Earticle

An empirical formula proposed by Petersson and Plunt(PP's formula) and finite element analysis for impedance calculation of ship equipment foundations are investigated by comparing the analysis results with those of experimental results. The PP's formula well estimates resonant frequency of the foundations and impedance level except around the resonant region although the impedance level around the resonant frequency is heavily dependent upon the assumed loss factor. The results show that the PP's formula and finite element models can be complementarily used to estimate the impedance characteristics of various types of foundation of ships in design stage.

Railway bridge is the most problematic thing in the railway is due to noise and vibration. To solve these problems, there have been studies. However, a fundamental alternative to the noise and vibration. It has not so far not shown, and to minimize the problem is focused. As a result, developed a lot of noise reduction measures, but the vibration is not much for reduction. In this study, to support the superstructure of the bridge vibration possible for spherical elastomeric bearing is a technical review. And it applies to the railway bridge, the numerical analysis was carried out.

This paper studies the finite element modeling and analytical parameters for the numerical evaluation of dynamic stiffness of large foundation for shipboard equipments such as marine diesel engine. For the purpose, numerical method and procedure to evaluate the dynamic stiffness are established based on the impact test method, which are applied for the dynamic stiffness evaluation of a real diesel generator foundation of ship. Numerical investigations compared with the measured data are carried out to evaluate the effects of modeling ranges of ship substructure, finite element sizes, lower support structures and damping coefficients. From the results, modeling and analytical parameters for proper evaluation of dynamic stiffness of large foundation of shipboard equipment are suggested.

내진기술의 한 방안으로서 지진격리받침을 설치하여 지진력을 감소시키고, 지진피해를 최소화하고자 하는 연구가 계속되고 있다. 이와 같은 지진격리시스템의 설계 및 시공을 위해서는 먼저 지진격리받침의 제작시 지진격리받침의 균일한 품질유지 및 내진에 대한 성능검증이 뒤따라야 한다. 이를 위해 본 연구에서는 지진격리받침인 납-적층고무받침(LRB)와 적층고무받침(RB)의 전단특성 평가시험을 실시하였으며. 온도변화에 따른 전단특성 변화를 파악하기 위해 온도의존성 시험도 실시하였다. 시험후 측정값을 설계 기준값과 비교하여 전단성능에서의 오차를 조사하고, 이를 도로교 설계기준의 허용한계와 비교 분석하였다. 시험결과 지진격리받침의 상당수가 도로교 설계기준의 허용한계를 넘거나 근접해 있는 것으로 나타났다. 그리고 공용중에 전단특성을 변화시키는 온도변화에 의한 영향도 매우 큰 것으로 파악되었는데, 제작 초기의 품질오차가 이런 영향과 중첩된다면 처음 설계값보다 50% 이상 큰 전단강성 변화를 보일 가능성도 있는 것으로 나타났다.

Seismic isolation has been studied continuously as a solution of the seismic engineering to reduce the sectional forces and the damages of structures caused by earthquakes. To certify reliable design and installation of the seismic isolation systems, seismic isolation bearings should be fabricated under well planned quality control process, and proper evaluation tests for their seismic performance should be followed. In this study, shear property evaluation tests for the lead rubber bearings(LRB) and the rubber bearings(RB) were implemented and the temperature dependency tests were also implemented to evaluate the changes of shear properties according to the changes of temperature. After evaluation tests, the measured shear properties were compared to their design values and their deviation was analyzed comparing with the allowable error ranges specified in Highway Bridge Design Specifications. These results showed that a considerable number of isolation bearings have so large deviations from their design values that their error ranges were over or very close to the allowable ranges. And the test results for temperature dependency showed that the shear properties of isolation bearings would be changed in great degree by the change of temperature during their service period. If these two types of changes in their shear properties are superposed, it would possible that the changes of shear properties from their original design values are over than 50%.

This paper deals with the structural vibration characteristics for an outdoor units support of an air-conditioner. Even though main noise sources are compressor noise and fluid noise which is caused by the fan, the structural modification of the outdoor units support may affect vibration and noise. In this paper, damping ratios for two kinds of an outdoor units support of an air-conditioner are measured through the modal testing. In order to reduce the structural borne noise due to an outdoor units support of an air-conditioner, four kinds of rubber materials are selected and tested.

