• Earthquakes and Structures
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• v.11 no.3
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• pp.461-481
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• 2016

The research described in this paper investigates the seismic behaviour of lightly reinforced concrete (RC) bearing sandwich panels, heavily conditioned by shear deformation. A numerical model has been prepared, within an open source finite element (FE) platform, to simulate the experimental response of this emerging structural system, whose squat-type geometry affects performance and failure mode. Calibration of this equivalent mechanical model, consisting of a group of regularly spaced vertical elements in combination with a layer of nonlinear springs, which represent the cyclic behaviour of concrete and steel, has been conducted by means of a series of pseudo-static cyclic tests performed on single full-scale prototypes with or without openings. Both cantilevered and fixed-end shear walls have been analyzed. After validation, this numerical procedure, including cyclic-related mechanisms, such as buckling and subsequent slippage of reinforcing re-bars, as well as concrete crushing at the base of the wall, has been used to assess the capacity of two- and three-dimensional low- to mid-rise box-type buildings and, hence, to estimate their strength reduction factors, on the basis of conventional pushover analyses.

• Journal of the Korea Concrete Institute
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• v.17 no.1 s.85
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• pp.149-155
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• 2005

The purpose of this study is to investigate the flexural strengthening effects of CF(Carbon Fiber) sheet for the full-scale RC beams with multi-layer CF sheets. The partial strength reduction factors of CF sheets are suggested from the full-scale RC beams tests strengthened with multi-layer CF sheets up to six layers as well as material tests. From the material tensile tests, it was observed that the average tensile strengths of CF sheets per layer are decreased as the number of CF sheets is increased. Also the steep strength reductions of CF sheets in material test results at rupture are observed compared with the structural tests results for the full-scale RC beams strengthened with multi-layer CF sheets. Finally, the partial strength reduction factors far CF sheets up to six layers are suggested considering the effects of multi-layer and unit weight of CF sheets.

• Journal of the Korea institute for structural maintenance and inspection
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• v.25 no.6
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• pp.90-94
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• 2021

With the increased interest on quiescent place for residential place, the noise generation from facilities needs to be minimized. One important noise source include sounds from operation of elevators. The elevator operates between floors and generates significantly annoying sounds to the nearby living spaces. It is recognized as the significant contributor inducing noise annoyance to residents. Elevator is supported to the building structure at several locations for movements between floors. In this study, the vibration reduction by use of polymer concrete on the support location was demonstrated. By measuring and comparing the vibration generation when supported on cement and polymer concrete, the noise reduction performance was evaluated. The polymer concrete was made in the form of being inserted into the wall that imitates the hoistway. The impact vibration was induced to the bracket and vibration transfer magnitude was measured. The damping ratio was evaluated through normalization and curve fitting of transient response, and comparison was performed for each resin mixing ratio. By use of polymer concrete, it was possible to reduce the vibration generation in an effect manner without sacrifice on the structural rigidity.

• International conference on construction engineering and project management
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• 2009.05a
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• pp.794-799
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• 2009

The temperature control of in-place concrete is the most important factor for an early age of curing concrete. Heat stress of mass concrete caused by the heat of hydration can induce the crack of concrete, and a frost damage from cold weather casting concrete results defect on compressive strength and degradation of durability. Therefore, success and failure of concrete work is dependant on the measurement and control of concrete temperature. In addition, the compressive strength assessment of in-place concrete obtained from the maturity calculated from the history of temperature make a reduction of construction cycle time, possible. For that purpose, wireless temperature measuring system was developed to control temperature and assess strength of concrete. And, it was possible to monitor the temperature of concrete over 1km apart from site office and to take a proper measure; mesh-type network was developed for wireless sensor. Furthermore, curing control system that contains the program capable to calculate the maturity of concrete from the history of temperature and to assess the compressive strength of concrete was established. In this study, organization and practical method of developed curing control system are presented; base on in-place application case.

• Journal of the Korea Concrete Institute
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• v.15 no.6
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• pp.915-923
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• 2003

This paper presents the test results of total 35 direct tensile specimens to investigate the effect of high-strength concrete on the tension stiffening effect in axially loaded reinforced concrete tensile members. Three kinds of concrete strength 25, 60, and 80 MPa were included as a major experimental parameter together with six concrete cover thickness ratios. The results showed that as higher strength concrete was employed, not only more extensive split cracking along the reinforcement was formed, but also the transverse crack space became smaller. Thereby, the effective tensile stiffness of the high-strength concrete specimens at the stabilized cracking stage was much smaller than those of normal-strength concrete specimens. This observation is contrary to the current design provisions, and the significance in reduction of tension stiffening effect by employment of high-strength concrete is much higher than that would be expected. Based on the present results, a modification factor is proposed for accounting the effect of the cover thickness and the concrete strength.

• 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.

• Proceedings of the Korea Concrete Institute Conference
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• 2001.11a
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• pp.733-738
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• 2001

Although there are strong needs for evaluating statistical characteristics of strengthened reinforced concrete beams under flexure, many researches have been performed mostly on the mechanical properties and failure mechanisms. Different material properties and resulting reinforcing effect could alter the probabilistic values of the strengthened beams. Existing equations suggested for predicting flexural strengthened reinforced concrete beam with CFRP and steel plate are selected and best-fitting one is used in evaluating probability of failure based on Monte-Carlo method. Influential factors are statistically examined and approximate strength reduction factors are suggested. It was found that the factor is more sensitively influenced by predictive equations as well as characteristics and amounts of strengthening materials.

• Proceedings of the Korea Concrete Institute Conference
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• 2005.11a
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• pp.699-702
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• 2005

This study evaluates the properties of porous concrete for pavement according to content of silica fume and steel fiber. The results of the test indicate that in every condition, the void ratio and the coefficient of water permeability of porous concrete for pavement satisfy both the domestic standards and proposition values. Among the properties of strength, the compressive strength satisfies the standards in the specification of KNHC as for every factor of mixture but in the case of the flexural strength, more than $0.6vol.\%$ of steel fiber satisfied the JCI proposition values. The case when silica fume and steel fiber are used simultaneously presents the strongest durability and Noise Reduction Coefficient is 0.48 to prove that it possesses almost $50\%$ sound absorption.

• Proceedings of the Korea Concrete Institute Conference
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• 1997.04a
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• pp.605-610
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• 1997

An experimental investigation was conducted to examine the feasibility of Carbon Fiber Sheet(CFS), a kind of high strength fiber, for a repair and reinforcement method of concrete structures. The experimental program included tests of flexural beams different in wrapping method and amount of CFS. The beams were subjected to monotonic loading. Although the flexural strength for concrete members increases with wrapping methods of CFS., the reduction factor due to the distribution, amount bond of CFS should be completely examined. This study approached the effectiveness and application of CFS, along with reinforcement effects of CFS on reinforced concrete beams through tests. Test results indicated that the increase in the number of CFS layer caused the increase in strength of beams in strength.

• Proceedings of the Korea Concrete Institute Conference
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• 2006.11a
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• pp.505-508
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• 2006

This experimental study is to evaluate the effects of recycled coarse aggregate replacement level on the mechanical properties of concrete produced at Batcher plant. The main test parameter was replacement level of recycled coarse aggregate with the ratio of 0, 30, 60 and 100% to the natural coarse aggregate. From the test results, it was found that compressive strength, elastic modulus and splitting strength are decreased with the increased proportion of replacement level. Therefore, some design coefficients or recommendations for elastic modulus and splitting strength of concrete need to be reconsidered with minor reduction factor of '0.85'.