نشریه مهندسی عمران
سال پنجاه و یکم شماره 5 (آذر و دی 1398)

The failure of the bridge caused by local scour, the importance and necessity of studying the prediction of scour depth and ways of reducing it. One of the important method to reduce the effects of erosion factors is to use a thin plate around the bridge pier called collar. Collar dimensions and the position have great factors on reducing local scour around bridge pier. In this research, collar with four forehead length (lca ) equal to B, 2B, 4B and 9B(B is width of the pier) are examined. The collars were installed in four levels equal to: on the bed, 0.12B under the bed, 0.5B and B above the bed. The experiments have been conducted with three Froud Numbers equal to 0.13, 0.16 and 0.19 in clear water condition. The experiments have been done on a flume with the length of 6 m, width of 73 cm, and a depth of 60 cm with a slope near zero in Hydraulic Laboratory of Shahid Chamran University of Ahvaz. The results showed that increasing dimensions of collar will increase the efficiency of performance and the best dimention lca (length of oblong collar in the front of the pier) were B and 2B. The best position to install the collar were on the bed and 0.12B under the bed. In these situations the collar had 100% and 88% efficiency in respectively reducing the scour depth.

In first part of this paper, the theory of design of X-braces using different steel grades introduced and its effects on different frames verified using nonlinear static analyses. It was found hat using lower grade steel in X-braces increases the stiffness, energy absorption capacity, dampingand ductility of system and decreases its lateral drift. In order to completely investigate behavior of steel structures with X-bracing system in design with different steel grades and consider their dynamic behavior, the frames with different stories studied using advanced nonlinear static and Incremental Dynamic Analyses (IDA). The results presented as comparative diagrams and tables. The near and far field earthquakes used for dynamic analyse sand their seismic performance studied. Therefore, this research can lead to better investigation of seismic behavior of X-braced systems in design with different steel grades. The proposed theory along with analyses show that building codes and steel seismic design specifications can consider the effects of steel grades in seismic parameters definition of structures.The comparative diagrams and tables show that the seismic behavior of X-braces designed with lower grade steel improves considerably. In addition, the response of structures under near field earthquakes is bigger than related parameters under far field earthquakes.

The leakage losses from the unlined canals are a major contributor to water losses in the agricultural sector. An understanding of the nature of leakage losses can help to improved water conveyance efficiency and provides solutions to solving water scarcity problems. In this research, numerical simulation was used to study the effective factors on seepage from earth canals. To verify the available information, some of the earthen canals in Zayandehrud irrigation network were used. A number of 246 numerical models including different sections of trapezoidal, rectangular and triangular earthen canals were performed using SEEP/W software. The results showed that, for numerical simulation a width of 15 times the width of the water surface in the canal would be required for the modelling of the left and right lateral boundaries. The comparison of seepage with empirical relationships showed that the empirical relationships show a large error in the seepage estimation, although Moritz's relation with the coefficient of determination 0.373 was better than the rest. Linear and nonlinear multivariate regression relationships provide a suitable match for seepage discharge estimation. Linear relationship was preferable due to small root mean square error (RMSE) and its simplicity. Wetted perimeter has been distinguished effective parameter in seepage from canal, but canal side slope had low effect on seepage. It is suggested that in future studies, the effect of groundwater depth on leakage from the canal should be considered.

The excavation impact (e.g. due to Blasting, TBM drilling, etc.) induces an excavation damaged or disturbed zone around a tunnel. The presence of a damage zone around a tunnel boundary is of significant concern mainly with regard to safety, stability, costs and the overall performance of the tunnel. The damaged zone is essentially characterized by reduction in strength and stiffness, and increase in permeability. However, the dimensions of the restricted damaged zone is restricted. The effect of this zone is generally considered by a disturbance factor used for the whole rock masses. In this paper, the behavior of tunnels under different damage conditions is examined. In this regard, a fully analytical solution is proposed. The solution is presented for tunnels excavated in elastic–brittle–plastic rock masses with Hoek–Brown failure criterion. The damaged zone is assumed to have cylindrical shape with varied parameters. The results obtained by the proposed solution indicate that, the effects of the alteration of rock mass properties in the damaged zone may be considerable. In practice, the global damage induced by blasting is taken into account by using the damage factor D . In traditional methods, the blast damage factor D is applied to the entire rock mass surrounding the tunnel. This is a common modeling method which can greatly underestimate the strength and stability of the overall rock mass. In this regard, the result show that the blast damage factor D is more appropriate to be applied to the actual zone of damaged rock.

