فهرست مطالب محمدرضا اصفهانی

Corrosion of rebars is one of the most important problems in reinforced concrete structures. It may reduce the load capacity or cause failure of structural members. When corrosion occurs, the structure member can be strengthened/repaired using different methods. Due to the durability of FRP (Fiber Reinforced Polymer) materials in corrosive environments, these materials can be used to strengthen/repair the damaged reinforced concrete members against corrosion.In this study, the effect of Carbon FRP sheets on the flexural behavior of steel reinforced concrete beams in moisture and corrosion conditions is studied. For this purpose, ten reinforced concrete beam specimens with the cross-sectional dimensions of 150 x 200 mm and a length of 1400 mm were made. One specimen was considered as the control specimen without strengthening, and other specimens were subjected under accelerated corrosion conditions with different corrosion rates of 5, 10, and 15 percent. A comparison of the experimental results showed that the corrosion of longitudinal rebars affects the flexural behavior of reinforced concrete specimens. With increasing corrosion, the load capacity of the specimens decreased. Strengthening of the corroded specimens with CFRP sheets increased the load capacity of the corroded specimens up to 35% compared to the un-strengthened specimen. The results of specimens exposed to re-corrosion condition after strengthening showed that the strengthening of specimens by CFRP sheets effectively reduced further corrosion up to 26.9%.

The aim of this study is to determine the effect of replacing polyvinyl alcohol (PVA) fibers, fly ash (FA), and silica aggregate with polypropylene (PP) fibers, ground blast furnace slag (GBFS), iron furnace dust, limestone powder (LSP), natural sand, and microsilica to improve the mechanical properties and ductility of Engineered Cementitious Composites (ECC). Twelve different mixtures of ECC were designed and prepared. For each mixture, flexural and compression specimens were made and tested. The combination of microsilica and GBFS increases the strength and ductility of the composite, making it a viable alternative to fly ash. Replacement of silica sand with LSP that contains the appropriate composition can enhance ECC. The best results were achieved in ECC when the cementitious materials ratio was 1.25. By increasing the percentage of PP fibers from 1 to 1.5, the flexural strength increased by 65 percent, the middle span deflection of the flexural specimen increased by 21.7 percent, and the optimal amount of PP fibers to initiate hardening was 1.5 percent.

In this study, an analytical method is developed to predict the behavior of deficient reinforced concrete beam-column joints after strengthening. Deficient joint is a joint without shear reinforcement. In this analytical method, different types of failure are estimated using principal stress-strain relationships in the joint and by determining the final capacity of beam and column. The use of relations between principal stresses in the joint accounts for the variation of the axial stress of the column in equations and joint capacities. The equations are obtained by considering the strength and deformation limit states in the joint, and a numerical method is employed to solve them. The proposed analytical method provides useful information regarding the strengthened joint capacity as well as how different types of strengthened methods work. This information can be used to select the strengthening method of the deficient joints. In the study, the calculation sequence of beam-column joints is illustrated using column axial force versus flexural capacity relationship of the joint members, employed as a criterion to determine the method and the amount of strengthening materials. In the experimental part of the study, 3 specimens with axial load variation and 3 specimens with constant axial load were conducted. The specimens were strengthened using either near-surface mounted steel reinforcement (NSM) or externally bonded reinforcement (EBR) with CFRP sheets. The experimental results indicated that the behavior of joints was significantly affected by considering the column axial force. Additionally, strengthening the joints by NSM method with steel bars rather than EBR method led to more ductile behavior. Finally, the proposed analytical method was compared with the results of the experimental specimens from other studies and 6 experimental specimens conducted in this study. Comparison of the experimental results with the values of the analytical method demonstrated that the proposed analytical method could adequately predict the behavior of beam-column joints.

The present study investigates the properties of cementitious mortars in which different portions of cement were replaced with mineral materials including electric arc furnace dust (EAFD), red mud (RM), marble powder (MP), and glass powder (GP). Compressive strength at ages of 7, 28, and 90 days, tensile strength at ages of 7 and 28 days, water absorption with durations of 30 minutes, 24 hours, and 72 hours after 90 days of curing, and chemical resistance against sulfuric acid tests were carried out on hardened specimens cured for 28 days. The results show that replacing 15% of cement with marble powder significantly increased the compressive strength of specimens cured for 7, 28, and 90 days. Furthermore, replacing cement with 5 and 15% glass powder or 5% of red mud increased the tensile strength. In order to investigate the performance of the repair mortars, one of them was chosen for strengthening RC beams. Three RC beams were manufactured and tested through 4-point bending scheme. The results indicate that the load-carrying capacity of the strengthened beam by CFRP sheet and repair mortar was the same as the specimen strengthened by CFRP sheet and epoxy resin, and was 60% higher than that of un-strengthened specimen.

