• Computers and Concrete
• /
• v.28 no.5
• /
• pp.479-486
• /
• 2021

Reinforced concrete (RC) slabs are exposed to several static and dynamic effects during their period of service. Accordingly, there are many studies focused on the behavior of RC slabs under these effects in the literature. However, impact loading which can be more effective than other loads is not considered in the design phase of RC slabs. This study aims to investigate the dynamic behavior of two-way RC slabs under sudden impact loading. For this purpose, 3 different simply supported slab specimens are manufactured. These specimens are tested under impact loading by using the drop test setup and necessary measurement devices such as accelerometers, dynamic load cell, LVDT and data-logger. Mass and drop height of the hammer are taken constant during experimental study. It is seen that rigidity of the specimens effect experimental results. While acceleration values increase, displacement values decrease as the sizes of the specimens have bigger values. In the numerical part of the study, artificial neural networks (ANN) analysis is utilized. ANN analysis is used to model different physical dynamic processes depending upon the experimental variables. Maximum acceleration and displacement values are predicted by ANN analysis. Experimental and numerical values are compared and it is found out that proposed ANN model has yielded consistent results in the estimation of experimental values of the test specimens.

• Journal of the Korean Society of Safety
• /
• v.32 no.5
• /
• pp.62-68
• /
• 2017

It is necessary to analyze on the compressive strength among material properties of concrete for confirming damages of architectures due to large explosion. A non destructive test is known as the representative methods estimating compressive strength and ultrasonic pulse velocity, rebound hardness test are widely used because of their simplicity, convenience. But combined method supplementing two types is applied at now as they are affected by the characteristics of test specimen. In this research to check damages on the members of structure before and after explosion, the characteristics of compressive strength are compared and analyzed through a real explosion test prior to full scale structures. The test results showed that the larger the TNT powder and the shorter the distance, the greater the decrease in strength before and after the explosion and that the largest displacement and moment for the explosive load and the greatest decrease in the strength at the central part. Due to the surface condition and the thickness variation of the concrete specimens, the standard deviation value is the smallest in the combining method of fusion of the ultrasonic method and rebound hardness method. Thus, the combining method can be one of appropriate methods to evaluate the strength in the reinforced concrete structures damaged by the explosion.

• Journal of the Korea institute for structural maintenance and inspection
• /
• v.16 no.5
• /
• pp.137-147
• /
• 2012

In the steel-free bridge concrete deck, steel straps are generally used instead of conventional steel rebar while laterally restrained in the perpendicular direction to the traffic in order fir the arching effect of concrete deck. In this paper, the minimum amount of FRP bar is to be suggested based on the structural strength, crack propagation, stress level and others in order to control cracks. As a result of laboratory tests, the structural strength of deck with 0.15 percentage of steel strap showed improved structural strength including ductility. The long-term serviceability of steel strap deck with FRP bar proved to satisfy the requirements and to be structurally stable while showing the amount of crack and residual vertical displacement within the allowable limits after two million cyclic loadings. The structural failure of RC bridge deck is generally caused from the punching shear rather than moment. Therefore, the ultimate load at failure could be estimated using the shear strength formula in the two-way slab based on ACI and AASHTO criteria. However the design criteria tend to underestimate the shear strength since they don't consider the arching effects and nonlinear fracture in bridge deck with lateral confinement. In this paper, an equation to estimate the punching shear strength of steel strap deck is to be developed considering the actual failure geometries and effect of lateral confinement by strap while the results are verified in accordance with laboratory tests.

• Magazine of the Korea Concrete Institute
• /
• v.11 no.1
• /
• pp.243-254
• /
• 1999

This paper presents a numerical study for developing the moment magnifier method that is applicable to RC flat plates subject to combined axial compressive and floor load. For the nonlinear finite element analysis, a computer program addressing material and geometric nonlinearities was developed. The flat plates to be studied are designed in accordance with the Direct Design Method in Korean Building Code for Structural Concrete. This paper proposes the buckling force and the moment magnification factor for the flat plate under the governing load condition that is the combined vertical and subsequently applied uniaxial compressive load. The buckling force is defined with two ingredients: the buckling coefficient and the effective flexural rigidity. Parametric studies are performed to investigate variations of the buckling coefficient and the effective flexural rigidity. Based on the numerical results, this paper provides the design values of the buckling coefficient and the effective flexural rigidity, and the design procedure for the moment magnifier method.