The purpose of seismic isolation system among them is to lengthen the period of structure and make its period shift from the dominant period of earthquake. In this study, the seismic behavior of arch structure with lead rubber bearing(LRB) and friction pendulum system(FPS) is analyzed. The arch structure is the simplest structure and has the basic dynamic characteristics among large spatial structures. Also, Large spatial structures have large vertical response by horizontal seismic vibration, unlike seismic behavior of normal rahmen structures. When horizontal seismic load is applied to the large spatial structure with isolation systems, the horizontal acceleration response of the large spatial structure is reduced and the vertical seismic response is remarkably reduced.

In this paper, impedance of the chiller foundation for ships is studied by using FEM and prediction is compared to measurements. Small and medium weight hammer are used to cover high and low frequency ranges in impedance measurements. Comparison shows that measurement and prediction is in good agreement in which coherence is higher than 0.98 for the frequency ranges of 40-50 Hz to 1600 -2000 Hz.

Non-contact underwater explosions against surface ships could cause extensive equipment damage and render the ship inoperative. As an analytical method, DDAM(dynamic design and analysis method) is used for ship shock design. In this paper, in order to verify the finite element model of large shipboard equipment, modal test of equipment was performed. Major objective of this paper is to describe shock analysis methodology for large shipboard equipment attacked to the top and bottom foundations.

본 연구에서는 교량의 내진보강을 위하여 기존 교량에 지진격리장치를 추가하는 접근법을 제안하였다. 기존 받침을 지진 격리받침으로 완전히 대체하는 접근법도 이미 제안되어 있지만 본 연구에서는 경제성과 안전성을 고려하여 기존 받침을 제거하지 않고 활용하도록 하였다. 이는 지진격리받침이 상부 수직하중을 분담하지 않고, 수평방향의 지진운동에 대한 주기 이동과 감쇠 역할만 한다. 이 접근법의 실험적 검증을 위해 실제 교량을 대상으로 납-적층고무받침(LRB)을 설계하고 실물크기로 기존 받침과 LRB를 제작하였다. 이 지진격리시스템의 가상 지진입력에 대한 응답은 유사동적실험으로 구하였다. 아울러 범용해석프로그램을 통한 지진응답해석과 비교하여 실험결과의 신뢰성을 확인하였다. 실험결과 제안된 지진격리시스템은 지진시 안정적인 거동을 보였다.

In this study, an approach that installs seismic isolation bearings was proposed for the seismic retrofit of the existing bridges. The method that replaces all existing bearings with seismic isolators was proposed already. However, in this study, we recommend to utilize the existing bearings for the benefit of safety and cost. According to our proposal, the seismic isolators do not support vertical loads but they Just function as the period shifter and the horizontal damper. To verify this approach experimentally, the real scale bearings and lead rubber bearings far the real highway bridges were designed and fabricated. And the responses of this isolated bridges to the assumed earthquakes were determined by the pseudo dynamic test scheme. The test results were also compared to the responses computed by the well known structural analysis software to check the reliability of the test. From the test results, we found that the retrofitted bridges using the proposed method showed stable performances under earthquakes.

도로교의 내진설계기준이 국내에 도입되어 적용된 것은 10여년에 불과하므로 아직 많은 교량에 내진성능 보강이 필요하다. 본 논문에서는 받침이 노후된 교량의 내진성능 보강방법으로서 적층고무받침으로 교체하는 방법의 타당성에 관하여 논하였다. 이를 위하여 내진상세가 없는 실물크기 RC교각 시험체를 제작하고 POT받침, 적층고무받침(RB), 납-적층고무받침(LRB)를 각각 설치하였다. 유사동적 실험을 통하여 이들 시험체의 지진시 거동을 모사하고 성능을 비교하였다. 실험결과로부터 제안된 내진보강기법의 타당성을 확인하였다.

