• Computers and Concrete
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• 제9권4호
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• pp.311-325
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• 2012

In this paper, we examine the behavior of the High-Rate Brittle Microplane (HRBM) concrete model based on a series of penetration experiments. These experiments were conducted with three different slab thicknesses (127, 216 and 254 mm) that provided a significant challenge for the numerical simulations. The 127 mm slab provided little resistance, the 216 mm slab provided nominal resistance and the 254 mm slab approached the perforation limit thickness of the projectile. These experiments provide a good baseline for evaluating material models since they have been shown to be extremely challenging; in fact, we have not encountered many material models that can provide quantitatively predictive results in terms of both projectile exit velocity and material damage. In a companion paper, we described the HRBM material model and its fit to various quasi-static material property data for WES-5000 concrete. In this paper, we show that, when adequately fit to these quasi-static data, the HRBM model does not have significant predictive capabilities, even though the quasi-static material fit may be exceptional. This was attributed to the rate-dependent response of the material. After various rate effects were introduced into the HRBM model, the quantitative predictive nature of the calculations dramatically increased. Unfortunately, not much rate-dependent material property data are in the literature; hence, accurate incorporation of rate effects into material models is difficult. Nonetheless, it seems that rate effects may be critical in obtaining an accurate response for concrete during projectile perforation events.

• Structural Engineering and Mechanics
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• 제54권2호
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• pp.257-289
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• 2015

Shear connectors are generally used to link the slab and girders together in slab-on-girder bridge structures. Damage of shear connectors in such structures will result in shear slippage between the slab and girders, which significantly reduces the load-carrying capacity of the bridge. Because shear connectors are buried inside the structure, routine visual inspection is not able to detect conditions of shear connectors. A few methods have been proposed in the literature to detect the condition of shear connectors based on vibration measurements. This paper proposes a different dynamic condition assessment approach to identify the damage of shear connectors in slab-on-girder bridge structures based on power spectral density transmissibility (PSDT). PSDT formulates the relationship between the auto-spectral densities of two responses in the frequency domain. It can be used to identify shear connector conditions with or without reference data of the undamaged structure (or the baseline). Measured impact force and acceleration responses from hammer tests are analyzed to obtain the frequency response functions at sensor locations by experimental modal analysis. PSDT from the slab response to the girder response is derived with the obtained frequency response functions. PSDT vectors in the undamaged and damaged states can be compared to identify the damage of shear connectors. When the baseline is not available, as in most practical cases, PSDT vectors from the measured response at a reference sensor to those of the slab and girder in the damaged state can be used to detect the damage of shear connectors. Numerical and experimental studies on a concrete slab supported by two steel girders are conducted to investigate the accuracy and efficiency of the proposed approach. Identification results demonstrate that damages of shear connectors are identified accurately and efficiently with and without the baseline. The proposed method is also used to evaluate the conditions of shear connectors in a real composite bridge with in-field testing data.

• 방사성폐기물학회지
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• 제16권2호
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• pp.243-260
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• 2018

