. Selecting the slope leading to Ilam-Salehabad Road in western Iran as our case study, we studied the stability of this slope at different nail lengths and angles. Methodology: The slope leading to Ilam-Saalehabad Road (after the Karbala Road tunnel) was selected as the case study. To determine the mechanical parameters of the soil, we provided soil samples from the slope site and tested them at the laboratory in accordance with ASTM code to obtain the required soil characteristics. The powerful geotechnical software FLAC2 was subsequently used for modeling the slope leading to the road. Upon completion of analysis, we compared the settlement obtained from the software at two points on the earth slope with similar measurements obtained from the instruments, and observed a good agreement between them, with an approximate maximum error of 3%. In the following, the effect of soil nailing angle (with the horizontal line) as well as the length of the nail on the nail safety factor and nail tensile force is discussed. Discussion and Conclusion: Our results showed that increasing the soil nailing angle (i. e., nail driving angle defined as the angle between the soil nail and the horizontal line) from 0 to 30 degrees would increase the nail safety factor by about 23%. Thereafter, increasing the nail driving angle from 30 to 45 would cause a reduction of 2. 8% in the safety factor. A further increase of nail angle (with the horizon) caused a corresponding increase in the tensile force induced in the nails, so that the maximum tensile force at 30 degrees increased by about 6%. The maximum nail driving angle efficiency was observed at the points undergoing maximum shear strain: increasing the drive angle to 30 degrees led to a 10-fold increase in the tensile force developed in the nails at points with maximum shear strains. On the other hand, increasing the nail length increased nail safety factor, so that increasing the nail length by 1 meter would increase nail safety factor by 4. 3%. However, increasing the nail length beyond 1 meter reduced the rate of increase of the safety factor. Accordingly, the optimum length increase in the nails was taken as 1 meter.

At about 8. 00 am of 20th December 2015, a fire started in a shop in Plasco building, located in center of Tehran, which at the end resulted in catastrophic collapse of the building and claimed the lives of 22 fire fighters and other people. According to the findings of the investigations, the main reason of ignition was non-permitted extension of cablings in the shop of the scene; for use of electrical heating devices. Plasco building was constructed before compiling of national building codes of Iran; hence fire safety rules were not properly implemented in the design of the building. In the other hand, the national building codes of Iran consists only the requirements for the new buildings and approximately no regulation has been pointed there for existing buildings. The incident was an alarm to the general public and accounted organizations that there might be many other buildings like Plasco in the large cities, which are threatening the safety of the users and the city. Therefore a national committee was appointed to investigate the different aspects of the incident and offers the solutions and measures which should be taken to prevent the similar experiences in the future. The fire safety problems of the building were investigated. Some important shortages were as follows: high fire load in the building, especially because of high content of flammable textiles and clothes, open stairways without a protected shaft, open connection between false ceilings of all shops and corridors in the stories, lack of fire resistant shafts of mechanical installations between floors, lack of fire protection of steel structure, lack of any fire detection and automatic sprinkler in the building. The existing hose-reels didn’ t have a regular maintenance and hence they could not be properly used by fire fighting forces. The Plasco was collapsed after about three and half hours of the ignition. Therefore the question was arisen how was the scenario of the fire growth and temperature rise in the building. Different tests were carried out on the sample materials taken from the debris of the building. The place of the building and depot of debris was visited by different special teams. Steel, concrete and other materials, which some of them were molten due to high temperature, was taken for further experimental works. Physical, mechanical, XRD/XRF, petrography and other tests have been carried out, from them only heat release test is discussing in this paper. The results showed high amount of HRR of the burned textile specimen. There were more than 580 mercantile units in Plasco, which most of them were clothing shops or related works. This high content of the textiles and clothing created a high fuel load in the building. A fire modeling was carried out using FDS software and showed how the flames could be raised through windows, shafts and stairways to upper floors. The temperature rise was also investigated by the model. The results showed that the temperature rise, especially in floors 10 and 11 was suit for collapse of structural elements which was widely discussed in report of structure committee.

