نشریه مهندسی سازه و ساخت
سال ششم شماره 4 (پیاپی 29، زمستان 1398)

Fiber concretes are a new type of composite material in the manufacturing industry, due to lack of information, identification behavioral characteristics requires laboratory studies. In this research, the bending behavior one layer and multi-layer slabs made with high performance self-compacting concrete reinforced by steel and plastic fibers has been studied. The slabs made in this study differ from 10 models, 4 models one layer and 6 models with three layers make-up, in which the type and volume the fibers vary in layers. Two sample were made from each model and a total 20 slab samples with dimensions 40*40*7.5 cm the three-point bending test slab were performed, in order to evaluate the effect adding steel and plastic fibers and their layout on the bending behavior of the slabs. The results showed that the steel fibers can significantly improve the bending behavior of the slabs, so that, after the first cracking crack, the cracking was done on the cracks and its extension was prevented, the creep behavior the unbleached concrete slabs They have increased their bending strength and ductility considerably. If plastic fibers were much less effective than steel fibers. The flexural behavior three-layer slabs with a fixed volume fibers distributed in such a way that the percentage fibers in the outer layers is more than the middle layer, improved compared to single-layer slabs, which can be due to an increase in the percentage fibers In the outer layers, because these layers are more tense than the middle layer.

The use of fiber reinforced polymers, FRP, is one of the methods for strengthening and retrofitting concrete structures. In this research, the strengthening of reinforced self-compacting concrete beams against shear, torsion and bending has been investigated using GFRP. For reinforcing the beams against shear, bending and torsion, the strips of GFRP were used in the forms of U-shape, straight on the bottom surface and screwed around the beams respectively. In this study, the experimental results were compared with the results of the numerical models and their accuracies were confirmed. Then reinforcement sheets were applied in one and two layers on concrete beam models. By studying the numerical results obtained from Abaqus software, it was observed that with the increase of cracks in the concrete beams, their stiffness decreased and then the stresses were tolerated by the adhesive layers and the GFRP sheets, which has led to an increase in the bearing capacity of the beams. The results of numerical finite elements modeling show that by reinforcing the concrete beams with one layer of GFRP, the load bearing capacities of the beams improved in shear and torsion about 32% and 47% respectively. Moreover, if two layers of reinforcement sheets were used, the shear and torsion capacities of the beams increased about 45% and 61% respectively. The bending capacities of the concrete beams strengthened with one and two layers of GFRP increased up to 32% and 48% respectively.

Self-compacting concrete (SCC). was developed about four decades before since that time it has been used very scarcely due to a number of problems including : separation, lack of flowability and filling ability, high cracking potential, and thereupon low compressive and tensile strength. In this study, properties of SCC containing viscosity modifying agent, steel and polypropylene fibers were investigated. polypropylene fibers with dosages of 0.1, 0.125, 0.20, 0.150, 0.185, 0.205, and hook end steel fibers with volume fractions of 0.5, 1, 1.5, 0.2 and 2.5 were employed; fresh and hardened SCC were examined. The results of the fresh concrete tests revealed that rise of the both fiber types reduces the slump flow and raises the T50 time. In the V-funnel test, the time shortened with polypropylene fibers up to dosage of 1.25%, and then soars. Growing steel fibers elongate the time of the V-funnel test. Adding both types of the fibers reduces the passing ability of concrete in the L box test. Hardened concrete tests indicated that the compressive strength is falling by rising the dosage of steel fibers. The compressive strength at the age of 7 and 28 days improves up to the polypropylene fiber dosage of 1.50% and then declines. At the age of 90 days, strength trend changes in dosage of 0.1. Tensile strength grows as the both fibers increase. The crack test results show that the length and width of the cracks lower with the growth of the fibers. Adding steel fibers boosts the number of cracks.

