|Abstract: ||在鋼筋混凝土構件中，現階段鋼筋端部仍普遍使用傳統90o或180o標準彎鉤之錨定特性，以縮短鋼筋直線發展長度，提供載重所需之強度。近幾年T頭鋼筋已漸漸地應用在橋梁及建築結構上，2008年版美國ACI 318設計規範於機械錨定章節中，更針對T頭鋼筋之設計提出建議，其設計規定包括鋼筋強度不得超過420MPa、混凝土強度上限為42MPa、鋼筋淨間距不得少於4db、淨保護層不得少於2db及T頭端板面積必須不可少於5倍鋼筋斷面積。本研究目的欲突破上述規定之適用限制，以擴大T頭端錨之實際應用範圍。|
To ensure the reinforcement concrete structure to reach the design strength, one of the criteria is the bonding behavior between reinforced steel and the concrete. To provide the necessary bonding resistance force, bended-hook steel bar is commonly used in these days. This traditional design usually results in too many reinforced steel in the area of beam –column joint which arises difficulties in construction field. Thus, in this study, we attempt to investigate another technology which is the T plate-ended reinforced steel to examine if it can provide a suitable bonding resistance.
The T plate-ended reinforced steel has been applied in the structures of bridge and building in many other countries. In ACI 318 (2008), the recommendation of T plate-ended reinforced steel used in the building are the strength of steel must be less than 420MPa, the strength of concrete must be less than 42MPa, the clearance between steels must be larger than four times of the diameter of the steel (4db), the lower bounds of the side clearance and the area of T plate-ended is 2db and 4db, respectively. In this study, in order to fully capture the mechanism of anchorage behavior between reinforced steel and concrete, we perform 52 CCT Node tests and 26 pull-out tests.
In the tests, the design parameters are the strength of steel and concrete, size of T plate-ended steel, clearance between steels and the confinement conditions. From the tests, we learn that the T plate-ended steel provide a better bondage effect which is about 15% ~ 50% more than the traditional design. The bigger the T plate-ended steel is, the better the strength of anchorage is. In general, T plate-ended steel with 3db can reach the same design target of the traditional straight reinforced steel. The effect of clearance is not significant. Also, increase the strength of concrete can have a better anchorage performance. However, this trend does not hold when the strength of concrete is over 56MPa. The arrangement of confinement reinforcement can also enhance the integrated strength about 10% ~30%. The closer the confined reinforcement is, the bigger the integrated strength is.
Based on the test results, the bigger the T plate-ended steel is, the smaller the slip of the bar is. The amount of slip is only 20% of the regular reinforcement. Thus, it is concluded that the increase of confinement can enhance the anchorage effect. The tests conducted in this study provide different failure modes which is valuable for further investigation.