• Proceedings of the Korea Concrete Institute Conference
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• 2003.05a
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• pp.925-930
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• 2003

Provisions for ACI 318-02 and NZS 3101 pertaining to shear design of shear walls evaluated the applicability of high-strength, concrete shear walls subjected to lateral loads. Results of 73 tests of reinforced concrete shear walls were reviewed. Evaluation of test results conducted in Korea, England, America, Japan, and Australia for low-aspect ratio walls indicates that the nominal unit shear strength($\phi$=1.0) calculated using the provisions of ACI and NZS does not represent the observed shear strength well. Based on the limited database considered in this study, a reasonable lower bound to the shear strength of high-strength concrete shear walls is found to be $\sqrt[0.4]{f_{cu}}$ MPa. Similar to that of normal strength concrete walls, the rate of increase of the measured shear strength with $$\rho$_n/ㆍf_y$ is less than 1.0. Therefore, the rate of increase of shear strength attributable to the web reinforcement in shear walls appears to be overestimated by the modified truss analogy.

• Journal of the Korean Society of Environmental Restoration Technology
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• v.5 no.6
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• pp.9-13
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• 2002

This study has been performed to investigate the physical and mechanical characteristics of compaction, volume change and compressive strength for reinforced soil mixed with cement. And confirm the reinforcing effects with admixture such as cement. To this end, a series of compaction test and compression test was conducted for clayey soil(CL) and cement reinforced soil. In order to determine proper moisture content and mixing ratio, pilot test was carried out for soil and cement reinforced soil. And the mixing ratio of cement admixture was fixed 3%, 6%, 9% and 12% by the weight of dry soil. As the experimental results, the maximum dry unit weight(${\gamma}_{dmax}$) was increased with the mixing ratio and then shown the peak at 10% reinforced soil, but the optimum moisture content(OMC) and the volume change was decreased with the ratio increase. And the compressive strength volume change was decreased with mixing ratio increased.

• International Journal of Concrete Structures and Materials
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• v.10 no.2
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• pp.249-256
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• 2016

This paper deals with the effects of silica fume content and polymer-binder ratio on the properties of ultrarapid-hardening polymer-modified mortar using silica fume and ethylene-vinyl acetate redispersible polymer powder instead of styrene-butadiene rubber latex to shorten the hardening time. The ultrarapid-hardening polymer-modified mortar was prepared with various silica fume contents and polymer-binder ratios, and tested flexural strength, compressive strength, water absorption, carbonation depth and chloride ion penetration depth. As results, the flexural, compressive and adhesion strengths of the ultrarapid-hardening polymer-modified mortar tended to increase as increasing polymer-binder ratio, and reached the maximums at 4 % of silica fume content. The water absorption, carbonation and chloride ion penetration resistance were improved according to silica fume content and polymer-binder ratio.

• Journal of the Korea Institute of Building Construction
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• v.8 no.3
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• pp.75-83
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• 2008

In this paper, concrete material tests were carried out to investigate influence of steel fiber volumn ratios on variations of workability and strength characteristics of steel fiber reinforced high-strength concrete, $50MPa{\sim}90MPa$ of compressive strength, according to increase of fiber volume. Test specimens were arranged with six levels of concrete compressive strength and fiber volumn ratios, 0.0%, 0.5%, 1.0%, 1.5%, 2.0%. The test results showed that steel fiber reinforced high-strength concrete($70MPa{\sim}90MPa$, 1.5% fiber volumn ratio) with good workability of slump 20cm could be used practically and effects of steel fiber reinforcement in improvement of concrete strength and toughness characteristics such as splitting tensile strength, flexural strength, and diagonal tensioned shear strength, were more distinguished in high-strength concrete than general strength concrete. And the test results indicated that splitting tensile strength of fiber reinforced concrete was proportioned to the product of steel fiber volumn ratios, $V_f(%)$ and sqare root of compressive strength, $\sqrt{f_{ck}}$, and the increasing rate was in contrast with that of flexural strength, and increase of diagonal tensioned shear strength was remarkable at steel fiber volumn ratio, 0.5%.

• Steel and Composite Structures
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• v.25 no.5
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• pp.617-624
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• 2017

In this study, a new empirical method is presented to obtain Dynamic Increase Factor (DIF) in nonlinear static analysis of structures against sudden removal of a gravity load-bearing element. In this method, DIF is defined as a function of minimum ratio of difference between maximum moment capacity ($M_u$) and moment demand ($M_d$) to plastic moment capacity ($M_p$) under unamplified gravity loads of elements. This function determines the residual strength of a damaged building before amplified gravity loads. For each column removal location, a nonlinear dynamic analysis and a step-by-step nonlinear static analysis are carried out and the modified empirical DIF formulas are derived, which correspond to the ratio min $[(M_u-M_d)/M_p]$ of beams in the bays immediately adjacent to the removed column, and at all floors above it. Therefore, the new DIF can be used with nonlinear static analysis instead of nonlinear dynamic analysis to assess the progressive collapse potential of a moment frame structure. The proposed DIF formulas can estimate the real residual strength of a structure based on critical member.

