فهرست مطالب ابراهیم خلیل زاده وحیدی

Composite shear wall consisting of steel sheet with reinforced concrete cover is one of the most common systems resistant to lateral loads in tall structures. The main purpose of this study is to investigation the effect of reinforced concrete cover, steel sheet thickness, door and window opening on the seismic behavior of steel frame with composite shear wall. For this purpose, in the present study, after validation of numerical modeling, 19 specimens of composite steel shear wall with a height of 3.2m and a span length of 5m are modeled. The results of this study show that the utimate strength, stiffness, dissipated energy and ductility in the model with reinforced concrete cover without opening and with a steel sheet with a thickness of 15 mm, respectively 12.24, 63.78, 7.82 and 4.37 times the reference model and in the same model without reinforced concrete cover, these values are 8, 41.61, 4.46 and 6.24 times the reference model, respectively. In other words, the reinforced concrete cover, due to the prevention of buckling of the steel sheet due to compressive force, has increased the utimate strength, dissipated energy and ductility. Also, in reinforced concrete cover, increasing the thickness of the steel sheet from 10 to 15 mm has little effect on the utimate strength.

Concrete beam-column joint perform an important role in structural ductility, energy absorption and delaying breakdown. In this study, the effect of engineered cementitious composites containing carbon nanofibers (CNF-ECC) on the behavior of T-shaped concrete beam-column connections under cyclic loading is investigated. The tensile strain hardening behavior of ECCs has made a powerful material with high energy absorption and high cracking potential before failure. Since ECC is a relatively new material, much of the research has focused on understanding the nature of these materials, their different constituents, different mixing ratios, the stress-strain curve relationships, the invention of new composites. Research has also been done on its practical applications in structures. But these studies are not as extensive as research on the behavior of materials themselves, and require a great deal of analytical ad laboratory work. In this study, three concrete joints were tested, one of which was replaced as a reference specimen and the other two joints were replaced with ECC and CNF-ECC. The main parameters considered include hysteresis Moment curves - relative drift, energy absorption capacity, and crack distribution. Experimental models were subjected to cyclic loading at the end of the beam with displacement control. The loading continued until the load reduction reached more than 30-40% of the maximum load. The results show that by using these high- performance materials, the ductility and energy absorption of these joints are effectively improved. The results showed that using these powerful materials, the ductility and energy absorption of these joints were effectively improved and the cracks created in the connection spring as a dense network of micro-cracks with very shallow depth and width. respectively.

The main purpose of this study is to experimental investigation the properties of concrete containing recycled concrete aggregates and waste rubber with micro silica. For this purpose, recycled concrete aggregates at the amount of 0%, 25%, 50%and100% by weight have replaced with coarse aggregate and micro silica at the amount of10% by weight have replaced with cement. Also, in two specimens with50% recycled concrete aggregate, first without micro silica and second with micro silica, waste rubber with 30% by volume of fine aggregate has been replaced and used. In the next step, the amount of slump, compressive strength, tensile strength, flexural strength, stress-strain curve, density and permeability of the specimens are evaluated. The results of this study show that the presence of recycled aggregates reduces the compressive strength from3.2% to 14.5%and also adding waste rubber powder to the specimen with 50% recycled aggregates reduces the compressive strength to the71% compared to the reference specimen (specimen with natural aggregates and without micro silica). All specimens with micro silica have higher compressive strength than similar specimens without micro silica. The highest compressive strength is related to the specimen with 25% recycled aggregate and micro silica, which is 9.6% higher than the reference specimen. specimens containing50% recycled aggregate in the presence and absence of waste rubber powder have55 and72% lower tensile strength and 30 and 67% lower flexural strength, respectively, than the reference specimen. The lowest water absorption is for the specimen without recycled aggregates with micro silica at the amount of0.5%.

