مقالات رزومه دکتر جلیل شفایی

The observed damage during the past earthquakes shows that the damage of the masonry infill in the in-plane and the reduction of the contact surface between the masonry infill and the surrounding frame led to an increase in the vulnerability out-of-plane. Considering the different contact conditions of the masonry infill with the surrounding concrete frame, the interaction, and influence of the out-of-plane on the in-plane behavior of the masonry infills, which is a new topic in the field of seismic performance of the masonry infills. In this paper, the effect of different boundary conditions the masonry infill and the reinforced concrete frame, which include four edges supported by the frame, three edges supported by the frame, two horizontal edges supported by the frame, and one edge supported by the frame, by analyzing three types of loading, which are: 1-out-of-plane loading only, 2-the out-of-plane loading after in-plane loading, 3-the in-plane loading after out-of-plane loading, have been evaluated by using the finite element software ABAQUS. The results demonstrated that the absence of proper connection between the frame structure and the infill increases the Out-of-plane direction vulnerability, and does not prevent their collapse. Previous damage due to in-plane loading, which reached a maximum drift of 3%, can reduce about 70% of the out-of-plane capacity of the infill frame and consequently, the strength and stiffness were affected by the boundary conditions and type loading.

Masonry infills are an unavoidable member of any building. The presence of openings in a masonry infill alters its behaviour and reduces the load strength and stiffness of the infilled frame. Considering the reality of the masonry infill, the capacity of masonry infill is defined in two separate modes of in-plane (IP) force and out-plane (OOP) force (Asteris et al., 2017). In this paper, the main goal is to investigate masonry infills with different window and door openings with different dimensions and locations under three types of loading, which are: 1-Out-of-plane Loading of masonry infill under different accelerations. 2-Out-of-plane loading after in-plane loading at relative displacements (drift) of 0.5%, 1%, 2%, and 3% and check for Out-of-plane damage. 3-In-plane loading up to 6% relative displacement (drift) after out-of-plane loading and checking for in-plane damage. The numerical models are generated in finite element ABAQUS soft. Nonlinear pushover analyses have been conducted for each of the three loading. At the end, reduction factors of effective stiffness and ultimate strength are suggested. By using these suggested reduction factors, the design engineer can model the interaction effects in-plane and out-of-plane using the compression diagonal struts method. The average reduction of the infill stiffness was calculated by considering the interaction in-plane and out-of-plane 30%.

Permanent deformation after an earthquake increases the cost of the retrofit and even the implementation of the rehabilitation plan. A resisting system to control the lateral forces due to earthquakes is to use shear walls with good energy dissipation capability. Permanent deformation and cracking in the border and critical areas of the wall after relatively strong earthquakes leads to a decrease in the seismic performance of the wall. In this research, the responses and cyclic behavior of concrete shear walls under the cyclic loading protocol are investigated. For this purpose, using OPENSEES software platform, concrete shear wall modeling based on SFI-ΜVLEM method or wall modeling using multiple vertical elements based on the macro fiber method has been studied. The main models analyzed in this study include 2 concrete walls with steel rebars and memory alloy (SMA) with different dimensions and arrangement of reinforcements and innovative concrete wall with separate border elements in the form of concrete columns made of engineered concrete (ECC) and SMA rebars.  Validation of the models was based on previous studies. After validation of the initial models, the parametric study of the models was performed in order to investigate the effects of the dimensions of the boundary areas, the type and arrangement of the reinforcements and the amount of gravitational forces on the shear walls in the models. The results obtained from the outputs show that the use of SMA materials in the boundary areas of the wall has a significant effect on the self-centering behavior of the wall and the energy dissipation of the shear wall is reduced by using SMA materials.

