• Rubber Technology
• /
• v.9 no.1
• /
• pp.1-12
• /
• 2008

Effects of silane modifier, bis(triethoxysilylpropyl) tetrasulfide (TESPT(S4)) and bis(triethoxysilylpropyl) disulfide (TESPD(S2)), on silica filled compound were investigated upon processability, dynamic, mechanical, heat build-up, blowout properties, and silica dispersion in natural rubber (NR). The temperature of the S2 treated silica compound generated higher than that of the S4 treated compound during internal mixer compounding. The shear viscosity of the S2 compound exhibited lower than that of the S4 compound and the viscosity measured in dynamic mode was close to each other. The elongation modulus of the S2 compound exhibited lower than that of the S4; however, the tear resistance strength of the S2 compound exhibited higher than that of the S4 compound. The loss tan$\delta$ values of the S2 compound exhibited higher than those of the S4 at room temperature. The augmentation of the test temperature lowered the tan$\delta$ values of each compound, which results in close tan$\delta$ values to each other at $100^{\circ}C$. The S2 compound deformed less than the S4 compound, and the blowout time of each compound was close to each other. The S2 compound generated more heat build-up than the S4 compound. The abrasion loss of the S2 compound was less than that of the S4 compound. The size of the silica agglomerate reduced on both S4 and S2 compounds upon vulcanization. The addition of the bifunctional silanes (S2 and S4) on silica filled NR compound improved the processability of each compound and their effects were more significant on the S2 compound than the S4 compound. After vulcanization the silica agglomerate size of each compound reduced compared with before vulcanization.

• Structural Engineering and Mechanics
• /
• v.14 no.3
• /
• pp.287-306
• /
• 2002

The assessment of structural performance of transfer structures under potential seismic actions is presented. Various seismic assessment methodologies are used, with particular emphasis on the accurate modelling of the higher mode effects and the potential development of a soft storey effect in the mega-columns below the transfer plate (TP) level. Those methods include response spectrum analysis (RSA), manual calculation, pushover analysis (POA) and equivalent static load analysis (ESA). The capabilities and limitations of each method are highlighted. The paper aims, firstly, to determine the appropriate seismic assessment methodology for transfer structures using these different approaches, all of which can be undertaken with the resources generally available in a design office. Secondly, the paper highlights and discusses factors influencing the response behaviour of transfer structures, and finally provides a general indication of their seismic vulnerability. The representative Hong Kong building considered in this paper utilises a structural system with coupled shear walls and moment resisting portal-frames, above and below the TP, respectively. By adopting the wind load profile stipulated in the Code of Practice on Wind Effects: Hong Kong-1983, all the structural members are sized and detailed according to the British Standards BS8110 and the current local practices. The seismic displacement demand for the structure, when built on either rock or deep soil sites, was determined in a companion paper. The lateral load-displacement characteristic of the building, determined herein from manual calculation, has indicated that the poor ductility (brittle nature) of the mega-columns, due mainly to the high level of axial pre-compression as found from the analysis, cannot be effectively alleviated solely by increasing the quantity of confinement stirrups. The interstorey drift demands at lower and upper zones caused by seismic actions are found to be substantially higher than those arising from wind loads. The mega-columns supporting the TP and the coupling beams at higher zones are identified to be the most vulnerable components under seismic actions.

• Journal of the Korea institute for structural maintenance and inspection
• /
• v.9 no.2
• /
• pp.181-190
• /
• 2005

The objective of this work is to study the flexural strengthening effectiveness of Carbon Fiber Mesh (CFM) in reinforced concrete beams. Flexural strengthening for a simply supported reinforced concrete (RC) beam using CFM is developed by bonding CFM to the soffit of the beam. In this experimental program, five medium-sized reinforced concrete beams strengthened with CFM are tested in bending to evaluate reinforcing effects of the CFM. The beams are designed to have high shear capacity so that expected dominant failure mode of specimens is bending. The reinforcing effect of CFM is small at crack initiation, but is considerable in flexural rigidity of the beam after crack initiation. In comparing the behaviors of strengthened and virgin beams each other, it is shown that the strength of RC beams can be enhanced by attaching CFM. A fairly good agreement between the measured values and the calculated ones is obtained at both the cracking strength and yield strength of the strengthened beams.

