مجله پژوهش های زیرساخت های عمرانی
سال پنجم شماره 1 (پیاپی 8، بهار و تابستان 1398)

Reinforced concrete flat slabs are widely employed in structural systems. The location of the slab-column connection is the most sensitive part of the flat slab due to the existence of a high flexural anchor and shear force. On the other hand, the utilization of flat slabs directly resting on columns, in the case of punching shear failure, reveals their vulnerability that the presence of openings will increase the probability of punching shear failure. This study is the numerical study of the effect of strengthening the reinforced concrete flat slabs with opening and external steel plates on the punching shear capacity. Initially, verification of the numerical model by the experimental sample conducted. Then some reinforced concrete flat slabs with reinforced opening and external steel plates with various dimensions and thickness as well as diameter, length, number and order of the different shear studs under the load, by using the finite element method analysis and the results of the various samples were compared with each other. The strengthening of the reviewing slabs improved the condition of stiffness and increased the punching shear capacity. The reviews also indicated that this situation improve dependent on the dimensions and the thickness of the plate and the diameter, length, number, and order of the shear studs. The results of this research suggested that if you use the right behavioral model in the simulation process, the finite element method can be a useful tool for analysis and secure and optimum design of reinforced concrete slab.

Reinforced concrete squat walls with an aspect ratio less than 2 are prevalent in low-rise construction and at lower levels of tall buildings or nuclear power plants. They show a significant amount of shear deformation as compared to bending deformation. Shear strength governs the design of such walls. Prediction of seismic behavior, and followed by the design of these systems need an efficient modeling method. this study calibrates the effective modeling parameters of squat shear walls in small and large scales based on the test results. The modeling to be accomplished initially with non-linear finite element software on small scale (Vector2) and then with software by large scaleability (OpenSees), and the results were calibrated with test results. The study results show nonlinear finite element software has high accuracy in squat shear wall modeling. However, if a large-scale squat shear wall modeling along with a three-dimensional structure is required, on condition of a suitable aspect ratio, this paper is recommended to use OpenSees software.

In this study, a comparative study of non-linear static methods with time history method for Chevron braced structures (with LRB seismic base isolator at the base level) is performed. To find out the effect of the building's height on seismic responses of isolated structures, in this study 3 isolated building structures by LRB isolators with 3 different number of stories of 4, 7 and 10, located in a high seismicity area have been modeled in 3D by assuming the soil type C. Pushover non-linear static analysis procedures, with target displacements according to ASCE41-13 code and using three lateral load patterns, including structure's first mode, uniform and triangular have been analyzed using spectral dynamic, PSC and the results have been compared with those of non-linear dynamic analysis subjected to selected far-field earthquakes. The results show that in the estimation of maximum displacement of LRB isolators and also the amount of base shear, ASCE41-13 has a high degree of accuracy in structures with different heights. In estimating the displacement of maximum floors, first mode methods, uniform, spectral dynamic have had enough accuracy in all discussed heights. In estimating the relative displacement of structures' floors, by increasing the height of the structure, the accuracy of the triangular load's pattern reduces significantly. In contrast with it, the PSC method has high accuracy.

Fluid storage tanks, especially above ground tanks, are categorized as important and essential in energy infrastructure. These storages, which are mostly used to store petroleum fluids and fire water supplies, are therefore of great importance to the exploitation of tanks after the earthquakes. Fragility or vulnerability curve is one of the most effective tools for estimating the damage caused by the earthquake. Preparing the seismic fragility curve of above ground tanks on a pile is the aim of this research. This fragility curve is achieved regardless of tank body damage and only by focusing on the structural behavior of the foundation. These tank types are primarily built on low load bearing areas. In this study, three tank types that have been designed in accordance with API650-13 have been investigated in a practical project. For this purpose, using the static nonlinear analysis method, the structural capacitance curve of tanks was first obtained. Then, the seismic performance of these tanks was obtained for 12 spectra from different records with different accelerations. After calculating the damage indexes on the structure, the appropriate statistical distribution for the failure criteria was chosen. Finally, the calculation of the probability of failure for the fracture curve of the required tanks was obtained Fluid storage tanks, especially above ground tanks, are categorized as important and essential in energy infrastructure. These storages, which are mostly used to store petroleum fluids and fire water supplies, are therefore of great importance to the exploitation of tanks after the earthquakes. Fragility or vulnerability curve is one of the most effective tools for estimating the damage caused by the earthquake. Preparing the seismic fragility curve of above ground tanks on a pile is the aim of this research. This fragility curve is achieved regardless of tank body damage and only by focusing on the structural behavior of the foundation. These tank types are primarily built on low load bearing areas. In this study, three tank types that have been designed in accordance with API650-13 have been investigated in a practical project. For this purpose, using the static nonlinear analysis method, the structural capacitance curve of tanks was first obtained. Then, the seismic performance of these tanks was obtained for 12 spectra from different records with different accelerations. After calculating the damage indexes on the structure, the appropriate statistical distribution for the failure criteria was chosen. Finally, the calculation of the probability of failure for the fracture curve of the required tanks was obtained.

