土建外文翻譯文獻(xiàn)

1、<p>　　Residual bond strength between steel bars and concrete after elevated temperatures</p><p>　　A. Ferhat Bingöl Rüstem Gül</p><p>　　Civil Engineering Department, Atatü

2、;rk University, Erzurum, Turkey</p><p><b>　　ARTICLE </b></p><p>　　Article history </p><p>　　Received in revised form </p><p>　　Revised 28 March 2009.</p

3、><p>　　Accepted 3 April 2009. </p><p>　　Available online 6 May 2009.</p><p><b>　　Keywords </b></p><p>　　Concrete; </p><p>　　Elevated temperatures;

4、</p><p><b>　　Pull-out;</b></p><p>　　Bond strength;</p><p>　　Cooling regimes</p><p><b>　　Abstract</b></p><p>　　The effects of elevat

5、ed temperatures and cooling regimes on the residual (after cooling) bond strength between concrete and steel bars are investigated. For this study, ribbed steel bars of 8 mm diameter are embedded in to C20 and C35 concre

6、te blocks with embedment lengths of 6, 10 and 12 cm. Unsealed specimens are heated to 12 different temperatures ranging between 50 and 700 °C and then cooled in water or in air. Pull-out tests are carried out on the

7、 specimens, and the effects of elevated temp</p><p>　　Increases in bond strength are observed for temperatures up to 150 °C; however, there is decrease for all other temperatures. The effect of the cool

8、ing regime is less pronounced for the concrete-bar bond strength. Moreover, it is concluded that concrete-bar bond strength increases with the increase in compressive strength of concrete and embedment length of the bar.

9、</p><p>　　1. Introduction </p><p>　　Reinforced concrete, one of the most widely used construction materials for a variety of structures, is a composite material consisting of reinforcing bars in

10、 a hardened concrete matrix. Concrete is unique for its versatility and large capacity to resist compressive stresses. However, its low tensile capacity makes it imperative to incorporate another material capable of resi

11、sting and transmitting tensile stresses. Steel is recognised worldwide as the most competent reinforcing material in struc</p><p>　　More attention has been paid to the mechanical properties of concrete at hi

12、gh temperature or to the residual properties of concrete after exposure to high temperatures. Concrete may be exposed to elevated temperatures during a fire or when it is closer to furnaces and nuclear reactors. Its mech

13、anical properties such as strength, modulus of elasticity and volume deformation decrease and this results in structural quality deterioration of concrete [2], [3], [4], [5], [6], [7] and [8]. Of particula</p><

14、;p>　　Deterioration in mechanical properties of concrete upon heating may be attributed to material factors and environmental factors. Material factors are properties of aggregate, properties of cement paste and aggreg

15、ate–cement paste bond and their thermal incompatibility between each other. Environmental factors can be listed as heating rate, duration of exposure to maximum temperature, cooling rate, loading conditions and moisture

16、regime [11] and [12]. Siliceous aggregates containing quartz may cau</p><p>　　The structure of concrete material can be approximately classified into micro level (less than 1 μm), meso level (between 1 μm an

17、d 1 cm), and macro level (greater than 1 cm). For concrete subjected to high temperature, with the increase in temperature, strength and Young's modulus decrease at macro level, internal structures degenerate and mic

18、ro defects develop at micro and meso levels [13].</p><p>　　The effect of fire and high temperature on the behaviour and properties of reinforced concrete studies includes compressive strength, modulus of ela

19、sticity, shear modulus, thermal conductivity, specific heat and creep of concrete along with modulus of elasticity and coefficient of thermal expansion and tensile strength of reinforcing steel. Information on the bond b

20、etween concrete and steel is limited. In studying bond strength, pull-out tests are applied and average loads are used to calculate </p><p>　　Most research data of residual properties of concrete after expos

21、ure to high temperature were obtained under conditions of natural cooling, which should differ obviously from cooling regimes in a real fire, where water spraying is usually used for fire extinguishing and consequently t

22、hermal shock is induced to concrete. It has been reported that water cooling caused more severe decrease in strength compared to natural cooling. Therefore, the effect of cooling regimes on the mechanical properties</

23、p><p>　　As a result of these reasons summarised above, the effects of elevated temperatures and cooling regimes after the heating process on the residual bond strength between concrete and steel bars are examin

24、ed in this experimental investigation. Normal strength concrete mixtures with the initial compressive strengths of 20 and 35 MPa, which are commonly used in buildings in Turkey, are tested throughout the study. Reinforce

