軟化壓拉桿模型在建築結構剪力設計上之應用研究

Abstract

本研究探討軟化壓拉桿模型於實務上預測及設計鋼筋混凝土剪力強度的應用。實務上常因為設計問題，造成鋼筋混凝土構件產生局部的應力集中現象，並可能造成剪力破壞。本研究針對以下幾個常見的問題進行深入研究。 工地常須對梁穿孔，以便於管線的配置，然而塑鉸區(2倍梁深)不得穿孔的規定，已造成困擾。本研究利用開孔剪力牆模型模擬開孔梁之行為，建議可於1倍至2倍梁深區域內開孔，但開孔大小必須進一步限制，並於開孔周圍增加鋼筋，以確保開孔不會影響梁的剪力強度。 混合結構日漸盛行，鋼骨鋼筋混凝土構造物的比例也逐漸上升，預測其構件的剪力強度是一大挑戰。本研究利用軟化壓拉桿模型，提出一套適用於鋼骨鋼筋混凝土構件剪力強度的預測方法，並建議在設計時，考慮鋼骨和鋼筋混凝土之間的複合效應，以提高預測的準確性。 隨著都市更新的推動，舊的高樓若須拆除重建，而新的建築往往需要重複利用舊建築的基樁與筏基板，而舊樁與新柱之錯位會使基礎板產生極大的需求剪力。本研究利用樁帽剪力強度模型來保守計算基礎板之設計剪力，並提出相關的配筋細節，以提高基礎板之安全性。 非結構牆的設置，常常會造成短梁的發生，引致高剪力作用，其設計造成困擾，本研究建議可以連接梁設計之。在設計地震作用下，連接梁除了滿足剪力設計外，同時也要避免過度設計彎矩強度，以免梁端產生更大的彎矩而增加剪力需求。在高撓曲需求的設計下，軟化壓拉桿模型能夠減少對角鋼筋量，以便施工；低撓曲鋼筋量設計時，須注意混凝土可能提早擠碎，造成不可預期的破壞。 本研究顯示，軟化壓拉桿模型能有效提升鋼筋混凝土剪力強度預測的準確性，並為工程實務提供可靠的設計依據。

This study investigates the application of the softened strut-and-tie model in the practical prediction and design of shear strength in reinforced concrete. In practice, design issues often lead to local stress concentrations in reinforced concrete components, potentially causing shear failures. This research delves into several common problems. Construction sites often need to perforate beams for pipeline arrangements. However, the regulation prohibiting openings within the plastic hinge zone (twice the beam depth) has caused issues. This study uses the shear wall with opening model to simulate the behavior of beams with opening and suggests that opening can be made within one to two times the beam depth. However, the size of the opening must be further restricted, and additional reinforcement should be placed around the opening to ensure it do not affect the shear strength of the beams. As hybrid structures become more prevalent, the proportion of steel reinforced concrete (SRC) structures is also increasing. Predicting the shear strength of SRC components is a significant challenge. This study uses the softened strut-and-tie model to propose a method for predicting the shear strength of SRC members and recommends considering the composite effects between steel and reinforced concrete during design to enhance prediction accuracy. With the promotion of urban renewal, if old high-rise buildings need to be demolished and rebuilt, the new buildings often need to reuse the old building piles and raft foundation slabs. The dislocated of the old piles and the new columns can result in significant shear demands on the foundation slabs. This study uses the pile cap shear strength model to conservatively calculate the design shear strength of the foundation slabs and proposes related reinforcement details to improve the safety of the foundation slabs. The placement of non-structural walls often leads to the creation of short beams, resulting in high shear forces, posing design challenges. This study recommends applying coupling beam design principles. Under design basis earthquake, coupling beams should not only meet shear design requirements but also avoid over-designing moment strength to prevent excessive moments at the beam ends, which would increase shear demand. For designs with high flexural demands, the softened strut-and-tie model can reduce the amount of diagonal reinforcement, facilitating construction. For low flexural reinforcement designs, early concrete crushing should be monitored to prevent unexpected failures. This study shows that the softened strut-and-tie model effectively enhances the accuracy of shear strength predictions in reinforced concrete, providing reliable design bases for engineering practice.