預力混凝土樑的剪力性能採用高強度材料

Abstract

本研究透過一系列 12 項實驗測試結果，對預力混凝土 (PC) 工字樑的剪切行為進行了全面研究。 前六次試驗結果主要關注混凝土混合物對PC 梁剪切性能的影響。 研究的三種類型的混凝土配合比設計是高性能混凝土（HPC）和自密實混凝土（SCC），以及作為對照樣本的傳統混凝土（CC）。 使用指定的兩個混凝土抗壓強度等級：fc MPa 為普通強度，fc MPa 為高強度。 測試結果表明，無論混凝土強 度如何，HPC 和 CC 樑都表現出相似的剪切行為。 由於 SCC-N 混合物的填充能力更好，SCC-N 比 CC-N 顯示出更高的 ult n V V 比和更高的極限位移。 SCC-H 樑的 ult n V V 低於 CC-H 梁，可能是由於 SCC-H 的粗骨材量比 CC-H 梁低 19%。 此外，也建立了PC 梁剪切試驗資料庫，進一步研究粗骨材用量對梁抗剪強度的影響。 經分析，粗骨材用量對Vu 的影響具有統計顯著性，粗骨材用量每減少100kg/m3， ult n V V 平均下降18.5%。最後六個 PC I 梁使用兩種類型的鋼筋作為抗剪鋼筋建造：高強度鋼 (SD790) 和普通強度鋼 (SD420W)。 試驗結果表明，直接用高強度鋼取代鋼筋可提高PC 樑的抗剪承載力。 指定屈服強度 790 MPa 的等效剪切強度替換顯示極限剪切強度下降；因此，不建議在剪切設計計算中使用fy =790 MPa。 此外，以假定屈服強度 fy = 600 MPa 進行等效剪切強度替換可得到與普通強度抗剪鋼筋 (fy = 420 MPa) 類似的極限剪切強度。 此外，根據ACI 318-19 和AASHTO LRFD 2020 對實驗結果進行了評估。研究結果表明，ACI 中的屈服強度限制可以提高至600 MPa，同時保持 合理的保守水平。 然而，AASHTO 使用 690 MPa 作為屈服強度極限仍然具有高度保守性。 此外，仔細測量並評估了實驗過程中腹板剪切裂縫寬度的發展。 提出了一種預測模型，透過考慮抗剪鋼筋中的應變發展來估計傾斜剪切裂縫寬度。 此外，所提出的傾斜剪切裂縫寬度估計建議包含在設計過程中以控制剪切裂縫。 這項研究獲得的結果對增強現有的 PC 梁設計規範做出了重大貢獻。

This research presents a comprehensive investigation into the shear behavior ofprestressed concrete (PC) I-girder through a series of 12 experimental test results. Thefirst six test results were focused on the influence of concrete mixture on the shear behavior of PC girder. Three types of concrete mix design investigated are highperformanceconcrete (HPC) and self-consolidating concrete (SCC), along withconventional concrete (CC) as a control specimen. Two grades of concrete compressivestrength specified were used: 41.4 c f   MPa as normal-strength and 68.9 c f   MPa as high-strength. Test results showed that the HPC and CC girders exhibited a similar shear behavior regardless of the concrete strength. SCC-N showed a higher ult n V V ratio and a higher ultimate displacement than CC-N due to the better filling ability of the SCC-N mixture. The SCC-H girder showed a lower ult n V V than the CC-H girder, which may beattributed to the SCC-H having a 19% lower coarse aggregate amount than the CC-Hgirder. Furthermore, a shear test database of PC girders was established to investigate further the effect of coarse aggregate amount on the girder shear strength. Based on the analysis, the coarse aggregate amount is statistically significant affecting the ult n V Vwhich decreasing on average by 18.5% for 100 kg/m3 reduction of coarse aggregate amount. The last six PC I-girders were constructed using two types of rebar as shearreinforcement: high-strength steel (SD790) and normal-strength steel (SD420W). The testresults indicate that a direct rebar replacement with high-strength steel increases the shearcapacity of the PC girder. The equivalent shear strength replacement with specified yield strength 790 MPa shows a decrease in ultimate shear strength; thus, the use of y f = 790 MPa in shear design calculation is not recommended. In addition, the equivalent shear strength replacement with an assumed yield strength of y f = 600 MPa gives a similar ultimate shear strength as normal-strength shear reinforcement ( y f = 420 MPa). Furthermore, the experimental results were evaluated based on ACI 318-19 and AASHTO LRFD 2020. The findings show that the yield strength limitation in ACI can be increased up to 600 MPa while maintaining a reasonable level of conservatism. However, using 690 MPa as the yield strength limit in AASHTO still provides a high degree of conservatism. Furthermore, web-shear crack width development during experiments was measured carefully and evaluated. A prediction model is proposed to estimate inclined shear crackwidth by considering strain development in shear reinforcement. Moreover, the proposed inclined shear crack width estimation suggests to be included in the design process to control the shear crack. The findings obtained through this study have significantly contributed to enhancing the existing design codes for PC girders.