Sharif Digital Repository

The aim of this paper is to study the influence of the column-to-beam strength ratio on the seismic strengthening of a column with a Fiber-Reinforced Plastic (FRP) wrapping system. FRP wrapped Reinforced Concrete (RC) columns are analyzed to obtain moment-curvature curves using FRP confined concrete characteristics. A pushover analysis of a 2D model was performed on one and three-story moment-resisting frames, with different column-to-beam strength ratios. The results indicate that FRP strengthening is more efficient in frames with a low ratio of column-to-beam strength, due to the type of lateral failure mechanism of the frame. Also, high values of the column-to-beam strength ratio can be... 

This paper presents the behavior of high-strength lightweight concrete columns confined with small size diameter hoop reinforcement. The concrete had a strength of up to 87.2 MPa (12,500 psi). The experimental program consisted of axial load tests on eight column specimens. The cross-sectional shape of the column specimens was elliptical, with dimensions of 152 × 229 mm (6 × 9 in.) and height of 762 mm (30 in.). The only longitudinal reinforcements used were four 4.52 mm (0.178 in.) diameter wires that were tack-welded to the lateral reinforcement to maintain the desired configuration of the lateral reinforcement. The influencing parameters included concrete strength and amount and spacing... 

This paper presents a simplified Multi-Degree-Of-Freedom (MDOF) model through modification of fish-bone model (or generic frame). Modified Fish-Bone (MFB) model is developed through three enhancements: (i) the moment of inertia for half-beams is reduced slightly to modify the assumption of equal rotation at each story joints, (ii) a number of truss elements are inserted to the fish-bone model to simulate flexural deformation of moment frames due to axial elongation and contraction of columns, and (iii) moment-rotation relationship of representative rotational springs is supposed to be bilinear instead of trilinear in order to consider simultaneous yielding at both ends of the beam in moment... 

This article presents an investigation of multi-mode effect of tall buildings subjected to near-field pulse-like ground motions. Multi-story buildings are modeled as an equivalent continuum structure consisting of a combination of a flexural cantilever beam and a shear cantilever beam. The simplified model is subjected to near-field ground motions and the representative simplified pulses. The maximum interstory drift spectra and its location along the height are calculated on the basis of modal summation approach. So, the method is largely based upon the assumption of linearity of the system. The effects of shear to flexural deformation ratio, structural to input pulse period ratio, and the... 

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... 

In this study, test results of four precast concrete beam-column connections and one monolithic concrete connection are presented. The tests constituted the second phase of an experimental program on a 2/5-scale model precast connection. The objective of the test program was to design a simple moment-resisting precast connection for regions of high seismicity. The connection transfers bending moment by a combination of lap-splicing and end anchorage of bars. The end portions of precast beams sit on the column bearing area at the beginning of subassemblage construction. The variables examined were the level of axial load on column, spacing of beam stirrups in the connection length region,... 

This paper discusses the sensitivity of softening reinforced concrete frame structures to the changes in input ground motion and investigates the possibility of localizations for this type of structure in static and dynamic analysis. A finite element model is used in which the sections resisting force are calculated using a proposed differential hysteretic model. This model is especially developed for modelling softening behaviour under cyclic loading. To obtain parameters of the differential model the moment-curvature of each section is evaluated using a microplane constitutive law for concrete and bi-linear elasto-plastic law for reinforcements. The capability of the procedure is verified... 

Different types of gas reservoir such as Liquid Natural Gas (LNG) are among the strategic infrastructures, and have great importance for any government or their private owners. To keep the tank and its contents safe during earthquakes especially if the contents are of hazardous or flammable materials; using seismic protection systems such as base isolator can be considered as an effective solution. However, the major deficiency of this system can be the large deformation in the isolation level which may lead to the failure of bearing system. In this paper, as a solution, the efficacy of an optimally designed combined vibration control system, the combined laminated rubber isolator and... 

The purpose of this investigation is to investigate the axial and lateral behavior of low strength concrete confined by glass fiber reinforced polymer (GFRP) wraps. A total of 48 cylindrical samples having 150 mm diameter and 300 mm height were strengthened and examined. The mix designs were provided with four different target strength (5, 10, 15, and 20 MPa). The axial and lateral strain were studied to evaluate the axial strain relation and the lateral strain for axial compression. The results of this investigation present a comparison between the nine models previously reported for normal strength concrete and the lesser-known context of low strength concrete confined by fiber reinforced... 

In this study, the effect of agglomeration and non-uniform dispersion of silica particles on the mechanical and microstructural properties of cement paste incorporating silica fume and nanosilica (NS) with various specific surface areas (SSA) is experimentally investigated. The SSA and replacement percent of silica particles were considered as test variables and four series of mixes were made including one set of mixes for silica fume with a SSA of 20 m2/g and three sets of mixes for three different types of NS with SSA equal to 90, 200 and 380 m2/g. In each series of mix designs three different cement replacement percents of 1.5%, 3% and 5% were applied. The results indicate that as the SSA... 

