مجله پژوهش های زیرساخت های عمرانی
سال نهم شماره 2 (پیاپی 17، پاییز و زمستان 1402)

In this study, several methods have been experimentally evaluated to increase the efficiency of reinforcements in the bearing capacity of a strip footing on sand. The capacity of the foundation in five different configurations including single and multilayer reinforcements was evaluated with free and wraparound anchored end, different thickness, and nailed with different numbers of nails and patterns. According to the results of these tests, dividing the length of the reinforcement and using it in more layers increases the efficiency of the reinforcement, but this division of the length of the reinforcement has a certain limit that reducing this limit reduces the efficiency. The use of wraparound anchorage caused more interaction between the soil grains and the reinforcement surface and as a result increased the bearing capacity of the foundation. Increasing the thickness of the reinforcements was another parameter studied in this study. Increasing the thickness of the reinforcement caused the bearing capacity to increase.  The results of the experiments show that the pattern of nails has a significant effect on the performance of the reinforced soil.

Roller-Compacted Concrete (RCC), which is a kind of dry consistency concrete with zero slump, has two various main applications, pavement and dams. But, owing to the benefits such as cost efficiency, low hydration heat, durability, and high speed of execution, RCC is particularly preferred in the construction of airstrips, military sites, and nuclear plants. In order to evaluate the effect of non-steel fibers on the Vebe time, modulus of elasticity, and also compressive strength, flexural strength, and splitting tensile strength of RCC as the aim of this research, a basic mix was used by adding three types of fibers including Barchip, Emboss and Glass fibers with percentages of 0.1, 0.3 and 0.5, the less percentage for controlling shrinkage cracks and higher amount for improving mechanical properties. The results showed that the addition of non-steel fibers to RCC reduced or increased compressive strength up to 5%, little decrease in Modulus of Elasticity and flexural strength and increasing up to 20% in tensile strength. Also, the fibers decreased the consistency and increased the vebe time of the basic mix. Barchip and Emboss fiber compared with Glass fibers showed better softening behavior after cracking. The amount of toughness was increased with the volume percentage of fiber, and this increase was higher for the Barchip fiber than the Emboss fiber. The best behavior after cracking was shown by Barchip fiber with a volume percentage of 0.5.

The Smoothed Particle Hydrodynamics (SPH) method is among the numerical methods that have attracted the attention of many researchers in recent years. This method as a Lagrangian method based on the movement of particles is also one of the meshless methods. In this method, the initial location or distribution of particles can play an important role in reducing numerical errors and its computational efficiency. In this research, based on wave modeling, which is one of the most conventional hydraulic phenomena, and using previous modeling experiences, six optimal and common distributions of particles including square distribution (SC), Triangular distribution, distribution based on WVT algorithm, distribution based on Greedy algorithm, Hexagonal distribution and Fibonacci distribution based on Fibonacci al-gorithm have been investigated. Based on the results of the pressure, velocity and the free surface level of the fluid in the location of the reference gauges of the laboratory model, it was determined that the square, triangular, WVT, Greedy, Hexagonal and Fibonacci distributions have a modeling error equal to 13.85%, 13.75%, 12.63%, 13.24%, 9.07% and 9.37%, respectively, and the two primary hexagonal and Fibonacci distributions have a modeling error of less than 10%, and in other words, it has the best performance in using the SPH method in order to improve the efficiency of the computational model.

The aim of the current research is to evaluate the effect of placing a compound sharp-crested weir at different angles in the channel on its hydraulic performance. For this purpose, Flow-3D software was used to simulate the effect of the placement angle of the compound sharp-crested weir in the channel, considering four angles: zero (perpendicular to the flow pass), 15, 30, and 45 degrees. The comparison of the error percentage obtained between the results of the flow discharge and the depth of the upstream weir from the numerical results and the laboratory data was 0.39% and 2.86%, respectively. The results of the flow pattern passing through the compound sharp-crested weir showed that the flow lines are closer to each other when approaching the crest of the weir at the narrowing place, and the accumulation of flow lines increases in the place of the flow narrowing. The interference of flow lines at the narrowing place reduces the flow coefficient of the flow passing over the weir. The increase in transverse constricting and the decrease of 25 and 50% in the length of the weir crest caused a decrease in the flow discharge coefficient of 14.4 and 9.81%, respectively, compared to the sharp-crested weir of the same channel width. By creating a constant for the weir crown in the width of the compound weirs and placing them at a maximum angle of 45 degrees, the flow rate coefficient is increased 8.91% compared to the angle of the compound sharp-crested weir to the flow.