In the present Experimental research, the behaviour of exterior RC beam-column connections subjected to cyclic loading is studied using steel and Glass fiber-Reinforced Polymer (GFRP) reinforcing bars. In this research, 8 specimens of exterior RC beam-column connections were tested in which four specimens included GFRP reinforcing bars and the remaining four specimens included steel bars. The confinement of beam longitudinal bars was different in the connections. Also, two types of concretes were used with the strengths 30 and 45 MPa, respectively. The specimens were tested under cyclic loading.The results show that GFRP has great ability in dissipation of energy, yet the amount of the dissipated energy by GFRP is less than that of steel bars. Although the amount of energy absorbed by GFRP materials was lower than steel bars, they could be used instead of steel bars or in combination with steel bars due to the resistance of corrosion. Load-story drift envelop for GFRP strengthened specimens with high strength concrete has the essential requirements for acting as a member of a moment frame in seismic regions, while all the specimens with steel bars have these requirements. In case of GFRP strengthened specimens with high and normal strength concrete, increasing the cyclic loading results in flexural failure of the beam in the beam-column connection region. Increasing the confinement of concrete beams leads to the reduction of crack width. Furthermore, at higher drifts, spalling was not observed in concrete surface in beam-column connection region.

Water quality degrades due to the complex physical, chemical and biological processes passing through the transmission lines. One of these widely attracted processes is contaminant intrusion due to a transient event. When the negative pressure wave of water hammer reaches a structural deteriorations such as a leakage, it can suddenly sucks pollution from the surrounding area of leakage to the main pipeflow which can in turn endanger public health. The purpose of this study is to determine the effect of hydraulic parameters on the duration of negative pressure and the magnitude of negative pressure and subsequently the volume of contaminant intrusion in a reservoir-pipe-valve system with leakage. In this study, the Eulerian method of characteristics was used to model the transient flow. The total Volume of Contaminant Parcel (VCPt) from the leakage site taken from Lagrangian solution of the advection equation used as criterion to compare various transient senarios.The results are provided in a number of graphs which quantify the influence of each system parameter. The results indicate that the volume of contaminant intrusion is mostly dominated by the amount of negative pressure at leak. The amount of intrusion is investigated via several case studies..The reservoir pressure head, fluid velocity inside the pipe, the wave speed, the pipe diameter, the leak diameter and the leakage location are respectively the effective hydraulic parameters on contaminant intrusion. Investigation of the interaction of these factors in the volume of contaminant intrusion can be considered as a subject for future research.

Soft clayey soil generally has high compressibility and low strength. Presence of this soil type in the site of ‎civil projects can always be a challenge for construction issues. Soil stabilization is one of the useful ways to ‎improve problematic soils. Cutter Soil Mixing (CSM) is almost a new method for deep stabilization. This ‎experimental study, investigate the effect of different depths on soft clay ‎properties which stabilized by CSM ‎method. To simulate various depths and related surcharge pressures, new devices were designed, modified ‎and used for laboratory tests. Moreover, mixture of blast furnace slag and hydrated lime slurry was used in this ‎method for the first time. The samples were cured for 28 and 56 days ‎under various surcharge pressures, which actually represent different depths. The results revealed that by increasing the depth, mositure content and saturated/dry densities of the samples were decreased and increased respectively. In addition, by ‎passing the critical depth, fewer changes were obsorved in the moisture contents and saturated/dry densities of the samples. Finally, the strength parameters of stabilized samples were icreased significantly.