A gravity dam is a dam constructed from concrete or stone masonry and designed to hold back water by primarily using the weight of the material alone to resist the horizontal pressure of water pushing against it. Gravity dams are designed so that each section of the dam is stable, independent of any other dam section. Gravity dams generally require stiff rock foundations of high bearing strength (slightly weathered to fresh); although they have been built on soil foundations in rare cases. The bearing strength of the foundation limits the allowable position of the resultant which influences the overall stability. Also, the stiff nature of the gravity dam structure is unforgiving to differential foundation settlement; which can induce cracking of the dam structure. Gravity dams provide some advantages over embankment dams. The main advantage being that they can tolerate minor over-topping flows as the concrete is resistant to scouring. Large over-topping flows are still a problem, as they can scour the foundations if not accounted for in the design. A disadvantage of gravity dams is that due to their large footprint, they are susceptible to uplift pressures which act as a de-stabilising force. Uplift pressures (buoyancy) can be reduced by internal and foundation drainage systems which reduces the pressures. During construction, the setting concrete produces a exothermic reaction. This heat expands the plastic concrete and can take up to several decades to cool. When cooling, the concrete is in a stiff state and is susceptible to cracking. The increasing need for clean water and energy resources for human societies has led them to optimize the old technologies with the best in research and studies to make the most of them. One of these inventions is dams, structures that are created on the rivers. In the past, the creation of dams was generally aimed at providing drinking water and irrigation of farms, but nowadays it is not only a source of water, but also electric energy. In many studies, dynamic analysis is used to assess the vulnerability and damage damages during an earthquake. Despite the precision of this method, there are many uncertainties in the analysis stages that make the study costly and prolonged. Therefore, using nonlinear static analysis method, researchers increased the speed of analysis and reduced costs. Pushover analysis is a simplified nonlinear analysis technique that can be used to estimate the dynamic demands imposed on a structure under earthquake excitations. It is a static-nonlinear analysis method where a structure is subjected to gravity loading and a monotonic displacement-controlled lateral load pattern which continuously increases through elastic and inelastic behavior until an ultimate condition is reached. Lateral load may represent the range of base shear induced by earthquake loading, and its configuration may be proportional to the distribution of mass along building height, mode shapes, or another practical means. The purpose of this study is to investigate the seismic performance of concrete gravity dams using nonlinear static analysis (pushover analysis). For this purpose, load patterns used in the pushover analysis are applied in both directions upstream and downstream of the dam structure. Observations show that, apart from the rectangular load pattern, all load patterns used in this research can adequately correlate Detect the crack in the dam body correctly.

The efficiency of the RC core system in buildings that are taller than 35 to 40 story is modestly reduced. In these structures, connecting two towers with a bridge can be considered as one of the solutions for controlling displacement and also energy dissipation. This paper examines the types of energy needs in high-rise buildings of 40 and 60 floors, each of which has two reinforced concrete core of the same height with a truss bridge. The trusses of the bridge are made by buckling restrained elements. Initially, this structure is designed using the response spectrum analysis method according to the valid codes. This paper examines the types of energy needs in high-rise buildings of 40 and 60 floors, each of which has two reinforced concrete core of the same height with a truss bridge. The trusses of the bridge are made by buckling restrained elements. Initially, this structure is designed using the response spectrum analysis method according to the valid codes. Then, by constructing a non-linear model of the structure in the PERFORM-3D software and performing a time history analysis subjected to the near and far fault ground motions, kinetic energy, input energy, damping energy, and non-elastic energy are studied, and the contribution of the wall and bridge is studied in energy dissipation. Single plastic hinge and extended plastic hinge approaches are considered for the core. In a single plastic hinge approach, only a plastic joint is allowed at the bottom of the RC core, and the rest of the RC core regions are elastic, and nonlinear time histories analysis is done. In an extended plastic hinge approach, the entire core has the ability to expand plasticity. On average, in extended plastic hinge approach the core share is about 48%, and the share of the bridge with buckling restrained members is about 52% in term of non-elastic energy, and these values are 34% and 66% in the single plastic hinge approach. Then, by constructing a non-linear model of the structure in the PERFORM-3D software and performing a time history analysis subjected to the near and far fault ground motions, kinetic energy, input energy, damping energy, and non-elastic energy are studied, and the contribution of the wall and bridge is studied in energy dissipation. Single plastic hinge and extended plastic hinge approaches are considered for the core. In a single plastic hinge approach, only a plastic joint is allowed at the bottom of the RC core, and the rest of the RC core regions are elastic, and nonlinear time histories analysis is done. In an extended plastic hinge approach, the entire core has the ability to expand plasticity. On average, in extended plastic hinge approach the core share is about 48%, and the share of the bridge with buckling restrained members is about 52% in term of non-elastic energy, and these values are 34% and 66% in the single plastic hinge approach. Studied structures, connecting two towers with a bridge can be as one of the solutions for controlling displacement and also energy dissipation.