The present study aims to compare the flexural behavior of reinforced concrete (RC) beams strengthened by fiber reinforced polymer (FRP) with that of fiber reinforced cementitious matrix (FRCM) sheets. Accordingly, 6 RC beams were manufactured and strengthened by FRP and FRCM. Other parameters such as strengthening method and tensile reinforcement ratio were investigated. The results show that in externally bonded reinforcement (EBR) method, strengthening by FRCM sheets leads to the improvement of load carrying capacity by 12.8% and 16.8%, respectively, in specimens with and compared to the specimens strengthened by FRP sheets. Furthermore, the failure mode of specimens strengthened by EBR method was debonding in case of FRP sheets while the failure mode of FRCM strengthened specimens was fiber rupture. In externally bonded reinforcement on grooves (EBROG) method, the load carrying capacity of specimens strengthened by FRP and FRCM was almost the same, while their failure mode was debonding with partial cover separation and complete cover separation. Finally, the experimental results were compared to the existing models and different code provisions. It was observed that by increasing the tensile reinforcement ratio in FRP strengthened beams, the predicted results by analytical models become closer to the experimental results.

Due to existence of cracks in concrete structures, the conventional strength criteria may not be able to predict their failure. It has been shown that the theories of fracture mechanics can predict the behavior of these structures, appropriately. In this experimental and analytical study, by using fracture mechanics theories, fracture parameters of flexural different specimens made of Engineered Cementitious Composites (ECC) are investigated. 24 flexural specimens with notch at their mid-length were manufactured and tested. Six of these specimens with the dimensions of 350×100×100 mm were conducted under Work of Fracture test Method (WFM) and other 18 specimens with the dimensions of 190×70×70 mm, 380×140×70 mm and 760×280×70 mm were studied under Size Effect test Method (SEM). The materials used for ECC included polypropylene fibers, cement, iron furnace slag, silica fume and stone powder. Two ratios of fibers (1 and 2%) were used in different mixtures of ECC. It was observed that by increasing fibers from 1% to 2%, the amount of flexural strength, fracture energy and failure toughness (KIC) of the specimens increased. On the other hand, compressive strength, characteristic length (Lch) and brittleness number of specimens decreased. The Bazant size effect law was also discussed for the ECC specimens.

In the present study, steel and alumina industrial wastes (ground granulated blast-furnace, electric arc furnace dust, and red mud) were used as a partial replacement for cement to form cement-based repair mortars. By substituting 5%, 10%, and 15% of cement with these materials a total of 14 mixtures were formed and an experimental program comprising three distinct parts was carried out. In the first part of the experimental program, the microstructure and chemical composition of all the constituent materials were examined. In the second part, resistance to acid sulfuric, water absorption, and electrical resistivity tests were conducted to evaluate the durability performance of the mortars, and compressive strength and tensile strength tests were performed to assess the mechanical properties of the mortars. In the last part of the experimental program, one reinforced concrete beam was strengthened in shear using repair mortar and carbon fiber reinforced polymer (CFRP) sheets and it was compared with a reinforced concrete beam without strengthening and a beam strengthened in shear using epoxy and CFRP sheets. The beams were tested by implementing a concentrated load and their shear capacity was compared to evaluate the performance of repair mortar. The results indicate that strengthening using repair mortar resulted in 23% increase in the shear capacity compared to the control specimen, while the shear capacity of the specimen strengthened with epoxy increased by 14% compared to the control specimen.

