• Proceedings of the Korean Institute of Building Construction Conference
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• 2009.11a
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• pp.117-120
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• 2009

It has been gradually increased with the use of resin based membrane forming agent for curing method, which plays a role in protecting moisture evaporation by forming resin membrane at the surface of concrete. In this paper, tests were carried out to examine moisture retention capability of cement mortar applying membrane forming agent. Dosages and types of the membrane forming agent were varied. It is found that sheet curing sealed with the surface of concrete closely has favorable moisture retention capability. However, the application of membrane forming curing method had superiority in moisture retention capability at early stage but at later age, its capability is deteriorated. Hence, further study regarding altering application method was necessary to secure enhanced moisture retention capability.

• KCI Concrete Journal
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• v.12 no.1
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• pp.35-46
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• 2000

A research program was initiated at the University of Colorado at Boulder to develop computational models that can be used for seismic risk assessments. To assess the overall performance of bridge structures including the nonlinear effects of bridge piers, the research focused on two levels of capabilities, i.e. global and local pier levels. A 3-D concrete model was used to evaluate the behavior of individual piers under combined axial, bending, and shear loadings using 3-D finite element analysis. Whereby the response curve reached the peak strength of the R/C column under the constant axial and monotonically increasing lateral loads. Experimental results on reinforced concrete bridge piers, which were obtained at the University of California at San Diego were used to validate the seismic performance of bridge piers at the two levels, globa1 and local.

• Proceedings of the Korea Concrete Institute Conference
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• 2004.11a
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• pp.153-156
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• 2004

Most concrete is recently made of an aggregate which is properly absorbed. and carried in it in order to do capability at every fields. We have been close to demand new capability of high flowing and enduring for specific concretes. That is difficult to cope with claiming the efficiency on deterioration from lack of a high quality aggregate. Therefore. For solving the problems we apply to a packing method for using dried materials. That is to say it is a kind of making into an instant. In this study. There is a purpose to present fundamental data. comparing and analyzing a phenomenon about aggregate's absorption following the rate of adding water. for using existing materials.

• Journal of the Korea institute for structural maintenance and inspection
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• v.12 no.1
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• pp.143-150
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• 2008

There is possibility of poor-state concrete filling condition due to segregation of aggregate and paste in reinforced concrete structure. This study was conducted to evaluate the flexural and shear behavior of reinforced concrete beams with different concrete filling conditions. Different concrete filling conditions were intentionally made such that the specimens was soundly cast to obtain the perfect concrete filling condition and cast in such a way that up to the longitudinal tensile reinforcement from the top, good concrete was filled while poor concrete was poured for the bottom part to simulate the poor strength, workability and unsatisfactory compaction. The test results indicate that have no effect of concrete filling conditions on the yielding strength of structures. But, have a great influence on the flexural ductility and shear capacity of structures.

• Computers and Concrete
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• v.22 no.6
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• pp.539-550
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• 2018

Concrete is highly non-linear material which is originating from the transition zone in the form of micro-cracks, governs material response under various loadings. In this paper, the constitutive models published by many researchers have been used to generate novel stiffness parameters and constitutive curves for concrete. Following such linear material formulations, where the energy is conservative during the curvature, and a nonlinear contribution to the concrete has been made and investigated. In which, nonlinear concrete elastic modulus modeling has been developed that is capable-of representing concrete elasticity for grades ranging from 10 to 140 MPa. Thus, covering the grades range of concrete up to the ultra-high strength concrete, and replacing many concrete models that are valid for narrow ranges of concrete strength grades. This has been followed by the introduction of the nonlinear Hooke's law for the concrete material through the replacement of the Young constant modulus with the nonlinear modulus. In addition, the concept of concrete elasticity index (${\varphi}$) has been proposed and this factor has been introduced to account for the degradation of concrete stiffness in compression under increased loading as well as the multi-stages micro-cracking behavior of concrete under uniaxial compression. Finally, a sub-routine artificial neural network model has been developed to capture the concrete behavior that has been introduced to facilitate the prediction of concrete properties under increased loading.