Side channel spillways are widely used in dam outlet works for irrigation and drainage networks; and also in water and wastewater facilities. A special type of these spillways is the Three-sided channel spillway in which the flow enters the side channel through both the end and sides of the spillway. There is a variety of names for these spillways, including bathtub spillways, U-shaped spillways, and duckbill spillways. Those are used in situations where a spillway with a long crest is required. In Three-side spillways, the flow enters through a U-shaped weir (in plan) into the side channel that serves to deliver water downstream. The flow in the side channel is a spatially varied flow with increasing discharge and is especially designed with a nonprismatic cross section (increasing bed width along the flow direction) to avoid channel flow effects on influent flows. Several studies have been carried out to gain a clear understanding of the effective factors and the relations dominating the flow in one-sided channels. Few studies have been done on hydraulic performance of Three-sided channel spillways, however, most studies have only focused on specific applications of the situations of these spillways and have aimed at improving the hydraulic performance of flow. Also, in some studies, determining the optimized values of three design parameters; including side channel bed slope, the appropriate elevation, and shape of the end sill for the spillways were investigated and concluded that the effective crest length for two-sided, L-shaped spillways, taking into account the effect of each of the corners of the spillway on reducing crest length. In this study, the three-dimensional flow filed of U-shaped spillway and end-sill of the side channel are simulated using Flow3D and the effect of flow turbulences have been modelled by RNG closure. Comparison of the numerical and experimental results revealed that this model with RNG closure has capable to carefully simulate the turbulence flow field on these structures. The effect of making stepped the ogee profile of the three-sided spillway on flow depth and dynamic pressure fluctuations has been numerically evaluated; the non-dimensional turbulence index has been used to investigate the fluctuations of the dynamic pressure. The results revealed making stepped the ogee profile causes to reduce the encounter of the side overfalls, and to increase the flow depth in the side channel, in which this lead to considerable decrease in pressure fluctuation intensity. Also the results showed that it is better this type of spillways to be designed in low-flow heads, so as to raise discharge. Using long sideling lateral arms will have a positive effect on the discharge coefficient. Finally, in these spillways the flow from their lateral channel is discharged with delay and in high flow rates is immediately submerged due to severe interference of dropping layers of flow. The area that experiences the most reduction in effective length of the spillway is the part that two side arms and the normal part (perpendicular to the central axis of the side channels) are linked together. By reducing this area and having a short connection between them, the effective length reduction can be reduced.

The dynamic response of the double-layer girds (a kind of space trusses) can be determined by means of the software based on the finite element method. However, it is always needed the approximate techniques by which one can easily and quickly obtain the suitable estimation of the dynamic behavior of the structures. This need may be caused by: 1-providing an appropriate estimation in the first stage of designing the members, and 2-verification of the results of the computer programs. In this study, an approximate method is suggested for seismic analyses of the double-layer grids with the spatial square on square layout, the square or rectangular plan and simple supports around the structure. The method is on the basis of the simulation of double-layer grid to the equivalent beam and plate. Here, the smallest circular frequency of the vertical vibration is computed by using Rayleigh’ s method. In addition, the seismic forces caused by the vertical acceleration of the earthquake are evaluated by employing the equations of the dynamics of the structures and estimating the shape function of the first mode of the vertical vibration. There are the deflections of the structural nodes in the achieved equation for estimating the circular frequency; therefore, an initial estimation for the sizes of the members of the double-layer gird is required. In fact, since the weight of the structure should be considered in evaluating the applied loads, an approximate design must be performed. For this purpose, a step by step technique is suggested based on the AISC Specification to initially design the structure. In addition, the assessment of the deflection of the double-layer girds is done based on the uniformly distributed loads and non-uniformly distributed loads. Finally, to assess the suggested approximate method, 21 models of the double-layer grids with the spatial square on square layout are considered. These models have the horizontal and diagonal (web) members with the equal lengths. The supports of the double-layer girds are simple. The bays have 30 to 60 m with the step of 5 m and the number of 10, 12 and 14 horizontal members along the span. In order to analyze and design the models, the members are considered to be connected to each other as bending free connections. The spectrum analysis is done to take into account the seismic effects. Also, SAP2000 is used to analyze and design the models in question, and the results achieved by this software are considered as exact outcomes. On the other hand, the models are analyze by the suggested approximate method and the obtained results including frequencies, seismic vertical forces of the members of the models are compared with the exact outcomes in diagrams. The findings show that the proposed method can be evaluated the dynamic properties of the double-layer girds with a suitable precision which prove the robustness of the derived scheme. In fact, the maximum error in estimating the frequency is about 15%, and 12% if it is considered the variation of the weight of the double-layer girds and if it is not considered, respectively. Furthermore, the comparison of the achieved forces of the members between the exact and approximate results is revealed that the maximum error is about 11%, which is a good estimation for an approximate method.

