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1. Experimental investigation of the bearing capacity between short hollow glass columns and a transparent thermoplastic interface material

   https://doi.org/10.1016/j.engstruct.2024.119407  

   Yost, Joseph Robert; Cregan, Matthew; Bolhassani, Damon; Chhadeh, Philipp Amir; Schneider, Jens; Lu, Yao; Akbarzadeh, Masoud (February 2025, Engineering Structures)

   In this research study, the fracture strength of flat 10 mm thick annealed glass sheets having an abrasive water-jet cut surface and bearing against a transparent interface material is experimentally investigated. The transparent interface material is necessary to provide axial-compressive force continuity in modular compression-dominant all- glass shell structures. A series of short glass columns were tested in axial compression under a variety of load cases, which included cyclic, creep, and monotonic-to-fracture loading. A target glass fracture bearing stress of 36.6 MPa is identified and represents an upper bound bearing stress for annealed glass compression members failing in a flexural buckling mode. The study concludes the transparent thermoplastic material, known as Surlyn, was able to achieve a fracture strength that exceeds the target value and that the fracture strength is not affected by cyclic or creep loading. Consequently, column-related failure limit states will occur before glass fracture is associated with interface bearing. Glass fracture occurs in Type-I mode, reflecting the presence of interface tensile stress. Furthermore, the monotonic bearing stiffness in the service range of 5 to 15 MPa is increased by 20 % and 16 % for samples subjected to cyclic and creep loading, respectively, relative to monotonic-only samples. 

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2. Behavior of Reinforced HPFRCC Columns Subjected to Axial and Lateral Loads

   Almeida, Joseph A; Bandelt, Matthew J (September 2023, ACI, Rilem, fib)

   Massicotte, Bruno; Mobasher, Barzin; Plizzari, Giovanni (Ed.)

   While widely adopted prescriptive-based design practices work to limit the probability of complete collapse, relatively little attention and emphasis is placed on the damage levels and functionality of structures after seismic events. High-performance fiber reinforced cementitious composites reinforced with steel (R/HPFRCCs) have been of growing interest for such seismic applications to improve structural level damage and performance. In order to progress the implementation of these materials at the structural level, a systematic approach toward understanding the mechanics of R/HPFRCC columns is warranted. Therefore, in this study, an existing numerical framework for R/HPFRCC beams was extended to the analysis of columns across a range of materials, reinforcement ratios, and axial load levels to evaluate the change in component level response. It was observed that axial load can considerably increase the nominal bending moment capacity of R/HPFRCC columns as well as affect the drift capacity. A shift from failure on the tension side of the element (e.g., reinforcement fracture) to the compression side (e.g., crushing of the HPFRCC) of the numerically tested column occurred between an axial load ratio of 10 and 20%. Lastly, changes in bond stress due to the material level tensile strength were shown to considerably impact the ultimate component drift capacity. 

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3. Modeling of Composite MRFs with CFT Columns and WF Beams

   https://doi.org/10.12989/scs.2022.43.3.000  

   Herrera, R. (May 2022, Steel And Composite Structures)

   A vast amount of experimental and analytical research has been conducted related to the seismic behavior and performance of concrete filled steel tubular (CFT) columns. This research has resulted in a wealth of information on the component behavior. However, analytical and experimental data for structural systems with CFT columns is limited, and the well known behavior of steel or concrete structures is assumed valid for designing these systems. This paper presents the development of an analytical model for nonlinear analysis of composite moment resisting frame (CFT MRF) systems with CFT columns and steel wide flange (WF) beams under seismic loading. The model integrates component models for steel WF beams, CFT columns, connections between CFT columns and WF beams, and CFT panel zones. These component models account for nonlinear behavior due to steel yielding and local buckling in the beams and columns, concrete cracking and crushing in the columns, and yielding of panel zones and connections. Component tests were used to validate the component models. The model for a CFT MRF considers second order geometric effects from the gravity load bearing system using a lean on column. The experimental results from the testing of a four story CFT MRF test structure are used as a benchmark to validate the modeling procedure. An analytical model of the test structure was created using the modeling procedure and imposed displacement analyses were used to reproduce the tests with the analytical model of the test structure. Good agreement was found at the global and local level. The model reproduced reasonably well the story shear story drift response as well as the column, beam and connection moment rotation response, but overpredicted the inelastic deformation of the panel zone. 