One of the favorable structural mechanism to mitigate the progressive collapse in reinforced concrete structures and increase the load-carrying capacity is the mechanism of compressive membrane action. In the present study, for predicting the compressive membrane capacity, an analytical model for analysis of reinforced concrete beams is used. This analytical model is formulated based on a sectional analysis approach to establish equilibrium and compatibility conditions at each section along the length of the beam. Programming of the analytical model for analysis of RC beams was carried out with FORTRAN software. In order to investigate the membrane action in slender RC beams, several beam specimens with different span-depth ratio are analyzed in parametric studies. Analyzes are carried out to investigate the effect of four parameters of concrete compressive strength, reinforcement ratio, axial stiffness and rotational stiffness of the support on the membrane action in RC beams. The results show that with increasing the span-depth ratio, the effect of membrane action on beams decreases. It is also observed that the effect of all four parameters on the load-carrying capacity is greater in short beams. In evaluating the effect of support stiffnesses on the membrane action response, it was also observed that membrane action capacity increases with restraint stiffness only in the regime of weak restraints. Axial stiffness and span-depth ratio have the highest effect on axial restraint response, and also it is observed that rotational stiffness of the support and span-depth ratio have the highest effect on the maximum midspan deflection response.

According to increasing the use of PET products, the present study aimed to the use of PET fibers in the concrete industries. Moreover, the behavior of normal concrete contained recycled fibers is not studied and the guidelines aren’t published yet. The aim of this study was to determine the effect of polyethylene terephthalate fibers on the mechanical properties of hardened concrete. Fibers were used in three volumetric percentages of 0.15%, 0.30%, and 0.45% with the lengths of 1, 2, and 3 centimeters, separately. So, 10 combinations of specimens including the control specimen and 9 combinations of PET fiber reinforced concrete were made. All mixtures were examined for compressive strength, tensile strength, flexural strength, shrinkage, durability, and impact loading.The results showed that by adding the PET fibers, the compressive strength, the bending strength, and energy absorption increase 5 to 18 percent, 6 to 30 percent, and 30 to 156 percent, respectively. However, no noticeable change was observed in tensile strength , while even a reduction in tensile strength is monitored. The impact strength of the fiber concrete was increased two to seven times in comparison with the control concrete. By comparing the experimental results it was determined that the combinations that contained 2 cm fibers with 0.45% volume had the best performance compared with the other mixtures.

Load capacity and ductility are two main characteristics of the flat slab-column connection in high seismic areas. To date, different methods have been employed to strengthen the connection against shear punching, including column capital, drop panel, high strength concrete, and shear reinforcement. In the current experimental study, the effect of using Engineered Cementitious Composite (ECC) to upgrade the strength shear punching behavior of flat slabs under an unbalanced moment was investigated. ECC can provide the composite with features such as the ability to spread multiple cracks under load, strain hardening, shear force and scabbing strength, and high deformation. For this purpose, seven reinforced concrete flat slab specimens with a dimension of 1000mm*1000mm*100 mm under the load with the eccentricity of 150mm were examined. The slabs were made from two layers of normal concrete and ECC in their thickness. The variable parameters included the unbalanced moment effect, improved interaction of the two materials, and ECC thickness. It was observed that improving the contact surface of normal concrete and ECC increases the shear capacity. In addition, the replacement of slab concrete with ECC increases the punching capacity and post-punching strength of the slab without a large and sudden drop in load. The change in failure mechanism was observed from a sudden and abrupt failure to a formable failure with high-energy absorption when using more ECC layer thicknesses.

The use of lightweight aggregates in concrete has been widely increased to reduce the weight of concrete members. On the other hand, the fracture behavior of lightweight concrete is different with that in normal concrete. Due to the limitations of conventional designing methods for concrete members, researchers and design codes have led to consider the analysis of fracture mechanics in predicting the behavior of concrete structures. In this experimental and analytical study, the fracture behavior of lightweight aggregate concrete (LWAC) is investigated on notched beams using the work of fracture method (WFM) and size effect method (SEM). Also, the mechanical properties and shrinkage of LWAC are studied. A total of 30 bending prismatic specimens and 42 compressive samples were constructed and tested to determine the fracture parameters, mechanical properties and shrinkage of LWAC. The results of experiments and analyses show that the Bazant’s size effect theory can evaluate the fracture behavior of lightweight concrete members, appropriately. The total fracture energy G_F of LWAC is by 68.1% less than that of normal concrete due to its lower load-bearing capacity. However, the initial fracture energy G_f obtained from the SEM in LWAC is approximately higher than that in normal concrete. According to the diagrams obtained from the SEM, the LWAC has more ductility and less brittleness than normal concrete. Additionally, the SEM is more accurate than the WFM to study the fracture behavior of LWAC. The use of lightweight aggregates instead of normal aggregates reduced the concrete shrinkage.

