In this study, we applied a diagnostic imaging system, which is an upgraded version of a previously proposed diagnostic imaging technology, to the actual damage inspection of timber houses damaged in the 2021 Fukushima earthquake. We also examined the relationship between pixel resolution and damage detection accuracy as a basic study of the imaging method, with an eye to self-diagnosis by occupants using smartphones. The results of damage detection and damage rate calculation using images with a pixel resolution of 0.3 mm/px or less showed that the error in the image diagnosis results was 0.133%, compared to the maximum deviation of 0.567% (assumed to be a permissible error) in the visual measurement by three persons, indicating that the damage rate could be calculated with the same or higher accuracy as the visual measurement.
This study focuses on the effect of hanging wall and transverse wall associated with CLT shear wall on the mechanical behavior. While structural analysis model for CLT constructions is introduced in the current design manual, how the above members contribute to the shear capacity is not well-understood. In this paper, static lateral loading tests for single-story frame structure with hanging wall and single-wall connected to transverse wall were conducted. The test results were analyzed using simplified model, and the effect of the stiffness/strength balance of each member was discussed.
A brace is an effective structural member against earthquakes that gives the buildings strength and stiffness. However, it has the weakness that buckling occurs when a compressive force is applied. Therefore, we proposed a new buckling-restrained steel-plate brace using glued laminated timber. In this paper, we show an overview of the proposed brace. Then, in order to confirm its structural performance, a statical loading test was conducted on a specimen of about 1/2 scale. The outline of the test and the test results are shown. In addition, various considerations were made on the test results. Various findings were obtained from the tests, and technical data for practical use was accumulated.
The authors propose to replace a reinforced concrete slab with a cross-laminated timber (CLT) floor panel as a method to increase the use of timber in moderate- or large-scale buildings. In previous work, a push-out shear experiment was conducted on the joint of CLT floor and steel beam to investigate the shear performance. An in plane shear test and the push-out shear test were carried out in order to investigate difference of layups of CLT. The experimental variables considered include layups, thickness of lamina and a length of headless stud bolts. From the push-out shear test results, the yield shear strength per stud are approximately 15kN, and the slip displacement at the yield strength is less than 1.0mm. The calculated yield shear strength based on European yield theory was in good agreement with the shear strength at the yield point in the shear test.
Objectives of this study were to examine deformation capacities of reinforced concrete columns with side walls failing in flexure. Deformation capacities mainly depend on the compressive performance of the edge region of the side wall. From this view point subjected axial load and confinement of the edge region of the side wall were varied. For this purpose static loading tests of side wall specimens were conducted using high strength concrete. Drift angles calculated using some evaluation equations were compared with observed ultimate drift angles and found to be not conservative for specimens with high strength concrete. Currently used design indecies expressing deformation capacities (member rank) were also compared with test results.
In this paper, databases of concrete and rebar strength in the Taisho and Showa era are shown. The results are as follows.
1. The 1718 concrete compressive strength data of buildings completed from 1911 to 1980 are extracted from documentary records. The means, standard deviation, coefficient of variation and estimated strength are calculated. It shows that the compressive strength of Taisho and early Showa era is relatively high.
2. The 153 yield strength rebar data of buildings completed from 1911 to 1979 are also extracted. Most of the strength data before 1939 are higher than material strength of SR24.
The purpose of this paper is to examine the bond slip performance of corroded small diameter reinforcing bars in concrete and double pull tests were carried out on specimens in which small diameter reinforcing bars corroded by electrolytic corrosion were embedded in concrete. From the strain distribution of reinforcing bars, the relationships between bond stress(τ) and slip(S) were delived and the effe ct of slip of reinforcing , amount of corrosion and crack width occurred on concrete surface on maximum bond strength were obtained.
The results obtained are as shown below.
1. The τ S relationship of corroded reinforcing bars is significantly different from the case where reinforcing bars are not corroded
2. In the case of corroded reinforcing bar the initial bond rigidity is high and it reaches τmax with smaller slip.
3.The value of τmax is highly correlated with the corrosion crack width.
