Restoring Force Characteristics Research Articles

Multi-scale simulation of freeze-thaw damage to RC column and its restoring force characteristics

The frost damage of reinforced concrete (RC) is of great complexity than plain one tested in laboratory, because of damage levels depending on various shapes and scales of structures, ambient conditions as well as detailed arrangement of reinforcing bars. In fact, damaged parts of locality in structural concrete may not contribute equally to overall mechanical performances. This paper presents an integrated life-time simulation which starts from the micro-pore formation and follows micro-scale frost action to the non-uniform frost damage considering temperature distributions, arrangement of reinforcing bars as well as the water uptake from the boundary, and finally to structural mechanical performances such as capacity and ductility. In this study, RC columns are simulated after different numbers of freeze–thaw cycles (FTC) and following repeated loads in order to investigate the seismic performances affected by frost damage. The numerical results clearly show the non-uniform damage of 3D extent at early FTC, which is closely related to the temperature field and reinforcement layout. The later stage of FTC shows localized frost damage, which mainly attributes to water filling in existing cracks. The seismic responses are also examined by comparing with previously reported experiments, and fair reproduction of restoring force characteristics is verified. Finally, the effect of lateral tie reinforcement is investigated numerically, and its effects on frost damage itself, as well as the residual seismic performances are discussed in detail.

Research and Development of Rubber Bearings for Sodium-Cooled Fast Reactor: Ultimate Properties of Half-Scale Thick Rubber Bearings Based on Breaking Tests

This paper describes the results of static loading tests using a half-scale thick rubber bearing to investigate ultimate properties application for a sodium-cooled-fast-reactor (SFR). Thick rubber bearings which have a rubber layer that is roughly two times thicker in comparison with existing rubber bearings have been developed by the authors to ensure seismic safety margins for components installed in the reactor building, and to reduce the seismic response in the vertical direction as well as the horizontal direction. The thick rubber bearings, 1600 mm in diameter at the full scale, have been designed to provide a rated load of about 10,000 kN, at the compressive stress of 5.0 MPa, with a horizontal natural period of 3.4 s and a vertical natural period of about 0.133 s. The restoring-force characteristics, including variations, and breaking points, for the thick rubber bearings have not been cleared yet. These validations are essential from the point of view of probabilistic risk assessment (PRA) for a base-isolated nuclear plant as well as a verification of the structural integrity of the thick rubber bearings. The purpose of this paper is to indicate the variation of the stiffness and damping ratios for restoring force characteristics, and the breaking strain or stress, as ultimate properties through static loading tests using half-scale thick rubber bearings. In addition, an analytical model for the thick rubber bearings which is able to express the nonlinear restoring force, including the breaking points, is presented.

EFFECT OF STRAIN-STRESS RELATIONSHIP OF STEEL TUBE ON THE INITIAL STIFFNESS OF SQUARE CFT COLUMNS

The restoring force characteristic of a concrete filled steel tubular (CFT) column is modeled with three straight lines which show the relation of M-R. The initial stiffness is calculated by assuming that the steel and concrete portions are fully effective and materials are elastic. The first break point is the yield bending moment of the CFT column. The yield bending moment is defined by the bending moment when a part of the cross-section yield or the allowable strength for short-term loading obtained by the superposed strength method. It is supposed that the theoretical initial stiffness obtained by assuming that the whole cross section is effective is different from the real one. This study aims to clarify effects of strain-stress relation on the yield strength and allowable strength for short-term loading and the initial stiffness. Three types of stress-strain relations for steel are used, elastic-perfectly plastic model, Menegotto-Pinto's model and Morino's model. According to the analytical results, the difference between allowable strength and yield strength becomes larger as the axial load ratio, indexes Rh and k which are used in Menegotto-Pinto's model and Morino's model increase.