This study experimentally examines types of rotational-friction dampers with two slip load and numerically analyze the behavior of a reinforced concrete frame with these dampers under cyclic loading. To this goal, the study will explain the mechanism of proposed damper’s action after the introduction. In the next step, two specimens of rotational-friction dampers with two different slip load are investigated in the laboratory. Using OpenSees software, the proposed behavioral model is validated by experimental results. In the final step, a frame of one-story reinforced concrete that had one bay was analyzed under cyclic loading in four states including (1) without damper, (2) with a rotational-friction damper that had one slip load (RFD), (3) with a rotational-friction damper that had two slip load type S01, and (4) with a rotational-friction damper that had two slip load type S02. The obtained results were discussed and examined after these analyses. The results of the numerical analysis also show that the concrete frame with S01 damper has better seismic performance. This is because its ultimate strength and dissipated energy are respectively 15% and 164% more than the ultimate strength and dissipated energy of the frame without damper, at the last cycle.

The potential danger of fire is one of the important phenomena that may cause Irreparable damages the structure. Therefore, add fire protection is essential for columns as the main components of a structure that require sufficient fire resistance for increase in safety. In this study, the effect of expandable paint coating on the temperature distribution at the cross section and time of fire resistance of concrete-filled steel columns that are suitable for high seismic areas and tall buildings have been studied. For this purpose, in first step the finite element model of a steel column filled with concrete under ISO 834 standard fire was prepared and analyzed according to available laboratory data. After validation of the results from the finite element model in comparison with the laboratory data, various specimens of columns that protected with Intumescent Fire Coating and with circular, rectangular, square and oval sections, designed according to the Iranian Steel Code and has been modeled and analyzed by Abacus finite element software. The results show that the expandable paint coating increases the fire resistance of concrete-filled steel columns with circular, square, rectangular and oval cross sections by 2.2, 3.3, 4.14 and 3.36 equality has been afforded to those without protective cover.

Buildings may be subject to various external threats throughout their lives. These threats can cause progressive Collapse to the structure by damaging the critical structural elements. Studies on structural systems failure in recent years highlight the importance of the progressive collapse phenomenon caused by abnormal loading like crashes, terrorist attacks, explosions, earthquakes, and so on. In this study, the performance of 6-story masonry infilled reinforced concrete frames with varying percentages of openings in progressive failure due to varying span length and floor height is investigated. The frames examined have RC moment-resisting frames that are designed by the Iranian Building code. Progressive collapse simulation by alternative path method by removing the middle column of frames in OpenSees software with nonlinear static analysis. According to the results, In the case frames with 10%, 20%, and 30% openings in the infilled masonry wall, their maximum strength reduced by about 23%, 31%, and 39%. Also, the frame with openings reduces about 62% of the maximum force against the without openings frame. The results show that increasing every 0.5 m of span length from 4 to 6 m, on average, increases the force by about 9%. Also, increasing the height of the floor from 3 to 4 meters, on average, increase the strength of the frames by 13%. The results of this study showed the positive effect of infill, increased span length from 4 to 6 meters and height from 3 to 4 meters, the class is in the process of progressive collapse of RC frames.

Carbon nano-materials, especially Carbon nanotubes (CNTs(, are the most prospective advanced materials for application in cement-based products for the construction industry due to their excellent material properties. An appropriate design for beam-column joint structures is required to meet the requirements of strength and ductility to prevent any sudden failure. Under seismic action, this beam-column joint zone is considered the most sensitive zone that undergoes different shear stresses in different deflections. The seismic performance of beam-column connections and joints can be enhanced by using improved details in the joints, ensuring a strong connection behavior. However, the use of dense reinforcements brings about executive problems such as lack of concrete condensation. This paper investigates the effect of Engineering Cementitious Composites containing Carbon Nanotubes (ECC-CNT) on the behavior of RC exterior beam-column joints under reversed cyclic loading. In this study, three beam-column concrete joints were tested, one of which was the reference specimen. The two other joints of the critical area of beam-column connection were replaced with Engineering Cementitious Composite (ECC) and ECC-CNT. The main parameters considered include the moment-deflection relationship, the energy absorption capacity, hysteresis curve, and crack propagation. The specimen was subjected to a reversed cyclic loading under control deformation at the tip of the beam. Loading continued until the load dropped to more than 30-40% of the maximum load. Also, to simulate the actual sample, the compressive load of fifteen tons continuously entered the column. The mixing technique for producing highly dispersed nanomaterial in cement mortar is crucial as it directly affects the mechanical properties of the cementitious composite. In this study, a surfactant (plasticizer) and Arabic Gum were used in order to get a homogenous dispersion of CNT in water. According to the results in the sample containing CNT in the plastic joint, it absorbs the highest amount of energy at the end of loading, which was 28% and 55% higher than ECC and NC, respectively. In addition, results indicated that the use of ECC-CNT in the plastic bonding zone had a significant effect on the energy absorption and relative deformation of the joints.