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4. Hybrid hemp/glass fiber reinforced high-temperature shape memory photopolymer with mechanical and flame-retardant analysis

   https://doi.org/10.1038/s41598-023-44710-6  

   Mahmud, Sakil; Konlan, John; Deicaza, Jenny; Li, Guoqiang (October 2023, Scientific Reports)

   Abstract Cultivated natural fibers have a huge possibility for green and sustainable reinforcement for polymers, but their limited load-bearing ability and flammability prevent them from wide applications in composites. According to the beam theory, normal stress is the maximum at the outermost layers but zero at the mid-plane under bending (with (non)linear strain distribution). Shear stress is the maximum at the mid-plane but manageable for most polymers. Accordingly, a laminated composite made of hybrid fiber-reinforced shape memory photopolymer was developed, incorporating strong synthetic glass fibers over a weak core of natural hemp fibers. Even with a significant proportion of natural hemp fibers, the mechanical properties of the hybrid composites were close to those reinforced solely with glass fibers. The composites exhibited good shape memory properties, with at least 52% shape fixity ratio and 71% shape recovery ratio, and 24 MPa recovery stress. After 40 s burning, a hybrid composite still maintained 83.53% of its load carrying capacity. Therefore, in addition to largely maintaining the load carrying capacity through the hybrid reinforcement design, the use of shape memory photopolymer endowed a couple of new functionalities to the composites: the plastically deformed laminated composite beam can largely return to its original shape due to the shape memory effect of the polymer matrix, and the flame retardancy of the polymer matrix makes the flammable hemp fiber survive the fire hazard. The findings of this study present exciting prospects for utilizing low-strength and flammable natural fibers in multifunctional load-bearing composites that possess both flame retardancy and shape memory properties. 

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5. Design and Implementation of Experiential Learning Modules for Steel Design

   Carroll, J. Chris; Aidoo, John; Derks, Alec; Lovell, Matthew D.; Kershaw, Kyle (June 2022, ASEE Annual Conference proceedings)

   Introductory steel design courses focus on the analysis and design of primary members, which typically include tension members and connections, compression members, flexural members, and beam-columns. Introducing structural steel design concepts to students presents its fair share of challenges. First, it is difficult for students to visualize and accurately predict the potential failure modes of a tension member: yielding of the gross section, rupture of the net section, and block shear. Second, it is also difficult for students to visualize the buckling modes of steel columns, which vary with shape and type of bracing. Students particularly struggle with the determination of buckling modes between strong and weak axes based on effective lengths. Third, flexural failure modes of steel beams are very difficult for students to visualize and understand when each mode controls. The failure modes are complex and fall into three categories for compact shapes: yielding of the cross section, inelastic lateral torsional buckling, and elastic lateral torsional buckling, which is dependent on the unbraced length of the compression flange. Non-compact sections also include local buckling of the flange or web, but identifying the relationship between the unbraced length and beam span and how the unbraced length affects the flexural capacity tends to be the most difficult concept for students to grasp. This paper provides a detailed overview of the design, fabrication, and implementation of three large-scale experiential learning modules for an undergraduate steel design course. The first module focuses on the tension connections by providing physical models of various failure types including yielding of the gross section, rupture of the net section, and block shear; the second module focuses on the capacity of columns with different amounts of lateral bracing about the weak axis; and the third module focuses on the flexural strength of a beam with different unbraced lengths to illustrate the difference between lateral torsional buckling and flange local buckling/yielding of the gross section. The three modules were used throughout the steel design course at Saint Louis University and Rose-Hulman Institute of Technology to illustrate the failure mechanisms associated with the design of steel structures. 

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