Journal of Rehabilitation in Civil Engineering
Volume:8 Issue: 3, Summer 2020

The paper aims to extract the dynamic properties of existing structures without utilizing the analytical models. The ambient vibration testing could be used on any type of frame such as concrete, steel and masonry to investigate the structural vulnerability. The method could be the first stage and necessarily for the retrofit process. To achieve this aim, the ambient vibration testing can also be employed. The experimental data obtained from the method can be used to monitor the health, evaluating, and damage detection structures at present. The achieved data can be compared in future with the recorded signals at different times. So, the ambient vibration test was carried out on the building of Imam Hossein Hospital at Mashhad. Then, its dynamic characteristics of the acceleration records are obtained by using Data Acquisition System with three accelerometers in two perpendicular coordinates. The method is more accurate and practical compare with analytical models of the existing buildings. The ambient vibration test prevents of several points such as destructive testing or may irreparable damage to the building as well as high cost. Even, the ambient vibration test maybe required for every couple of decayed, when noticed of any changes in the condition of buildings after construction. These type of changes could be quality of concrete or welding or some changes in the location of walls that can be affected the dynamic specifications of the building. The method provides real lateral load pattern and actual modes that can evaluate existing condition of the building compare with the time of construction.

Mashhad city is located on alluvial deposits where the expanded area of this city, especially the central and eastern areas surrounding Imam Reza holy shrine, are built on weak and fine-grained deposits. Therefore, the soil improvement would be inevitable due to construction of high-rise buildings such as hotels and commercial complexes in these areas, as well as restructuring old buildings. Today, the use of waste rubber tire to stabilize the soil is not only efficient to secure human health and clean the environment but also as an inexpensive additive to improve the behavior of problematic soils. In this research, waste rubber tires in three different dimensions 

This paper investigated the effects of seawater curing of concrete made by Micro-Nano Air Bubbles (MNAB) on compressive, flexural and tensile strengths of the concrete. This product will be applicable for rehabilitation or repair of coastal RC structures. In this research, the effect of different combinations of concrete ingredients including 0-100, 25-75, 50-50, 75-25, and 100-0 percent seawater and MNAB, respectively, on compressive strength of concrete was investigated. A total of 93 specimens were experimentally examined to study the compressive, flexural and tensile strength of MNBA concrete (MNABC) through ASTM Standard for cube, cylinder, and beam samples. The samples were cured for 1, 7, 28 and 90 days. Results revealed that MNABC cured in seawater had about 30 % higher compressive strength at ages 7 and 28 days, but it decreased in longer periods. The flexural strength of MNABC slightly increased, about 6%, after 28 days of curing in seawater. In general, the mechanical properties of MNABC at an early age revealed a considerable increase, whereas, in the longer period of time, they were decreased gradually.

In this study, the co-operation of steel and concrete in composite columns is considered. Using numerical modeling to study the behavior of these sections, a new type of sections, namely Concrete Filled Double-Skin steel Tubular (CFDST) columns, is introduced. The parameters and techniques that influence the numerical simulation that bring this modeling closer to the laboratory conditions are determined by varying the dimensions and geometry as well as the properties of materials such as the compressive strength of concrete and width to thickness ratio on the strength of circular section columns at internal and external skins are investigated by the ABAQUS finite element software. The purpose of this paper is to investigate the effect of concrete compressive strength on the axial performance of CFDST columns. In this paper, the effects of concrete with different compressive strength, concrete confinement, bearing capacity and width-to-thickness ratio on the overall strength of tubular cross-section columns in their inner and outer skins are investigated. The results of the study indicated that the bearing capacity of CFDST columns under axial pressure increases by increasing the concrete compressive strength in the inner skin and decreases by increasing width to thickness ratio (D/t).Also, studies have shown that with increasing cross-sectional area, the bearing capacity in circular columns decreases by about 3%.

