Modares Civil Engineering journal
Year:2021 | Volume:21 | Issue:3|Papers Count:10

Weirs are widely used in many different shapes to control a water level, facilitate flow diversion and to regulate the flow of water. Given that the overflow zone is often laterally restricted, the overflow depths can become excessive. As a result, non-linear weirs e. g., Labyrinth with different forms have been developed to increase weir length and discharge capacity within a fixed overflow width. Accurate estimation of the maximum possible depth of scour at weirs is important in decision-making for the safe depth of burial of footings. The design of labyrinth weirs foundations based on equilibrium clear water scour depths may yield considerably greater values than if the flow is of short duration. For a known time-to-peak value of design flood hydrograph, smaller scour depths may be obtained, which reduce the total cost of construction. Therefore, investigation of temporal variation of clear water scour at labyrinth weirs is important to estimate the possible extension of the scour hole. This would provide useful information for the safe design of footing and the selection of scouring counter-measure to be implemented. In the present study, temporal variation of scour and at labyrinth weirs was studied. In experiments, labyrinth weirs were used and seven head to weir height ratios (H/P=0. 1-0. 7) for cycles with 6 different sidewall angles (150, 300, 450, 67. 50, Linear). In this study, the effect of H/P and sidewall angles on temporal variation of scour depth and scour depth location were investigated. The results indicated that the mechanism and the value of scouring at weir varied for the different value head and sidewall angles. When head to height weir increased, the value of instantaneous scour depth significantly increased. The results also showed that in all experiments, the scour rate is more severe in the early stages and 80% of the development of scour depth occurs in the early 10% of equilibrium time. Furthermore, When H/P increased 5 times, the equilibrium time of scour depth increased to 6, while whit increasing of the sidewall angles to 6 times, equilibrium time decreased 45%.

Structural damages in arch dams, are often of major concern and should inevitably be evaluated for probable rehabilitation to ensure safe regular normal operation and safe behavior in future under unusual loading. These are crucial to prevent any catastrophic or failure consequences for the life time of the dam. If there is a specific major infection such as a large crack in the dam body, the assessments will be necessary to determine the current level of safety and predict the resistance of the structure to various future loading, such as earthquakes, etc. In this research, Morrowpoint dam is selected as a case study to assess the dam performance and its safety level, at the presence of an actual crack with almost known geometry created in the dam body during the sequence of its reservoir first impounding. Three-dimensional modeling of the dam and its foundation is constructed for several different crack types with specific geometry and different mechanical properties. For modeling of both the existing cracks, and the vertical contraction joints of the arch dam, no-tension, zerothickness joint elements with variable compression-shear behavior are used. The applied loads include normal or service loads (weight and hydrostatic water pressure) as well as abnormal load of water penetration into the crack surface. In the first set of analyses, concrete material is assumed as linear. By observing the high tensile stresses, non-linear concrete materials with plastic damage model is introduced for selected cases although the foundation materials remain as linear. Safety factors of shear and compressive tractions are calculated at the surfaces of the contraction joints and the cracks. For the safety factor of the dam body mass concrete surfaces, a 2-D failure criterion is employed. In applying the weight load, the construction sequence of 3D blocks of the dam, and the stages of grouting the contraction joints have been fully accounted for. The results indicate that for cracking with an extension depth of half the thickness of the dam body, for both cases of penetration and non-penetration of water load into the cracks, safety factors are only slightly reduced and thus the dam safety in normal loading condition remains acceptable. However, in the case of increasing the depth of crack extension into the entire thickness of the dam body, the friction angle of the cracked surface is crucial, and if reduced, the normal loading safety factors of stresses and joints tractions are reduced significantly even when neglecting water penetration effects in cracks. When water penetration into the cracks is added during normal loading case, the situation is of much concern and great damages are expected. Simultaneously, it is observed that, the foundation interface also suffers of much shear safety loss.