• Journal of the Computational Structural Engineering Institute of Korea
• /
• v.14 no.4
• /
• pp.481-494
• /
• 2001

An enhanced degenerated shell finite element (FE), which has been developed for inelastic analysis of reinforced concrete structures is described in this paper. Generally, Reissner-Mindlin (RM) assumptions are adopted to develop the degenerated shell FE so that transverse shear deformation effects is considered. However, it is found that there are serious defects such as locking phenomena in RM degenerated shell FE since the stiffness matrix has been overestimated in some situations. As remedies of locking phenomena, reduced integration, incompatible mode and assumed strain method have been used. Especially, the assumed strain method has been successfully used in many FEs. But contrarily, there is a few investigation on the performance of the assumed strains in the inelastic analysis of concrete structures. Therefore, shell formulation is provided in this paper with emphasis on the terms related to the stiffness matrix based on assumed strain method and microscopic concrete material model. Finally, the performance of the present shell element is tested and demonstrated with several numerical examples. From the numerical tests, the present result shows a good agreement with experimental data or other numerical results.

• Structural Engineering and Mechanics
• /
• v.75 no.3
• /
• pp.401-414
• /
• 2020

Unlike the existing truss models for shear and torsion analysis, in this study, the torsional capacities of reinforced concrete (RC) members were estimated by introducing multi-potential capacity criteria that considered the aggregate interlock, concrete crushing, and spalling of concrete cover. The smeared truss model based on the fixed-angle theory was utilized to obtain the torsional behavior of reinforced concrete member, and the multi-potential capacity criteria were then applied to draw the capacity of the member. In addition, to avoid any iterative calculation in the existing torsional behavior model, a simple strength model was suggested that considers key variables, such as the effective thickness of torsional member, principal stress angle, and strain effect that reduces the resistance of concrete due to large longitudinal tensile strain. The proposed multi-potential capacity concept and the simple strength model were verified by comparing with test results collected from the literature. The study found that the multi-potential capacity could estimate in a rational manner not only the torsional strength but also the failure mode of RC members subjected to torsional moment, by reflecting the reinforcing index in both transverse and longitudinal directions, as well as the sectional and material properties of RC members.

• Advances in concrete construction
• /
• v.9 no.3
• /
• pp.313-326
• /
• 2020

Glass fiber-reinforced polymer (GFRP) bars have been introduced as an effective alternative for the conventional steel reinforcement in concrete structures to mitigate the costly consequences of steel corrosion. However, despite the superior performance of these composite materials in terms of corrosion, the effect of replacing steel reinforcement with GFRP on the seismic performance of concrete structures is not fully covered yet. To address some of the key parameters in the seismic behavior of GFRP-reinforced concrete (RC) structures, two full-scale beam-column joints reinforced with GFRP bars and stirrups were constructed and tested under two phases of loading, each simulating a severe ground motion. The objective was to investigate the effect of damage due to earthquakes on the service and ultimate behavior of GFRP-RC moment-resisting frames. The main parameters under investigation were geometrical configuration (interior or exterior beam-column joint) and joint shear stress. The performance of the specimens was measured in terms of lateral load-drift response, energy dissipation, mode of failure and stress distribution. Moreover, the effect of concrete damage due to earthquake loading on the performance of beam-column joints under service loading was investigated and a modified damage index was proposed to quantify the magnitude of damage in GFRP-RC beam-column joints under dynamic loading. Test results indicated that the geometrical configuration significantly affects the level of concrete damage and energy dissipation. Moreover, the level of residual damage in GFRP-RC beam-column joints after undergoing lateral displacements was related to reinforcement ratio of the main beams.