This paper describes analysis models that can reproduce historical characteristics of RC columns during large deformation. Inorder to continue to use RC buildings hit by a severe earthquake, it is essential to suppress not only damage to the skeleton but also residual deformation. Furthermore, analysis models that can reproduce the hysteretic characteristics of RC members in detail are required for more appropriate evaluation of residual deformation. In this paper, new analysis models that combine two multi-springs with different hysteretic characteristics are proposed. The analysis results using these analysis models can accurately reproduce the experimental results of RC columns on complicated loading protocols.
Three precast concrete walls, reinforced by weakly bonded ultra-high strength (SBPDN) rebars within their edge zones, were fabricated and tested under reversed cyclic lateral load to investigate effects of anchorage detailing of SBPDN rebars in wall-base joint and embedment length of SBPDN rebars on seismic behavior of precast concrete walls. Experimental results have indicated that if the embedment length of sheath duct housing SBPDN rebars was five times its diameter, the precast concrete walls reinforced by SBPDN rebars could exhibit as high drift-hardening capability as the cast-in-site shear walls.
The purpose of this study is to clarify the seismic behavior of precast concrete walls reinforced with SBPDN rebars, which are ultra-high strength rebars with low bond strength. Four precast wall specimens were designed and fabricated with the axial load ratio and construction method (cast-in-site and precast) as experimental variables. These walls were tested under reversed cyclic lateral load and constant axial force to investigate the seismic performance of the precast walls. Test results have indicated that housing each SBPDN rebar separately in the sheath duct could prevent the pulling-out of the SBPDN rebars at large drift, and ensuring precast walls as high drift-hardening capability as the cast-in-site walls. Analytical method is also presented to evaluate cyclic response of concrete walls with SBPDN rebars, cast-in-site and precast, and the theoretical predictions exhibited fairly good agreement with the test results.
Two half-scale R/C column specimens were constructed and tested under varying axial loads to investigate the shear behavior and the ultimate shear strength. One specimen (C specimen) was modeled the soft-first story column of the condominium which was heavily damaged in the 2016 Kumamoto Earthquake. Another specimen (CW specimen) had a thick wing wall with sufficient confinement on either one side. Both specimens failed in shear, and the maximum capacity of CW specimen was approximately 1.9 times that of C specimen. Three-dimensional FE analysis was conducted and captured the experimental maximum capacity of both specimens in good accuracy. Based on the results of a parametric study using FE analysis, some modifications were added to the existing numerical evaluation and improved its prediction accuracy.
One of the main causes of the collapse of “Tensyudai”, base of castle tower, of Japanese castles is the inertia of the masonry wall stones during the earthquake. The purpose of this study is to evaluate collapse acceleration when horizontal acceleration acts on the masonry walls. Inclining experiments of masonry wall models are conducted to statically represent the horizontal load, and the collapse mechanism is discussed. The collapse mechanism of the masonry walls is constructed considering the three-dimensional mechanical characteristics under horizontal loading as inertia force due to horizontal ground motion acceleration, and the critical states equations is derived. It is confirmed that there is good correspondence between experimental and theoretical collapse accelerations.
The ceiling structure is required to have a rational construction method to avoid interference with equipment. In this study, we propose a non-braced ceiling structure that does not cause interference between the ceiling material and the equipment. At this time, the proposed ceiling structure uses moment resistance joining using lightweight square steel pipes. In this study, these ceiling structures are called "framed ceiling".
First of all, we report on the results of the materialtensile test of the steel materials used for the ceiling structure. Next, a static loading test was conducted to grasp the mechanical characteristics of the ceiling structure. In this paper, we report the results of these tests.
The purpose of this study is to establish a computational morphogenesis method for unreinforced concrete shells. In this study, the morphogenesis method in which only body force such as gravity and seismic inertial forces act on the rectangular parallelepiped design domain is used. By such a method, various optimum shell morphologies can be created simply by giving the boundary shape that supports the shell. However, the method (IESO) proposed in Reference 7) did not accurately consider the effect of body force on the element sensitivity number. Therefore, in this paper, we improve the element sensitivity number of IESO method by adding the sensitivity of body force. In order to verify the effectiveness of the improved method, we show analysis examples in which the support boundary of the shell is square or rectangle.
