نشریه مهندسی عمران
سال پنجاه و پنجم شماره 2 (اردیبهشت 1402)

Offshore jacket platforms play an important role in the oil and energy industry, so controlling the vibrations of these structures and increasing their useful life is of great importance. In this study, the dynamic response of the offshore jacket platform under the effect of wave load with a return period of 100 years has been investigated. To reduce the dynamic response of the oil rig deck, a self-powered semi-active mass damper (SP-SATMD) was used and its mass ratio was set at 3% by default. The magneto-rheological damper (MR) energy in a semi-active tuned mass damper is supplied by the vibration of the tuned mass damper through an energy extraction system. This system includes DC direct current generator, rack and pinion. The rack and pinion convert the linear motion of the mass damper into an angular motion and apply it to a DC generator to generate electrical energy. The energy extraction system itself can also act as an electromagnetic damper (EM) and a proportional control algorithm in determining the damping of the magneto-rheological damper. The results show that the maximum displacement and acceleration of the offshore jacket platform deck in its semi-active control mode decreased by 15 and 16.24%, respectively, compared to the uncontrolled mode.

In the optimal design of the core of earthen dams, the type of material, its dimensions and shape are very important. So that with the least volume of materials, it has the greatest effect in reducing the amount of seepage from the dam body and maintaining its stability. The purpose of this research is to develop a model for optimizing the core geometry of Hajilerchai dam near Tabriz city based on the integration of the equations obtained from the simulation of seepage, hydraulic gradient and stability reliability factor with the Simplex algorithm. In this study, two objective functions were considered, one is the volume of soil material per unit length of the dam and the other is the seepage rate from the dam body. Then, by defining 50 different sections of the core of the earth dam and using the results of numerical analysis of seepage regression relationships, stability coefficient and hydraulic gradient were obtained. In order to validate the regression relationships, the values of stability coefficient, hydraulic gradient and percolation obtained from the optimal core model were compared with the results obtained from GeoStudio software models in three sections. This comparison showed a high correlation of about 99%. The results of the model developed to determine the optimal dimensions of the earth dam core were compared with the actual dimensions of Hajilerchai dam which indicated a reduction in the volume of materials required for the construction of the dam core by about 12%, which also provides the necessary stability.

Considering the environmental pollution resulting from the consumption of fossil fuels, replacing clean energy with fossil fuels has become one of the most critical issues in the world. In order to exchange the heat between superstructures and the ground, the use of energy piles can be considered as one of the approaches of taking advantage of clean energy. In order to maintain safety and serviceability of structures built on energy piles, it is necessary to properly study the effects of heat exchange between energy piles and the ground on the mechanical response of energy piles and the influence of various parameters on the interaction between piles and the soil. In this paper, a 3D finite difference model was initially created using FLAC software for the thermo - mechanical analysis of energy piles, and it was validated by comparing the results of the present model with those of field tests and numerical models Performed by other researchers. Using the present numerical model, the effects of changing the thermal expansion coefficient of energy pile and clayey soil on axial stress, shaft friction, and axial displacement along the energy pile under cyclic thermal loading have been investigated. The results indicate that changing the thermal expansion coefficient of pile materials causes significant changes in the behavior of energy piles under heating and cooling conditions; however, changing the thermal expansion coefficient of the soil has little effect on the mechanical behavior of the energy pile only during heating thermal loading.

Civil infrastructures, nowadays, are an indispensable part of society, and any unpredicted damage can cause severe economic and life loss. Hence, developing smart structures has been the topic of many studies during the past decades. In this article, developing a smart structure by synthesizing structural control and health monitoring is suggested by extracting damage-sensitive features from the active control force. The autoregressive models have been deployed to extract damage sensitive features in the time domain. Then, quadratic discriminant analysis is utilized to discriminant between different damage states of the structure. The active control force is obtained by two model reference adaptive controllers, namely the MIT rule and Lyapunov stability theorem, to attenuate the structural vibration caused by Gaussian white noise excitations. The proposed approach has been numerically studied on a three-story shear building with active ideal controllers in all floors. Results indicate that the proposed approach can detect the potential damage, as well as its severity and location precisely, and control forces subjected to controlled structures using active devices can be sensitive features for health monitoring purposes.