Shear strength of the soil as a granular material depends on the stress level, confinement, cohesion. and the friction between its solid particles. Geosynthetics are widely used to improve the mechanical properties of the soil. Inclusion of geosynthetics as reinforcement elements increases the confinement and the shear strength of the soil. The bearing capacity of foundation on reinforced soil depends on the type, length, depth, and mechanical properties of the reinforcements and their interface with the soil. Since the placement pattern of the reinforcements has a great impact on the stress distribution within the soil mass, therefore, it could be an important parameter on the bearing capacity of the foundations on the reinforced soil. Proper placement of the reinforcements within the soil mass could be employed to increase the effectiveness of the reinforcements on the bearing capacity improvement of the foundation on the reinforced soil. This paper presents the results of an experimental study on the effect of the pattern of reinforcement placement in reinforced soil on the bearing capacity of a strip foundation. A steel box filled with sand with the dimensions of 100×25×30 cm (Length, widths, and height) was used as the test base. The strip footing was simulated by a steel plate with dimensions of 25×7. 5×2 cm. The sand used in this study was a poorly graded sand (SP) according to the unified soil classification system. A woven type geotextile was used as reinforcement. The effect of the reinforcement’, s placement pattern on the bearing capacity of the foundation was investigated with nine different layouts including single, double, and three-layered reinforcement layouts. All the specimens prepared with a similar initial unit weight and void ratio. The tests conducted using a displacement-controlled loading device. The loading was applied with a rate of 1 mm/second. All the tests repeated at least three times to assure the accuracy and the repeatability of the results. The results of these tests indicated that the bearing capacity of the foundation increases as the length of the reinforcement increases but up to a certain limit and then remains constant. Although increasing the number of reinforcements layer increased the bearing capacity of the foundation, however, the effectiveness of the geotextile in the improvement of the bearing capacity decreased. Placement of the reinforcements in a discrete pattern improves the effectiveness of the reinforcement on the bearing capacity improvement. In multi-layer reinforcement layouts, using discrete strips of reinforcements in each elevation without overlapping with upper-and lower-layers of reinforcements, resulted the maximum efficiency of reinforcements influence in the improvement of the bearing capacity of the foundation. In the recent case, for a specific cross-sectional area of the reinforcement, the bearing capacity of the foundation could be increased by 20% using 17% less reinforcement. The results of this study indicate that the layout of the reinforcement pattern is a very important factor in the bearing capacity of foundations on reinforced soil. With a proper placement of reinforcements, the maximum bearing capacity of the foundation could be achieved with a minimum amount of reinforcement material.

Intake of water from rivers has recently become a major subject of study in hydraulic projects, such as water transfer systems and power plants. Intake from water resources can be carried out by different methods. Lateral intake is influenced by various factors, such as topographic conditions, type of the river, and the plan target and water conveyance system is a common method using an open channel or a pipe. Because of various conditions in different regions, a general recommendation for selecting the intake method for all regions cannot be a robust solution,therefore, it is necessary to select suitable lateral intake by extensive and accurate studies and consider the conditions technically and economically. Lateral Intake which uses a pipe is a hydraulic structure that has been utilized in water intake from rivers and channels, especially in those situations in which the area topography do not allows to build a lateral channel for water intake. There have been few studies conducted on the above mentioned structures and that what is the optimal condition in water intake using a pipe still have not really characterized. This study deals with the numerical investigation of effective geometrical parameters on lateral intake efficiency with a pipe in an outdoor direct rectangular channel by using software FLOW3D. The parameters categorize into three group including the direction of the pipe intake aligning with the current, the characteristics of pipe intake opening, and also the position of pipe intake opening. The results show that among different angles of the intake, the 90-degree angle divert the highest discharge,because it has more pressure gradient difference than the others. Increasing the discharge leads to diverted sediment increase to lateral intake. For this purpose, at 90-degree angle the highest sediment divert to the pipe happens. Since the criterion of choosing the best angle intake is anti-sediment coefficient. Comparing the Anti sediment coefficient among different angles showed that the 90-degree angle has the best efficiency of intake. Also an analogy of diverted discharge results for different levels of pipe intake indicated that if the water intake happens at relative height level of 0. 28 to 0. 57, the diverted discharge would be more than the simulated case. Furthermore, by comparing anti-sediment coefficient for different levels demonstrate that if the pipe intake locates near the surface of current, anti-sediment coefficient will have an acceptable value. Hence, results of diverted discharge at different depressions pipe intake demonstrate that the less the rate of pipe intake depression, the more discharge will be diverted. Also an analogy of anti-sediment coefficients at 45 and 90-degree angle show that the influence of pipe intake depression on intake efficiency change when affected by angle intake. So, finally results indicate that divert flow, when the characteristics of intake opening change, depend on angle intake would show a different behavior himself. As regards to optimum location of the intake, it was observed that location of the pipe intake inlet in almost 40% of the main channel width could yield a quite acceptable performance for the pipe. Furthermore, location of the pipe intake near the free surface could yield a high performance of the pipe intake as a result of low sediment concentration and high flow velocity. However, it should be considered that near the free surface, wavy flow and water surface fluctuations can influence the intake performance.

