علیرضا خالو

Steel Plate Shear Walls (SPSWs) are being increasingly utilized as one of the efficient lateral load-resisting systems in seismic zones. Adopting openings in the infill plate of SPSWs is sometimes essential owing to the architectural requirements, structural reasons, as well as constructional limitations. This study aims at investigating the influence of strip openings on the structural performance of perforated steel plate shear walls with different infill plate boundary conditions. In this regard, a variety of perforated SPSWs with vertical and horizontal strip openings are designed and then numerically simulated possessing different aspect ratios and opening features. The effects of the dimensions and orientations of the strip openings are evaluated through response parameters in terms of drift and stress ratios corresponding to the flexural strength, axial and shear forces. According to the simulation results, in general, introduction of the horizontal and vertical openings attenuates the stiffness of perforated SPSWs, and in turn, the drift response of the structure becomes more pronounce. A non-dimensionalized parameter is also introduced to indicate how the boundary conditions and opening dimensions affect the drift response of the structure. The results indicate that an increase in the width and length of the opening can exacerbate the induced stress values corresponding to the axial forces, flexural moments, and their combination in the columns and beams. In addition, the use of perforated SPSW with opening of less than 0.25m2 can offer similar seismic performance as compared to that of SPWS with infill plate and without opening.

This paper is devoted to investigating the effect of applied torsional moment on the out-of-plane behavior of horizontally curved beams (HCBs) subjected to the excitation induced by a moving mass. As the mass travels along the top surface of HCBs, a torsional moment will be introduced into the system due to the eccentricity of the in-plane centrifugal action with respect to the shear center of the HCB section. The differential equations governing the HCB-moving mass system are first established considering the effect of mass inertia, Coriolis and centrifugal forces, and then numerically solved within the transition matrix approach. Thereafter, a parametric study is conducted to evaluate the influence of radius of curvature and central subtended angle of HCB, as well as the mass and velocity of the moving object. In general, with an increase in the values of radius of curvature and subtended angle of HCBs, a decreasing effect in the response of the system is observed. Moreover, a general magnifying effect is essentially experienced due to an increase in the mass and velocity of the moving object. As the results suggest, the magnifying effect of the induced torsional moment due to the in-plane centrifugal force is at most six percent for the results studied herein. For long-span HCBs, the torsional effect can be deemed as insignificant on the out-of-plane response of HCB-moving mass systems. In conclusion, it is indicated that considering the contribution of the torsional moment can offer a more realistic response estimation regarding the dynamics of HCBs acted upon by a moving inertial load.

Concrete quality control tests usually focus on the compressive strength of concrete, while neglecting other important properties such as impact and explosion resistance, which are essential for creating resilient concrete structures. Additionally, in the process of refining sugarcane, Bagasse, a yellow fiber that is considered a waste product, is produced. Khuzestan province alone produces around one million tons of Bagasse annually, which leads to environmental concerns. To address these issues, this research investigates the mechanical properties and impact resistance of concrete containing lightweight LECA aggregates and Bagasse fibers under compressive and impact loads. Initially, a target mix scheme is determined, and samples are made and tested after curing without the addition of Bagasse and LECA. Then, samples are made with the mentioned mixing design and the combination of Bagasse and LECA by weight ratio of (Bagasse unit, LECA unit). Additionally, samples using LECA (without Bagasse) with 10%, 20%, and 30% replacement of aggregates are made and tested after curing. Compressive and impact tests are performed on all samples in accordance with regulations using appropriate testing machines and procedures. Results indicate that concrete containing lightweight LECA and Bagasse fibers has a higher impact resistance than ordinary concrete, and that the use of LECA in concrete can create structural lightweight concrete.

