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Sherman, Ryan J.

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Author: Phillips, Matthew L. × search.filters.applied.f.resourcesubtype: Technical Report ×

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    Enhanced Characterization of the Flexural Resistance of Built-Up I-Section Members
    (Georgia Institute of Technology, 2022-07) Slein, Ryan ; Kamath, Ajit M. ; Phillips, Matthew L. ; Sherman, Ryan J. ; Scott, David W. ; White, Donald W.
    The AISC 360 Specification Chapter F I-section member flexural resistance provisions are a central part of structural steel design in the United States. The “unified” procedures of Sections F4 and F5 address general singly and doubly symmetric I-section members. Analytical studies and experimental tests subsequent to the implementation of these provisions within the 2005 AISC Specification suggest that the corresponding inelastic Lateral-Torsional Buckling (LTB) and Tension Flange Yielding (TFY) resistance calculations can be improved. Sixteen new large-scale experimental tests on thirteen specimens are targeted in this research to further investigate these predictions. In addition, extensive shell finite element analysis (FEA) test simulation studies are performed correlating with and parametrically extending the experimental results. The broad objective is to provide additional supporting data for improvements to the AISC Specification Section F3 to F5 provisions for general built-up I-section members. These improvements provide: (1) reductions as well as increases in calculated capacities via changes to the anchor points (Lp, Mmax) and (Lr, ML) in the LTB resistance equations, (2) increases in calculated capacities recognizing inelastic reserve strength in members experiencing early yielding in flexural tension, via a number of advancements, and (3) substantial shortening and streamlining of the Specification provisions by eliminating all TFY resistance checks and addressing the corresponding behavior in the primary limit states calculations. This report discusses the design and execution of the 16 experimental tests and hundreds of test simulations, including the details of how the test fixtures and bracing systems are configured to minimize incidental restraint in the physical tests, as well as the direct modeling of residual stresses and geometric imperfections in the test simulations. Updated professional factors, Mtest /Mn, obtained from the new tests and test simulations, considered in conjunction with recommended Chapter F provisions, show significant improvements relative to values obtained using the current Specification rules. The updated professional factors exhibit mean values close to 1.0, with relatively small dispersion, across the entire range of the design space. The results from the current research, combined with an updated assessment of historical test strengths versus predictions from the recommended procedures, shows close to a uniform reliability index, β, of 2.6 (for building design and a live-to-dead load ratio of 3.0) across the design space evaluated at the completion of this research.
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    Residual Stress Measurement of Built-Up I-Section Members via the Center-Hole Drilling Method
    (Georgia Institute of Technology, 2022-05) Phillips, Matthew L. ; Slein, Ryan ; Sherman, Ryan J. ; White, Donald W.
    The objective of this study was to measure the residual stresses of two built-up I-girders (one doubly symmetric and one singly symmetric) that are representative of all the experimental specimens tested in the lateral torsional buckling (LTB) investigations conducted by Slein et al. (2022) and Phillips et al. (2022). The measured residual stress profiles were compared to the one-half Best-fit Prawel residual stress profile used in a series of complementary shell finite element analysis (FEA) simulations conducted by Slein et al. (2022), Deshpande et al. (2021), and Phillips et al. (2022). Residual stresses are introduced into components during the manufacturing and fabrication processes and are independent of any externally applied forces or thermal loads. Resulting from mechanical, thermal, and/or metallurgical processes, residual stresses are introduced into built-up I-girders during the manufacturing of the individual plate elements and the welding of the plate components during fabrication. The residual stresses are self-equilibrating, meaning that the corresponding cross-section tensile and compressive forces must balance across the section. Applied stresses are additive to the residual stresses. For the stability limit state, compressive residual stresses at the flange tips have a detrimental impact on the overall buckling strength of the member due to the resulting premature yielding. Two primary classifications for residual stress measurement techniques exist: destructive and non-destructive. Destructive techniques involve the process of removing a small volume of material and then measuring the resulting strains, while non-destructive techniques involve using grain structure and material properties to measure the internal stresses of a member without any physical alterations. For the current study, the semi-destructive technique of center-hole drilling was selected. Center hole-drilling is semi-destructive as it involves the removal of a volume of material, but the holes are generally small enough that they could be repaired without hinderance to the performance of the specimen. The center-hole drilling technique is described in detail in ASTM E837 (2020). All the measurements performed during the current work were conducted in accordance with the governing standard. The measured residual stress profiles for the two specimens considered were small. All flange measurements resulted in a similar profile, where the outer thirds of the flange widths had littleto- no residual stress and the middle third had a spike in tensile residual stress apparently associated with the web-to-flange weld. Both the webs demonstrated an approximately uniform compressive residual stress throughout the web. The measured stresses suggest that the one-half Best-fit Prawel distribution provides a reasonable-to-conservative estimate of the residual stress profiles of the evaluated members; hence the use of the one-half Best-fit Prawel distribution is justified for the complementary shell FEA simulations.