Dynamic properties of a structure tested using a shake table could be estimated correctly, if one uses an appropriate transfer function between the structural motion and table motion measured. A unique method to construct the transfer function including the effect of rocking motion of the three-dimensional (3D) shake table is proposed. By using an analytical model of five-story building, the method is shown to be much more accurate than the conventional method that considers table motions of only the horizontal direction. The method is also applied to estimate equivalent linear modal properties of a full-scale five-story building tested by using the E-Defense, the world's largest 3D shake table. Different cases of the building having linear dampers, nonlinear dampers, or no dampers, with elastic or slightly yielding frame are considered, and applicability of the method discussed.

View full abstract

We proposed a new procedure for evaluating the parameters of the asperity models for predicting strong ground motions from inland earthquakes caused by long strike-slip faults. The evaluation formula of averaged dynamic stress drops obtained by Irie et al. (2010)¹⁾ for surface ruptured faults 15 to 100 km long was adopted in our procedure, because the evaluation formula of the averaged static stress drops for circular cracks, commonly adopted in existing procedures, could not be applied to surface ruptured faults or long faults. The dynamic stress drop averaged on the entire fault was estimated to be 34 bars from the data of the rupture areas and the seismic moments of actual earthquakes, and the dynamic stress drop on the asperity was estimated to be 122 bars from the data of the short-period levels and the seismic moments of actual earthquakes. These results led to the conclusions that the asperity areas were 23 % of the entire ruptured areas.

View full abstract

We present numerical results for hydrodynamic vibrations of an upstream circular cylinder in tandem arrangement which is mounted in a uniform flow. Two circular cylinders are assumed as each rigid body, and the upstream circular cylinder is supported by damper-spring systems in in-line and cross-flow directions. In our computations, the gap ratios of two kinds between the centers of two circular cylinders are taken into consideration and they are given as 2 and 3 which are smaller than the critical gap ratio. In addition, the Scruton number is set as 0.99. Vibration amplitudes in the in-line and cross-flow directions of the upstream circular cylinder are computed by a third-order upwind finite element scheme and the numerical results are discussed in detail.

View full abstract

A method is proposed to control seismic response of a high-rise building considering function maintenance of an elevator. When a cost function for optimal control is formulated to reduce response of rope, response of a building deteriorates especially in high frequency range. In order to overcome this drawback, the proposed method employs frequency shaping linear quadratic Gaussian control and variable gain feedback. Time history analysis is carried out using simulated ground motion and it is verified that the proposed method can reduce the response of both a building and rope effectively.

View full abstract

A control method is proposed based on frequency shaped LQG and variable gain feedback in order to choose proper control objective and prevent saturation of control force considering intensity of ground motion and level of building response. The controller examines exceedance rate of building response over a threshold and the maximum required control force estimated from ground acceleration in order to reduce response of both a building and elevator rope efficiently preventing saturation. It is demonstrated that the proposed method can suppress unpreferable response of building layers near the top induced by control force.

View full abstract

This paper shows application of viscous mass damper with restriction mechanism to base-isolated structures, and its effectiveness. Damper force restriction mechanism was modeled by complex stiffness model and it shows the response characteristic of this system based on equivalent linearization method. The effectiveness of this system was examined by non-linear time history response analysis using seismic waves. These results confirmed that it is possible to apply large added mass to base-isolated structures, and that large displacement reduction effect was achieved by using damper force restriction mechanism. At this time, damper force restriction mechanism clearly showed that damping force can be controlled.

View full abstract

Elasto-plastic behaviors of the one-bay and one-story gable steel frame structures, subjected to the repeated variable lateral loads under constant vertical ones, are analyzed using the hybrid stress finite element method. The specific and promising approach, which is shown in the Refs.1)-3) and is very advantageous to trace the elasto-plastic responses of steel structures under repeated variable loading, is employed. The skeleton and steady hysteretic characteristics of the frame under consideration are examined critically and circumstantially, comparing with the ones under monotonic loading, and their cause and mechanism are discussed and reasonably explicated.

