• Steel and Composite Structures
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• 제25권5호
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• pp.603-615
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• 2017

This experimental research presents the seismic performance of steel reinforced high-strength concrete (SRHC) short columns. Eleven SRHC column specimens were tested under simulated earthquake loading conditions, including six short column specimens and five normal column specimens. The parameters studied included the axial load level, stirrup details and shear span ratio. The failure modes, critical region length, energy dissipation capacity and deformation capacity, stiffness and strength degradation and shear displacement of SRHC short columns were analyzed in detail. The effects of the parameters on seismic performance were discussed. The test results showed that SRHC short columns exhibited shear-flexure failure characteristics. The critical region length of SRHC short columns could be taken as the whole column height, regardless of axial load level. In comparison to SRHC normal columns, SRHC short columns had weaker energy dissipation capacity and deformation capacity, and experienced faster stiffness degradation and strength degradation. The decrease in energy dissipation and deformation capacity due to the decreasing shear span ratio was more serious when the axial load level was higher. However, SRHC short columns confined by multiple stirrups might possess good seismic behavior with enough deformation capacity (ultimate drift ratio ${\geq}2.5%$), even though a relative large axial load ratio (= 0.38) and relative small structural steel ratio (= 3.58%) were used, and were suitable to be used in tall buildings in earthquake regions.

• Computers and Concrete
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• 제31권2호
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• pp.123-137
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• 2023

To fully understand shear mechanisms and composite effects of circular concrete-filled steel tube (CFST) columns, systematic numerical investigations were conducted in this paper by improved finite element models. The triaxial plastic-damage constitutive model of the concrete and the interactions between the concrete and steel tube were considered. Afterwards, the critical and upper bound shear span ratios of the circular CFST column under lateral shear loading were determined. The composite effects between the two materials were analyzed by comparing the shear resistance with plain concrete column and hollow steel tube. In addition, a method that predicts the shear bearing capacity of a circular CFST column was proposed. The confining effects on the concrete core and the restraining effects on the steel tube were considered in this method. The proposed formula can predict more accurate results than the methods in different codes and references.

• 한국안전학회지
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• 제30권5호
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• pp.67-73
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• 2015

In this paper, the simple truss model was modified to predict the punching shear strength of long-span prestressed concrete (PSC) deck slabs under wheel load including the effects of transverse prestressing and long span length between girders. The strength of the compressive zone arounding punching cone was evaluated by the stiffness of inclined strut which was modified by considering aging effective modulus. The stiffness of springs which control lateral displacement of the roller supports consists of the steel reinforcement and prestressing which passed through the punching cone. Initial angle of struts was determined by the experimental observation to compensate for uncertainties in the complexities of the punching shear. The validity of computed punching shear strength by modified simple truss model was shown by comparing with experimental results and the experimental results were also compared with existing punching shear equations to determine level of predictability. The modified simple truss model appeared to better predict the punching shear strength of PSC deck slabs than other available equations. The punching shear strength, which was determined by snap-through critical load of modified simple truss model, can be used effectively to examine punching shear strength of long span PSC deck slabs.

• 한국공간구조학회논문집
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• 제15권1호
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• pp.57-64
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• 2015

This paper shows the test results of continuous reinforced concrete beams with external post-tensioning rods. Six three-span beams were prepared and tested to fail. Three beams were designed to have flexure-dominating behavior and the others to have shear-critical behavior. In each group, one beam without external post-tensioning rods was designated as a control beam and two beams had the external post-tensioning rods of 18 mm or 22 mm diameter. External post-tensioning rods were installed within an interior span of 6000 mm. They show V-shaped configuration because two anchorages were located at the top of interior supports and a saddle pin at mid-span was installed at the bottom of the beam. Test results show that the load and shear capacities of strengthened beams were increased when compared with the control beam. Additionally, the measured shear strength was compared with the strength predicted by ACI 318-11 code equations. The detailed ACI 318-11 equation predicted the measured shear strength and failure location of the continuous beam reasonably well.

• Structural Engineering and Mechanics
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• 제76권4호
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• pp.491-503
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• 2020

This study extends previous experimental research on the shear behaviour of macrosynthetic fibre-reinforced concrete beams and compares them to steel fibre-reinforced concrete beams with similar mechanical and geometrical properties. This work employed two fibre types: 60/0.9 (long/diameter) double hooked-end steel fibre and 60/85 monofilament polypropylene fibre. Beams were tested by shear loading covering parameters, such as two different cross-section widths, two shear-span-to-effective-depth ratios, two fibre types and using repetitions with and without transverse reinforcement. For quantitative comparison purposes, crack pattern evolution was studied along increasing loads levels. Effects were studied by photogrammetry, including influence of fibres on crack propagation in uncracked and dowel zones, influence of fibres on stirrup behaviour, and shear deformation or kinematics of critical shear cracks. The results evidenced similar effectiveness for both fibre types in controlling shear crack propagation and horizontal dowel cracking. Both fibres provided similar shear ductility and shear deflections. Consequently, the authors confirm that residual flexural tensile strengths are a convenient parameter for characterising the shear behaviour of fibre-reinforced concrete beams.

