Hiroyasu Sakata

Seismic Retrofit Using Rocking Walls and Steel Dampers

A retrofit system of prestressed concrete rocking walls and steel dampers is used to control the seismic damage mode and increase the strength and energy dissipating capacity of an 11 story steel reinforced concrete frame in Japan. Important details of the retrofit design are introduced. The seismic performance of the structure before and after the retrofit is evaluated through extensive nonlinear time history analysis. Results show that the rocking system can significantly reduce both the seismic responses to different earthquake ground motions and their scattering. This makes the damage mode and the seismic performance of the retrofitted building more predictable, leading to a possibility of more reliable performance-based seismic design.

In-Plane Behavior of Timber Frames with Masonry Infills under Static Cyclic Loading

AbstractThe good in-plane behavior of timber frames with masonry infills, characterized by an excellent ductility capacity, is presented and explained as observed during static cyclic experimental tests on wall panels. The aim of the study was to characterize the seismic behavior of the timber frames with rectangular masonry infill panels (without timber diagonals). Tests of materials and subassemblies were performed to identify the parameters influencing the performance of the system. Thus, the contribution of each component (masonry, timber) in the lateral force–resisting mechanism, the local interaction between masonry and timber elements, and final failure pattern are highlighted in this paper. A numerical model of the wall panel with masonry infill is described, as it was developed with FINAL v11 software, and it reasonably matches with experimental results.

Experimental Study on Timber-Framed Masonry Structures

Timber-framed masonry buildings are found all over the world, from common residential houses to important cultural heritage buildings. However, there is no design standard or published method to systematically evaluate the seismic capacity of this type of building. Therefore, an experimental study was developed to assess the mechanical behaviour of these structures. This study uses the construction details of Pombaline style Portuguese timber-framed masonry heritage buildings but without timber diagonals (St. Andrew’s cross). This Pombaline style timber-framed masonry structure without diagonals can be found in other countries such as Romania, Italy, Nepal, and China. Given the cultural heritage value of these types of buildings a research project was initiated at the Center for Urban Earthquake Engineering of Tokyo Institute of Technology with the objective of quantifying the effect of different seismic retrofitting methods using aramid fiber sheets in different layouts. However, to evaluate the effect of different retrofitting methods the evaluation of a non-retrofitted structure is needed first. This paper presents the results of an experimental program conducted on non-retrofitted masonry panels, timber frame, and a timber-framed masonry wall.

Lessons from the Behavior of a Monitored 11-Story Building during the 2011 Tohoku Earthquake for Robustness Against Design Uncertainties

Specifically detailed pin-supported walls with steel dampers have been used to seismically strengthen an 11-story steel reinforced concrete building. By looking at the observed damage and monitored motions of the building during the M9.0 Tohoku earthquake in 2011, it is demonstrated that nonstructural reinforced concrete partition walls have had a major effect on its seismic behavior during the earthquake, the neglect of which constitutes a major design uncertainty. A finite element model used to assist the retrofit design is calibrated, taking advantage of the accelerograms obtained during the earthquake. The results of nonlinear time-history analysis investigations with the modified model identify both the positive and negative effects of the nonstructural walls at various ground motion intensities, and suggest that the pin-supported wall-frame system exhibits higher robustness against both record-to-record and modeling uncertainties than its bare-frame counterpart does.

Subassemblage Cyclic Loading Tests of Buckling-Restrained Braced RC Frames with Unconstrained Gusset Connections

AbstractAn unconstrained gusset connection for buckling restrained braces in reinforced concrete frame structures is proposed and tested as an effort to mitigate the complicated and usually harmful interactions between the steel gusset plate and the adjoining reinforced concrete column. Local damage control incorporating the rearrangement of beam flexural strength is also proposed to enhance the reliability of the gusset connection by moving the potential plastic hinge of the beam away from the connection region. Two different connecting methods, one with posttensioned steel rods and the other embedded stud groups, were considered. The results of the cyclic loading tests on reinforced concrete (RC) beam-gusset connection subassemblies confirmed that both connecting methods are available as long as the local damage control is implemented, which is not only helpful in eliminating the unfavorable deformation loss at the connection, but more importantly, can prevent the buckling restrained braces (BRBs) from ...

