• Structural Monitoring and Maintenance
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• v.3 no.3
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• pp.277-296
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• 2016

There is a need for rapid and objective assessment of concrete bridge decks for maintenance decision making. Infrared Thermography (IRT) has great potential to identify deck delaminations more objectively than routine visual inspections or chain drag tests. In addition, it is possible to collect reliable data rapidly with appropriate IRT cameras attached to vehicles and the data are analyzed effectively. This research compares three infrared cameras with different specifications at different times and speeds for data collection, and explores several factors affecting the utilization of IRT in regards to subsurface damage detection in concrete structures, specifically when the IRT is utilized for high-speed bridge deck inspection at normal driving speeds. These results show that IRT can detect up to 2.54 cm delamination from the concrete surface at any time period. It is observed that nighttime would be the most suitable time frame with less false detections and interferences from the sunlight and less adverse effect due to direct sunlight, making more "noise" for the IRT results. This study also revealed two important factors of camera specifications for high-speed inspection by IRT as shorter integration time and higher pixel resolution.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.19 no.2 s.72
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• pp.171-185
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• 2006

A sophisticated reliability analysis method is proposed to evaluate the reliability of real nonlinear complicated dynamic structural systems excited by short duration dynamic loadings like earthquake motions by intelligently integrating the response surface method, the finite element method, the first-order reliability method, and the iterative linear interpolation scheme. The method explicitly considers all major sources of nonlinearity and uncertainty in the load and resistance-related random variables. The unique feature of the technique is that the seismic loading is applied in the time domain, providing an alternative to the classical random vibration approach. The four-parameter Richard model is used to represent the flexibility of connections of real steel frames. Uncertainties in the Richard parameters are also incorporated in the algorithm. The laterally flexible steel frame is then reinforced with reinforced concrete shear walls. The stiffness degradation of shear walls after cracking is also considered. The applicability of the method to estimate the reliability of real structures is demonstrated by considering three examples; a laterally flexible steel frame with fully restrained connections, the same steel frame with partially restrained connections with different rigidities, and a steel frame reinforced with concrete shear walls.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.30 no.1
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• pp.39-46
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• 2017

In this paper, a model updating procedure based on the response surface method combined with the multi-objective optimization was proposed and applied for updating of the FE models representing a low-rise reinforced concrete building before and after the seismic retrofit. The dynamic properties to be matched were obtained from vibration tests using a small shaker system. By varying the structural parameters according to the central composite design, analysis results from the initial FE model using a commercial software were collected and used to produce two regression functions each of which representing the errors in the natural frequencies and mode shapes. The two functions were used as the objective functions for multi-objective optimization. Final solution was determined by examining the Pareto solutions with one iteration. The parameters representing the stiffnesses of existing concrete, masonry, connection stiffness in expansion joint, new concrete, retrofitted members with steel section jacketing were selected and identified.

• Geomechanics and Engineering
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• v.21 no.2
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• pp.95-102
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• 2020

Population concentration in urban areas has led traffic management a central issue. To mitigate traffic congestions, the government has planned to construct large-cross-section tunnels deep underground. This study focuses on estimating the damage caused to frame structures owing to tunnel excavation. When constructing a tunnel network deep underground, it is necessary to divide the main tunnel and connect the divergence tunnel to the ground surface. Ground settlement is caused by excavation of the adjacent divergence tunnel. Therefore, predicting ground settlement using diverse variables is necessary before performing damage estimation. We used the volume loss and cover-tunnel diameter ratio as the variables in this study. Applying the ground settlement values to the settlement induction device, we measured the extent of damage to frame structures due to displacement at specific points. The vertical and horizontal displacements that occur at these points were measured using preattached LVDT (Linear variable differential transformer), and the lateral strain and angular distortion were calculated using these displacements. The lateral strain and angular distortion are key parameters for structural damage estimation. A damage assessment chart comprises the "Negligible", "Very Slight Damage", "Slight Damage", "Moderate to Severe Damage", and "Severe to Very Severe Damage" categories was developed. This table was applied to steel frame and concrete frame structures for comparison.

• The Transactions of the Korean Institute of Electrical Engineers P
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• v.56 no.2
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• pp.104-108
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• 2007

This paper deals with an approach to the reduction of potential rise according to the buried depth of structure. In order to analyze the surface potential rise of structure, an electrolytic tank which simulates the semi-infinite earth has been used. The potential rise has been measured and analyzed for types of structure using an electrolytic tank experimental apparatus in real time. The structure models were designed through reducing real buildings and fabricated with four types on a scale of one-one hundred sixty. When a test current flowed through structure models, potential gradient was the highest value in case of the outline frame type(structure model A). The distributions of surface potential rise are dependent on the resistivity and absorption percentage in concrete attached to structure model.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2016.10a
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• pp.132-133
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• 2016

This research team has developed single silk white bubble sheets to be used as surface sheath curing material for spring, summer, and autumn. But though its effects for spring and autumn temperature conditions have been proved, there haven't been any studies for summer temperature conditions. Therefore in this study, single silk white bubble sheets and single silk transparent bubble sheets as well as aluminum metalizing single silk bubble sheets have been applied to actual box-frame apartment slabs in construction, in order to compare temperature backgrounds of the concrete and other qualities. Upon application, the temperature of concrete cured in summer temperature conditions showed excellent scores, being the lowest for aluminum metalizing single silk white bubble sheets, then single silk transparent bubble sheets. But the aluminum metalizing single silk bubble sheet gave off a harmful glare, so for actual use, white single silk bubble sheets are recommended.