In this study, the effects of a subway station on the surface ground motion subjected to uniform and the non-uniform propagating seismic wave is investigated. Numerical analysis is carried out by finite difference method using FLAC soft-ware. Seismic wave scattering considering and ignoring the effects of the underground station in the case of uniform and non-uniform excitation is performed, and corresponding am-plification factors on the fee field displacement are discussed. The major results of this study indicated that the possible large amplification factor on seismic waves considering the underground station is obtained. Therefore, it should be paid more attention to seismic design for surface structures.

Steep slopes developed on the loose ground, either natural or artificial, are prone to landslide phenomena. During con-struction activities for the development of new Qaen-Afin road in South Khorasan and adjacent to Ravoshk village, a sudden landslide occurred in a shale slope, and newly-built stone bridge for the road destructed. In this paper, using geologic conditions, satellite images, the field evidence of landslide and SLIDE6 and Phase2 programs, the type, and cause of the landslide will be examined. The survey conducted with the help of satellite images and field visits showed that the land-slide occurred is a circular landslide with dimensions of ap-proximately 50×80 m. It had happened a few months ago, but unfortunately, no attention paid to it, and continued construc-tion activities in the rainy season stimulated the sliding mass and led to extreme conditions. The geometrical condition of the slope, just before the slope failure, was determined by us-ing GPS, surveying meter, and satellite images. Using this in-formation, the two-dimensional model of the natural slope, before any construction activity, created in SLIDE6. Slope stability analysis was performed using the simplified Bishop limit equilibrium method, and failure of the slope predicted successfully. Finite element analysis of the slope in Phase2 software arrived at similar results. This paper has shown that a lack of attention to first slope movements and continuing construction work was the primary cause of financial losses incurred.

Today, one of the challenges in safety management of under-ground excavations is the water inflow into them. The tunnels and underground constructions are causing to remove a pile of soil and rock area and significant changes in the state of tension it’s around environment. Invasion of groundwater in-to the excavation area is a major problem in excavation of tunnels that is located below the hydrostatic levels. The un-derground-water inflow into the tunnels is an important issue in the tunnel engineering. The subsidence of the ground in hydrostatic levels, reduce the aqueduct water resources and springs that are located in downstream of the tunnel, are en-vironmental problems of the tunnel excavation operations. In the present study, the groundwater inflow into the Kouhin tunnel railway is modeling with FLAC2D software. The effects of groundwater inflows in the tunnel that while excavation are studied by numerical model. In other hands, initially in-vestigated the adverse environmental effects caused by the Kouhin railway tunnel excavation (subsidence the ground water levels and changes in the groundwater inflow in the region) and then provide some strategies for reducing these effects. The strategies that can be used in prevention of groundwater flow into the underground tunnels are: Under-ground water level recovery with application of concrete sealing operations without drainage and simultaneous use of forepoling methods that to be presented as a solution to re-duce environmental impact. Doing this requires using of con-crete lining with high strength properties to withstand hydro-static pressure of water collected on the back cover.

