• Structural Engineering and Mechanics
• /
• v.83 no.5
• /
• pp.627-644
• /
• 2022

In past major earthquakes (1994 Northridge, 1995 Kobe, Chi-Chi 1999, Kocaeli 1999), significant damages occurred in the liquid storage tanks. The basic failure patterns were observed to be the buckling of the tank wall and uplift of the anchorage system. The damages in the industrial facilities and nuclear power plants have caused the spread of toxic substances to the environment and significant fires. Seismic isolation can be used in liquid storage tanks to decouple the structure and decrease the structural demand in the superstructure in case of ground shaking. Previous studies on the use of seismic isolation systems on liquid storage tanks show that an isolation system reduces the impulsive response but might slightly increase the convective one. There is still a lack of understanding of the seismic response of seismically isolated liquid storage tanks considering the fluid-structure interaction. In this study, one broad tank, one medium tank, and one slender tank are selected and designed. Two- and three-dimensional elastomeric bearings are used as seismic isolation systems. The seismic performance of the tanks is then investigated through nonlinear dynamic time-history analyses. The effectiveness of each seismic isolation system on tanks' performance was investigated. Isolator tension forces, modal analysis results, hydrodynamic stresses, strains, sloshing heights and base shear forces of the tanks are compared. The results show that the total base shear is lower in 3D-isolators compared to 2D-isolators. Even though the tank wall stresses, and strains are slightly higher in 3D-isolators, they are more efficient to prevent the tension problem.

• Structural Engineering and Mechanics
• /
• v.39 no.3
• /
• pp.427-447
• /
• 2011

The progressive collapse phenomenon is generally regarded as dynamic. Due to the impracticality of nonlinear dynamic computations for practitioners, an interest arises for the development of equivalent static pushover procedures. The present paper proposes a methodology to identify such a procedure for sudden column removals, using energetic evaluations to determine the pushover loads to apply. In a dynamic context, equality between the cumulated external and internal works indicates a vanishing kinetic energy. If such a state is reached, the structure is sometimes assumed able to withstand the column removal. Approximations of these works can be estimated using a static computation, leading to an estimate of the displacements at the zero kinetic energy configuration. In comparison with other available procedures based on such criteria, the present contribution identifies loading patterns to associate with the zero-kinetic energy criterion to avoid a single-degree-of-freedom idealisation. A parametric study over a family of regular steel structures of varying sizes uses non-linear dynamic computations to assess the proposed pushover loading pattern for the cases of central and lateral ground floor column failure. The identified quasi-static loading schemes are shown to allow detecting nearly all dynamically detected plastic hinges, so that the various beams are provided with sufficient resistance during the design process. A proper accuracy is obtained for the plastic rotations of the most plastified hinges almost independently of the design parameters (loads, geometry, robustness), indicating that the methodology could be extended to provide estimates of the required ductility for the beams, columns, and beam-column connections.

• Structural Engineering and Mechanics
• /
• v.60 no.4
• /
• pp.567-594
• /
• 2016

The main objective of the current research is estimating the flexural behavior of ferrocement Ribbed Plates reinforced with composite material. Experimental investigation was carried out on fifteen plates; their dimensions were kept constant at 1200 mm in length, 600 mm width and 100 mm thick but with different volume fraction of steel reinforcement and number of ribs. Test specimens were tested until failure under three line loadings with simply supported conditions over a span of 1100 mm. Cracking patterns, tensile and compressive strains, deformation characteristics, ductility ratio, and energy absorption properties were observed and measured at all stages of loadings. Experimental results were compared to analytical models using ANSYS 10 program. Parametric study is presented to look at the variables that can mainly affect the mechanical behaviors of the model such as the change of plate length. The results showed that the ultimate strength, ductility ratio and energy absorption properties of the proposed ribbed plates are affected by the volume fraction and the type of reinforcement, and also proved the effectiveness of expanded metal mesh and woven steel mesh in reinforcing the ribbed ferrocement plates. In addition, the developed ribbed ferrocement plates have high strength, ductility ratio and energy absorption properties and are lighter in weight compared to the conventional RC ribbed plates, which could be useful for developed and developing countries alike. The Finite Element (FE) simulations gave good results comparing with the experimental results.