• Smart Structures and Systems
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• v.15 no.6
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• pp.1543-1567
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• 2015

In this study, a wireless crack sensor is developed for monitoring cracks propagating in two dimensions. This sensor is developed by incorporating a laser-based optical navigation sensor board (ADNS-9500) into a smart wireless platform (Imote2). To measure crack propagation, the Imote2 sends a signal to the ADNS-9500 to collect a sequence of images reflected from the concrete surface. These acquired images can be processed in the ADNS-9500 directly (the navigation mode) or sent to Imote2 for processing (the frame capture mode). The computed crack displacement can then be transmitted wirelessly to a base station. The design and the construction of this sensor are reported herein followed by some calibration tests on one prototype sensor. Test results show that the sensor can provide sub-millimeter accuracy under sinusoidal and step movement. Also, the two modes of operation offer complementary performance as the navigation mode is more accurate in tracking large amplitude and fast crack movement while the frame capture mode is more accurate for small and slow crack movement. These results illustrate the feasibility of developing such a crack sensor as well as point out directions of further research before its actual implementation.

• Steel and Composite Structures
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• v.20 no.2
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• pp.431-445
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• 2016

Seismic behavior of new composite structural system with a fabricated floor was studied. A two-bay and three-story structural model with the scale ratio of 1/4 was consequently designed. Based on the proposed model, multiple factors including energy dissipation capacity, stiffness degradation and deformation performance were analyzed through equivalent single degree of freedom pseudo-dynamic test with different earthquake levels. The results show that, structural integrity as well as the effective transmission of the horizontal force can be ensured by additional X bracing at the bottom of the rigidity of the floor without concrete topping. It is proved that the cast-in-place floor in areas with high seismic intensity can be replaced by the prefabricated floor without pouring surface layer. The results provide a reliable theoretical basis for the seismic design of the similar structural systems in engineering application.

• Journal of the Earthquake Engineering Society of Korea
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• v.28 no.3
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• pp.129-139
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• 2024

In this study, the SBC system, a new mechanical joint method, was developed to improve the constructability of precast concrete (PC) beam-column connections. The reliability of the finite element analysis model was verified through the comparison of experimental results and FEM analysis results. Recently, the intermediate moment frame, a seismic force resistance system, has served as a ramen structure that resists seismic force through beams and columns and has few load-bearing walls, so it is increasingly being applied to PC warehouses and PC factories with high loads and long spans. However, looking at the existing PC beam-column anchorage details, the wire, strand, and lower main bar are overlapped with the anchorage rebar at the end, so they do not satisfy the joint and anchorage requirements for reinforcing bars (KDS 41 17 00 9.3). Therefore, a mechanical joint method (SBC) was developed to meet the relevant standards and improve constructability. Tensile and bending experiments were conducted to examine structural performance, and a finite element analysis model was created. The load-displacement curve and failure pattern confirmed that both the experimental and analysis results were similar, and it was verified that a reliable finite element analysis model was built. In addition, bending tests showed that the larger the thickness of the bolt joint surface of the SBC, the better its structural performance. It was also determined that the system could improve energy dissipation ability and ductility through buckling and yielding occurring in the SBC.

• International conference on construction engineering and project management
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• 2013.01a
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• pp.553-557
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• 2013

Roof and exterior wall are designed and constructed in a manner that prevents the accumulation of water within the wall and roof assembly in the formal building. However, in a freeform building there is no clear distinction between exterior wall and roof. In other words, the exterior walls and roof systems of the freeform building are integrated as a surface, unlike the formal building envelope. Therefore, freeform architecture needs a systemized envelope design method to perform functions of exterior wall and roof. However, in many cases, construction methods for roof and exterior wall are applied to freeform buildings without necessary alterations, which lead to incomplete design, leakage, cracks and other problems. Freeform architecture is thus designed and constructed differently from formal buildings. In order to more easily and inexpensively actualize freeform architecture, Building Information Modeling (hereinafter referred to as BIM) has recently been applied in the construction industry. The studies and case analysis are not sufficient to identify the implications and contributions of freeform buildings in future similar projects. Therefore, this research will study design and construction methods for freeform surfaces. This study attempts to analyze the pros and cons of each method for the concrete surface frame, and then presents the panel options for envelope system of the freeform architecture.