預鑄小梁與版接合部性能試驗研究

Abstract

本研究旨在以實驗探討預鑄混凝土工程設計規範與解說(2023)中合成預鑄構材接合之力學行為，並提出一套較合理之接合部剪力強度計算方式。合成預鑄構材接合分為KT板與梁接合、小梁與大梁接合兩種形式，兩者同樣在上覆板以鋼筋連接至支承構材，但前者KT板會直接坐落於大梁混凝土保護層，後者小梁會在末端預埋剪力接合器再跨坐至大梁預埋之承壓板上；前者參閱文獻得知其混凝土承壓強度十分足夠，因此無須擔心；後者接合方式特殊而少有相關文獻可供參考，尚存疑點包括：小梁與板的上層筋是否可兼作剪力摩擦鋼筋、箍筋形式是否可以協助錨定上層筋、以剪力接合器跨坐至承壓板可以發揮多少混凝土承壓強度等，因而亟需設計試驗驗證與釐清。 本試驗共設計八組試體，試體參數包括小梁斷面形式（T形斷面或矩形斷面）、小梁上層主筋支數（2支或3支）、小梁箍筋形式（點焊鋼線網或180度彎鉤）、混凝土承壓面積（小承壓板或大承壓板）。試驗結果顯示，混凝土承壓與剪力摩擦都可以發揮比混凝土結構設計規範(2023)所規定之公式計算值高的強度，然而進一步分析發現，小梁端部負彎矩對接合部強度有正向助益，若小梁為簡支（亦即端部無彎矩），接合部的強度可能會低於本次試驗結果。另，各參數對於接合部的影響大致可歸納如下：增加小梁上層主筋支數未必能線性增加接合部強度、板筋同樣可作為剪力摩擦鋼筋並有效提升接合部強度、180度彎鉤確實有助於錨定小梁上層主筋並提升接合部韌性。 根據試驗結果，本研究提出合成預鑄構材接合之強度計算方式與細部設計建議，整理於第六章。強度計算方面，本研究建議接合部剪力強度可將剪力摩擦強度與下部強度相加計算，其中下部強度為剪力接合器強度與混凝土承壓強度取小者，套用規範公式計算可足夠保守，混凝土承壓面積甚至可一定程度放大；細部設計方面，本研究整理與合成預鑄構材接合相關之細部設計方法與規定，包括伸展長度、支承長度、承吊鋼筋、剪力釘配置、承壓板厚度等，供查閱者作為設計指引。以上研究成果與建議希冀可提供預鑄設計規範未來修訂方向之參考。

This study aims to experimentally investigate the structural behavior of composite precast component connection as outlined in the "Design Specifications and Commentary for Precast Concrete Engineering (2023)" and to propose a more reasonable method for calculating the shear strength of the connetion. The composite precast component connection are categorized into two types,which are KT slab to beam, beam to girder. In both types, the upper slab is connected to the supporting components with reinforcement bars. However, in the KT slab type, the slab rests directly on the concrete cover of the girder, while in the beam type, shear connectors (which is a steel plate) are embedded at the end of the beam to span across the bearing plate embedded in the girder. According to the literature, the concrete bearing strength in the KT slab type is sufficient and not a concern. However, the unique jointing method of the beam type lacks sufficient literature references, raising several questions: Can the upper longtitude reinforcement of beam and slab also serve as shear friction reinforcement? Can stirrups effectively anchor the upper reinforcement? How much concrete bearing strength can be achieved by spanning across the bearing plate with shear connectors? Therefore, experimental validation and clarification are urgently needed. The experiment designed eight specimens, with parameters including the cross-sectional shape of the beam (T-shaped or rectangular), the number of upper longtitude reinforcement in the beam (2 or 3), the type of stirrups in the beam (welded wire fabrics or 180-degree hooks), and the concrete bearing area (small or large bearing plate). The results show that both concrete compressive strength and shear friction can achieve higher strengths than those calculated using the formulas specified in "Design Specifications for Concrete Structures (2023)". However, further analysis reveals that the negative moment at the end of beam has a positive effect on connection strength; if the end of beam is simply supported (i.e., without moment at the ends), the connection strength may be lower than the results of this experiment. Additionally, the influence of each parameter on the joint can be summarized as follows: Increasing the number of upper longtitude reinforcement in the beam does not linearly increase the connection strength, upper longtitude reinforcement of slab can also serve as shear friction reinforcement and effectively enhance joint strength, and 180-degree hooks can effectively anchor the upper reinforcement of the beam and improve joint ductility. Based on the experimental results, this study proposes a method for calculating the strength of composite precast component connection and provides detailed design recommendations, compiled in Chapter 6. For strength calculation, it is recommended that the joint shear strength be calculated by adding the shear friction strength and lower strength (the smaller of shear connector strength and concrete bearing strength) of connection, all of which can be conservatively calculated using formulas of the specification, with some allowance for enlarging the concrete bearing area. For detailed design, the study organizes methods and regulations related to composite precast component connection, including development length, supporting length, hanger reinforcement, shear stud configuration, and bearing plate thickness, providing a design guide for practitioners. The results and recommendations of this study are expected to offer a reference for future revisions of precast design codes.