نشریه مهندسی عمران
سال پنجاه و چهارم شماره 1 (فروردین 1401)

The cyclic triaxial test has been widely used to evaluate the liquefaction potential of soil over the past few decades. When a specimen is subjected to repeated shear loading, the sand particles tend to rearrange their stacking into a denser state. While drainage is prevented, the generation of pore pressure and loss of effective stress have resulted. This paper presents a systematic experimental investigation into liquefaction behavior of saturated sand subject to seismic loading with various relative densities such as 30, 50 and 70 percent. Dynamic triaxial tests were run on saturated firozkooh sand using irregular time history loads that recorded during the 1999 Chi-Chi earthquake in Taiwan. The records could be classified as shock and vibration type waveforms. The effect of each type of waveforms and relative densities of sand samples on liquefaction potential of sand was evaluated also in order to compare these results with previous studies, some cyclic tests have been done with various relative densities 30, 50 and 70 percent. The triaxial test results indicate that the pore pressure generation and liquefaction resistance of sand are influenced by the relative densities and the type of irregular loadings. Also with the increasing duration of the records in the same PGA, the vibration waveform have more liquefaction potential than shock waveform.

The Muskingum model in both types of the linear and non-linear is one the most common models in the flood routing through the river reaches. Because of the similarity between the shape of the flood hydrograph and pollution breakthrough curves, it is tried to examine the applicability of the non-linear Muskingum model in the prediction of the contaminant concentration in downstream of the river reaches. The field data series of the MONOCACY and ANTIETAM Creek Rivers which were gathered by USGS have been used. During the tests, Rhodamine were used and the concentration pollute graphs were acquired in the four and eight cross sections of the mentioned rivers, respectively. The triple sets of the model parameters have been extracted in each reach, then the BC curves have been simulated in each position using them. It is observed that this model can rebuild the dimensions of the exit BC curve properly but, it also has some limitations in the modeling of the convection term of the pollution using average flow velocity. For its solution, the extracted BC curves have been transported along the time axis with magnitude of L/u in which L is reach length and u is the average flow velocity. Also, for better understanding of the effects of the model parameters in the simulated concentrations, the sensitivity analysis have been performed and it is found that the parameters of the m, k and x are the most to less effective parameters in the concentration calculation, respectively.

In recent earthquakes, many buried structures, including tunnels and lifelines, have been seriously damaged. It is noteworthy that the phenomenon of soil liquefaction has a significant role in the occurrence of these damages. The enormous damage because of soil liquefaction, has motivated the study of uplifting of lifelines. Therefore, in this research, it has been attempted to study uplift of buried pipe in liquefiable soil by physical modeling. The soil used in this study was Gum tape sand and the shaking table was used to simulate the seismic load. Also, due to the importance of the deformation mechanism in this process, particle image velocimetry technique has been used. The buried pipe (at three depths of 1.5, 2.5 and 5 times the diameter of the pipe) has been subjected to seismic load and then deformation mechanism of it has been discussed. The results show that by decreasing the buried depth of the pipe, due to the relatively high pore water pressure at the lower soil depth, the overpressure created after the dynamic loading tends to dissipate and flow to low pressure points (surface area) and because of upward flow in the surface area, the uplift will continue to some extent. Also, the displacement vectors around the pipe are circular rings that try to uplift the pipe.

Sand production, which is a critical phenomenon in the oil and gas well walls, is numerically investigated in this research. The main goal is to study the particulate mechanism of sand ‎‎production in unbonded assemblies and examine the effects of stress level and pressure drawdown on the ‎model. Discrete Element Method (DEM) in combination with the Lattice-Boltzmann Method (LBM) is selected to simulate the fluid flow ‎through porous media. The Immersed Moving ‎Boundary method is used to couple the DEM and LBM methods. After developing a computer ‎program, a 2D model of sand production is simulated under radial flow. The simulation results show that as the confining stress ‎increases, the number of produced particles and sand production rate increases. After the initiation of sand production, the sanding rate decreases in all models ‎due to the formation of sand arches around the central hole. These sand arches are weak and ‎usually unstable, and after the collapse of every arch, the new arch is formed and replaces the ‎previous one with a larger diameter. The results also show that the pressure drawdown has a negligible effect on sand production at low stress levels. However, at high stress levels, the increase of pressure drawdown significantly increases the number of produced particles (a 50% increase in pressure led to more than twice produced particles). It is also found that the 2D coupled DEM-LBM is a ‎promising tool to predict the mechanism that governs sand production and its main influencing ‎factors‎.

