AMIRKABIR JOURNAL OF CIVIL ENGINEERING (AMIRKABIR)
Year:2018 | Volume:50 | Issue:3 |Papers Count:17

Due to architectural reasons and constraints on the plan structure, openings such as doors, windows and installations ducts have been created on the concrete shear wall. It causes some changes in behavior, stiffness, load capacity and failure mechanism of specimens. In this paper, ABAQUS software is used for finite element modeling and investigating the parameters. In order to verify the results of this software, a scaled six stories wall with two bands of openings are modeled in ABAQUS software and compared with experimental results. After verification, parameters of opening area and position, bands of opening coupling, beam dimensions and diagonal reinforcement are investigated by non-linear finite element method using concrete damage plasticity model (CDPM) under the monotonic loading. Results further confirm that if dimensions of opening do not change the failure mechanism of the wall, the opening position will be more effective than the opening area. In specimens with two bands of opening, making a ratio of lateral pier length to middle pier length more than 50%, increases effective compressive area and coefficient correlation and thus the sample has reached its maximum load capacity. Setting the diagonal reinforcement both on coupling beam and in other compressive parts of the wall (base wall), decreases the crack propagation and augments the compressive area of the wall. It also leads to increase the load capacity of specimens by 19. 6 %. The comparison of results also showed that a specimen with coupling beam height to height floor ratio of 0. 52, the use of diagonal reinforcement on the coupling beam and putting up them in the base wall can be a suggestion for appropriate design of concrete shear wall with an opening.

In order to evaluate the effect of fiber part in the municipal solid waste on its shear strength, a study was conducted on the Kahrizak waste disposal landfill in Tehran. Shear strength of the waste samples was evaluated through the large-scale tri-axial consolidated and undrained (CU) tests on reconstructed fresh and 9 years old waste specimens. Evaluation and comparison between the results is done on the reconstructed waste samples with a density of 11 kN/m3 in the non-fibrous state and containing the 12%-weighing plastic fibers. To study the fibers effect, three different types of the plastic bags with three ranges of the tensile strength including 7, 16 and 21 Mpa was used that their dimensions is 2. 5*8 cm. In the next step these sheets and the waste samples were mixed. The results show that the fiber part of waste material samples is one of the main factors in providing the shear strength of the waste material. As the tensile strength of the fibers increases, the shear strength of the waste masses increases too. As an initial result an increase about 200% in the tensile strength of the fiber, causes an additional tension increase more than 100% in the waste sample. The plastic fibers in the samples caused a reduction in cohesion (C), and increase the internal friction angle (Φ ) of the samples that could be seen in the old waste samples more than fresh ones. In addition to the tensile strength, the elasticity and the amount of deformation before the fracture of the fiber part can influence the behavior of the waste mass.

Occurrence of extreme storm waves predisposes natural beaches to erosion. During occurrence of these storm waves, infra-gravity swash energy plays an important role in the amount of erosion created. The available formula for infra-gravity swash is only based on wave heights and wave length and its accuracy is low. Recently, model trees have been introduced as one of the new methods in the data mining approaches that give all possible relations between the involved parameters. In this paper, a new model based on hydrodynamic parameters including the surf similarity, momentum flux and non-dimensional characteristic velocity parameters is presented by using the M5′ and MARS model trees. To generate and evaluate models, all of 579 field data available in literature was used. The results indicated that the developed MARS model improves the RMSE and R values by 42% and 26%, respectively, and the M5′ model improves these values by 16% and 12%, respectively, in respect to the most common empirical model. According to sensitivity analysis of MARS model and also results of M5′ model, the non-dimensional characteristic velocity parameter showed the most correlation and the surf similarity parameter showed the least correlation with infra-gravity swash motions. The performance of developed models is also compared with a numerical study implemented on Tizimin beaches in Mexico.

Million tons of waste are produced annually in mining and processing of dimension stone in Iran. In most cases, the waste is released in nature that would cause environmental hazards. In this work, artificial stone slabs were manufactured by combination of coarse waste and sludge powder of stone cutting factories. The results show that the manufactured stone slabs have physical and mechanical specifications according to Iranian national standards for building stone. With increasing the amount of resin in the composition, the flexural and tensile strength were increased and the compressive strength and water absorption coefficient were decreased. The slabs produced from granite waste compare to the slabs produced from marble waste had better physical and mechanical specifications. At the optimum condition, with the aim of using more waste, with a composition of 90% marble waste and 10% resin, artificial stone slabs were produced which have compressive strength about 143 MPa, flexural strength of 21 MPa, tensile strength of 25 MPa, water absorption coefficient 1% and density equal to 2. 32 g/cm3.