In this article, seismic vulnerability of one of the ancient monuments ‎in Iran, Falakol aflak Castle, located in ‎Lorestan, is evaluated. In this ‎regard, by conducting field surveys, the damages in different parts of ‎the ‎building were categorized. The results of these investigations ‎indicated erosion and cracking in the ‎construction of the building, ‎settlements of parts of the building that caused cracks in some parts ‎of the building, ‎and rising dampness due to the presence of water ‎flow in the foundation of the building. Next, by modeling the ‎building ‎in Abaqus software, the seismic vulnerability of the building was ‎studied through incremental analysis. The ‎results of this analysis ‎indicated the vulnerability of different parts of the building, which ‎indicated the necessity of ‎presenting a seismic improvement plan. By ‎using in-situ piles and micro piles in the soil as well as vertical ‎reinforced ‎cores in the walls, the results of numerical analysis showed ‎that a significant improvement in the seismic ‎performance of the ‎building has occurred. The intensity of the original maximum plastic ‎strains and its extent were ‎much less compared to the unretrofitted ‎building. Also, the force-displacement diagrams of the building in ‎different ‎directions indicated a significant decrease in the ‎deterioration of the building's stiffness, which indicates the ‎reduction ‎of its vulnerability due to the addition of the proposed improvement ‎system. ‎

In this study, the shear-lag effects are evaluated on the performance of L-shaped reinforced concrete (RC) shear walls. At first, 42 L-shaped RC shear walls are simulated employing the FlashLab program, and then, the numerical analyses are performed due to the cyclic loading applied within the framework of ABAQUS software. Based on the results of the numerical studies and taking into account the shear-lag effects, axial strain as well as axial deformation distribution are obtained for L-shaped RC shear walls. Thereafter, on the strength of the evolutionary polynomial regression (EPR) and genetic algorithm, new expressions have been developed and introduced for L-shaped sections which allow quick estimation of the axial strain and deformation distributions. The reliability of the proposed expressions has then been examined based on the coefficient of determination, of which the average values for the axial strain and deformation are 80 and 72 percent, respectively. Also, the results of the proposed expression are compared with those of the previous studies for non-rectangular RC shear walls. Finally, on account of the Mean Absolute Relative Error (MARE) index attained for the proposed expressions to that of the previous studies available in the literature, the uniform distribution exhibits the best performance in the response prediction of L-shaped RC walls. Furthermore, calculation of the MARE values indicates that the established formulations can respectively predict the axial strain and deformation of L-shaped RC shear walls with average error of 65 and 54 percent of the MARE values of the available expressions addressed in the literature.

Effective width is known as an important parameter in the analysis and design of non-rectangular Reinforced Concrete (RC) shear walls. Current design codes, i.e., ACI, CEN, UBC, and BS, propose a constant value for the effective width calculation of flanged sections, which proved to be conservative and ineffective in some cases. Of the conventional non-rectangular RC shear walls, the L-shaped sections have rarely been investigated in the technical literature. As the L-shaped RC shear walls can extensively be employed for structural and architectural reasons, a reliable assessment of the effective width of L-shaped sections is essential. Therefore, this paper attempts to propose applicable formulations for the effective width estimation of L-shaped RC shear walls. In that regard, a number of numerical investigations involving finite element analyses have been conducted in the ABAQUS software in order to evaluate the cyclic performance of L-shaped RC shear walls. The numerical results including the axial strain and displacement distributions have been attained for 42 L-shaped RC shear walls with three different aspect ratios, at which the shear-lag effects have been taken into consideration. In addition, on the basis of the evolutionary polynomial regression (EPR) analyses, applicable formulations have been established to be utilized for the initial estimation of the effective width of the L-shaped sections. The effectiveness of the proposed expressions has been examined by assessing the R-factor of the estimations. On account of the average R-factor of 0.88, the capability of the proposed expressions has been ascertained in assessing the effective width of L-shaped sections. Moreover, in order to further highlight the unavoidable effects of level of axial loading and drift values on the variation of the effective width, different curves have been presented. Furthermore, calculation of the Mean Absolute Relative Error (MARE) index demonstrates that uniform distribution can well estimate the effective width of L-shaped RC walls.