• Earthquakes and Structures
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• 제8권3호
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• pp.713-732
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• 2015

The application of the compressive force path method for the design of earthquake-resistant reinforced concrete structural walls with a shear span-to-depth ratio larger than 2.5 has been shown by experiment to lead to a significant reduction of the code specified transverse reinforcement within the critical lengths without compromising the code requirements for structural performance. The present work complements these findings with experimental results obtained from tests on structural walls with a shear span-to-depth ratio smaller than 2.5. The results show that the compressive force path method is capable of safeguarding the code performance requirements without the need of transverse reinforcement confining concrete within the critical lengths. Moreover, it is shown that ductility can be considerably increased by improving the strength of the two bottom edges of the walls through the use of structural steel elements extending to a small distance of the order of 100 mm from the wall base.

• International Journal of Concrete Structures and Materials
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• 제10권4호
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• pp.407-424
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• 2016

This study tests ten full-size simple-supported beam specimens with the high-strength reinforcing steel bars (SD685 and SD785) using the four-point loading. The measured compressive strength of the concrete is in the range of 70-100 MPa. The main variable considered in the study is the shear-span to depth ratio. Based on the experimental data that include maximum shear crack width, residual shear crack width, angle of the main crack and shear drift ratio, a simplified equation are proposed to predict the shear deformation of the high-strength reinforced concrete (HSRC) beam member. Besides the post-earthquake damage assessment, these results can also be used to build the performance-based design for HSRC structures. And using the allowable shear stress at the peak maximum shear crack width of 0.4 and 1.0 mm to suggest the design formulas that can ensure service-ability (long-term loading) and reparability (short-term loading) for shear-critical HSRC beam members.

• Computers and Concrete
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• 제3권1호
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• pp.65-77
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• 2006

This study reports the details of the finite element analysis of eleven shear critical partially prestressed concrete T-beams having steel fibers over partial or full depth. Prestressed concrete T-beams having a shear span to depth ratio of 2.65 and 1.59 and failing in the shear have been analyzed using 'ANSYS'. The 'ANSYS' model accounts for the nonlinear phenomenon, such as, bond-slip of longitudinal reinforcements, post-cracking tensile stiffness of the concrete, stress transfer across the cracked blocks of the concrete and load sustenance through the bridging of steel fibers at crack interface. The concrete is modeled using 'SOLID65'-eight-node brick element, which is capable of simulating the cracking and crushing behavior of brittle materials. The reinforcements such as deformed bars, prestressing wires and steel fibers have been modeled discretely using 'LINK8' - 3D spar element. The slip between the reinforcement (rebar, fibers) and the concrete has been modeled using a 'COMBIN39'-non-linear spring element connecting the nodes of the 'LINK8' element representing the reinforcement and nodes of the 'SOLID65' elements representing the concrete. The 'ANSYS' model correctly predicted the diagonal tension failure and shear compression failure of prestressed concrete beams observed in the experiment. The capability of the model to capture the critical crack regions, loads and deflections for various types of shear failures in prestressed concrete beam has been illustrated.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2004년도 춘계 학술발표회 제16권1호
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• pp.68-71
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• 2004

In the shear strengthening with FRP sheets, beams are wrapped around the webs and tension face of critical shear span by fiber sheets. The shear strength of RC beam strengthened with FRP sheets must be calculated based on the effective strain that can be developed in the FRP sheets at ultimate stage because the final failure modes of beams are governed by premature debonding of FRP sheet due to the limitation of bonded length by beam depth. An experimental study is carried out to evaluate the shear strengthening effect of AFRP or GFRP sheets with respect to shear reinforcement ratio of rebar. From the test results, it was found that the additional shear strength provided by GFRP or AFRP can be estimated by $p_w{\cdot}f_w$ based on the maximum effective strain of FRP sheet $4,000m{\mu}$ proposed by ACI 440 committee.

• International Journal of Concrete Structures and Materials
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• 제9권3호
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• pp.267-281
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• 2015

Six full-scale prestressed concrete (PC) I-beams with steel fibers were tested to failure in this work. Beams were cast without any traditional transverse steel reinforcement. The main objective of the study was to determine the effects of two variables-the shear-span-to-depth ratio and steel fiber dosage, on the web-shear and flexural-shear modes of beam failure. The beams were subjected to concentrated vertical loads up to their maximum shear or moment capacity using four hydraulic actuators in load and displacement control mode. During the load tests, vertical deflections and displacements at several critical points on the web in the end zone of the beams were measured. From the load tests, it was observed that the shear capacities of the beams increased significantly due to the addition of steel fibers in concrete. Complete replacement of traditional shear reinforcement with steel fibers also increased the ductility and energy dissipation capacity of the PC I-beams.