Many highway bridges in Korea need seismic retrofit because only one decade has passed since the seismic design criteria was introduced. For the highway bridges of which bearings are worn and dysfunctional, the validity of seismic retrofit method using laminated rubber bearings was discussed in this study. Real scale RC pier specimens without seismic details were constructed. And then, Pot bearing, Rubber bearing (RB), Lead-rubber bearing (LRB) were applied to these specimens. Through pseudo dynamic test method, dynamic behavior of these RC piers under earthquake was simulated and compared. From the test results, proposed seismic retrofit method was found to be valid.

This study discussed the effect on rail's axial force due to thermal and seismic loads according to supporting conditions of railway bridges; the considered supporting conditions are 1)simply supported, 2)roller at both ends, and 3)roller with horizontal spring at both ends. Closed form solutions are used to calculate the axial farces on rails. The roller at both ends of a bridge span decreases the compressive axial force on rail due to thermal load compared with the simply supported condition. However, the lateral springs at roller are not helpful to decrease the rail's compressive axial force.

이 연구는 적층고무받침을 사용한 철근콘크리트 교각의 내진 성능평가를 하는데 그 목적이 있다. 사용된 프로그램은 철근콘크리트 구조물의 해석을 위한 RCAHEST이다. 재료적 비선형성에 대해서는 균열콘크리트에 대한 인장, 압축, 전단모델과 콘크리트 속에 있는 철근모델을 조합하여 고려하였다. 이에 대한 콘크리트의 균열모델로서는 분산균열모델을 사용하였으며 적층고무받침의 거동을 예측하기 위해서 지진격리요소를 개발하였다. 이 연구에서는 적층고무받침을 사용한 철근 콘크리트 교각의 내진 성능평가를 위해 제안한 해석기법을 신뢰성 있는 연구자의 실험결과와 비교하여 그 타당성을 검증하였다.

The purpose of this study is to evaluate seismic performance of reinforced concrete bridge piers supported by laminated rubber bearings. A computer program, named RCAHEST(Reinforced Concrete Analysis in Higher Evaluation System Technology), for the analysis of reinforced concrete structures was used. Material nonlinearity is taken into account by comprising tensile, compressive and shear models of cracked concrete and a model of reinforcing steel. The smeared crack approach is incorporated. Seismic isolator element is developed to predict behaviors of laminated rubber bearings. The proposed numerical method for seismic performance evaluation of reinforced concrete bridge piers supported by laminated rubber bearings is verified by comparison with reliable experimental results.

This paper presents the LRB-based hybrid base isolation system employing additional semiactive control devices for seismic protection of cable-stayed bridges by examining the ASCE first generation benchmark problem for a cable-stayed bridge. In this study, ideal magnetorheological dampers (MRDs) are considered as additional semiactive control devices. Numerical simulation results show that the hybrid base isolation system is effective in reducing the structural responses of the benchmark cable-stayed bridge under the historical earthquakes considered. The simulation results also demonstrate that the hybrid base Isolation system employing semiactive MRDs is robust to the stiffness uncertainty of the structure. Therefore, the LRB-based hybrid base isolation system employing MRDs could be appropriate in real applications for full-scale civil infrastructures.

The effects on structures caused by the replacement of the bridge bearings are investigated in this study. The bearings of the bridge are seriously deteriorated because of the breakage of lower concrete and the corrosion of the bearing itself. Also, the negative reaction states are created at some bearings on the abutment. Then, the bridge has occurred excessive vibrations and severe noise and impact whenever heavy trucks pass the above joints. The existing bearings are replaced using the adjustable bearing. The height of the bearings is adjusted to minimize the level difference of above joint and also to induce the appropriate distribution of live loads The effects of replacing the bearings are investigated by measuring the behaviors of the bridge without and with replacing works. The results without replacing the bearing show that the distribution of displacements and stresses is distorted in comparison with the analytical results. Also the bridge without replacing the bearing shows that the impact and vibration from the heavy trucks are larger than those with replacing the bearing. Load carrying capacity of the bridge increase about 1.8 times through replacing the bearing. The above results show that the structural performance of the bridge is improved by replacing only bridge bearings.