In this study, the effects of the concrete rings as well as the far and near field earthquake on the frequency and seismic behavior of the intake tower have been investigated. For modeling and analysis with considering the interaction of water and structure, ANSYS software which is based on the finite element method is used. For a better analysis of these models, two far and near field earthquakes have been selected and scaled to the same maximum value acceleration. To evaluate the effects of concrete rings on the behavior of the intake tower, 33 intake tower models have been modeled by considering concrete rings in different number and height levels. In the following, 66 analyzes have been performed for three modes of the tower, including only the structure of the intake tower without a reservoir, the intake tower with the surrounding reservoir and without inside water and the intake tower with the surrounding reservoir and inside of the tower is full. The results of displacement, stress, and base reactions of the intake tower under the relevant analyzes have been compared with each other. Based on the results, it was found that the effects of a near-field earthquake at maximum displacements and stresses are far greater than a far-field earthquake. However, the values of the responses depend on the frequency of the earthquake in addition to its proximity to the field. The results also showed that surrounding water and internal water have different effects on the seismic response of intake towers affected by near and far field earthquakes. The presence of water increases the effective duration of the earthquake on the response of the intake tower, especially in the near field earthquake. The results showed that by adding circular rings, the frequencies of the intake towers undergo significant changes, which require seismic analysis to evaluate its effects. In the case of a intake tower without a surrounding reservoir and a intake tower with a surrounding reservoir and without inside water, the maximum values of displacement decrease with increasing the height of the concrete rings and decreasing the distance between them. For a intake tower with a surrounding reservoir and full inside, in the case of far field earthquake analysis, the greatest reduction in displacement occurs for a intake tower with a ring at 25 meters, while for a near field earthquake in this case the amount of displacement is further reduced with increasing height level of concrete rings. The pattern of changes in the first principal stresses for all the studied models is also in accordance with the changes in the values of the maximum displacement. The maximum values of the base reaction for the intake tower without surrounding reservoir and the intake tower with the surrounding reservoir and without inside water for near field earthquake are greater than for the far field earthquake while for the intake tower with surrounding reservoir and full inside for far field earthquake it is more than a near field earthquake which is due to the frequency content of the desired earthquakes. Eventually, the results showed that adding concrete platforms at high and close to each other has very good and positive effects also reduces the maximum values of stress, base reaction, displacement, and relative displacement.