• Journal of Korean Society of Steel Construction
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• v.12 no.2 s.45
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• pp.133-142
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• 2000

This study deals with behavior of steel box girder bridges according to the concrete slab casting sequences and sectional types. The time dependent behavior of bridges caused by the differential setting of slab concrete resulting from time gap for each part of slab deck in a sequential placing method produces is analyzed. In correlation studies between girder section types and placing sequences, time dependent effects of concrete creep and shrinkage are implemented in the analytical model proposed in the previous study. Finally, field recommendations in terms of concrete slump and relative humidity are suggested to prevent early transverse cracking of concrete slabs.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2009.11a
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• pp.23-26
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• 2009

Despite vigorous studies on ultra high-strength concrete in Korea, it still faces many challenges in application to on-site construction methods. This study intends to evaluate the applicability of the VH separated-pouring method which is currently used and was designed to pour ultra high-strength concrete with a design strength of 60, 100N/㎟ separately to girder and beam. When it comes to VH separated-pouring, there is a difference in the required design strength between a girder and a beam, which tends to be larger for ultra high-strength concrete. The tensile strength and cold joint at the joint end have not been commonly evaluated and thus the inevitably of its use is dependent on a structural analysis of the structural stress of reinforcement. In the study, potential problems with respect to the building material which might occur during the pouring of ultra high-strength concrete was evaluated and issues on joint surface performance, the hydration energy contained in the members, and the effects of contraction in concrete were considered as the key elements for study.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.26 no.4A
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• pp.565-575
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• 2006

When concrete is confined, its strength is enhanced by confining stress. Thus, increasing confining stress makes concrete strength higher. But a brittle failure may occur in hollow RC(Reinforced Concrete) column although its concrete is confined by transverse reinforcements. This brittle failure results from the absence of internal confinement and it decreases the strength and the ductility of a hollow RC column. To overcome this brittle failure problem, a hollow RC column which has a internal steel tube was developed. In this study, an experiment was performed to investigate the existence of to internal confinement by a settled steel tube. Thirty six specimens were tested and test results show the existence of internal confinement by the increase of concrete strength.

• Proceedings of the Korea Concrete Institute Conference
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• 2004.05a
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• pp.454-457
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• 2004

Due to social problems such as the increasing of land price and the expanding of city, buildings require more complex and bigger components and structure. However, the complex and massive building projects need new technology to solve effect of local buckling and the needs for more space. Hence, Concrete Filled Tube Steel (CFT), the tube steel to hold concrete during pouring and curing of concrete procedure, which helps to reduce local buckling and space, was developed. Most researches on CFT might not be focused on the characteristic of concrete 'filled in tube but structural analysis. However, it is the essential factor to increase the strength of concrete on CFT for having efficient results. Therefore, this paper will describe how to apply CFT into the construction site through examining High Strength Concrete $(800kg/cm^2)$, the strength of core, and bleeding during pouring strategy.

• Proceedings of the Korea Concrete Institute Conference
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• 2006.05a
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• pp.178-181
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• 2006

The purpose of this study is to investigate the inelastic behavior of precast segmental prestressed concrete bridge piers. A computer program, named RCAHEST (Reinforced Concrete Analysis in Higher Evaluation System Technology), for the analysis of reinforced concrete structures was used. Material nonlinearity is taken into account by comprising tensile, compressive and shear models of cracked concrete and a model of reinforcing steel. An unbonded tendon element based on the finite element method, that can represent the interaction between tendon and concrete of prestressed concrete member, is used. A joint element is newly developed to predict the inelastic behaviors of segmental joints. The proposed numerical method for the inelastic behavior of precast segmental prestressed concrete bridge piers is verified by comparison with reliable experimental results.