The use of post tensioned flat slabs is common in structures that require the construction of long span. The main advantages of using this type of slabs are increasing the span to thickness ratio, deflection control and reducing the thickness of the floor. Post tension slabs are usually designed to withstand gravitational loads in the building. However, slab column connections in these systems must be able to withstand the deformations created by lateral loads and have sufficient ductility. In this research, an exterior unbonded post tensioned slab column connection is validated in ABAQUS finite element software. After ensuring the accuracy of the numerical model results, the effect of concrete compressive strength, the amount of effective prestressing levels and the tendon bonding influence in the seismic behavior of post tension slab joints are investigated. The results showed that the compressive strength of concrete and the prestressing level of concrete have a significant effect on the load-bearing capacity and ductility of the joints, while the bonding condition does not have much effect on the behavior of the joints.

In recent years, a new type of fiber-reinforced concrete, consisting of several different types of fibers, known as hybrid fibers reinforced concrete, has attracted the attention of researchers. The aim of this paper for experimental evaluation of the effect of replacement ratio of recycled aggregates with natural aggregates on the mechanical properties of reinforced concrete with hybrid fibers (steel and polypropylene fibers). To this end, reinforced concrete with hybrid fibers with volume fractions of "0.0%" , "0.5%" , and "1%" of steel fibers and "0.0%" and "0.4%" of polypropylene fibers and replacement ratios of "0.0%" , "25%" , and "50%" recycled coarse aggregate of natural coarse aggregates were tested for compressive strength, Brazilian tensile strength, and flexural strength by four-point bending tests. The results show that increasing the replacement ratio of recycled aggregate leads to a decrease in compressive, tensile, and flexural strength. If polypropylene and steel fibers are added to concrete containing recycled aggregates, the compressive, tensile, and flexural strengths of concrete increase, whose steel fibers are more efficient in improving the tensile and flexural strength of concrete than polypropylene fibers. The combination of polypropylene fibers with steel fibers increases energy absorption and increases the flexural toughness of concrete containing recycled aggregates. Moreover, reinforced concrete with hybrid fibers does not disintegrate after breaking, and hybrid fibers play an important role in maintaining the cohesion of concrete.

Nowadays, the use of recycled concrete has increased significantly for economic and environmental reasons. Increasing the replacement percentages of recycled aggregates change the mechanical properties of concrete. In this research, the mechanical properties of concrete containing recycled aggregates with different percentages of steel fibers and polypropylene fiber has been investigated in the structural laboratory. A total of 36 cylindrical compression specimens, 36 cylindrical tensile specimens with dimensions of 20 * 10 cm and 36 flexural specimens with dimensions of 10 * 10 * 35 cm were tested. Recycled aggregates (coarse aggregates) in ratios of 25 and 50% (weight ratio) replaced with natural materials (coarse aggregates). Also, steel and polypropylene fibers were added to recycled concrete samples in ratios of 0%, 0.5%, 1% and 0%, 0.4%, respectively. Fiber concrete samples containing recycled aggregates under compressive force, indirect tension and three-point bending are tested and factors such as compressive strength, tensile fracture toughness, modulus of elasticity, flexural strength and fracture energy were investigated. The results show that the increase in porosity in recycled concrete is affected by the increase in the percentage of replacement of recycled aggregates and reduces the specific gravity of concrete. Increasing the composition of 1% steel fibers with polypropylene fibers without the presence of recycled aggregate has a greater effect on increasing the specific gravity of concrete than polypropylene fibers (alone). By increasing 25 and 50% replacement of recycled aggregate, 0.8% and 2.5% of specific gravity of concrete were reduced, respectively. Compressive strength decreases with increasing replacement percentage of recycled aggregate. Increasing the percentage of replacement of recycled aggregate due to poor transmission area reduces the amount of energy absorption. So that by replacing 25% and 50% of recycled aggregate, the energy absorption rate decreases by 21.7% and 26%, respectively, compared to the control samples. Polypropylene fibers have a positive effect on increasing compressive strength and combination of polypropylene fibers with 0.5 and 1% steel fibers increases the energy absorption. Also, increasing the replacement percentage of recycled aggregates reduces the hardness. Maximum tensile strength decreases by 3% and 13% with 25 and 50% increase in replacement of recycled aggregate, respectively. The results of flexural strength test show that increasing the replacement percentage of recycled aggregate has a negative effect on reducing the final load and reduces the final load in flexural specimens. Also, polypropylene fibers have a positive effect on increasing the loads and preventing the collapse of concrete, and combining polypropylene fibers with 0.5 and 1% steel fibers, respectively, increases the final load by 20% and 95% in 25%, replacing recycled aggregates and increasing 19% and 21% of rainfall in 50% recycled aggregate replacement. Increasing the percentage of steel fibers, the amount of deformation in the area after cracking and the amount of energy absorption increases, so that by increasing the amount of steel fibers to 0.5% and 1% by volume of concrete, the amount of energy absorption to 2 and it increases 3 times. The use of polypropylene fibers in the area after cracking has little effect and increases the load capacity.