Nowadays one of the challenges that engineers and structural designers encounter is reduced vibrations of structures due to lateral forces such as earthquakes and winds. Taking into consideration that the design and construction of tall buildings is one of the most common methods of land-use in highly populated urban areas, the necessity and importance of identifying methods of controlling structural vibrations is felt more keenly than before. One of the methods of structural motion control is passive structural motion control with friction dampers. In this study, the main focus on the application and performance of friction dampers is new ideas for using the friction phenomenon to control structural vibrations and the design challenges of structures with friction dampers. For this purpose, first, we try to point out the important concepts in vibration control. Then, the goals, methods and results of various existing researches are examined to provide a clear view of friction dampers for structural engineers and as a start for future research to develop and improve the performance of friction dampers.

Iran is a land of seven thousand years old civilization, one of the oldest civilizations of the ancient world, because of its rich cultural and artistic history, there are many monuments, most of which are in high seismic danger areas. Bam Citadel was built in the 5th century BC and covers an area of 180,000 square meters was located on the Silk Road, one of the world's largest adobe structures. The superstructure and valuable damaged during the earthquake and unfortunately it was destroyed more than 80 percent. In other words, one of the lessons that can be learned from the Bam earthquake is that the historic adobe structures are extremely vulnerable. Therefore, due to its rich history and rich artistic heritage including architecture, masonry and pottery, the need to preserve remains of the past is felt more and more. In this article, after highlighting the importance and necessity of preserving historic adobe structures, their architectural features are discussed. The next step will be discussed the seismic performance of historic adobe structures and methods of the seismic retrofit and restoration of them investigated. Finally, studies on the retrofitting and restoration of adobe structures will be reviewed.

The constant ``F'' is of significant importance when it comes to the design and theoretical understanding of crack expansion under fatigue or impact loads. Even though numerous papers on the failure of materials via the cracked disc have been published, almost no method vis−acutea-vis vis the optimization of the shape factor ``F'' has been proposed. Thereupon, this study strives to determine the stress intensity factor (SIF) for the semi-circular disc model under uniform compressive load and also to calculate the optimized shape factor. In this research, inspired by the geometry of the Brazilian disc, the stress intensity factor (SIF) and the optimized shape factor (F) under uniform compressive load have been proposed. In this paper, to assess KI under uniform compressive load, the experimental results of photo-elastic materials and also the finite element results have been employed. The shape factor of the Edge Cracked Semicircular Disk (ECSD) under uniform compressive load can experimentally be tested more conveniently and therefore by altering the value of the factor beta, the optimal shape factor is obtained.The angle beta varies from zero (purely vertical load) to 10 degrees. Also, the length of the crack changes from 1 to 29 mm. After the carried-out investigations, it can be ascertained that the value for KI reduces as the angle increases. The reason behind that is the reduction of the tensile area in the edges of the semi-circular disc. Further, in a particular angle, as the crack length increases, KI initially rises and then, due to the tip of the crack approaching the compressive area of the disc, it undergoes reduction. The'' zero degree'' diagram is considered to be the limit state and is perpetually increasing and it should not be crossed by any other diagram. To achieve the optimal shape factor, the values of ``SIF'' and the length of the normal crack should first angles, the optimum geometric shape factor of the cracked semi-circular disc was determined to be equal to 1.325 at the angle beta=20

