高強度鋼纖維混凝土開口剪力牆行為研究與設計流程

The study of Behavior and Designing Process of High Strength Steel Fiber Reinforced Concrete Walls with Opening

李宇翔(Yu-Hsiang Li)

指導教授 ： 廖文正

國立臺灣大學/工學院/土木工程學研究所/碩士(2021年)

https://doi.org/10.6342/NTU202103660

摘要

近年來，高強度混凝土漸漸被廣泛使用，國內的相關規範也逐漸更新並採用之，且為了滿足現今建築的使用性，常增設許多的剪力牆版，有些還具有門型或是窗型開孔。然而，高強度混凝土的材料性值十分脆性，為了維持足夠的耐震能力，需在不連續區域配置大量圍束鋼筋，這反而造成施工上綁紥鋼筋之不易；再加上增設這些剪力牆後，雖能提高整體結構之勁度，但當地震來襲時，常是整體結構中較先損傷的部分。而因開孔分割出不同的牆段，其傳力機制與破壞路徑皆與未開口剪力牆不同，在台灣一般震損調查中，可發現破壞經常集中在開孔左右兩側之垂直牆段上。當這些RC剪力牆遭受破壞時，雖然結構仍未有崩塌之處，但使用機能完全癱瘓，且後續補強不易，民眾也無法信任其安全性而繼續居住。
添加鋼纖維於高強度混凝土之中能有效減緩其脆性破壞，再根據歷年同研究群的研究結果顯示，使用鋼纖維混凝土可提高其韌性與抗剪強度，且因鋼纖維之間的橋接效應而具有高拉力強度能有效抑制裂縫生成，並能大幅減少橫向箍筋的配置，解決施工上的問題。在剪力牆中，因其鋼纖維混凝土的高剪力容限、抑制裂縫發展等優越力學特質預期除能大幅增加開口剪力牆結構之耐震能力、解決箍筋過密、取代ACI規範中開口上下配置之水平補強筋，也能解決現今開口牆因裂縫造成建物無法使用的問題。然而，根據先前的研究結果，已知使用鋼纖維混凝土在結構不連續區的效果顯著，但其力量傳遞行為在街頭與剪力牆中仍有待釐清，其設計應用將可直接回饋給工程師做相關計算，簡化剪力牆的設計流程。
本研究從剪力與撓曲強度下手，預計提出鋼纖維混凝土剪力牆之設計建議與適當的強度預測模型。首先，蒐集國內外New RC與添加鋼纖維後的低矮型剪力牆資料庫，並以ACI、軟化壓拉桿與各經驗公式為基礎比較，統整一個適用於計算各情況鋼纖維混凝土剪力牆的強度預測模型。之後，設計了四座試體，參數包括牆版鋼筋量、開孔有無與開孔形式不同，使用在資料庫中統整後的強度預設模型來計算四座試體，且合理的預測各試體的結果，包括強度預測、破壞模式、側力位移曲線等，此預測結果可有效提供之後做實驗時參考比對，並確認其準確性。

關鍵字

高性能混凝土 ； 鋼纖維混凝土 ； 開口剪力牆 ； 剪力強度 ； 軟化壓拉桿模型 ； 設計建議

並列摘要

High-strength concrete has been widely used in recent years, relative regulations in Taiwan has also been updated. In order to achieve the usability of buildings nowadays, shear walls have been used frequently, some even with openings. However, concrete becomes more brittle while the compressive strength increases, so more transverse reinforcement is required to maintain the seismic ability, which causes construction difficulties; although shear walls can improve the overall stiffness, but it often becomes the first damaged part of the structure when an earthquake happens. The force transmission mechanism and failure path are different from tradition shear walls and those with openings; in the general inspection of seismic loss in Taiwan, it can be found that the damage is often concentrated on the vertical wall sections on the both sides of the opening. When the damage occurred on shear walls with, even the structure hasn't completely collapsed, but the function is completely paralyzed and has difficulties in retrofit, which may cause safety concerns.
Adding steel fibers into high-performance concrete can effectively mitigate brittle damage. Based on research results of the previous projects, using SFRC can enhance its toughness and shear strength; within the high tensile strength of the steel fiber can effectively inhibit the formation of crack, which result in the significantly reduce of the usage of transverse reinforcement. Despite its excellent mechanical characteristics such as high damage tolerance and resistance of crack propagation, which are expected to not only increase the seismic ability, solve the over-density of stirrups, and replace the required horizontal reinforcements arranged above and below the opening in the ACI specification, but also solve the problem that the current shear walls with opening cannot be used due to cracks in the building. Based on the previous research results of beam-column joints, the usage of SFRC has significant advantage in discontinuity, but force transmission mechanism still needs to be discussed in shear walls, which design applications can directly feedback to engineers to simplify its design calculation.
A comprehensive experimental program, including shear and flexural strength, were conducted, it is expected to propose design suggestions, flowchart and accurate strength prediction models for SFRC shear walls with opening. By collecting domestic and foreign New RC projects and the low-rise steel fiber shear wall database, and comparing them based on ACI specification, softened strut-and-tie model, and various empirical formulas, this study integrates a strength prediction model for calculation of various steel fiber concrete shear wall. Consequently, four specimens were designed, parameters include the web reinforcement ratio, with or without opening, and the form of openings, furthermore, reasonably predict the results of each specimen, including compressive strength, failure mode, and load-displacement curvature, based on the prediction model of the database, this prediction can effectively be used to provide a reference comparison for subsequent experiments and confirm its accuracy.

並列關鍵字

High-performance concrete ； steel fiber concrete ； shear walls with opening ； shear strength ； softened strut-and-tie model ； design suggestions

參考文獻

[1]ACI Committee 318, 2019, “Building Code Requirements for Structural Concrete and Commentary (ACI 318-19).”, American Concrete Institute, Farmington Hills, Michigan

[2]Hwang, S.-J., Lee, H.-J., “Strength Prediction for Discontinuity Regions by Softened Strut-and-Tie Model.”, Journal of Structural Engineering, ASCE, Vol. 128, No 12, pp. 1519-1526, Dec., 2002.

[3]Hwang, S.-J., Yu, H.-W., “Evaluation of Softened Truss Model for Strength Prediction of Reinforced Concrete Squat Walls.”, Journal of Structural Engineering, Vol. 131, No 8, pp. 839-846, Aug., 2005.

[4]Paulay, T, Priestley, M.-J.-N.and Synge, A.-J., “Ductility in Earthquake Resisting Squat Shearwalls.”, ACI Structural Journal, V. 79, NO.4, pp. 257-269, May.-June., 1982.

[5]Hwang, S.-J., Tsai, R.-J., Lam, W.-K., Moehle, J.-P., “Simplification of Softened Strut-and-Tie Model for Strength Prediction of Discontinuity Regions.”, ACI Structural Journal, V. 114, NO.5, pp. 1239-1248, Sep.-Oct., 2017.