Journal of Rehabilitation in Civil Engineering
Volume:8 Issue: 2, Spring 2020

In this paper, in addition to introduce a hybrid structural system contained local isolators and dampers, its behavior and functional capabilities were studied on a conventional structure. For this purpose, an RC frame building with six-story was designed based on valid codes and then, in four cases based on the number of spans, it was split into two separate adjacent frames. Base isolation was done underneath the columns of one frame, while the bottom connections of the other frame’s columns were remained fixed and viscous dampers provided the connection of two adjacent frames on the same floors. Nonlinear time history analysis (NTHA) under three near-fault and three far-fault earthquakes and frequency-domain analysis are performed. Displacement, drift, acceleration and shear forces of the stories in the four proposed hybrid cases with two limited cases, full base-isolated and full base-fixed frames, as well as nonlinear hysteresis behavior of a damper and an isolator are assessed. The results showed that using the novel hybrid control method in most cases can mitigate deteriorating effects of all types of seismic motions observed in the conventional structural systems. However, among them, two cases (2 isolated columns -5 fixed columns and 3 isolated columns -4 fixed columns) had the best significant influence on seismic performance and structural response reduction. Furthermore, frequency response functions of displacement and acceleration with respect to ground acceleration demonstrated that the two proposed cases further suppress the responses of the limited cases, over a wide range of frequencies including all natural frequencies. Due to decrease about 50-70% in the number of base isolators (compared to full isolation) lead to considerable construction cost savings. In spite of the limitation of ASCE7-10 code on separately using base isolators and dampers on structure, applying the proposed combination technique of these two dissipating devices can overcome the limitation.

Even though steel bar is a conventional reinforcement in soil stabilization systems, the problem of corrosion of steel may lead to vast damages especially in aggressive environments. In the past decades, Fiber Reinforced Polymer (FRP) materials have offered an effective solution to overcome the corrosion problem. Despite numerous bond stress-displacement models for reinforcements in concrete, there is a lack of models for FRP nails in grout. In this paper, the usability of four bond stress models (Malvar, EPB, CMR and Soroushian) of reinforcements in concrete was evaluated to predict the bond stress of FRP nails in grout. For this purpose, the results of several experimental pullout tests were used to calibrate the reinforcement-concrete bond stress models and the constant parameters were obtained. To evaluate the accuracy of the calibrated models, four statistical criteria of R2, SSE, RMSE and MAPE have been also determined for each model. Results showed that Malvar model with R2 of 0.94 and MAPE of %21 was deemed suitable for the prediction of bond stress of GFRP nails while CMR model is not recommended.

Seismic isolation is a method to reduce the destructive effects of earthquakes on a structure in which the structure is separated from its foundation by devices called seismic isolators. As a result, the horizontal movements of the earthquake transmitted to the structure are reduced. The seismic isolation is used for both newly constructed structures as well as for retrofitting the existing buildings. Due to the appropriate functioning of the isolators in past earthquakes, many structures are now equipped with these earthquake-resistant systems. So far, some review research works have been conducted on the seismic isolation techniques but in the limited and regional application form. In this paper, a historical evolutionary review of the isolation techniques has been conducted in chronological order. The methods of seismic isolation have been categorized based on their mechanism. The advantages and disadvantages of these methods are discussed. In addition, the latest advances and new methods developed in this field have been introduced.

The significance of the seismic rotational components have been overlooked in the seismic evaluation of structural behavior. As researchers have measured seismic components more accurately using sensitive rotational velocity sensor, it was observed that the magnitude of rotational components is considerable and could not be neglected. Hence, some parts of seismic damage or failure of structures cannot be exclusively attributed to the translational components. In this regard, this paper used seven accelerograms in which rotational components were measured by advanced sensors. The considered RC buildings which designed as per intermediate moment-resisting frame system were analyzed using OpenSees in nonlinear dynamic domain. In the numerical modeling, lumped plasticity model was used to simulate the behavior of RC component members considering the rotational motions and soil-structure interaction as main parameters. The results of numerous nonlinear time history analyses showed that the contribution of rotational components to the seismic behavior of RC frames is considerable and should be included in the seismic design codes.

In this paper, a new method proposed for structural damage detection from limited number of sensors using extreme learning machine (ELM). One of the main challenges in structural damage identification problems is the limitation in the number of used sensors. To address this issue, an effective model reduction method has been proposed. To condense mass and stiffness matrices, the second-order approximation of Neumann series expansion (NSEMR-II) has been used. Mode shapes and frequencies of damaged structures and corresponding generated damage states used as input and output to train extreme learning machine, respectively. To show the effectiveness of presented method, three different examples consists of a truss structure, irregular frame and shear frame have been studied. The obtained results show the ability of the proposed approach in identifying and estimating different damage cases using limited numbers of installed sensors and noisy modal data.

