• Journal of the Korean Geotechnical Society
• /
• v.19 no.2
• /
• pp.189-197
• /
• 2003

In this paper, deformation characteristics of fiber-mixed-soils were studied at small strain range(0.0001%～1%) using resonant column test and triaxial test, and reinforcement effect was evaluated by the measure of maximum shear moduli. The effects of the major parameters such as fiber content, aspect ratio and fiber type on reinforcement were comparatively assessed. The specimens were remolded from Jumunjin Sand randomly mixed with discrete polypropylene staple fibers. Maximum shear moduli of fiber-mixed-soils increased by up to 30% and modulus reduction was also restrained in nonlinear range. Shear moduli increased as the aspect ratio increases. The reinforcement was more effective with fibrillated fiber than with monofilament fiber. The most effective reinforcement was achieved with the specimen of 0.3 % fiber content.

• Advances in concrete construction
• /
• v.17 no.2
• /
• pp.75-92
• /
• 2024

High Strength steel reinforced Reactive Powder Concrete (RPC) Beam is a new type of beams which has evident advantages than the conventional concrete beams. However, there is limited research on the shear bearing capacity of high-strength steel reinforced RPC structures, and there is a lack of theoretical support for structural design. In order to promote the application of high-strength steel reinforced RPC structures in engineering, it is necessary to select a shear model and derive applicable calculation methods. By considering the shear span ratio, steel fiber volume ratio, longitudinal reinforcement ratio, stirrup ratio, section shape, horizontal web reinforcement ratio, stirrup configuration angle and other variables in the shear test of 32 high-strength steel reinforced RPC beams, the applicability of three theoretical methods to the shear bearing capacity of high-strength steel reinforced RPC beams was explored. The plasticity theory adopts the RPC200 biaxial failure criterion, establishes an equilibrium equation based on the principle of virtual work, and derives the calculation formula for the shear bearing capacity of high-strength steel reinforced RPC beams; Based on the Strut and Tie Theory, considering the softening phenomenon of RPC, a failure criterion is established, and the balance equation and deformation coordination condition of the combined force are combined to derive the calculation formula for the shear bearing capacity of high-strength reinforced RPC beams; Based on the Rankine theory and Rankine failure criterion, taking into account the influence of size effects, a calculation formula for the shear bearing capacity of high-strength reinforced RPC beams is derived. Experimental data is used for verification, and the results are in good agreement with a small coefficient of variation.

• Journal of the Korea Concrete Institute
• /
• v.13 no.3
• /
• pp.195-205
• /
• 2001

This Paper describes a numerical method to evaluate the flexural strength of reinforced concrete members exposed to fire. An analytical method is developed for the moment-curvature relationship for the cross section which is subjected to high temperature. The method performs heat-transfer analysis for the cross sections and subsequently performs numerical analysis using the stress-strain relationships of concrete and reinforcing steel in various heat conditions. The results of the numerical studies are ; 1) the residual flexural strength exposing at high temperature is affected by the heating time, the depth of concrete cover and reinforcement ratio, 2) the residual flexural strength after exposed at high temperature is recovered of its original strength at minimum ratio of reinforcement, while members having half of maximum ratio and maximum ratio of reinforcement do not recover its original strength, 3) furthermore, the concrete may reach its maximum capacity before reinforcement yields in reinforced concrete members having maximum ratio of reinforcement.

• Geomechanics and Engineering
• /
• v.33 no.6
• /
• pp.553-565
• /
• 2023

As the structure of broken rock mass is complex, with obvious discontinuity and anisotropy, it is generally necessary to reinforce broken rock mass using grouting in underground construction. The purpose of this study is to experimentally investigate the mechanical properties of broken rock mass after grouting reinforcement with consideration of the characteristics of broken rock mass (i.e., degree of fragmentation and shape) and a range of reinforcement methods such as relative strength ratio between the broken rock mass and cement-based grout stone body (λ), and volumetric block proportion (VBP) representing the volumetric ratio of broken rock mass and the overall cement grout-broken rock mass mixture after the reinforcement. The experimental results show that the strength and deformation of the reinforced broken rock mass is largely determined by relative strength ratio (λ) and VBP. In addition, the enhancement in compressive strength by grouting is more obvious for broken rock mass with spherical shape under a relatively high strength ratio (e.g., λ=2.0), whereas the shape of rock mass has little influence when the strength ratio is low (e.g., λ=0.1). Importantly, the results indicate that columnar splitting failure and inclined shear failure are two typical failure modes of broken rock mass with grouting reinforcement.