Nowadays, building structures encounter with challenges such as construction speed and cost, especially in high seismicity zones. To accomplish this, steel structures was developed to accelerate the construction process and other economic issues. According to high strength ductility and energy dissipation, steel structure systems have been used widely in active seismic regions. The idea of application of shear panels has been using from many years ago as systems with high energy dissipation capability in EBFs as link beams and steel shear walls. The purpose of the EBFs design is the yielding of link beam and remaining the adjacent member at elastic region. According to the available criteria in design codes, shear in beams is a force-controlled action that exceeding the specified value as nominal strength is not permissible and the capacity design theory should be considered. Increasing the web thickness is the main effective factor achieving the needed shear strength and leads to the enhancement of plastic flexural capacity. The result of this action is more seismic demands in other structural members to keep in desirable operational level. So the shear plastic hinges is introduced instead of flexural plastic hinges at both ends. At this case because of uniform shear yielding through the web, energy dissipation capability is much better than the flexural yielding which begins from the outer face of the beam located on flanges. The web panels of built-up sections restrained by top and bottom flanges and two-sided transverse stiffeners have the ability to carry further loading beyond the web buckling load. The small lateral web displacements produced by excessive loading are not substantial because of available components to supply more resistance. Using adequate stiff transverse to resist against the out-of-plane deformation resulted from post-buckling,tension field actions are developed in shear panels before reaching the maximum shear strength by forming a truss with tension diagonals and compression verticals fixed by stiffeners. The concept of shear resisting frames with non-prismatic beams were presented with the scope of reduction in link beam rotation, elimination of architectural limitations, restrictions on the ratio of span free length to beam total depth and high energy dissipation capacity. Shear yielding and out of plane deformations caused by tension action field mainly control the frame behavior and energy dissipation. The proposed system is made up two strong side columns connected to the link element with weaker section in the middle of the frame as shear fuse with non-prismatic beams. Tendency to use haunched beams makes it feasible to achieve any link length ratio especially less than 1. 0. This paper presents the introducing, design and performance of 1-storyshear resisting frames with different link length ratios (ranges from 0. 5 to 1. 6 with 0. 1 variations) and shearcontrolled behavior. The goal is achieved by implementing pushover and cyclic analyses numerically with ABAQUS software. But at first a verification analysis is done to validate the modeling procedure and reach a good conformity between numerical and experimental results. The outputs are presented in the form of response modification factor, displacement ductility and overstrength factor for pushover analyses and hysteresis behavior, backbone curve, energy dissipation capability and overstrength factor for cyclic analysis. Also at the end, 3, 5 and 7-story-frames were studied through pushover analysis and values of response modification factor and overstrength factor of the total frames presented. The results indicate desirable behavior of 1-story-shear resisting frames from the point of stiffness and strength degradation with high values of response modification factor equal to 9. 18.

One of the critical environmental factors that affect the deformation of flexible pavements is the depth temperature of asphalt layers. This is due to the viscoelastic behavior of the asphalt mixtures. The stiffness of the asphalt layers has a significant effect on the structural capacity of flexible pavements. This property is a function of the asphalt layer temperature and changes daily and seasonally. As the temperature increases, the stiffness of the asphalt layer decreases, which increases the stress in the base and subbase layers of the pavement. Therefore, the pavement response to the applied loads is affected by the depth temperature. Hence, the depth temperature of asphalt layers is one of the most important and main factors in the analysis, design, and rehabilitation process of flexible pavements. Some predictive models have been developed to determine the depth temperature of asphalt layers in pavement maintenance and rehabilitation activities. These models, as an alternative to field and laboratory measurements of this factor, are low-cost, rapid, and simple methods to determine the depth temperature of asphalt layers. It should be noted that these models are based on the limited field and laboratory data, therefore, there is a need for developing new models for prediction of the depth temperature of asphalt layers in different traffic and climatic conditions. The objective of this study is to develop a model for predicting the depth temperature of asphalt layers based on climatic data. In recent years, Artificial Neural Networks (ANNs) have shown good performance as a useful tool for modeling physical events. The modeling method used in this study is a Back-Propagation Neural Network (BPNN) model that predicts the average hourly depth temperature of asphalt layers based on several variables, including the time of the day, desired depth from the pavement surface, average hourly air temperature, average speed and direction of the wind, minimum air humidity and total solar radiation. Data was extracted from the Long-Term Pavement Performance (LTPP) database. After extracting and preparing raw data, all the needed data were acquired from different data tables and linked to each other in a database. As a case study, data points collected from pavements in Ohio, USA, has been used for modeling. Also, to ascertain the presence or absence of multicollinearity between independent variables, the Pearson correlation test has been conducted. For this reason, the maximum speed and direction of the wind and maximum air humidity parameters were removed from the data set. According to the results of the Pearson correlation test, the average hourly air temperature has the most powerful impact on the average hourly temperature of the asphalt layer depth (correlation=95. 2%). After training and testing the neural network, the performance of the developed model has been evaluated, and results were compared with a non-linear quadratic regression model. The results show that the developed model is more accurate than the regression-based model. In addition, the ability of the developed model in predicting the depth temperature of asphalt layers based on existing climatic data with a very good prediction accuracy (R2=0. 96) and very low bias and error has been shown. Furthermore, the performance of the developed model has some restrictions for the prediction of depth temperature of asphalt layers. Other factors such as material characteristics can be scrutinized and applied to enhance the performance and applicability of the model.