Previous studies and observations of the earthquake have shown that frame filled with concrete 3d panel wall, can have adverse effects on the seismic behavior of structures. On the other hand, yielding dampers that used with steel braces, have a high capacity to absorb and depreciating energy from the earthquake. In this paper, targets are reducing damage to the infills and moment frame in during of the earthquake, reduce the horizontal and vertical irregularities in structure. To rech these targets, Three experimentally models with half scale were constructed and tested on the shaking table under 7 scale accelerated. Also, for investigate the Effective of parameters in the seismic behavior of moment frames, using Abaqus software, finite element analysis was performed after verification of model behavior with experimentally results. Experimentally results showed that use the yielding connection between wall and frame, reduces the lateral displacement and plastic strain in the structure. Numerical analyzes showed that by adding the yielding connection to the frame and infill wall, The frame has linear behavior In high intensity earthquake, and not be created plastic hinges in the members of the frame. The input energy is amortized only in the connections. So the number and geometric specification of these connections can affect the lateral hardness and lateral strength of the structure.

CFT column significantly used in tall building and bridges due to high load bearing capacity. Considering the importance and position of these types of columns in structural engineering science and because they are used in specific structures partial damage may result in larger and unrecoverable damage before detection. Accordingly, the basis for the identification of damage in this structural element is more of a researcher's attention. One of the possible damages in these columns is the separation of the steel wall from the concrete core. In this study, the detachment damage was simulated by a thin layer of polystyrene of 6 x 40 cm in one of the columns between the concrete core and the steel wall and modal data of columns have been determined and analyzed. Comparison of frequency, shape of modes, and MAC and COMAC data of healthy and damaged specimen show which occurred in the structure of the damage. In addition, wavelet transform has been used to identify the location of damage. The results of the analysis show that sudden jump occurred in 0.2m and 0.6m in any of the main structures. Which, in the wavelet transform method, indicates discontinuity in the form of the structure's modulus, In this way, the location of the damage is identified with the least possible error.

All buildings need a system that resists the lateral forces such as wind and earthquake. Such systems are commonly known as Lateral Force Resisting (LFR) Systems. The steel slit shear wall system is a new LFR system intended for zones with high seismicity. One of the essential constituent of the steel slit shear wall system is the slit. The shear wall has columns with slits forming links in between them. In the presence of lateral forces, these links work as a series of small flexural members in parallel and behave in double curvature reaching yield at both ends. The most notable advantages of such a system are ductile behavior and high ability to dissipate energy. In this paper, numerical analysis using Abaqus is performed to evaluate the effect of moment inertia of beam on the behavior of steel slit shear wall. In order to verify the efficiency and accuracy of the employed finite element method, Cortes and Liu tests are conducted. After wall, twelve frame models with different beams are established. The hysteresis curves, energy dissipation capacity, initial stiffness, and ultimate strength of frames are compared and analyzed. It is observed that by increasing the moment of inertia, deformation and dissipated energy of slit steel shear wall with defined slit increase. It should be noted that, initial stiffness of steel slit shear wall with ordinary slit is higher.

The design and construction of irregular buildings has always been the focus of attention due to the demand for a beautiful and unique structure. Furthermore, the use of Shape Memory Alloys (SMAs) has expanded due to the improvement of the behavior of RC structures in the last decade. The main advantages of using this alloy are its super-elasticity and the reversibility of inelastic displacements of the structure. In this paper, the behavior of reinforced concrete structures with SMA alloy in regular, torsional irregularity and extreme torsional irregularity are investigated. The effect of using this alloy has been shown using fragility curves in different degrees of irregularities than conventional concrete structures. In this regard, the effects of memory-shaped alloys as longitudinal reinforcement in short-order, intermediate, and high-order structures with three different arrangements of longitudinal reinforcements have been investigated. Different types of reinforcement arrangements are the case of full Steel, the case of SMA at the plastic region of the beams and steel reinforcement in other regions and finally the case of SMA reinforcement over the entire length of the beams.Then, several increasing nonlinear dynamic analysis (IDA) were performed under the influence of the 10 selected accelerometers, and maximum drift of each analysis was obtained and the fragility curves were calculated in accordance with the HAZUS instruction for each structural case. The results indicate that the presence of memory alloy in irregular buildings will reduce the damaging effects of irregularities, including maximum drift and residual drift of the structure. This result suggests that the use of SMA alloy in torsional irregular and extreme torsional irregular buildings can reduce the structural damage caused by a possible severe earthquake.

