Sharif Digital Repository

Hexapod robots gives us the ability to study walking robots without facing problems such as stability in many aspects. It has a great deal of flexibility in movement even if a leg becomes malfunctioned. Radially symmetric (hexagonal) hexapods have more flexibility in movement than rectangular leg alignments. Because of symmetry they can move in any direction and time efficiently. Inverse kinematic problem of this kind of hexapods is solved through a modular mobile view considering six degrees of freedom for the trunk. Then typical tripod and wave gaits are analyzed and simulated through the presented formulation. In Reinforcement Learning algorithm for walking it is important how to make... 

This research studies the effect of glass fiber-reinforced polymer (GFRP) bars as compressive reinforcement in reinforced concrete (RC) beam members. Three singly and six doubly reinforced GFRP-RC beams were tested under a four-point loading configuration. The effect of compressive reinforcement on the load-bearing capacity, ductility, stiffness, and failure mode is determined. Also, the compressive performance of GFRP bars is evaluated by testing GFRP-RC cylinders. According to the results, GFRP bars in compression had a limited contribution to enhancing flexural strength, and the maximum increment in the flexural capacity of doubly reinforced beams compared to singly reinforced specimens... 

An architectural modification method was utilized to improve fracture toughness of discontinuously reinforced aluminum (DRA) composites. Al-DRA composites having a structure similar to that of reinforced concrete were fabricated. The number of reinforcing DRA rods within Al matrix and volume fraction of SiC particles in DRA were altered to evaluate their effect on fracture behavior of these materials. It was found that architectural modification does not have any destructive influence on elastic modulus and yield strength of the composite. Moreover, the success of this method on toughness improvement strongly depends on the occurrence of debonding between Al and DRA regions upon loading  

Interface shear strength between soil and structural materials is dependent on the confining pressure. To increase the confining pressure, different methods of reinforcement and materials, such as carbon-fiber-reinforced polymer (CFRP) can be used. The shear strength of CFRP-improved soil is dependent on the interface properties of the soil and CFRP. The objective of this study is to investigate the interface properties (friction angle and adhesion) of sand and FRP experimentally using the direct shear test apparatus. To increase the surface roughness to improve the interface properties, a layer of sand was placed on saturated carbon fiber during the curing period [spark plasma sintering... 

This study examined the bond at the interface of masonry bricks and fiber-reinforced polymer when exposed to five environments. Three fabrics (aramid, carbon, and glass) and one type of epoxy resin were used. A total of 375 brick-fiber-reinforced polymer specimens were made using wet lay-up technic and exposed to chemical solutions at four pH values (2.5, 7, 10, and 12.5) and substitute seawater. The effect of dry heat on the bond at the interface was also investigated. Single-lap shear tests were then carried out on the samples after 2, 4, 6, 8, 10, and 13 weeks of exposure. The experimental results indicated that freshwater and seawater had a considerable effect on the bond strength of... 

In this paper we proposed a new real-time learning method. The engine of this method is a fuzzy-modeling technique which is called ink drop spread (IDS). IDS method has good convergence and is very simple and away from complex formula. The proposed method uses a reinforcement learning approach by an actor-critic system similar to Generalized Approximate Reasoning based Intelligent Control (GARIC) structure to adapt the IDS by delayed reinforcement signals. Our system uses Temporal Difference (TD) learning to model the behavior of useful actions of a control system. It is shown that the system can adapt itself, commencing with random actions. © 2008 IEEE  

This paper focuses on the performance evaluation of several concrete models in reinforced concrete (RC) structures subjected to seismic loading. Despite many studies conducted on implementing different characteristics of concrete in constitutive models, there is an essential need for investigating the ability of these models in predicting the behavior of structures in seismic applications. In this paper, several developed plasticity-based constitutive models with the combination of fracture and continuum damage models are investigated for application in seismic loading conditions. Damage-based isotropic and anisotropic models and smeared cracking approach have been applied as complementary... 

Reinforced concrete slabs are common structural elements that could be exposed to impact loading. Although use of reinforced concrete slabs and utilization of Fiber Reinforced Polymer (FRP) as alternative to traditional steel reinforcement slabs are growing, but the influence of various parameters on their response under impact loads is not properly evaluated. This study investigated the effect of rebar's material, amount and arrangement of reinforcements, concrete strength and slab thickness on dynamic behavior of reinforced concrete slabs using both laboratory experiments and numerical simulations. Performance of fifteen 1000 × 1000 mm concrete slabs, including two 75 mm thick plain slabs,... 

It is well known that shear strength of beams without stirrups shows a strong size effect. At present, several formulas of size effect are used by some codes and suggested by various researchers. Most of those formulas are not in agree with fracture mechanics. Recently, a simple formula based on modified compression field theory, MCFT, was proposed (Collins and Kuchma [1], Lubell et al. [2]), which shows a size effect stronger than the size effect formula based on fracture mechanics, proposed by Bazant (e.g. Bazant and Kazemi [3], Bazant and Yu [4]). In this paper it is shown that with some refined considerations, formulas are resulted in agree with Fracture Mechanics concept. In the derived... 