One of the most critical issues in the world is the disposal of waste materials. The expansion of the automotive industry has led to the existence of used tires as one of the environmental pollutants in recent decades. The global growth of the automobile industry and the increase in the use of cars as the main means of transportation has led to production of large accumulations of used tires. These solid wastes decompose very slowly and produce many pollutants such as insect growth. Recently, there has been an increasing trend toward the use of sustainable materials. Sustainability helps the environment by reducing the consumption of non-renewable natural resources. Concrete –,the second most consumed material in the world after water –,uses a significant amount of non-renewable resources. Efforts aimed at producing environmentally friendly concrete can play a major role in securing sustainable construction. Candidate technologies for sustainable concrete materials include the incorporation of supplementary cementitious materials (SCMs) such as, silica fume as a partial replacement for Portland cement,the incorporation of recycled materials in concrete production. As a result, an experimental investigation was conducted to study the mechanical properties of concrete made with 10% and 15% recycled tire rubber (fine and coarse) as well as 6% silica fume. This experimental program consisted of ten mix designs. (1) Control samples with natural aggregates and without silica fume, (2) Samples with natural aggregates and 6% silica fume (S6), (3) Samples with 10% replacement of coarsegrained recycled tire rubber by weight without silica fume (C10), (4) Samples with 10% replacement of coarsegrained recycled tire rubber by weight and 6% silica fume (C10S6), (5) Samples with 15% replacement of coarse-grained recycled tire rubber by weight without silica fume (C15), (6) Samples with 15% replacement of coarse-grained recycled tire rubber by weight and 6% silica fume (C15S6), (7) Samples with 10% replacement of fine-grained recycled tires by weight without silica fume (F10), (8) Samples with 10% replacement of fine-grained recycled tier rubber by weight and 6% silica fume (F10S6), (9) Samples with 15% replacement of fine-grained recycled tier rubber by weight without silica fume (F15) and finally (10) Samples with 15% replacement of fine-grained recycled tier rubber by weight and 6% silica fume (F15S6). According to the experiments carried out and the comparison of the obtained results with the important regulations as well as the available data from previous studies, the following results are achieved: (1) Adding silica fume to concrete due to its pozzolanic properties has increased the compressive strength compared to conventional concrete up to 17%. Furthermore, it has a significant effect on tensile strength and increases tensile strength by more than 23%. (2) Replacement of natural aggregate with coarse-grained recycled tire rubber for 10 and 15% by weight has resulted in a 33 and 45% reduction in compressive strength compared to conventional concrete after curing time of 28 days, respectively. Addition of silica fume to these samples reduced the reduction percentage to 8% and 30%, respectively. (3) Replacement of natural aggregate with fine-grained recycled tire rubber for 10 and 15 percent results in 42 and 54% reduction in compressive strength after curing time of 28 days compared to conventional concrete. The addition of silica fume to these samples has reduced the reduction percentage to about 30%. (4) The tensile strength of concrete made with coarsegrained recycled tire rubber of 10 and 15% by weight, respectively, has decreased by 3 and 13% after curing time of 28 days compared to conventional concrete. Furthermore, adding 6% silica fume to these samples has reduced the reduction percentage to about 10%. (5) Tensile strength of concrete with fine-grained recycled tire rubber of 10 and 15% by weight, respectively, has decreased by 23 and 38% after curing time of 28 days compared to conventional concrete. Furthermore, adding 6% of silica fume to these samples reduced it by 3% and 30%, respectively. (6) Tensile strength relationships presented in US, European and AASHTO regulations were conservative for 35%, 85% and 20% of present data for concrete made with recycled tire rubber and for Japan, Australia and CEB-FIP regulations 100% of data were conservative. (7) Statistical studies show that 100% of the tensile strength data for concrete made with recycled tire is in the range of 95% of data for conventional concrete.