伝統木造T字型仕口の回転めり込み特性と定式化

The important structural elements of traditional timber structures in Japan are rotational resistances of column-beam joints. The restoring forces characteristics of their structures depend on the rotational resistances of the joints. Therefore, the elasto-plastic restoring force characteristics of embedment of joints are the most significant in order to evaluate the seismic performances of traditional timber structures. The authors have already made clear the embedment mechanism of crosspiece joint which is the most basic and their rotational center is easily understood, and formulated the elasto-plastic restoring force characteristics of embedment of joints by using Elasto-plastic Pasternak Model (abbreviated to EPM). However, there are many types of joints and their resisting mechanisms may be different. The crosspiece joint is the most simple and basic because of the symmetry in rotational mechanism. The formulation of restoring force characteristics of T-type joint including Sashikamoi has not been made because it is difficult to find the rotational center. Of course, it is possible basically to find the rotational center based on the geometrical and force conditions. However, the solution is complicate and it is difficult to express the position in a closed form. Therefore, the authors assume the rotational center by T-type joint loading test results, focusing on the movement of the center of joint and rotational center. They assume the rotational center on the surface of Nuki (Fig. 11) and under the edge of Sashikamoi (Fig. 12). Then, the restoring forces characteristics are formulated based on the EPM, and parameters are determined in order to trace the restoring forces characteristics of the test results. The loading tests are carried out as follows; The test setup is shown in Fig. 2. The column is made of steel and test specimens of Nuki and Sashikamoi are made of Japanese Cypress. Nuki consist of A, B, C, D, E, F and G types and Sashikamoi are S and K as shown in Fig. 3 and Table1. The test results of joints are shown in Photo1～Photo4. The movement of the center of joint A-2 and S-2 are shown in Fig. 6 and Fig. 7. Then, the rotational center C is searched from the geometrical relation between the center of joint and rotational center. Distribution of the rotational center C is plotted in Fig. 9 and Fig. 10. As a result, the rotational center C mostly situates on the surface for Nuki, and under the point V for Sashikamoi. Thus, the authors assumed the position of the rotational center and rotational embedment models are shown in Fig. 11 and Fig. 12. The EPM formulation of the Nuki and Sashikamoi are proposed in equations from (4) to (36). The restoring force characteristics of test results are simulated based on the EPM formulation and obtained the EPM parameters as shown in Table2 and some examples of simulated results are drawn in Fig. 13～Fig. 16. As a conclusion, the simulated results of M-θ relations are fairly well comparing with the test results and the proposed formulations are confirmed to be adequate.

Study on Ultimate State and Mechanical Characteristics of Connection Joint of Damaged H-Shaped Bracing Structure

In Japan, various kinds of failure modes in steel structures have been reported in severe past earthquake disasters. Also, the various type of repair method for damaged building structure is suggested, and it has been published as restoration manual and guideline. However, it is guessed that these repair methods have some difficulties related to construction technique and estimation of recovery of seismic resistant performance after repair. This study focuses on the seismic ultimate state of steel brace connection of original state and repaired state after damaged, and the effective restoration method is suggested herein. In our past researches, new repairing method for damaged steel bracing joint which has angle-section brace member has been suggested already, and its applicability and feasibility were investigated experimentally. Herein, H- shaped section brace members are focused which are adopted on middle-rise or high-rise steel building structures, and also, various kinds of failure modes of these bracing structure has been reported after past terrible seismic disasters in Japan. So, the effective restoration method is proposed here. First, to reproduce the seismic ultimate state, the vertical loading test on H-shaped bracing test specimen are performed as parameters with bolt layout, thickness of gusset plate, that is, out-of-plane rigidity of joint. Next, the damaged bracing joints are repaired. Finally, the loading test is done on repaired specimen again. From test results, the restoring force characteristics after repair can be recovered, and any type of failure modes are observed. So, 3D model of damaged bracing joint is constructed by using 3D scanner, and it helps to identify the failure mode and yield lines on gusset plate. Furthermore, the plastic limit analysis is performed by reference of 3D model, and it can predict the ultimate state of test results well.