사용후핵연료 건식저장 시스템과 관련하여 고온 및 방사선으로 인한 콘크리트 손상과 열화특성에 대해 포괄적으로 문헌분석을 수행하였다. 고온에 의한 장기열화를 방지하기 위한 콘크리트의 임계온도는 일반적으로 $95^{\circ}C$이며, 온도경사는 콘크리트 균열방지를 위해 $60^{\circ}C$ 이하가 되도록 설정하고 있다. 열화정도는 노출온도와 노출시간에 비례하여 증가하는 경향을 나타내며, 압축강도에 비해 인장강도가 고온에 보다 민감한 특성을 보인다. 한편 방사선의 에너지가 $10^{10}MeV{\cdot}cm^{-2}{\cdot}s^{-1}$ 이하일 경우에는 핵반응으로 인한 가열을 무시할 수 있다. 하지만 콘크리트가 $10^{19}n{\cdot}cm^{-2}$ 이상의 중성자에 혹은 $10^{10}$ rad를 초과하는 감마선량에 노출된다면 콘크리트의 역학적 물성이 점차 감소하는 경향을 보이며, 그 손상정도는 콘크리트 구성재료의 특성에 의존적이다. 콘크리트에 대한 방사선 조사시 재료의 역학적 물성변화는 주로 온도상승으로 인한 콘크리트 내부 함수량의 변화 및 재료간의 열적물성 차이로 인한 체적증가와 균열발생으로 발생한다. 따라서 건식저장과 관련된 기술의 조속한 확보 및 인 허가를 위해서는 그 간의 선행연구 결과를 최대한 활용할 필요가 있으며, 본 연구결과는 향후 사용후핵연료 건식저장 콘크리트 캐스크 관련 국내 자체기술 개발에 중요한 기초자료로 활용될 수 있을 것이다.

• Structural Engineering and Mechanics
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• 제46권4호
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• pp.459-486
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• 2013

A novel damage classification method based on wavelet packet transform and statistical analysis is developed in this study for structural health monitoring. The response signal of a structure under an impact load is normalized and then decomposed into wavelet packet components. Energies of these wavelet packet components are then calculated to obtain the energy distribution. Statistical similarity comparison based on an F-test is used to classify the structure from changes in the wavelet packet energy distribution. A statistical indicator is developed to describe the damage extent of the structure. This approach is applied to the test results from simply supported reinforced concrete beams in the laboratory. Cases with single and two damages are created from static loading, and accelerations of the structure from under impact loads are analyzed. Results show that the method can be used with no reference baseline measurement and model for the damage monitoring and assessment of the structure with alarms at a specified significance level.

• Computers and Concrete
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• 제20권5호
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• pp.563-572
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• 2017

Ordinary reinforced concrete (RC) and prestressed concrete bridges are two popular and typical types of short- and medium-span bridges that accounts for the vast majority of all existing bridges. The cost of maintaining, repairing or replacing degraded existing RC bridges is immense. Detecting the abnormality of RC bridges at an early stage and taking the protective measures in advance are effective ways to improve maintenance practices and reduce the maintenance cost. This study proposes a systematic method from influence line (IL) identification to damage detection with applications to RC bridges. An IL identification method which integrates the cubic B-spline function with Tikhonov regularization is first proposed based on the vehicle information and the corresponding moving vehicle induced bridge response time history. Subsequently, IL change is defined as a damage index for bridge damage detection, and information fusion technique that synthesizes ILs of multiple locations/sensors is used to improve the efficiency and accuracy of damage localization. Finally, the feasibility of the proposed systematic method is verified through experimental tests on a three-span continuous RC beam. The comparison suggests that the identified ILs can well match with the baseline ILs, and it demonstrates that the proposed IL identification method has a high accuracy and a great potential in engineering applications. Results in this case indicate that deflection ILs are superior than strain ILs for damage detection of RC beams, and the performance of damage localization can be significantly improved with the information fusion of multiple ILs.

• 한국국방경영분석학회지
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• 제28권1호
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• pp.29-46
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• 2002

This study focuses primarily on the construction of the wartime sealift operation model from US to Korea. There are some uncertainties in the process of sealift operation such as the procurement rate of materiel in US, the distribution of KFS on four initial position locations at the start of the activation, and the number of ports and berths in the SPOES and SPODS. The sealift capability, based on the allocation of sealift assets such as the number of vessels, berths, and ports, is evaluated through simulation. The simulation is executed with a baseline wartime scenario and then the results are analyzed through a sensitivity analysis. The military planner may use of this model as a standard for establishing effective and concrete sealift operation plan in the near future.