The main purpose of this research is to develop optimal cable arrangement and the damping of nonlinear structural system reinforced by non-compression resistant cables when it vibrates. The object is the moment-resisting frames which reinforced by the no initial tension cable. First, we clarified the cable arrangement which could lower the displacement at the time of the earthquake vibration by analysis using 3-layer 2-span moment-resisting frames which installed cables. Second, we conducted free vibration experiment using small models. It was revealed that there was damping peculiar to non-linear vibration to the structure reinforced cables from the result. It could be considered to be damping by a cable repeating the tension state and the deflection state.
This paper studies the seismic performance of a flat steel space roof which is supported by RC columns on the front and rear sides, while supported by RC frames at both gables. Between the roof and RC columns, a kind of H section steel columns are installed to reduce the seismic response of the RC columns. First, several reinforced concrete columns of different sections are set up as the substructure, and several different types are set up for the H section steel columns. Second, focusing the difference in the vibration characteristics between the RC columns and the steel roof, a parametric study is conducted to make clear the differences of vibration characteristics between the RC columns and the roof, based on which this study classifies seismic forces to the RC columns and proposes a seismic force as a total structure. Subsequently, elasto-plastic response analysis, static and dynamic, are performed to study the static and dynamic seismic responses. Finally, it is confirmed that the H steel columns can suppress the deformation of the RC columns as a substructure. Based on the results, necessary conditions both to strength and rigidity are classified for the H sections and RC columns, for realizing a stable total structure to refrain from large plastic deformation.
This paper proposed an optimization technique to obtain the optimal wave directions and wave heights of corrugated shells. The finite element method is applied to the structural analysis of the corrugated shells. Rhinoceros and Grasshopper are used for modeling and optimization of the analytical model. The constituted law of an anisotropic flat plate is used for the material of the shell element to achieve the same effective stiffness as the corrugated plate. The objective function is the strain energy under self-weight. The wave direction is defined by the contour direction of a B-spline surface in Rhinoceros, the wave heightis given by the z coordinate of another B-spline surface. The design variables are the control points of the B-spline surface. A genetic algorithm plug-in on Grasshopper is used for optimization. The optimal solutions for two EP shell with different support condition are show as a numerical examples. The optimal wave directions and heights with low strain energy and high stiffness under self-weight were obtained, thus confirming the effectiveness of the proposed method. It was found that in the optimal corrugated shells, the wave direction occurs towards the support point and the wave height tends to be higher near the support point.
Multi-span steel frame structures are often used in school gymnasiums and factories. When braces are placed on the gable walls and roof surface of the structure, the seismic load is transferred between the frames, and the rigidity and shear loading capacity of the structure against seismic motion is increased. However, the collapse behavior becomes difficult to predict without the three-dimensional nonlinear structural analysis. The purpose of this paper is to predict the ductility index F, the plastic hinge rotation angle and the roof brace plastic modulus without static incremental analysis and eigenvalue analysis for the three-dimensional structure. Only the stiffness and shear loading capacity of each plane gabled frame are used, and the plastic deformations of the three-dimensional structure is predicted by some simple spreadsheet calculations. The results of the proposed method and three-dimensional time history response analysis are compared to confirm the effectiveness of the method.
The present paper discusses a method for estimating the yield seismic intensity of arch structures based on the continuum arch theory. First, the modal parameters, which are natural periods and dynamic eigen modes, are estimated based on the continuum arch theory. The equivalent static seismic load is evaluated by the estimated modal parameters. The maximum responses obtained by the time history response analysis are compared with the maximum responses obtained by the proposed seismic force, and the validity of the proposed seismic load is investigated. Second, the buckling behavior and initial yield seismic intensity are investigated based on elastoplastic analysis using the equivalent static seismic loads. Finally, a method for estimating initial yield seismic intensity based on continuum theory without FEM analysis is proposed and the validity is discussed.
Spherical domes and cylindrical roofs have long been used as structures to cover large spaces because they are easy to construct. The existing domes have withstood a variety of external forces and have been reconstructed by thickening the boundaries of the shell and adding tension rings. The main materials used are stone and concrete. Since these materials are resistant to compression but not to tension, the best shape would be one that does not generate tensile stress and has low compressive stress. The purpose of this paper is to find a shape that does not generate tensile stress and has low compressive stress in the stress distribution across the spherical dome by varying the shape of the top and bottom surfaces of the shell within a certain range from the boundary of the spherical dome, and to evaluate the degree of effectiveness of this shape.