伝統木造の束の回転めり込みメカニズムと定式化

The important structural elements of traditional timber structures in Japan are rotational resistances of column-beam joints. The restoring forces characteristics of their structures depend on the rotational resistances of the joints. Therefore, the elasto-plastic restoring force characteristics of embedment of joints is the most significant in order to evaluate the seismic performances of the traditional timber structures. The authors have already applied Pasternak Model (abbreviated to PM) to the embedment and established the formulation of embedment mechanisms of partial compression of wood, which is the most appropriate embedment mechanical model for embedment problems. Furthermore, they developed the Elasto-plastic Pasternak Model (abbreviated to EPM) for the elasto-plastic embedment mechanism considering the strain hardening behavior. However, there are many types of joints and their resisting mechanisms are different. Thus, the mechanisms of different types of joints should be made clear. The authors have already established the formulation of crosspiece joint applying the EPM of the mechanism and confirmed the formulation based on the static loading tests. In this paper, the authors focus on the strut which has not been considered as a structural element so far, and propose the formulation of embedment mechanism of the strut, as a model of rotational embedment under the constraint conditions. Then, they carried out loading tests of the struts, and obtained their restoring forces characteristics. The loading test of two types of struts were carried out; one is Y-series (six specimens) which support the floor beams standing on the base stone. The other is T-series (three specimens) which stand between two beams, called, “Taihei tuka”. The dimentions of the strut are: depth:120mm, breadth:120mm, height:280mm. Beams depth:180mm(Y-1～3) and 90mm(Y-4～6), and 150mm (T-1～3). All species of specimens are Japanese cedar (Sugi). The test results showed that the maximum horizontal resistances of Y-1～3 were 8～11kN, the maximum normal loads were 36～50kN. The maximum horizontal resistances of Y-4～6 were 6～7kN, the maximum normal loads were 18～28kN. T-1～3 were the maximum horizontal resistances of 12kN, the maximum normal loads were 48～53kN and had the large deformability up to 200mm. The resisting mechanism of strut joints due to horizontal loads is “Diagonal Effect” which push up the beam, rotating and embedding into the beam in accordance with the rotation of the strut. The mechanism is due to geometrical fact that the diagonal line of the strut is longer than the height of the strut. Another mechanism is the distance between beams decreases due to inclination of column. The same mechanism is found in short beams between inclined columns and panel walls within the frames. The authors considered the mechanism of struts is rotational embedment of strut into beams under the constraint conditions and proposed Elasto-plastic Pasternak Model formulation established by the author, in order to analyse them appropriately. Then the formulation is discussed and verified by the simulation based on the Elasto-plastic Pasternak Model formulation. As a result, the deformability is very large and the strut should be considered as a structural element for exact seismic estimation of traditional timber structures.

鉄筋コンクリート造多層平面骨組の地震応答と柱梁接合部の耐震設計

Non-linear time history earthquake response of reinforced concrete multi-story moment resisting frame structures are calculated with a model of beam-column joints considering their restoring force characteristics which represents the interaction of moment, axial force and shear (Figure 1). The influence of the failure mechanism and strength degradation of beam-column joint are investigated by the comparison of the simulation of twenty-seven model frames (Table 1) satisfying the current seismic provisions in Japan, the model parameters for which are combination of column-to-beam strength ratio of 1.2, 1.5, and 2.0 and joint hoop reinforcement ratio of around 0.2% to 0.6% which are neglected as design parameters affecting the seismic safety in design practice in Japan. Statically cyclic response analyses of the model frames subjected to lateral load distribution pattern of Ai by displacement control at the top floor are calculated to classify the type of hysteresis loop and strength degradation (Figure 3). Then dynamic analyses of the model frames are carried out subjected to five artificial base ground motions conformed to maximum considered intensity design (MCD) spectrum and five observed strong motions (Figure 4). It is found that there is significant difference in the story drift response of the structures with different beam-column joint attributes. Particularly, in some cases, the story drift ratio increased significantly due to concentration of lateral deflection to several stories and large residual drift remains to one direction (Figure 5). It is confirmed that the differences are due to softening of stiffness and strength degradation of the beam-column joints. It is caused by the mechanism identified as joint hinging (ref. 1) which features the yielding of longitudinal reinforcement within the beam-column joint and repetition of diagonal crack open and close. The state-of-the-practice analytical model for frames does not consider the joint hinging so it significantly underestimates the story drift responses by far than seismic design criteria (Figure 8). The response of frames with beam-column joint failing in joint hinging is very sensitive to base ground motions which were synthesized with same target response spectrum. So the prediction of the response is difficult by non-linear static procedure nor non-linear time history procedure the model of which consider plastic deformation only by non-linear rotational springs at beam-ends considering hysteresis model with slip behavior. The results of incremental dynamic analysis (IDA) shown in Figure 9 reveals that the amplification less than 50% of MCD yields little difference in the response of the models whilst the amplification of 100% of MCD causes near collapse to four-story model and concentration of story drift exceeding 6% to the models failing in joint hinging mechanism, which is far beyond seismic design criteria for MCD. The current Japanese seismic design practice for beam-column joint obviously lacks the necessary reinforcing detailing provision such as minimum column-to-beam strength ratio and design of required joint hoop ratio which is much behind the seismic provisions found in current NZ3101 and ACI 318 building codes.

