فهرست مطالب محمد صادق معرفت

One of the most widely used techniques in the rehabilitation of concrete structures is the application of post-installed adhesive anchors in concrete. The main purpose of this study is to evaluate the efficiency and safety of post-installed adhesive anchors under domestic Iranian workshop conditions. This study focuses on the effects of parameters such as adhesives used in Iran, embedment depth, edge distance, and either single or group behavior of post-installed anchors on both reinforced and plain concrete members. The design procedure is in accordance with ACI 318-19 guidelines. For this purpose, eight tension and eight shear tests were performed on post-installed adhesive anchors in reinforced and plain concrete members to evaluate the types of failure and the factors affecting its behavior. The results show that by increasing embedment depth and distance from the edge of the concrete member, respectively, both tensile and shear capacities increase. In group installation, by reducing the rebar spacing, the nominal bond strength between adhesive and concrete decreases due to the initiation of cracks between two rebars. Finally, the comparison of experimental results with ACI 318-19 equations showed that the code predicts the tensile and shear failure capacities with safety factors of at least 1.5 and 2, respectively.

One type of structural systems that has received growing attention in recent years, includes post-tensioned flat slabs and steel columns. This system has significant economic and professional advantages. But, seismic behavior of the connection between flat slab and steel column, which is principally designed for gravity loads, is in doubt. In this regard, these connections should have sufficient ductility under lateral deformations. Although details for the connections of nonprestressed slabs to steel columns are published in the technical references, which usually include steel shear heads, but specific details for post-tensioned slabs have rarely been published in the literature. In this study, new details have been proposed for the connections of post-tensioned flat slabs to steel columns. These details include horizontal steel plates, vertical steel stiffeners and high strength shear bolts. To evaluate the proposed details, a half scale test specimen was built and was subjected to lateral cyclic loading with increasing amplitude. The test shows that the proposed connection could withstand relatively large displacements up to a drift of 6%, without loss of strength and/or gravity bearing capacity and/or significant failure. According to this study, the proposed details have sufficient ductility under lateral loading and provide a favorable seismic performance.

The old-type RC buildings constructed before 1970s are mostly designed according to gravity loads and lack seismic detailing. In these buildings, the strong column-weak beam concept is not usually observed, and due to the probability of soft-storey event, they are vulnerable to seismic loads. Therefore, the flexural strengthening of the columns is proposed as one of the top priorities in seismic retrofitting of these buildings. This paper experimentally studies the flexural strengthening of old-type RC columns with near surface mounted (NSM) technique. Six half-scale columns, including two control columns and four columns strengthened via NSM method with GFRP and steel bars, were tested under constant axial load and increasing lateral load; the effect of strengthening method and materials were also investigated. The mean flexural strength and energy dissipation capacity of the strengthened columns with GFRP bars increased respectively by 62% and 46% compared to corresponding control columns; but the equivalent hysteresis damping of these columns did not have a substantial increase. In addition, the mean flexural strength, energy dissipation capacity, and equivalent hysteresis damping of the strengthened columns with steel bars increased respectively by 86%, 197%, and 104% compared to the corresponding control columns. The results indicate that NSM technique remarkably increases the flexural strength and improves the seismic parameters of columns, especially when steel bar are used as NSM reinforcement.

In recent years, a new type of fiber reinforced concrete (FRC), called hybrid FRC, comprised of fibers of the same material but with different geometry has been developed. The aim of this paper is to investigate the influence of volume fraction and aspect ratio of steel fibers on the basic engineering properties of hybrid steel fiber reinforced concrete. To this end, steel fiber reinforced concrete composites, comprised of different combinations of fiber volume fraction and fiber size/shape, are experimentally tested and compared in terms of compressive, splitting tensile strengths and flexural toughness by four-point bending tests. The results indicate that both micro and macro size steel fibers generally improve various engineering properties of concrete, despite advantages of one on the other for different mechanical properties. Straightforward relations are proposed relating the significant mechanical properties of hybrid steel FRC to the volume fraction of micro and macro steel fibers in the composite.

There are a large number of old arch bridges in Iran designed to carry the service loads that have been increased in the past decades. Capacity assessment of these bridges has become a vital need. Due to their complex behavior, essential field and loading tests are required. An accurate and appropriate modeling of these types of bridges was the first key paid attention to, in this research. Parameters such as number, length and geometry of spans and strength of materials are the most significant features to achieve this goal. Field load testing of old railway bridge in km–24 of Tehran–Qom railway have revealed important characteristics of the bridge such as primary stiffness, rigidity and pattern of fraction. The bridge is a plain concrete arch with five identical six-meter spans. The effect of number of spans on the yielding strength of the bridge has been carried out using ANSYS software. Based on the results obtained, a plain concrete arch bridge with a single span has a totally different behavior with the multi span ones. Also it has been revealed that bridges with more number of spans have less yielding strength and higher amount of crown displacement value. At last, novel relations for computing the yield strength and displacement value of six-meter span plain concrete bridges have been suggested.