This study aims to analytically investigate the impact response of FRP-retrofitted RC slabs. In this regard, based on the orthotropic plate theories, an applicable formulation is derived to assess the displacement of simply supported RC slabs due to the applied impact loading induced by dropping an impactor. The results have then been compared with the experimental data available in the literature. The proposed analytical formulation is proved to be reliable and efficacious to an extent that the displacement can be attained up to seven percent error. The effect of number of FRP layers and compressive reinforcement ratio have also been examined on the impact response of FRP-retrofitted RC slabs. The results indicate that adding 7 layers of GFRP strips to the bottom face of the RC slabs can attenuate the displacement values up to 33 percent. Moreover, the effect of compressive reinforcements on improving the impact response of RC slabs was estimated to be 30 and 23 percent, respectively, for RC slabs being examined.

A paucity of parametric study does exist that has investigated the influential parameters affecting the effective flange width of non-rectangular reinforced concrete (RC) shear walls. Therefore, this paper attempts to present a novel approach to parametrically study the effective flange width of non-rectangular RC shear walls. In this regard, an analytical formulation has been established in the elastic region to estimate the effective flange width of a non-rectangular RC shear wall with a general geometry. Based on the proposed analytical formulation and by considering the shear-lag phenomenon, the influential parameters have then been determined which affect the stress distribution, and in turn, the effective width of the section. Moreover, a dimensional analysis has been carried out employing the Buckingham's Pi Theorem to derive the effective flange width of the section as a function of dimensionless parameters. The findings indicate that the influential parameters are respectively the flange width, axial as well as lateral force, and height of the wall which appear in the predictive formulations. Nevertheless, the exciting codes neglect the effect of the applied loading to the wall structure which fail to accurately predict the effective flange width of the wall section.

Passive energy dampers have been identified as efficient and economical tools to improve the seismic behavior of structures against seismic loads. Among all types of passive energy dampers, steel dampers are more popular because of their ease of construction, availability, affordability, economical aspect. In addition, these types of dampers have performed well in the laboratory and numerical studies, as well as in past earthquakes. Although these types of dampers are more economical than other dampers, they are not economical to use in conventional structures compared to other conventional lateral load systems. Therefore, in this paper, an innovative damper with shear mechanism is introduced which is easy to construct and operate and is economical to use. This proposed damper is easily replaceable after severe earthquakes. Numerical results show that the proposed damper improves the seismic behavior of the RC frame. It is usually not easy to increase the stiffness and ductility of the structure at the same time, but numerical results show that the proposed dampers increase the stiffness and ductility of structures. It also causes energy dissipation to the structure by increasing the damping in the nonlinear area. In this paper, the necessary equations for calculating the ultimate stiffness and strength of the system as well as its design are proposed.

The main objective of the present study is to investigate the effects of incorporating the low ratios of different Nanosilica types on concrete resistivity against bars corrosion embedded in High-Performance Concrete (HPC). Three ratios of water to binder are considered in the experiment: very low, low, and moderate ratios equal to 0.25, 0.30, and 0.35, respectively. In addition to implementing different ratios of w/b, different types of nanosilica were applied, a coarser and a finer one, respectively, with specific surface areas of 200 and 380 . Moreover, two low ratios of nanosilica 0.75% and 1.50% were considered to replace with cement according to previous studies. Compressive strength test, electrical resistivity, and non-destructive ultrasonic test were conducted in this study. In addition, the workability of the mixtures was kept constant by adjusting the superplasticizer. Although the performance of different types and ratios of nanosilica were variable due to its great activity, it was significant that nanosilica with a lower specific surface area outperformed the control specimen and the specimen with finer one. It should be noticed that due to very much fine size of pyrogenic nanosilica used in this study, it was highly agglomerated. Thus, by using a high shear speed mixer, nanosilica was mixed with partial mixture water. It was shown that a lower water-to-binder ratio had more compressive strength and also, more electrical resistivity was addressed indicating more durability due to lower water-to-binder ratios. It was also noticeable that using nanosilica in mixtures made the HPC more durable and increased compressive strength. Nanosilica of Coarser grade sounded quite better in terms of durability characteristics and also, showed more corrosion resistivity based on ACI222r01. As a result, mixtures of lower water-to-binder ratio with higher replacement of cement (1.5%) with coarser nanosilica (lower specific surface area) had the most compressive strength, electrical resistivity, and non-destructive ultrasonic pulse velocity, indicating the best concrete resistivity against corrosion of deformed bars.