Failure modes in recent earthquakes on lightly reinforced shear walls includes rebar fracture and out of plane buckling of its boundary elements. In latest edition of ACI 318 and also latest amendment of NZS 3101-2006 to avoid rebar fracture in boundary elements, the minimum reinforcement ratio for shear walls is increased. This experimental study investigates that rather than increasing reinforcement ratio, is it possible to avoid rebar fracture by use of plain rebars in boundary elements of lightly reinforced shear walls. Experimental program includes specimens with plain and deformed rebars tested under monotonic and cyclic loading. Strain profile of the rebars are evaluated employing correlation between hardness and residual strain. Results indicate that failure of specimens with plain rebars occurs on single crack, however they have more uniform strain profile. On the other hand, in the specimens with plain and deformed rebars, out of plane buckling occurs at same crack width, but at different elongations. It is shown that local strain demand (crack width) has better correlation with out of plane buckling in comparison with average axial strain.

Ultra-high performance concrete (UHPC) is a developing concrete and today is increasing to interest using it in structures due to its advantages such as high-compressive strength, modulus of elasticity, highly durability and low-permeability. Therefore, it is necessary to provide models for prediction of nonlinear behavior of this material. This study is aimed to investigate the tension-stiffening phenomenon for UHPC and to propose a model for the post-cracking behavior of the reinforced concrete members under tension. For this purpose, in this study, 24 cylindrical concrete specimens reinforced with a rebar in its center were prepared using UHPC and Two rebar types including steel and GFRP (Glass Fiber Reinforced Polymer). Three specimen diameters (65 mm, 100 mm, and 125 mm), and two rebar diameters (12 mm and 16 mm) were considered. All specimens were tested under direct tension. According to the experimental data, a tension-stiffening model was proposed for UHPC. The proposed model has suitable correlation with experimental results.

Dynamic modulus characterizes the viscoelastic behavior of asphalt materials and is the most important input parameter for design and rehabilitation of flexible pavements using Mechanistic–Empirical Pavement Design Guide (MEPDG). Laboratory determination of dynamic modulus is very expensive and time consuming. To overcome this challenge, several predictive models were developed to determine dynamic modulus of asphalt mixtures instead of laboratory testing. Present study utilizes a large database of 1320 dynamic modulus test results developed at the University of Maryland to evaluate the performance and accuracy of different dynamic modulus predictive models. For this purpose, six conventional dynamic modulus predictive models including Witczak, Modified Witczak, Hirsch, Al-Khateeb, Global and Simplified Global models were considered and dynamic moduli of asphalt mixtures were determined. These moduli were then compared with those determined from laboratory test results. Performance evaluation of the models showed high prediction accuracy and low prediction bias with good correlation between predicted moduli and measured values for Witczak and Global models.

This paper summarizes the lessons learned from a full-scale test on two RC frame prototypes that have recently been tested on LNEC shaking-table using four pairs of biaxial synthetic ground motion records during 15WCEE Conference (2012). The reference structures are two single-story RC frames which are geometrically identical but with different reinforcement details. The simplified inelastic models including ‘one-component’ inelastic elements with lumped plastic hinges at their ends are used to model the reference structures. The displacement demands of the RC frames are determined by using the nonlinear dynamic analyses and then compared with the exact test results for four different seismic hazards (intensities). In the initial pre-test analyses, the modeling parameters and deformation capacities for each RC element are determined using ASCE/SEI 41-13 standard. However in the post-test studies, the experimental equations developed by Panagiotakos and Fardis (2001), Haselton and Deierlein (2008) are used to obtain more accurate structural responses. A detailed comparison is carried out between the analytical results with those given by the tests. The results clearly show that there is fairly good agreement between the analytical and test results. The simplified inelastic modeling techniques are also identified accurate enough in estimating the seismic response of RC buildings under biaxial excitations.