Corrosion in reinforced concrete structures reduces the strength capacity and ductility of members and concrete elements. The use of fibers to improve mechanical properties of concrete has long been considered by engineers. In this study, an experimental study was conducted to investigate the effect of macro-polymeric fibers and hooked metal fibers on corrosion-free, non-corrosive reinforced concrete beams. Two types of macro-polymeric fibers and hooked metal fibers with 0% and 0.5% volume percentages were tested at three levels of corrosion of 0%, 7% and 9%. An accelerated corrosion test was used from a 3% salt pool. Finally, the reinforced concrete beams were subjected to bending loading tests. Structural behavior of reinforced concrete beams in corrosion beams and non-corrosion beams and with fibers and non-fibers were evaluated and compared. Based on experimental results, corrosion reduces the ductility of the specimens and the use of metallic and polymeric fibers in non-corrosion and corrosion specimens of the first and second surfaces causes a two-fold increase in ductility. Macro polymer fibers are more effective in increasing the shape of the samples compared to the hook metal fibers in corrosion samples. Increasing the percentage of corrosion in non-fibrous specimens decreased the maximum resistance of the specimens, but in specimens with fibers, no significant change was observed in the bearing capacity of the samples with increasing corrosion percentage.

This research presents an analytical model for developing a fiber frame element based on local stress field theory. The proposed formulation is developed through the Lagrangian kinematics assumption to derive the weak form of the equations in large strain conditions. In this regard, the effect of bond-slip has been considered by removing the perfect bond assumption. The governing equations for each element are developed by the directional stiffness matrix in weak form. The extracted formula is based on Timoshenko's beam theory, with axial, bending, and shear interaction effects in the domain of each element. The components of the stiffness matrix are defined through directional derivatives of the semi-linear form of the equations. Moreover, the suggested approach evolves from cubic Hermitian polynomials and the local stress field theory. The validation of the analytical method is provided by the available experimental tests. The implemented code could cover the overall behavior of reinforced concrete members, as well as, the maximum crack width, slip profile, and crack growth. The results show that such a modeling method is capable of simulating RC members.

AbstractIn this study, the toughness and durability of concrete with recycled aggregates and magnetic water against melting and freezing cycles and mechanical properties such as compressive and tensile strengths are investigated. Variables include the number of different cycles of water in the magnetic field, different amounts of super-plasticizer, steel fibers and micro-silica. A total of 242 samples were made in 11 different mix designs. It should be noted that half of the samples mentioned contains steel fibers. The results of most experiments have shown that magnetic water, although having a very high effect on the mechanical properties of concrete, should not be used alone as a compensating agent for defects caused by recycled aggregates. Using microsilica as a mineral admixture with magnetic water improves the concrete properties, significantly. The toughness indices were determined by ASTM C1018, JSCE and PCS method and concrete durability test by BS EN 140: 2003. Among the recycled aggregate concrete mixes, the best toughness results were for the samples containing microsilica and steel fibers. Also, ten round magnetic water resulted in an increase in the durability of recycled aggregate concrete by approximately 25% compared to one round of magnetization.

The present study investigates the punching shear behavior of flat slabs strengthened by ECC concrete. In addition, it studies the effect of magnetic water in a mixture of ECC concrete. In the experimental part of the study, nine reinforced concrete slab specimens with the dimensions of 1000times1000 mm with the same reinforcement ratio were constructed and tested. The reinforcement ratio of the slabs was . The slab thickness varied in different specimens. One specimen with mm thickness was made of plane concrete. Six specimens were made by combining the plane concrete and ECC concrete layers with different thicknesses of and mm. Two of the specimens were made by ECC concrete with mm thickness. The mixture of plane concrete incorporated an ordinary Portland cement with a water-cement matrix ratio of . This ratio was for ECC Concrete. In some specimens, the U-shaped shear studs were used for a better connection between the ECC concrete and plane concrete layers. ECC concrete has been used on the tension side of the slabs. Both punching shear strength and displacement of each specimen were measured by a Linear Variable Displacement Transducer (LVDT). During the punching shear tests, the load and maximum deflection were recorded by a data acquisition system and ‌onsequently, the load-displacement curves were drawn. The tests were conducted using a testing machine to apply the load at an average rate of kg/sec. A hydraulic jack was fixed to the frame and used to apply the concentric load on the column stub. The hydraulic jack had a maximum capacity of kN. The results of the tests indicated that the ECC concrete enhanced the punching shear strength of slabs. The magnetic water improved the ECC concrete flow and load-carrying capacity of the slabs. U-shaped shear studs increased the load-carrying capacity of the specimens.