Purpose - The purpose of this paper is to present a shape optimization technique for powder forming processes based on the genetic algorithm approach. The genetic algorithm is employed to optimize the geometry of component based on a fixed-length vector of design variables representing the changes in nodal coordinates. The technique is used to obtain the desired optimal compacted component by changing the boundaries of component and verifying the prescribed constraints. Design/methodology/approach - The numerical modeling of powder compaction simulation is applied based on a large deformation formulation, powder plasticity behavior, and frictional contact algorithm. A Lagrangian finite... 

In this paper, the computational aspects of large deformation frictional contact are presented in powder forming processes. The influence of powder-tool friction on the mechanical properties of the final product is investigated in pressing metal powders. A general formulation of continuum model is developed for frictional contact and the computational algorithm is presented for analyzing the phenomena. It is particularly concerned with the numerical modeling of frictional contact between a rigid tool and a deformable material. The finite element approach adopted is characterized by the use of penalty approach in which a plasticity theory of friction is incorporated to simulate sliding... 

In this paper, the influence of powder-tool friction on the mechanical properties of the final product is investigated in pressing metal powders. A computational algorithm is presented for simulation of frictional contact in the compaction process of powder. The large deformation finite element (FE) formulation is characterized by the use of penalty approach in which a plasticity theory of friction is incorporated to simulate sliding resistance at the powder-tool interface. The constitutive relations for friction are derived from a Coulomb friction law. A double-surface cap plasticity model is employed together with the nonlinear contact friction behavior in numerical simulation of powder... 

Fracture process of fiber-reinforced concrete notched beams is investigated here. Polypropylene macrosynthetic fibers are utilized for reinforcing concrete specimens, and a high-strength mix design is used to produce strong bonds between the embossed polypropylene fibers and the cementitious matrix of beams. Considering different locations for the notch, this study focuses on bridging mechanism under different conditions using both experimental and numerical approaches. First mode of fracture occurs due to opening of crack faces. This mode of failure is simulated by imposing symmetric boundary conditions on middle-notched beams. Inducing the notch with an offset from the middle, mixed-mode... 

Dynamic response of large concrete tower structures with passive or active damping is important in terms of performance under dynamic loads. Structural instability mostly arises as a result of losing the energy capacity in the system, which forces the system to act as a mechanism. The purpose of this paper is to present three different finite element models to investigate the linear and nonlinear response of the Tehran telecommunication tower. The tower is ranked the fourth tallest structure in the world and has been under construction since 1997. Using a mathematical model, an efficient method is used to take into account the cracking and crushing of the reinforced concrete material as well... 

Fracture process of fiber-reinforced concrete notched beams is investigated here. Polypropylene macrosynthetic fibers are utilized for reinforcing concrete specimens, and a high-strength mix design is used to produce strong bonds between the embossed polypropylene fibers and the cementitious matrix of beams. Considering different locations for the notch, this study focuses on bridging mechanism under different conditions using both experimental and numerical approaches. First mode of fracture occurs due to opening of crack faces. This mode of failure is simulated by imposing symmetric boundary conditions on middle-notched beams. Inducing the notch with an offset from the middle, mixed-mode... 

In this paper an approach was described for determination of direction of sliding block in rock slopes containing planar non-persistent open joints. For this study, several gypsum blocks containing planar non-persistent open joints with dimensions of 15?15?15 cm were build. The rock bridges occupy 45, 90 and 135 cm2 of total shear surface (225cm2 ), and their configuration in shear plane were different. From each model, two similar blocks were prepared and were subjected to shearing under normal stresses of 3.33 and 7.77 kg/cm-2 . Based on the change in the configuration of rock-bridges, a factor called the Effective Joint Coefficient (EJC) was formulated, that is the ratio of the effective... 

A disaster is an adverse event resulting from natural processes of the Earth or sometimes from terrorist attacks. Since the concept of disaster resilience has become prominent, research and practice for making the cities resilient play an important role in urban management. Cities are composed of a variety of structures and providing the structural resiliency can protect them. Resilient structures are composed of a number of ideal performance criteria, which based on analysis, experiment, and past experience, are capable to withstand the required level of stress and deformation. In addition, durability, fire resistance, and other capabilities, such as being environmentally friendly with no... 

Pervious concrete (PC) has been detecting application in pavement and concrete structures such as dams, small retaining walls, and etc during the past decades. Also, in recent years, the types of resins have been introduced to apply in concrete owing to the enhancing in mechanical and durability characteristics. However, few studies have investigated the mechanical behavior of high performance pervious concrete (HPPC) incorporated by polyester and epoxy resins as polymeric composites, where ordinary cement material has been completely deleted. The purpose of this investigation is to compare the mechanical properties, permeability, and durability of HPPCs made by polymeric composites (i.e.... 

Steel plate shear walls (SPSWs) have shown a desirable performance in experimental studies and past earthquakes. The advantages of the SPSW and its good performance against lateral loads persuade designers to utilize the system in their practical projects. Some important aspects of the SPSW have remained unknown in spite of valuable experimental and numerical studies. One of these unknown characteristics is the effect of cracks on the SPSW behavior. Several experimental studies have reported fracture in SPSW due to crack propagation during testing, but the experimental studies have not investigated the crack effect. Due to low thickness of steel plate and inherence of crack, the crack...