In this research, the punching shear strength of flat plate lightweight self-consolidating concrete and lightweight concrete slabs is studied. The experimental work consisted of 9 rectangular slab specimens with either 100 or 150 mm depth, 1000 mm length and 1000 mm width. The type of concrete, strength of concrete and reinforcement varied in different tests. The slab dimensions and the area of reinforcing bars in slabs have been carefully designed so that the slabs failed due to punching shear. In a test, load and displacement were measured using a data acquisition system. Using the results, the behavior of slabs, cracking pattern and the slab stiffness were studied. The experimental results have been compared with the provisions of different codes. The comparison showed that the BS-8110 code estimates the punching shear of lightweight slabs most accurately. The slabs made by leca lightweight aggregates can be used in structures providing that they have a good mix concrete design.

Coupling beams made of high performance fiber reinforced cementinous composite (HPFRCC) are capable alternative compared to traditional concrete and resulting to increasing capacity, ductility, energy dissipation and also reducing the congested amount of longitudinal, transverse and diagonal reinforcement. This article investigate the influence of HPFRCC replacement with normal concrete in coupled shear wall with connecting beam. The first specimen of coupling beams designed and made with normal concrete and second specimen of coupling beams designed and made with HPFRCC and tested under cyclic loading. The results indicated that HPFRCC increased tensile capacity of concrete, prevented the increasing the crack widths and increased absorbed energy. also increased rigidity compared to plain concrete specimen and shear-tensile failure was changed to shear-slippage failure. amount of shear strength for HPFRCC coupling beams were 117 percent than normal concrete and the use of fibers increased the energy absorption about 60 percent.

Problematic soils are those that make the construction of foundations extremely difficult. These soil should be replaced or modified. These types of soils are problematic, such as swelling soil, dispersive soil and the soils that loss their strength at saturated conditions. As silty soil and quicksands have low strength at saturated condition, it seems that stabilization of these soils is necessary. In literature, stabilizing these soils by cement is more effective. On the other hand, by developments in nanotechnology within last three decades, researchers discovered a material with unique properties, named as carbon nanotube. The carbon nanotube has very high strength even higher than steel, high elastic module and toughness and other unique properties. Within last three decades, many studies are concerned in applying this material in cement composites, but only we can find a few works related to use of this material in soil stabilization. Since carbon nanotube attract each other, we should separate nanotube particles. In this study, different values of ultrasonic energy (as mechanical agent) and polycarboxilate based super plasticizer solution (as chemical agent) was used to overcome carbon nanotubes agglomeration problem. As it is not possible to use carbon nanotubes in dry state, to investigating the effect of carbon nanotubes on the soils, the aqueous solution of carbon nanotube was added to the soil, using wet mix method. The samples were cured in water for 7 days. After performing direct shear test the shear strength and its parameters were evaluated. The results show using 0. 125 % carbon nanotube and applying different ultrasonic energy to the carbon nanotubes solution the highest benefit of ultrasonic energy achieved when it used as 500j/ml. Comparing to the samples that threated by defective ultrasonic energy, it is observed that the shear strength of silty and sandy soil was improved as 19. 7% and 21%, respectively.

The present research investigate the discharge coefficient and energy loss flows of semi cylindrical wire-gate. The experiments were conducted in rectangular flume with the length of 8 m, width of 0. 282 m and height of 0. 3 m. In fact, the soil conservation and watershed management research that occurred in laboratory, used the physical models with diameters of 70, 120 and 160 mm in height of the opening between zero until radius and differently discharging. The ratio of cylindrical structure diameter to channel width (D/B) was included range of 0. 25 to 0. 57 and the Froude number was conducted range of 0. 012 to 0. 55. The research showed that all angles alignment structure discharge coefficient and dimensionless parameter Hf/H (the ratio of energy loss to the water depth upstream) cases curvature upstream and curvature of the downstream respectively with increasing dimensionless parameter H/P, increases and decreases. The constant a (H / P), discharge coefficient and dimensionless parameter Hf / H when the curvature is upstream semi cylindrical wire-gate due to the gradual shrinkage of flow lines and thus decrease the input is less than the curvature is downstream structure.

