| Author: | Lin, Xuemei |
| Title: | A study of the structural performance of bearing-type high strength steel bolted connections |
| Advisors: | Yam, C. H. Michael (BRE) Chung, K. F. (CEE) |
| Degree: | Ph.D. |
| Year: | 2022 |
| Subject: | Steel, High strength Mild steel Steel, Bearing Hong Kong Polytechnic University -- Dissertations |
| Department: | Department of Building and Real Estate |
| Pages: | xxi, 226 pages : color illustrations |
| Language: | English |
| Abstract: | Due to the high strength-to-weight ratio of high strength steel (HSS) material, the section size and self-weight of HSS structural members are usually smaller and lower than those of mild steel (MS) members. Hence, considerable economic and environmental benefits can be realised by applying HSS to civil engineering structures. However, HSS materials have lower ductility and ratio of the ultimate strength (fu) to yield strength (fy) than do MS materials, which may affect the structural behaviour and tensile strength of HSS bolted connections under tension. Thus, the applicability of the current design rules for bolted connections, which were developed mainly based on the testing of MS specimens, to the design of HSS bolted connections needs to be re-examined. In this study, 105 bolted plate connections of various geometric configurations under double shear were designed to fail in net section fracture or block shear failure mode. The main test parameters included the bolt spacing, the edge distance, the number of bolt rows, the bolt pattern, and the steel grade. Two grades of HSS, namely Q690 and Q960, were tested, as was one grade of MS (Q345) for comparison. A finite element (FE) analysis of the specimens was conducted considering both geometric and material nonlinearities. The effects of both stress triaxiality and Lode angle on the metal plasticity and ductile fracture were considered for the specimens failing in block shear. The HSS specimens exhibited a lower mean test-to-predicted ratio (i.e., the ratio between the test ultimate load and the calculated net section resistance or block shear strength) and lower overall deformation capability than did the MS specimens. The test results showed that the HSS connections could achieve the net section resistance (Anetfu, where Anet is the net section area, which is determined based on the s2/4g rule if the net section fracture is through a staggered path). The results were mainly attributed to: (1) the HSS materials possess sufficient ductility to allow for efficient stress redistribution across the net section, and (2) the biaxial stress effect induced by the bolt holes increased the ultimate capacity of the perforated main plate. A correction factor accounting for the effect of the gauge-to-bolt-hole diameter ratio on the prediction accuracy of the inclined section area was introduced to modify Cochrane's original equation. In general, the s2/4g rule provides good predictions of the net section resistance. A reliability analysis indicated that the current design equation for net section resistance of HSS (S460-S700) in EN 1993-1-12 with a partial factor (yM12) of 1.25 is applicable to the bolted connections made using higher steel grade (such as Q960) without or with staggered bolts. The test and the FE analysis results of the block shear specimens revealed that the failure mode was a combination of fracture of the net tension plane and yielding of the effective shear plane (which is located between the net and gross shear planes). A modified design equation was proposed to account for the effect of the fu/fy ratio which provides good predictions of the block shear strength of both MS and HSS connections. A reliability analysis showed that the resistance factor (Ø= 0.75) as specified in ANSI/AISC 360-16 and CSA S16-14 can be used in conjunction with the proposed equation, leading to a safety index of 4.7 for all of the investigated bolted connections. |
| Rights: | All rights reserved |
| Access: | open access |
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