• Proceedings of the Korea Concrete Institute Conference
• /
• 2000.10a
• /
• pp.697-700
• /
• 2000

Fatigue damage to reinforced concrete bridge decks have been found in many bridges. Failure mode of most reinforced concrete decks is caused by local punching shear rather than flexural moment due to cumulated damage. In this study, mechanical degradation of unstrengthened and strengthened bridge deck specimens is experimentally investigated. The unstrengthened deck specimens were damaged under the pulsating loading condition. After the test, deteriorated deck specimens were strengthened with Carbon Fiber Sheet, then loaded to observe the improvement of the fatigue behavior. It is shown that fatigue damaged specimens are similar to real bridge rather than static damaged specimens.

• Advances in Computational Design
• /
• v.8 no.1
• /
• pp.13-36
• /
• 2023

The Puebla-Morelos Earthquake (Mw 7.1) occurred in Mexico in 2017 causing 44 buildings to collapse in Mexico City. This work evaluates the non-linear response of a 6-story reinforced concrete (RC) frame prototype model with masonry infill walls on upper floors. The prototype model was designed using provisions prescribed before 1985 and was subjected to seismic excitations recorded during the earthquakes of 1985 and 2017 in different places in Mexico City. The building response was assessed through a damage index (DI) that considers low-cycle fatigue of the steel reinforcement in columns of the first floor, where the steel was modeled including buckling as was observed in cases after the 2017 earthquake. Isocurves were generated with 72 seismic records in Mexico City representing the level of iso-demand on the structure. These isocurves were compared with the location of 16 collapsed (first-floor column failure) building cases consistent with the prototype model. The isocurves for a value greater than 1 demarcate the location where fatigue failure was expected, which is consistent with the location of 2 of the 16 cases studied. However, a slight increase in axial load (5%) or decrease in column cross-section (5%) had a significant detrimental effect on the cumulated damage, increasing the intensity of the isocurves and achieving congruence with 9 of the 16 cases, and having the other 7 cases less than 2 km away. Including column special detailing (tight stirrup spacing and confined concrete) was the variable with the greatest impact to control the cumulated damage, which was consistent with the absence of severe damage in buildings built in the 70s and 80s.

• Structural Engineering and Mechanics
• /
• v.3 no.4
• /
• pp.341-358
• /
• 1995

The results of a series of ten W-shaped test specimens subjected to monotonic, quasi-static cyclic loading and fatigue type of loading in the form of constant amplitude tests are presented. The objectives were to assess and compare the rotation capacity and energy absorption of monotonically and cyclically loaded beams, and for the latter specimens to document the deterioration in the form of low cycle fatigue due to local buckling. In addition, strength and energy dissipation deterioration and damage models have been developed for the steel beam section under consideration. Finally, a generalized model which uses plate slenderness values and lateral slenderness is proposed for predicting rate in strength deterioration per reversal and cumulated damage after a given number of reversals.

• Earthquakes and Structures
• /
• v.7 no.5
• /
• pp.609-626
• /
• 2014

The capabilities of a high-resolution Digital Image Correlation (DIC) system are presented within the context of deformation measurements of full-scale concrete columns tested under reversed cyclic loading. The system was developed to have very high-resolution such that material strains on the order of the cracking stain of concrete could be measured on the surface of full-scale structural members. The high-resolution DIC system allows the measurement of a wide range of deformations and strains that could only be inferred or assumed previously. The DIC system is able to resolve the full profiles of member curvatures, rotations, plasticity spread, shear deformations, and bar-slip induced rotations. The system allows for automatic and objective measurement of crack widths and other damage indices that are indicative of cumulated damage and required repair time and cost. DIC damage measures contrast prevailing proxy damage indices based on member force-deformation data and subjective damage measures obtained using visual inspection. Data derived from high-resolution DIC systems is shown to be of great use in advancing the state of behavioral knowledge, calibrating behavioral and analytical models, and improving simulation accuracy.

• Journal of the Korea institute for structural maintenance and inspection
• /
• v.9 no.1
• /
• pp.243-250
• /
• 2005

In elevated irrigation aquaducts, one can observe a common damage pattern. That is, cracks, and crushing of concrete are usually repeated at a certain interval even if no faults are found in the design and construction of the structures. To investigate the causes of this damage, longitudinal deformations of several aquaducts have been measured. The analysis of the measured data suggests that the damages are mainly caused by cumulative repetition of extension and contraction due to temperature changes.

