• Journal of the Korea Concrete Institute
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• v.12 no.2
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• pp.21-30
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• 2000

In the Ultimate Strength Design, the design strength of a member is determined by multiplying the strength reduction factor to the nominal strength. This concept may be a reasonable approach, however it can not consider failure modes appropriately. Moreover, column design strength diagram show an abrupt change at a low level of axial load, which does not seem to be reasonable. This research compares the design strength determined by the strength resistance factors. As the material resistance factors for flexure and compression, 0.65 and 0.90 are proposed for concrete and steel, respectively. The design strength calculation process by applying material resistance factors addresses failure modes more effectively than by applying member strength reduction factor, and provides more resnable design strength for reinforced concrete flexural and compression members.

• Computers and Concrete
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• v.12 no.6
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• pp.831-850
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• 2013

The high strength materials have been more widely used in reinforced concrete structures because of the benefits of the mechanical and durable properties. Generally, it is known that the ductility decreases with an increase in the strength of the materials. In the design of a reinforced concrete beam, both the flexural strength and ductility need to be considered. Especially, when a reinforced concrete structure may be subjected an earthquake, the members need to have a sufficient ductility. So, each design code has specified to provide a consistent level of minimum flexural ductility in seismic design of concrete structures. Therefore, it is necessary to assess accurately the ductility of the beam sections with high strength materials in order to ensure the ductility requirement in design. In this study, the effects of concrete strength, yield strength of reinforcement steel and amount of reinforcement including compression reinforcement on the complete moment-curvature behavior and the curvature ductility factor of doubly reinforcement concrete beam sections have been evaluated and a newly prediction formula for curvature ductility factor of doubly RC beam sections has been developed considering the stress of compression reinforcement at ultimate state. Based on the numerical analysis results, the proposed predictions for the curvature ductility factor are verified by comparisons with other prediction formulas. The proposed formula offers fairly accurate and consistent predictions for curvature ductility factor of doubly reinforced concrete beam sections.

• Proceedings of the Korea Concrete Institute Conference
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• 1995.10a
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• pp.267-272
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• 1995

The objective of this study is to investigate the effect of concrete strength on the stirrup effectiveness factor(K) of reinforced concrete beams with stirrup based on previous test results(a/d$\geq$2.5). In the procedure of the estimation of K, it was assumed that the ultimate shear strength for beams without stirrup is equal to the concrete contribution to shear strength for beam with stirrup. A model equation for calculation the stirrup of compressive strength of concrete. It was shown that the stirrup effective factor of compressive strength of concrete. It wah shown that the stirrup effective factor is greater than 1.0 up to compressive strength 85MPa. Therefore the current ACI Code equation for predicting the shear strength and the stirrup effectiveness factor of 1.0 is conservative for nomal and high stength concrete beams with stirrup.

• Journal of Advanced Marine Engineering and Technology
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• v.26 no.1
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• pp.59-67
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• 2002

The comparison of $J_{Rice}$-resistance considering a few strength ratio in Rice J-integral formula and $J_{\delta}$-resistance curves converted from experimental CTOD using appropriate strength chosen according to strain hardening level, n=10.6 (A533B steel) and n=8.1 (BS4360 steel) is carried out. The optimal dimensionless strength ratio like the factor of revision, (see full text)reflecting strain hardening level in Rice\`s experimental formula is found out and the reliability of appropriate reference strength chosen according to strain hardening level in different materials is investigated through doing that CTOD is transformed from $J_{\delta}$-integral using relationship between J-integral and CTOD. The results are as follows; 1) The optimal factor of revision is when m equals to 3 in (see full text) for Rice's and the above optimal factor of revision multiplies by coefficient, η in Rice's experimental formula instead of n=2, 2) and the pertinent reference strength for high strain hardening material like BS4360 steel is ultimate strength, $\sigma_{u}$ and for material like A533B steel is ultimate-flow strength, $\sigma_{u-f}$. The incompatible of the behavior of both experimental J-resistance curves using Rice's formula and CTOD-resistance curves for A533B and BS4360 steel by Gordon, et al., could be corrected using the optimal factor of revision in Rice\`s and the pertinent reference strength in J=$m_{j}$${\times}$$\sigma_{i}$${\times}$CTOD.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.32 no.6
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• pp.512-518
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• 2008

This study would like to evaluate the influences with the strength mismatch and the variation of the welding width of the narrow gap welding for the plastic parameter, the major constant determining the plastic ${\eta}$-factor of J-Integral, using 3-D FEM. For this, we evaluate the plastic ${\eta}$-factor according to the variation of the strength mismatch of weldment with same materials and welding width through FEM. Also, we proposed the equation of plastic ${\eta}$-factor considering the variation of the strength mismatch of weldment with similar materials and welding width.

