【正文】
ine with stiffening ponents added. In this article, the stress—strain behavior of SFRC under uniaxial tension Was analyzed for different types of fiber. The tensile characteristics of SFRC influenced by the matrix strength and the steel fiber content were studied also. In addition, the stress—strain curves of high strength SFRC with different factors were well acquired. The mechanism of fiber reinforced concrete to enhance research, to obtain steel fiber reinforced concrete in tension curve of the whole process, using the most appropriate method of axial tension, but to make sure the testing methods improved, and the testing machine must have enough stiffness to ensure the testing process stability. Is well known in engineering practice, process, technology and economic conditions due to construction constraints, SFRCdoped fiber volume in the rate of generally not more than 2%, while most of the engineering example, the fiber fraction are about 1%. In this paper the design of the axial tension SFRC material testing, fiber dosage to take 1%, and using different types of fiberreinforced forms, were analyzed. 2 Experimental Content The specimens were tested on a 60 kN universal testing machine. Four high steel bars were added to enhance the stiffness of the testing machine. In addition, spherichinges were used to abate the initial axial eccentricity of the specimens.. It was ensured that specimens should be pulled under uniaxial tension by adjusting the four high strength bolts which connect the specimens to the crossbeam. And the difference between the tensile strains of the opposite sides of the specimen should be less than 1 5% of their mean value. When the fiber content was low (0 and % by volume), the cyclic quire the whole stress—strain. 2. 1 Materials Four types of steel fibers shown in Table were chosen for this test. Three of these fibers (F1, F2 and F3) were hooked—end and the other one(F4)was smooth. Three concrete mixtures, shown in Table 2, were investigated. Water reducing agents were used in C60 and C80 mixes(DK 一 5 made by Dalian Structure Research Institute and Sika made in Switzerland respectively). The pressive strengths of these C30, C60, C80 mixes were determined according to “Test Methods Used for Steel Fiber Reinforced Concrete”(CECS 13: 89)8 3 at 28 days using 150 mm150 mm 150 mm cube s. Averaged results for 3 specimens are given in Table 2. 0rdinary Portland cement(yielded by Dalian Huaneng Onoda Cement Company)of 32. 5 and 52. 5 (according to China standard) were chosen. River sand(modulus of fineness is )and crushed limestone coarse aggregates(5—20 Bin) were used. Table Matrix code Strength grade Of Cement Kg/m3 u/c ratio Sand ratio Sand Kg/m3 Crushed Strne Water reducing Compressive Strength cement (ISO) Kg/m3 Mpa C30 450 4 667 1155 C60 500 5 602 1223 DK5 C80 600 9 535 1190 Sika 2. 2 Specimen The tensile specimen was bonded to steel padding plates at both ends by tygoweld. A total of 1 1 0 specimens were divided into 22 groups according to certain parameters. The parameters of these specimens are shown in Table 3. 2. 3 Items At the age of 28 days. plain concrete and steel fiber concrete specimens were tested for tensile strength, respectively .The tensile stress—strain curves were acquired. Many other tensile characters of the high strength steel fiber concrete such as tensile work, etc were calculated also. Enhanced class steel fiber reinforced concrete toughness category than the strength of steel fiber reinforced concrete an average of 13%。通過對實驗曲線的分析與回歸,給出了考慮上述影響因素的鋼纖維高強混凝土軸拉應力應變全曲線表達式。 (5)引入了軸拉韌性指數來評價鋼纖維高強混凝土的韌性,鋼纖維混凝土的軸拉韌性要大大優(yōu)于同配比的索混凝土,并且受基體強度和鋼纖維特性和 摻量的影響。 (3)提高鋼纖維摻量對鋼纖維高強混凝土的抗拉強度特性的改善作用比對普通強度混凝土的改善作用明顯。 六、實驗結論 (1)試驗 結果表明:鋼纖維高強混凝土劈拉強度略高于軸拉強度,兩者有較好的相關性,鋼纖維高強混凝土軸拉強度可取為劈拉強度的 倍。 五、 理論曲線與試驗結果的比較 鋼纖維高強混凝土軸拉應力一應變理論曲線和試驗曲線的比較如圖 l2所示 (以試件 F3— 6010為例 )。邊界條件 x=l和 y=1自然滿足。 因此公式 (6)可以轉換為: (7) 下降段公式 下降段數學的模型為: ( 8) 式中: 和 為與基體和鋼纖維特性有關的參數。 在公式( 3)中 上升段的公式 上升段的數學模型為: ( 4) 這里: 和 為與基體和鋼纖維特性有關的參數。 曾經有許多鋼纖維混凝土軸拉應力一應變全曲線模型提出大多數為分段函數,以應力峰值點為分界點。這是因為長直形鋼纖維的拔出過程是相對連續(xù)和柔和的 . 四、研究分析 由 4種鋼纖維混凝土的典型拉伸應力 應變曲線可以看出:在軸拉條件下, 1%摻量的鋼纖維遠遠沒有達到使混凝土材料實現應變強化的地步,大部分試驗曲線都在達到峰值后,出現荷載驟降段。 當基體強度較高時,由于纖維拔斷的出現使得 F2 和 F3 型鋼纖維試件的軸拉曲線下降端呈階梯狀。 Fl 型纖維的曲線是幾種鋼纖維中最豐滿的,并且在拉應變?yōu)榇蠹s 10000個微應變時出現了第二峰值。另外,鋼纖維摻量的提高可以大大地改善曲線的豐滿程度。下降段存在拐點。 鋼纖維鋼筋混凝土單軸拉伸應力 —— 應變曲線 典型的鋼纖維高強混凝土軸拉應力一 應變全曲線 (為了便于比較,每組試件選出條典型曲線作為代表 ),表述了軸拉曲線隨基體強度的變化規(guī)律;表述了軸拉曲線隨鋼纖維 (F3 型 )摻量的變化規(guī)律。由于端鉤的存在使得在基體強度不太高時 (C30 和 C60), F3 型鋼纖維的增韌作用優(yōu)于 F4 型。摩擦力隨基體強度的升高而增大,且該黏結類型的拔出破壞是一個持續(xù)過程,因此基體強度升高對摻有這兩種鋼纖維的混凝土韌性起積極作用。這兩種纖維均為剪切型,表面較粗糙。 在四種類型纖維種 F1型纖維的增韌效果