A review of previous studies shows that there are two general views on how to determine demand in structures through incremental nonlinear static analysis. In the first view, multi-modal methods are used to determine demand in structures. In this view, the applied load pattern is applied to the structure according to the shape of each vibration mode, assuming that the structure deformation follows the shape of the vibration mode, the capacity spectrum is drawn and after determining the target displacement and the corresponding demand for each vibration mode, the final demand is determined by combination of response modes. In the second view, structural analysis is performed as a single run nonlinear static analysis and the effect of different vibration modes is shown in one load pattern. In this method, the load pattern that has somehow the effect of different modes is applied to the structure and the structure is analyzed under this load pattern. In the second view, due to the non-conformity of the structure deformation and the lateral load of a particular vibration mode of the structure, the conventional capacity spectrum method cannot be used. Therefore, the purpose of this paper is to propose a method for drawing the capacity spectrum and determining the target displacement in single run nonlinear static analysis for non-adaptive load patterns. After presenting the equations, 3-storey, 9-storey and 20-storey frames have been selected and the results of the proposed method have been evaluated along with modal pushover and time history analysis for the frames.

The main objective of this study was to numerically assess the effect of boundary elements with different types of steel and concrete materials on nonlinear behavior of composite steel–reinforced concrete wall (CSRCW) by employing ABAQUS software. Two types of common steel profiles including box and I-shaped sections, located at the middle and extremities of the wall, were employed to assess the ultimate strength of CSRCW. In addition, effects of concrete confinement on boundary elements were investigated for fully and partially encasement degrees. Following this, steel materials with three yield stresses of 300, 400 and 500 MPa, and concrete in two grades with compressive strengths of 30 and 40 MPa were used. The theoretical results demonstrated that numerical models predicted the fracture zones similar to experimental observations, where the failure modes of CSRCWs appeared to have ductile mechanisms. In addition, based on the numerical outputs, the presence of I-shaped steel section in the middle of CSRCW participated to effectively distribute the stress throughout the shear wall, which was found to be 6.5% higher than that conventional shear wall. Furthermore, the use of steel boundary elements with higher strength caused to obtain the highest amount of the ultimate strength for CSRCW up to 397.1 kN.

ABSTRACT The issue of environmental protection has led researchers to pay serious attention to waste tires. Civil engineers have found that waste tires can increase bearing capacity, earth slope stability, and other useful applications in civil engineering. In this paper, a series of experimental modeling have been performed to investigate the effect of waste tires on increasing the stability of sand slopes. The position and height of the waste tire are investigated to find the most suitable location to use the waste tire. Digital images were taken during the loading on the slope. Particle image velocity (PIV) is used to measure the deformation of the slope during loading. The results show that the reinforced waste tires reduce displacement by 78% and increase the bearing capacity up to 260%. The optimal position of tire pile with reinforcement heights of B, 2B, 3B inside the slope is upslope in terms of bearing capacity and displacements.

By increasing the demolition of old concrete structures and the interest of civil industries to consume cheaper materials, using Recycled Concrete Aggregate (RCA) can cause environmental protection and decrease the construction costs. On the other hand, the high potential of Recycled Aggregate Concrete (RAC) in concrete industry was established by extensive experimental researches were performed to examine the properties of RAC. Like in conventional concrete, core test cut from RAC can be used to assess the in-place concrete compressive strength and sometimes it becomes an important test for monitoring in-situ properties of concrete to taking up retrofitting/strengthening measures. So the core test is often mentioned in most codes for concrete testing. The layout of this study includes four concrete mixes, two concrete grades (20 and 40 MPa), three core diameters (46, 69, and 100 mm), five length-to-diameter (L/D) ratios (1, 1.25, 1.5, 1.75, and 2), two sizes of maximum coarse recycled aggregates (10 and 20 mm), two directions of core drilling which are vertical and horizontal and three ages of the specimen (14, 28 and 90 days). The core test results were compared to cylindrical and cube specimens. Results imply that the core strength of recycled concrete reduces with the increase in aspect ratio, by decreasing the core diameter, increasing the size of coarse aggregates in recycled concrete. By analyzing the results a comparison was made between recycled concrete in this study and conventional concrete in other studies, as well as code instructions.