預力混凝土梁扭力行為之統整研究

An Integrating Review Study on Torsion in Prestressed Concrete Beams

呂頌暉(Song-Hui Lu)

指導教授 ： 鄭全桓

國立暨南國際大學/科技學院/土木工程學系/碩士(2020年)

https://doi.org/10.6837/ncnu202000076

摘要

本研究延續前期研究，執行中空預力混凝土(Prestressed Concrete，簡稱PC)梁扭力實驗，設計製作兩組不同斷面尺寸、混凝土強度、壁厚比及預力比之中空PC梁試體，進行純扭力試驗，並比較實驗結果。
本論文並蒐集前人文獻5組共43支PC梁扭力實驗試體以及本系列已完成實心7支、中空9支PC梁試體實驗結果，與開裂扭矩公式、初始勁度公式、極限扭矩公式及軟化桁架模式（Softened Truss Model，簡稱STM）計算分析值做比較，以探討PC梁扭力行為。
研究結果顯示，將Jeng et al. (2018 及2019)發展的實心與中空PC桿件開裂扭矩公式，應用於大部分文獻試體與本系列實驗試體，所計算的開裂扭矩值比ACI318-14規範開裂扭矩公式更能準確預測其實驗值。其次，以ACI 318-14規範方法計算極限扭矩，使用修正的α =22.746∙〖(f_pc/(f_c^' ))〗^(-0.172) 經驗公式比使用規範允許值 α= 37.5∘更能準確計算各試體的極限扭矩值。
本論文並詳述，一組新推導的實心PC桿件扭轉角公式和初始勁度公式，與上述PC桿件開裂扭矩公式，合併使用可得到簡化的開裂前(pre-cracking)扭矩-扭轉角雙線性（bi-linear）曲線，並經由比較此計算雙線性曲線與實驗曲線探討新扭轉角與初始勁度公式之適用性。並且，本論文亦將STM模式應用於蒐集之PC梁扭力實驗試體，將分析結果與實驗值、實驗曲線做比較，發現STM分析所得最大扭矩值與實驗值相當貼近。

關鍵字

預力混凝土梁 ； 開裂扭矩 ； 極限扭矩 ； 雙線性曲線 ； 軟化桁架模式

並列摘要

Following a series of previous research of torsion in prestressed concrete (PC) beams, this study conducted test on two hollow PC beam specimens subjected to pure torsion. This thesis describes the experimental project and presents the experimental results. In addition, 43 torsional PC beam specimens from the literature, and 7 solid and 9 hollow torsional PC beam specimens from this series of research were also collected, and their experimental results were compared with computed analytical values to investigate the torsional behavior of PC members.
The results of this study shows that the T_cr-formula proposed by Jeng et al. (2018, 2019) accurately predicted the T_cr values of most collected specimens, and that using the empirical equation α =22.746∙〖(f_pc/(f_c^' ))〗^(-0.172) in the ACI-318-14 method of predicting torsional strengths predicted the torsional strengths of the specimens more accurately than using α= 37.5∘.
Two newly derived formulae for cracking twist (θ_cr) and initial torsional stiffness for solid PC members are also described in this thesis. These two formulae and the aforementioned T_cr-formula can be combined to provide a convenient bilinear simplification of an entire non-linear pre-cracking torque-twist curve. The computed bilinear pre-cracking curves of the collected specimens were compared with their experimental curves to investigate the feasibility of these formulae. This study also applied the STM model on the collected specimens, finding that the computed T_u-values using STM agreed with the experimental values very well.

並列關鍵字

prestressed concrete beam ； cracking torque ； torsional strength ； bi-linear curve ； STM

參考文獻

一、英文部分

ACI Committee 318, Building Code Requirements for Structural Concrete

(ACI 318-14) and Commentary, American Concrete Institute, Farming Hills, Mich., 2014, 519 pp.

Bernardo, L., Lopes, S., and Teixeira, M. (2020). “Experimental Study on the Torsional Behavior of Prestressed HSC Hollow Beams.” Applied Sciences, Vol. 642, No. 10.

Chao, M., and Jeng, C.-H. (2017), “Pre- and Post-cracking Torsion in Prestressed Concrete Beams: Experimental Study,” Magazine of Concrete Research, Vol. 69, No. 11, pp. 555-575.