View full abstract

Recently, the environmental impact has been required to be explicitly taken into account in the life cycle design of building structures besides the initial economical efficiency which has been ordinarily required up to the present days. Consequently, it is important not only to design the building structures so as to be safe as well as economical at the initial stage of completion of the building but also to pay attention and take into account the total behaviors of the designed and constructed building structures during all stages of their life cycles. The former paper by the authors has proposed the way to deal with the life cycle design of building structures with consideration of a hierarchy according to the ranks of building construction systems by using genetic algorithms as the optimization scheme with respect to both ecology and economy for evaluations. Authors have been developing computational software for the life-cycle design of structures through utilization of Genetic Algorithm. In this paper, the presumption method for the lifetime of structures is introduced, by which easy usage as well as practicality of the tool are expected. For evaluation of the lifetime of structures, the lifetime of each portion is individually evaluated where surrounding situations of them, such as near from water, exposed to outside of building and so on, are taken into consideration. This newly introduced treatment is expected to exclude the arbitrariness on the evaluation time of the life-cycle design and make the tool much more suitable for practical use.

View full abstract

Vertical loading tests were performed on the enlarged grouted base of nodular pile using pressurized sand tank for studying the effects of strength of enlarged grouted base and the length between the pile tip and tip of enlarged grouted base on the pile bearing capacity. The main conclusions based on the studies are as follows. 1) When the tip length was zero and the strength of enlarged grouted base was greater than 10 N/mm², the bearing capacity was equivalent to the case when the strength was 20 N/mm² until the settlement reached 10% of the pile diameter. 2) When the strength of the enlarged grouted base was 15 N/mm², there was no effect of the tip length on the load-settlement curve. 3) For all cases, even when the enlarged grouted base failed, the bearing capacity continued to increase.

View full abstract

Seismic deformation method with earth pressure and sidewall friction acting on an embedded footing has been developed, to evaluate pile's stress during soil liquefaction. To verify the effectiveness of the proposed method, the dynamic centrifuge tests were conducted. The following conclusions were reached: (1) The bending moment at the pile head, estimated by the proposed method, showed good agreement with the centrifuge tests results; (2) The estimated amplitudes of the resultant force of earth pressure and sidewall friction, and the phase difference between the resultant force and the structure inertia force agreed well with the experimental results.

View full abstract

A shape and section optimization method is presented for free-form steel structures considering cost of connections. Two types of rigid connections are considered. One is a conventional full-strength connection, and the other is a partial-strength connection using for example fiber reinforced mortar. The inherently different costs of the two are made continuous by introducing a cost increase function of the latter. A nest-structure optimization, consisting of a shape and section optimization as the main problem and cost minimization of each connection as the sub-problem, is proposed to minimize the total cost of members and connections. Examples of a single-layer lattice roof are shown to demonstrate the effectiveness of the proposed method.

View full abstract

In the precast-wall RC structures, the cotter-bars installed in the joints have been flare-welded. However, in terms of the assurance of the quality at construction cite, non-welding method is preferable for the connection of cotter-bars. In this research, in order to develop non-welding method, static loading tests are carried out for the total of 17 specimens with I-, T-, L-shaped vertical and horizontal joints utilizing clip-type splices as well as flare-welding. Each specimen has practical configuration of shear-cotters. Major findings include: (1) vertical joints utilizing clip-type splices exhibit the ultimate strength similar to those utilizing flare-welding, and (2) T- and L-shaped vertical joints exhibit approximately 0.8 times ultimate strength of I-shaped vertical joints due to the inclination of the angles of concrete compression struts developed in in-plane and out-of-plane walls.

View full abstract

The lateral bracings are usually set to upper flanges of H-shaped beams in the moment resisting frames, and then the stress of the braced flange may become tensile. If the bracings are connected to the tensile flange of H-shaped beams, its lateral buckling strength is more increased than that without bracing. The bracing connected to tensile flange must restrain torsion to increase the lateral buckling strength of the beams.
In this paper, the elasto-plastic lateral buckling load for H-shaped beams with lateral and rotational bracings is presented, and the relationship between the bracing stiffnesses and strength is estimated.

