Conference Presentations by Cristopher Moen
The goal of this paper is to highlight promising methods in current thin metallic shell design pr... more The goal of this paper is to highlight promising methods in current thin metallic shell design practice and to define a future needs framework from which research can launch. Thin shell structural members are a staple in many industries – from aerospace, ship building, to offshore oil and gas to residential and commercial buildings. Shell types and geometries are numerous including ship hulls, silos, tanks, pipelines, chimneys and wind turbine towers. Despite large research investments there is still wide debate and uncertainty when designing thin shell structural members. Failure modes are complex and sensitive to initial geometric imperfections. The types of loadings vary widely– including axial, shear, flexure combined with internal or external pressure – making calculation-based methods challenging. Shell geometry – including longitudinal and transverse stiffeners and conical, tapered along a member – compound the complexity. This paper synthesizes these current approaches and organizes the most promising ideas into a framework for future research. A specific focus will be on research needed to expand current GMNIA (geometrically and materially nonlinear analysis with imperfections included) capabilities.
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Papers by Cristopher Moen
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Journal of Structural Engineering, May 1, 2013
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Conference Proceedings of the Society for Experimental Mechanics Series, 2015
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Journal of Structural Engineering, 2015
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Journal of Structural Engineering, Apr 3, 2012
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Thin-Walled Structures, 2016
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Journal of Structural Engineering, Aug 11, 2012
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Transportation Research Record Journal of the Transportation Research Board, Feb 3, 2015
ABSTRACT This paper details a study of the structural behavior of hybrid-composite beams (HCBs), ... more ABSTRACT This paper details a study of the structural behavior of hybrid-composite beams (HCBs), which consist of a fiber-reinforced polymer (FRP) shell with a tied concrete arch. The HCB offers advantages in life-cycle costs through reduced transportation weight and increased corrosion resistance. Through a better understanding of system behavior, the proportion of load in each component can be determined, and each component can be designed for the appropriate forces. A long-term outcome of this research will be a general, structural analytical framework, which can be used by transportation departments to design HCBs as rapidly constructible bridge components. This study focused on the identification of the load paths and load sharing between the arch and FRP shell in an HCB and on the test of an HCB with a composite bridge deck. Tests were performed through the application of point loads on simple span beams (before the bridge deck was placed) and with a three-beam, skewed composite bridge system, which resulted in strain data for the arch and FRP shell. The test results showed that strain behavior was linear elastic at service loads, and the FRP shell had a linear strain profile. Curvature from strain data was used to find internal bending forces, and the proportion of load within the arch was found. A stress integration method was used to confirm the internal force contributions. The arch carried about 80% of the total load for the noncomposite case without a bridge deck. When composite with a bridge deck, the arch made a minimal contribution to the HCB stiffness and strength, because most of the arch was below the neutral axis and cracked under the maximum live load expected for the bridge. For this composite case, the FRP shell and prestressing strands resisted about 80% of the applied load, while the bridge deck carried the remaining 20% to the end diaphragms and bearings.
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Strut and tie models (STM) are widely used by designers of reinforced concrete and prestressed co... more Strut and tie models (STM) are widely used by designers of reinforced concrete and prestressed concrete structures. Selection of an efficient model, however, becomes a challenging task for complex design domains, such as 3d domains with cutouts. Topology optimization has therefore been promoted as means of automating the development of highly efficient (minimum strain energy) STM. Current drawbacks of such methods are that solutions may complex and fail to properly account for secondary tensile stresses; that is, the case where the major principal stresses are compressive and minor principal stresses are tensile. A hybrid truss-continuum topology optimization scheme was recently developed to overcome these challenges in 2D concrete design. That work is modified and extended herein to three-dimensional domains and mechanics models. The stiffness of the elements are formulated such that truss elements carry only tensile forces and thus represent straight steel rebar, while the continu...
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Structural topology optimization is increasingly being used to remove the guesswork in identifyin... more Structural topology optimization is increasingly being used to remove the guesswork in identifying natural force flow paths for reinforced concrete and prestressed concrete, particularly for complex 3D design domains. Tension and compressive forces that follow the principle stress trajectories, i.e., ties and struts, are automatically identified with topology optimization using a formulation that minimizes strain energy, or equivalently that minimize crack widths. While a useful alternative to trial-and-error process of generating strut-and-tie models (STM), the approach falls short of design objectives as it neglects constructability and rebar detailing, which is often the governing cost. This paper uses a new advancement in topology optimization for addressing constructability issues by considering both material and construction costs. By assigning different construction costs for each tension tie (rebar or prestressing), the placement of steel can be controlled to a large extent ...
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Cold-formed steel wood-sheathed floor diaphragm system behavior is analyzed from a system reliabi... more Cold-formed steel wood-sheathed floor diaphragm system behavior is analyzed from a system reliability perspective. Floor systems consisting of oriented strand board (OSB), cold-formed steel (CFS) joists, tracks and screw fasteners are modeled using shell and spring elements in ABAQUS. (Dassault-Systems ())The models consider typical seismic demand loads, with careful treatment of light steel framing diaphragm boundary conditions and OSB sheathing kinematics, i.e., two sheets pulling apart or bearing against each other at an ultimate limit state, consistent with existing experimental results. The finite element results are used to build surrogate mathematical idealizations (series, parallel-brittle and parallel-ductile) for the critical system components. System reliability and reliability sensitivity, defined as the derivative of system reliability with respect to component reliability, are studied for these idealizations. These results represent mathematical upper and lower bounds ...
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The governing limit state for cold-formed steel purlins used in a metal building can be distortio... more The governing limit state for cold-formed steel purlins used in a metal building can be distortional buckling, where the compressed flange in contact with corrugated metal roof panels deforms in up-down half-waves along the length of the member. Current code equations for calculating distortional buckling capacity were derived experimentally with four-point bending tests; however, the controlling gravity load case for roof purlins can be snow or wind that may suppress these distortional buckling half-waves. This paper presents an experimental and computational study to explore and quantify the distortional buckling flexural capacity of metal building Zee purlins with and without through-fastened panels considering both four-point bending and a uniform pressure applied to the metal roof panels. A total of 12 tests were conducted on a typical metal building roof system employing a vacuum chamber, the results of which are compared to AISI Direct Strength Method capacity predictions. A ...
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AEI 2015, 2015
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Structures Congress 2014, 2014
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Journal of Structural Engineering, 2015
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Journal of Engineering Mechanics, 2015
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Conference Presentations by Cristopher Moen
Papers by Cristopher Moen