The recent changes in urban communities and consequently the need for thinner strong concrete structures has caught researchers' attention. Structural performance characteristics such as ultimate loads, maximum loads, and ductility along with formation and propagation of cracks in prestressed concrete beams have been studied by many researchers. In this paper, an experimental study was carried out to investigate the effect of amount and arrangement of non-prestressed longitudinal and transvers bars on improving the performance of six prestressed concrete beams with identical geometry and concrete properties under static loads. Cracking strength, formation and propagation, ultimate load carrying capacity and ductility of beams were determined. Unbonded post-tensioning is applied to 7-wire strand tendons with Grade 270 and diameter of 0.5in that are positioned with constant eccentricity within the beam. The test results indicate that adding non-prestressed reinforcement to concrete beams generally has a significant effect on properties of prestressed concrete beams such as ultimate load, maximum load, ductility and pattern of crack formation and propagation and also have a significant reduction in brittleness and showed better ductility. The response of beams significantly depends on the method of confinement by transverse reinforcement and also the distribution of longitudinal reinforcement.

Fiber Reinforced Polymer (FRP) bars with significant resistance against the corrosion lead to an improvement in the performance of concrete structures and a significant reduction in costs. High ratio of tensile strength to weight, being non-conductive, and non-magnetic are other features of them. Recent international design standards, such as ACI 440.1R-15 do not recommend including FRP reinforcement in compression and replace them by concrete in calculations. In this study, due to the prediction of the effect of the GFRP compression bars on the flexural strength and ductility of GFRP reinforced concrete beams, the thirteen concrete specimens were modeled using finite element software, ABAQUS. Concrete elastoplastic behavior after the peak was defined using the concrete damaged plasticity model in software. Experimental data from previous studies were used as a criterion for numerical investigations and the model results were validated using numerical modeling. The results demonstrated that the displacement-force graphs, obtained from numerical analysis, were in good agreement with the respective curves obtained from the laboratory analysis. According to the numerical evaluation, GFRP reinforced concrete beams included higher flexural strength, i.e., the average flexural strength of steel-reinforced concrete beam was about 90% of the GFRP reinforced concrete beam. Also, the ductility of GFRP concrete beam specimens was greater than that for the steel beam specimen. Increasing the percentage of GFRP compression reinforcement resulted in higher energy absorption and ultimately higher ductility of the GFRP concrete beams. The numerical results indicated that GFRP compression reinforcement does not significantly increase the flexural strength of beams.

Concrete is widely used in civil engineering because of its high compressive strength and efficiency. Low resistance of concrete against tensile stresses, especially in low confinement systems necessitates the use of steel-concrete composite systems. In concrete-filled steel tubes, the confinement of concrete is supplied by steel and the local buckling of steel is improved by concrete core. In this paper, using the Abaqus software finite element method, the numerical results of the CFST column are compared with the experimental results and have been assured of the correctness of the modeling. Then, the effect of changing the thickness of the steel and the compressive strength of the concrete on the behavior of CFST columns is investigated. To consider the effect of changing these parameters, 9 CFST column models with three different steel thicknesses and three different compressive strengths of concrete have been used. Nonlinear behavior of steel using a mixed hardening model incorporating both isotropic and kinematic hardening was used in modeling. Concrete’s stress-strain relations and compression-tensile damage parameters are fully described. The effect of increasing thickness of steel and concrete strength on structural energy absorption, initial stiffness and column capacity were investigated. According to the results of the analysis, the effect of increasing the thickness of steel on the performance of CFST columns relative to the increase in concrete strength is significant. Investigating the energy absorption capacity and the resistance of the CFST columns shows that the effect of changing the compressive strength of concrete for confinement steel with less thickness is significant. In confinement steel with high thickness, the change in concrete compressive strength does not have a significant effect on energy absorption and increases the column's strength slightly. As a result, to improve the performance of structures with CFST columns, in terms of energy absorption, stiffness and capacity, it is desirable to use suitable thickness for steel and normal strength for concrete.

