Determining shear capacity of ultra high performance

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274 M Pourbaba and A Joghataie Scientia Iranica Transactions A Civil Engineering 26 2019 273 282. Investigation into di erent mechanical charac UHPC required increased energy input compared to. teristics and properties of UHPFRC as well as its conventional concrete the mixing time was increased. potentials in order to replace conventional concrete To ensure that the UHPC did not overheat during. has recently attracted the attention of a large number mixing and to make the process more convenient the. of researchers 3 5 7 Among these many properties temperature of the constituents was lowered and a. those relevant to structural design have been relatively mixture of ice and water was used instead of water. more frequently investigated Researchers have focused alone As recommended by Graybeal rst silica. on the compressive and tensile strength modulus of fume was mixed with all the sand for approximately 5. elasticity Poisson s ratio creep and shrinkage 7 minutes 3 5 Then before adding water cement and. Furthermore a large number of studies on UHPC have ground quartz were added and dry mixed for at least. concentrated on exural 8 11 and shear behaviors in 5 minutes Then in order to improve owability su. this development 12 18 perplasticizer was added gradually After a number of. Currently the fact is that shear failure is di cult trials a water cement ratio w c of 0 24 was obtained. to predict accurately This di culty is more particu for the nal mixture Straight high strength steel ber. larly observed in high strength concrete and UHPFRC was added by 6 1 of the weight in order to improve the. beams In spite of many decades of experimental mechanical properties of concrete especially in terms. research some of which was reviewed above and the of tensile strength and ductility The superplasticizer. use of highly sophisticated analytical tools practically used was AURAMIX 4450 FOSROC which was a. accurate enough methods and equations for estimating polycarboxylic ether based superplasticizer. shear capacity are not fully understood yet More While the 9 beams were made using generic mix of. particularly there is no adequate knowledge about local material in Tabriz a commercial product known. rectangular UHPFRC beams without stirrups as Ductal similarly including cement silica fume. In fact the previous experimental and theoretical ground quartz and sand was used in Miami to make. studies were mainly concentrated on UHPFRC beams specimens with a w c of 0 20 and steel ber of 6 4. with pre stressing strands and basically I shaped and by weight The rest of the process including mixing. P shaped beams 19 22 Taking this gap into account procedure in Miami was similar to that in Tabriz. the present paper seeks to study the shear strength of Cubes of 100 100 100 mm and cylinders of 100. rectangular UHPFRC beams with longitudinal tension 200 mm specimens were also made to determine the. rebar and without transverse reinforcement for which compressive strength of UHPFRC The specimens were. the estimations of di erent guidelines regulations and kept under water in Tabriz and in the laboratory with. codes are compared with the results obtained by recent almost constant temperature in Miami because of high. experiments 23 humidity The compressive strengths were obtained. to be 125 MPa and 137 MPa for the specimens in, 2 Materials and methods Tabriz and Miami respectively Figures 1 and 2 show. the mixing process in Tabriz and Miami It should, 2 1 Specimens and parameters be noted that as Graybeal reported cube specimens. Nineteen beam specimens were made at the labora 100 100 mm had compressive strengths about 5. tories of Tabriz University Iran and Florida Inter higher than the cylinder specimens 100 200 mm so. national University US The beams were of 3 dif, ferent sizes and their dimensions were 152 152 559. 102 203 559 and 152 76 559 mm The materials,of specimens consisted in Portland cement ne sand. silica fume superplasticizer steel bers and water for. UHPFRC straight high strength steel ber with the,length of 13 mm diameter of 0 18 mm and speci ed.
tensile strength of 2700 MPa for bers and deformed. steel bars for longitudinal steel with speci ed yield. points of about 400 MPa 60 and 690 MPa 100, The mix design and curing process of specimens were. detailed in a previous study by the rst author 23, which is also explained brie y here Nine beams were. cast from one batch of UHPC in Tabriz using the,above mentioned materials In order to make the. project economical local materials and a conventional. concrete mixer were used The mixer was reinforced by Figure 1 Drum strengthened by plate used for UHPFRC. adding steel plates inside the drum Moreover since mixing in Tabriz Iran. M Pourbaba and A Joghataie Scientia Iranica Transactions A Civil Engineering 26 2019 273 282 275. erties of specimens tested by Pourbaba 23 All the, beams were 559 mm in total length having a span of. 457 mm While the widths of specimens were only,152 and 102 mm they had di erent total depths of.