Weirs are one of the most important hydraulic structures used in dams, which are built for safe discharge of flood flows. In order to increase the weir discharge capacity, labyrinth weirs are used in small openings. In the present study, 2 different geometries in the design of trapezoidal labyrinth weirs with equal (B model) and unequal (quintet F models) Indentation lengths were investigated in a laboratory and for different flow rates. Has been The experiments were conducted with the aim of reducing the interference of water blades and increasing the efficiency and discharge coefficient (C) of the mentioned weirs. The results show that; In most cases, the discharge coefficient of labyrinthine weirs with unequal Indentations is higher than that of equal Indentations. The highest weirs discharge coefficient is when the Ht/P ratio is at its lowest value. In this situation, by increasing the volume of water passing through the flume until the Ht/P ratio is less than 0.3, the trend of changes (C) in relation to Ht/P is decreasing, and from this point on, with the increase of the Ht/P ratio to more than 0.3, in all the built samples of F models, due to the interference of the water blades and also due to the absorption of the weir Indentations, the changes in C are very insignificant compared to the increase in the Ht/P ratio, and practically the weir discharge coefficient in discharge the above is almost constant and unchanged. In other words, in unequal labyrinth weirs where the rate of decrease in the collision length of their blades is between 15 and 27.5%, the discharge coefficient compared to labyrinth weirs with equal Indentation length has increased at least 32.4% and at most 35.3%.

Earthquake is one of the natural disasters that have physical, economic and life-threatening outcomes. Therefore, in order to be prepared and reduce the risk before an earthquake occurs, the amount of damage and vulnerability assessments and planning are necessary. This research was conducted with the aim of evaluating the seismic vulnerability of existing hospitals in Kabul City. In the present study, 23 hospitals that have 60 existing reinforced concrete buildings were assessed for seismic vulnerability using the Rapid Visual Screening technique. The buildings were scored and analyzed based on the key indicators approved in FEMA P-154 and Iranian Code #364. None of the buildings received Cut- Off Score in the seismic vulnerability assessment. Despite the hospitals of Kabul City are active under normal conditions; in critical conditions, factors such as weak structural and non-structural resistance and non-compliance with design criteria can cause malfunctions and ineffectiveness of hospitals. Considering the Final Scores, the probability of collapse attributed to these buildings in a MCE (Maximum Considered Earthquake) seismic event, are between 3.16 and 45.6%, which indicates that during the occurrence of destructive phenomena such as earthquakes, there will be a possibility of damaging the buildings and getting out of their special cycle of use. According to the result, there is a possibility of seismic vulnerability of existing reinforced concrete hospital buildings in Kabul City during an earthquake. The degree of this seismic vulnerability varies from low to high. Therefore, these buildings should be subjected to a detailed seismic vulnerability assessment.

One of the novel methods for stabilization of deep excavations is the use of top-down method. In this method, while reducing the execution time and controlling the deformation of the excavation wall, the necessary conditions for constructing structures in limited spaces or crowded urban areas are provided. In this paper, the Iranian top-down method is introduced. In order to evaluate this method, horizontal and vertical deformation of Iranian top-down is compared with diaphragm wall top-down method and nailing method. Diaphragm wall top-down with a wall thickness of 0.45 m, Iranian top - dawn with two different wall thicknesses of 0.45 and 0.65 m and  Nailed pile wall method with 0.45m thick wall, is studied numerically by using the finite element software MIDAS GTS NX. Niayesh parking lot in Tehran with a depth of 29 m is select for the case study. The results of this research show that Iranian top-down has a 20 - 25 percent lower horizontal deformation than the diaphragm wall top-down. Nailing method has three to four times more deformation compared to both types of top-downs and their difference increases by increasing the depth of excavation. The greater thickness of the wall in Iranian top-down has a negligible impact on the deformations and the effect can be ignored. Also, in Iranian top-down the ground surface settlement is 10 - 15 percent less than diaphragm wall top-down. The new method mentioned here shows that the construction of the diaphragm wall in a few steps can lead to reduction of deformations.

Cold emulsion asphalts have advantages and disadvantages. The advantages of this type of mixture are related to the low temperature of production, environmental considerations, and its portability to long distances. One of the main reasons for the poor performance of this type of asphalt is its moisture content. The water penetration hinders the fracture of emulsion bitumen, and after that, the mixture's resistance to moisture is reduced. The present research used the modified Marshall method to determine the optimal bitumen percentage. For this reason, one to three percent by weight of the asphalt-cement mixture and 0.3 to 0.5 percent by weight of fiber mixture containing fatty arbocell were added. The resulting samples were subjected to the Marshall strength, Marshall index modified Lottman and Nicholson tests. Based on the results, the Marshall strength was 47.88%, the Marshall index was 139%, adhesion was 41%, the ratio of indirect tensile strength was 21%, and the fluidity was 36.47%. According to the data obtained from this research, it is suggested that 3% cement and 0.3% fatty arbocell fibers should apply in cold asphalt mixtures.