Using the control tools is an efficient method to decreasing the responses of the structure under the external excitations. In this regard, this study investigates the performance of two structures equipped with MR dampers and Orifice dampers under the blast-induced vibration. In addition to stimulating the underground blast induced vibration (Due to the different nature of these loads), seismic excitation has also been used to evaluate the efficiency of these dampers. These dampers are semi-active devices, which change the output force of the damper by changing the input voltage and magnetic field of dampers. Also, in this paper, clipped-optimal algorithm was used. This algorithm can generate optimal damper force by changing the voltage at each time step based on the input forces. In this research, structural responses based on optimal and maximum voltage are considered. Also, Numerical results of structure are compared with LQR algorithm. LQR algorithm is considered as a criterion for reducing structural responses to the blast-induced vibration. The results indicate that the proposed method (the different locations and types of dampers) is efficient for decreasing the responses of structure.

Many improvement methods have been proposed in the world which is one of the most common methods of chemical stabilization using lime or cement, which are not compatible with the environment. Therefore, nowadays, the use of pozzolans and geopolymeric cements instead of Portland cement has attracted the attention of various researchers. In this study, the stabilization of sandy soil in Ahvaz city with the help of metakaolin as an additive has been investigated. In this research, the effect of different amounts of variables such as the percentage of metakaolin, the ratio of sodium silicate to sodium hydroxide, the concentration of sodium hydroxide, and the ratio of alkaline activator solution to the additive at the curing ages of 7 and 28 days have been discussed. Samples are subjected to unconfined uniaxial compressive strength (UCS) evaluation and microstructural investigation, X-ray diffraction (XRD) and scanning electron microscopy (SEM) analyzes are used. The results of this research show that in order to achieve optimal resistance, it is necessary to mix 20% metakaolin, the ratio of sodium silicate to sodium hydroxide is 2.5, the concentration of sodium hydroxide is 12 Molar, and the ratio of activator solution to additive is 0.5. The strength of the sample with 28-day curing reaches about 5 MPa, which is about 3 times more than cement samples and 23 times more than unstabilized soil, which can be seen in the microstructural analysis of the presence of N-A-S-H gel as the main factor in increasing the strength in the geopolymerization process.

The walk oriented pattern is an alternative travel pattern for daily trips; that a person walks more than her/his regular pattern. In order to examine the tendency to this pattern, it is necessary to examine the role of different types of barriers on pedestrian walking. This study intends to address the role of personal barriers which avoid people to walk more in their daily work trips. The studied barriers include laziness/tend to wake up late, physical and health problems, not interested in more walking, the importance of neat appearance at work and not feeling good about being seen on streets. For this purpose, a sample of 432 employees living in Rasht has been used. Therefore, the studied variables are classified into three categories: socio-economic, travel and environmental characteristics. Five ordered logit models have been calibrated to investigate the importance of personal barriers including 11 variables of socio-economic characteristics, 6 variables of travel characteristics and 5 variables of environmental characteristics. The results show that firstly, the effect of socio-economic characteristics on each of the personal barriers studied is different and secondly, the contribution of these characteristics on each of the five barrier: laziness/tend to wake up late, physical and health problems, not interested in more walking, the importance of neat appearance at work and not feeling good about being seen on streets are 41, 30, 13, 7 and 8 percent, respectively.

Corrosion is one of the crucial damages that may occur to reinforced concrete structures. It also may affect the expected performance of the structure during the possible earthquakes. Onshore reinforced structures, bridges exposed to deicing salts in winter and also the pillars of marine structures under tidal waves, all of which are examples of corrosion damages. Corrosion mostly occurs due to two main reasons: chloride and carbonation which cause pitting corrosion and uniform corrosion, respectively. Corrosion starts with reaching of those two ions to the bar surface, passing by the physical and chemical passive covers. Corrosion also affects the mechanical properties of the steel and the concrete and reduces the seismic performance of the structure. One of the most important parameters in studying the corrosion and its effects on the seismic performance and life cycle of the structure is the corrosion initiation time. According to Fick’s law, the initiation time is a function of surface and critical chloride, chloride diffusion coefficient and concrete cover on armatures. In the present study, the chloride-based corrosion is considered. Besides, corrosion initiation time is determined by deterministic and probabilistic Monte-Carlo methods considering the uncertainties in the effective parameters. In the end, by comparing these two methods, the effect of uncertainties in the possibility of corrosion initiation time is presented. Furthermore, parameters like the distance from the sea and the water to cement ratio are discussed in a parametric study.