• 한국방재학회:학술대회논문집
• /
• 2011.02a
• /
• pp.32-32
• /
• 2011

최근 국내외에서 친환경건축물에 관한 관심이 매우 높아짐으로 인해 콘크리트의 물량을 절감하여 이산화탄소량을 줄이는 중공슬래브는 다양한 형태로 세계적으로 개발이 되고 있는 추세이다. 특히 이방향 중공슬래브는 환경적인 측면에서 이방향 중공슬래브는 중공부 생성에 재생플라스틱을 활용하여 폐자원을 재사용하고, 콘크리트와 철근의 사용량 절감에 따른 화석에너지 및 이산화탄소 발생량을 감소한다는 장점이 있다. 또한 시스템 측면에서 이방향 중공슬래브는 기존의 철근콘크리트 플랫플레이트 바닥구조 시스템의 자중을 절감하여 구조체를 경량화 시키고, 이에 따라 장스팬 구현이 가능하며, 단열효과가 뛰어나다. 이와 같이 이방향 중공슬래브는 장점이 많지만 플랫플레이트 슬래브의 취약점인 뚫림전단 파괴에 주의해야 한다. 이에 본 연구에서는 선행으로 실시된 이방향 중공슬래브-기둥 접합부 뚫림전단 성능평가 실험을 바탕으로 하여 경량체가 이방향 중공슬래브-기둥 접합부 뚫림전단 성능에 미치는 영향을 살펴보기 위해 범용 유한요소해석 프로그램인 ABAQUS를 사용하여 경량체량 및 위치를 주요변수로 한 해석적인 변화를 검토하였다. 본 연구를 통해 경량체가 삽입된 이방향 중공슬래브의 뚫림전단 성능에 대해, 해석결과 경량체 량과 위치에 따라 최대 뚫림전단강도는 기준 실험체에 비해 74.3%, 73%의 강도저하를 나타내는 것으로 알 수 있었다. 이는 실험상의 강도저하 값인 84.1%, 56.4%와 다소 차이가 있으며, 해석에서 중공부 주위의 응력집중 현상이 제대로 반영되지 않은 것으로 판단된다. 또한 이방향 슬래브에 경량체를 삽입 할 경우 경량체가 시작하는 부분에서 응력이 급격히 감소하는 현상이 나타났으며, 이러한 급격한 응력감소는 기둥 주위 위험단면의 변화를 가져오는 것으로 추정된다. 즉, 위험단면의 변화는 기둥으로부터 경량체 사이의 거리에 따라 달라지며, 위험단면 내의 콘크리트 단면 손실은 뚫림전단 강도를 감소시킨다. 본 연구에서는 이방향 중공슬래브의 뚫림전단강도를 산정할 수 있는 근사식을 제안하였으며, 보다 정확한 이방향 중공슬래브의 뚫림전단강도의 산정식을 위해서는 위험단면의 변화와 콘크리트 단면손실로 인한 전단강도 저하의 관계에 대한 추가적인 연구가 필요하다.

• Journal of the Korea Concrete Institute
• /
• v.16 no.1 s.79
• /
• pp.18-26
• /
• 2004

The cost of underground work is a dominant factor to determine the total construction fee. It is generally 2 ${\~}$ 2.5 times higher than that of above ground for building with the same height. 'A new precast prestressed framing plan for underground parking building' was suggested with the beam of the least depth - U-type beams. The depth of regular rectangular reinforced concrete beam which is currently used in the underground parking of apartments could be reduced up to 12 ${\~}$ 34cm/story due to the development of a U-beams from the optimum process. Two full scale prototype U-beams were tested in this study. It was found that the Wide U-beams in the test showed higher strength than calculated nominal and design, however need to provide temporary supports to meet the flexural moment of construction load at the simply supported state before the lopping concrete hardens.