Study on Ultimate Seismic Behavior and Repair Method of Damaged SteelFrames

Recently, there are many discussions about repairability and recovery on damaged buildings. It is desirable to establish the design manuals for recovery considering continuous use of structures. In our previous researches, the damaged steel members of H-shaped and square tube section were reproduced by loading test. From the loading test results, the inelastic behavior and restoring force characteristics were clarified, and also the analytical model were proposed which can chase test results well. It means that we have already conducted the member based research on repairability. So, in this study, to investigate the inelastic behavior and restoring force characteristics of repaired steel frames, the loading test is performed on half size scaled - partial frame model as parameters with strength ratio of column-beam and panel-beam. It is assumed that the various type of failure mode is generated on original state and repaired state. During loading test on original state, local buckling is observed on H-shaped steel beam. Therefore, the damaged area is repaired by welding cover plates method which is recommended by Japanese restoration manual for damaged building structure by severe seismic disasters. And also, the loading tests on repaired state is performed, and it is confirmed that the strength is restored at the same or high level compared with original state. However, in case of beam failure mode on original state, different failure mode is observed on repaired state. Furthermore, a finite element analysis is performed, and the resistant mechanism during ultimate state is investigated analytically in detail.

Experimental study of using cantilever type steel plates for passive energy dissipation

In recent years, the use of seismic energy dissipation devices for passive control of both new and existing buildings has increased exponentially. However, these devices developed for structures in high seismic regions cannot be determined to be effective in the structures in regions of low-to-moderate seismicity, such as Korea. When an energy dissipation device is applied to the structures in Korea, it may not be necessary the ultimate energy dissipation capacity required in the strong earthquake regions. This paper experimentally investigates a new type of steel damper, based on the yielding of cantilever type steel plates for seismic protection of building structures. To increase the energy dissipation of the device, the optimized geometry of a steel plate was firstly developed. The hysteretic behavior and energy dissipation capacity were then investigated, via component tests under cyclic loads. The experimental results indicated that the damping device has stable restoring force characteristics, and a high energy dissipation capacity. In addition, the load-displacement curve of the device was predicted, based on the theoretical formulae and test results.

原子力施設RC床スラブの面内せん断性状に関する実験研究

A high degree of seismic safety is required in nuclear power plants. To evaluate accurately the seismic behavior of a nuclear reactor building, it is effective to use an analysis model that takes in-plane shear characteristics of the floor slab into consideration. However, few experimental studies of the in-plane elasto-plastic shear characteristics of the floor slab that is constantly subjected to out-of-plane dead and live loads have been reported. Therefore, fundamental data needed to decide on restoring force characteristics and shear strength to be used for an analysis model is insufficient. In this study, the static loading tests were carried out to identify the elasto-plastic behavior of a reinforced concrete floor slab subjected simultaneously to uniformly distributed out-of-plane load and in-plane shear force. Prior to test planning, as a first step, a fact-finding survey was conducted to collect data on representative nuclear power plants in Japan including the dimensions (length, width, thickness) of typical floor slabs, dead loads, live loads and the amount of reinforcement. The configuration of test specimens and test parameters were determined on the basis of the results thus obtained. A total of seven test specimens were prepared, and the amount of reinforcement and out-of-plane distributed load level of the floor slab were used as parameters. The configuration of the test specimens is basically the same as that of specimens for a typical sheer wall test. In the tests, first, distributed loads were applied to the specimen as out-of-plane forces and were kept constant, and, next, in-plane shear forces were applied. The results of the tests revealed that cracking patterns and the in-plane failure mode depends on parameter differences. The test results also clarified the effects of each parameter on the load－deformation relationship and in-plane shear strength. Using the experimental results thus obtained, the strain behavior of reinforcing bars, deformation components, a method of setting restoring force characteristics in analysis model were studied in detail. Also, a method of evaluating in-plane shear strength taking account of the influence of out-of-plane forces was proposed. From the results of this study, the following conclusions can be drawn: (1) Within the range of out-of-plane force acting on a floor slab of a typical nuclear power plant, the influence of out-of-plane force is small, and the failure mode due to in-plane shear is similar to shear failure of a wall. (2) In practicing the evaluation of the earthquake resistance of a nuclear power plant, the in-plane shear behavior of a floor slab can be evaluated by using the restoring force characteristics model for a shear wall shown in JEAC4601-2008. (3) In cases where out-of-plane force exceeds the limit considered in the standard design process, as out-of-plane force increases, the influence of punching shear failure due to out-of-plane force tends to increase and in-plane shear strength tends to decrease. (4) By referring to previous studies, a method of evaluating the in-plane shear strength of a plate member in the case where it is subjected to uniformly distributed out-of-plane loading has been proposed. The proposed method makes it possible to accurately evaluate the in-plane shear strength of a floor slab subjected to a large out-of-plane force exceeding the limit assumed in the design.