Field testing of an old railway bridge at the 23rd km of Tehran–Qom railway showed important characteristics of the bridge such as initial stiffness, yield strength, nonlinear response, cracking pattern and the governing mechanisms of structural behavior. Nevertheless, due to the practical limitations of field testing, the ultimate load capacity of the bridge had not been determined. In this article, an attempt is made to use the limited test results to predict the maximum strength and nonlinear response of the bridge. Therefore, while the finite element method is used, the pattern of cracks is modeled. The load–deflection curve is determined and compared with the test results. The numerical results are calibrated with test data such that they are extended to better prediction respect to the limited test data. Consequently, the load-deflection curve up to the maximum strength, formation of four hinges in the bridge arch and the collapse mechanism of the bridge are predicted.

1. Concrete buildings reinforced by plain (smooth) bars are one of the special types of old reinforced concrete buildings. They were generally built before 1970’s; mostly in Europe, Asia and Oceania. Some of the older cases of such buildings were probably designed just for gravity loads and do not have special seismic detailing for structural members (e.g. beams, columns, joints, etc.) because the old codes did not include special seismic provisions at that time. After recent earthquakes, seismic vulnerability of old reinforced concrete buildings has became more highlighted and subsequently, demand for seismic evaluation and rehabilitation of such buildings have experienced a remarkable growth in recent decade. The first stage for proposing a rehabilitation strategy for an existing building is the seismic vulnerability assessment. In this stage a structural engineer tries to understand the behavior of the structure under seismic excitations. This behavior is controlled mostly by the weak links of the structure. Recognition of the structurally weak links under earthquake ground motions helps the engineer to define a proper rehabilitation strategy for the improvement of structural seismic performance. To achieve a better understanding of structural seismic behavior, it is essential to perform a proper analysis considering the nonlinear behavior of structural members. As columns are generally the most important structural members of a framed structure, understanding their realistic seismic behavior is very helpful in estimating structural deformations, forces and energy dissipation capacities. Furthermore, in most of old framed building structures, columns play a key role in the final behavior because of strong beam-weak column conditions. 2. Methodology2.1. Experimental study: Four cantilever half-scale column specimens were tested in this study under monotonic and cyclic loading protocols. Specimens had square sections and were conneced to a strong foundation. Concrete casting was done in two steps in vertical position. All of the specimens’ reinforcements consisted of four longitudinal plain (smooth) bars of 12 mm diameter. To investigate the effect of various types of old splice detailing practices, three types of specimens with various longitudinal reinforcement splicing were considered: specimens Without Overlap Splice (WOS specimens) which were the representative for column detailing below the floor level, Specimen with Straight Overlap Splice (SOS specimen) of 40 times of the bar diameter length representing old American practice for column detailing over the floor level and finally specimen with Hooked Overlap Splice (HOS specimen) of 20 times of the bar diameter length which was introducing old European practice for column detailing over the floor level. WOS specimens were built twice, one for monotonic test (WOS-M) and one for cyclic test (WOS-C). Transverse reinforcement details were similar in all of the specimens; i.e. plain bars with the diameter of 8 mm in 200 mm spacing intervals. The distance was adopted to be equal to the column effective depth. Full details of specimens are presented in Fig. 1. All of the specimens were tested under constant axial load equal to 15% of concrete gross section axial capacity. Loading history protocol according to ACI T1.1 [1] recommendations was applied. The history was displacement (drift) control with preliminary target drifts. Target cylindrical compressive strength for concrete specimens at the age of 28 days was 22.5 MPa.3. Results and discussion3.1. Test observations: Similar crack patterns were observed in all the tested specimens up to drift ratio of 2.20%. Three flexural cracks were formed in three elevations; i.e. base elevation (base-crack), approximately half-depth from base elevation (h/2-cracks) and approximately one-depth from the base elevation (h -cracks). In WOS-M and WOS-C specimens base-cracks were the most active cracks with larger openings; meanwhile h/2-cracks were more active than h cracks and had an inclined trend like flexure-shear cracks. In SOS-C and HOS-C specimens (-C represents cyclic loading protocol), base-cracks were similarly the most active cracks same as WOS specimens; however, h-cracks were more active than h/2-cracks and presented an inclined trend. It was visually obvious that base-cracks play a key role in total deformations of specimens and dictate a rocking like mode for all of the specimens; even in small drift ratios.3.2. Force-drift response of specimens: The response curve of WOS-M specimen was approximately linear up to drift ratio of 0.63% and then turned to nonlinear phase. WOS-C specimen had an origin-oriented hysteresis response. In the unloading phase, after fast degradation of shear strength, the curve was tending to the origin. In other words, high pinching and low residual drifts were the main characteristics of hysteresis response. SOS-C specimen same as WOS-C specimen demonstrated