Frames with masonry infill are the most common type of structures used in developing countries. Masonry infill affected the initial stiffness and strength of reinforced concrete buildings. The presence of opening in masonry infill is often used for placing doors and windows and it may reduce the seismic performance of the RC frame structure. Nowadays, the impact of the frame and infill on structure is one of the challenges in engineering researches. Engineers generally ignore infill in designing the building and consider it as non-structural part. When the masonry infill is placed in the concrete frame, significantly changes its mechanical properties, the stiffness and strength of the structure increase and ductility of the concrete frame reduce. There is interaction between masonry infill and itchr('39')s frame, so, the frames with infill behave differently than those frames without infill. Disregarding the effect of masonry infill, they can be safe and reliable in terms of resistance in design, since the increasing strength around frame has a positive effect on earthquake strength and overall structural stability, however, it should also be considered that masonry infill will increase the stiffness of the infill-frame and larger portion of the lateral load would attracted by frames. This can be a negative factor when ignore the infill masonry in the design. In the present study, by numerical modeling by nonlinear finite element method, the effect of the presence of masonry infill with different door and window openings on the behavior of concrete frames with seismic and non-seismic details at different axial load levels and different masonry infill thicknesses in seismic performance of frames concrete has been examined. For this purpose, the proposed models are first validated using laboratory results in ABAQUS finite element software. The results of the analysis show that increasing the axial load increases the final strength, effective stiffness and reduces ductility in specimens with masonry infill with different opening of doors and windows and reinforced concrete frame with seismic characteristics. The ultimate strength in specimens with reinforced concrete frame with seismic characteristics shows a slight increase compared to similar samples with reinforced concrete frame with non-seismic characteristics, which can be ignored. Increasing the thickness of the specimens increased the ultimate strength and effective stiffness of the specimens with seismic and non-seismic details. The results of these studies show that the different positions of the openings have significant effects on the behavior of the frames. If the opening is large or moves away from the center of the masonry infill, the final strength drop and stiffness effective reduction will be more.

The use of steel braces in buildings with a moment resisting frame system can significantly control the lateral displacement of the structures. One of the problems with the conventional bracing system is their buckling in compressive loads which reduces the amount of energy absorption of the structure. The buckling restrained braces (BRBs) have been proposed by the removing the buckling at the pressure of common bracing, but overweight, high prices and rigorous implementations have led to the introduction of a new type of buckling brace called Reduced Length Buckling Restrained Brace (RLBRB). However, in RLBRB, due to the low cyclic fatigue phenomenon, the length of bracing can‍‍‍‍‍ not be over-reduced so that it can be replaced as an inactive system after an earthquake. In this research, a new and innovative idea called Reduced Length Buckling Restrained Brace with S-shaped Core is introduced, which, despite its very short length, can overcome all the problems with the RLBRB and BRB system. Therefore, we first validate the analytical models of RLBRB and BRBs in the ABAQUS finite element software based on the experimental results of previous experimental research program. Then, according to the results of the analysis, the hysteresis response of the buckling braces with the S-shaped core is compared with the RLBRB and BRB braces. The results from the comparison of the proposed pattern with conventional buckling braces indicate that, despite the smaller and lighter ones, proposed braces have the same behavior as the BRB braces.