25、ment bars are embedded into concrete specimens with 3 different embedment leng</p><p>　　2. Materials and methods</p><p>　　ASTM Type I, Portland Cement (PC), from A?kale Cement Factory in Erzurum

26、, Turkey, was used in this investigation. Natural aggregate (NA) with a maximum size of 16 mm was obtained from Altunkent region in Erzincan, Turkey. Aggregate used in this study was river sand and gravel and it was sili

27、ceous aggregate. The chemical composition of PC is summarised in Table 1, physical and mechanical properties of PC are given in Table 2 and the properties of aggregate are shown in Table 3. The diameter of th</p>

28、<p>　　Two different concrete mixes with initial compressive strengths of 20 and 35 MPa are produced in laboratory-type mixer with the capacity of 60 dm3. Ribbed steel bars 8 mm in diameter are embedded into concrete

29、 blocks with the embedment lengths of 6, 10 and 16 cm. For each group, six samples of 100 mm diameter and 200 mm height cylinders are prepared for all temperature values. Three of them are cooled in water and the other t

30、hree specimens are cooled in laboratory conditions after heating. The s</p><p>　　For investigating the effect of high temperatures over the bond strength between concrete–steel bars, the temperature values a

31、re chosen as 50, 100, 150, 200, 250, 300, 350, 400, 450, 500, 600 and 700 °C in this study. Also unheated specimens are produced and tested for comparing with the heated specimens. For the heating process a laborato

32、ry-type furnace, capacity of 1000 °C, is used. The rate of temperature increase of the furnace is 12–20 °C/min. After heating specimens up to the reference tem</p><p>　　3. Results and discussion<

33、;/p><p>　　3.1. Bond strength between concrete–steel bars exposed to elevated temperatures</p><p>　　After the effect of the elevated temperatures in a range of 50–700 °C, the bond strengths are

34、 shown in Fig. 2 and Fig. 3 for C20 and C35 concretes, respectively. The change ratios of the bond strengths by the effect of elevated temperatures are also presented in Table 6, Table 7 and Table 8, and are discussed be

35、low.</p><p>　　Increases in residual bond strengths are observed up to 150 °C for all embedment lengths. This is thought to be due to the increase in residual compressive strength for the same temperatur

36、es. The highest increase amounts of 6 cm embedment length are 14% and 12% for C20 and C35 concretes, respectively. These values are both taken from the specimens that are heated to 50 °C and then cooled in water. Ab

37、ove 150 °C, bond strength decreases with increase in temperature. For the temperature of 700 °C, </p><p>　　For 10 cm embedment length, bond strengths of C20 specimens increased 10% and 9% for 50 an

38、d 100 °C, but then there are decreases for all other temperatures. Bond strengths of specimens produced with C35 concrete showed losses for all temperatures, except for an increase with the amount of 5% for 100 

39、6;C. Above 100 °C, both air-cooled and water-cooled specimens’ bond strengths are found to be less than the unheated specimens for C20 and C35. The maximum strength loss is observed for 700 °C. For th</p>

40、<p>　　Bond strength of samples with 16 cm embedment length was similar to 10 cm embedment length, at elevated temperatures. Increases in residual bond strength were recorded up to 150 °C for C20 and up to 100

41、 °C for C35, but bond strengths decreased at higher temperatures. The bond strength losses of 16 cm embedment length are 45% for C20 and 47% for C35. These losses are obtained after 700 °C on the air-cooled sam

42、ples.</p><p>　　The effect of cooling regimes was more significant for C20 specimens. Water-cooled samples lost more residual bond strength compared with air-cooled samples for the same temperature. But this

43、effect is less pronounced for C35. For both concrete types effect of cooling regime cannot be seen at 6 cm embedment length.</p><p>　　3.2. Compressive strength–bond strength relationship</p><p>

44、　　Compressive strengths of concretes after elevated temperatures were determined for both air- and water-cooled specimens, and the relationship between compressive strengths and bond strengths is illustrated in Fig. 4 fo

45、r C20, and in Fig. 5 for C35. With the increase of temperature residual compressive strength and residual bond strength losses were observed. As it can be seen briefly from the graphics, the bond strengths of specimens i

46、ncrease with the increase of compressive strength, for both co</p><p>　　4. Conclusions</p><p>　　The results of this experimental study can be concluded as follows.</p><p>　　In the r

47、ange of 50–150 °C, an increase in residual bond strength was observed for C20 and C35 concretes. Also residual compressive strengths increased for these temperatures, so increase in the residual bond strength is a r

48、esult of increase in residual compressive strength. Above 150 °C, residual bond strength between concrete and ribbed steel bars decreased for both concrete type and for all embedment lengths. Increase in the embedme

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