In this paper, a simultaneous experimental and numerical analysis of opening mode toughness in The Pre-joined Brazilian disc using Brazilian tests are carried out. These numerical results are compared with the existing experimental results. For this purpose, two concrete disc specimens of 54 mm diameter and 27 mm thick were prepared. These specimens have a central joint of 20 mm in length and an opening in mm 1. Specimens are made from a mixture of water, fine sand, and cement with a ratio of 1-5 / 0-1. The same specimens are numerically simulated by a two-dimensional particle flow code (PFC).The results indicate that the crack formed from the tip of the joint and grows parallel to the load and connects to the edge of the specimen. The Fracture toughness obtained from the numerical method is in good agreement with experimental results.

In recent decades, concrete column retrofitting methods and their seismic behavior under cyclic loading, especially from ductility and energy absorption standpoints, have been extensively focused by researchers. Significant amount of this research has been allocated to confinement of concrete elements in order to advance the ductility and energy absorption capability of the concrete structures facing the forces induced by earthquake. In this study four methods of concrete column retrofitting methods, including FRP plates, steel jackets, and concrete jackets, have been assessed and thoroughly compared with each other in terms of seismic behavior advancement measurements.
To achieve this objective, different retrofitting methods were simulated in ABAQUS FEA software, based on prominent finite element analysis and numerical modeling. The modeling results were verified with equivalent experimental tests which further validates the accuracy of the modeling approach. In addition, the impact of the following variables were studied using sensitivity analysis on the replicated models: Core concrete strength, texture and number of layers of FRP plates, size and thickness of steel plates, and dimensions of concrete jacket, along with diameter and placing of stirrups and bars.
Strength, ductility, and energy absorption capacity of the simulated models were recorded in order to compare efficiency of each retrofitting method. Results have shown that retrofitting through FRP plates leads to increasing ductility. Retrofitting using concrete jackets, despite increasing the energy absorption capability and maximum shear strength, will not result in acceptable ductility. On the under hand steel jackets, along with improving a maximum shear strength and energy absorption ability of the element, shows promising improvement in ductility. Moreover, for the models with the same axial load and lateral load capacity, steel jacketing and concrete jacketing methods have proved to show better ductility, compared to FRP. Plus, steel jacketing resulted in the highest energy absorption capability among all the three methods under the aforementioned condition.

Reactive powder concrete is a new type of high-strength concrete, which due to extra fine materials and pozzolans in addition to high hydraulicly active materials is refered to as Reactive Powder Concrete (RPC). The objective of this paper is to make feasibility study on construction and production of RPC using locally available materials in Assalooyeh region. In this research study, some of the properties of RPC are investigated. Six mixes, using 0%, 10%, 15%, 20%, 30% and 40% silica fume, based on required cement content,water to cement ratio and optimized super-plasticizer are designed. Experimental program included reology of fresh mixes, compressive and flexural strengths, three types of curing condition and micro-structure of the concretes. Test results and analysis indicate that mixes with 15% silica fume provide the highest compressive and flexural strengths for the three types of curing regimes.