• KIEAE Journal
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• 제16권5호
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• pp.39-45
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• 2016

Purpose: The purpose of this study is to analyze the energy saving and cost benefit analysis of the Low-income Energy Efficiency Treatment Program supported by KOREF(Korea Energy Foundation). This program was launched in 2007 and performs building energy retrofit for the low-income and energy poverty houses. Method: Energy simulation and cost benefit analysis were accomplished for the low-income detached houses. The structure of detached house was a lot og block structure, wood frame (single glass) and concrete roof. Baseline model of the low-income detached houses was proposed. Result: Annual heating energy consumptions were decreased by about 3.2% with the window system replacement(Case 1), 9.3% with reinforcement of insulation(Case2), and 12.5% with both(Case 3) compared to those of baseline model. The construction cost will be recouped within 5 years for the Case 1, 3 years for the Case 2, and 3 years for the Case 3. Case 3 was the most cost beneficient construction method in the analyzed cases in this study.

• Smart Structures and Systems
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• 제6권5_6호
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• pp.579-593
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• 2010

Low-power radio frequency (RF) chip transceiver technology and the associated structural health monitoring platforms have matured recently to enable high-rate, lossless transmission of measurement data across large-scale sensor networks. The intrinsic value of these advanced capabilities is the allowance for high-quality, rapid operational modal analysis of in-service structures using distributed accelerometers to experimentally characterize the dynamic response. From the analysis afforded through these dynamic data sets, structural identification techniques can then be utilized to develop a well calibrated finite element (FE) model of the structure for baseline development, extended analytical structural evaluation, and load response assessment. This paper presents a case study in which operational modal analysis is performed on a three-span prestressed reinforced concrete bridge using a wireless sensor network. The low-power wireless platform deployed supported a high-rate, lossless transmission protocol enabling real-time remote acquisition of the vibration response as recorded by twenty-nine accelerometers at a 256 Sps sampling rate. Several instrumentation layouts were utilized to assess the global multi-span response using a stationary sensor array as well as the spatially refined response of a single span using roving sensors and reference-based techniques. Subsequent structural identification using FE modeling and iterative updating through comparison with the experimental analysis is then documented to demonstrate the inherent value in dynamic response measurement across structural systems using high-rate wireless sensor networks.

• Smart Structures and Systems
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• 제1권1호
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• pp.29-46
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• 2005

In this study, a wavelet packet based method is proposed for identifying damage occurrence and damage location for beam-like structures. This method assumes that the displacement or the acceleration response time histories at various locations along a beam-like structure both before and after damage are available for damage assessment. These responses are processed through a proper level of wavelet packet decomposition. The wavelet packet signature (WPS) that consists of wavelet packet component signal energies is calculated. The change of the WPS curvature between the baseline state and the current state is then used to identify the locations of possible damage in the structure. Two numerical studies, one on a 15-storey shear-beam building frame and another on a simply-supported steel beam, and an experimental study on a simply-supported reinforced concrete beam are performed to validate the proposed method. Results show the WPS curvature change can be used to locate both single and sparsely-distributed multiple damages that exist in the structure. Also the accuracy of assessment does not seem to be affected by the presence of 20-15dB measurement noise. One advantage of the proposed method is that it does not require any mathematical model for the structure being monitored and hence can potentially be used for practical application.

• 한국해양공학회지
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• 제23권1호
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• pp.114-121
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• 2009

In this study, acceleration responses of caisson structures under various environmental conditions are experimentally examined as a basic study to develop the health assessment technique for harbor structures. To achieve the objective, three approaches are implemented. Firstly, a target caisson structure is selected and its small-scaled caisson is constructed in the laboratory. Secondly, a finite element model of the caisson is generated to identify dynamic responses of the baseline structure. Thirdly, experimental tests are performed on the caisson model to examine dynamic responses under various boundary conditions and impact locations. Four different boundary conditions, 'standing on concrete floor', 'standing on styrofoam block', 'standing on sand-mat' and 'hanging by crane', are considered and correlation coefficients of frequency response functions between four states are analyzed.