• The Journal of Advanced Prosthodontics
• /
• v.12 no.4
• /
• pp.218-224
• /
• 2020

PURPOSE. The objectives of this study were to evaluate the fracture strength and fracture patterns of provisional crowns fabricated from different materials and techniques after receiving stress from a simulated oral condition. MATERIALS AND METHODS. A monomethacrylate-based resin (Unifast Trad) and a bis-acryl-based (Protemp 4) resin were used to fabricate provisional crowns using conventional direct technique. A milled monomethacrylate resin (Brylic Solid) and a 3D-printed bis-acrylate resin (Freeprint Temp) were chosen to fabricate provisional crowns using the CAD/CAM process. All cemented provisional crowns (n=10/group) were subjected to thermal cycling (5,000 cycles at 5°-55℃) and cyclic occlusal load (100 N at 4 Hz for 100,000 cycles). Maximum force at fracture was tested using a universal testing machine. RESULTS. Maximum force at fracture (mean ± SD, N) of each group was 657.87 ± 82.84 for Unifast Trad, 1125.94 ± 168.07 for Protemp4, 953.60 ± 58.88 for Brylic Solid, and 1004.19 ± 122.18 for Freeprint Temp. One-way ANOVA with Tamhane post hoc test showed that the fracture strength of Unifast Trad was statistically significantly lower than others (P<.01). No statistically significant difference was noted among other groups. For failure pattern analysis, Unifast Trad and Brylic Solid showed less damage than Protemp 4 and Freeprint Temp groups. CONCLUSION. Provisional crowns fabricated using the CAD/CAM process and the conventionally fabricated bis-acryl resins exhibited significant higher fracture strength compared to conventionally fabricated monomethacrylate resins after the aging regimen. Therefore, CAD/CAM milling and 3D printing of provisional restorations may be good alternatives for long term provisionalization.

• International Journal of Fluid Machinery and Systems
• /
• v.10 no.3
• /
• pp.287-295
• /
• 2017

The most detrimental pressure pulsations in high-head pump-turbines is caused by the rotor-stator interaction (RSI) between the guide vanes and runner blades. When the pump-turbine operates in the S-shaped region of the characteristic curves, the deteriorative flow structures may significantly strengthen RSI, causing larger pressure pulsations and stronger vibration with an increased risk of mechanical failure. CFD simulations were carried out to analyze the impacts of flow evolution on the pressure pulsations in the S-shaped region of a model pump-turbine. The results show that the reverse flow vortex structures (RFVS) at the runner inlet have regular development and transition patterns when discharge reduces from the best efficiency point (BEP). The RFVS first occur at the hub side, and then shift to the mid-span near the no-load point, which cause the strongest pressure pulsations. The locally distributed RFVS at hub side enhance the local RSI and makes the pressure fluctuations at the corresponding sections stronger than those at the rest sections along the spanwise direction. Under the condition of RFVS at the mid-span, the smaller flow rate make the smaller difference of pressure pulsation amplitudes in the spanwise direction. Moreover, the rotating stall, rotating at 35.7%-62.5% of the runner rotational frequency, make the low frequency components of pressure pulsations distribute unevenly along the circumference in the vaneless space. However, it have little influence on the distributions of high components.

• Proceedings of the Korea Concrete Institute Conference
• /
• 2008.04a
• /
• pp.317-320
• /
• 2008

These days, the amount of waste concrete has been increasing due to reconstruction and redevelopment. So, the use of recycled aggregates is recommended to solve environmental problems. Some investigations have been carried out to study the flexural behavior of reinforced concrete beams with recycled aggregates. But these have some limitation due to the use of low quality recycled aggregates and small-scale specimens in the laboratory. The purpose of this experimental study is to evaluate flexural behavior of RC beam with recycled fine aggregates. Three RC beams were manufactured with different replacement level of recycled fine aggregates. From the test results, the flexural behavior of the beam is described in terms of crack patterns and failure modes. And the flexural strength of RC beam with different types of recycled fine aggregates is compared with the provision of KCI code.

• Journal of Korean Dental Science
• /
• v.12 no.1
• /
• pp.29-37
• /
• 2019

Purpose: This study was aimed to compare the survival and success rates, and long-term crestal bone loss according to the use of 2 connection types of dental implants (submerged-USII and non-submerged-SSII; Osstem $Implant^{(R)}$) by analyzing the change in alveolar bone height after 1 year under load and during final follow-up period. Materials and Methods: Between December 2004 and August 2008, patients with two types of Osstem implants (USII and SSII) were retrieved retrospectively. A total of 92 patients with 284 implants (USII=60, SSII=224) was finally selected. Their mean follow-up period was 7.5 years. The mesial and distal alveolar crestal bone changes were measured using radiographic images and the average was calculated at 1 year after loading and during final follow-up period. Result: Among the 284 implants, 4 USII and 7 SSII implants were removed, indicating 93.3% and 96.9% survival rates. Of the survived implants, mean crestal bone loss 1 year after loading was 0.39 mm for USII and 0.19 mm for SSII (P=0.018). During the final follow-up, mean crestal bone loss was 0.63 mm and 0.35 mm for USII and SSII, respectively, without statistical significance (P=0.092). According to the criteria for the success and failure of the implant by Albreksson and colleagues, final success rate was estimated as 86.7% for USII and 91.5% for SSII, respectively. Conclusion At 1 year after loading, the average crestal bone loss was significantly different between USII and SSII; however, both types met the criteria for implant success. During the final follow-up, both groups showed insignificant bone resorption patterns and did not show any pathological clinical symptoms. Therefore, both implants exhibited high long-term stability.