べき関数型等価線形系解析手法とGAを用いた免震積層ゴムの最適化に関する研究

The hysteresis restoring force characteristic of the seismic isolation rubber has the nonlinear characteristics depending on the displacement. A method to reduce the damage of structure in the earthquake with a seismic isolation laminated rubber is discussed and the vibration characteristics of the rubber which minimize the response of the structure in earthquakes is optimized. In this research, PFT-ELS (Equivalent Linear System using the Restoring Force Model of Power Function Type : PFT-ELS) method is applied to the nonlinear vibration analysis of the rubber. And, the building model of 15 layers with the seismic isolation laminated rubber is modeled. Next, the hysteresis restoring force characteristic of the seismic isolation rubber which minimize the response of the structure in earthquakes is optimized by Genetic Algorithms (GA). As earthquakes, Kobe earthquake, the hypothetical Nankai-Tonankai-Tokai connected earthquakes and Kumamoto earthquake (16 April 2016) are used. From these results, we consider about the optimum solutions of the restoring force characteristic by different earthquakes, and we verify the availability and valuable of this optimization method. As a result, it is clarified that the vibration characteristics of the seismic isolation rubber for minimizing the damage of the structure at the design phase through developed optimization system.

伝統的構法の楔の復元力特性に及ぼす効果

著者らは、伝統的構法の木造建築物の楔をもつ仕口のメカニズムの解明に取り組み、楔打ち込みにより導入される支圧力により回転抵抗と摩擦抵抗が増大するメカニズムを解明した。本論では、さらにテフロンシートの有無により摩擦係数が変化することに着目した十字型接合部の載荷実験を行い、摩擦係数の変化による復元力への影響を明らかにする。さらに、楔と摩擦の効果をより立ち入って分析することで、楔の復元力特性に及ぼす重要な効果を解明し、その定式化とシミュレーションを試みる。