The development of underground spaces and its benefits encompass all sectors of society. Because of its enclosed space, the safety of traffic passing through urban tunnels is very important. Recent years of statistical progress in accident modeling, including regression analysis with generalized linear models and generalized additive models, considered a new approach to identifying more complex relationships between independent and dependent variables. Despite the high frequency of tunnel crashes, lower than open roads, such as highways and freeways, research has shown that tunnel crashes are more severe. The purpose of this study was to use the Generalized Model as a non-parametric approach to identify traffic factors affecting accident frequency in urban tunnel access and input areas and a parametric approach is to compare results with the generalized linear model. For this purpose, the accident data was received from the Tehran City Tunnel Control and Management Center during the three consecutive years (2010 to 2012) along with traffic data. There are teleservice systems and video surveillance in tunnel traffic systems. The traffic system is used to collect information and traffic parameters from tunnel entry level, such as: velocity and occupancy rate, and video surveillance system, to manage traffic flow and record events, including accidents occurring inside the tunnel. Data in this paper including records of 1047 accidents in the tunnel's access and entry areas. Traffic volume, heavy vehicle percentage and speed deviation from the speed limit of the highway as the independent variables were selected. Based on the results of the generalized linear model, the linear effect of daily traffic volume, percentage of heavy vehicles and daily average speed deviation from speed limit was reported Meaningful in crash model frequency. However, the three-degree and first-order relationship for the heavy vehicle percent and daily average speed deviation was confirmed by the frequency of accidents using the generalized model, in addition to the significance of the daily volume logarithm. The result of comparing generalized and generalized linear model using a good fit criterion and Akaic criterion shows that the generalized additive model is better suited to estimating the frequency of accidents dependent variable. A generalized additive model of superiority of this model was shown by the higher fitting coefficient (0. 99) and lower Akaic information criterion (3823) compared to the generalized linear model. Drivers at high speed approaching the tunnel are at higher risk of collisions. The velocity fluctuations generated when entering tunnels to adapt to tunnel environmental conditions, such as lighting conditions, may be one of the factors that adversely affect traffic safety when passing through the tunnel. One accident is often expected with the increase in traffic volume and the percentage of trucks, but this proposition is not true for all situations. With the increase in the percentage of heavy vehicle in free flow conditions, the frequency and repetition of lane changing and overtaking increase, which could be one of the reasons for the increase in accidents compared with almost dense traffic conditions.

Current design philosophy for conventional lateral resisting systems is that the frames should not collapse during major earthquakes, however significant structural damage in elements such as beams, braces and sometimes columns may occur. The presence of residual drift due to inelastic deformations may hinder building occupancy or functionality after major earthquakes, and may increase associated repair costs significantly. During last two decades, practicing engineers and researchers have tried to develop seismic resisting systems that can minimize and potentially eliminate residual drift due to earthquakes. Proposed structural systems utilize the so-called “ self-centering” systems that can improve the seismic behavior, provide higher resiliency and overcome the significant residual drift of conventional systems. Self-centering (SC) seismic resistant systems, introduced in the literature are developed for both steel and concrete structures. For the steel structures, they may be categorized into three primary groups: SC moment frames, SC rocking systems and SC braced frames. The most important similarity between self-centering systems is that the lateral load resistance of the system has a flag-shaped hysteretic loop. That is the characteristic of systems that self-center after large lateral displacements. Considering the normal practices of construction industry in Iran, it is more feasible and favorable to use metal yielding dampers instead of viscous or friction dampers. Also considering the economic issues, self-centering mechanisms which use pretension tendons are more feasible compared to shape memory alloys. A yielding metallic damper called comb-teeth damper (CTD) provides energy dissipation mechanism. CTD is made of steel plates and includes a number of teeth that dissipate energy through in-plane flexural yielding. The new self centering brace (SCB) can substitute the conventional braces to provide desired seismic performance and to reduce residual deformations and repair costs. The proposed brace can be easily disassembled in the field which provides the possibility of inspection of the core after a large earthquake. Parameters of this system should be selected so that they can provide appropriate stiffness, strength and energy dissipating capacity. In this paper, initially the overall mechanical behavior of the device has been defined in terms of its internal components, based on an analytical approach. The mechanical equations for the SCB were decomposed into two portions, which are the pretension tendons that cause the self-centering behavior and the CTD links that support the energy dissipation mechanism. Also finite element analysis has been conducted to verify the hysteretic responses and mechanics of the proposed SCB. Based on the results, the characteristics of finite element responses have good similarity with the analytical results and show that either of the approaches are reasonable to predict the SCB behavior. Then a parametric finite element analysis has been conducted by varying the mechanical properties of steel elements to optimize the properties of the system. The results show that the desired self centering and energy dissipating capacities would be achieved using the new SCB. Lastly, nonlinear time history analyses have been performed to investigate the characteristics of some 6 story steel buildings equipped with the new SCBs. The results confirm the feasibility of using the new SCBs in braced frame structures.

