Journal of Rehabilitation in Civil Engineering
Volume:10 Issue: 1, Winter 2022

Seismic base isolators and dampers are commonly used as control tools in building frames to mitigate earthquake damage. This study proposes and investigates a structural system consisting of a central fixed core and an isolated section, the two parts of which are connected to each other by a damper. In new structures, called partially isolated (PI) structures, the interaction between conventional frames with fixed bases and frames equipped with control tools including isolators and dampers is measured using a three-mass model by three simplified differential equations of motion. Validating the proposed model provided good results. The model with various modes of partial isolation and certain mass ratios was subjected to seven near-fault and seven far-fault earthquakes to be evaluated. The mean displacement, acceleration, and shear responses of the structural-isolating-damping model were compared with those of fully isolated (FI) and fully fixed (FF) structures. The results showed that by connecting the two parts, responses of the fixed part to FF structure and those of the isolated part to FI structure significantly improved. Under near-fault earthquakes, the displacement response reduction of the fixed part to FF model was estimated to be about 20% and the response of the isolated part to FI model was about 50%. Due to the functional weaknesses observed in FI structures including large displacement of the structure base, poor performance of the isolator in near-fault earthquakes, and high costs of preparing and installing the isolation system, these points were significantly resolved in PI structures.

The current investigation used 16 model tests with two alternative foundation shapes, one strip and the other square, for a total of eight model tests for each foundation type. A model test was conducted only on natural soils to evaluate the two types of foundation and both circumstances of improvement utilizing RAP. The model square footing was laid on a layer of (RAP), with the varied widths (1.25B and 1.75B) and different thicknesses (0.25 B, 0.50 B, and 0.75 B in which B=footing width). Six model tests are tested in two widths (1.25B and 2.50B) in model strip footing treated (RAP), and three thicknesses (0.50B, 1B, and 1.5B) in each width are done. ‎The settlement improvement factor was utilized to show the (RAP) layer's influence. The data suggested that the (RAP) layer beneath the foundations influenced settlement significantly.‎ The RAP material in a square footing with a depth of 0.75 B offered the most efficient settlement reduction, with the lowest settlement improvement factor of all model tests. ‎ A model test was run with a RAP width of B and a depth of 0.25 B. It was discovered that RAP soil treatment reduced settlement by 0.34, implying that treated soil settled by 34% less than untreated soil.

The aspects of the durability of concrete that need significant attention in the current world demand the intense focus towards inventions in self-repairable materials. Bioengineered concrete using Bacillus sphaericus is one such novel trial. One needs to arrive at such an optimum combination of materials that involve the contribution of bacteria to resolve the issues of repair and rehabilitation effectively. The inherent properties of Bacillus sphaericus paved the way to arrive at the compatible combination of bacteria with nutrients in concrete to achieve self-repairable bioengineered concrete. Since the repairing agent used here performs at a micro level to precipitate stable calcite there is an indeed study carried out through SEM, XRD, EDAX, and Digital microscopic images to come out with an ideal solution for concrete repair work at the micro-level along with standard tests such as compressive strength. The results of these different tests on the bioengineered concrete using four Bacillus species of bacteria show that the best performance both in strength and durability is attained by bacteria Bacillus sphaericus with calcium lactate as a nutrient medium.

Because uncertainty is inherent in engineering structures, it is essential to improve the procedures of structural control. The present study focuses on applying a probabilistic fuzzy logic system (PFLS) in active tendons for the covariance response control of buildings. In contrast to an ordinary fuzzy logic system, PFLS integrates the probabilistic theory into a fuzzy logic system that can handle the linguistic and stochastic uncertainties existing in the process. To investigate the proficiency of the proposed controller, a single degree of freedom (SDOF) system and a three-story multiple degree of freedom (MDOF) system with different arrangements of tendons on the floors are considered. The structures are subjected to a random dynamic load modeled using Gaussian white noise, and the modeling parameters such as damping, stiffness, and mass are considered to be random Gaussian samples with a dispersion coefficient of 10%. The results of the proposed intelligent control scheme are compared with those of an uncontrolled structural model and a linear quadratic regulator (LQR) controller model. The numerical results reveal that the probabilistic fuzzy logic controller (PFLC) is more efficient than the LQR controller in decreasing the structural covariance responses. Moreover, the maximum and minimum reductions in displacement responses for the MDOF structures are, respectively, about 36% and 12.5%compared to the LQR controller. It is also showed that the PFLC is more accurate because it includes stochastic uncertainty.

The present study aims at investigating the pull-out resistance efficiency of single and double nails. In sandy soils, where the distance between nails is less than the minimum required distance, the pull-out resistance is reduced. Besides, when the minimum required distance is met, the nail pull-out capacity is not under the effect of the neighboring nail. The parameters affecting the efficiency of the nail group are investigated in this study; including, a type of nail, nail intervals and overburden type of pressure. One of the most important parameters – in order to determine the efficiency of the group – is the nail surface roughness coefficient, which is dependent on factors such as the number of the ribs in each unit length of nail and, also, the depth of the ribs to the size of soil particle. The nail surface roughness coefficient is used to determine the apparent friction coefficient on the nail surface. In all tests, the pull-out force-displacement curve had distinct peak values, accompanied by a reduction in the pull-out force value. The results indicated that the minimum distance required for the full involvement of the pull-out resistance of the nails was strongly subservient to the roughness coefficient of the nail surface.