• Proceedings of the Korean Society of Precision Engineering Conference
• /
• 1996.11a
• /
• pp.913-920
• /
• 1996

In this study, the counting method for multi-axial and multi-point load states was proposed. Using this counting method, the load spectrum is generated from the service load history which is measured for boom structure of excavator. Loading state for loading points of boom structure is described as a multi-dimensional state space. From this load spectrum, the stress spectrum was generated by FEM analysis using the superposition of the unit load. The cumulated damage at the severe damage point of In nm structure by the failure example is calculated by Palmgren-Miner's rule. As a result of this study, the fatigue life estimation using the multi-axial and multi-point load counting method is useful.

• Journal of the Korean Recycled Construction Resources Institute
• /
• v.7 no.4
• /
• pp.438-444
• /
• 2019

In this study, the effect of polypropylene fiber on the freeze-thaw damage of mortar was evaluated experimentally. The effects of the reinforcing of polypropylene fiber on the compressive and bending performance of mortar after 300 cycles of freeze-thaw test were evaluated by comparing the normal mortar and the mortar with polyvinyl alcohol fiber. In addition, the mass loss, relative dynamic elastic modulus, and cumulated pore volume of mortar were measured by each cycle of freeze-thaw test. As a result, it was confirmed that the fiber reinforced mortar, regardless of the fiber type, was effective not only in maintaining the performance of the compressive strength and the bending strength but also suppressing the mass loss after the freeze-thaw test of 300 cycles. Meanwhile, it was confirmed that not only polyvinyl alcohol fibers but also polypropylene fibers can effectively act to suppress the damage of the mortar by freeze-thaw. However, in order to improve the freeze-thaw resistance of mortar mixed with polypropylene fiber, it is necessary to increase the bonding performance with the cement matrix which can be expected from polyvinyl alcohol fiber.

• Journal of Korean Society of Rural Planning
• /
• v.28 no.4
• /
• pp.93-104
• /
• 2022

Agriculture is one of the most vulnerable sector to droughts, and drought damage on the agriculture sector could have effects on other sector. Droughts have different characteristics compared to other extreme events, which means more sophisticated methods considering the characteristics of droughts are required when measuring their damage. The purpose of this study is to analyze the damage of droughts based on limited computational general equilibrium model. To be specific, we constructed a CGE model focusing on the agriculture sector in Korea. Also, to limit changes in land use and labor, we limited them, and assume droughts only have effects on productivity of value-added. Lastly, we simulate drought effects on rice production in Korea based on several climate scenarios and GCM to identify the economic effects of droughts. The results show that 1) the cumulated damage of droughts during 2021~2040 is higher than other periods (2040~2061, 2081~2100), 2) the correlation between the damage of droughts and SSP scenarios is insignificant. This result implies the necessity of the effective drought risk management to prevent future droughts effects, irrespective of mitigation policies. 3) Due to increases in rice price, GDP of rice sector is increased. However, GDP of the other sector and consumer welfare are decreased. This result show that indirect effects of droughts would be more important when measuring drought effects on agriculture sector.

• Journal of the Korean Operations Research and Management Science Society
• /
• v.30 no.2
• /
• pp.63-71
• /
• 2005

In the field of nuclear reactor safety study, common cause failures (CCFs) became significant contributors to system failure probability and core damage frequency in most Probabilistic risk assessments. However, it is hard to estimate the reliability of such a system, because of the dependency of components caused by CCFs. In order to analyze the system, we propose an analytic method that can find the parameters with lack of raw data. This study adopts the shock model in which the failure probability increases as the shock is cumulated. We use two-step Expectation and Maximization (EM) algorithm to find the unknown parameters. In order to verify the analysis result, we perform the simulation under same environment. This approach might be helpful to build the defensive strategy for the CCFs.

• Journal of Aquaculture
• /
• v.16 no.4
• /
• pp.223-228
• /
• 2003

An exfoliation, the detachment of juvenile abalones from a culture substrate, is essential for selection and population density control in abalone culture. Physical instruments and anesthetics are currently available for the exfoliation but the latter is regarded as more effective in reducing physical damage to the animals. In the present study, urea ($Co(NH_2)_2$), a chemical fertilizer, was selected as a anesthetic, and its optimal concentration and sea water temperature for exfoliation of Haliotis discus were determined in order to develop an exfoliation technique which is more economical and effective. A 97% cumulated exfoliation rate was observed within 3 min at all temperatures observed when the concentration rate of urea was 9∼15%. This range of urea concentration can be ideal for both exfoliation and recovery. Also it was found that the higher concentration of urea and temperature the higher exfoliation rate, however, these conditions reduced the recovery rates of the animals tested. These results could indicate that urea is a good tool for exfoliation of various species of young abalones, and urea could substitute for all techniques and anesthetics methods currently available for abalone exfoliation.