• Journal of the Korea institute for structural maintenance and inspection
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• v.15 no.5
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• pp.101-112
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• 2011

This paper shows a study carried out on the estimation of nominal flexural strength for CFRP-plated RC beams failed by intermediate crack debonding. A strength reduction factor is proposed to consider the effect of the intermediate crack debonding for the determination of nominal flexural strength. The proposed factor is derived from experimental data and utilizes the ratio of effective stress(or strain) in the CFRP plate to its ultimate strength(or strain) which is called effective strain model. An analytical equation for the estimation of the nominal flexural strength is formulated as a function of strength reduction factor. The validity, accuracy and efficiency of the proposed factor are established by comparing the analytical results with the experimental data, and the major design codes, as well as a number of factors given by researchers. The analytical results presented in this paper indicate that the proposed factor can effectively estimate the flexural nominal strength of CFRP-plated reinforced concrete beams failed by intermediate crack debonding.

• Earthquakes and Structures
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• v.2 no.1
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• pp.65-88
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• 2011

A new method for the seismic design of plane steel moment resisting frames is developed. This method determines the design base shear of a plane steel frame through modal synthesis and spectrum analysis utilizing different values of the strength reduction (behavior) factor for the modes considered instead of a single common value of that factor for all these modes as it is the case with current seismic codes. The values of these modal strength reduction factors are derived with the aid of a) design equations that provide equivalent linear modal damping ratios for steel moment resisting frames as functions of period, allowable interstorey drift and damage levels and b) the damping reduction factor that modifies elastic acceleration spectra for high levels of damping. Thus, a new performance-based design method is established. The direct dependence of the modal strength reduction factor on desired interstorey drift and damage levels permits the control of deformations without their determination and secures that deformations will not exceed these levels. By means of certain seismic design examples presented herein, it is demonstrated that the use of different values for the strength reduction factor per mode instead of a single common value for all modes, leads to more accurate results in a more rational way than the code-based ones.

• Journal of the Korea Institute of Building Construction
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• v.8 no.5
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• pp.59-65
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• 2008

In the evaluation method of KS on the activity factor of fly ash, same amount of cement should be replaced with fly ash. Therefore, contradictory effects on concrete strength exist, i. e. strength decease due to low content of cement and strength increase of strength due to filling-pore-function of fly ash. European Committee for Standardization (CEN) specifies the method 1 to 4. adding fly ash without reducing the content of cement, for the evaluation method on activity factor of fly ash. This study investigates the applicability of the method 2 of CEN to mix design of concrete. The followings are derived ; There is a key ratio of f)y ash mixing which enhances the incremental ratio of mixing water to improve fluidity of mortar. The incremental ratio of mixing water is maximized about 11% ratio of fly ash mixing. Compressive strength most slightly increases at that ratio of fly ash mixing. Activity factor of fly ash increases as water-cement ratio becomes low and contents of fly ash becomes high. Moreover, quality of fly ash and condition of mix design affect the applicable amount of fly ash and available range of water-cement ratio. However, this method has some problems for practical purpose because activity factors of fly ash for some cases are over 1.0. Further research should be conducted to develop more useful method of evaluating activity factor of fly ash.

• Steel and Composite Structures
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• v.11 no.4
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• pp.273-290
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• 2011

In current ductility-based earthquake-resistant design, the estimation of design forces continues to be carried out with the application of response modification factors on elastic design spectra. It is well-known that the response modification factor (R) takes into account the force reduction, strength, redundancy, and damping of structural systems. The key components of the response modification factor (R) are force reduction ($R_{\mu}$) and strength ($R_S$) factors. However, the response modification and strength factors for structural systems presented in design codes were based on professional judgment and experiences. A numerical study has been accomplished to evaluate force reduction, strength, and response modification factors for special steel moment resisting frames. A total of 72 prototype steel frames were designed based on the recommendations given in the AISC Seismic Provisions and UBC Codes. Number of stories, soil profiles, seismic zone factors, framing systems, and failure mechanisms were considered as the design parameters that influence the response. The effects of the design parameters on force reduction ($R_{\mu}$), strength ($R_S$), and response modification (R) factors were studied. Based on the analysis results, these factors for special steel moment resisting frames are evaluated.

• Journal of the Korea Institute of Building Construction
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• v.13 no.4
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• pp.400-406
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• 2013

In high-rise buildings, high-strength concrete is widely used to reduce the section of structure members under axial load. Also, the price increase of materials is very important item in the high-rise buildings. Especially, concrete used high-pressure pump due to consecutive structural assembly. Unlike slump type of ordinary concrete, high strength concrete has different properties of concrete pumping due to viscosity. However, there have been no Korean studies on the pumping properties of high strength concrete. Therefore, this paper measures the friction factor of high strength concrete with changes in the pressure of concrete pumping. We analyzed the trends of the friction factor based on changes in the pressure of concrete pumping, and then calculated the quantity of concrete deposited for each specified concrete strength and location of placement. After comparing these results with the quantity of concrete deposited measured in field, we evaluated the pumping properties of high strength concrete. Through the tests and the review, we attempt to suggest some basic information for the In-Situ application of high strength concrete.