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1. Applications of Polynomial Chaos-Based Cokriging to Simulation-Based Analysis and Design Under Uncertainty

   https://doi.org/10.1115/DETC2020-22369  

   Nagawkar, Jethro; Leifsson, Leifur (August 2020, Proceedings of the ASME 2020 International Design Engineering Technical Conferences & Computers and Information in Engineering Conference IDETC/CIE 2020)

   null (Ed.)

   Abstract This paper demonstrates the use of the polynomial chaos-based Cokriging (PC-Cokriging) on various simulation-based problems, namely an analytical borehole function, an ultrasonic testing (UT) case and a robust design optimization of an airfoil case. This metamodel is compared to Kriging, polynomial chaos expansion (PCE), polynomial chaos-based Kriging (PC-Kriging) and Cokriging. The PC-Cokriging model is a multi-variate variant of PC-Kriging and its construction is similar to Cokriging. For the borehole function, the PC-Cokriging requires only three high-fidelity samples to accurately capture the global accuracy of the function. For the UT case, it requires 20 points. Sensitivity analysis is performed for the UT case showing that the F-number has negligible effect on the output response. For the robust design case, a 75 and 31 drag count reduction is reported on the mean and standard deviation of the drag coefficient, respectively, when compared to the baseline shape. 

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2. From Testing to Codification: Post-tensioned Cross Laminated Timber Rocking Walls

   Pei, S.; Dolan, J.; Zimmerman, R.; McDonnell, E.; Line, p.; Popovski, P. (October 2019, Proceedings of the International Network for Timber Engineering Research (INTER))

   Blass, Hans (Ed.)

   Wood buildings in North American has been predominantly constructed using light-framed wood systems since early 1900’s, with only limited exception of heavy timber construction in some non-residential applications. This situation is likely to change in the future with the growing acceptance of mass timber construction in the region. In fact, a number of mass timber buildings have been constructed in recent years in the U.S. and Canada, including low- to mid-rise mixed-use buildings (e.g. UMass Student Center, T3 building) and tall towers (e.g. Brocks Commons at UBC). Most of these buildings utilized cross laminated timber (CLT) or nail laminated timber (NLT) floors and heavy timber framing systems to support gravity loads, and a non-wood lateral system such as concrete shear walls or a braced steel frame to resist wind and seismic loads. Although CLT material and glulam products have been recognized in the U.S. and Canada (IBC (2018) and NBCC (2015), there is currently no mass timber lateral systems in the U.S. and only one system (platform style panelized CLT shear wall) in Canada that is currently recognized by the building codes. As a result, special design procedures and review/approval processes must be followed for any building intended to use a mass timber lateral system. There is a need to promote codification of mass timber lateral systems in order to help further develop mass timber building market in North American. At the time of this paper, there has been an on-going effort to devel-op seismic design parameters for panelized CLT shear walls in the U.S. (ref) following the FEMA P695 procedure for platform construction. The other lateral system that at-tracted significant attention and research resources is post-tensioned CLT rocking wall system, which has the potential to be applicable to balloon framed low-rise to tall wood buildings. This paper will focus on recent research development on CLT rocking wall system in the U.S. and the effort to develop a seismic design procedure for this system for inclusion in the NDS Special Design Provisions for Wind and Seismic (SPDWS)(2008). While the expensive and time consuming process of the FEMA P695 process would provide the ability to use the equivalent lateral force method for design purposes, this path is not part of the discussion included here. 

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3. Aerodynamic Shape Optimization for Delaying Dynamic Stall of Airfoils Using Cokriging Regression

   https://doi.org/10.2514/6.2021-0340  

   Raul, Vishal V.; Leifsson, Leifur T. (January 2021, AIAA SciTech 2021 Forum)

   null (Ed.)