152 203 and 76 mm Also given that di erent size, bars were used the e ective depth of reinforcement. was also di erent from specimen to specimen The,e ective depths were about 126 180 and 55 mm As. indicated in Table 1 the longitudinal reinforcements. included 3 25 3 22 3 20 3 19 3 18 2 20 2 16,3 14 3 12 and 3 10 Figure 3 shows the three. dimensional view and bar placement of the specimens. It is worth mentioning that the specimens used in, the above mentioned research contained no transverse. Figure 2 Site with equipment used for UHPFRC mixing reinforcing bars. in Miami US Figure 4 presents the test setup designed for the. experiments explained in Pourbaba s dissertation 23. the compressive strengths obtained for cube specimens As shown in Figure 4 the shear span was a 153 mm. were reduced by 5 4 203 51 for all the specimens however the ratio of. The shear strength of each of the 19 specimens shear span to depth a d was di erent for di erent. was determined by 4 point loading test at the labora specimens. tories of Tabriz University and Florida International. University Also the shear strength of each specimen 2 2 Review of various codes regulations. was estimated using various codes and regulations guidelines and design methods. including ACI 318 RILEM TC 162 TDF Australian 2 2 1 ACI 318 building code requirements for. guideline and Iranian National Building Regulations structural concrete American concrete. as will be explained in the next sections To assess the institute. estimation capability of the codes and regulations the ACI Code presents the basic shear equations in terms. ratio of experimental shear strength to predicted shear of shear forces not shear stresses In fact in order to. strength EP was calculated This ratio EP was used obtain the total shear forces the average shear stresses. to compare the codes are multiplied by the e ective beam areas The shear. Table 1 provides the information about the prop strength of the concrete denoted by Vc is obtained by. Table 1 Properties of tested UHPC beams by Pourbaba 23. Name Section b h Rebars d As fc0 fy a d,mm mm MPa MPa.
B1 152 152 3 25 125 1473 137 690 0 078 1 2,B2 152 152 3 22 126 1473 137 690 0 060 1 2. B3 152 152 3 25 125 1473 137 414 0 078 1 2,B4 152 152 3 22 126 1473 137 414 0 060 1 2. B5 152 152 3 19 128 1473 137 414 0 044 1 2,B21 152 152 3 20 127 942 5 125 400 0 049 1 2. B22 152 152 3 18 128 763 4 125 400 0 039 1 2,B23 152 152 3 20 127 942 5 125 400 0 049 1 2. B24 152 152 3 18 128 763 4 125 400 0 039 1 2,B29 102 203 2 20 178 628 3 125 400 0 035 0 9.
B30 102 203 2 16 180 402 1 125 400 0 022 0 8,B35 152 76 3 14 54 461 8 125 400 0 056 2 8. B36 152 76 3 12 55 339 3 125 400 0 040 2 8,B37 152 76 3 10 56 235 6 125 400 0 027 2 7. Based on data from Pourbaba s dissertation 23, These specimens were tested in duplicates a and b in Miami to con rm repeatability. 276 M Pourbaba and A Joghataie Scientia Iranica Transactions A Civil Engineering 26 2019 273 282. Figure 3 Three dimensional view of specimens tested by Pourbaba 23 units are in mm. even higher and consequently be obtained by Eq 2, in the following in which the e ects of the longitudinal. reinforcing as well as the moment and shear magnitudes. have been taken into consideration 24 25,p Vu d bw d p.
Vc fc0 120 w,0 30 fc0 bw d 2,where w As bw d is the reinforcement ratio and. Mu is the moment occurring in combination with shear. force Vu at the cross section considered Also accord. Figure 4 Test setup used by Pourbaba 23 to test ing to ACI in the above equation for Vc Vu d Mu. UHPC specimens shall not be taken greater than unity 23 24 Taking. Figure 4 into account in our case Vu P 2 and, the following equation Mu Vu a P a 2 consequently Vu d Mu d a. According to the last column of Table 1 Vu d Mu,p d a 1 d a is smaller than 1 except for B29 and. Vc b d 1 B30 where the ratios are 1 11 and 1 25 i e marginally. 6 w above the ACI limit, where is the speci ed compressive strength of concrete Using Eqs 1 and 2 the shear strength of. at age of 28 days bw is the width of a rectangular beam the beam specimens was determined of which the. and d is the e ective depth results are tabulated in the third and fourth columns. Furthermore according to ACI Code Vc can go of Table 2. M Pourbaba and A Joghataie Scientia Iranica Transactions A Civil Engineering 26 2019 273 282 277. Table 2 Maximum experimental shear forces and predicted shear forces using various codes. Ultimate Predicted shear strength kN,shear ACI Iranian national.
strength RILEM Australian building regulations,kN Eq 1 Eq 2 Eq 12 Eq 13. B1a 416 37 52 103 123 27 40,B1b 476 37 52 103 123 27 40. B2a 468 37 48 104 125 27 37,B2b 436 37 48 104 125 27 37. B3a 462 37 52 103 123 27 40,B3b 357 37 52 103 123 27 40. B4a 367 37 48 104 125 27 37,B4b 388 37 48 104 125 27 37.
