Document Type : Article
Authors
1
Islamic Azad University Semnan Branch
2
Dept. of Civil Engineering Semnan University
Abstract
High Performance Fiber Reinforced Cementitious Composites; HPFRCC, are cement matrices with strain hardening responses under tension loading. In these composites, the cement mortar with fine aggregates is reinforced by random distributed fibers and may be used for various applications, such as rehabilitation of structural members. In this paper, the mechanical properties of HPFRCC materials are reviewed briefly. Moreover, a one-bay and one-story reinforced concrete frame, which had been tested by Cranston, is selected and investigated, using high performance materials with different tensile and compressive strengths, instead of concrete, in the connection zone and the whole frame. Analytical results show that using HPFRCC material instead of regular concrete increases the ductility and loading capacity of the frame. In this investigation, by increasing the amount of compressive and tensile strength of HPFRCC, the loading capacity of the composite frames increased about 40% compared to the RC frame. Ductility factors of these composite frames also increased about 50% and 70%
compared to the RC frame, respectively. The cracking patterns of these frames are compared to each other.
Cranstons experimental investigation was undertaken to corroborate the analytical work and lend further insight into the nature of finite element items in the frame structure. The structural properties of normal concrete are
constant during this investigation, but the structural properties of HPFRCC are variable, including different compressive and tensile strengths. Compressive strengths of HPFRCC are 28, 35 and 39 MPa, and tensile
strengths are 3, 4 and 5 Mpa. Lateral load-deflection curves and cracking patterns of the RC (full reinforced concrete frame), RH (full reinforced HPFRCC frame) and RCH (reinforced concrete frame with HPFRCC material in its connections) frames with $varepsilon_{tu}=1%$ are investigated. Analytical results show that maximum ductility occurs in the RCH frame with compressive and tensile strengths of 28 and 5 MPa, respectively. The
maximum amount of ultimate lateral load occurs in the RH frame with compressive and tensile strengths of 28 and 5 MPa, respectively. The maximum amount of ultimate lateral displacement occurs in the RH frame with compressive and tensile strengths of 35 and 3 MPa, respectively. This improvement in the lateral behavior of frames with HPFRCC materials is concluded from the large ultimate tensile strain of the HPFRCC material,
which is altered instead of normal concrete with low $varepsilon_{tu}=1%$ and, consequently, increases both the load and deflection capacity of the structure. In addition, another factor that has an important role to play in
the ascending trend of the mentioned curves is steel reinforcements. When concrete is altered by HPFRCC, because of the higher $varepsilon_{tu}=1%$ of HPFRCC, steel rebars can reach a closer amount of the plastic strain value of steel and, hence, lateral deflection and force increase simultaneously. In the other word, the main role of HPFRCC is to assist the work of steel by keeping the unity of the HPFRCC and steel as a composite material by forming multiple cracking and avoiding a concentrated failure plane. It can be used in critical parts of reinforced concrete frames to increase the capacity of the structure.
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