1、PDF外文：http:/ 17 外文原文： Research Letters in Materials Science Volume 2008 (2008), Article ID 814137, 4 pages doi:10.1155/2008/814137 Research Letter Properties of Reinforced Concrete Steel Rebars Exposed to High Temperatures İlker Bekir Topu and Cenk Karakurt Department of Civil Engi
2、neering, Eskiehir Osmangazi University, 26480 Eskiehir, Turkey Received 12 February 2008； Accepted 31 March 2008 Academic Editor: Rajiv S. Mishra Copyright 2008 İlker Bekir Topu and Cenk Karakurt. This is an open access article distributed under the Creative Commons Attribution License, which permit
3、s unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Abstract The deterioration of the mechanical properties of yield strength and modulus of elasticity is considered as the primary element affecting the performance of steel structures
4、 under fire. In this study, hot-rolled S220 and S420 reinforcement steel rebars were subjected to high temperatures to investigate the fire performance of these materials. It is aimed to determine the remaining mechanical properties of steel rebars after elevated temperatures. Steels were subjected
5、to 20, 100, 200, 300, 500, 800, and 9 5 0 C temperatures for 3 hours and tensile tests were carried out. Effect of temperature on mechanical behavior of S220 and S420 were determined. All mechanical properties were reduced due to the temperature increase of the steel rebars. It is seen that mechanic
6、al properties of S420 steel was influenced more than S220 steel at elevated temperatures. 1. Introduction Fire remains one of the serious potential risks to most buildings and structures. Since concrete is widely used in construction, research on fire resistance of 18 concrete becomes m
7、ore and more important. Many researchers all over the world have done some researches on this subject. The mechanical properties of all common building materials decrease with elevation of temperature. The behavior of a reinforced concrete structure in fire conditions is governed by the properties o
8、f the constituent materials, concrete, and steel, at high temperature. Both concrete and steel undergo considerable change in their strength, physical properties, and stiffness by the effects of heating, and some of these changes are not recoverable after subsequent cooling 1. It is necessary to hav
9、e safe, economical, and easily applicable design methods for steel members subjected to fire. However, without fire protection, steel structures may suffer serious damage or even collapse in a fire catastrophe. This is because the mechanical properties of steel deteriorate by heat during fires, and
10、the yield strength of conventional steel at 600C is less than 1/3 of the specified yield strength at room temperature 2. Therefore, conventional steels normally require fire-resistant coating to be applied 3. The temperature increase in the steel member is governed by the principles of heat transfer
11、. Consequently, it must be recognized that the temperature of the steel member(s) will not usually be the same as the fire temperature in a compartment or in the exterior flame plume.Protected steel will experience a much slower temperature rise during a fire exposure than unprotected steel. Also, f
12、ire effect on steel member is influenced with its distance from the center of the fire, and if more ventilation occurs near the steel in a fuel-controlled condition, wherein the ventilation helps to cool the steel by dissipating heat to the surrounding environment 4. Especially, temperature increase
13、 of steel and concrete in composite steel-concrete elements leads to a decrease of mechanical properties such as yield stress, Young's modulus, and ultimate compressive strength of concrete 5. Thus, load bearing of steel decreases when steel or composite structure is subjected to a fire action.
14、If the duration and the intensity of the fire are large enough, the load bearing resistance can fall to the level of the applied load resulting in the collapse of the structure. However, the failure of the World Trade Centre on 11th September 2001 and, in particular, of building WTC7 alerted the eng
15、ineering profession to the possibility of connection failure under fire conditions 6. In this study, S220 and S420 ribbed concrete steel rebars were subjected to 7 different temperatures to determine the high temperature behavior of reinforcement steels. 2. Experimental Study Experimental studies we
16、re conducted with 10 and 16mm in diameter and 200mm in length S220 and S420 reinforcement steel rebars. Test specimens 19 were subjected to 20, 100, 200, 300, 500, 800, and 950C temperatures in a high furnace for 3 hours, respectively. At the end of the curing process, steels were cooled natu
17、rally to the room temperature. Subsequently, tensile tests were applied to steel reinforcement rebars. According to EN 10002-1 tensile strength, yield strength and elongation of the steel rebars were determined for elevated temperatures 7. The steel specimens tensile strength tests were performed wi
18、th 60 tons of loading capacity universal tensile strength test machine. The loading speed of the test machine is adjusted according to TS 708 code 8. 3. Test Results and Evaluations 3.1. Stress-Strain Relations The average values for stress-strain relationship for specimens that were exposed to vari
19、ous temperatures are given in Figures 1 and 2. The curves in Figures 1 and 2 were drawn with the average test results of 10 and 16mm in diameter steel specimens. The test conditions were meant to simulate a building that had a fire so the changes in the mechanical properties of reinforcing steels us
20、ed in structures exposed to high temperature could be determined. As seen from Figure 1, temperatures below 500C have no significant effect on mechanical properties of preheated and cooled S220 steel rebars. The yield strength and splitting tensile strengths of S220 steels were similar up to this te
21、mperature. However, the yield strength and splitting tensile strength of the S220 steel rebars are reducing with the increase of temperatures over 800C. A similar behavior can be seen from the test results of S420-ribbed steel rebars (Figure 2). All high temperature subjected steel specimens became
22、more ductile temperatures above 800C. Figure 1: Stress-strain curve of S220 steel rebar. Figure 2: Stress-strain curve of S420-ribbed steel rebar. 3.2. Yield Strength Yield strength of both reinforcing steel rebars was affected with the elevated exposure temperatures. It can be concluded from Figure 3 that there is no variation in yield strength of reinforcing steels with cover up to 300C. Plain reinforcing steel rebars have experienced the strain hardening already for this temperature. According to Eurocode and TS EN 1993, before 400C there is no