B5a 402 38 45 105 126 27 34,B5b 383 38 45 105 126 27 34. B21 349 36 44 86 125 26 34,B22 332 36 42 87 126 26 33. B23 335 36 44 86 125 26 34,B24 336 36 42 87 126 26 33. B29 409 34 40 81 117 24 31,B30 342 34 36 82 118 25 28. B35 106 15 16 37 53 11 12,B36 85 16 16 37 54 11 12.
B37 71 16 15 38 55 11 12,Based on data from Pourbaba s dissertation 23. 2 2 2 RILEM TC 162 TDF test and design methods mouth opening displacements and can be determined. for steel ber reinforced concrete by means of the following expression. The residual exural tensile strength fR i is de ned. as an important parameter which characterizes the 3FR i L. fR i N mm2 3, post cracking behavior of steel ber reinforced concrete 2b h2sp. To achieve this property three point bending test on where b is the width of the specimen hsp is the distance. notched beams according to EN 14651 2005 26 was between the tip of the notch and the top of the cross. conducted by Pourbaba the results of which are used section and L is the span of the specimen all in mm. in the current research 23 Hence the following RILEM TC TDF 162 2003. The methods of conducting the above mentioned equations standard method have been used to obtain. test have been discussed in some sources such as the nominal shear strength of UHPC beams 14 27. RILEM TC 162 TDF recommendation 2003 27 EN, 14651 2005 26 and b model code for concrete Vu Vc Vf Vs 4. structures 2010 28, The three point bending test on notched prisms Vc Vconcrete 0 12k 100 l ffck 1 3 0 15 cp bw d. was conducted in accordance with EN 14651 2005 to 5. determine the post cracking behavior under tension. and used to predict shear resistance of the beams Vf V bers 0 7kf k fd bw d 6. without shear reinforcement The specimens had a, height of 150 mm a width of 150 mm a span of where.
500 mm and a length of 550 mm with an initial notch r. of 25 mm in the middle 23 200 As,According to RILEM TC 162 TDF 2003 the. residual exural tensile strengths fR 1 and fR 4 are. respectively de ned at 0 5 mm and 3 5 mm crack fd 0 12fRk 4 7. 278 M Pourbaba and A Joghataie Scientia Iranica Transactions A Civil Engineering 26 2019 273 282. where kf is for T sections and As is the tension of concrete for concrete beams subjected to shear. reinforcement in the section considered in mm2 b and combined with bending. d are respectively the section width and the e ective. depth in mm and Vs is contribution of the shear Vu d. Vc 0 95vc 12 w b d 14, reinforcement due to stirrups which in our case was Mu w. equal to 0,where w is the reinforcement ratio and w. 2 2 3 Australian design guidelines for ductal As bw d also Mu is the moment occurring in combi. prestressed concrete beams nation with shear force Vu at the cross section Similar. According to the Australian design guidelines for duc to ACI code the Iranian National Building Regulations. tal prestressed concrete beams 29 the following for limit the value of VMuud to 1 0 In addition the Iranian. mula gives the shear strength of a prestressed concrete Building Regulation require that Vc should be equal. section to or less than 1 75 vc bw d 30 In our case when. considering the overview of beam and applied loads. Vu Vuc Vus Pv 8 shown in Figure 4 Vu P 2 and Mu Vu a P a 2. where Vuc is the contribution of the concrete to the a is shear span of specimens therefore Vu d Mu. shear strength Vus is the contribution of the transverse d a. shear reinforcement and Pv is the transverse compo. nent of the prestressing force 3 Results and discussions. TDF Australian guideline and Iranian national building regulations To compare the code estimations the ratio of experimental shear strength to predicted shear strength was calculated for each code This ratio is in fact a measure of safety factor on the one hand and a measure of precision of the estimation on the other hand Based on the results of both studies the authors concluded that

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