The use of multilayer elastomeric bearings in bridges has showed that application of this bearings improved seismic behavior of this types of infrastructures during recent earthquakes. Applications of the elastomeric isolation bearings in long-spans or tall pier bridges can experience rotation due to flexure of the deck or the piers, that it can be effective on their seismic performance. In current study, a two-dimensional mechanical model of elastomeric bearings, under the simultaneous effect of pressure, shear and end rotation is investigated. This mechanical model consists of three layers of axial springs with nonlinear hysteresis behavior that play the role of bending and compressive deformation distribution. The model can take into account end rotations of the bearing, and the overall rotational stiffness includes the effect of the variation of vertical load on the bearing. Comparison of the results of nonlinear static bending tests of this model with the results of laboratory studies shows very well agreement. The results indicate that rotational stiffness increases with higher values of vertical pressure, however decreases with increasing shear deformation. As conclusion, end rotation does not affect the critical displacement appreciably, but it significantly influences on the critical shear force.

The large scale pullout test is used to investigate the pullout behavior of the geogrid in the anchorage zone. When pullout force is applied, tensile force gradually transmitted from the front part to end of geogrid. The active length is the part of the geogrid sample on which the activation of interaction mechanism resists against the applied force. In order to investigate more accurately the interaction between soil and geogrid, the geogrid pullout behavior should be evaluated based on the active length. In this study, a series of large scale pullout tests carried out to investigate the distribution of shear stress, pullout interaction coefficient and longitudinal strain of two types of uniaxial PET geogrid with same geometry and different stiffness embedded in two types of sandy soil and sand containing 20% clay based on active length. The results showed that, the pullout force required to move the last transverse bar of geogrid, increased with increasing of vertical effective stress in both type geogrid. Moreover, the active strain of stiffer geogrid embedded in clean sand and clayey was greater than that measured in the more extensible geogrid in both transfer load and pullout stage. At small frontal displacements, increasing the geogrid stiffness decreases the active shear stress in sandy and clayey sand soil. In all pullout tests, the lowest active pullout interaction coefficient occurred at the beginning of the pullout phase.

Speeding -as the most frequent driving violation- has been the cause of 21% accidents in the first three months of 1398 in Tehran. Over speeding behavior has roots in drivers’ individual attitudes which has not been studied enough for drivers in Tehran. This study examined the association between speeding violation frequency and drivers' attributes including socioeconomic characteristics and their attitudes toward driving. A Zero-inflated negative binomial regression model was built using a cohort of 470 adult drivers data the number of tickets they received in three month periods and their individual attributes. Results show that hours of physical activity and exercise per week, some perceptions such as "other drivers move slowly" and "Traffic violations are an immoral act" affect the occurrence and the frequency of speeding. Besides, having delays in most trips that require driving, less than five years of driving experience and having vehicle body insurance directly affect the frequency of speeding. Based on the results, it can be concluded that reviewing the rules can be effective in reducing speeding violations, for instance, adding some penalties in body insurance contracts for the number of speeding violations. Also, education courses for raising public awareness toward violations can be effective, especially for drivers with more experiences and speeding violations.

Weirs are common hydraulic structures that can be used in conveyance water canals for increasing the water depth upstream of turn outs or measurement of flow discharge. In this study the effect of hydraulic parameters and creation conditions of undular flow in broad crested weirs were investigated numerically using the finite volume method and the results were evaluated by the experimental method of other researchers. Results indicated that discharge coefficient (Cd) for experimental data are between 0.321-0.332, whereas Cd for numerical simulation (using ANSYS FLUENT) are between 0.301-0.354. Over the crest where the minimum water depth (dmin) is happen, when Fr1 is less than 1.5 (Fr10.1. Thus it can be resulted that long broad -crested weirs (H/L

