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>