   The dynamic stall phenomenon produces adverse aerodynamic loading, which negatively affects the structural strength and life of aerodynamic systems. Aerodynamic shape optimization (ASO) provides a practical approach for delaying and mitigating dynamic stall characteristics without the addition of an auxiliary system. A typical ASO investigation requires multiple evaluations of accurate but time-consuming computational fluid dynamics (CFD) simulations. In the case of dynamic stall, unsteady CFD simulations are required for airfoil shape evaluation; combining it with high-dimensions of airfoil shape parameterization renders the ASO investigation computationally costly. In this study, metamodel-based optimization (MBO) is proposed using the multifidelity modeling (MFM) technique to efficiently conduct ASO investigation for computationally expensive dynamic stall cases. MFM methods combine data from accurate high-fidelity (HF) simulations and fast low-fidelity (LF) simulations to provide accurate and fast predictions. In particular, Cokriging regression is used for approximating the objective and constraint functions. The airfoil shape is parameterized using six PARSEC parameters. The objective and constraint functions are evaluated for a sinusoidally oscillating airfoil with the unsteady Reynolds-averaged Navier-Stokes equations at a Reynolds number of 135,000, Mach number of 0.1, and reduced frequency of 0.05. The initial metamodel is generated using 220 LF and 20 HF samples. The metamodel is then sequentially refined using the expected improvement infill criteria and validated with the normalized root mean square error. The refined metamodel is utilized for finding the optimal design. The optimal airfoil shape shows higher thickness, larger leading-edge radius, and an aft camber compared to baseline (NACA 0012). The optimal shape delays the dynamic stall occurrence by 3 degrees and reduces the peak aerodynamic coefficients. The performance of the MFM method is also compared with the single-fidelity metamodeling method using HF samples. Both the approaches produced similar optimal shapes; however, the optimal shape from MFM achieved a minimum objective function value while more closely satisfying the constraint at a computational cost saving of around 41%. 

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4. Evaluation of seismic performance factors for post-tensioned mass ply panel rocking walls

   https://doi.org/10.52202/069179-0337  

   Ho, Tu X; Uarac, Patricio; Barbosa, Andre R; Sinha, Arijit; Simpson, Barbara; A_Araújo, Gustavo; F_Orozco, Gustavo (January 2023, World Conference on Timber Engineering (WCTE 2023))

   This paper presents the statistical and numerical investigation of the seismic performance of a three-story post-tensioned mass ply panel (MPP) rocking wall lateral force-resisting system prototype whose main components are MPP, U-shaped flexural steel plates (UFPs), and high-strength steel post-tensioned rods. Uncertainties in material properties and geometry of the components are considered in the assessment of the performance of this lateral forceresisting system based on recent experimental data on MPP, experimental data available in the literature for the UFPs and post-tensioning rods, as well as some additional structural design considerations. In the assessment of the seismic performance factors, first, random realizations of the structural design are generated using Monte Carlo simulation. Second, for each realization, a nonlinear finite element model is developed. For each realization, two types of analysis are performed, nonlinear static analyses, and incremental dynamic analyses. Results of the nonlinear static and dynamic analyses are then used to estimate the seismic design factors (e.g., R-factor) and limit state-based fragility functions, the latter being based on exceeding limit states defined for each component based on existing experimental data. 

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5. Full-scale shake table test of resilient six-story hybrid mass timber and steel structure

   https://doi.org/10.52202/080513-0301  

   Field, Tanner J; Barbosa, Andre R; Sinha, Arijit; Pryor, Steve; Lindt, John_W_Van De; Simpson, Barbara; P, Patricio_A Uarac; Mishra, Prashanna; Kontra, Steven; McBain, Morgan (January 2025, World Conference On Timber Engineering 2025)

   Mass timber solutions are becoming more and more viable for high-seismic regions while remaining sustainable, efficient, and affordable. The industry is driving innovation leading to the development of resilient hybrid steel-mass timber solutions that can minimize post-earthquake losses and downtime. A resilient six-story hybrid mass timber structure with: [i] laminated veneer lumber (LVL) beams and columns, [ii] a cross-laminated timber (CLT) selfcentering rocking wall (SCRW) in one direction, and [iii] a steel moment frame/concentric braced frame (MF/CBF) in the other direction was tested at the University of California, San Diego (UCSD) large high-performance outdoor shaketable facility. The dynamic testing included uni-, bi-, and tri-directional ground motion time histories applied at increasing intensities, including 43- and 225-year hazard levels, design earthquake (DE) level, and risk-targeted maximum considered earthquake (MCER) level per ASCE 7-16 for a location in Seattle, Washington. Four (4) design earthquakes and two (2) risk-targeted maximum considered tri-directional earthquakes were applied to the structure. Testing resulted in peak story drift ratios of 2.4% and 1.4% in the SCRW and MF/CBF directions, respectively. Even at MCER levels of shaking, the performance-based seismic design allowed for (1) the CLT-SCRW to remain essentially undamaged and (2) the MF to remain essentially elastic, providing elastic restoring forces, while the CBF provided stable and controlled hysteretic energy dissipation. After testing, residual drifts were smaller than 1.6 mm (1/16 inch) at the roof, indicating that resilient hybrid mass timber-steel structures are viable. This paper presents the specimen design and summarizes the preliminary results from the shake-table testing. 

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