• Earthquakes and Structures
• /
• v.11 no.2
• /
• pp.217-243
• /
• 2016

The linear and nonlinear seismic responses of steel buildings with perimeter moment resisting frames and welded connections (WC) are estimated and compared with those of buildings with post-tensioned connections (PC). Two-dimensional (2D) and three-dimensional (3D) structural representations of the buildings as well as global and local response parameters are considered. The seismic responses and structural damage of steel buildings with PC may be significantly smaller than those of the buildings with typical WC. The reasons for this are that the PC buildings dissipate more hysteretic energy and attract smaller inertia forces. The response reduction is larger for global than for local response parameters. The reduction may significantly vary from one structural representation to another. One of the main reasons for this is that the energy dissipation characteristics are quite different for the 2D and 3D models. In addition, in the case of the 3D models, the contribution of each horizontal component to the axial load on an specific column may be in phase each other during some intervals of time, but for some others they may be out of phase. It is not possible to observe this effect on the 2D structural formulation. The implication of this is that 3D structural representation should be used while estimating the effect of the PC on the structural response. Thus, steel frames with post-tensioned bolted connections are a viable option in high seismicity areas due to the fact that brittle failure is prevented and also because of their reduced response and self-centering capacity.

• Journal of the Korea Concrete Institute
• /
• v.23 no.2
• /
• pp.235-244
• /
• 2011

Failures of segmental bridges have been attributed to the inadequate joint connection techniques, which led to corrosion of the post-tensioned tendons connecting the segmental joints. The principal objective of this study is to evaluate the performances of the in-situ cast joint and epoxy applied shear key joints as a function of shear and ultimate strengths. Furthermore, shear behavior and strength of shear key joints in ultra high performance precasted concrete segmental bridges are experimentally evaluated to understand its shear failure behavior. The test parameters of shear key shape and type, load-displacement relations, cracking behavior, concrete strength, and fracture modes are considered in the study. Also, several parameters which influence the mechanical behavior of the shear key joint are analyzed. Based on the study results, the optimal shear key shape and joint type are proposed for the joint design and analysis guidelines.

• Journal of the Korean Recycled Construction Resources Institute
• /
• v.4 no.3
• /
• pp.259-268
• /
• 2016

The service life evaluation in RC(Reinforced Concrete) structure exposed to chloride attack can be classified into deterministic and probabilistic method, and it significantly varies with design parameters. The present work derives PDF (Probability of Durability Failure) and the related service life considering time-dependent diffusion coefficient and internal parameters such as reference diffusion coefficient, critical chloride content, and time-exponent. When critical chloride content increases to 133.3%, the changing ratios of service life are 134.0~145.4% for deterministic method and 149.2%~152.5% for probabilistic method, respectively. In the case of increasing time-exponent to 200%, they increase to 323.8% for deterministic method and 346.0% for probabilistic method. Through adopting time-diffusion coefficient for probabilistic method, reasonable service life evaluation can be achieved, and it is also verified that increasing time-exponent through mineral admixture is very effective to extension of service life in RC structure.

• The korean journal of orthodontics
• /
• v.50 no.6
• /
• pp.373-382
• /
• 2020

Objective: To compare computer-aided design and computer-aided manufacturing (CAD/CAM) customized nitinol retainers with standard stainless-steel fixed retainers over a 12-month study period. Methods: This randomized controlled trial (RCT) was conducted on 62 patients randomly allocated to a control group that received stainless-steel retainers or a test group that received customized CAD/CAM nickel-titanium retainers. Four time points were defined: retainer placement (T0) and 1-month (T1), 6-month (T2), and 12-month (T3) follow-up appointments. At each time point, Little's irregularity index (LII) (primary endpoint) and dental stability measurements such as intercanine width were recorded in addition to assessment of periodontal parameters. Radiological measurements such as the incisor mandibular plane angle (IMPA) were recorded at T0 and T3. Failure events (wire integrity or debonding) were assessed at each time point. Results: From T0 to T3, LII and other dental measurements showed no significant differences between the two groups. The data for periodontal parameters remained stable over the study period, except for the gingival index, which was slightly, but significantly, higher in the test group at T3 (p = 0.039). The IMPA angle showed no intergroup difference. The two groups showed no significant difference in debonding events. Conclusions: This RCT conducted over a 12-month period demonstrated no significant difference between customized CAD/CAM nickel-titanium lingual retainers and standard stainless-steel lingual retainers in terms of dental anterior stability and retainer survival. Both retainers eventually appeared to be equally effective in maintaining periodontal health.

• The Journal of Engineering Geology
• /
• v.21 no.3
• /
• pp.247-257
• /
• 2011

In this study the infinite slope model, one of the physical landslide models has been suggested to evaluate the susceptibility of the landslide. However, applying the infinite slope model in regional study area can be difficult or impossible because of the difficulties in obtaining and processing of large spatial data sets. With limited site investigation data, uncertainties were inevitably involved with. Therefore, the probabilistic analysis method such as Monte Carlo simulation and the GIS based infinite slope stability model have been used to evaluate the probability of failure. The proposed approach has been applied to practical example. The study area in Boeun area been selected since the area has been experienced tremendous amount of landslide occurrence. The geometric characteristics of the slope and the mechanical properties of soils like to friction angle and cohesion were obtained. In addition, coefficient of variation (COV) values in the uncertain parameters were varied from 10% to 30% in order to evaluate the effect of the uncertainty. The analysis results showed that the probabilistic analysis method can reduce the effect of uncertainty involved in input parameters.