an origin oriented hysteresis response but in different flag-shaped appearances. Similarly, reversal curves tend to zero drifts with a negative slope in the second step of unloading phase after fast shear strength degradation and finally, near the zero drifts, the curves were tending to the origin. Consequently, high pinching and low residual drifts existed same as WOS-C specimen. The hysteresis response curves of HOS-C specimen are very similar to SOS-C specimen but with more pinching effects because of lower initial strength degradation at the first steps of unloading phase.3.3. General mode of behavior of specimens: The main characteristic of behavioral mode of specimens was rocking movement around a point near the toe. The distance between the rocking rotation point and toe (contact depth) had an approximately constant value of 50 mm after 1% drift ratio (based on experimental observations). Contact depth was spalled at drift ratio of 2.20% and then it was crushed at drift ratio of 3.5%. After the crushing, rocking continued around a point near the previous point. One may conclude here that the main governing phenomenon for specimen deformations is rocking action which is restrained by two rows of plain bars at both sides.3.4. Restrained-rocking model: As mentioned before, restrained rocking mechanism was the governing behavior mode of specimens, such as rocking of a rigid body block around its toe. However, the block was not rigid itself in this case and it was deforming in flexure and shear modes. The formation of some cracks (1 or 2) at the bottom height of specimens was evident. The cracks were active until the end of test period and contributed in total deformation of the specimens. To achieve a better understanding of load-displacement hysteresis response of the specimens, it was initially assumed that the specimens did not have longitudinal reinforcement continuity between the column and foundation. In other words, a concrete block was assumed under an axial load. The block was loaded horizontally as well. Roh and Reinhorn [2] studied the behavior of such an element and called it rocking element. Next, it is assumed that plain bars are added to the rocking element. It was obvious that before the total bond deterioration of dowel bars, yielding strength of bars at tension and compression was added to the rocking strength; thereafter, bond resistance was added. Hysteresis response curve was located approximately between two linear upper and lower bound lines which were nearly parallel to the apparent negative stiffness part of the rocking curve. The upper bound line was parallel but apart from the rocking curve negative stiffness line for a constant added strength above it, while the lower bound line was similarly parallel the rocking curve but apart for another constant value below. The upper bound line passed through maximum displacement points of hysteresis curve for cycles with peak drift ratio more than 2.2%. In other words, it had a common part with the negative stiffness slope line of backbone curve which was initiated at Negative Stiffness Initiation (NSI) point that coincided with spalling occurrence onset. The lower bound line passed through points of slope changing in unloading branch for cycles with peak drift ratio more than 2.2%. Better understanding can be achieved if we consider two upper and lower bound curves instead of upper and lower bound lines. The upper bound added strength before the NSI point can be referred to the yield properties of plain bars. After NSI point, it can be referred to the bond properties of dowel bars, especially in SOS-C and HOS-C specimens; while in WOS-C specimen, it can be referred to a combination of yield and bond properties. It’s worth noting that shear strength dropped between upper bound and lower bound curves (at the first step of unloading stage), passed through the rocking action curve. It may be assumed that the strength difference between upper bound and rocking curve arises from full tension yielding release or full tension bond deterioration. On the other hand, the distance between rocking curve and lower bound curve arises from compression yielding development or compression bonding development in the opposite direction of concrete block movement. In fact, the lower bound curve is the rocking action curve minus an opposite yield or bond resistance. The described sequences are demonstrated in Fig. 2. The main concept here, is the fact that the shear strength difference between upper and lower bounds is the summation of two strength values; one is the released strength from upper bound to rocking curve (f1 or f3) and the other one is developed from rocking curve to the lower bound (f2 or f4); totally form an origin oriented flag-shaped hysteresis response curve.4. According to the monotonic and cyclic tests that were performed on four half-scale cantilever column specimens under low axial loads, the following main conclusions are developed;•Damage pattern of concrete columns with plain bars consists of limited numbers of flexural cracks that are formed at the bottom of the column specimen, in which the base crack (crack at the interface between column and foundation) has large opening. •Hysteresis force-drift curves of plain bar specimens are origin oriented in the specimen without overlap splice and are flag-shaped in specimens with overlap splices. High pinching effects and low residual displacements are the main characteristics of all the hysteresis curves. •General mode of behavior of all specimens seems to be restrained rocking action, independent from types of splice detailing. This is proved through experimental calculated rotations which are derived from LVDT readings.•A simple theory for the explanation of hysteresis force-displacement response of specimens is proposed. The theory assumes a concrete block rocking element which is restrained with plain bars at both ends.