R e s e a r c h e r s h a v e a l w a y s p a i d g r e a t a t t e n t i o n t o s a f e a n d e c o n o m i c a l d e s i g n a n d, t h e r e f o r e, d i f f e r e n t c o d e s i n d i f f e r e n t a r e a s h a v e b e e n f o r m e d. T h e A C I 318-2011 c o d e i n s i s t s t h a t t w o-w a y p o s t-t e n s i o n e d s l a b s s h a l l b e c l a s s i f i e d a s c l a s s U (w i t h o u t c r a c k i n g), w h i c h m e a n s t h e s e c t i o n m u s t b e u n c r a c k e d i n b o t h s e r v i c e a n d t r a n s i e n t c o n d i t i o n s (c o d e r e f e r e n c e 18.3.3). I n a d d i t i o n, t w o-w a y p o s t-t e n s i o n e d s l a b s m u s t b e p o s t-t e n s i o n e d i n b o t h d i r e c t i o n s f o r 100% o f t h e l o a d, w i c h m e a n s t h a t o n e-w a y b e h a v i o r f o r t h i s t y p e o f s l a b i s a s s u m e d. I n t h i s s t u d y, t w o-w a y p o s t-t e n s i o n e d s l a b s w i t h v a r i o u s s p a n s u n d e r d i f f e r e n t l o a d i n g s h a v e b e e n d e s i g n e d, b a s e d o n t h e A C I c o d e. T h e n, u s i n g t h e L e e-F e n v e s i s o t r o p i c d a m a g e p l a s t i c i t y m o d e l f o r c o n c r e t e, t h e n u m e r i c a l s i m u l a t i o n o f p o s t-t e n s i o n e d s l a b s w a s p e r f o r m e d t h r o u g h t h e f i n i t e e l e m e n t m e t h o d. T h e i s o t r o p i c d a m a g e p l a s t i c i t y u s e d a y i e l d c r i t e r i o n t h a t m a t c h e s t h e e x p e r i m e n t a l d a t a f o r b o t h e l a s t i c a n d p l a s t i c p a r t s o f t h e s t r e s s-s t r a i n c u r v e s o f c o n c r e t e. T h e o n s e t a n d p r o p a g a t i o n o f c r a c k i n g c a n b e e v a l u a t e d b y s i m p l e p o s t p r o c e s s i n g o f t h e f i n i t e e l e m e n t p l a s t i c i t y s o l u t i o n. T h e a c c u r a c y o f t h e m o d e l w a s c h e c k e d b y t h e d a t a p r o v i d e d b y p r e v i o u s r e s e a r c h e r s w h i c h i n d i c a t e s s i m u l a t i o n w a s p r e c i s e. T h e l i n e a r e l a s t i c-p e r f e c t l y p l a s t i c s t r e s s s t r a i n r e l a t i o n w a s u s e d f o r s t e e l u s i n g t h e V o n-m i s e s y i e l d c r i t e r i o n, w h i l e t h e t e n d o n s w e r e s i m u l a t e d b y b i l i n e a r s t r e s s s t r a i n c u r v e a n d V o n-m i s e s y i e l d c r i t e r i o n. B y u s i n g n o n l i n e a r f i n i t e e l e m e n t s o f t w a r e (A b a q u s) a n d t h e a b o v e - m e n t i o n e d y i e l d c r i t e r i o n, s e v e r a l s l a b s a r e s t u d i e d. N u m e r i c a l s i m u l a t i o n s h o w s t h a t s o m e l a w s o f t h e A C I c o d e a r e n o t s a t i s f i e d i n s o m e c a s e s, i n c l u d i n g c r a c k e d s l a b s i n b o t h s e r v i c e a n d t r a n s i e n t c o n d i t i o n s. I n a d d i t i o n, o v e r p o s t-t e n s i o n i n g o f s l a b s r e s u l t s i n n e g a t i v e d e f l e c t i o n a n d n o n-e c o n o m i c a l d e s i g n. A t t h e e n d s o m e s u g g e s t i o n s f o r b e t t e r d e s i g n s a r e p r e s e n t e d.

In this study، the application of high performance mortar in order to cast thin ferrocement element by the use of nano-silica particles is investigated. Variable parameters consist of the amount of nano-silica particles respect to cement quantity in the ordinary Portland cement mortar (1%، 2%، and 3%) and super-plasticizer used to achieve similar workability. To compare the mixes، mortars with high and similar workability were casted which guarantee the identical pomp-ability of ferrocement to cast the elements. In addition، regarding to examining the micro-structure and mechanical properties of recycled concrete، Scanning Electron Microscopy (SEM) test and compressive strength have been applied respectively.