著者

中田 幸造 山川 哲雄 金田 一男 黒木 正幸 ヌリ モハンマド ザヒッド ジャバディ パシャ

出版者

日本建築学会

雑誌

日本建築学会構造系論文集 (ISSN:13404202)

巻号頁・発行日

vol.85, no.778, pp.1633-1642, 2020

被引用文献数

1

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<p> An economic and convenient seismic retrofitting technique based on the thick hybrid wall (THW) technique reported by Yamakawa¹⁾ is proposed. In the proposed technique, a cast-in-site partial hybrid wing-wall is built using additional concrete sandwiched by steel plates and high-strength steel bars (PC bars) prestressing. The aim of this technique is to enhance the lateral strength, stiffness, and ductility of soft-first story reinforced concrete (RC) buildings that are vulnerable to large seismic excitations. In the THW technique, the retrofitted section consisting of an additional wing-wall with short depth and the existing RC column are unified together as one unit using channel-shaped steel plates and tightened with PC bars. Since the additional wing-wall is not reinforced by longitudinal or transverse bars, the technique is convenient and cost effective. The important structural aspect of the THW technique is increasing the flexural strength as well as ductility by ensuring that all the longitudinal bars in the existing RC column yield in tension due to the increment of the internal moment lever arm, which results from the increase in the neutral axis depth into the additional wing-wall. To verify the efficiency of the proposed THW technique from the perspective of flexural strength, the equations to evaluate ultimate moment resistance in the retrofitted THW column section was proposed³⁾ based on the ACI stress block parameters, which consider the condition that all longitudinal bars yielded under tension in the existing RC column, and the additional wing-wall was in the compression side. Furthermore, the equation to calculate the minimum additional wing-wall length ratio was also proposed to estimate the affordability of the THW technique in Ref. 3).</p><p> This study aimed to experimentally investigate the shear resistance and shear strength of the arch mechanism of the RC column retrofitted by the THW technique. From the test results of the retrofitted RC column showing a flexural failure mode, the proposed equations of the ultimate moment resistance³⁾ of the THW technique were verified.</p><p> Experimental investigations were conducted on six specimens. In this study, two types of specimens were considered. One was a retrofitted RC column with no bonding force between the concrete and embedded longitudinal bars, thereby generating the arch mechanism. The other was a retrofitted RC column with bonded longitudinal bars to evaluate the flexural strength. In brief, the conclusions are as follows: (1) Bonded specimens for which the THW technique is applied showed flexural behavior with high ductility involving the tension yielding of all longitudinal bars in the existing RC column, and the calculated results of proposed equations are in good agreement with the test results. (2) The application of the THW technique not only creates a connection between the RC column and additional wing-wall, but also increases the shear resistance greatly. (3) In the unbonded specimens, the compression zone of the RC column for the arch mechanism was greater than 0.5D, and the zone was distributed from 0.8D to 1.0D. (4) Based on the test results and observations, an equation was proposed to evaluate the shear strength in the case of the THW technique following the proposed concept of the shear resistance (arch) mechanism with a nonuniform section of compression strut. The calculated results of the proposed equation are in good agreement with the test results showing shear failure mode.</p>

著者

中田 幸造 山川 哲雄 JAVADI Pasha NOORI Mohammad Zahid 金田 一男

出版者

日本建築学会

雑誌

日本建築学会構造系論文集 (ISSN:13404202)

巻号頁・発行日

vol.85, no.767, pp.97-104, 2020

被引用文献数

2

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<p> A strength–ductility–type seismic retrofit technique for soft first-story reinforced concrete (RC) buildings via addition of wing walls or panel walls was proposed by Yamakawa⁴⁾. This method is called the thick hybrid wall (THW) technique and is performed by jacketing an RC column and an additional wing wall using channel-shaped steel plates connected together by high-strength steel bars (PC bars). The steel plates and PC bars make steel formworks inside the RC frames during the additional concrete casting. Furthermore, they can serve for shear strengthening and confinement of RC columns after hardening of additional concrete. No longitudinal and transverse reinforcements or anchorage systems are provided in the additional wing wall; therefore, the construction is easy and cost-effective. The previous investigation⁶⁾ of the one-bay one-story RC frame retrofitted by the THW technique verified that both lateral strength and ductility are considerably improved compared to those of the non-retrofitted RC frame. This study aims to propose equations that can be used to estimate the ultimate moment resistance and the minimum wing-wall length of RC columns retrofitted by the THW technique.</p><p> The ultimate moment resistance of the RC column with a wing wall (THW technique) is calculated by considering the whole section as a united section. In the proposed method, the strain distribution of the THW column section is divided into three fields, such as field A, B, and C, based on the location of the neutral axis changes according to the axial force levels. The unified THW column section is asymmetric about the centerline of the square column section; hence, the wall side is considered in compression only. The moment capacity equation is derived by considering the equilibrium of internal tension and compression forces with the external vertical axial load. Assuming the location of the neutral axis depth, a generalized equation is obtained based on the equivalent rectangular stress block parameters for concrete in compression that is adopted by the American Concrete Institution (ACI). Practically, the THW technique is applied in the field A, where all the rebars in the tension and compression sides of the existing RC column yield in tension, and the limit axial force ratio of the field A is represented as <i>η</i>₁.</p><p> The ultimate moment resistance of the THW column section is more accurately calculated by the fiber model method. The stress-strain model of concrete in the fiber model analysis is considered as Monder's model¹¹⁾. In Section 4, the calculated results of the proposed equation, fiber model analysis, and simplified equations⁸⁾ are in good agreement with the previous test results of both-sided (R03WC-P200S)⁴⁾ and one-sided wing-wall (R03WO-S)⁵⁾ specimens retrofitted by the THW technique.</p><p> The equation used to calculate the minimum wing-wall length of the THW technique is proposed in Section 5 based on the limit axial force ratio (<i>η</i>₁) in the field A. The calculated results based on the minimum wing-wall length equation show that the additional wing-wall length ratio <i>β</i> increases with increasing the axial force ratio <i>η</i>. Furthermore, <i>β</i> decreases with increasing the ratio of the compressive strength of concrete <i>κ</i> and depends on the tensile rebar ratio <i>q</i>.</p>