Providing of semi-autogenous (SAG) mill models for prediction of its effectiveness is one of the most useful tools for better design of grinding circuit. Many SAG mill models have been presented in the literature, but in most of them have not been predicted the mill performance in industrial scale. Semi-autogenous mill power has an effective impact on the mill performance. So in this study, a new model based on combination of radial artificial neural network and principal component is presented to predict semi-autogenous mill power. The feed moisture, mass flowrate, mill load cell weight, SAG mill solid percent, inlet and outlet water to the SAG mill and work index selected as input variables and evaluated the effect of them on the mill power. The results showed that the trained hybrid model of artificial neural network and principal component with R=0. 8456 and RMSE= 68. 0752 can be used to predict the semi-autogenous mill power in industrial scale. The sensitivity analysis results showed that all model input parameters had a significant effect on the output.

Transportation infrastructure imposes enormous costs, along with several negative consequences, on the governments. Confronting such issues, freight transport policy analysts struggle to shift truck movements to rail to diminish transportation externalities that include environmental costs and safety issues. Therefore, policy-makers need to be aware of the consequences of their decisions beforehand. This study is mainly focused on two policies targeting fuel price and access to rail. A nation-wide freight mode choice model is developed for Iran, based on which, shippers’ tendency to choose rail or truck is analyzed, given shipping cost, commodity weight, commodity type, and rail accessibility. Total fuel consumption and air pollution costs are compared in 30 scenarios. We found that total transportation costs will be reduced by more than 20 percent as a result of modal shift from truck to rail, if the government reallocates the gasoline subsidy to construction of prioritized railroads.

Bridges are known to be one of the most vital and vulnerable components of any transportation system. A majority of highway bridges in the world have curved superstructure configurations and also have in-span hinges. The curvature and in-span hinges in multi-frame bridges lead to significant differences in bridge dynamic response during seismic excitations. This article explores the seismic response of concrete curved bridges considering columns height differences and the effects of span number. Five bridge models have been studied including: a four-span bridge model with equal column height as the base model, two bridge models with non-uniform columns height, a three-span bridge and a five-span bridge models having different span numbers. Several dynamic non-linear time history analyses are performed based on seven different records. The results showed that increasing the height of columns and reducing the number of spans in this subclasses of bridges lead to increase the peak of columns drifts and consequently the bridge seismic vulnerability.

In recent years, using of baffle sloped culverts is improved in order to energy dissipation and facility and improvement of fishes passage. In the present study, asymmetric shape w overflow is used as obstacles in Open Calvert. As spillway event angle two 40 degrees angle in 10 and 15 cm weir height to flume bottom were used. Experiments of present research are done in a steep flume with bottom width of 25 cm length that w-shaped spillways attached at about 5 km from the flume, and the distance between barriers, variable slope from 3 to 7. 6 percent in different discharge was scheduled. In this study, three physical model including models with 30 obstacles of kind of asymmetric w shape spillway, with relative distance of 6/0 (λ =0. 6), and a model with 15 barriers with relative distance of 1. 2, and a model with 10 models with relative distance of 1. 8, was setup. The results obtained from these experiments showed that by increasing the relative distance, Manning coefficient and Darcy-Weisbach coefficient is decreased, and also by increasing the slope, Manning and Darcy-Weisbach coefficient decreases. Based on the obtained results in the slope of 3%, Manning roughness coefficient, reaches from 0. 065 on the 0. 6 relative distance reaches to 0. 048 in the 1. 8 relative distance. The square root of the Darcy-Weisbach coefficient, in slope of 3%, in relative distance of 1. 8, reaches from 0. 87 to 0. 65.

Although hydraulic fracturing has many applications, but breakdown pressure from hydraulic fracturing process is very important, since this pressure is related to the in situ stresses. The hydraulic fracturing fluid over time, injected into a borehole until it reaches to the limit such that tensile fractures occur in the wellbore wall. At the moment of occurrence of fracture, fluid pressure within the wellbore, said the breakdown pressure that is equivalent to the peak point of the pressure-time curve. There are simple and classical relations that related breakdown pressure to the in situ stresses. Estimation of in-situ stresses is a major challenge in Geomechanic. In this paper, the finite difference modeling of hydraulic fracturing will be discussed. Modeling is base on two-dimensional plane strain assumptions. The purpose of the modeling is to study on parameters affecting the breakdown pressure, parameters that do not exist in the classical relations but affect the breakdown pressure. After validation of the model and in accordance with the results of this paper, breakdown pressure not only is related to the in-situ stresses and rock tensile strength but also wellbore radius and pre-existing cracks in the wall of the wellbore are parameters that involved in hydraulic fracturing and breakdown pressure. For isotropic in situ stresses variation of wellbore radius don’ t effect on the breakdown pressure but for non-isotropic in situ stresses with increasing wellbore radius breakdown pressure decreases and with increasing deviatoric stresses (difference between in situ stresses), the rate of breakdown pressure reduction increases.