Recently, the advantages of using of asphalt concrete in the core compared to clayey core have increased the application of core asphalt concrete in embankment dams. Due to the importance of interfacial behavior the asphaltic core and soil filter in the stability of these dams and the need for a more detailed investigation of the complex behavior of materials in the core- filter interface, in present research, interfacial behavior of soil filter and asphalt core in the Mijran embankment dam (Mazandaran province) was investigated. For this purpose, a direct shear apparatus in the large scale is used. Soil materials , including clayey gravel (GC) and poorly graded gravel (GP), are according to the grain size distribution used in Mijran dam construction . In this research, the influence of factors such as compaction percentage of filter material and shear rate were investigated on shear strength and interlocking parameters ( dilatancy angle and shear stiffness) , as well as interaction ratio in the soil of filter and the core asphalt concrete interface. In this investigation, the ratio of the interfacial friction angle of soil material- asphalt concrete to the soil materials friction angle was defined as the interaction ratio. According to the findings, upon increasing the compaction level, the increase amount in the interaction ratio in the interface GP material was higher compared to the GC material in the interface. On the other hand, the influence of the shear rate on the interaction ratio was similar in both the GC and GP materials in the interface.

Project delays are one of the main causes of damage in construction projects, so extensive research has been done to deal with it or reduce its consequences. In this regard,too much project implementation in this area has the greatest impact because of the large volume of operations in dam projects. In this study, a case study of Marvuk Dam located in Lorestan province was studied. Based ont he background of previous research and experiences gained from projects were used to explain 10 factors of delay in projects. Experts of dam construction projects are given a score from 1 to 10 for identifying factors that affect the delays of the project. Obviously,the effect of each factor that should have been announced by the questioner was requested with a coefficients of 10 and 1 as the most effective and the least effective.The experts selected the variables of manpower, machinery, contractor financial resources and lack of technical drawings as the most important factors in the delays. Then, using Vensim simulation program and project information, the model was created and the simulation results were used to determine the predictable latency of the whole project and the share of each factor. The general conclusion is that project management in the first 4 months of the project has a key role in project delays.

One of the effective methods to improve the behavior of problematic bed containing soft lens is using stone column. The capability of this soil improvement method increases by simultaneous use of the stone column and geosynthetic encasement, especially in the presence of soft lens near to the ground surface or where the possibility of bulging failure is probable. In this research, the efficiency of using stone column embeded in a saturated sandy bed containing soft lens have been investigated in terms of bearing capacity and failure mode. Also, the efficiency of reinforcing the stone column has been investigated in the presence of soft lens with different thicknesses and placement level. The results of numerical analysis obtained by finite element software (Abaqus) and validated by laboratory results of small-scale physical model experiments in real stress conditions shows that in the presence of soft lens, the change in the length of a stone column has no effect on the occurrence of bulging failure and decreasing placement level of the soft lens, increases the bulging failure occurrence proportional. On the other hand, increasing the thickness of the soft lens reduces the bearing capacity of the ordinary and reinforced stone column. The phenomenon of bulging can occur at the level of the lens placement and up to a depth of about 4 times the diameter of the ordinary column because of existence of a soft lens in a relatively loose sandy bed, while mechanism of failure is not bulging anymore if using encasement.

Durability is an important property that determines the long-term behavior of cement-based materials. In this study, graphene oxide nanoparticles (GO) are proposed to prevent the ingress of the water in the concrete. GO are the product of chemical exfoliation of graphite and contain a range of reactive oxygen functional groups that enable it as a suitable candidate for reaction in cementitious materials through physical functionalization. The experimental program is performed to study the unsaturated transport properties under different hydrostatic pressures and mechanical behavior of GO-reinforced concrete. The “Cylindrical chamber” method were employed for penetration tests. The results of absorption and penetration tests indicate that the incorporation of a very low fraction of GO can effectively hinder the ingress of water molecules in both direction (casting and perpendicular to it). It can be concluded that adding GO improve the transport properties of concrete which subsequently improves its durability. The compressive strength of concrete incorporating 0.1% by weight of cement GO increased by 25% and 50% than those of concrete without GO after curing for 28 days and 90 days respectively. The strengths enhancement can be attributed to the promotion of hydration and the finer pore structure of cement paste incorporating GO .The results of compressive strength anisotropy showed that the addition of GO decrease anisotropy. This can be attributed to the random orientation of the GO sheets in the concrete matrix.