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Slip and yield resistance of friction type of high ...

1711 INTRODUCTION As for field joints of steel bridges, friction type of high strength bolted connections have been commonly adopted. The friction between main plate and splice plates due to bolt tightening force makes the stress trans-mission. The limit states of this type of connections are usually regarded as slip between main and splice plates and yielding of main or splice plate. Therefore, these two limit states are checked in the design phase1)-3). In a steel bridge erection site, it is sometimes difficult to adjust the hole of main plate to the hole of splice plates because there are several variations of bolt-hole pitch due to the field welding and/or supporting condi-tion.

173 3.2 Slip load and yielding load Slip load defined as the load when the slip occurs during the tensile test. The slip can be distinguished by big sound, sudden enlargement displacement of …

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Transcription of Slip and yield resistance of friction type of high ...

1 1711 INTRODUCTION As for field joints of steel bridges, friction type of high strength bolted connections have been commonly adopted. The friction between main plate and splice plates due to bolt tightening force makes the stress trans-mission. The limit states of this type of connections are usually regarded as slip between main and splice plates and yielding of main or splice plate. Therefore, these two limit states are checked in the design phase1)-3). In a steel bridge erection site, it is sometimes difficult to adjust the hole of main plate to the hole of splice plates because there are several variations of bolt-hole pitch due to the field welding and/or supporting condi-tion.

2 In these cases, the over-sized hole is sometimes required and utilized in order to modify the problem and make an erection easy. Here, the over-sized hole is defined as the hole diameter larger than bolt diameter (M22) by or more. Normal bolt-hole diameter is (bolt diameter + ) in Japanese stan-dard1). In this study, in order to examine the influence of over-sized holes on the slip resistance and the yield resis-tance of the friction type of high strength bolted connections, tensile tests have been performed on the bolted connections fabricated in consideration of slip to yield resistance ratio.

3 Here, several kinds of specimens are prepared and designed by means of slip to yield resistance ratio ( ; ratio of design slip resistance Ps to design yield resistance Py). If value is less than unity, slip precedes yielding. Yielding precedes slip when the value is larger than unity. 2 METHOD OF TENSILE TESTS FOR CONNECTION WITH OVER-SIZED HOLE Specimen The specimens used for tensile tests are butt connections with two friction surfaces as shown Figure 1. The material of plates and bolt is SM490Y and F10T-M22 specified in Japan Industrial Standard, respectively.

4 Bolt hole diameters of main and splice plates are , , Main plate thickness is determined as 16, 19, 22 and 25mm so that the design slip to yield resistance ratio is , , or in case of hole of in diameter. The friction surface of main plate and splice plate is grid-blasted to remove a mill-scale. The arrangements of bolt holes consist of six types as shown Figure 2. From type 1 to 3, hole diameter is var-ied as , and Type 4, 5 and 6 have hole diameter of , but the hole of splice plate is IABSE-JSCE Joint Conference on Advances in Bridge Engineering-II, August 8-10, 2010, Dhaka, Bangladesh.

5 ISBN: 978-984-33-1893-0 Amin, Okui, Bhuiyan (eds.) slip and yield resistance of friction type of high strength bolted connections with over-sized holes Takeshi Mori Hosei University, 2-33 Ichigaya-Tamachi Shinjuku-ku, Tokyo 162-08743, Japan ABSTRACT: It is sometimes difficult to adjust the hole of the splice plate to the hole of the main plate cor-rectly in a friction type of high strength bolted connection at the construction site. In order to modify this problem and make an erection easy, the over-sized holes is sometimes required and utilized.

6 In this study, in order to examine the influence of over-sized holes on the slip resistance and the yield resistance of the friction type of high strength bolted connection, tensile tests have been performed on the bolted connections in con-sideration of slip to yield resistance ratio. As a result, following conclusions have been obtained. The slip re-sistance does not depend on the hole diameter. The yield resistance is decreasing in proportion to the reduc-tion of net sectional area of the main plate due to the over-sized hole.

7 However, the yield resistance can be regarded as about times of one calculated from the net sectional area because of stress transmission due to the friction between a main plate and splice plates. 172sifted from the hole of main plate. As for the type 1, 2 and 3 specimens, the plates of all the plate thickness (16, 19, 22, 25mm) have been utilized, but only plate of 25mm thickness has been employed for the type 4 to 6 specimens. Method of tensile tests The tensile tests are performed until both slip and yielding are observed using universal tensile test equipment with load capacity of 2000kN.

8 The measured items are shown in Figure 3. The gap variation between main plates due to applied load is measured by clip-gauge and the yielding of main plate is observed by strain gauge adhered on the edge side of the plate. The strain gauge is also put on the side of splice plates to confirm the stress transmission from main plate to splice plates. The high strength bolt with strain gauge is adopted to measure the variation of bolt tightening axial force during test. Before the tensile test, the relaxation of bolt axial force is measured on right after fastening and the just before the tensile test (12 24 hours after fasten-ing).

9 The side of main and splice plates are machined by about 5mm in order to remove residual stress due to flame cut. 3 RESULTS OF TENSILE TESTS Relaxation of bolt axial force The relaxation has been measured 34 days after fastening on the type 1-5 of slip proceeded connection (t=25mm). The axial force reduction of each type was , , , , and , respectively. Therefore, it can be said that the difference of relaxation due to diameter of bolt hole ad shifting bolt has not occurred. In 12 to 24 hours measurement mentioned last chapter, significant variation of relaxation of bolt tightening force due to the difference of type of specimens was not observed.

10 Type1 Typ e2 Typ Typ e4 55 25 25 25 Figure 2. Combination of Bolt Hole Figure 1. Shape and Dimensions of Test Specimen B A A B 9 16 10 19 12 22 13 25 slip load and yielding load slip load defined as the load when the slip occurs during the tensile test. The slip can be distinguished by big sound, sudden enlargement displacement of the gap and decreasing load. Yielding load is obtained from the load-strain curves at gauge shown in and defined as offset load.


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