نشریه مصالح و سازه های بتنی
پیاپی 2 (پاییز و زمستان 1395)

In this paper, a strengthening method based on embedded carbon fiber reinforced polymer (CFRP) strips in near surface on concrete cover was applied for improving flexural capacity of reinforced concrete columns with low strength compressive concrete subjected lateral cyclic loads. The debonding phenomena is prevented in this suggested method and the strip capacity is completely used and there is more protection against fire. In order to investigate the flexural behavior of near surface mounted (NSM) strengthened RC columns, a finite element method is sued. poly-linear behavior of concrete and steel was used. There was good similarity between finite element and experimental results that indicates suggested model was calibrated. The new models consisting of different variables such as embedded steel bar diameter, concrete strength, and the numbers of CFRP strips were considered. The test results show that by using the NSM technique, the flexural strength and lateral load capacity of the columns increase significantly. The numerical results were also compared with the results obtained from the analytical study that was conducted based on strain compatibility. A good agreement between analytical and experimental results was observed.

Infilled frames significantly increase the stiffness, strength, and also change in ductility of structures compared to non-infill structures. Therefore, they cause changes in the seismic response of these structures. However, in our country, not enough attention is paid to the effect of infill on the seismic behavior of structures yet. So, structures are usually designed without considering the effects of infill on their seismic behavior. The reason could be the absence of the required procedural rules and also a lack of knowledge about the mentioned effect. In this study, for conducting a detailed assessment of the behavior of buildings with concrete frame and masonry infill, we studied the effect of infill thickness (by modeling of five types of samples with thicknesses of 200 to 310 mm), the number of spans and floors (by modeling of seven types of different samples) on the amount of initial stiffness, ultimate strength of the wall, mode of failure, and the maximum stresses in the wall. The results of these models are compared and shown in the tables and graphs. These comparisons show that the period is reduced to structures with infill. Therefore, structures with infill have a higher stiffness compared to non-infill structures. Moreover, by increasing the thickness, the strength and the bearing capacity of the structure will slightly increase.

In this paper, a simultaneous experimental and numerical analysis of opening mode toughness in The Pre-joined Brazilian disc using Brazilian tests are carried out. These numerical results are compared with the existing experimental results. For this purpose, two concrete disc specimens of 54 mm diameter and 27 mm thick were prepared. These specimens have a central joint of 20 mm in length and an opening in mm 1. Specimens are made from a mixture of water, fine sand, and cement with a ratio of 1-5 / 0-1. The same specimens are numerically simulated by a two-dimensional particle flow code (PFC).The results indicate that the crack formed from the tip of the joint and grows parallel to the load and connects to the edge of the specimen. The Fracture toughness obtained from the numerical method is in good agreement with experimental results.

Fiber reinforced polymers (FRP) are one of the most commonly used materials for rehabilitation and retrofit of structures. In some cases like the improvement of ancient buildings, these materials do not play a good role and show some defect in their performance. Fiber Reinforced Mortars (FRM) is a new generation of reinforcing materials is invented as external structural and seismic reinforcement. One of the most desirable functions of this type of materials is related to the in-plane shear strength of masonry walls. This paper aims to propose a formula for estimating the shear strength capacity of this kind of walls by using computational intelligence methods, ANN-GMDH was used for this purpose. This approach used 48 experimental dataset results to propose a model to be able to predict the shear strength of FRM strengthened masonry. The proposed model has a correlation coefficient of 0.95, which represents the high efficiency of the model.

Nowadays explosion in city centers and residential building areas is a dangerous threat to all buildings. Bomb explosion within or nearby a building can cause catastrophic damage to the buildings external and internal structural frames. The analysis and design of structures subjected to blast loads require a detailed understanding of blast phenomenon and the dynamic response of various structural elements subjected to blast loads. Comparison between response and behavior of reinforced concrete frame and shear wall systems under blast loading is rare in literature. In this paper, response of the RC frames subjected to lateral blast loads is investigated using explicit finite element (ABAQUS). This paper also examines the response of RC moment frames subjected to lateral blast loads and compares it with concrete shear wall system. A nonlinear finite element program is used to model 1 to 3 stories RC moment frames and concrete shear walls. In this study, displacement, stress, damage type and strain energy in the models under blast loading are compared. According to the main results, damage pattern of moment frames is concentrated in base columns and beam to column joints. In the shear wall models damage is distributed through beams, columns, joints and shear walls. Also, energy absorption in shear wall system is much more than moment frame.

attachment fiber reinforcd polymers (FRP) with epoxy has emerged as an advanced reinforcement technology for repairing and reinforcing concrete structures. Although the bonding of FRP layers with epoxy has many advantages,but most of the rupture modes of the reinforced beams occur with this method in a crisp way (or without a sign), which is called a premature rupture. The most prevalent condition of these premature rupture (DEBONDING) is the breakdown of concrete cover and the joint detachment of concrete and reinforcement layers.
In this research, concrete beams, in addition to the reinforcement of the classical method (reinforced solely by the fibers under the beam as a whole) with CFRP fibers, as well as L-shaped reinforcement (strengthened by fibers at the bottom of the beams and continued to the edges of the beam) with CFRP fibers And GFRP, were subjected to a four-point bending test, which delayed this phenomenon in L-shaped reinforced beams compared to the classical method.

Self-compacting concrete is a concrete that compresses without applying any external energy under its own weight. This concrete, which is a very fluid and fluid mixture, has been studied in recent years to study the effect of minerals on the physical and mechanical properties of self-compacting concrete.Since the country has vast areas of large reserves of iron ore, so in this study, the physical, mechanical and concrete properties of self-compacting magnetite density were studied.In this study, 2, 5 and 10 wt% cement magnetite particles with size 0 to 2 mm were used to determine the mechanical, physical, behavioral and effective parameters of self-compacting concrete. The compressive strength tests, tensile strength, flexural strength and ultrasonic emission velocity were used to study the mechanical properties of the samples.The results showed that with increasing magnetite percentage, the mechanical and physical properties of self-compacting concrete decreased in the early ages, but with the age of the samples, these properties would be compensated. Also, the mechanical properties of the specimens in the 2% difference were not significantly different with the control samples without magnetite.In studying the properties of self-compacting concrete, it was determined that with increasing magnetite percentage, the loss of metadata fractures and the loss of biodiversity and inundations due to reduced adhesion of cement and aggregates and increased porosity and subsequently reduced water absorption.

In recent years the use of composite materials in various industries has been developed. A new and useful field in civil engineering is to apply of fiber reinforced polymer composite materials for strengthening and retrofitting of the reinforced concrete structures. Retrofitting of reinforced concrete columns by these materials causes to increase strength, ductility and flexural capacity. In this paper, both unconfined and confined concrete columns with composite carbon fiber reinforced polymer (CFRP) have been modeled by ABAQUS finite element software under constant axial loading and cyclic lateral loading.The FE results have been compared with the experimental results and analytical equations and a very good correlation has been obtained. Retroffited columns in this way resulted in a change in early shear mode to the flexural mode, reducing of column displacement in longitudinal and lateral directions in the plastic hinge region of the column, increasing of flexural capacity, increasing of ductility, increasing of axial compressive strength, increasing of column axial strain and increasing of rotational capacity at the joints.