• Journal of Radiation Protection and Research
• /
• v.44 no.3
• /
• pp.97-102
• /
• 2019

Background: Dose rate meters are the most widely used, and perhaps one of the most important tools for the measurement of ionising radiation. They are often the first, or only, device available to a user for an instant check of radiation dose at a certain location. Throughout the world, radiation safety practices rely strongly on the output of these dose rate meters. But how well do we know the quality of their output? Materials and Methods: This review is based on the measurements 1,158 commercially available dose rate meters of 116 different makes and models. Expected versus the displayed dose patterns and consistency was checked at various dose rates between $5{\mu}Gy{\cdot}h^{-1}$ and $2mGy{\cdot}h^{-1}$. Samples of these meters were then selected for further investigation and were exposed to radiation sources covering photon energies from 50 keV to 1.5 MeV. The effect of detector orientation on its reading was also investigated. Rather than focusing on the angular response distribution that is often reported by the manufacturer of the device, this study focussed on the design ergonomics i.e. the angles that the operator will realistically use to measure a dose rate. Results and Discussion: This review shows the scope and boundaries of the ionising radiation dose rate estimations that are made using commonly available meters. Observations showed both inter and intra make and model variations, occasional cases of instrument failure, instrument walk away, and erroneous response. Conclusion: The results indicate the significance of selecting and maintaining suitable monitors for specific applications in radiation safety.

• The Journal of Advanced Prosthodontics
• /
• v.13 no.3
• /
• pp.180-190
• /
• 2021

Purpose. This study aimed to assess the influence of various micromechanical surface conditioning (MSC) strategies with or without coupling agent (silane) application on the micro-shear bond strength (µSBS) of resin- matrix ceramics (RMCs). Materials and Methods. GC Cerasmart (GC), Lava Ultimate (LU), Vita Enamic (VE), Voco Grandio (VG), and Brilliant Crios (BC) were cut into 1.0-mm-thick slices (n = 32 per RMC) and separated into four groups according to the MSC strategy applied: control-no conditioning (C), air-borne particle abrasion with aluminum oxide particles (APA), 2W- and 3W-Er,Cr:YSGG group coding is missing. The specimens in each group were further separated into silane-applied and silane-free subgroups. Each specimen received two resin cement microtubules (n = 8 per subgroup). A shear force was applied to the adhesive interface through a universal test machine and µSBS values were measured. Data were statistically analyzed by using 3-way ANOVA and Tukey HSD test. Failure patterns were scrutinized under stereomicroscope. Results. RMC material type, MSC strategy, and silanization influenced the µSBS values (P<.05). In comparison to the control group, µSBS values increased after all other MSC strategies (P<.05) while the differences among these strategies were insignificant (P>.05). For control and APA, there were insignificant differences between RMCs (P>.05). The silanization decreased µSBS values of RMCs except for VE. Considerable declines were observed in GC and BC (P<.05). Conclusion. MSC strategies can enhance bond strength values at the RMC - cement interface. However, the choice of MSC strategy is dependent on RMC material type and each RMC can require a dedicated way of conditioning.

• Computers and Concrete
• /
• v.31 no.5
• /
• pp.405-417
• /
• 2023

The submerged floating tunnel (SFT) is tethered by mooring lines anchored to the seabed, therefore, the structural integrity of the anchor should be sensitively managed. Despite their importance, reaction forces cannot be simply measured by attaching sensors or load cells because of the structural and environmental characteristics of the submerged structure. Therefore, we propose an effective method for estimating the reaction forces at the seabed anchor of a submerged floating tunnel using a structural pattern model. First, a structural pattern model is established to use the correlation between tunnel motion and anchor reactions via a deep learning algorithm. Once the pattern model is established, it is directly used to estimate the reaction forces by inputting the tunnel motion data, which can be directly measured inside the tunnel. Because the sequential characteristics of responses in the time domain should be considered, the long short-term memory (LSTM) algorithm is mainly used to recognize structural behavioral patterns. Using hydrodynamics-based simulations, big data on the structural behavior of the SFT under various waves were generated, and the prepared datasets were used to validate the proposed method. The simulation-based validation results clearly show that the proposed method can precisely estimate time-series reactions using only acceleration data. In addition to real-time structural health monitoring, the proposed method can be useful for forensics when an unexpected accident or failure is related to the seabed anchors of the SFT.