Overburdens are stones that lack the required properties of minerals to be extracted and are piled adjacent to mine, while they may be used as aggregates in the asphalt mixture. Set-tlement is a cheap mineral composed of iron oxide, silicone and aluminum oxide, application of iron, silica and aluminum as aggregates in pavement industry has great effect on per-formance of asphalt mixtures. In this study, we investigated the effect of using Sillimanite aggregate material as an alter-native for Limestone aggregates on resilient modulus, Mar-shall Strength and skid resistance parameters at various tem-peratures. The modeling was carried out by using finite ele-ment software based on the elastic behavior of the layers to determine the effect of elasticity modulus variations due to the change in aggregate type on the pavement response. The re-sults indicated that the use of Sillimanite aggregates in the asphalt mixture led to a lower optimum bitumen percent than Limestone material; and also, in the asphalt mixture made of Sillimanite aggregates with optimum bitumen percent, Mar-shall Strength was increased by 15% and the resilient modulus by 25% compared to the mixture with Limestone material. Application of Sillimanite material in the asphalt mixture could enhance the friction resistance of the mixture against the abrasion resulting from traffic loading due to its higher hardness compared to Limestone material. The results of nu-merical analysis showed that the aggregate’s type had the lowest effect on the critical tensile strain at the bottom of the asphalt layer, then came the percentage of bitumen in the mix-ture and, finally, the bonding of the layers had the highest ef-fect.

Accumulation of consumable or produced materials in out-door areas and exposed to the airflow is an important issue of environmental concern. Also, wind erosion of raw materials from the storage piles in some industries causes environmental problems and economic consequences. The materials are accumulated in various volumetric shapes in an outdoor environment, which is usually pyramidal and conical. The subject of this study is about the percentage of wind erosion from the surface of the pile and the intensity of the particle deposition due to the free-stream flow passing through the various points of the pile’s surface. In this research, the wind erosion or in other words, the movement and deposition of particles from the surface of the pile have been discussed. So, a comparison between the piles with different shapes has been performed according to the reduction of wind erosion. So, a comparison between the piles with different shapes has been performed according to the reduction of wind erosion.

For a given channel width, duckbill and oblique weirs have longer effective length, and this could be effective on their dis-charge coefficients and efficiency. In this study, we tried to examine the role of some of the hydraulic and geometric parameters of mentioned weirs and their height on the discharge coefficient into the channel using the Fluent numerical model and the results of this model compared with the Flow-3D model and experiments data. The pressure, velocity, turbulence, and the free surface of the flow were modeled by k-ε RNG and volume of fluid (VOF) algorithms, respectively. The NRMSE of the Flu-ent model in the simulation of the discharge coefficient was 0.0565, which indicates the high accuracy of the model. Results showed that in both weirs, the discharge coefficient decreases with increasing discharge or upstream head. The maximum dis-charge coefficient was found in the H/P≤ 0.35 in both weirs. The results indicated the oblique weirs had a higher discharge coefficient compared with duckbill weirs and thus had higher flow capacity.

In this research, due to the importance of identifying the mechanisms affecting the scouring on this types of bridge piers, the effect of the geometric shape of the piles installed under the inclined piers and also the effect of the pile cap leveling in the sedimentary bed have been investigated and the properties of the scouring around the inclined pier group was studied numerically using the FLOW-3D software. The study of total shear stress in the flow bed at different leveling of the pile caps shows that the highest shear stress is created when the pile cap position is at the same level as the river bed; by installing the pile cap at a lower level than the river bed, the maximum shear stress decreases. This may be due to the fact that in this case, the distance between the pier group increases and the presence of the second pier decreases the flow rate in the pier group and different pier in the one pier group acts as the two independent piers in the formation of the flow pattern. By comparing the final longitudinal sections of the scouring at different leveling of the pile cap, it is concluded that the largest reduction in scouring depth occurs in aerofoil-shaped pile caps and pile caps with the sharper nose and better aerodynamic shapes are good options to control the horseshoe vortices and will reduce the scouring depth around the inclined pier group.

In the present study, hydraulics of vertical slot is simulated, using Flow-3D. k-ε turbulence model had the most performance among different turbulence models. Next, the velocity pattern, volume of fish rest-area, and flow turbulence in the channel were analyzed in order to evaluate the performance of fishway with different geometries. In this regard, the influence of geometry on the performance of fishway is investigated. Results showed that by decreasing the ratio of the length of the large wall to the small wall, the longitudinal component of velocity was decreased by an average of 25.11%. By increasing the end of the large-wall angle with respect to the pool wall, the volume of the rest area was increased by 3%. By increasing the end of the large-wall angle with respect to the pool wall parameter, the turbulence energy was increased by an average of 30.66%. In general, the ratio of the length of the large wall to the small wall has a greater effect on reducing the flow velocity for the fish to cross the fishway and also by increasing the end of the large-wall angle with respect to the pool wall, the rest area of the fish and turbulence energy has increased.