In this research, the effects of temperature and number of heating–cooling cycles on the mode I, mode II and the effective value of the mixed-mode I-II fracture toughness of concrete were investigated. In the first series, the effect of temperature was studied in a heating–cooling cycle at ambient temperature (25°C) and 60, 150, 200, 300, 500, and 700°C. The highest and lowest mode I, mode II and the effective value of the mixed-mode I-II fracture toughness were, respectively, observed at 150 and 700°C. In the second series of tests, the effect of number of heating–cooling cycles was investigated on the mode I, mode II and the effective value of the mixed-mode I-II fracture toughness of concrete specimens at 150°C and a crack inclination angle of 45°. According to the results, the mode I, mode II and the effective value of the mixed-mode I-II fracture toughness increased in the first cycle and decreased with increasing the number of heating–cooling cycles. As the crack inclination increased, the effective value of the mixed-mode I-II fracture toughness of the concrete specimens increased. The mode II fracture toughness increased up to a crack inclination angle of 45° and then decreased. Moreover, with increasing the crack inclination angle, the mode I fracture at the inclination angle of 0° was changed into the mixed-mode (tension–shear) fracture at inclination angles smaller than 28.8°. The mixed-mode tension–shear fracture was changed into the mixed-mode compressive–shear fracture at crack inclination angles larger than 28.8°.

In this study, a series of 1-g shaking table tests using variable-amplitude harmonic excitations were performed on 0.8 m high MSE/Soil nail hybrid wall models to investigate the seismic behavior of this innovative retaining system. Ten finite element models were also prepared with different wall height and nail length to carry out a parametric study. It was found that in models with constant length of steel strip, the deformation mode of MSE/Soil nail hybrid walls highly depends on the length of nails, so that the combination of a base sliding and overturning deformation mode was observed as the predominant mode of deformation. Irrespective of different nail lengths, the pattern of the observed failure mechanisms included a moving block and a combination of a reverse curve and flat failure surface with certain intersection point. Also, a range of ∆x/H = 0.62 - 1.10 % as a transitional level from quasi-elastic to plastic state and based on starting the development of active wedge failure, a range of ∆x/H = 5.0% - 5.6 % as a transitional level from plastic to failure state were determined. On the other hand, according to the significant increase in wall displacements by decreasing the L/H ratio of 0.7, L/H= 0.7 was presented as the critical ratio in seismic conditions.

With the increase in the population of cities and the lack of spaces for construction, the creation of diverse uses, architecture and beauty of structures, ،he performance of a magnetic damper with a fuzzy controller to reduce the vibrations of an irregular hard structure under near and near earthquakes has been investigated. In the present study, the performance of a magnetic damper with a fuzzy controller reduce the vibrations of an irregular stiffness structure under near and far field earthquakes has been investigated. The capacity of the introduced magnetic damper is equal to 1000 kN, which is installed in the first floor between the floor level and the ceiling level of the first floor. Three different types of irregularities in height, including hardness irregularities with a coefficient of 60%, are used in a 10-story structure and are modeled in the OpenSees software. These irregularities have been investigated in three different elevation locations including the lower half of the structure height (floors 1 to 5), the lowest floor (1st floor) and the middle floor of the structure (5th floor). Based on the numerical analyzes performed for these structures under the excitation of near and far field earthquakes, the residual displacement is reduced by an average of 23.15% and 45.64%, respectively. In addition to improving criteria such as maximum displacement, shear, and base anchorage in both types of earthquakes, the most improvement occurred for the irregular structure on the first floor and the least for the irregular structure in the middle floor.

Simulteness of this two additive due to take advantage of softing property of crumb rubber and harddenin property of PET can be lead to elimation of these two material from the nature as well as making more resistance asphalt mixture. The additive used in this study is a combination of rubber powder and polyethylene terephthalate, which is found in percentages (0 and 100), (25 and 75), (50 and 50), (75 and 25) and (100 and 0), are combined to form a dual additive. The desired additives were mixed with bitumen in 10% and 15%. Dynamic creep tests, modulus of erosion, moisture sensitivity and ITS have been used to evaluate asphalt mixture. In the numerical part, ANFIS neural network method has been used to estimate the results. The results showed that the addition of PET increased viscosity and also reduced density. The addition of PET to the additive (25% modifier) reduces the psychological number. On the other hand, the addition of 15 % modifier containing 0.75 CR increases the dynamic creep and reliesient moduls by about 52 %. Also, the addition of 15 % modifier containing 0.75 % PET increases the indirect tensile strength (Kpa) by about 14 % , to test the moisture sensitivity, a sample containing 10% rubber powder only improves about 11% of the moisture sensitivity of the mixture The ANFIS method is used to estimate the results of experimental test.