• Magazine of the Korea Concrete Institute
• /
• v.11 no.2
• /
• pp.177-186
• /
• 1999

The purpose of this study is to analyze the interface debonding of RC beams strengthened by carbon fiber sheet(CFS). The behavior of damaged RC beams strengthened with CFS is analytically investigated next using linear elastic fracture mechanics(LEFM) approach and the finite element method. The study includes an investigation of the separation mode by interface fracture of the strengthening materials due to the interfacial shear and normal stresses. The numerical method is presented to obtain the value of interfacial fracture parameter such as the strain energy release rate. Based on the results of this study, it is found that the critical case occurs when the interfacial cracks occur within a short region of the flexural crack. The CFS strengthening has not an adequate factor of safety against interfacial debonding of CFS. Furthermore, for the thicknesses of the adhesive studied[1mm~3mm], it is no noticeable effect on the strain energy release rate.

• Journal of the Korean Recycled Construction Resources Institute
• /
• v.6 no.1
• /
• pp.66-71
• /
• 2018

In general, when an existing pier is enlarged and reinforced using a small diameter pile, bonded anchor with deformed reinforcing bars is used to maintain the integrity of the joint. However, in the case of bonded anchors, the performance depends largely on the type of joint material. Nevertheless, unlike mechanical anchors, there is no standard method for designing appropriate design methods and proper performance evaluation. Therefore, in this study, the performance of the anchoring anchor was evaluated by performing a model experiment using the reinforcing bars and anchor reinforcing bars. Experimental results show that the structural performance of the unbonded specimen is the best, and the failure mode is the punching shear failure. The deflection of the end of the member is smaller than that of the unconnected member, The deflection of the connected member is larger than the deflection of the small connected member. As the load increases, the possibility of slippage of the anchor steel or fold connection rebar is high.

• Tunnel and Underground Space
• /
• v.13 no.1
• /
• pp.44-51
• /
• 2003

Changes of the hydraulic conductivity resulting from the redistribution of stresses by underground excavation are examined using the strain-dependent hydraulic conductivity modification relation, where the modulus reduction ratio and induced strain are the major parameters. The modulus reduction ratio is defined in terms of RMR(Rock Mass Rating) to represent the full gamut of rock mass condition. Though shear dilation has the effect on the modification of hydraulic conductivity, the extent of it depends on RMR When the extensional strain is applied to a fracture, the hydraulic conductivity increases with the decrease of RMR Loading configuration has the effect on the modification of hydraulic conductivity, where the differential stress mode with a magnitude of the minimum principal stress $($\sigma$_x)$ fixed and a magnitude of the maximum principal stress $($\sigma$_y)$ varied is found to exert the greatest effect on the change of hydraulic conductivity.

• Transactions of the Korean Society for Noise and Vibration Engineering
• /
• v.11 no.5
• /
• pp.89-100
• /
• 2001

The Ritz method Is applied In a three-dimensional (3-D) analysis to obtain accurate frequencies for thick. linearly tapered. annular plates. The method is formulated for annular plates haying any combination of free or fixed boundaries at both Inner and outer edges. Admissible functions for the three displacement components are chosen as trigonometric functions in the circumferential co-ordinate. and a1gebraic polynomials in the radial and thickness co-ordinates. Upper bound convergence of the non-dimensional frequencies to the exact values within at least four significant figures is demonstrated. Comparisons of results for annular plates with linearly varying thickness are made with ones obtained by others using 2-D classical thin place theory. Extensive and accurate ( four significant figures ) frequencies are presented 7or completely free. thick, linearly tapered annular plates haying ratios of average place thickness to difference between outer radius (a) and inner radius (b) radios (h$_{m}$/L) of 0.1 and 0.2 for b/L=0.2 and 0.5. All 3-D modes are included in the analyses : e.g., flexural, thickness-shear. In-plane stretching, and torsional. Because frequency data liven is exact 7o a\ulcorner least four digits. It is benchmark data against which the results from other methods (e.g.. 2-D 7hick plate theory, finite element methods. finite difference methods) and may be compared. Throughout this work, Poisson\`s ratio $\upsilon$ is fixed at 0.3 for numerical calculations.s.