The present research aims to conduct laboratory assessment on fatigue phenomenon in warm mix asphalt modified with nano-silica and including reclaimed asphalt pavement materials by the aid of review on self-healing behavior and measurement of validity of laboratory results by modeling via neural artificial network in neutral network of SPSS software. For this purpose, 2% weight of sasobit and 3, 5 and 7 % weights of base bitumen-to-bitumen (85-100) were added and they were stirred up by high-cut mixer. Then, the specimens of four-point flexural test were made by the reclaimed bitumen samples. The quantities of 0, 70 and 100% of reclaimed asphalt materials were utilized for aging simulation process in warm mix asphalt to build four-point flexural tested slabs. The findings indicate that adding nano-silica may essentially affect rising self-healing level in warm mix asphalts. The current study intends to present a model based on neural artificial network technique to predict behavior of warm asphalt specimens including different nano-material contents and to compare them with the laboratory results for measurement of validity of the given model. The given results show high precision of the model at level of 0.951.

Two-phase flow regimes are affected by conduit position, alignment, geometry, flow direction, physical characteristics, and flow rate of each phase as well as the heat flux toward the boundaries. Due to the importance of two-phase flow, numerous regimes have been identified. The first step in studying micro-bubble formation inside a venturi tube is to recognize the type of flow regimes. In this study, which is devoted to the study of micro-bubble formation, a numerical investigation by OpenFOAM software and a VOF model was conducted. Results suggest that flow regime inside the venturi tube is roughly similar to flow regimes inside the horizontal tubes. For having bubble flow and consequently forming micro-bubble, flow rate of gas phase should be very smaller than liquid phase flow rate while the air inlet diameter should be chosen much smaller than water input diameter. Numerical simulations indicate that the best results are achieved for the water velocity of about 1-2m/s.

There are various methods for stabilizing excavations in urban areas which one of them is the nailing method. Designing a nailing system and analyzing the performance of excavations is done by various software applications. One of these computer programs is PAXIS software which run based on the finite element method (FEM). In the present study, a numerical analysis of the performance of the excavations was investigated under different soil model and the most appropriate model was introduced. In addition, the excavation performance was evaluated based on certain designing conditions affected by the soil resistance specifications (cohesion and internal friction angle) and surcharge. The results indicated that, using an appropriate behavioral model which contains increasing soil stiffness with depth, shows results close to reality. They also indicated that under certain designing conditions, the lateral deformation of the soil nail wall and ground settlement decrease as soil resistance specifications increase.

One practical excavation support system is the inclined struts connected to adjacent buildings. This method is very common in small excavations, because of simplicity and minimum cost, when soil is cohesive and depth of excavation is less than stability depth (Hcr) but adjacent structures is at risk of damage due to weakness, old age or lack of proper skeleton frame. Although this method has been used in many small excavations, it is not entirely investigated. This study describes the performance of struts based on field observations and the results of numerical analysis. A small strain constitutive model (Duncan-Chang) was used for analysis. The efficiency of struts was evaluated by comparing the movements of the real case of excavation with struts and the same case but without struts. The results indicate that movements are decreased substantially using struts. A mechanism of struts during excavation is proposed and the effect of installation of the inclined strut on deformation patterns is discussed. The study introduces simple instrumentation designed in the course of the study that can be used in common engineering practice for small to medium-sized excavations.

Pavement maintenance and rehabilitation have been neglected in Nigeria for a very long time and has resulted to maintenance backlog. Design agencies in Nigeria still use California Bearing Ratio (CBR), even though the method is outdated. An introduction of Dynamic Cone Penetration Test (DCPT) was pertinent, even though the method is relatively old in some developed countries, it has not gain much prominence in Nigeria. A flexible pavement, constructed from Bida to Mokwa,, Nigeria, was Rehabilitated after 22 years of construction. This was done by placement of stone base course in one section and lateritic base course in the other. The stretch of the road was then overlaid with asphalt surfacing. Before commencement of the rehabilitation, DCPT tests were conducted on the road to evaluate performance of the pavement base and subgrade. Two years after the rehabilitation, an evaluation was carried out at five selected positions (two at crushed stone base and three at lateritic base) to evaluate the performance of the two base courses. The evaluation was carried out by coring the asphalt concrete and DCPT test below the hole created by corer to indirectly estimate the in-situ CBR of the base and subgrade courses. The results from both the stone base and lateritic base sections satisfy the minimum specifications based on standard. The study also showed that pavement failure along the road is not as a result of the materials used in the base course, but as a result of the excessive axle loads experienced by the road.

Nowadays, new materials are widely used for improving the bearing capacity of the soils and geosynthetics include the type of these materials which are utilized in this regard. In addition, the geofoam panel type of geosyntethic materials is useful and an alternative for backfill in retaining wall or pavement layers. The present research mainly aimed to investigate sthe effects of geofoam particles (0.2, 0.5, & 1%) on improving the bearing capacity of the clay-sand mixture. To this end, dune sandy soil (passed from sieve No.30 and residue on sieve No.50) was provided from Shore of the Lake Urmia and mixed with kaoline industrial clay at 15, 30, and 50 percentages. Then, compaction, uniaxial in three loading speed (0.5, 1, & 1.5 mm/min), direct shear (in vertical stresses 1, 2, & 3 kg/cm2), and falling head permeability tests were performed to evaluate the influence of geofoam particles on geotechnical properties of the mixed soil. The results showed that maximum dry density and elastic modulus increased by a 0.5% increase in the geofoam in the soil mixture. Meanwhile, the shear strength of the specimens increased as well. Finally, permeability and the drainage condition improved by adding geofoam to the specimens.