Diverse methods of dynamic analysis of structures are associated with natural modes concept which are equal to characteristic vectors in math. The common approach for determining of natural mode shapes is a characteristic values problem. In this approach a characteristic matrix is made by having stiffness and mass matrices. An equation will be obtained when the determinant of the characteristic matrix is equal to zero. That equation roots are natural frequencies. Finally, modal vectors will be obtained for every frequency. This paper method is established on the base of node concept, which is the point of a mode shape with zero displacement. In this method a system with two or more degrees of freedom is transformed to two or more isolated systems with one- DOF. Those systems are isolated in node places and vibrate with same frequencies in every mode. Each spring which located between two adjacent lumped mass will be converted to series combination of two separated springs. Proposed method provides a good physical understanding about the concept of vibration modes. Besides, this method is accurate and sometimes is simpler and quicker than common method.

The general purpose of this paper is to select effective features and model soil stress in earth dams at the time of construction with the neural network using an optimization algorithm and then compare the results of the artificial neural network model with usual ANFIS and GEP methods. Five features including fill level, dam construction time, reservoir level (dewatering), dewatering speed and embankment speed were selected as hybrid model inputs. By performing hybrid algorithm and sensitivity analysis and feature selection method, fill level and dam construction time, the most effective features were in modeling the total stress in selected cells, because the dual composition including fill level and construction time in TPC25.1, TPC25.3 and TPC25.4 cells, The error values (MSE) of 1.523, 2.747 and 0.750 were the most effective features in these cells, respectively. In TPC25.2 cell, the selection of three features including fill level, construction time and dewatering level according to the error (MSE) value of 5.245, has the greatest effect in modeling the total soil stress in this cell. Comparison between ANN model with ANFIS and GEP showed that although the difference in the accuracy of the models is very small, it can be said that all three models had acceptable answers. The results also show that the higher the dispersion of the model input data, the more the ANFIS model has the ability to simulate than the two models ANN and GEP,

It seems necessary to develop a simplified design approach in order to evaluate the shear strength of web panels under fire condition as the size of furnaces is limited, the cost of experiments aimed at testing the fire resistance of structures is quite high and access to simulation software packages such as ANSYS and ABAQUS is not always guaranteed. In this paper, web panel shear design relationships of AISC360-16 and AASHTO-14 specifications are exploited to be used in fire conditions. To this end, the stress-strain reduction factors provided in EN 1993- 1-2 are directly applied. Afterwards, the design curves are proposed for prediction of the ultimate shear strength and limiting temperature of steel plate girders under fire by taking into account the strength degradation caused by high temperatures and the effects due to sectional instability. According to the results, the proposed curves are more accurate in compact plates with plastic shear buckling at both ambient and high temperatures. However, by increasing the web slenderness, the difference is increased. At ambient temperatures, the maximum difference for compact, noncompact, and slender web plates is about 1.1%, 23%, and 28%, respectively. The difference at 400 C0 reaches to almost 3% and 7% for non-compact and slender web panels, respectively. In addition, at 600 C0, especially for slender plates, proposed curves yield values that are nonconservative for ultimate shear strength such that the difference is about 11%. Also, the maximum difference for existing experimental and numerical studies is about 20% and 4%, respectively.

Determining the quality of groundwater is one of the key elements of water usage in drinking, agriculture and industry sectors. Rafsanjan plain is one of the most economical plains in the country due to the existence of pistachio orchards. Therefore, proper management and careful study of groundwater in this plain is essential. The present study was conducted to evaluate the groundwater quality of the Rafsanjan plain with agricultural applications. In the first stage, after selecting the effective parameters in water quality assessment, weighting was performed by Analytic Hierarchy Process (AHP) and then the groundwater quality of the study area was modeled using GIS software. According to the results of the final zoning of groundwater quality, about 1.6% of the study area has very good quality water, 20% has medium quality, 52.7 has poor quality and 25.7 has very poor quality. In addition, based on the statistical analysis of Wilcox diagram, 1.5%, 16.2%, and 60.2% of the wells in the study area had good, medium and poor quality, respectively. Moreover, 22.1% of the wells are not included in the diagram due to very poor quality. This research revealed that a GIS-AHP based method can analyze this kind of data spatially and consistent results could be obtained.