Reinforced concrete columns with insufficient transverse steel reinforcement are not capable to dissipate seismic energy due to lack of necessary ductility. In this research, six RC columns with poor transverse reinforcements are tested under cyclic and axial loads as control columns and retrofitted ones. Prestressed and non-pre-stressed CFRP strips used as external transverse reinforcement to evaluate the benefits of active and passive confinement. Results indicate that additional confinement due to the use of CFRP strips enhances the strength, ductility and energy dissipation capacity of columns. The advantages of active confinement versus passive confinement are demonstrated too. © 2006... 

An experimental study of the. flexural behavior of Reinforced-Concrete (RC) arches strengthened with Glass Fiber-Reinforced Polymer (GFRP) layers was performed. A total of 36 specimens including 3 un-strengthenod (control) and 33 strengthened RC arches were tested under centrally concentrated point load. The variables of this study were steel reinforcement ratio, number of GFRP layers, and location and arrangement of GFRP layers. Failure mode, load-displacement response of specimens, crack propagation patterns, and GFRP debonding were examined. The extrados strengthening method was shown to Ix1 more effective than the intrados strengthening one in improving the failure load and rigidity of... 

Buckling-restrained braces (BRBs) have been spread widely, especially in high seismic hazard zones due to their excellent energy absorption capacity. BRBs are composed of a main load-carrying steel core restrained with other elements mostly made of concrete and steel casing to preserve it from buckling. Although BRBs provide excellent cyclic behavior, a problem is with their heaviness, which leads to difficulties such as installation and transportation. This study presents a numerical and experimental investigation on a BRB with a new proposed restraining system composed of concrete panels confined with partially carbon fiber reinforced polymer (CFRP) strips to reduce the weight of the... 

Seven half-scale reinforced concrete (RC) columns with supporting beam were experimentally studied under combined axial and lateral cyclic loading. The specimens were categorized in two groups based on reinforcement ratios. Three specimens were strengthened with carbon fiber reinforced polymer (CFRP) and glass fiber reinforced polymer (GFRP) sheets. Other specimens were strengthened using a high strength mortar reinforced with textile mesh (textile reinforced concrete (TRC)). Strengthening of specimens were carried out using a vertical layer and a horizontal layer of FRP sheet or two vertical and two horizontal layers of textile meshes for TRC specimens. Since the weight of each layer of... 

The bond of fiber-reinforced polymer (FRP) reinforcement is expected to be more sensitive to the strength and geometry of the ribs than conventional steel reinforcement. In this study, the effect of carbon fiber mat anchorage on the pullout behavior of glass fiber-reinforced polymer (GFRP) bars embedded in normal concrete is studied. The studied parameters were the compressive strength of the concrete (16 MPa, 24 MPa, and 37 MPa), and, the length and diameter of the anchorage. In total, 15 variables were studied. Ribbed GFRP bars with 10 mm nominal diameter and 80 mm embedment length, ld, (which is 8 times the bar diameter) were considered. Based on the results for concretes with the... 

The concept of smart grid (SG) has been introduced to improve the operation of the power systems. In modern structures of power systems, different reasons prompt researchers to suggest integrated analysis of multi-carrier energy systems. Considering synergy effects of the couplings between different energy carriers and utilising intelligent technologies for monitoring and controlling of energy flow may change energy system management in the future. In this paper, we propose a new solution which is entitled ‘smart energy hub’ (SEH) that models a multi-carrier energy system in a SG. SEH solutions allow homeowners to manage their energy consumption to reduce their electricity and gas bill. We... 

In this study, a novel network reinforcement model incorporating optimal wind farms (WFs) integration to power systems is proposed. Based on the reinforcement model, new transmission lines are added to the network for eliminating the transmission network congestion. In addition, a methodology for determining the WFs optimal capacities, the economical WF lines transfer rates and the appropriate reinforcement plan, whereas maximising the total benefit using cost-reliability analysis is presented. In this way, the objective of the proposed optimisation problem has been divided into a master problem and two subproblems. Benders decomposition is employed to connect the master and subproblems of... 

Influence of length and volumetric percentage of steel fibres on energy absorption of concrete slabs with various concrete strengths is investigated by testing 28 small steel fibre reinforced concrete (SFRC) slabs under flexure. Variables included; fibre length, volumetric percentage of fibres and concrete strength. Test results indicate that generally longer fibres and higher fibre content provide higher energy absorption. The results are compared with a theoretical prediction based on random distribution of fibres. The theoretical method resulted in higher energy absorption than that obtained in experiment. A design method according to allowable deflection is proposed for SFRC slabs within... 

Composite aluminum-SiC foam was manufactured by injection of air and addition of reinforcement particles into the liquid aluminum. Microstructure and mechanical properties of the Al/SiC foams were investigated by scanning electron microscopy and compression tests. Results showed that both the cell size and the wall thickness augmented with increasing of the SiC reinforcement particles; while SiC particles resulted in the reduction of the plateau border length. With more SiC particles, plateau stress became larger; but maximum plateau strain became smaller. The stress-strain curves exhibited serrations in the plateau region due to addition of the SiC particles