In crowded cities, building structures are usually constructed in close proximity to one another because of restricted availability of space. In many cases, every building in a block is in full or partial contact with its neighboring buildings. Because of insufficient separations, their different heights and seismic-resisting systems collision can occur between adjacent buildings during strong ground motions. This collision can make partial or general damages to the structural elements and accelerate their failure by affecting their stiffness. This phenomenon is commonly referred to as structural pounding. Pounding between inadequately separated buildings has been observed in most previous major earthquakes. Each time pounding occurs, building structures will sustain short duration large impact force not specifically considered in conventional designs. The severity of the impact depends on the dynamic characteristics of the adjacent buildings in combination with the earthquake characteristics. options to minimize the effect of pounding have to do with the decreasing of lateral motion by joining adjacent buildings at critical positions so that their motion could be in-phase or by increasing the damping capacity of building pounding by means of energy dissipation, for example, by passive structural control systems. Modern seismic design codes have many pioneering provisions on the non-linear behavior of structures, but amongst others, they do not consider structural pounding, a phenomenon with strong non-linearities, for which codes usually suggest a sufficient separation between adjacent buildings. On the one hand, irregularity in lateral stiffness (a soft or very soft story) due to the different use of the first floor of the building is one of the most common types of irregularity. Aiming to prevent such collisions, these study estimates demand of separation gap angle at the highest level of collision between two adjacent structures in regular steel moment frames with irregularity in the lateral stiffness (with changes in the height of the first floor) under seismic records of a near-field earthquake. Models were considered as two-dimensional, ductile, steel moment frames of 2, 4, 6, 8, 10, 12, 14, 16, 18, and 20-story 3-span buildings. In order to create an irregularity in the lateral stiffness on the first floor, the height of this story was increased from 3. 5 m to 4. 5 and 5. 5 m while the cross-section of the column at the first two stories was kept unchanged. These frames can be placed alongside in seven binary groups considering priority in the arrangement. Each group represents 100 different binary arrangements of the frames. In total, 700 cases of various adjacency were studied. The OPENSEES software was used to analyze the dynamics of the nonlinear history considering 20 perpendicular components to the fault with a progressive orientation of near-field earthquake records of pulse-like faults. The results suggest the increase in the irregularity in the lateral stiffness in the first floor of the building can increase the separation gap angle. On average, the combination of regular and irregular frames with the first-floor height of 4. 5 and 5. 5 m, is increased 1. 19 and 1. 38 times, respectively, compared to the combinations of regular frames. Moreover, among various adjacent combinations of regular and irregular frames, in case the taller structure is associated with lateral stiffness (soft floor), the average increase in the separation gap angle is larger than other cases.

In the present study, discrete element method is used to simulate undrained two-dimensional behavior of polygonal particles in which, the cylinder method is used. By this method, pore pressure of the voids in a sample can be studied independently. In the cylinder method, it is assumed that there are channels among adjacent pores and the possibility of water exchange among the centers of the pores is provided. The pipes connect the adjacent pores center. Therefore, the pipe length is equal to the center distance of two adjacent pores. The diameter of all pipes is identical which represents the permeability of the soil. First, by using this method, the variations of average pore pressure versus deviatoric strain and pore pressure distribution contour in a sample with polygonal particles were compared with another study with elliptical particles that showed good conformity. The constant volume method was also used to simulate the undrained behavior of the sample and the results of both methods were compared. In the constant volume method, it is assumed that the sample volume stays constant during loading. The simulation was done for samples by two methods. These samples were subjected to confining pressure of 200 kPa and after consolidation, were loaded under deviatoric stress. The results showed that the output obtained by the cylinder method are in good agreement with the constant volume method and by increasing the stiffness of the water, the results of both methods containing the variations of the deviatoric stress and the pore pressure are closer to each other. In following, the undrained behavior was investigated by using cylinder method in terms of shear strength and pore water pressure in a sandy sample at the confining pressures of 200, 400, 800 and 1600 kPa. The Simulation results are in good agreement with laboratory results in such a way that more confining pressure, the shear strength and pore pressure are more positive, but by increasing confining pressure, the amount of pore pressure decreases in the specimen. The pore pressure distribution contour at the strains of 10% and 30% was presented by means of cylinder method and the effect of cylinder diameter changes on the pore pressure distribution contour was investigated. Investigating the pore pressure distribution contour at the strains of 10% and 30% showed that pore pressure in the sample center has the lowest value. The pore pressure in the sample pores closes by increasing the cylinder diameter, while the smaller the diameter of the cylinder, the greater the water pressure difference among the pores. At last, the effect of pore position on the pore pressure was studied. For this purpose, four positions were considered through the sample and the variations of the average pore pressure versus axial strain at three pipe diameters of 40, 200 and 450 micrometers were investigated. The results showed that the pressure of the whole sample pores get closer by increasing the pipe diameter. As the pipe diameter decreased, the pressure difference between the sample pores gets higher and this difference will be greater in the larger strains.