Because unreinforced welded connections (WUFs) were brittle and prematurely fractured in the 1994 Northridge earthquake in the area of penetrating welds in the beam-to-column connection, the researchers proposed RBS connections to improve the seismic behavior of rigid connections. The brittle failure of weld in the beam-to-column connection and the lateral buckling of the beam flange in the reduced sections of the beam flange led to the proposed modified forms of this type of connection. The new type of connection includes drilled flange connection (DFC) with parallel rows of holes. In order to improve the performance of these DFCs, in this study, beam flange drilling arrangements were used with an inclined arrangement of holes with different hole diameters. The study showed that in the inclined arrangement of a hole, the amount of plastic rotation is 0.059 radians, which is 7.3% more than the plastic rotation of the same RBS connection. Also, in the connection sample DFC7 with the most suitable oblique drilling arrangement, the equivalent plastic strain index in the center and corner of the penetration welding line has decreased to 92.3% and 87.7%, respectively, compared to conventional RBS connections. Mises index in this connection in the center and corner of the penetration welding line has decreased to 45.5% and 39.9% compared to RBS connections, respectively, indicating better performance and less sensitivity of this type of connection to the problems of the penetration welding area of the beam-to-column connection compared with conventional RBS connections and DFC connections with the parallel arrangement.

Risk allocation, the definition and division of responsibility associated with a possible future loss or gain, seeks to assign responsibility for a variety of hypothetical circumstances should a project not proceed as planned. The result of improper risk allocation is increased costs, project delays and services which fail to deliver value-for-money to the community. A decision support system based on the graph model is presented for systematically resolving construction Risk Allocation. In this model mainly assumed success of a contract needs to agreement on how risks allocated by parties. The Risk Allocation analysis process considers the decision participants, their decision options, and their relative preferences when modeling the negotiation. This model is then used to perform an in-depth stability analysis in order to ascertain the possible compromise resolutions or equilibria. The model predicts the sequence of decisions that took place in the dispute and furnishes an array of useful strategic insights about the Risk Allocation. Moreover, a sensitivity analysis is executed to determine how changes in preferences can affect the equilibrium results. This Risk Allocation procedure is useful for both researchers and practitioners to better deal with the dispute-prone nature of the construction industry.

The roller-compacted concrete pavement (RCCP) surface is almost smooth and without texture due to the vibrating rollers in the construction process. The lack of texturing causes a decrease in skid resistance in RCCP. For this purpose, different scenarios were proposed to create surface texture at micro and macro levels and provide the necessary friction. To provide friction at micro-scale, siliceous and calcareous sand and a combination of 50-50 of them with broken and natural aggregate shape was used in the construction of 8 RCCP mixing designs. In addition, in order to provide macro-texture, each of the eight mixing designs was texturing by methods such as seeding (three cases), stamping (two cases), and brooming (two cases). The purpose of this paper is to investigate the durability of various micro and macro textures created on RCCP surfaces by the simulation method proposed in the ASTM C 944 standard. The results showed that different textures have almost the same abrasion resistance. Among these, the seeding texture with the grain size of 4.75-9.5 mm has the weakest, and the stamp texture of 4 x 4 cm has the most durable abrasion resistance. Changes in abrasion resistance were associated with more changes in the mixing design. This means that crushed silica sand had the highest and natural lime sand had the lowest abrasion resistance. The results demonstrated that the combination of calcareous and siliceous materials improves abrasion resistance. In this regard, the higher the fracture rates of combined sand, the better the abrasion resistance.

Concrete has high compressive strength but has very low tensile strength, and relatively high fragility has made the tensile strength of concrete impossible in design regulations. The use of steel fibers in concrete matrices reduces the brittleness and fragility of concrete. Improving the mechanical properties makes the reinforced concrete matrix with metal fiber a suitable material for structural applications. In the present study, the mechanical properties of cement-based reinforced composites with different fiber volume percentages (1% and 2%) have been investigated. The cement-based matrix has a compressive strength of 64 MPa and fibers used by the Dramix family (3D, 4D, and 5D). In this study, to evaluate the flexural strength, a 4-point flexural test was performed on flexural elements reinforced with different percentages of steel fibers. Bending parameters such as displacement force diagram, crack state, energy absorption, and flexural stress are evaluated and compared. The results show that in some samples, the stiffening behavior occurs before the crack and rupture concentration, and then the strain-softening behavior. The occurrence of hardening behavior improves the mechanical properties of the material. In this case, the rupture of the specimens occurs through the creation of multiple cracks.