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.

Masonry infilled reinforced concrete frame buildings built prior to the introduction of modern seismic provisions have been observed to undergo damage in and around the masonry infill walls during most recent moderate to severe earthquakes. Considering interaction between masonary infill and frame is one of the challenges in the field of engineering research. Observation of past earthquake indicates that in the pre-damaged infill wall in the in-plane mode, the probability of out-of-plane failure of infill walls will increase. However various studies have shown that if the infill wall correctly restrained by the frame, there is a significant capacity, in terms of force and displacement against the out-of-plane demands. The prediction of interaction and effect of in-plane behavior on the out-of-plane beahaviour of infill, is one of the new issues in the field of seismic evaluation of masonary infills. This paper present comparative parametric review of the strength and displacement capacity models that predict the infills out-of-plane responses. Also, models that consider influence of in-plane damage on the out-of-plane capacity, it has also been investigated. The parametric comparison of different models in the capacity estimation of masonary infills in out-of-plane mode is shown that interaction of in-plane and out-of-plane beahviour of infills has a significant effect on capacity reduction of infills in out-of-plane mode and the model presented in FEMA360 for out-of-plane capacity of infills has a conservative results.

One of the latest innovations in nano-technology is the use of Micro-Nano Air Bubbles (MINAB) as a substitute for water in concrete. Using MINAB as a substitute for water used in concrete can be used to improve the properties of concrete. The use of super- Plasticizer can have an effective role in reducing negative effects MINAB on concrete properties. In this study, to investigate the effects of MINAB with water in concrete in the presence of different super- Plasticizer percentages, the effect of MINAB on the setting time, cement mortar flow and compressive strength of cement mortar is investigated. For this purpose, 16 samples of VICT needles, 48 samples of cement mortar and 16 samples of cement mortar flow were used to check the curing time, compressive strength and cement flow with different percentages of super- Plasticizer (0.5, 0.9 and 1.4) were tested in the presence and absence of MINAB. The results showed that the compressive strength of cement mortar with MINAB increased by 16 and 7%, relative to water at 7 and 28 days respectively. The compressive strength of cement mortar with MINAB has increased in presence of super- Plasticizer in comparison to cement mortar with water in presence of super- Plasticizer at the age of 7 and 28 days, with the highest resistance in 0.5% super- Plasticizer, which increased by 21% at 7 days and increased by 10% at the age of 28.

The construction of reinforced concrete buildings with masonry infill walls has been a very common practice in Iran. Nowadays, the impact of the RC frame and masonry infill on the structure is one of the major challenges in engineering researches, and often engineers ignore infill in designing the building. Due to the damages observed in past earthquakes, masonry infill can have both positive and negative impacts on the seismic performance of RC structure. In this paper, the effect of masonry infill on the in-plane behavior of the concrete frames and the impact of seismic and non-seismic details with the effect of level of axial load and thickness of infill in lateral resistance of concrete frames is investigated, by the nonlinear finite element method. First, the proposed models have been validated using the experimental results in ABAQUS finite element software. Results show that the increasing axial load causes to increase in ultimate strength and effective stiffness and reduces the ductility of the seismic frame. The ultimate strength, effective stiffness, and ductility of frame and infill-frame with seismic detailing were increased compared to the frame and infill-frame with non-seismic properties. Increasing the thickness of masonry enhance the infill behavior in terms of strength, effective stiffness and ductility in both seismic and non-seismic frame.

Recent Iranian earthquake damages like the damages caused by the Kermanshah earthquake, revealed that RC buildings having soft story irregularities experienced more seismic vulnerability. Moreover, earthquake aftershocks increased the seismic failures in past earthquake events. But RC buildings having soft story irregularities and effects of earthquake aftershocks are not included in recent seismic design codes. In this article, for assessing the effects of soft story irregularities and also the effects of earthquake aftershocks, three, five, and eight story RC building models having intermediate sway moment frames are designed and then modeled in OPENSEES software platform and then IDA analysis are performed in order to producing the seismic fragility curves consistent with HAZUS definitions. The analytical results of seismic fragility curves revealed that the influence of soft story irregularities and also main earthquake shock-aftershock sequences on the vulnerability of considered RC building models. By increasing the height of the RC building structures, the effects of soft story irregularities and the earthquake aftershocks decreased in seismic vulnerability of the considered RC buildings.