• KSCE Journal of Civil and Environmental Engineering Research
• /
• v.32 no.5B
• /
• pp.313-320
• /
• 2012

A hybrid floating structure system combined with pontoon and semi-submersible type modules is proposed. This new system can reduce tensile forces of bottom slabs which could cause fatal damage of concrete floating structures. We performed a parametric study on the dimensions of this new system and investigate the sensitivity of the parameters to the behavior. In order to investigate various cases efficiently, we developed a simple two-step static analysis method for the fluid-structure interaction. An optimum system is derived from the investigation of the analysis results, weights and drafts of the hybrid structure. This study shows that introducing this new system to concrete floating structures is an effective way to reduce the tensile force of the bottm slab of such a floating structure. Also, it was found that when the length of the semi-submersible module is about 15%, the behavior would be optimal in the considered case.

• Journal of the Korea institute for structural maintenance and inspection
• /
• v.19 no.1
• /
• pp.53-61
• /
• 2015

This paper reports the test results of the floating floor system used to reduce the floor noise of apartment buildings. Recently, many soft resilient materials placing between the reinforced concrete slab and finishing mortar are used. The resilient material should not only reduce the floor impact sound vibration from the floor but also support the load on the floor. Thus, even if soft resilient materials satisfy the maximum limitation of light-weight impact sound and heavy-weight impact sound, these materials may not support the load on the floor. The experimental program involved conducting sixteen sound insulation floating floor specimens. Three main parameters were considered in the experimental investigation: resilient materials, loading location, and layers of floor. Experimental results indicated that the stiffness of resilient material significantly influenced on the structural behavior of floating floor system. In addition, the deflection of the floating concrete floor loaded at the side or coner of the specimen was greater than that of the floor loaded at the center of the specimen. However, the aerated concrete did not effect on the cracking strength of floating floor system.

• Magazine of the Korea Concrete Institute
• /
• v.11 no.1
• /
• pp.231-242
• /
• 1999

This paper presents a numerical study on the flat plates in deep basements, subjected to out-of-plane floor load and in-plane compressive load due to soil and hydraulic lateral pressure. For nonlinear finite element analysis, a computer program addressing material and geometric nonlinearities is developed. The validity of the numerical model is established by comparison with existing experiments performed on plates simply supported on four edges. The flat plates to be studied are designed according to the Direct Design Method in Korean Building Code for Structural Concrete. Through numerical study on the effects of different load combinations and loading sequence, the load condition that governs the strength of the flat plates is determined. For the plates under the governing load condition, parametric studies are performed to investigate variations of the strength with reinforcement ratio, aspect ratio, concrete strength, and slenderness ratio. Based on the numerical results, the floor load magnification factor is proposed.

• Magazine of the Korea Concrete Institute
• /
• v.8 no.6
• /
• pp.223-234
• /
• 1996

The purpose of this paper is to present an analysis method by using the finite element method which can exactly analyze load-deflection relationships, crack propagations. and stresses and strains of reinforcements, tendons, and concrete in behaviors of elastic. inelastic and ultimate ranges of reinforced and prestressed concrete slabs under monotonically increasing loads. For t h i s purpose, the m a t e r i a l and geometric nonlinearities are taken into account in this study. The total Lagrangian formulation based upon the simplified Von Karman strain expressions is used to take into account the geometric nonlinearities of the structure. The material nonlinearities are taken into account by comprising the tension, compression. and shear models of cracked concrete and models for reinforcements and tendons in the concrete : and also a so-called smeared crack model is incorporated. The reinforcements and t,endons are assumed to be in a uniaxial stress state and are modelled as smeared layers of equivalent thickness. For the verification of application and validity of the method proposed in this paper, several numerical examples are analyzcd and compared with experimental results. As a result, this method can successfully predict the nonlinear and inelastic behaviors throughout the fracture of reinforced and prestressed concrete slabs.