Assessment of the remaining load carrying capacity of masonry arch bridges has been studied by many researchers in the recent years. Most of the masonry bridges have been built several decades ago، and have been designed for live loads and service conditions that have been changed over time. The residual strength of those structures cannot be predicted، in a reliable manner، because of time dependent effects such as fatigue and creep، environmental defects such as cracking and corrosion، participation of non-structural elements such as fill material and pavement layers، variation in restrain conditions، and differences between as-built and design specifications. To overcome such restrictions، field tests provide a dependable solution. On the basis of construction material، masonry arch bridges may be divided into three groups، namely، brickwork arch، stone arch، and plain concrete arch. Numerical and experimental studies of brickwork and stone arches have been reported frequently. Despite frequent study of brick masonry arches، load test of plain concrete arches have been published only in a few documents. There are a large number of old arch bridges in Iran that have been serving as railway bridges for more than seventy years. Field load testing of an old railway bridge in km 24 of Tehran-Qom railway has revealed important characteristics of the bridge and has proven that there is still large capacity under service load. This paper reports results of a study to predict the maximum and yield load capacity of a plain concrete arch bridge. The bridge has already been tested under vertical load static up to 5000 KN. For figure out the behavior of these types of structures، model updating is necessary. Appropriate modeling of arch bridges is the subject that is highly regarded by researchers in recently year. The complexity in the behavior of these structures will seek more accurate studies and researches، so the field tests are an integral part. In this article، uses numerical modeling in order to determine yield strength and ultimate strength of Akbar Abad Bridge. This bridge is a plain concrete arch and consists of five identical 6m and formerly has tested، due to operational and field limitation، possibility of loading until limit ultimate and Set maximum load capacity and yield strength has not been possible. In this paper with ANSYS software، an accurate modeling has done. In this model has used strain analysis. Considering the existence of initial cracks in bridge، they have been modeled as empty space. Behaviors of the material are assumed nonlinear and have used Dracker-Prager criterion. Finally، according to pattern of cracks appeared in test and result of field testing of a similar bridge (km-23 of Tehran-Qom railway)، the ultimate load and yield strength is estimated and The pattern of formation of plastic hinges conforms to the patterns reported in the literature for arch masonry bridges.

Concrete buildings that have been built before 1960 are mainly reinforced by plain bars. Because of defective bond between plain bars and concrete, the response of such buildings to earthquakes is uncertain. Despite several experimental reports of cyclic behavior of such beams, their mechanical and physical modeling is vague, and little report on this issue can be found in the well-known literature. It is known that the displacement of concrete beams reinforced by plain bars consists of three components: slip, bending, and shear. In this paper, an attempt has been made to develop a model for flexural behavior of beams with plastic hinges, and to expand a formulation for slip of plain bars in concrete. The theoretical model has been verified by tests of three beams. The results show that the effective stiffness of plain-bar- beams is equal to 22% of that of gross section. In addition, displacement ductility of the beams is about 4.5. These properties vary with ratio of longitudinal reinforcement, ratio of sectional dimensions, and arrangement of reinforcements, where all these parameters have been assessed in the study.

Dynamic tester using candles) PDA, now constitutes a new method in the estimation of pile cargo capacity is used. Currently, compliance information chart force - time calculated with the data registered and selected variables, soil resistance, using the complementary software) CAPWAP}, to obtain the experimental process is pile cargo capacity. Therefore, considering the nature of trial and error in the algorithm programs and diversity in the number of variables affecting soil CAPWAP during the process of obtaining the best match of the uses may be selected variables to the index matching identical results Bearing capacity varies achieved. In the first part has been trying to change the amount of soil variables and its effect on the distribution of cargo capacity between the wall and pile tip and overall cargo capacity, to achieve a similar adaptation index for a specific measure, they review. Also continuing on the reliability analysis of samples has been studied. In this analysis using the design load and resistance coefficients and considering the results of both static and dynamic analysis on Nmvnhyy given a reliability index versus rupture time obtained from static analysis results and effect change on the PDA reliability index calculation and design safety level has been investigated.