In recent earthquakes, masonry structures have not been resistant to earthquake due to high weight and low ductility and low shear resistance, and they have experienced a lot of damage. The improvement and strengthening of masonry structures is a serious discussion in urban construction. The walls of masonry are not resistant to the earthquake and their basic weakness is in ductility; its ductility is reduced when the length ratio increases to the wall height, in addition to the wall resistance. The purpose of this study is to investigate the seismic performance of masonry structures with two aspect ratio of 0.5 and 0.7 with scale 1: 2 and strengthening of masonry walls using different layouts of steel tie. The analytical evaluation of seismic behavior of reinforced masonry structures has been done using ABAQUS finite element software. In the FEMA356 method, the displacement curve of all samples is bilinear. Analytical results were compared in dominant resistance, effective stiffness and ductility. The ultimate strength, effective stiffness and ductility of strengthened specimens using steel tie increased in comparison to the control sample.

Beam–column connections in reinforced concrete (RC) structures play an important role when the frame is subjected to seismic loading. The overall stability of the structure and the formation of the optimal energy absorption mechanism in the beam plastic hinge zone depends on the role of the beam-column joints. The non-seismic detailing in the joint panel area can cause a partial or total collapse of the structure. Beam-column connections with non-seismic detailing in buildings with moment resisting lateral load bearing systems, are the major cause of post-earthquake damage. The optimal shape and energy absorption of the moment frame structure is dependent on the design and perfect execution of the beam-column connections. In the beam-column connections, the lack of positive reinforcement of the beam in the joint area and non-extension of the column stirrup in the joint area are common defects of the joints in accordance with new regulations. Researchers have provided a lot of experimental studies on beam–column connections, while experimental studies are usually costly and time consuming, and can be restricted by the test facilities and space. The behaviour of the RC beam–column joint is very complex and several parameters such as axial load ratio, reinforcement detailing, concrete strength have significant influences on its seismic performance, it is impractical to fully investigate all parameters through a limited number of experimental tests. Finite element modelling using ABAQUS software platform can provide an opportunity to study the various parameters governing the monotonic and cyclic behaviour of the beam–column joints. In this study, by examining several parameters in the finite element model of the RC Beam–column connections in ABAQUS software, such as specifications of strain-hardening for steel, bushinger effects, concrete damaged plasticity (CDP) in tensile and compression, concrete confinement effects, presence of lateral beam, and also bond-slip of reinforcing bars was investigated and leads to provides recommendations for finite element modelling of the RC frames. For this purpose, the behaviours of the seismically and the non-seismically detailed beam–column joints under monotonic and cyclic lateral loading were evaluated in different conditions of the presence of lateral beam. The finite element models with seismic and non-seismic detail were considered and validate with laboratory tests by considering sliding effect of longitudinal beam reinforcement using modified steel stress-strain curve. Then, the effect of different lateral beam conditions around the joint was considered. The results showed well that the finite element model is more consistent with the experimental results when considering the slip effects of the longitudinal beam reinforcement. Also comparing the results of the models with the different lateral beam conditions showed that confining the non-seismic joints can increase the joint strength against lateral loads. The general behaviour mode for the seismically detailed specimen was flexural yielding in the beam at the column face whereas for the non-seismically detailed specimens joint shear failure occurred generally before the beam section reached its ultimate flexural strength. The finite element model of beam-column joint specimens was calibrated by test results and good agreement was found between the experimental and numerical hysteretic behaviour. The model was able to capture the modes of failure, peak load and initial stiffness of the tested specimens.

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.