رفتار لرزه ای با اتصالات کامپوزیتی سیمان تقویت شده با عملکرد بالا
Abstract
1- Introduction
2- Materials
3- Experimental program
4- Test results and discussions
5- Conclusions
References
Abstract
High-performance fiber-reinforced cementitious composite (HPFRCC) has potential to greatly improve the fire resistance and seismic behavior of concrete structures. This paper reports an experimental investigation on post-fire seismic behavior of two-bay two-story frames with HPFRCC joints. Four reinforced concrete frames were fabricated; three of them were tested in compartment fire for 60 min. The fire was regulated following ISO-834 temperature curve. Two different fire scenarios (one- and two-bay fire) were investigated. Two frames were made of monotonic conventional concrete; the other two frames had HPFRCC joints. Each frame was tested under a constant vertical load and a pseudo-static cyclic horizontal load with increased magnitude until the frame failed. The effects of the HPFRCC and fire scenarios on the failure mechanism, hysteretic loops, envelope curve, stiffness degradation, and energy dissipation of the frames were evaluated. The experimental results revealed that the fire exposure reduced the load capacity and deformability of the frames. In the two-bay fire scenario, the use of HPFRCC joints increased the post-fire load capacity by 11%, ultimate deformation by 6%, initial stiffness by 30%, and energy dissipation by 21%. The cyclic behavior of the frame in one-bay fire was better than that in two-bay fire. The frames with HPFRCC joints demonstrated better cyclic behaviors than the virgin reinforced concrete frame.
Introduction
Fire hazards continue to occur in civil engineering structures such as buildings, tunnels, and bridges, and cause catastrophic consequences. The fire behaviors of beams [1–3], slabs [4–6], and columns [7] and frames [8,9] were investigated through experimentation and/or finite element analysis. Effects of different fire scenarios, fire duration, and structural design variables on the structural degradation were evaluated [1–9]. It is agreed that fire exposure can reduce the load-bearing capacity of civil engineering structures. In a fire hazard, the elevated temperature reduces the mechanical strengths of concrete [10,11] and steel bars [10,12], as well as the bond between concrete and steel bars [13,14]. In addition, the elevated temperature may cause explosive spalling in concrete [15]. Concrete spalling may expose steel bars to fire and thus accelerate the degradation of the structure. In recent years, different families of high-performance fiber-reinforced cementitious composites (HPFRCCs) have been developed to improve the mechanical performance, resilience and durability of concrete structures [16,17]. Ultra-high-performance concrete (UHPC) is a family of HPFRCC with extreme compressive and tensile strengths, durability and flowability due to the refined microstructure and welldesigned chemistry [18–21]. Typically, UHPC has a very low water-tobinder ratio (w/b < 0.25) and uses finely ground silica sand. Most recently, river sand and high-volume supplementary cementitious materials such as fly ash and/or ground granulated blast slag have been used to reduce the materials cost and carbon footprint [16,17]. However, the very dense microstructure makes UHPC susceptible to explosive spalling at elevated temperatures due to continuous buildup of internal vapor pressure [15].