Punching shear failure is usually the critical failure mechanism for flat slab reinforced concrete structures. The special brittleness of slab-column connections is due to the relative ease with which the flexural reinforcement in the top of the slab can be torn out of the concrete once an inclined failure surface has formed. If unpredictable loads are applied to the flat slab-column connections, punching shear failure occurs with almost no warning signs. According to the brittle manner of this failure, the load carried by the slab-column connection redistributes to adjacent supports and can cause overloading to these supports. It is necessary to provide a secondary load carrying mechanism after punching shear failure. In this Paper, Suggestions for establishing a supporting mechanism in the flat slab connections after punching shear failure are proposed. For this purpose, an experimental study was performed to investigate the post-punching behavior of 11 slab specimens with various reinforcement layouts. The effects of integrity, compressive, shear and bent-up reinforcements on the post-punching behavior of slab-column connections were studied. The results of the experiments show that Integrity reinforcements significantly increased the post-punching shear strength. These reinforcements can develop tensile membrane action and through alternative load paths to transfer the load. These reinforcements did not have much influence on the punching shear strength. In the column strip, compressive bars (except integrity reinforcements) did not have much influence on the punching and post-punching shear strength. The bent-up integrity reinforcements significantly increase punching and post-punching shear strength. The additional bent-up reinforcements increase punching shear strength but these reinforcements are not effective to the post punching phase and cannot increase the post punching shear strength. The shear reinforcements increase punching shear strength, but these reinforcements cannot increase post-punching shear strength. Furthermore, if the shear reinforcements are effectively extended, the behavior flat slabs will be more ductile.

Post-tensioned coupled shear wall system is characterized by good seismic specifications like a self-centering capability and an ability to sustain large nonlinear lateral deformations with little damage and negligible residual deformation. In this system, the coupling beam is not embedded into the walls, and coupling of concrete walls is performed by posttensioning beam to the walls using unbonded post-tensioning (PT) steel strands. In this paper, the seismic behavior of hybrid coupled wall systems with post-tensioned steel coupling beam was investigated experimentally. In order to dissipate seismic energy and reduce displacements of system, two friction dampers were used in the beam-to-wall connection region. To study the behavior of the system, a friction damper was first tested at different frequencies; then, four 2/3-scale posttensioned hybrid coupled wall sub-assemblages equipped with friction dampers were tested subjected to reversed-cyclic lateral loading. Each sub-assemblage included a half-length steel coupling beam and the adjacent concrete wall region at a floor level. The test specimens consisted of one control specimen without friction damper and three specimens equipped with friction dampers with various damper normal forces and different initial beam post-tensioning (PT) steel stresses. The test results showed that the system had very good lateral stiffness, strength, and ductility with little damage up to 8% lateral drift. The nonlinear deformation in this system occurs because of the gap opening at the beam-to-wall interface. The friction damper uses these gap opening displacements to provide supplemental energy dissipation. Friction dampers provide considerable energy dissipation at the system, while the self-centering capability of the system remains. The restoring effect of the post-tensioning steel strands causes closing the gap upon unloading and provides a self-centering behavior and flag-shaped hysteresis loops for specimens equipped with friction dampers. Based on the test results, the system, even after a severe earthquake, suffers limited damage and requires little repair.