Functionally Graded Materials (FGMs) are kinds of composite materials which exhibit continuous variation of material properties from one surface to another. With regard to the continuity of mixture of constituent materials, FGMs have more effective mechanical properties compared to laminated composite materials, which leads to eliminate the interlayer stress concentration. The most common usage of such materials is in thin-wall structures, such as plates and shells. Plates due to their extensive surface and low thickness, not only have low resistance against the blast loads, but also experience large displacements. Hence, utilizing FGM plates because of their constituents materials which have a power distribution in the direction of thickness, will lead to resistance improvement and displacement reduction. In this research, ABAQUS finite element software has been used to study geometric nonlinear dynamic response of Stainless steel-Silicon nitride FGM plates against the blast loads. The effect of volume fraction index, plate aspect ratio, plate thickness, the amount of explosive material and its distance and also the effect of Replica scale with Hopkinson scale are investigated in this study. The results show that with rising in the volume fraction index (from zero to infinity), increasing in the distance of explosion center to the plate (from 500mm to 900mm) and plate thickness (from 6mm to 18mm), the maximum amount of displacement of the plate have decreased by %29/1, %43/64 and %87/74 respectively. On the other hand, by expansion of the plate dimensions ratio (from 1 to 2) and increasement in the amount of explosive material (from 5 to 25gr), the maximum displacement of the plate have increased by 1/06 and 3/09 respectively. Also, it has been observed that changes in materials properties along with plate thickness don’t have any effect on scaling.

Today, restrictions on access to natural aggregate resources in concrete production have become one of the problems in many countries. Concrete, as one of the most widely used human products, is a factor in consuming a large amount of aggregate. To meet this need, today many developed countries use different types of recycled aggregates as a suitable alternative to natural aggregates. The present study investigates the effect of complete replacement of recycled concrete coils instead of coarse natural aggregates in concrete. In order to improve the quality of recycled concrete, the pozzolans like as micro-silica, natural zeolite and fly ash were used in different percentages. In order to determine and compare the mechanical properties of concrete, 11 mixing designs were made and compressive strength tests at 7, 28 and 91 days, indirect tensile strength (SPT), modulus of elasticity and ultrasound velocity tests at 28 days of age were performed. The results showed that micro-silica, especially at the 10% replacement level, has a dramatic effect on the improvement of the compressive strength of fully recycled concrete compared to other pozzolans. The results of the application of natural zeolite in fully recycled concrete showed that this pozzolan, especially in the 10% substitution, act as a cementitious reducing agent and play a lesser role in improving the mechanical properties of recycled concrete compared to recycled concrete without pozzolan. On the other hand, pozzolanic materials, in a way that improves the compressive strength of recycled concrete, are not able to improve the tensile strength and the modulus of elasticity of the recycled concrete compared to conventional concrete.

Blast loads may result Irretrievable damages in structures due to their high amount of applied energy to them during a short period of time. Strengthening and rehabilitation of the structures subject to these sort of loads would be a proper approach to mitigate these damages. Among the available approaches, use of composites so-called Fiber Reinforced Polymers (FRPs), because of their desire properties such as ease in installation and high strength to weight ratio, has been considered the most common solution in recent years. These composites, however, possesses some disadvantages such as low resistance against fire, low glass transition temperature, difficulties in application at low temperatures, impossibility of application on wet surfaces and lack of vapor permeability which have led to use innovative composite materials as alternative. These are normally made of cementitious matrix reinforced by continuous fibers (FRCM). These composites with cement based matrices have good mechanical performances, excellent resistance to high temperature and fire, and also good vapor permeability. Moreover, they can be applied on wet surfaces and in cases of low temperature. Therefore, FRCM materials may constitute an alternative to FRP materials for the strengthening of RC structures. In this paper, performance of RC columns which are subject to blast loading and strengthened with FRP and FRCM composites is investigated using Pressure-Impulse (P-I) diagrams. The results obtained in this study demonstrate that strengthening of structures by FRCM is more efficient in comparison to that of FRP in most cases of damages and therefore could be implemented to protect structures better against blast loads.