In this paper, the effect of seismic pounding of adjacent structures on buildings isolated by double (DFPB) and triple friction pendulum bearings (TFPB) is investigated. The seismic gaps between buildings are calculated based on the Instruction for Seismic Rehabilitation of Existing Buildings, standard No. 360 of Iran, which is not considered for friction pendulum bearings in the previous studies. To this end, a three-dimensional single-story building model is created in the MATHLAB program considering two scenarios including the case without pounding and the case with it. In addition, fifteen different TFPBs and six DFPBs are utilized as seismic isolators to cover a wide range of fundamental periods of the isolation system. Finally, nonlinear time history analyses with seven pairs of ground motion records are conducted to obtain some of the seismic responses of buildings including base shear, drift, story acceleration and maximum displacement of the isolation system. The results show that the seismic pounding considerably increases responses of base-isolated buildings. For example, the floor acceleration and the drift ratio of isolated building with TFPB increased 2 and 6 fold because of seismic pounding. It shows that the seismic gaps calculated by the formula of standard No. 360 may not be sufficient to prevent severe seismic poundings and increase of seismic responses.

The I-shaped beam to circular column connections can be constructed by curved cutting of the beam flanges or by installing external diaphragms around the column, which cause both economic and practical difficulties. A practical method proposed for construction of these connections consists of welding a link channel to the circular column and welding the beam to the link channel. As this method is new, the effect of link channel dimensions, I-shaped beam section dimensions, circular column dimensions and the link channel stiffeners on the connection behavior is not known well. Accordingly, this paper presents a FE investigation on the cyclic behavior of I-shaped beam to circular column moment connections with link channel. The main novelty of the research is the parametric evaluation of the affecting parameters, considering the stiffness and strength degradation from ultra-low-cycle fatigue, which is made possible by including ductile damage for metallic materials in ABAQUS software. For this purpose, first, the parameters of the damage model are calibrated by comparing the numerical results with the laboratory data, and then, the connection models are analyzed under a displacement-control quasi-static cyclic loading. Based on the results, the thickness of the link channel plate has the most significant effect on the overall behavior of the connection compared to other link parameters. It is also observed that the link channel stiffeners increase overall stiffness and strength of the connection. However, they cause extension of yielding towards the beam to link connection, and cause rapid growth of plastic strain in this area.

Due to developments in the field of fast transportation, increase in permitted speed and load capacity, moving loads can have significant effects on the dynamic forces of bridges. To consider the dynamic effect in the design of the structure, the dynamic impact factor is introduced as ratio of the dynamic response to the static response. Accurate evaluation of these coefficients helps in safe and economic designs for new bridges. However, the evaluation of the dynamic impact factor is difficult due to the vehicle-bridge interaction and the influence of many parameters that affect the dynamic impact factor, including the dynamic characteristics of the bridge and the vehicle, road surface conditions, vehicle speed, traffic conditions,. In this research, by applying live load of vehicles step by step and performing time history analysis, dynamic analysis under moving load has been done. Three different types of cable-stayed bridges with different spans and cable layouts have been investigated in the form of two-dimensional models. This study analyzes the impact coefficient of bending and shear forces of deck components and pylons, as well as the axial forces of cables, and the results are compared with the coefficients proposed in the design regulations. Also, the effect of changes in load passing speed on the dynamic impact factor in cable-stayed bridges has also been evaluated and studied. This research tries to improve and optimize the design and performance of cable-stayed bridges in order to deal with dynamic changes and increase the speed of loads.

Nowadays, extensive nonlinear dynamic analysis is widely used in different fields of research and design of structural and earthquake engineering. It has been applied in performance-based design, resilience-based design, and also other probabilistic fields and optimization. This extensive analysis imposes a high computational cost on the researcher. However, using simplified models is an appropriate approach. The Substitute Frame is a simplified model for steel and RC moment frames, which on the one hand predicts the displacement responses of the frame with very good accuracy and on the other hand, reduces the analysis time by several times. Despite numerous evaluations of the substitute frame model in nonlinear dynamic analyses, incremental dynamic analyses, and fragility analyses, the model's accuracy has not yet been investigated for predicting moment frames' force responses. In performance-based engineering, force-control actions should be designed to prevent the undesirable failure mechanism. Hence, in this study, first, the force response of the columns was predicted using the substitute frame model, and then its accuracy was evaluated comparing to the original frame response. The results of evaluations showed that the substitute frame predicts the columns bending moments, shear forces, and axial forces of the original frame with more than 90% accuracy.