This paper presents the studies of the characteristics of dynamic behavior of single layer latticed domes with laminated rubber bearing and establishes the effectiveness of the system. The base isolation system installed between base and structures reduces the responses due to earthquake motions and increases the natural period of structures. Numerical analysis is carried out using modal superposition method and Newmark-βmethod which is linear acceleration method with (equation omitted) : 1/2 and β : 1/6. The time interval Δt for response calculation is 0.001 sec. Damping ratio is 2 % as Rayleigh damping and El Centro NS(1940) as earthquake motion is the input excitation data. The acceleration response of dome with base isolation is reduced to 30 % of the response of non-isolation system. From the results of the numerical studies on the models, it is confirmed that base isolation system effectively suppresses the responses of the domes subjected to horizontal earthquakes.

Base Isolation system is an effective design strategy that provides a practical substitute for the seismic design of bridge. In this study, the dynamic tests were performed on two kinds of aseismic bridge bearings : Hydampot (hysteretic damping bearing) and Dynapot . Then, the dynamic analysis was carried out far a bridge using the experimental results to estimate the seismic performance of the bearings. Analysis was performed for four types oi earthquake loadings. The results of the dynamic test and theoretical analysis indicate that the performance of both bridge bearings is appropriate fur the earthquake loading.

Base Isolation system is an effective design strategy that provides a practical substitute for the seismic design of bridge. In this study, the dynamic tests was performed on HDB (Hysteretic Damping Bearing) and Dynapot. Then, the dynamic analysis was carried out for a bridge using the experimental results to estimate the seismic performance of bearings. Analysis for bridge was performed for four types of earthquake loadings. The result of dynamic test and theoretical analysis indicate that the performance of HDB and Dynapot is appropriate for the earthquake loading.

Stone cultural properties(pagoda, Buddhist statue etc.) is moved in original place for many reasons and restored after taking to pieces for structural safety. With the movement and restoration after taking to pieces, the cast iron is used for the sake of a fixation and horizontality. The stone cultural properties are spoiled the beauty and accelerated the weathering because of the corrosion product of cast iron. So we need to substitute for the improved property in all aspects. We are executed the corrosion test and inquired the property of material on the usable material for the shim of stone cultural properties. That is the Cast iron, Stainless steel, Titanium and Fiber Reinforced Plastics. In the result of the physical property and strength, the Stainless steel and Titanium was superior to the Cast iron. And the Stainless steel and Titanium was slower than the Cast iron in the corrosion velocity for the acid, salt and rain. If the shim is substitute the Stainless steel or Titanium for the Cast iron, the stone cultural properties are able to reduce the pollution of stone cultural properties by corrosion product and should not happen in the matter of stone pagoda.

The concept of seismic design was induced in our country which was poor in it for the scarcity of recognition and insufficiency of funds. Recently many specialists are enforcing the provisions of seismic design. But because seismic force of seismic design is very great and all the seismic force are concentrated on the fixed bearings and substructure the bearings are the seismic force are concentrated on the fixed bearings and substructure the bearings are destroyed so that seismic design lose its basic concept. In addition when the earthquake which exceeds seismic design force takes place the bridge is collapsed. For these reasons the developed seismic isolation design concept was appeared which diminishes seismic force itself by period shift and additional damping distributes it to each superstructures evenly. Therefore this study introduced the method which combines PC-LEADeR(design program for L.R.B) with SAP 2000(linear elastic analysis) and performs the seismic isolation design more elaborately and simply verified the propriety of that method and examined the force control of L. R. B.

Elastomeric bearing is used as one of the most useful way for isolation structures, because the horizontal stiffness is much lower than the vertical stiffness. The quality of Elastomeric bearing depends on the vulcanization procedure to manufacture, which produces the elasticity of the rubber from the compound of rubber and sulphur. The durability of Elastomeric bearing is affected by the deterioration due to ozone and ultra-violet attack. but the durability during the design life of bridges can be assured by the sufficient size of the bearing in spite of the deterioration in surface. In the design criteria of Elastomeric bearing, the stability of the bearings is evaluated by shear strain due to compression, lateral displacement, and rotation. The question how soft rubber can sustain heavy structure is now able to be solved by Ultimate capacity test of Laminated elastomeric Bearings, which results 1,200kg/$\textrm{cm}^2$ of the max. compressive stress and this shows what a sufficient safety factor Elastomeric bearing has!