著者

中田 幸造 黒木 正幸 山川 哲雄 菊池 健児

出版者

日本建築学会

雑誌

日本建築学会構造系論文集

巻号頁・発行日

vol.82, no.737, pp.1071-1080, 2017

被引用文献数

2

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&nbsp;A ductility-type seismic retrofitting technique is proposed for reinforced concrete (RC) columns. This involves arranging high-strength steel prestressing bars (PC bars) on the four faces of an RC column as external hoops. Hence, active confinement due to the tensile forces in the PC bars as well as passive confinement and transverse reinforcement can be expected. With regard to the active and passive confinements, previous authors have shown that the compressive strength and ductility of confined concrete are greatly improved and have proposed a stress&ndash;strain relation for confined concrete. The aim of the present study is to experimentally investigate the shear strength and shear resistance mechanism of RC columns retrofitted by this technique.<br>&nbsp;The retrofitting details of the test specimens are shown in Table 1. The elevation and cross-section are shown in Fig. 1. To investigate the shear resistance mechanism (truss or arch mechanism), two types of specimen are considered in this study. One is a retrofitted RC column with no bond force between the concrete and the embedded longitudinal reinforcement, thereby generating the arch mechanism. The other is a retrofitted RC column with bonded rebars to evaluate the truss mechanism, which relies heavily on the bond resistance between the rebars and concrete. The column specimens used in this test had a square cross-sectional dimension of 250&times;250 mm², a height of either 500 mm or 750 mm, and a shear span-to-depth ratio (<i>M/VD</i>) of either 1.0 or 1.5. The longitudinal reinforcement ratio (<i>p_g</i>) of the retrofitted specimens with bonded rebars was either 3.67% (8-D19) or 5.51% (12-D19) and that of the specimens with unbonded rebars was 1.36% (12-D10). The shear reinforcement ratio (<i>p_w</i>) of the column specimens was 0.08%. The test parameters of the column specimens are the initial tension strain of the PC bars, their spacing, the axial force ratio, shear span-to-depth ratio, and the bonded/unbonded nature of the rebars.<br>&nbsp;In Chapter 3, the following main points are discussed. (1) The initial tension force of the PC bars enhances the shear strength of the truss mechanism. (2) Applying a lateral confinement pressure to an unbounded RC column, the shear strength of the arch mechanism can be increased. (3) For the bonded specimens, the measured gradient of the compressive diagonal force of the truss mechanism, which is one of the internal forces of an analogous truss comprising PC bars that act as tension members, the bond force of rebars, and the diagonal concrete force was nearly 45&deg;. (4) The shear strength of the arch mechanism increases with increasing axial force. (5) In the unbonded specimens, the slope of the line of thrust and the depth of the compression zone of the arch mechanism correlate with the lateral confinement pressure and the vertical axial load. (6) In the bonded specimens, the depth of the compression zone of the arch mechanism had no correlation with the lateral confinement pressure and the vertical axial load.<br>&nbsp;Chapter 4 describes the comparison between the experimental shear strength and calculated results based on the modified Arakawa mean and Minami equations shown in Figs. 17 and 18. These figures show that the test results are in agreement with the modified Arakawa mean equation, and that the modified Minami equation can reasonably be applied to assess the shear strength considering the truss and arch mechanisms.

著者

原口 貴臣 中田 幸造 山川 哲雄

出版者

一般社団法人日本建築学会

雑誌

日本建築学会研究報告. 九州支部. 1, 構造系

巻号頁・発行日

no.51, pp.533-536, 2012-03-01