Removal of petroleum hydrocarbons from soil using electrokinetic method or biological processes has been considered in recent century. The most limiting factors in the electrokinetic process are extreme changes in pH around the electrodes and non-polarity of some pollutants. On the other hand, the key factor of biological treatment is simultaneous presence of microorganisms, pollutants, electron acceptors, and essential nutrients for microorganisms’ growth. But in fine-grained soils with low permeability, it is difficult to uniformly distribute bacteria, electron acceptors and nutrients, or making pollutants available for microorganisms. To solve these problems, bioelectrokinetic method is used to eliminate the limitations of both biological and electrokinetic processes in treatment of fine-grained soil contaminated with organic compounds. The aim of this study is determining the equations and conditions governing on bioelectrokinetic process in removal of crude oil from clayey soil. For this reason, the numerical method of FTCS finite-difference was applied for modeling the pollutant biodegradation and transmission in clayey soil under electric field. In order to develop and validate the model, the first step was to set up a bioelectrokinetic system in a laboratory scale. In this study, each test was conducted in cylindrical cell made of Plexiglas with the length and diameter equal to 55 and 5 cm respectively, for 35 days. They were performed in various conditions of pollution amount and electric field intensity in the presence of Pseudomonas putida strain. Experimental results showed the removal efficiency was obtained about 34% in minimum voltage gradient (1. 25 V/cm) and initial concentration of oil (4000mg/kg). While, increasing the voltage gradient and oil initial concentration respectively to 1. 5 V/cm and 10000 mg/kg could remove about 48% of pollutant. After determining and combining the governing equations on the electrokinetic and biodegradation system, the numerical solution of the equation was coded using Mat-lab software. In suggested mathematical model, the parameters like initial concentration of crude oil, voltage gradient, time step and spatial step were assumed as variables and parameters related to reactor, soil and pollutant such as the length of reactor, soil porosity and tortuosity, ion mobility, diffusion coefficient and electroosmosis permeability coefficient were considered as constants. In continue, by comparison the result of numerical solution of the suggested model with the experimental results, the same trend was observed in changes in crude oil concentration between the two. Because of differences between the model results and laboratory data and to make more accordance between the two, the modifying factor was used as the factor of microorganism transfer under electric field. In this way, a better accordance between them was observed and this difference reduced to minimum. Modeling results showed that electroosmosis, diffusion and electromigration mechanisms, unlike biodegradation, had little impact on the transmission and removal of crude oil from soil. According to the numerical solution, similar to bioelectrokinetic data, increasing the initial concentration of crude oil and voltage gradient caused the increase in removal efficiency of crude oil. In addition, the model has been able to predict the residual crude oil concentration after bioelectrokinetic treatment with a good accordance.

The unexpected increase in the price of bitumen and production capacity of cement have provided the tendency to replace Asphalt pavements with concrete. Considering the high cost of material supply and the implementation of pavement and despite the limitations of construction credits, there must be serious thought and comprehensive planning to improve the quality and increase the durability of pavement roads, which will consequently reduce maintenance costs. One of the most important breakdown of concrete pavement is cracking. Also one of the most widely used building materials, concrete has a brittle behavior. Adding fibers to concrete affect its tensile strength ductility behavior, flexural strength, elastic modulus, impact resistance as well as some mechanical properties. Fiber-reinforced concrete is a type of concrete that is mixed with fiber. Various types of fibers are used to produce fiber-reinforced concrete, which include glass, polymer, carbon and steel. In the present research, macro-synthetic polymer fibers with twisted shape were used. According to the past studies Some of the consequences of applying macro-synthetic fibers in concrete include reduced shrinkage of fresh and hardened concrete, increased ductility, increased strength against fatigue stresses, increased durability and lifetime of concrete, improved concrete mechanical properties (tensile strength, flexural strength, etc. ), control of secondary/thermal cracks of concrete, preventing the in-depth propagation of cracks, post-cracking chargeability and reduced permeability against chloride and sulfate ions. In most of the studies, the concrete sample's thickness is increased along with the increase in the beam's length; however, in the present work, only thickness of the beam samples with and without fibers was changed and other dimensions of the samples were kept constant in order to investigate merely the effect of increased thickness. Accordingly, effect of the size of macro-synthetic fiber-reinforced concrete sample at different thicknesses was assessed via fatigue life variations. The intertwisted fibers were added to the concrete mixture by 0. 4 vol. %. Then, from each sample, three specimens were made. The obtained results were averaged and, then, recorded in the relevant tables. The cases considered as the research objectives are Effect of sample size on fatigue life of concrete samples and Effect of adding macro-synthetic fibers on fatigue life. In order to evaluate the flexural fatigue life of concrete beams, the concrete mixture was designed based on ACI 211 Standard. All the concrete samples were made with the same mix design and 0 and 0. 4 volume percentages twisted fibers were used for the fibrous mixtures. Hence, an experimental study was conducted to provide an experimental model of the flexural fatigue life of macro-synthetic fiber-reinforced concrete by constructing concrete beams with three different thicknesses of 80, 100 and 150 cm. S-N models (Stress level – Number of loading) and H-N (Thickness-Number of loading) models were presented. The obtained results showed that increasing the thickness of the concrete samples and adding fibers to the concrete mixture would lead to the increased fatigue life. Also, the addition of fibers to concrete specimens showed the thickness of the specimen decreased for the stress level of 0. 7, 0. 8 and 0. 9 by 8. 24-12. 45%, 5. 5-22. 5% and 10-22. 95% Respectively.