Damage detection is a necessary part for structural health monitoring (SHM), being beneficial to SHM and determining the severity of damage. Application of statistical pattern recognition methods for SHM has gained considerable attention to detect changes in a structure. One of the advantages of these methods is that only data from undamaged state is needed in training phase (unsupervised learning) as opposed to supervised learning where data from both undamaged and damaged conditions is required to train the model. There are different approaches used by researchers and the success of a certain one may depend on the type of structure or structural changes. Most of studies focused on the application of statistical pattern recognition methodologies for SHM utilize the time series analyses for extracting damage-sensitive features. These features are statistical properties of time series models that directly depend on damage. Extracting damage-sensitive features is a fundamental step in damage detection process because pattern recognition algorithms can identify the state of structure unless these features are just dependent on damage.  The change in an environmental and operational condition during the data acquisition process is one of the problems that causes damage features to be depended on factors besides existence of damage. This can lead to incorrect structural state identification. On the other hand, after extracting damage-sensitive features, the application of a statistical novelty detection methodology for decision making on structural state is a significant topic in SHM. This paper proposes a new application of random decrement (RD) technique in order to choose appropriate and accurate damage features which are independent from environmental and operational conditions of structure. The RD technique transforms time series data of the structural response to free decay vibration form that only consist of dynamic properties information by averaging them at specific time. Moreover, a novel statistical method named as Bhattacharyya measure is applied as a robust method for damage diagnosis. The Bhattacharyya measure determines the discrepancy between damage features from different structural states through partitioning data and utilizing numerical information of each partition. Herein, before extracting damage features, time series data are averaged through RD technique. Then the Autoregressive-Autoregressive with exogenous output model (AR-ARX) is used to fit a mathematical model to the averaged time series data and the residuals are considered as damage features. The Bhattacharyya measure is utilized for damage identification and localization. The data obtained from an experimental study on a three-story frame structure model are exploited to validate the accuracy and reliability of the proposed algorithm. Random excitation is applied by varying amplitude level of the input force, simulating various environmental and operational conditions. Damage is induced at two different locations. The proposed algorithm is conducted on data from various environmental and operational conditions at two different locations. A comparative study is also carried out to demonstrate the superiority of the proposed algorithm over some exiting techniques. Results show that the application of random decrement technique reduces the influence of operational and environmental condition due to averaging and normalizing data and correctly determines the state of structure. In addition, using Bhattacharyya measure improves the structural health monitoring results in damage identification and localization.

If unpredictable loads are applied to the flat slab-column connections, punching shear failure occurs with almost no warning signs. According to the brittle manner of this failure, the load carried by the slab-column connection redistributes to adjacent supports and causes overloading to these supports. Due to this overloading and brittle nature of punching shear failure, progressive collapse may happen both horizontally or vertically. In order to prevent the progressive collapse of flat slab-column connections, it is necessary to provide a secondary load carrying mechanism after punching shear. In this Paper, Suggestions for establishing a supporting mechanism in the flat slab connections after punching failure are proposed. For this purpose, an experimental study was performed to investigate the post-punching behavior of 9 slab specimens with various reinforcement layouts and concrete covers. The effects of integrity, compressive and bent-up reinforcements, diameter of tensile reinforcements, and concrete cover of tensile reinforcements on the post-punching behavior of slab-column connections were studied. The results of the experiments show that the integrity reinforcements significantly improve the post-punching strength. The compressive reinforcements may not increase post-punching strength. The increase of the concrete cover of the tensile reinforcements and decrease of the diameter of the tensile reinforcement result in an increase of the post-punching strength. The bent-up reinforcement increases the punching and post-punching strengths, simultaneously.

One of the most effective methods for strengthening and repairing damaged corrosion elements is the use of fiber reinforced polymers. In this research, an experimental study was conducted to investigate the effect of GFRP on the retrofit of corroded RC beams. For this purpose, 15 concrete beams were constructed with two types of hooked metal fibers and polymeric macros with a volume percentage of 0% and 0.5%. The samples were tested at three levels of corrosion of 0%, 7% and 9%. An accelerated corrosion test was used from a 3% salt pool. Finally, corroded beams retrofitted with a GFRP composite polymer fiber layer were subjected to a flexural loading test. Based on experimental results, corrosion reduces the ductility of the specimens and the use of GFRP increases the ductility and bearing capacity of the specimens and reduces the number of cracks created and increases the depth of them and more focus on failure and damage is within the range of sheet separation.

Post-tensioned coupled shear wall system is a new type of seismic lateral force resisting systems with self-centering capability. In this system, the coupling beam is not embedded into the walls, and coupling of concrete walls is achieved by posttensioning beam to the walls using unbonded post-tensioning (PT) strands. In this research, the cyclic behavior of post-tensioned steel coupling beam with friction devices at the beam-to-wall connection region is experimentally evaluated. Three 2/3-scale specimens were tested subjected to quasi‐static lateral loading. The specimens consisted of one control specimen without energy dissipation system and two specimens equipped with friction devices with different levels of damper normal force. Friction devices are used at the beam-to-wall connections to slip and dissipate the seismic input energy. The test results revealed that the specimens equipped with friction devices have excellent lateral stiffness, strength, and ductility, and have significant energy dissipation capacity and negligible residual displacements under reversed cyclic loading. In addition, the specimens is able to tolerate large nonlinear rotations without significant damage in the beam and the wall region. Adding friction devices increased the load-carrying capacity by 47% to 62% and significantly increased the energy dissipation capacity of the specimens. With a 30% increase in the damper normal force, the load capacity increased by about 10%, the average relative energy dissipation ratio by about 15% and the mean cumulative energy dissipation capacity by about 33%.