The behaviour of gusset plates in concentric braced steel frames has been studied. Parameters studied are the thickness and shape of the gusset plate, use of linear and elliptical clearance, non-existence of clearance, edge, longitudinal and internal stiffeners, and use of a single- or double-profile bracing. Analysis has been performed by the three-dimensional non-linear finite element method using the ABAQUS code. Cyclic loading has been used. By eliminating the clearance, the plastic strains in weld between the gusset plate and bracing and plastic strains in the gusset plate are increased. In the weld between the gusset plate and bracing, the existence of any type of stiffeners has increased plastic strains compared to unstiffened gusset plates. In most cases, edge and longitudinal stiffeners have decreased plastic strains of the gusset plate and internal stiffeners have increased them The maximum energy dissipation has belonged to edge stiffeners with an increase of 15.4% compared to unstiffened gusset plates. By decreasing the thickness from 24 mm to 18.8 mm the maximum stress has been decreased by 3.5%. For similar gusset plates, use of single-profile bracing instead of double-profile bracing has not changed the value of maximum lateral load for compressive bracing. In this case, most of variation has belonged to the plastic strains of the weld between the gusset plate and bracing with an increase of 30% in a rectangular plate with a linear clearance and a reduction of 65% in a rectangular plate without clearance compared to a double-profile bracing.

Vortex is shed by flow collision with obstacles in its path. If the frequency of vortex shedding equals the frequency of natural oscillations of flow, resonance will be created and transverse oscillation perpendicular to flow with greatest wave amplitude will occur. In this study, in order to investigate the characteristics of the transverse wave caused by the vortex shedding of the obstacles, 135 cylinder barriers with a diameter of 20 mm in 5 different configurations were arranged in the laboratory flume. In total, 900 tests were carried out which variables were flow discharge, average flow depth, channel slope, longitudinal and transverse distance between obstacles. In each test, after the formation of transverse oscillations, their characteristics including amplitude and frequency of wave were recorded. Then, the effective variables on transverse wave characteristics and their effects on the involved dimensionless numbers were investigated. The results indicated whatever the flow discharge is increased, the maximum wave amplitude due to resonance occurs in larger average flow depth, which has more amount. Also by changing the longitudinal distance of obstacles, Roshko's changes relative to increasing of Ursell were ascending at the beginning and they were reversed after reaching a certain range of Ursell number; moreover, by increasing the flow discharge, the rate of Ursell changes relative to Roshko decreased. Finally, by using dimensional analysis and statistical software, the equations between Roshko with Ursell and Froude numbers were proposed for each of the modes I and II and the validation of equations were approved (R2= 0.92).

In this study we explore the efficiency and usefulness of integrating WRF model with CALMET model in order to generate high accurate wind field. On the first stage three dimentional wind field of the region was processed using WRF model and the result made available to CALMET model as an initital guess. On the second stage the WRF model was put aside and surface meteorological data along with the athmosphere above the Mehrabad meterological station. Finally, the CALMET model was implemented using the combination of WRF model data and observational data. Then the efficiency of mentioned methods was explored using statistical analysis, comparing temperature profiles, wind speed and simulated data with observational data of Imam Khomeni airport meterological station in the intended period. Results of the statistical indexs which were used in this study including index Of agreement (IOA), mean bias erro (MBE), root mean-square error (RMSE) and mean absolute error (MAE) indicate the high power of WRF/CALMET integrated model in simulating wind field of the region so that the value of index of agreement for wind speed in the first stage is 0.70-0.85, in the second stage is 0.59-0.83 and in the third stage is 0.76-0.90. Generally the results of this study shows that using and combining the outputs of WRF model with observational data as input for CALMET model is an efficient way for generating accurate metetological data for studying air quality modeling specially in countries like Iran in which the upper athmospher data is hardly measured.

The basis of seismic separators in reducing the acceleration applied to structures is based on an increase in the natural period of vibration of the structure. In high-rise structures, the natural period itself is high. In this case the flexibility of superstructure may be in conflict with its elastic behavior. In the present study, 240 structures were modeled and analyzed in the first step to the question of whether the addition or reduction of the stiffness of the substructure and superstructure (1-100 times and 0.001 to 1 times respectively) affected the acceleration distribution or not? The results of the analysis of structures that were of five types of plans and at elevations 10, 15, 20, 24 and 28 floors showed that adding the stiffness of the superstructure can lead to a decrease of about 30 percent of the maximum roof acceleration (relative to the isolated structure without increasing the stiffness of the superstructure); However, the use of base isolation in the structures decreased about 50% of roof acceleration. The significant decrease in roof acceleration was related to structures with a 10 times increase in the stiffness of the superstructure compared to normal structure. In the next step, with the push-over analysis of 15 structures of this set, it was determined that in all isolated structures (with varying stiffness), the superstructure will remain in elastic state and none of the hinges formed in the members, exceeded from IO region.

