Jaegyun Park

LOCAL COLLISION SIMULATION OF AN SC WALL USING ENERGY ABSORBING STEEL

This study evaluates the local damage of a turbine in an auxiliary building of a nuclear power plant due to an external impact by using the LS-DYNA finite element program. The wall of the auxiliary building is SC structure and the material of the SC wall plate is high manganese steel, which has superior ductility and energy absorbance compared to the ordinary steel used for other SC wall plates. The effects of the material of the wall, collision speed, and angle on the magnitude of the local damage were evaluated by local collision analysis. The analysis revealed that the SC wall made of manganese steel had significantly less damage than the SC wall made of ordinary steel. In conclusion, an SC wall made of manganese steel can have higher effective resistance than an SC wall made of ordinary steel against the local collision of an airplane engine or against a turbine impact.

STRUCTURAL TEST AND ANALYSIS OF RC SLAB AFTER FIRE LOADING

In the present study the behavior of fire and the residual strength of fire-ignited RC slabs are investigated by experimental tests and numerical simulations. The fire tests of RC slabs were carried out in a furnace using the ISO 834 standard fire. The load capacity of the cooled RC slabs that were not loaded during the fire tests was evaluated by additional 3 point bending tests. The influence of the proportion of PP (polypropylene) fibers in the RC slabs on the structural behavior of the RC slabs after the fire loading was investigated. The results of the fire tests showed that the maximum temperature of concrete with PP fiber was lower than that of concrete without PP fiber. As the concrete was heated, the ultimate compressive strength decreased and the ultimate strain increased. The load-deflection relations of RC slabs after fire loading were compared by using existing stress-strain-temperature models. The comparison between the numerical analysis and the experimental tests showed that some numerical analyses were reliable and therefore, can be applied to evaluate the ultimate load of RC slabs after fire loading. The ultimate load capacity after cooling down the RC slabs without PP fiber showed a considerable reduction from that of the RC slabs with PP fiber.

Analysis of soil-structure interaction considering complicated soil profile

The effect of soil-structure interaction (SSI) is an important consideration and cannot be neglected in the seismic design of structures on soft soil. Various methods have been developed to consider SSI effects and are currently being used. However, most of the approaches including a general finite element method cannot appropriately consider the properties and characteristics of the sites with complicated soil profiles. To overcome these difficulties, this paper presents soil-structure interaction analysis method, which can consider precisely complicated soil profiles by adopting an unaligned mesh generation approach. This approach has the advantages of rapid generation of structured internal meshes and leads to regular and precise stiffness matrix. The applicability of the proposed method is validated through several numerical examples and the influence of various properties and characteristics of soil sites on the response is investigated.

Structural Damping Effects on Stability of a Cantilever Column under Sub-tangentially Follower Force

A stability theory of a damped cantilever column under sub-tangential follower forces is first summarized based on the stability map. It is then demonstrated that internal and external damping can be exactly transformed to Rayleigh damping so that the damping coefficients can be effectively determined using proportional damping. Particularly a parametric study with variation of damping coefficients is performed in association with flutter loads of Beck column and it is shown that two damping coefficients can be correctly estimated for real systems under the assumption of Rayleigh damping. Finally a frequency equation of a cantilever beam subjected to both a sub-tangentially follower force and two kinds of damping forces is presented in the closed-form and its stability maps are constructed and compared with FE solutions in the practical range of damping coefficients.

Structural Damping Effects on Dynamic Instability of Subtangentially Loaded and Shear Deformable Beck’s Columns

A frequency equation of externally and internally damped and shear-flexible cantilever columns subjected to a subtangentially follower force is analytically derived in a dimensionless form with relation to the linear instability theory of Beck’s columns. Some parametric studies are then performed with variation of two damping coefficients under the assumption of Rayleigh damping. Based on the analysis results, it is demonstrated that three damping cases in association with flutter loads of Beck’s columns can be selected including one case representative of structural damping. Finally, stability maps of shear-flexible and damped Beck’s columns are constructed for the three damping cases and discussed in the practical range of damping coefficients and shear parameters. In addition, flutter loads and time history analysis results are presented using dimensionless FE analysis and compared with exact solutions.

A study on evaluation of the pipe wall decay constants of residual chlorine and affecting factors in reclaimed water supply system

AbstractWall decay reaction of residual chlorine in reclaimed water was evaluated through experiments using the PVC pipe reactor under the lab test conditions. As a result of evaluating the biofilm formation in the supply pipe of reclaimed water, it was confirmed that there were limitations to prevent reclaimed water supply system from the biofilm formation even though residual chlorine existed in reclaimed water. It was confirmed that biofilm was a dominant factor to increase the wall decay constants. The range of wall decay constants under the lab test conditions was within 0.012–0.20 m/d. It implies that wall decay constants showed great dependence on water temperature, initial chlorine concentration, and pipe diameter. Wall decay constants appeared to increase as water temperature increased. Wall decay constants were higher at lower initial chlorine concentration regardless of water temperature and pipe diameter. Depending on pipe diameter, the increased pipe diameter was led to the decreased wall dec...

Evaluation of seismic performance and effectiveness of multiple slim-type damper system for seismic response control of building structures.

This paper presents the evaluation of seismic performance and cost-effectiveness of a multiple slim-type damper system developed for the vibration control of earthquake excited buildings. The multiple slim-type damper (MSD) that consists of several small slim-type dampers and linkage units can control damping capacity easily by changing the number of small dampers. To evaluate the performance of the MSD, dynamic loading tests are performed with three slim-type dampers manufactured at a real scale. Numerical simulations are also carried out by nonlinear time history analysis with a ten-story earthquake excited building structure. The seismic performance and cost-effectiveness of the MSD system are investigated according to the various installation configurations of the MSD system. From the results of numerical simulation and cost-effectiveness evaluation, it is shown that combinations of the MSD systems can effectively improve the seismic performance of earthquake excited building structures.