The behavior of drivers on the roads is elicited from the state of the surrounding environment. The author's research shows that the vehicle starts to decelerate at a certain distance from the tunnel when it is observed, and they have the lowest speed when reaching the beginning of the tunnel. As soon as the tunnel is passed, the vehicle increases speed again in a certain length. The main purpose of this study is to model the speed of vehicles entering suburban tunnels based on the speed changes before entering the tunnel using the neuro-fuzzy network. Then, to validate the designed model, the data of 30 different drivers were used who travel in the same conditions by a Renault Logan vehicle with a manual transmission system. Using the Pearson correlation analysis method, the relationship between the variables of the speed of entrance to tunnel and changes in vehicle speed was investigated. The value of the correlation coefficient is equal to -0.7, which means the strong negative correlation between the two variables. The results show that the neuro-fuzzy network method has the ability to predict speed changes with a high accuracy based on the initial speed of entrance to the tunnel. The results of this study are used to analyze the behavior of drivers in suburban tunnels. Due to the importance of abrupt speed changes in an unusual way, especially on two-way routes, the safety of tunnels can be increased by reducing the stressors in drivers.

The topic of pounding of adjacent structures has greatly attracted the attention of researchers in recent years. Among the observed damages due to the earthquake, one could refer to those damages induced by pounding of the adjacent structures which is a prevalent phenomenon. The reason for this issue is the lack of separation joint or its inadequacy between two adjacent buildings. When an earthquake occurs, difference in the structures' frequencies would result in difference in their reaction relative to the ground acceleration and pounding would take place. In this article the effects of site soil type, structure type, its height and distance from the fault on the separation joint for the steel and reinforced concrete moment resisting buildings with 3, 5, 8 and 12 stories are investigated. The structural models are first designed by structural design software and then are analyzed under various time histories using Seismostruct software. The obtained results show that the highest hazard risks corresponding to collision between the adjacent buildings belong to areas near the faults located on soft soil types and collision of two buildings with different types is the most severe collision. Different conditions have been discussed in this paper and based on the results, some editions to criteria of seismic design code of Iran has been proposed considering to distance to active faults, soil conditions and type of structure.

Fatigue behavior of Asphalt pavement is dependent on different parameters, including the bitumen, Aggregate, and mixture design. This study aims to investigate the effects of different air void contents of asphalt mixes prepared using two common bitumen types in Iran, 60/70 and 85/100, and limestone as well as silica aggregates on the fatigue life of the asphalt mixes at 5℃. First, the optimal amount of bitumen was calculated for each aggregate using the Marshall test. Then, to determine the fatigue behavior of the asphalt samples, indirect tensile tests were performed with controlled stresses at the levels of 100, 200, and 300 kPa. The results indicated that the 60/70 bitumen sample had a longer fatigue life than the 85/100 bitumen sample. The effect of the changing the bitumen type from 60/70 to 85/100 on fatigue life is more noticeable than the effect of the changing the air void content. Furthermore, it was revealed that lime aggregates have a higher fatigue life in comparison to silica aggregates, and the influence of increasing the air void content on fatigue life reduction is larger than that of changing the aggregate type. Eventually, some models were proposed to describe the fatigue life of asphalt mixes with different materials and different air void contents based on experimental studies and numerical analyses.

Insufficient separation distance between two adjacent buildings can cause to collision when large lateral displacements are accrued due to seismic excitation. The impact force between structures induces many serious damages, which is called building pounding. In this study, pounding between two dynamic models is investigated and the impact force is numerically calculated. The impact is simulated based on special elements, including spring and dashpot, and the impact force and dissipated energy during the impact are determined. Both mentioned parameters depend significantly on the impact velocity, spring stiffness and the value of damping. For this purpose, the impact velocity of collision is parametrically measured and subsequently, coefficient of restitution is automatically determined. Furthermore, the impact damping ratio and nonlinear stiffness of spring are calculated to evaluate the impact between models. Finally, a new equation is presented to determine the value of damping and the accuracy of formula is confirmed, which is verified by three various approaches. In the first stage, an experimental test is considered and the peak impact force is extracted when a concrete ball is dropped on a rigid concrete surface. On the other hand, a numerical simulation is similarly assumed and the suggested formula is used to determine the peak impact force during collision. Then, the results of the peak impact forces between experimentally and numerically analyses are compared, which shows both are close to each other. Secondly, an estimated impact between two bodies has been studied. The results of the analysis are also compared between the dissipated and kinetic energies during impact. The comparisons indicate relatively low errors between the calculated and assumed values of the coefficient of restitution when the proposed equation is used. Finally, a value of the coefficient of restitution is selected and an impact is simulated to show hysteresis loop. The enclosed area of each loop is calculated as the dissipated energy and compared with the energy absorption. The above three comparisons show that the proposed formula is very effective and the accuracy of the impact force, calculated by the suggested formula as a parameter of the impact force model, is also acceptable.