This study focuses plastic buckling of axially compresses latticed cylinders. Following the past experimental studies, FE buckling analysis of relatively thick latticed cylinders made of aluminum was carried out. Axially symmetric buckling, the so-called ‘elephant leg’ buckling, was observed in plastic region. Axially symmetric imperfection was found more effective than the asymmetric 1st-eigenmode proportional imperfection in reducing plastic buckling load.
The tangent stiffness method was introduced, in which buckling load and deformation can be determined using linear buckling and plastic pushover analysis without geometric nonlinearity. As for the latticed cylinders in this study, the method was found quite effective to evaluate plastic buckling load and deformation capacity.
The cable structure has been widely used as structural elements for a large span structure. However, there is a lack of detailed design data, and based on the data of large-diameter cables currently used for bridges, the authors are constructing a design method for intermediate joints to be joined using small-diameter cables. The joint metal fitting becomes large. In addition, there is no experimental value for the spring constant in the lateral direction of the cable in the current design method. In this report, the authors experimentally grasp the value of spring constant in the lateral direction of cable and effect of lateral pressure on breaking load.
The main purpose of this paper is to evaluate ultimate strength of a concrete shell by applying reduction parameter to the linear critical load. Generally a concrete shell could show rather higher rigidity and load-carrying capacity than the other shell and spatial structures, such as lattice dome and tension structures. However the estimation for the ultimate strength of a concrete shell could be faced and accompanied with many difficult problems as for how to select the reliable analysis among rather complicated nonlinear numerical analysis and for how to prepare an effective model among much expensive experiments. In this paper the easy and convenient method to evaluate the ultimate strength of a concrete shell was investigated by applying stability analysis based on the Dulacska’s Revised Version of IASS Recommendation and by operating reduction parameters with several kinds of initial imperfection. As for a concrete shell kinds of materials were investigated, where one was a standard reinforced concrete by steel bar reinforcing. These results were discussed based on the failure numerical ones.
The buckling behavior of metal grid shells stiffened with tension braces is complex. During pre-buckling deformation, the braces are compressed and do not contribute to the stiffness of the shell. However, when the shell is about to buckle, some braces restrain the buckling deformation by changing the state from compression to tension. Thus, the buckling does not occur immediately, and the buckling load increases. In this paper, elastic buckling analysis and elasto-plastic buckling analysis are performed on the metal grid shells stiffened by the tension braces, and the buckling behavior subject to initial shape imperfections and load imperfections are investigated. The applicability of the estimation method of the elasto-plastic buckling load described in the "AIJ Recommendation for Design of Latticed Shell Roof Structures" to the grid shells is also investigated. The results show that the grid shells stiffened with tension braces are insensitive to initial imperfections and the estimation method of the elasto-plastic buckling load is applicable to the shells.
In this study, stub column tests using cold-formed steel lipped channel columns at elevated temperatures were conducted to clarify the local buckling strength and collapse temperatures. The effective width concept which has been improved by the past study was used to evaluate the local buckling strength, and it was clarified that the improved effective width concept offered the average values of the experimental results. Furthermore, the effective width concept using the design reduction factor was proposed for the fire resistant design of cold-formed steel structures.
This paper deals with the joint strength in the non-diaphragm connection of a CHS column to H-section beams to which different depth beams were joined in two orthogonal directions. The yield, plastic, and ultimate moment capacities of the cylindrical wall of the non-diaphragm connection subjected to biaxial-symmetrical bending moment were examined by using the finite element method. Additionally, prediction formulae to estimate the joint strength with a level difference at the lower flange were proposed by applying the formulae of joint with no level difference previously developed by the author, using linear interpolation. By comparing the prediction lines with the numerical solutions, it was confirmed that the prediction formulae demonstrated good accuracy.
The recommended design parameters of the built-up beams using hot-rolled channel steel are studied from the following 3 aspects:
1. To ensuring the stress safety of the built-up beams and the high tension bolts, S0/H=1 is given as the recommended distance from beam end to nearest bolts. “H”is cross-section height of built-up beam.
2. The bolt pitch of the built-up beams is recommended to be S/H =3. Under this condition, the gap between the channel steel is restrained.