擁壁が弾塑性特性を有する場合の簡易評価法への適用

We have proposed the simple modeling method for the lateral resistance of elastic retaining wall portion (retaining wall + backfill soil) using fiber model, and we have showed the collision analysis model using the method. This paper aims to confirm the applicability of the method in case of retaining wall with elasto-plastic property. First, we conduct the seismic response collision analysis of a base-isolated structure-soil interaction system using 3D-FEM and estimate the structural behavior and impulse force when it collides uniformly and without twisting into retaining wall. Figure 1 shows 3D-FEM analysis model. Basic specifications and conditions are same as reference No. 11. The thickness of retaining wall is taken as t =300mm, its flexural strength assumes two types of Mu≒145kN·m/m (“flexural strength 1.0 times type”) and Mu≒72.5kN·m/m (“flexural strength 0.5 times type”). Figure 5 shows the time-history response displacement of isolation layer in 3D-FEM collision analysis. The maximum response displacement for both types is the same as approximately 523mm, however their behavior after the maximum displacement is different. Figure 6 shows the time-history response acceleration of superstructure (top floor and 1st floor). With respect to maximum response acceleration (16.5m/s2) at the top floor of elastic retaining wall, flexural strength 1.0 times type is reduced by approximately 12%(14.6m/s2), and flexural strength 0.5 times type is reduced by approximately 23%(13.4m/s2). Meanwhile, with respect to maximum response acceleration (12.4m/s2) at the 1st floor of elastic retaining wall, which values of both types are almost the same. Figure 7 shows the time-history impulse force on lower edge position of girder directly above isolation layer at which maximum impulse force is obtained. Maximum impulse force of both types is reduced approximately 21% against elastic retaining wall. Next, we confirm the applicability of the simple modeling method in case of retaining wall with elasto-plastic property. The verification position is three cases; GL±0m, GL-1.2m, and GL-1.5m. Figure 12 and Figure 13 shows the hysteresis loop of retaining wall portion. In case of GL-1.5m, a difference occurs in the maximum response displacement because the simple modeling method may not accurately reproduce strength of retaining wall portion obtained from 3D-FEM analysis. Also, in case of GL±0m and GL-1.2m, a difference between 3D-FEM result analysis and the simple modeling method is large. This reason is considered to be not conformed the condition of maximum range 3t for the backfill soil considered as added mass because the maximum response displacement of elasto-plastic retaining wall is larger than elastic retaining wall. So, we modify the maximum range from 3t to 6t, and we re-estimate the lateral resistance of retaining wall portion. As a result, hysteresis loop shapes are greatly improved, and it shows relatively good agreement to 3D-FEM analysis result. Finally, we conduct collision analysis using the simple modeling method, and we compare the structure response with the 3D-FEM analysis results. Figure 18 shows the analysis model using the method. In the case of the collision springs taking into account axial stiffness of the girder directly above isolation layer, the method largely captures trends in restoring force characteristics of entire isolation layer (isolation layer + collision spring) from 3D-FEM analysis. The method estimates maximum response acceleration at 1st floor approximately 14% smaller compared to 3D-FEM analysis result. However, it shows relatively good agreement to 3D-FEM. Meanwhile, in the case of the rigid collision springs, the maximum response values are overestimated. This tendency is the same as case of elastic retaining wall.

Study of Equivalent Strength and Effects of the Type of Multi-story Steel Braced Frames

In recent years, the terrible earthquake events that are not expected in the design process have occurred in the world. So, it is necessary to estimate the seismic performance accurately. This paper focuses on the energy absorbing efficiency of steel braced frames. Steel brace members in frames show the complicated and unstable behavior because many kinds of buckling and fractures are combined. And evaluation method of restoring force characteristics and capacity have been studied in enormous past researches, however, there are some problems to adopt for seismic design procedure. Also the response characteristics of steel braced frames are affected by the interaction between frames and braces. This paper suggests the analytical method to evaluate the energy absorbing efficiency of steel braced frames as equivalent strength. The equivalent strength is formulated with yield shear coefficient of the frame and slenderness ratio of the brace. Also, to verify the applicability of multi-story steel braced frames response analysis of two types of 5-story steel braced frames (X bracing, inverted-V bracing) is conducted. As compared with energy absorbing efficiency of the response analysis result, it is confirmed that the equivalent strength can be accuracy of plus or minus 20 percent or so.

Optimum proportioning and restoring force characteristics of seismic dampers with rippled core plates

Optimum proportioning and restoring force characteristics of seismic dampers with rippled core plates

エスカレータートラス構造の復元力特性を考慮した振動解析モデルの構築

In the 2011 off the Pacific coast of Tohoku Earthquake, four fall accidents of the escalators occurred. These accidents, the escalator that linked the third floor from second floor dropped, occurred in the commercial facilities of the low-rise, steel-frame building. In general, the escalator is installed with one side of the leg or both sides as non-fixed style in order not to restrict motion of the escalator. However, the escalator truss might come off from the beams of the building, because interlaminar deformation with more than assumption was caused in the building where the accident happened. In new public notice about the reinforcement of the falling off prevention structure of the escalator after these accidents, the structure that an escalator never fall off was determined, 1 Structure to make enough overlap allowance, 2 Structure to take backup measures for. To make enough overlap allowance for, the escalator truss come off from the beam of building and is less likely to drop. However, it is considered that a non-fixed part collides with the beam of building by the big rolling of the earthquake; the collision may give compression and residual displacement to the escalator. From the above-mentioned background, the object of this research is to construct of an analytical model grasping behavior at earthquake for an escalator, which considered collision with the beam of building. In this paper, I perform earthquake response analysis in using the restoring force characteristics model, was built by the compression experimental value using the escalator truss of the original size, and Bi-linear model in this study until now, and I examine behavior at an earthquake for an escalator.