• Structural Engineering and Mechanics
• /
• v.67 no.4
• /
• pp.347-358
• /
• 2018

The main aim of this research was to investigate the shear strength of non-prismatic steel fiber reinforced concrete beams under monotonic loading considering different parameters. Experimental program included tests on fifteen non-prismatic reinforced concrete beams divided into three groups. For the first and the second groups, different parameters were taken into consideration which are: steel fibers content, shear span to minimum depth ratio ($a/d_{min}$) and tapering angle (${\alpha}$). The third group was designed mainly to optimize the geometry of the non-prismatic concrete beams with the same concrete volume while the steel fiber ratio and the shear span were left constant in this group. The presence of steel fibers in concrete led to an increase in the load-carrying capacity in a range of 10.25%-103%. Also, the energy absorption capacity was increased due to the addition of steel fibers in a range of 18.17%-993.18% and the failure mode was changed from brittle to ductile. Tapering angle had a clear effect on the shear strength of test specimens. The increase in tapering angle from ($7^{\circ}$) to ($12^{\circ}$) caused an increase in the ultimate shear capacity for the test specimens. The maximum increase in ultimate load was 45.49%. The addition of steel fibers had a significant impact on the post-cracking behavior of the test specimens. Empirical equation for shear strength prediction at cracking limit state was proposed. The predicted cracking shear strength was in good agreement with the experimental findings.

• Journal of the Korean Society of Hazard Mitigation
• /
• v.10 no.4
• /
• pp.17-24
• /
• 2010

The hollow RC(Reinforced concrete) pier has the merit of lightweight pier compared with solid RC pier. However, the hollow RC pier shows a low ductile behavior due to brittle failure of inside concrete. To overcome this problem, the internally confined hollow reinforced concrete column has been developed. In this study, the behavior of internally confined hollow RC piers were evaluated with safety ratio, ductility, total material cost, the total weight of the pier, etc. The chosen parameters for the study are hollow ratio, thickness of internal steel tube, intervals between vertical re-bars, numbers of horizontal re-bars, and strength of concrete. As a result of parameters study, the usage of a minimum necessary thickness of the internal steel tube is the most effective.

• Journal of Applied Reliability
• /
• v.14 no.2
• /
• pp.129-136
• /
• 2014

Reliability test is focusing to detect the unexpected reliability failure and solve them for the high quality of products. The test data should be used to assess and project the current level of interesting product reliability and so it is very important to have the accurately assessing methodology with test data. There are two type of trend for test data as constant and changing one during testing and this paper shows the difference in the assessing results of these two cases. There is less information how to define the existence of reliability growth rate changing and calculate the parameters of the reliability growth models to make an accurate assessment with such condition, so i established the process and mathematical model to calculate the parameters at such condition to make reliability growth curve with high Goodness of Fit. I validated the new method with the data made from Monte Carlo Simulation and case from Demko (1993). Even the assessed result with the new methodology may be different with the case by case because of very diversity in test condition and testing product quality, but the process and method founded in this research can be applied to any case using Duane and AMSAA model for their test data assessment. I also present the evaluation method to see the effectiveness with new one which is a conventional knowledge and not popular to use, so it is possible to compare the results with the newly presented and conventional method for better business decision.

• Structural Engineering and Mechanics
• /
• v.5 no.5
• /
• pp.507-521
• /
• 1997

The ultimate behavior of a reinforced concrete hyperbolic paraboloid saddle shell under uniformly distributed vertical load is investigated using an inelastic, large displacement finite-element program originally developed at North Carolina State University. Unlike with the author's previous study which shows that the saddle shell possesses a tremendous capacity to redistribute the stresses, introducing tension stiffening in the model the cracks developed are no longer through cracks and formed as primarily bending cracks. Even though with small tension stiffening effect, the behavior of the shell is changed markedly from the one without tension stiffening effect. The load-deflection curves are straight and the slope of the curves is quite steep and remains unchanged with varying the tension stiffening parameters. The failure of the shell took place quite suddenly in a cantilever mode initiated by a formation of yield lines in a direction parallel to the support-to-support diagonal. The higher the tension stiffening parameters the higher is the ultimate load. The present study shows that the ultimate behavior of the shell primarily depends on the concrete tensile characteristics, such as tensile strength (before cracking) and the effective tension stiffening (after cracking). As the concrete characteristics would vary over the life of the shell, a degree of uncertainty is involved in deciding a specified ultimate strength of the saddle shell studied. By the present study, however, the overload factors based on ACI 318-95 are larger than unity for all the cases studied except that the tension stiffening parameter is weak by 3 with and without the large displacement effect, which shows that the Lin-Scordelis saddle shell studied here is at least safe.

• Journal of the Earthquake Engineering Society of Korea
• /
• v.6 no.3
• /
• pp.1-10
• /
• 2002

A series of unreinforced masonry(URM) walls were analytically investigated by FEM for a limited version of seismic in-plane performance. For this, URM walls were assumed to be continum and modeled as isotropic plane stress elements, within which the nature of cracking was propogated. Accordingly, behavioral mode of cracking in URM was modeled by smeared-crack approach. Total of 70 cases were considered for various parameters such as axial load ratio, aspect ratio and effective section area ratio due to the existence of opening, etc. The analysis results indicate that these parameters significantly and interactively influence over the ultimate strength of URM walls. Finally, it is suggested that the response modification factor for URM adopted in the current Korean Standard should be validated considering various forms of brittleness and probable failure modes in URM.