• Journal of Korea Foundry Society
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• v.22 no.4
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• pp.155-159
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• 2002

Magnesium alloys have high strength to weight ratio and are extremely attractive for applications in transport industry. Most of structural magnesium alloys are manufactured by die casting process. The tensile properties of AZ91HP magnesium alloy were investigated after die casting under various die casting conditions. After die casting by using cold chamber machine, the volume porosity of specimens was examined with density method. With the increase of the volume porosity of specimens, both the tensile strength and elongation were significantly decreased, however the 0.2% offset strength was almost independent of the amount of porosity. With the increase of crystal pressure from 500 to 900 bar during die casting, the volume porosity was decreased, which resulted in the increase of the tensile strength. The mould temperature within the range of $150{\sim}250^{\circ}C$ has not influenced the microstructure with the eutectic phase and tensile properties of specimens. The tensile strength was the highest at 90m/sec of gate speed.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2003.06a
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• pp.797-801
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• 2003

The mechanical properties such as shear strength and the hardness of milli-size products that manufactured for various process parameters by forward extrusion using square dies are investigated. Shear strength test is implemented for the observation of relation between vickers hardness and shear strength in the interface of head and shaft part of a stepped pin. When the extrusion ratios of pure aluminum and pure copper billets increase, the hardness on both the surface and the center line of a pin also increase, especially the hardness on the surface is shown to be a little higher than on the center. The existence of knock-out pad in extrusion die caused hardness increase in the interface of a extruded pin. As compared shear strength with hardness of a pin, the approximated linear relations are suggested in this study.

• Journal of the Korean GEO-environmental Society
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• v.15 no.8
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• pp.51-58
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• 2014

In this research, the composite grounds including original clay and soil-cement were constructed for conducting uniaxial compression test. Strength and deformation properties were analysed using results of laboratory tests with variations of water content of clay, replacement ratio and cement content. Numerical simulation using 3D distinct element method was conducted for soil cement. For strength of composite ground that contains more than cement contents of 15 %, it is more effective to increase cement content than increase of replacement ratio. Strength and elastic modulus of composite ground could be predicted by regression equations using uniaxial compression strength of clay, cement content of soil cement and replacement ratio. For strength and elastic modulus of soil cement, which is most important things for predicting final strength and elastic modulus of composite ground, numerical simulation using the distinct element method adapted bonding model could be used to verify laboratory test, and predict strength and elastic modulus.

• Steel and Composite Structures
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• v.16 no.6
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• pp.611-637
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• 2014

A single plate shear connection, or shear tab, is a very popular shear connection due to its merit in ease of construction and material economy. However, problems in understanding the connection behavior, both in terms of strength and ductility, have been well-documented. Suggestions or design model for single plate connections in AISC Design Manual have been altered several times, with the latest edition settling down to giving designers pre-calculated design strength tables if the connection details agree with given configurations. Results from many full-scale tests and finite element models in the past suggest that shear strength of a bolt group in single plate shear connections might be affected by yield strength of plate material; therefore, this research was aimed to investigate and clarify effects of plate yield strength and thickness on shear strength of the bolt group in the connections, including the validity of using a plate thickness/bolt diameter ratio ($t_p/d_b$) in design, by using finite element models. More than 20 models have been created by using ABAQUS program with 19.0- and 22.2-mm A325N bolts and A36 and Gr.50 plates with various thicknesses. Results demonstrated that increase of plate thickness or plate yield strength, with the $t_p/d_b$ ratio remained intact, could significantly reduce shear strength of the bolt group in the connection as much as 15 percent. Results also confirmed that the $t_p/d_b$ ratio is a valid indicator to be used for guaranteeing strength sufficiency. Because the actual ratio recommended by AISC Design Manual is $t_p/d_b$ + 1.6 (mm) for connections with a number of bolts less than six and plate yield strength in construction is normally higher than the nominal value used in design, it is proposed that shear strength of a bolt group in single plate connections with a number of bolts equal or greater than seven be reduced by 15 percent and the $t_p/d_b$ ratio be limited to 0.500.

• Proceedings of the Korean Geotechical Society Conference
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• 2010.03a
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• pp.489-494
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• 2010

A geo-composite soil (GCS) is a stabilized mixture of bottom ash, cement and dredged soil. Various samples with different mass ratios of mixtures were tested under curing time of 7 and 28 days to investigate physical properties and compressive strength. This paper focused on the effect of bottom ash on the strength characteristics of Busan marine dredged soil. Cement has been added as an additive constituent to enhance self-hardening of the blended mixture. The unconfined compressive strength of GCS increases with an increase in curing time due to pozzolanic reaction of the bottom ash. The strength after 28 days of curing is found to be approximately 1.3 to 2.0 times the strength after 7 days of curing, regardless of mixture conditions. The secant modulus of GCS is in the range of 55 to 134 times the unconfined compressive strength. The correlation of unconfined compressive strength with bottom ash content and initial void ratio are suggested.