Masanobu Sakashita

Cyclic Performance of Lower Stories of Mid-Rise Reinforced Concrete Frame Buildings

This article reports on an experimental study on the cyclic behavior of the lower stories of a mid-rise reinforced concrete (RC) frame building, focusing on the complex interaction between columns, beams, and joints. The authors tested two, two-story frames with one bay; each represents the lower two stories of an 11-story RC frame building. The two frames differed only in the amount of variation of the axial loads. Both frames were designed in accordance with the Japanese design guidelines. The results of the study showed that although the overall load-displacement behavior of the two frames differed only slightly, the first-story column shear varied greatly with the level of column axial load. The columns and beams elongated during both the tests, with the second-floor beam elongation exceeding 1.5% of the clear span of the beam. In addition, axial load intensity affected the amount of cracking. The main damage was localized at the beam ends near the beam-column joints for a distance equal to half of the beam height. The authors conclude by proposing practical analytical models for predicting column elongation, based on a simple rocking model, and beam elongation, based on crack width evaluation.

Simulation of Seismic Load Resistance of Core-Walls for Tall Buildings

This paper addresses the seismic performance of core-walls based on an experiment and numerical analysis on two 1/7.5 scaled L-shaped concrete core-wall specimens. Concrete strength was 77 MPa and the yield strength of vertical reinforcement was over 700MPa. Test variable was the loading path on the axial load – lateral load relation. Axial load was varied as high as 6MN or 50% of the axial load capacity for one specimen and 4.2MN or 35% for the other specimen as a linear function of the lateral load. The lateral load-drift relations were recorded with local deformation and damage, focusing on the yield of reinforcement and crushing of concrete. Damage of columns was severe and indicated the importance of good confinement at this region for better seismic performance. The numerical models with finite shell elements well simulated the intensity and extent of damage in addition to backbone curves of lateral load - drift angle relations when the pullout of longitudinal reinforcement of columns is considered.

Direct Strut-and-Tie Model for Ultimate Shear Strength of Reinforced Concrete Structural Walls

A direct strut-and-tie model to calculate the ultimate shear strength of structural walls based on an interactive mechanical model (C.Y.Tang et al.) is presented. Two common failure modes, namely, diagonal splitting and concrete crushing, are examined in this paper. Ultimate shear strengths of structural walls are governed by both the transverse tensile stresses perpendicular to the diagonal strut, and the compressive stresses in the diagonal strut. Such proposed model is verified aganist three experimental case studies of structural walls. Generally, predictions by the proposed model are not only accurate and consistent in each case study, but also conservative.

Damage Assessment of Reinforced Concrete Columns under High Axial Loading

This paper describes how damage assessment has become more important than ever since structural designers have started to employ performance based design methods that require structural and member behaviors at different limit states be predicted precisely. This paper aims at clarifying the confining effect of concrete of a plastic hinge zone of a reinforced concrete column confined by shear reinforcement, so that a designer can accurately predict damage when columns experience seismic loadings that include large axial force and bilateral deformations. In an experimental program, eight half-scale columns and eight full-scale columns were tested under the reversal bilateral displacement with constant or varying axial load in order to study the effects of loading history and intensity on the confining effect. Since shear failure was inhibited by providing enough transverse reinforcement, as defined by the previous Japanese design guidelines, damage gradually progressed in a flexural mode with concrete crushing and yielding of reinforcing bars. The damage level depended on the bilateral loading paths and the axial load history. In an analytical program, a section analysis using a fiber model was employed and the effect of confinement on the behavior of core concrete was studied. The analysis predicted the observed deterioration of moment capacity and longitudinal shortening under different loading conditions and for different specimen sizes. The paper is considered to increase the accuracy with which damage in reinforced concrete columns subjected to severe loading is assessed.

BI-DIRECTIONAL LATERAL LOADING TESTS ON RC SHEAR-DOMINANT WALLS

京都大学工学研究科建築学専攻 修士(工学) 日本学術振興会特別研究員 DC 国立研究開発法人建築研究所構造研究グループ 主任研究員・博士(工学) 京都大学工学研究科建築学専攻 准教授・博士(工学) 京都大学工学研究科建築学専攻 教授・博士(工学) Grad. Student, Architecture and Architectural Engineering, Kyoto University, M. Eng., JSPS Research Fellow Senior Research Engineer, Department of Structural Engineering, Building Research Institute, Dr. Eng. Assoc. Prof., Architecture and Architectural Engineering, Kyoto University, Dr. Eng. Prof., Architecture and Architectural Engineering, Kyoto University, Dr. Eng. 日本建築学会構造系論文集 第82巻 第735号,683-692, 2017年5月 J. Struct. Constr. Eng., AIJ, Vol. 82 No. 735, 683-692, May, 2017 DOI http://doi.org/10.3130/aijs.82.683 【カテゴリーII】

Shear Resistance Mechanism of Posttensioned Precast Concrete Members

An analytical model to investigate the shear resistance mechanism of a posttensioned precast concrete (PPC) member is proposed. The model is based on the truss mechanism. The compatibility of strains and the equilibrium of stresses of the shear cracked concrete, prestressing steel, and shear reinforcement are applied to the shear model. The proposed truss model consists of three stress zones (zones 1, 2, and 3). Triangle struts of cover concrete subjected to uniaxial compressive stress are defined as zone 1. Biaxial stress zones of diagonally cracked concrete between the longitudinal bar and prestressing steel are defined as zone 2. Zone 3 is defined as the diagonally cracked concrete zone between both compression and tension prestressing steels. The model considers the bond characteristics of prestressing steel. The proposed truss model is useful to predict not only shear strength, but also the shear deformation, tensile stress in shear reinforcement, and failure mode of a PPC member. By comparison of experimental and analytical results, an accuracy of analytical results by the proposed method was verified. The proposed method evaluated experimental results, which are shear strength, shear strain, and tensile stress in shear reinforcement in a good accuracy.

Shear transfer mechanism of a multi-storied shear wall with peripheral members

In the current design code, cantilever shear walls are normally assumed to stand on a solid foundation, and foundation beams, slabs and piles are designed separately without considering their interactions. Moreover, the shear transfer mechanisms are neglected, which along the wall base vary depending on the cracks and inelastic deformation levels at the shear wall base. In this study, a 25% scaled specimen consisting of the lowest three floors of shear wall with a foundation beam, the first floor slab, and two piles in the transverse direction was tested to clarify the variation of the shear transfer mechanisms considering the interaction between a shear wall and other structural elements. Contrary to the design, the yielding of the shear wall preceded that of the foundation beam. From strain distributions of longitudinal reinforcements in the foundation beam, the transition of the shear transfer mechanism was confirmed.

FLEXURAL AND SHEAR BEHAVIOR OF PRECAST PRESTRESSED CONCRETE BEAM WITH HIGH STRENGTH SHEAR REINFORCEMENT

Seven half-scale post-tensioned precast concrete beams were tested under anti-symmetrical flexure. The experimental parameters were shear span ratio and shear reinforcement ratio. Multi-strands and high strength shear reinforcement with nominal yield strength of 785 MPa were used as post-tensioning steel and shear reinforcement, respectively. Yielding of shear reinforcement was not observed in any of the specimens. The flexural capacity evaluated by the ACI rectangular concrete stress block with plane section assumption agreed well to the experimental results. The shear capacity was estimated by the design equation 71.2a in the AIJ Standard for Structural Design and Construction of Prestressed Concrete Structures. The experimental results collected by literature survey to past research revealed that shear failure modes could be related to each of the experimental parameters (shear span ratio, shear reinforcement strength and shear reinforcement ratio).