Contaminant intrusion in pipelines is an important mechanism, which may lead to deterioration of the drinking water quality. One of these widely attracted processes is contaminant intrusion due to a transient event. When the negative pressure wave of water hammer reaches a structural deteriorations such as a leakage, it can suddenly sucks pollution from the surrounding area of leakage to the main pipeflow which can in turn endanger public health.In this research, numerical and mathematical modeling of a reservoir-pipe-valve system with leakage has been used to investigate the effect of the interaction of hydraulic parameters on the volume of contamination introduced into the pipelines during the waterhammer. In this study, the Eulerian method of characteristics was used to model the transient flow. The total Volume of Contaminant Parcel (VCPt) from the leakage site taken from Lagrangian solution of the advection equation used as criterion to compare various transient scenarios. In order to provide a better understanding of this phenomenon, in 72 different situations, contaminant intrusion has been investigated. The average rate of contaminant intrusion in the the long viscoelastic pipe line to elastic pipe is equal to 7.2%. This ratio is 49.6% in the case of a short viscoelastic pipeline.The results indicate that the volume of contamination sucked in the viscoelastic pipe in different conditions is less than that of elastic pipe. The results clearly outperform the viscoelastic pipe in preventing contaminant intrusion.

Rutting is one of the main reasons for reducing the life of the asphalt pavements. Asphalt binder modification using various additives is one of the most common methods for rutting reduction and asphalt modification. Many materials such as oils, ashes, polymers, and nanomaterials are used in asphalt binder to improve asphalt mixtures. In this paper, physical and rheological properties of asphalt mixture modified by titanium oxy di-fluoride (TiOF2) nanoparticles as an additive were investigated. The degree of penetration and the softening point tests on the control and modified asphalt binder showed increasing nanoparticles amount caused an increment in the softening point and decrement the degree of penetration due to friction increasing between needles and bitumen. Rheological properties were investigated by Dynamic Shear Rheometer (DSR) test on the control, modified asphalt binders and the asphalt binders obtained from the rolling thin film oven test. Repeated Load Axial (RLA) Test were performed to study the rutting properties of asphalt mixtures. The results showed that the addition of titanium oxy di-fluoride nanoparticles (gray titanium nanoparticles) to the asphalt binder increased the resistance of shear deformation and improved the elastic behavior.

Dynamic vibrations of mechanical equipment affect the magnificent performance of themselves, and the other structures installed on them. The gradual increasing of their angular velocity leads to some rare occurrence such as Resonance, Pseudo Resonance, Beating, Pseudo Beating phenomenon and so on, when it has gone on angular velocity of mentioned structures. Therefore, dynamic responses of these structures should be declined. In this study, active and semi-active control approaches have been used to going down the responses of a single degree of freedom structure subjected to the above-mentioned probabilistic phenomenon. In addition, some existence optimum functions have been applied to determining the TMD’s frequency and damping parameters. These parameters of semi-active TMD are predicted utilizing two different strategies, the Fuzzy Logic system and Ground-Hook algorithm. The logic of making alteration to damping ratio is based on regaining the equilibrium of structure as it vibrates. Copping with different phenomenon, results of this investigation indicate the advantages of semi-active tuned mass damper usage to drop dramatically the system displacement by 32 to 47 percent. Moreover, using of fuzzy logic systems in order to set damping parameters of TMD, results in 1.5 to 6.2 percent more downward trend in comparison to Ground-Hook algorithm. The done analysis for a wide range of optimal frequencies illustrate that fuzzy logic system is lowly sensitive to determination of TMD’s optimal frequency.