Open-channel junctions have been widely used in different hydraulic and agricultural networks. Formations of a low pressure zone with recirculating flow at downstream edge of the junction (with high sedimentation potential) accompanied by a high-velocity zone (with high erosion potential) located at the opposite wall of junction are the most characteristic features of flow in junctions. Literature addressed a lot of numerical studies on evaluation of flow pattern in open-channel junctions and elimination of aforementioned problems using geometrical modifications, application of lateral channel separating wall, implementation of oblique angles of lateral channel, and so on. Using submerged vane to reduce amount of erosion as well as sedimentation potential, has comprehensively been assessed in the present paper. First, the numerical model was validated by previous studies. Second, a large number of numerical models have been performed to evaluate the effects of mentioned solution in open-channel junctions. Moreover, optimal ranges of different submerged vane’ s parameters have been introduced. The results showed a comprehensive reduction in sedimentation and erosion potential of open-channel junctions. For example, 89% reduction in length of separation zone has been detected in one of the proposed solution. In addition, the best performance of these vanes was observed in discharge ratio of 0. 25. Moreover, applications of vane with height of more than 0. 5h (h represents the water depth) and/or angle of more than 40° are not suggested.

Due to destructive effects of near-field earthquakes on building structures, this paper attempts to investigate the seismic behavior of base-isolated building frames under the effect of near-field ground motions using the non-linear time history analyses (NLTHAs). For this purpose, two steel moment-resisting medium-rise frames including 9 and 12-story ones were isolated using the lead-rubber base isolation system considering three levels of stiffness i. e. Hard (H), Normal (N) and Soft (S) isolators. Non-linear time history analyses (NLTHAs) were conducted using different sets of near-field ground motions with forward directivity, fling step and no pulse characteristics. Also, for the purpose of comparison, the NLRHA was carried out using a set of far-field ground motion records. The effect of isolator stiffness under different types of ground motions as well as the effect of pulse period on the seismic responses is scrutinized. The results showed that the change in the stiffness of isolation system from hard type to soft and moderate types (that increases the damping and period of the structure) reduces the seismic demands of the structure. Also, the story drifts of base-isolated building frames with soft isolator (more damping) are smaller than those with hard and moderate types for different values of pulse period, Tp. On the other hand, the sensitivity of the responses of base-isolated building frames with hard isolators (low damping) to pulse period is large.

In this paper, the effects of gamma oxide nano-aluminum as the cement modifier; on volumetric and mechanical properties of problematic clay using an experimental research were described. Initially, the impact of cement was evaluated for soil improvement and in the following the impact of cement mixed with nano-aluminum on soil properties were investigated. Evaluation of these effects was done in curing period from 1 day to 28 days. Properties evaluated in this study included Atterberg limits, density and proctor compaction, uniaxial compressive strength, California bearing ratio and the power of hydrogen (pH). Scanning Electron Microscopy (SEM) analysis had also been used to monitor and evaluate the impact of nano-scale materials. Results of this study indicated that in the short-term behavior, the effect of nano-aluminum in increasing the strength and setting speed was very tangible. Also the very small percentage of nano-material could be alternative for a significant proportion of cement in the improvement and modification of soil, which reflects the economic impact of nano material as well.

The composite shear wall system is considered as one of the newest structural systems. In composite steel shear wall, reinforced concrete cover causes to increase shear capacity of steel shear wall up to in-plane shear yield limit rather than tension along the diagonal tensile field by anchoring steel plate and preventing its buckling. In innovative composite steel shear wall system, a gap is created between concrete cover and boundary beams and columns. Tests on traditional and innovative composite steel shear wall show a slight failure in innovative system compared to traditional system. In this paper, steel plate, concrete cover and frame were separated to calculate the stiffness of composite steel shear wall by their interaction (CPFI). To evaluate the effect of concrete stiffness on composite steel shear wall stiffness, the gap between concrete cover and boundary members has been discussed, and then two relationships have been proposed to calculate the stiffness of composite steel shear wall. The results show that the use of low yield stress steel plate with equivalent thickness to traditional steel plate will increase stiffness in composite steel shear wall. Also, concrete cover involvement in boundary members will increase the stiffness.