Effective Hamiltonians for Resonance Interaction Dynamics and Interdisciplinary Analogies

Resonance interactions of oscillators are responsible for fundamental effects in different areas of physics and classical mechanics. The resonance between any two oscillators/modes destroys their individuality by generating a new effective oscillator of energy flow between the two parent oscillators, which is known as beating. In particular, the fundamental character of such energy exchange oscillators is revealed by the fact of their exact integrability in many physically reasonable cases. The present work illustrates such a standpoint on elastic oscillators, discrete liquid sloshing models, and ‘macroscopic’ quantum dynamics related to Josephson's effects. In the case of elastic oscillations, a strongly nonlinear conservative oscillator describing the dynamics of energy partition between two identical linearly coupled oscillators with polynomial restoring force characteristics is analyzed.

Repair Method of Damaged Steel Framed Structures and Ultimate Seismic State of Repaired Steel Frames

Recently, a lot of building structures have been experienced severe natural disasters, and it was reported that various types of terrible collapse mode were occurred. And also, there are many discussions about repairability and recovery on damaged buildings over the world. In particular, there has been focused on new keyword a²¯ Resilience a²° in any field including structural engineering. In Japan, a technical guideline for repairing damaged buildings has been established. However, the applicability and feasibility of repair method and recovery has not been well reported. Herein, to investigate the recovery and ultimate seismic state of repaired steel framed structures, experimental and analytical studies are conducted. Herein, the actual repairing technique for steel framed structure is suggested. During experimental study, the damaged steel member is reproduced by loading tests with consideration of past reports of mega-earthquake disasters. The next, the damaged portion is repaired by proposed method by use of steel-cover plate technique. After this repair process, the loading test is done again. And the recovery of structural performance is estimated by comparison of original and repaired state. From the test results, it is confirmed that the strength and ductility are improved after repair. Furthermore, the analytical model and restoring force characteristics of repaired steel member are suggested by observation of ultimate behavior during loading test. Here, the purpose on seismic design is to guarantee the overall failure mode formation on frames. So, the structural demand of strength and rigidity and column-to-beam strength ratio on repaired state are discussing analytically.

Prediction Method of Maximum Seismic Response for Vibration Control Steel Frames With Scaling-Frame Device Installed

The innovated vibration control device called as scaling frame a²¯SFa²° structure has been proposed by the authors, and the SF structures are applied to low-rise wooden structures already. This paper aims to investigate the applicability of SF structure on steel frames. Herein, SF structure consists of beam-column frame, diagonal bracing, and SF device a²¯SFDa²° installed, and SFD is made of Steel or aluminum. And vibration energy is absorbed by the plastic behavior of the diagonal deformation of SF device. In previous study, the experimental study on SFD and steel frame specimen with SFD installed were conducted to clarify the seismic response and seismic mitigation effect. And also, from observation of test results, analytical method has been suggested. From the comparison of test results, the proposed method shows good agreements with test results. Furthermore, the enormous past studies have suggested prediction method of maximum seismic response of vibration control frames. So this study aim to develop the prediction method of seismic response on vibration controlled steel frames with SFD installed, and the simple design procedure can be provided. The first, the simplified restoring force characteristics which can chase the test results is applied on prediction method procedure. So the prediction method is reformulated to adapt the bilinear model and strain hardening rule. The time history response analysis is performed to investigate the applicability and effectiveness. From the comparison of analysis results and predictions, it is confirmed that the proposed prediction method shows enough accuracy.

Responses of reinforced concrete pile group in two-layered liquefied soils: shake-table investigations

During earthquakes, the response of pile foundations in liquefiable sand reinforced by densification techniques is still a very complex dynamic soil-structure interaction problem. Two shake-table experiments were conducted to investigate the behavior of a reinforced concrete (RC) low-cap pile group embedded in liquefiable soils. Discussion is focused on the behavior of soil-pile-superstructure systems prior to and during liquefaction of the medium-dense and dense sand stratums, which are involved in restoring force characteristics at the superstructure and pile group effect. The test results demonstrated a stiffness reduction and dependent nonlinear behavior appearing in the liquefied medium-dense sand; however, an overall stiffening response was observed in liquefied dense sand. The pile group effect seemed insignificant in liquefied medium-dense sand, but was very significant in the liquefied dense sand.