Today, in most of megalopolises such as Tehran, the lack of restriction on gasoline motorcycle traffic in contrast to restrictions on car usage such as odd-even scheme causes increasing in gasoline motorcycle usage. Therefore, to decrease air pollution and noise pollution produced by gasoline motorcycles, electric motorcycle usage has been encouraged. This study was carried out based on 503 interviews with gasoline motorcyclists who are working in the central part of Tehran and identified factors affecting their willingness to purchase electric motorcycles in case of gasoline motorcycle ban. Accordingly, the role of variables such as motorcycle characteristics, socio-economic characteristics and motorcyclists' attitudes toward gasoline motorcycle usage were investigated through a binary logit model. Results show that motorcyclists who have purchased their gasoline motorcycle because of its cheap price, those who drive more and those who have older motorcycles are less willing to purchase electric motorcycles. The paper provides a discussion regarding the model application.

Realization of the advantages of a higher degree of energy dissipation have created an increasing interest in stepped spillways. This study using a three dimensional, 1:50 scale, physical model was conducted to investigate the impact of variation downstream channel width of the converging stepped spillways with a curve axis. For this purpose, the converging stepped spillway with a curve axis was constructed and tested in four ratio of downstream channel width to spillway width ( ) ranging from 0.214 to 0.286. The results of the experiments indicated that in the converging steeped spillway by increasing total upstream head, the discharge coefficient will go up for each of the width ratio ( ) and before submergence stage for the spillway, the discharge coefficient is independent of downstream channel width variations. By contrast, when the spillway was submerged, there is a decrease in the coefficient of discharge can be caused by tailwater submergence and it causes the differences in the discharge coefficient for each of the widths ratio ( ). Also, the obtained data demonstrates that as increases, the flow depth and static pressure decreases at the bottom and the toe of the spillway model. Moreover, it was observed that as discharge increases, the energy dissipation decreases for all models, but model with higher ratio of lead to reduce more energy dissipation in higher discharge. In addition model with width ratio of due

The strong earthquakes recorded worldwide have shown that the damages and the failure mechanisms of the reinforced concrete structural walls depend on a series of factors, such as the shape in plan and elevation, the dimensions of the walls and openings. During the past several decades, extensive experimental and analytical studies have been conducted on the behavior of structural walls with openings. This article describes an Analytical study carried out on of reinforced concrete walls with eccentric opening. In order to achieve this goal, variations in various parameters including changes in the aspect ratio of the openings, the stiffness of the link beam, the aspect ratio of the openings with simple connection at the both end of link beams and the aspect ratio of the walls are studied. Story drift, center of mass displacement, shear and moment in coupling beams and axial load in columns which coupled with shear wall are analyzed and compared together. The results show that by decreasing the aspect ratio of the openings (ho/lo), the axial load in the column coupled with the wall decreases and with increasing rigidity of the link beam the shear forces in link beam increased and center of mass displacement and story drift are reduced. The strength of structural wall components becomes different in pull/push loading direction due to the eccentric opening location. Also, compared to seven buildings, decreasing the wall aspect ratio from the axial forces in the column and shear forces in the link beam decreases.

Acoustic Tomography (AT) Technology transmits reciprocal acoustic waves to measure the flow characteristics such as flow velocity, water temperature, suspended sediment concentration, salinity and the flow direction in rivers, dam storages, lakes, seas and the oceans. Although, this technique is widely applied in developed countries, it was not used in Iran yet. This research shows the first acoustic tomography experiment in Iran for measuring the flow velocity in a shallow lake located in the western of Shiraz City. Reciprocal sound transmissions were performed between the two acoustic stations located on both sides of the lake. The length of sound transmission line was 262m and the central frequency was set to 30 kHz. The experiment period was 20 minutes and the acoustical data was collected at time intervals of 40s. The surface temperature was measured by a Temperature Sensor (accuracy= 0.1 oC) at four positions along the acoustical ray path. The results showed the arrival time of acoustic waves were approximately constant and it was 177 ms. Finally, the depth- and range-averaged sound speed and the water temperature along the ray path were estimated from the mean travel time. The temperature varied between 19.7 to 19.9 oC that was confirmed by Temperature Sensor data. The temperature resolution of AT technique was estimated around 0.04 oC that shows the more accuracy than the Temperature Sensor. The result of this study showed the ability of acoustic tomography technique to monitor the water temperature in natural aquatic environments.