Five specimens one third scale three-story single bay steel plate shear wall with variant percentage of Ni-Ti shape memory alloys(SMAs) under cycling loading were analyzed by Opensees software. Also one specimen steel plate shear wall without SMA (SPSW-Base) wase analyzed under same cycling loading by the same software. The result of analysis of five specimens steel plate shear walls with shape memory alloy and one specimen of steel plate shear wall without SMA, compared with each other. All specimens had rigid beam-to-column connections. Shape memory alloys used in three different type in SPSW’s stories respectively in first type,in all stories in second type, in just one first and third story and in third type in just middle story. Also these materials used as kind of plates which surrounde all side ofsteel plate ofwalls, with similar thickness to steel plate and variant widthsuch a percent of widths steel plate of SPSWs. If th whole width of steel plate shear wall is showed by ‘B’ and the whole width of used material by ‘b’, each three types respectively consist offive specimens with b/B=9%,18%,27%,36%,45%. All specimens were analyzed under nonlinear static analysis. After analysis, all specimens with shape memory alloy showed more ductility in comparision with the one without shape memory alloy (SPSW-Base). Also by increasing SMA ductility increased in steel plate shear walls. In addition among three different types, second wich, used SMA just in first and third story, showed more and better ductility. As an example the ductility of SPSW-b/B=45% in this type is 70/41% more than SPSW-Base.

Over the recent years, different damage indices have been to predict the building damage, each of which uses different parameters to model the building damage. In this paper, 27 frames containing 18 frames with lateral load resisting systems of thin-steel shear wall type, as well as 9 frames with lateral load resisting systems of special steel moment frame, on three short (3-story), moderate (7-story) and tall ( 15 floors) height mode have been go under Incremental Load analysis and their failure index has been calculated at different levels of performance for 4 Park and Ang indexes including: maximum relative displacement , framing, and plasticity. The results show that the damage index for the frame with lateral load resisting systems of the steel shear wall in longer frames yields better results than other frames. So the use of this system is more justifiable. In addition, the results show that the maximum relative displacement index has different results than other indexes. Considering the performance levels achieved for short , medium and high-rise buildings, it can be concluded that the existence of two steel shear walls in the building is justified only in high-rise buildings. That is, the minimum number of openings that are responsible for drift of the structure is sufficient for a steel shear wall system, and the use of more openings affects the behavior of the structure and its function

Reinforced concrete structures need to be strengthened and retrofitted for various reasons, including errors during design and/or construction, and in most cases reinforcement of structural elements is much more economical than rebuilding the structure. Using HPFRCC with tensile stiffening behaviour has been developed to reinforce the concrete structures over the recent few years. In this paper, the usage possibility of HPFRCC for reinforcing two-way reinforced concrete slabs has been studied. .A total of five two-way slabs were constructed and tested to reach the rupture stage , that one of not reinforced slabs as control slab, and the rest of the slabs were reinforced in various forms. The reinforcements were carried out in two ways, once by installing veneer in the tensile area and once by installing veneer in both tensile area and compression area each time with different percentages of the fibres. The behaviour of bending and cracking, yielding and rupture of the laboratory samples were evaluated. The results revealed that the installation of pre-fabricated laminates of HPFRCC significantly improved the bending performance of reinforced slabs, so that the deformability, energy absorbance value, resistance to cracking and initial hardness of the slabs was increased and the crack width decreased. Therefore, they can be used to reinforce the weak slabs.

A large part of the dynamic force acted on the dam is the hydrodynamic force induced by dam and reservoir interaction which increases the seismic response of dam. Also, the water level has essential role in the creation of induced hydrodynamic force in reservoir because of interaction. In this paper, in order to investigation of the sensitivity of the seismic performance of system, Monte Carlo simulation with Latin Hypercube Sampling is used in which the reservoir height was selected as random input and the dam crest displacement, maximum value of hydrodynamic pressure and 1st and 3rd principle stresses in heel and toe of dam were considered as output responses and the sensitivity of responses were reliably examined under seismic loading. Considering of Pine Flat concrete gravity dam as case study, a finite element model is developed and implemented into a computer code using Ansys software for seismic analysis of system. Consider to obtained results, it is revealed that the reservoir height how can effect on seismic behaviour of system due to earthquake. Investigation of the obtained results it is obvious that the increasing of reservoir height around the greater than 70% height of full reservoir, considerable increase the seismic response of concrete dam body.