Asphalt binder has an important role in asphalt mixture behavior. Therefore binder fatigue characterization has been widely investigated. Significant research efforts were focused on developing reliable fatigue prediction models. Those efforts in the beginning were concentrated on relating initial responses, such as strain or stress levels of asphalt mixtures to their fatigue life. Such phenomenological relationships were usually developed by means of testing samples under different loading conditions and generating regression models. Considering different combinations of loading conditions, and the long time duration needed for a single fatigue test, the phenomenological approach requires extensive time and funding. Therefore, the mechanistic approaches which substitute excessive testing with analytic equations, have become more common in the field of fatigue behavior characterization. Viscoelastic continuum damage (VECD) mechanics is one of the wellstudied mechanistic approaches to characterize the fatigue life of viscoelastic materials. In this approach an internal state variable (ISV), called damage, is defined to stand as a representative of material structural state. Then the state of the modulus is determined as a function of damage, namely damage function. Determination of damage function can facilitate asphalt fatigue prediction under different loading patterns. However, VECD analysis has its own complications. The damage parameter needs to be calculated in each cycle during the test, while its calculation needs damage function trend to be known. Thus, damage parameter can only be determined using a procedure of try and error. In this research an inventive method has been introduced that can simplify efforts to yield damage function, requiring less time and fewer samples. A formulation framework has been presented here which is based on an analytical solution of the governing differential equation of damage evolution power-law. The solution is made assuming the ruling conditions of this study. These assumptions which are clarified in the paper could be reconsidered to form new formulations through a similar approach. Using the formulation, developed in this study, damage function can be found, using the data obtained from two constant-strain, or a single incremental-strain tests. According to this method Time Sweep Test can be performed at two different strain amplitudes and the developed models could be fit to the initial responses data of the material to yield VECD parameters needed to constitute the fatigue prediction model. This approach uses a nonlinear regression analysis to determine VECD parameters, even without calculating the values of damage during test. Afterward, the proposed procedure was validated by experimental tests. Time Sweep tests were performed on binder samples modified with SBS polymer. The binder samples were modified using SBS Polymer, due to its popularity among asphalt researchers. Such modification transforms a simple binder to a complex one. Results showed that the try and error procedure can be substituted by regression model to yield damage function in less time. The discrepancies between the data obtained from the two above-mentioned methods were negligible. It was concluded that the similar results are due to the same mechanism, used in try and error and regression methods which is performed through different approaches.

One of the essential points of interest for designers in constructing the tall building is to create a large entrance to the lower floors of the building. Such large openings are mainly because of architectural issues such as high traffic congestion, aesthetics, and parking. Creating these large openings, if accompanied by the removal of a column, connects the case with other structural issues such as the effect of the Construction sequence, progressive collapse, loads during execution, and the presence or absence of auxiliary supports (temporary piles) and making the problem more complicated. This study considered 36 regular structures of 10, 20, and 30 floors with a height of 40 to 120 meters with the Moment resistance frame system in the ETABS software. The Iranian National Building Code part 6 has used for load gravity of structures, and the Iranian standard No. 2800 has used for calculation and loading of lateral earthquake loads. After spectral dynamic analysis and Pushover analysis of the mentioned structures, we examined their behavior from the structural point of view and the effect of using bracing in one to four upper floors of the removed column. In the studied structures, evaluated the changes in plastic hinges formation, structural performance level, Demand-Capacity ratio (DCR) of structural elements, period of the first mode, and drift in the exterior (non-corner) column removal. Also studied the effect of elimination on the exterior column to create a large entrance to the building on the probability of progressive collapse of the 10-story steel structure. The results showed that braces to strengthen the large span beam is a convenient and economical solution. In particular, the V braces show better performance than the Chevron brace if the number of braced floors above the desired span is before the building's inflection point. Because when the braces enter the area adjacent to the building's inflection point, they reduce the building's performance level with failure in the pressure because of the low ductility in the pressure. The first plastic hinge at any performance level starts from the inflection point. As a result, the use of low ductility elements in these areas reduces the structure's ductility. In most cases, V brace structures have smaller elements than structures with Chevron braces and are more economical. Buildings that are reinforced only by increasing the beam and column sections' dimensions without adding bracing have more strength than bracing structures. However, many sections' measurements compared to the braced buildings sometimes increase several times in this case. Therefore, this increase in strength will be accompanied by an enormous increase in cost. The results of pushover analysis and performance-based design showed that if the structure was designed from the beginning according to the standard code design, assuming the absence of columns, the building does not experience a reduction in performance and is better than using braces with higher ductility.