In this article, strong correlations for the cementation factor and saturation exponent were discovered by genetic programming (GP) algorithm. The cementation factord GP-base model was trained by input variables such as porosity, permeability, and grain density derived from 175 routine core analysis (RCAL) samples of 21 carbonated oil fields. Also, porosity, permeability, and wettability index were considered as input variables of saturation exponent model. The proposed correlations using GP improved greatly the average absolute error for the Archie’s parameters. The root mean square error and correlation coefficient of validation data for the new cementation factor correlation were 0.062 and 0.91, and for saturation exponent model, they were 0.051 and 0.96 respectively. The importance of theses correlations is in their dependence on simple measurable parameters, and except wettability index all of the independent parameters are simple routine core analysis parameters which can be measured easily and at no considerable expense.

Bridges play a significant role in developing the roads and accelerating the serviceability in normal and emergency situations. The corrosion problem of steel reinforcing bars in reinforced concrete columns of bridges in humid environments results in the early deterioration of these structures. Therefore, it is vital to use the efficient and cost-effective strengthening methods to increase the serviceability of these structures in critical situations. In this study, the strengthening of circular reinforced concrete column to foundation connections with fiber reinforced polymers is investigated. In the experimental part of the study, four specimens of column-foundation connections were cast and tested. One specimen was used as the control specimen without strengthening. Two other specimens were strengthened with GFRP reinforcing bars of different sizes. The fourth specimen was strengthened with both of GFRP reinforcing bars and CFRP sheets. These specimens were under constant axial compressive load and cyclic lateral displacement, simultaneously. Initial stiffness, energy dissipation capacity, lateral load capacity and ductility of the specimens are studied. In order to investigate the ability of the ABAQUS software, the experimental specimens were simulated in the aforementioned software. Test results show that the amount of lateral load capacity, initial stiffness, energy dissipation capacity and ductility increase significantly due to flexural strengthening of circular reinforced concrete column to foundation connections with GFRP bars. The highest increase in the amount of the aforementioned parameters is observed in the specimen strengthened with GFRP bars and CFRP sheets. The analytical results also show good agreement with the experimental results. The main difference between the analytical and experimental results is due to the simulation of pinching effect of the experimental results.

Hybrid structures consisting of reinforced concrete columns and steel beams (RCS) have gained popularity because of reductions in concrete formwork, increased space availability, economics in construction, energy dissipation capacity of the structure and dead load reduction. On the other hand, the current provisions of codes for reinforced concrete columns to steel beams connections have led to some complex details in practice. In this paper, the behavior of RCS connections is examined, experimentally. Five real scale external connections of RCS with circular concrete columns were prepared and tested. The variable parameters in the specimens include the confinement of concrete columns around and inside the connection region and type of concrete. The confinement of concrete columns provided by the spiral reinforcement and CFRP sheets. The purpose of the study is to propose a connection with simple details and desirable behavior. The results show that the proposed connection can transfer the moment from the steel beams to concrete columns, appropriately. Also, the reinforcement in the connection region together with CFRP sheets increase the ductility and energy dissipation of the RCS connection.

Fiber reinforced polymers (FRP) are the safe alternatives to steel bars in reinforced concrete members in a humid environment. They have a very high durability against corrosion, especially in the extreme weather conditions. As a result of the low modulus of elasticity of these bars compared to the steel bars, the deflection and crack width are high in the beams reinforced with these bars. In this paper, the flexural behavior and cracking of concrete beams reinforced with GFRP bars are investigated. Twelve reinforced concrete beams with the cross-section of 250 × 250 mm and length of 2200 mm were manufactured and tested in a four-point bending setup. Eight beams were made with low reinforcement ratio, 4 of which were made of high-strength concrete and 4 were made of normal-strength concrete. In addition, 4 other beams were made with high reinforcement ratio made of normal-strength concrete. The parameters studied in this research are concrete strength, tensile bars arrangement and reinforcement ratio. The results show that the change in the strength of concrete as well as the change in the arrangement of tensile bars and reinforcement ratio lead to a change in the flexural behavior of the beams and also affect the cracking. Moreover, the experimental results are compared with the values predicted by ACI440.1R code.