3. To effectively prevent the lateral buckling of the built-up beams, the lateral support spacing is recommended as lb/b≤13. “b” is cross-section width of built-up beam.
Drilling tapping screw joints are generally used for the thin-plate lightweight steel structure. As the span of the building increases, the joint stress increases and the number of drill screws increases. This causes deterioration of workability of the joint. If the drill screw joints can be replaced with a high-strength bolted friction joints, the number of screws required will be reduced and the workability will be improved. The purpose of this study is to obtain basic data on bolted joint strength and tightening control of thin-plate galvanized steel. Tightening tests and slip tests are conducted, and the effects of various variables are clarified.
A large shaking table test of a steel-framed unit house specimen with a partition wall was conducted to obtain the relationship between the rotation angle (Rot) of a partition wall obtained from the gyro sensor and the inter-story drift ratio (IDR) of the frame. Additionally, damage classification using deep learning was performed from the images obtained by the monitoring camera employed to the shaking table test. Combining the IDR and/or Rot information obtained from the monitoring sensors and the visible damage information obtained from the monitoring cameras (as the damage state of DS1, DS2 and DS3), a method of updating the prepared fragility curve by Bayesian estimation is proposed. Furthermore, possibility of optimizing the prepared fragility curve by applying the appropriate IDR-Rot relation is discussed.
This paper aims to evaluate the applicability of the equivalent linear analysis method for reinforced concrete, which uses frequency-independent hysteretic damping with a small computational load, to the seismic design of reactor building of the nuclear power plant. To achieve this, we performed three-dimensional FEM analyses of the soil-structure interaction system, focusing on the nonlinear and equivalent linear seismic behavior of a reactor building under an ideal soil condition. From these results, the method of equivalent analysis showed generally good correspondence with the method of the nonlinear analysis, confirming the effectiveness. Moreover, the method tended to lower the structural stiffness compared to the nonlinear analysis model. Therefore, in the evaluation of the maximum shear strain, we consider that the results were more likely to be higher than the results of nonlinear analysis.
This study shows the modeling procedure for integrated structure-soil models by nonconforming meshes. Nonconforming meshes are modeled by s-version finite element mesh superposition method (s-FEM) with mesh protrusions. The s-FEM can combine 2 nonconforming meshes by adding unique boundary conditions to maintain the continuity of displacement in an analytical model. In order to derive the validity and the index of highly accurate modeling of the proposed technique, three analysis examples are presented in this paper. In the static analysis, the principal stresses and nodal displacements of the nonconforming mesh coincided with the corresponding reference results calculated by FEM with fine mesh. In the second example,the eigenvalues and eigenvectors calculated by the proposed method were in good agreement with the reference solution. It has been confirmed that the condition of mesh superposition affects the analytical accuracy in the time history response analysis.
There have been formwork methods which make it possible to strip early before the strength of concrete reaches designed strength using structural calculations. Sometimes, finite element method (FEM) is used for the purpose. However, FEM requires times to get satisfied results with “try and error”. In this research, in order to reduce the analysis cost, positions of remained props are determined using finite element analysis and multi-objective optimization whose objective functions are number of remained props and a function of safety factor of the members. The early stripping of formwork props with FEM and optimization is applied into a building that has a complex plan. As a result, the number of remained props is significantly reduced. Furthermore, a measurement of axial forces acting on the props is made during the actual construction. The validity of the finite element analysis is proved by the measurement.
In recent years, the use of anisotropic materials such as CLT has been increasing, but there is no slab design formula when anisotropic materials are used. Therefore, in this paper, we propose a design formula for orthogonal anisotropy slabs. When the boundary condition of the slab is fixed all around, the formula obtained from the cross-beam theory is used in the normal RC slab, but this formula calculates a value smaller than the FEM solution. In this paper, in order to maintain continuity with this standard formula, a design formula for orthogonal anisotropic slabswith safety similar to this formula is proposed. The proposed formula is expressed by multiplying the formula obtained from the cross-beam theory by a correction function, and shows that the error is within about 10%.
Recently, some examples have been reported about collapse of building structures by gravity as an outcome resulted from accidental action or excitation not prepared in the design process. Redundancy and a key-element have been taken from a viewpoint of assuring robustness of a structure even if it receives unexpected disturbance. In this study, a questionnaire investigation was performed to experts and non-experts about human judgments related to structural redundancy of framed structures against disappearance of a member. By abstracting the rules of fuzzy inference about the classification of structural redundancy, the membership function was composed related to humans’ decision-making.