Practical Method for Damage Evaluation Based on Point Estimate Considering Uncertainty of Structural Properties

This study introduces a practical method for evaluating structural damage based on a large-scale simulation targeting expansive areas, like whole cities. In such a seismic simulation that deals with numerous building structures, it is desirable to estimate the damage based on a stochastic evaluation considering the uncertainty of structural properties. This is because an accurate modeling of numerous building structures, according to each designed value, would require a great deal of time. However, a damage evaluation considering the model uncertainty generally involves numerous calculations and is inadequate for such a large-scale simulation. Therefore, we propose a method using the point estimate technique which can estimate the probability of damage under model uncertainty from a small number of calculations. The applicability and usefulness of the proposed method is evaluated by comparing it to the method based on a Monte Carlo simulation.

SIMPLIFIED DESIGN METHOD OF PASSIVELY CONTROLLED TIMBER HOUSES USING ALLOWABLE STRENGTH OF SHEAR WALLS

In order to mitigate seismic damage of timber houses, application of passive control devises is demanded. The authors have developed high performance shear walls with various types of dampers, which are called “energy dissipation walls”. For the future, new design method has to be proposed to generalize passively controlled timber structures. In this paper, a method to evaluate allowable strength of shear wall is proposed. Advantage of passively controlled structure is to reduce maximum deformation, and energy dissipation walls are added to a structure so that maximum deformation angle of the structure subjected to level2 earthquake is less than target deformation. Accuracy of the method is demonstrated through a lot of non linear time history analyses.

SHEAR FORCE—SLIP CALCULATION METHOD OF SINGLE BOLTED TIMBER JOINT WITH STEEL SIDE PLATES

We, in this article, propose a manual calculation method for the skeleton curb of single bolted timber joint. The calculation method takes into account the edge distance, the end distance, and the slenderness ratio as the parameters. The validity of the proposed calculation method was confirmed by the experimental results, the edge distance of 1d, 2d, 4d, 6d, 7d, the end distance of 1d, 2.5d, 4d, 7d, 10d, the slenderness ratio of 0.625 d, 3.75d, 7.5d, 10d.

EFFECT OF FLOOR SLAB ON MECHANICAL BEHAVIOR OF A CRUCIFORM FRAME USING P/C MILD-PRESS-JOINT

The PC-Mild-Press joint method is one of the methods which can control damage of structures with concrete. Authors have already carried out study and have clarified its mechanical behavior and damage. However, the effects of the floor slab on the structural behavior of the frame have not been clarified. In this study, experiments were conducted on a cruciform frame with a floor slab constructed by the PC-Mild-Press Joint method to determine its mechanical behavior and damage. The study focused on the effects of damage control when an prestress force was introduced into the floor slab using unbonded prestressing bars for the main floor slab reinforcement. The evaluation of damage in the floor slab derived from the crack width and the section analysis of interfaces M-θ are proposed.

TORSIONAL SEISMIC RESPONSE CONTROL BY VISCOELASTIC DAMPER FOR THREE-DIMENSIONAL WOOD-FRAME STRUCTURE WITH STIFFNESS ECCENTRICITY

Shaking table tests for full-scale wood frame specimens with large stiffness eccentricity are conducted. Specimen is single story, and its plan dimension is 1.82m in X-direction and 2.73m in Y-direction. Stiffness of specimens are unbalanced in X direction, along which input motions are provided by the shaking table. The eccentricity ratio Re, defined by Japan Building Standard Law is about 0.6 for the standard specimen. We test six specimens : one does not have any dampers and the others are provided with viscoelastic dampers in various arrangements. The performance of specimens is discussed by referring to story drift, damper deformation and dynamic properties.