• Structural Engineering and Mechanics
• /
• v.82 no.2
• /
• pp.173-189
• /
• 2022

This study presents an experimental and numerically study about the effects of fiber reinforcement ratio on the behavior of concrete-filled steel tubes (CFST) under dynamic impact loading. In literature have examined the behavior of GFRP and FRP wrapped strengthened CFST elements impact loads. However, since the direction of potential impact force isn't too exact, there is always the probability of not being matched the impact force of the area where the reinforced. Therefore, instead of the fiber textile wrapping method which strengthens only a particular area of CFST element, we used fiber-added concrete-filled elements which allow strengthening the whole element. Thus, the effect of fiber-addition in concrete on the behavior of CFST elements under impact loads was examined. To do so, six simply supported CFST beams were constructed with none fiber, 2% fiber and 10% fiber reinforcement ratio on the concrete part of the CFST beam. CFST beams were examined under two different impact loads (75 kg and 225 kg). The impactors hit the beam from a 2000 mm free fall during the experimental study. Numerical models of the specimens were created using ABAQUS finite element software and validated with experimental data. The obtained results such as; mid-span displacement, acceleration, failure modes and energies from experimental and numerical studies were compared and discussed. Furthermore, the Von Misses stress distribution of the CFST beams with different ratio of fiber reinforcements were investigated numerically. To sum up, there is an optimum amount limit of the fiber reinforcement on CFST beams. Up to this limit, the fiber reinforcement increases the structural performances of the beam, beyond that limit the fiber reinforcement decreases the performances of the CFST beam under transverse impact loadings.

• Proceedings of the Korea Concrete Institute Conference
• /
• 2002.05a
• /
• pp.253-258
• /
• 2002

An evaluation equation of the minimum shear reinforcement content for reinforced concrete beams was theoretically proposed. The proposed equation takes into account the effects of compressive strength of concrete, longitudinal reinforcement content and shear span ratio. The proposed equation was compared with the current ACI 318-99 and CSA A23.3-94 codes.

• Journal of the Korea Concrete Institute
• /
• v.21 no.2
• /
• pp.169-178
• /
• 2009

An equation for calculating confining reinforcement amount of RC bridge columns, specified in the current bridge design codes, has been made to provide additional load-carrying strength for concentrically loaded columns. The additional load-carrying strength will be equal to or slightly greater than the resistant strength of a column against axial load, which is lost because the cover concrete spalls off. The equation considers concrete compressive strength, yield strength of transverse reinforcement, and the section area ratio as major variables. Among those variables, the section area ratio between the gross section and the core section, varying by cover thickness, is a variable which considers the strength in the compression-controlled region. Therefore, the cross section ratio does not have a large effect in the aspect of ductile behavior of the tension-controlled region, which is governed by bending moment rather than axial force. However, the equation of the design codes for calculating confining reinforcement amount does not directly consider ductile behavior, which is an important factor for the seismic behavior of bridge columns. Consequently, if the size of section is relatively small or if the section area ratio becomes excessively large due to the cover thickness increased for durability, too large an amount of confining reinforcement will be required possibly deteriorating the constructability and economy. Against this backdrop, in this study, comparison and analysis were performed to understand how the cover thickness influences the equation for calculating the amount of confining reinforcement. An equation for calculating the amount of confining reinforcement was also modified for reasonable seismic design and the safety. In addition, appropriateness of the modified equation was examined based on the results of various test results performed at home and abroad.

• Proceedings of the Korea Concrete Institute Conference
• /
• 1999.10a
• /
• pp.463-466
• /
• 1999

Ductility is an important consideration in the design of reinforced high-strength concrete. Therefore, this research investigate the ductile behavior of rectangular high-strength concrete columns like as bridge piers with confinement steel. The effect on the ductility of axial load, lateral reinforcement ratio, longitudinal reinforcement ratio, shear ratio, and compressive strength of concrete were investigated analytically using layered section analysis. As the results, it was proposed the proper relationship between ductility and variables and formulated into equations.

• Proceedings of the Korea Concrete Institute Conference
• /
• 2005.05a
• /
• pp.123-126
• /
• 2005

The purpose of this study is to evaluate a effect of core reinforcement ratio to PC wide girder-column joint. Three half scale subassemblies were representing a portion of a protype structure were design, constructed, and tested to failure. From the test result, girder-column width ratio play an important role in the improvement of strength and ductility.

• Proceedings of the Korea Concrete Institute Conference
• /
• 2005.05a
• /
• pp.403-406
• /
• 2005

This paper deals with the propriety of the shear test data with stirrup reported in ACI and ASCE structural journal and the shear resistance characteristics affected by compressive strength of concrere($f_{ck}$), shear span-to-depth ratio (a/d), tensile reinforcement ratio($\rho$), and shear reinforcement ratio($rho_{v}$). The analysis was accomplished by the 242 shear test data. The test data include the flexural failure data around 40$\%$.