In the present study, using a square plan tall building models with various aspect ratios, characteristics of peak pressure coefficients, mean and fluctuating force coefficients and power spectra were systematically investigated through a series of wind tunnel tests. From the wind tunnel tests, the following were found. The peak pressure coefficients from the wind tunnel tests corresponded well to those from the AIJ-RLB (2015), and values prescribed in AIJ-RLB (2015) can be extended to the tall buildings with aspect ratio of 9.5. Mean force coefficients in X- and Y-axis increased with increasing aspect ratios, while fluctuating force coefficient CFX showed decreasing tendency and fluctuating force coefficient CFY showed increasing tendency with aspect ratio. Mean and fluctuating torsional moments were quite small and showed less variation when compared with force coefficients in translational directions. And, from the Den Hartog Criterion, it was found that aerodynamically unstable vibration could occur for tall buildings with aspect ratio larger than 3 for the current experimental conditions. Lastly, the shapes of power spectra of X-axis force coefficient SCFX(f) showed similar shapes regardless of aspect ratios, but for the power spectra of Y-axis force coefficient SCFY(f), peaks corresponding to the reduced frequency of 0.1 increased and became narrow band with increasing aspect ratios.
The present paper investigates the wind resistant performance of a mechanically-attached waterproofing system installed on flat roofs of middle-rise and high-rise buildings with or without parapets considering the wind pressure variations in both space and time. First, wind pressure distributions on the roofs were measured in a turbulent boundary layer. The condition providing the most critical negative peak pressure coefficient irrespective of wind direction and pressure tap location was detected for each building. Then, we developed a test method for evaluating the wind resistant performance of the roofing system using three Pressure Loading Actuators (PLAs) and a chamber to which a full-scale specimen was attached. The chamber was divided into three spaces by using thin silicon sheets. The PLAs generated different fluctuating pressures in these spaces using the time history of wind pressure coefficients measured at three different points near the windward corner of the roof in an oblique wind. The membrane deformations and the wind forces acting on the fasteners of the roofing system were measured. The results indicated that horizontal forces nearly equal to or larger than the vertical ones were generated on the fasteners, which may cause pulling out of fasteners more easily. The failure mode was found to be different from that observed in a ramp pressure loading test. Finally, we developed a model of finite element analysis, which was validated by the experiment. The results of analysis for a wide area of roofing system indicated that relatively large horizontal forces were generated on the fasteners in the field region of the roof for buildings with parapets.
Wind-induced dynamic response of a long-span flat roof is investigated on the basis of the computational fluid dynamics with large eddy simulation. First, the unsteady aerodynamic forces, which are represented by aerodynamic stiffness and damping, were computed using the results of forced vibration tests in a uniform flow as well as in a turbulent boundary layer. The dynamic response of the roof is evaluated on the basis of a spectral modal analysis, in which the unsteady aerodynamic forces are incorporated into the frequency response function. The unsteady aerodynamic forces acting on the roof depends intricately not only on the wind speed but also on the natural frequency of the roof. The results indicate that the dynamic response will be suppressed by the unsteady aerodynamic forces when the reduced wind velocity, defined by the mean wind velocity and the natural frequency and span of the roof , is less than 1.0.
An examination is performed on the use of soil-cement mixing walls that were treated previously as temporary structures left buried in the ground, as permanent piles to rationalize foundation structures and reduce environmental burdens. This study aims at utilizing the embedded portion of the soil–cement mixing wall as a permanent pile, and evaluates the bearing capacity and tensile resistance in the static axial reciprocal load tests. This paper firstly describes the background and the previous studies, and then summarizes the static axial reciprocal load tests for the single piles which is considered the construction method of soil-cement mixing wall. Subsequently, the evaluation method of bearing capacity and tensile resistance on the soil-cement mixing wall is discussed.