View full abstract

This research is concerned with the earthquake response of 3-dimensional multi-story steel moment frames with eccentricity. In this paper, we propose a simplified dynamic model for the frames. The model, which has six degrees of freedom for each story, is used to conduct earthquake response analyses. The results are compared with those from finite element method analysis using ABAQUS. It is clarified that the earthquake response of the frames is approximated through a numerical study using this model.

View full abstract

The objective of this study is to propose a new strength formula for beam-columns made of H-SA700 High-strength steel. The elastic lateral torsional buckling strengths of beam-columns subjected to axial force and bending moment at both ends are calculated by using the Galerkin method. In addition to the elastic lateral torsional buckling load, in-plane elastic limit strengths are calculated. As the analytical parameters, slenderness ratio and moment ratio of the smaller to the larger end moment are selected, and the analytical results are shown in interaction relationship between end moment and axial force. Examining the results, we proposed the strength formula basically composed of two equations that mean the strengths of lateral torsional buckling and elastic limit strength.

View full abstract

Lateral buckling is one of collapse modes of H-shaped beams and the effects of boundary conditions and end moment ratio on lateral buckling mode have not been clarified yet. The purpose of this paper is to propose new factors for evaluating lateral buckling strength. These factors are relevant to each conceivable condition based on elastic lateral buckling analysis in which boundary conditions and end moment ratio are considered. Also, in this paper the adaptation validity of these factors is mentioned through reviewing and comparing the previous studies subjected to evaluation of lateral buckling strength.

View full abstract

It is necessary to clarify the characteristics of the ideal viscous fluid material to examine a characteristic model of the viscous fluid damper of the various shapes. Here the small size testing equipment was used in consideration of the steel stiffness, the work efficiency and so on. But the correct grasp of the characteristic from the measured values with that equipment was difficult, because these values were not the ideal forces and were affected by the scale effect. Therefore, inspecting those unexpected forces and grasping the ideal values are important. First of all, part1 shows the method to consider properties of viscous fluid material under ideal condition with experiment and analysis, and the test outcomes performed in extensive strain, temperature and frequency.

View full abstract

The discussion on the title paper is focused on following points:
1. As for the proposed first evaluation method, an essential term is omitted which becomes important for the case of deeply embedded foundation and for higher frequency.
2. The range of applicability of the first method should be stated clearly not so as to be misused.
3. The second proposed method seems to require more numerical calculation step than the existing evaluation method proposed by Iguchi³⁾, and Kurimoto and Iguchi⁴⁾.

View full abstract

The authors would like to thank Prof. Michio Iguchi for his discussion, and the answers are as follows;
(1) We corrected the sign of Φ_y^* in the section 1 of equation (2). And also we corrected the description of related equations (3), (7), (15) - (18).
(2) We think the first evaluation method is useful as an approximate solution, though it is improved by considering the excavation force.
(3) We proposed that the first evaluation method should be used when the ratio of embedded depth and half foundation width is smaller than 3.0.
(4) About the numerical calculation step of the second evaluation method, we think it is a difference in approach about how to lead from the exact solution to a convenient solution.

View full abstract

Experimental and analytical achievements on the bearing stiffness and strength of wood in the above paper are discussed about the following items: 1) The proposed formula for bearing stiffness is based on an improper model of stress distribution. 2) The equation for calculating local stiffness in the vicinity of the contact region seems improper. 3) The bearing stiffness calculated from the proposed formula shows improper relations with bearing width as well as specimen height. 4) The size effect in bearing strength seems illogical.

View full abstract

The authors wish to thank Prof. Hitoshi Kuwamura for the discussion. The answer to his questions is as follows:
1) We verified stress distribution was rationally modeled. 2) We corrected a mistake in this article owing to Kuwamura's discussion. 3) The elastic modulus for calculations were calculated using average density of each conditions of specimen. 4) We verified that bearing strength was logical.

View full abstract