Labyrinth weir is one of the approaches to increase the discharge capacity. An arced configuration improves the orientation of the labyrinth weir cycles to the approach flow and increases the weir crest length for a given width. In this study, the effects of the entrance flow conditions on the hydraulic performance of the arced labyrinth weirs is studied experimentally. The effects of the angle between the entrance channel walls (Θ ′ ) on the discharge coefficient and the efficiency are investigated for different values of the headwater ratio (Ho/P), the downstream sidewall angle (α ), and the weir arc angle (Θ ). Experiments were conducted in a recirculating flume which is 10 m long, 2 m wide, and 0. 9 m deep at Tarbiat Modares University. To simulate the reservoir conditions, a specific setup was added to the flume, known as the reservoir simulator. The flume was launched from its two ends by two pipelines. The inflow passes from underneath of the reservoir simulator and enters into it through a semi-circular opening in its horizontal wall. After moving over the horizontal wall, the flow comes up through the gap between the vertical wall. Finally, it flows on the platform and moves towards the downstream channel. All the plates (including the platform and the simulator walls) have a semicircular plan-view with a porosity equal to zero. The weirs were mounted on the platform at the entrance of the downstream channel. Totally 132 experiments were conducted to investigate the effects of the mentioned parameters on hydraulic performance of arced labyrinth weirs. Due to the nappe interference, the local submergence forms in the downstream of the labyrinth weirs. The size of local submergence regions increase by increasing the headwater ratio and the arc angle. However, vice versa trend occurs with the downstream sidewall angle. In addition, for low values of the arc angle, the lateral flow from the side cycles to their adjacent cycles produces the surface turbulences. The results indicate that the discharge coefficient decreases by increasing the headwater ratio and the downstream sidewall angle. For low values of the headwater ratio, the discharge coefficient increases when the arc angle increases. However, a decreasing trend is observed in high head conditions. By increasing the arc angle and decreasing the downstream sidewall angle, the efficiency of a labyrinth weir can be increased. However, the efficiency gains diminish by increasing the headwater ratio. The efficiency of a labyrinth weir can slightly be increased by projecting of the cycles into a reservoir for low values of Ho/P, α , and Θ . However, in the wide range of the research domain, the efficiency decreases ween the angle between the entrance channel walls increases. According to the results of this research, the efficiency of a labyrinth weir can be increased up to 20% by channelizing abutments in high head conditions. However, the effect of Θ ′ is insignificant for higher values of Θ . In addition, as α decreases, the benefits and the losses of decreasing Θ ′ become more severe at higher and lower values of Ho/P, respectively.

The construction and maintenance of structural pavement was a high-cost problem in last decade. The mechanical properties of self-compacting concrete (SCC) required important factors. From its mechanical properties, the compressive strength (CS) is necessary to investigate experimental and computational intelligence analysis in construction materials. Developing models with accurate estimation for this key property caused to saving costs and time and producing an optimal blend. Because of the many advantages, using of SCC in structures is increasing. Construction of precast-prefabricated components, with the use of concrete has also recently been considered. Concrete properties have significant role in precast-prefabricated girders behavior. Exact prediction of these properties is the base of member’ s analysis and design. The main purpose of this study is presents new formulation to estimate the compressive strength of self-compacting concrete containing rice husk ash (RHA) using robust variant of genetic programming, namely gene expression programming (GEP) method. To evaluate the performance of the GEP-based proposed model, prediction was also done using classical data driven methods named artificial neural network (ANN) and multiple linear regression (MLR) models. A large and reliable experimental database containing the results of 156 compressive strength of SCC incorporating RHA is collated through an extensive review of the literature. The performance of proposed models of CS is then assessed using the database, and the results of this evaluation are presented using selected performance measures. New expressions for the estimation of CS of SCC are developed based on the database. To evaluate the modeling performances of the proposed GEP models for CS, different statistical metrics were used. Correlation coefficient (R), root mean square error (RMSE), mean absolute error (MAE) were used as the measure of precision. The results showed that the models developed using the aforementioned methods have accuracy over 90 percent in prediction of CS of SCC. The results of testing datasets are compared to experimental results and their comparisons demonstrate that the GEP model (R=0/94, RMSE= 4/308 and MAE=4/916) outperforms ANN (R=0/92, RMSE= 5/136 and MAE=5/624) and MLR (R=0/89, RMSE= 8/212 and MAE=9/472). Proposed models have a strong potential to predict compressive strength of SCC incorporating rice husk ash with great precision. The importance of different input parameters is also given for predicting the compressive strengths at various ages using gene expression programming. Performed sensitivity analysis to assign effective parameters on compressive strength indicates that cementitious binder content is the most effective variable in the mixture. The proposed design equation can readily be used for pre-design purposes or may be used as a fast check on deterministic solutions.