Steel pipe piles with wings are suitable for construction and environment. However, the wings at the tip of the pile installed to increase the bearing capacity disturb the surrounding ground after the penetration, which affects the frictional force on the peripheral surface of the pile and the coefficient of lateral subgrade reaction. In this study, the hardness of the surrounding ground after penetrating a steel pipe pile with wings made of flat steel plate into the sandy ground rotationally was measured by the cone penetration resistance, and the change in ground hardness before and after the pile penetration was grasped. In addition, it is considered that the steel pipe pile with wings has the effect of compacting the surrounding ground by penetrating the pile body without removing the soil. Therefore, in this study, we attempted to quantify the effect of ground disturbance for piles with wings to change the ground. hardness Moreover, we evaluated the effect of expanding the ground to harden the ground using the cavity expansion theory.
For a building with base seismic isolation or tuned mass damper (TMD), an inverse problem is formulated based on the pole allocation method in control theories. Each structural system is simplified as a 3DOF lumped-mass shear model. The natural frequencies and the corresponding damping ratios in the three vibration modes are set as the initial control target. The introduced closed-form expression clarifies how the isolator's or TMD's natural frequency and the damper's capacity are related to three natural frequencies and to the damping ratios. The expression explains the trade-off relationship among the modal damping ratios in each structural system. The similar mathematical equation has already been introduced for a 3DOF model with interstory seismic isolation. The trade-off expression commonly understands the control effect of base seismic isolation, interstory seismic isolation and TMD. The equation is also found in the 2DOF simplified system with base isolation or TMD. By linking the pole allocation for the 2DOF system with a TMD optimization theory, the TMD's mass ratio is calculated from the target supplemental damping. This process matches the performance-based design.
In recent years in Japan, various research and developments using oil dampers have been carried out to find a way to suppress the displacement of the seismic isolation structure in response to a large-amplitude seismic motion exceeding design specifications. As a countermeasure, the authors have proposed a velocity-dependent, multi-staged oil damper. For the performance of the seismic isolation device responds to a large-amplitude seismic motion, the repeated deformation dependence of the oil damper has been evaluated using time history response analysis by changing the damping coefficient from moment to moment and so far, there has been little research of detailed evaluation. In this paper, we report about a new function newly introduced in OpenSees, which takes into account the repeated deformation dependence of the oil damper, and verified the response suppression effect by the proposed damper, while conducting a seismic response analysis for the test seismic building. As a result, it is concluded that the velocity-dependent, multi-staged oil damper works effectively when the repeated deformation dependence of the seismic isolation device is taken into consideration.
The Q–Δ effect is a phenomenon that a column with different lateral stiffness generates a restoring torsional moment owing to geometric nonlinearity when its top displaces in two horizontal directions simultaneously. The Q–Δ resonance that is resonance of a torsional mode induced by the periodic torsional moment due to the Q–Δ effect could cause considerable torsional vibration even in non-eccentric buildings. However, the Q–Δ resonance in higher-order modes has not been investigated well. We first constructed a model of a two-story non-eccentricity structure and derived the conditions of the Q–Δ resonance considering higher-order modes. Then, we conducted shaking table experiments and finite element analysis to reproduce the experiments. As a result, it was confirmed that the second mode in the torsional direction was excited as predicted by the derived Q–Δ resonance condition. Moreover, the finite element analysis could reproduce the experimental result with high accuracy.
This paper investigates the effects of mass/stiffness ratio between stories with and without dampers, and the stories ratio on the Ds-value, which expresses the response-reduction effect, and the dampers’ energy absorption for a medium/low-rise building, aiming to contribute to the actual design of vibration control structures with dampers installed in partial stories. It also determines realistic constraints on the maximum shear coefficient and the maximum inter-story deformation angle of a 1-layer with respect to the design input energy, and propose a simple practical formula for the primary natural period of a main frame that copes with these constraints.
One of the objectives of this paper is to understand dynamic soil-structure interaction effects in a ground motion recorded at a seismograph of Nishihara village office during the main shock of the 2016 Kumamoto Earthquake. Another objective is to understand the impact of using the record containing the dynamic soil-structure interaction effects to interpret damages to wooden houses located around the seismograph. First, we conducted sensitivity analyses whose analysis parameters are the characteristics of ground motions and buildings to understand dynamic soil-structure interaction effects on observed records qualitatively. Next, assuming that the ground motion was recorded at the foundation of Nishihara village office, we estimated the ground motions on the free-field by inverse analyses using the dynamic interaction model of Nishihara village office. Finally, simulation analyses of two-story wooden houses were conducted using the estimated ground motions on the free-field.