Due to the influences of several parameters such as brick and mortar properties, interaction between brick and mortar and etc., engineers encounter challenges in modeling and evaluating procedure of the seismic behavior of masonry-infilled reinforced concrete (RC) frames. To predict the seismic behavior of these structural elements, the analytical model must be comprehensive and efficient in such a way that it can show the actual behavior of the structure. Modeling the behavior of masonry infilled reinforced concrete frames under in-plan load, has received much attention over the last decade. The main aim of this paper compares different methods of modeling infilled frame with experimental results in order to choose the appropriate method for modelling of infilled RC frames. To achieve the purpose, after describing the background to the application of each method, the specimen which was tested in the laboratory was modeled in three different methods. The first model was realized by simplified micro-modelling and, the second model was realized by macro-modelling procedure via Abaqus software. The third model was further made by equivalent diagonal compressive strut modelling in OpenSees software. The results showed that the macro-modeling method had maximum and the simplified micro-modeling had minimum accuracy in Abaqus software. The amount of observed differences between experimental results and macro-modeling approach, between experimental results and simplified micro-modeling approach, and equivalent diagonal compressive strut modeling were 2.65%, 9.25% and 10.12%, respectively. These findings maintain that macro-modeling technique in Abaqus software could have an appropriate performance in detecting cracks.

Usage of yielding dampers, through an effective guidance of damages to some restricted and predefined special areas of the structure. In addition to the energy dissipation of earthquake, leads to the simplicity and cost reduction of the repairs for the damaged structure after an earthquake. In this paper, a new connection detail with pipe dampers is proposed in which entrance energy is dissipated by the plastic behavior of steel material. The suggested dampers are quickly replaceable, which is a great advantage for serviceability of the structure after an earthquake. In this research, behavior of the suggested connection is compared with other moment resisting steel connections, such as conventional welded connections and moment connections with slit dampers. Results show that by using pipe dampers in beam in column connections, development of undesirable inelastic deflections in the main members, such as beams and columns, is prohibited. Moreover, stiffness, strength, and ductility of these connections stay in a suitable range are compared to the conventional moment-resisting connections. Stiffness, energy absorption, and strength of the connections with pipe dampers vary in the ratios of the capacity of the pipe damper to the plastic capacity of steel beam. This is a controllable parameter in the design of the dampers. Investigations on the effect of the capacity of the dampers show that using pipe dampers with capacity ratios more than 70% will cause plastic deflections in the main members, such as beams and columns. Based on these results, in order to take the optimized usage of the beam bending capacity and prevent the development of unsuitable plastic deflections in beams and columns, it seems that suggested pipe dampers should be designed so that their ultimate bending capacity can be about 50% of the beam plastic bending capacity.

In the present paper, compressive strength of cement mortar was investigated through two cases: case I in which just nano-clay (Nano clay to cement proportion equal to 3% and %5) is included, and case II in which both nano-clay and fly ash were considered (with the same values for Nano-clay as case I, and with fly ash to cement proportion equal to 15%). Gradual interaction of fly Ash with calcium hydroxide and alkalins resulted from cement hydration process, produces more C-S-H, spreading through concrete substructure free spaces. Results indicated that, all samples which contain nano-clay are denser than the reference sample. Adding fly ash and nano-clay have resulted in decreasing short term period (relating to three and seven days age) compressive strength of cement mortar. The 28 day age compressive strength of samples of case I, showed a dramatic increase about 27.2% for proportion value equal to 3%, and a considerable increase about 15.1%, for proportion value of equal to 5%. Results, also indicated a considerable increase in the 90 day age compressive strength that was about 28.4% and 22.4% respectively relating to two proportion values, 3% and 5%. The 28 day age compressive strength of samples of case II increased about 1.6% and 4.5% respectively, relating to two values of nano-clay to cement proportion equal to 3% and 5%. The 90 day age compressive strength of samples of case II, showed an increase about 10% and 16% respectively, relating to two values of nano-clay to cement proportion equal to 3% and 5%.