Earthquake sequences occur at many regions around the world where complex fault systems exist. These fault systems usually do not relieve all accumulated strains at once when the first rupture takes place. Therefore, high stresses formed at different locations causing sequential ruptures until the fault system is completely stabilized. The sequential ruptures along the fault segment(s) lead to multiple earthquakes which are often hard to distinguish them as fore, main and after-shocks, or a sequence of earthquakes from proximate fault segments. The most recent one sequences occurred are two foreshocks of magnitude 6. 2 and 6 followed by a magnitude 7 main shock between 14 and 15 April 2016 caused severe damage and injuries. The event of two earthquakes by magnitude 2. 6 and 6, which rocked the cities of Ahar, Varzaghan and Harris in East Azerbaijan in Iran in August 2012, is also a seismic sequence. Field investigations reported failure of structural systems under earthquake sequences, especially where structural retrofitting was not provided due to the short time between the earthquake sequences. In most failure cases the reported damage is mainly due to loss of stiffness and strength of structural elements as a result of material deterioration under earthquake sequences loadings. Buildings may have different configurations depending on the construction location and have different plan dimensions that would lead to irregularity in their planning. Limited research has addressed the seismic behavior of structures subjected to earthquake sequences especially irregular structures. This study investigates the effect of earthquake aftershocks on the steel buildings with irregularity in plan. For this purpose, we studied on structures of 8, 12 and 20 number of stories with special steel frame system under the earthquake sequences. Each of these structures consists of three cases: regular, irregular 1, and irregular 2 models that were designed in accordance to Iranian codes by SAP 2000 software. Geometric irregularities in the plan of the structure created in accordance to Iran's seismic code, a recess should be created in proportion to more than 2% of the total length of the building. In this paper, first irregularity has a recess by 5 meters (one span) and the second irregularity with a recess by 10 meters (two spans), which is 25% and 50% of the length of the building, respectively. The spectral dynamical analysis method has been used to design the structures. For nonlinear analysis, we use Perform-3D software, In Perform-3D, a frame element is used to model beams and columns. Then these structures were evaluated by nonlinear dynamic analysis under actual earthquake sequences. Six sequential earthquake categories that have a major earthquake spacing with corresponding aftershock occurred in less than a week in the area were selected from the PEER (Earthquake Strength Database). Finally, after discussion on parameters such as roof displacement, residual inter story drift and maximum inter story drift, it is observed that aftershock leads to increasing the response of the structures and as a result failure under aftershock. By increasing the irregularity in the plan, the instability of the structure increases under aftershock, which may cause structural failure.

Thin-walled cylindrical shells are extensively used in civil engineering. Due to thin wall thickness, they are vulnerable to stability failure in the form of shell buckling. The European Standard in design of steel structures is considered to be a pioneer in strength and stability assessment of shell structures. Wind pressure and seismic action lead to non-uniform distributed transverse loading on cylindrical shells. It has been shown that non-uniform loading may have a significant and deleterious effect on the structural stability of these structures. The present study deals with buckling behavior of short cylindrical shells under three non-uniform distributed transverse pressures. The loading patterns were adopted in a way to simulate the normal pressures due to ensiled materials in excited situation. It was done with respect to Eurocode design provisions for earthquake resistance of circular silos. Its aim is to produce useful information for the design of cylindrical shells against buckling under general transverse loading. An overview of Eurocode treatments of shell stability using finite element analysis is presented. In addition, the paper explores the effects of different forms of transverse loading on stability response of the structure. The numerical approach was selected to fulfill the stability evaluations. Eurocode has many provisions for the global analysis of shell structures using finite element analysis. Hence, a full suite of computational shell buckling calculations was performed according to this standard. Linear bifurcation analysis was undertaken, firstly. It served as a benchmark for further evaluations. Two different linear bifurcation eigenmodes were observed. The main mode of buckling was diagonal shear wrinkles near the base of silo with partial extension in circumferential direction. The other mode was local axial compression buckle at the foot of the shell. A wide range of imperfection sensitivity studies using these eigenmodes were conducted. The imperfections can take many forms and can have different amplitudes. Some imperfection forms may result in higher strength of the shell. This makes identifying the worst condition very challenging. A sample parametric study on imperfection amplitude in forms of eigenmodes, illustrated this kind of analysis. Additionally, the effect of plasticity was explored through the ideal elastic-plastic model for steel. It was shown that due to loading pattern, the plasticity may cause different amount of reduction in elastic load factor. To establish the actual plastic collapse load, the modified Southwell plots were used. To achieve more realistic evaluation of buckling and post-buckling behavior of thin-walled cylinders, the finite element analyses should include all possible source of strength reduction in stability of the shell structures. To this end the geometrically and materially non-linear analysis with explicit inclusion of imperfections (GMNIA) is considered to be the most advanced form of numerical analysis. The load factors derived from GMNIA analyses showed a stability reduction more than half as compared to linear bifurcation analyses in two load cases. The non-linear incremental buckling modes were also explored. Finally, the general shape of buckled short cylinders under transverse loading was characterized by combination of diagonal shear wrinkles and elephant’ s foot buckling mode.