Regional base hospitals require high performance to maintain their functions even in the event of a large earthquake. This study proposes a method to design the parameters of a linear quadratic regulator (LQR) for a seismic control device aiming at improving the resilience of a medical facility. First, fault tree analysis was conducted to reveal the factors that hinder the recovery of medical facilities. The fragility curves and recovery-time probability models were constructed for medical devices based on the literature review and the interviews with medical device manufacturers. Using these models, the recovery curve, which is the relationship between the functional level and time, can be evaluated for the building–medical equipment system under an assumed earthquake ground motion. We propose to minimize the time to recover up to the defined functional level, 95% or 80%, in designing parameters for an LQR control system. The effectiveness of the proposed control design method was investigated for a building with a control device installed on its top floor, and it was confirmed that the proposed method improved the resilience performance compared with the conventional control method.
The Pacific coast of Tohoku Earthquake, damage was caused by falling ceilings. The most common countermeasure for falling ceilings is reinforcement with increased rigidity of the joints. However, there is a risk of causing an increase in the response acceleration, which could lead to a higher-than-expected seismic force input to the ceiling. Therefore, the authors propose the application of a vibration control system using block and tackle to ceilings. In this paper, the response reduction performance of the block and tackle damping mechanism at the ceiling was confirmed by shaking table experiments.
In our previous studies, seismic forces for secondary systems (SS) such as nonstructural components are investigated using light-weight bending-beam models with boundary condition (BC) of both pin-supported ends or of both fixed ends. In this paper, seismic forces for SS modeled as beams with another BC of one fixed end and the other pin-supported end are examined. Structural frames and SS are assumed to be linear. A modal analysis method for them is derived. The results with different BCs are compared and clarify the effect of BCs on seismic forces for SS.
It is urgent problem to improve the earthquake resistance of existing wooden houses. As an alternative idea of ordinal seismic retrofitting method, seismic shelters are sometimes utilized. They are devices to protect human life from house collapse by inserting them inside wooden houses. However, this method has a major disadvantage that it cannot reinforce the building itself. The seismic retrofitting method by connecting shelter to existing houses with oil dampers was proposed in previous studies. In this paper, the method was extended to one-story buildings with eccentricity and to two-story buildings without enough strength on the first floor. The response control effect was confirmed by time history response analysis using the collapsing simulation program wallstat. The following results were obtained from this study: (1) In case of eccentric one-story houses, it is possible to reduce earthquake response by connecting shelter and the torsional behavior can be restrained. (2) For two-story houses, the response of the first layer can be reduced. In addition, the increase of the second layer response can be suppressed by connecting with oil dampers.
In this paper, a method of uniform inter-story drift angle of elasto-plastic equivalent shear-spring model in seismic response is discussed. The main contents are as follows. (1) A method to achieve a uniform inter-story drift angle response that envelops the maximum response values of multiple seismic motions is shown by setting the primary mode form, updating and adjusting the stiffness and the skeleton curve, and repeating the process. (2) Applying the response uniformity method for elasto-plastic buildings, a method of placing elastoplastic dampers in each story with the goal of uniform response is proposed. Good results are obtained in time history analyses, confirming effectiveness of these methods.
The authors developed a three-dimensional seismic isolation system to ensure isolation performance in the vertical and horizontal directions. This isolation system is required for a large-scale disc spring to achieve both the support and isolation functions. Additionally, two methods are required: one is to control the variance of restoring force, and the other is to predict the isolation performance using a response analysis. This paper describes an optimal combination method of disc springs to absorb the variance caused by the manufacturing process by calibrating the combination using a metaheuristic algorithm. Moreover, a method to identify the variables of the hysteresis loops caused by the combined disc springs is proposed using the metaheuristic algorithm. The applicability of these methods is verified using the static loading tests data obtained by a large-scale disc spring that expands the dimensions defined by the JIS B 2706:2013 and the ISO 19690-1:2017. The static loading tests were conducted using 72 disc springs with 350 mm in diameter and six−disc springs with 700 mm in diameter. This paper demonstrates that the proposed method can control the restoring force and identify the variables required for hysteresis loops accurately and efficiently.