低水泥量高性能混凝土樑之撓曲行為

Abstract

本文製作A、B兩系列實尺寸的高性能混凝土(HPC)樑，其水泥含量為A 系列250kg/m3、B系列350kg/m3，所有樑試體的混凝土工作度要求為坍度 (Slump) > 20cm及流度 (Slump flow) > 60cm 。研究上依變化拉力鋼筋 含量、壓力鋼筋含量及箍筋間距進行撓曲試驗，期對HPC樑試體的延展性 與彎曲強度有所了解。在實驗過程中除詳細觀察試體的破壞模式外，並依 所設定變數測取撓曲應變值，以求試體之各項性質。 試驗結果發現 ，以ACI等值矩形應力塊分析所得撓曲強度，對高強度HPC樑而言將偏於保 守。增加拉力鋼筋含量可提昇HPC樑的彎矩容量，但卻會使其延展性下降 。壓力鋼筋有助於延展性的提昇，但須在拉力鋼筋影響小於壓力鋼筋的前 提下。箍筋間距加大會造成延展性降低，同時會使壓力鋼筋容易挫屈。56 天之HPC圓柱試體極限應變未達0.003，但同齡期樑試體在最大載重下的混 凝土應變則可超過0.003。水泥量(C=250kg/m3)較低的HPC樑試體，由於勁 度或彈性模數較高，藉由拉力筋減少、壓力筋增加及箍筋間距減小，所獲 得的延展性改善，比高水泥量(C=350kg/m3)者明顯。

In this paper we produced two sets of full size specimens of High Performance concrete (HPC) beams which were set A andB . The cement content of set A is 250 kg/cm3 and that of B is 350 kg/cm3 . The workability requirement of all specimens was slump > 20 cm and slump flow > 60 cm. Flexural test conducted with variable tension steel content,compression steel content and the spacing of ties . We hope to get more knowledge of HPC beam in ductility and flexural strength . In the process of experiment we observed the failure mode and measured the deformation according to the variety to get detail quality . The results of experimentation show , the ACI code suggested rectangular compression stress block predication of flexural strength was conservative . Increasing the tension steel content can increase the moment capacity while it decrease the ductility . Increasing compression steel content can increase the ductility but the influence of tension steel must smaller than compression steel . Increasing the spacing of ties will decrease the ductility and the compression steel will bucking easily . The strain of the cylinder can not reach the value 0.003 on 56 days but that of the beam can over the value . The lower cement content (250kg/ cm3) HPC beams improve ductility more effective than high cement content (350kg/cm3) by decreasing tension steel content , the spacing of ties , and increasing compression steel .