Structural Engineering and Materials

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Computational Study of Tension Field Action in Gable Frame Panel Zones
Wei, Gengrui; Koutromanos, Ioannis; Murray, Thomas M.; Eatherton, Matthew R. (2018-04-01)
A computational study was conducted to evaluate the extent to which the column panel zone in a gable frame knee joint can develop tension field action when subjected to positive bending (top flange of the rafter is in tension). Past testing was reviewed and used to validate finite element models. The validated finite element modeling approach that utilized shell elements, was then used in a parametric study to evaluate the post-buckling strength of the panel zone beyond the shear buckling strength. In addition, a plastic mechanism model was used to derive an equation for the post-buckling shear strength of the panel zone and the derived equation was validated against the results of the parametric study. The result was a proposed equation for tension field action strength of the panel zone when subjected to positive bending that had an average error of 1% compared to the model results.
Developing and Validating New Bolted End-Plate Moment Connection Configurations
Jain, Nonish; Eatherton, Matthew R.; Murray, Thomas M. (2015-07-01)
End-plate moment connections are widely used, especially in metal buildings, between rafters (beams) and columns or at splice connections in rafters. References such as the AISC Design Guide 16 entitled “Flush and Extended Multiple-Row Moment End-Plate Connections” present design procedures, supported by physical experiments, to design these connections. It is desirable to develop and validate design procedures for additional end-plate moment connections, particularly those with larger moment capacity. In this report, four connection configurations are investigated. The selected end-plate configurations include eight-bolt extended four wide, eight-bolt extended stiffened, six bolt flush unstiffened, and twelve bolt extended unstiffened. Design procedures and some previous test data was available for the first two configurations, whereas no prior investigation was found in the literature for the latter two configurations. Design procedures including yield line analysis and bolt force models were proposed to calculate moment capacity associated with end-plate yielding, moment capacity for bolt rupture with prying action, and moment capacity for bolt rupture without prying action. Similar to the existing design approach for end-plate moment connections found in Design Guide 16, the design procedures are separated into thin end-plate behavior (the end-plate yields and then bolts fracture with prying action) and thick end-plate behavior (where end-plate yielding is prevented and bolts fracture without prying action). Design procedures found in the literature for the eight-bolt extended four wide and eight-bolt extended stiffened configurations were evaluated and modifications were proposed as necessary. Experimental data found in the literature for the eight-bolt extended four wide and eight-bolt extended stiffened end-plate configurations was analyzed and compared to moment capacities calculated using the proposed design procedures. For the eight-bolt extended four wide configuration, it was found that the experimental data from the literature corroborated the calculated moment capacities for a range of rafter depth and end-plate thickness. It was therefore concluded that no additional tests were required. For the eight-bolt extended stiffened configuration, reasonable match was found between the reported experimental data and predicted moment capacities, but the previous tested beam specimens did not exceed 36 inches depth. It was decided that two additional tests with deeper rafter sections (56 in. deep) would be useful in validating the design procedures for a wider range of rafter depth. A full-scale testing program was conducted including ten specimens that used three different end-plate moment connection configurations. Four specimens were designed for each of the two new configurations (six bolt flush unstiffened and twelve bolt multiple row extended unstiffened) such that there was a shallow rafter (36 in.) and deep rafter (60 in.) specimen predicted to exhibit both thin end-plate and a thick end-plate behavior. Also, two deep rafter (56 in.) specimens were tested with the eight-bolt extended stiffened configuration, one with thin end-plate and one with thick end-plate. The design procedures for all four investigated end-plate moment connection configurations appear reasonable. For the tested configurations, the predicted moment capacity associated with end-plate yielding was 5% smaller than the yield moment obtained during the test (conservative). The predicted moment capacities associated with bolt rupture were an average of 12% less than the experimentally obtained ultimate moment capacities. This conservatism in bolt rupture prediction was in part due to the use of nominal bolt strength in the calculations which is typically notably smaller than actual bolt strength.
The Effect of Powder Actuated Fasteners on the Seismic Performance of Protected Zones in Steel Moment Frames
Eatherton, Matthew R.; Toellner, Bradley W.; Watkins, Charles E.; Abbas, Ebrahim K. (2014-10-08)
Steel moment resisting frames rely on large inelastic strains in the beam plastic hinge region to dissipate seismic energy during an earthquake and protect the building against collapse. To limit the potential for premature fracture and because of a lack of test data, fasteners, attachments and defects are prohibited in the plastic hinge region, also referred to as the protected zone in the AISC Seismic Provisions. However, unauthorized attachments and defects occur in many buildings in practice. A set of twelve full-scale moment connection tests were conducted to explore the effect of powder actuated fasteners (PAF) and puddle welds on the seismic performance of steel moment connections. Both reduced beam section and extended end plate connections were tested with W24x62 and W36x150 beams. Five specimens included PAF or puddle welds representing typical steel deck attachment to the top flange of the beam. Three of the specimens included PAF in a grid over the top and bottom flange and on the web. All twelve specimens passed the qualification criteria for special moment resisting frames (SMRF) in the AISC Seismic Provisions as they were subjected to a cyclic displacement protocol up to 4% story drift while retaining 80% of their nominal plastic moment capacity. This suggests that moment connections with PAF and puddle welds within the bounds of what was tested, will produce ductile SMRF type seismic performance. Furthermore, PAF and puddle welds were found to have negligible effect on cyclic envelope, moment capacity, energy dissipation and strength degradation prior to fracture.
Energy Dissipation of Thin-Walled Cold-Formed Steel Members
Padilla-Llano, David A.; Moen, Cristopher D.; Eatherton, Matthew R. (2013-10-02)
Design of cold-formed steel (CFS) structures subjected to lateral seismic forces traditionally relies on the cyclic strength of subassemblages such as strapped/sheathed shear walls. Little regard is paid to the behavior of the individual components, their contribution to the lateral resistance of CFS structures, or to the actual seismic behavior of the structure as a whole. Understanding the cyclic behavior at the individual component level is necessary to develop accurate and computationally efficient models, a toolbox of nonlinear elements, capable of accurately and efficiently simulating the seismic behavior of CFS members and the infinite number of possible configurations in cold-formed steel structures. This report summarizes results from a research program designed to investigate the cyclic behavior and energy dissipation of cold-formed steel C–sections structural axial and flexural framing members. Twenty four axial tests and 24 flexural tests were performed to evaluate the energy dissipation characteristics of axial and flexural members experiencing global, distortional and local buckling deformations. Specimen cross-section dimensions and lengths were selected to isolate the specific buckling modes. A cyclic loading protocol is adapted for cold-formed steel members to evaluate the energy dissipation characteristics. The protocol target displacements are defined based on elastic buckling properties. Experimental data is utilized to calibrate a hysteretic model that represents the cyclic response of cold-formed steel C-section structural framing members. The model includes strength degradation, unloading stiffness degradation and pinching behavior of the observed experimental response. Model parameters and damage rules are calibrated for local, distortional and global buckling based on the hysteretic energy dissipated. The calibrated parameters can be utilized to develop a toolbox of nonlinear hysteretic springs to represent framing axial members in CFS structures for seismic analysis and facilitate performance based earthquake engineering of CFS structures.
State of Internal Design Review Process in Structural Engineering
Crocker, Kelly A.; Eatherton, Matthew R. (2023-05-16)
Internal design reviews serve as a major quality control measure in structural engineering firms. The process differs among firms and may be formal (documented) or informal (undocumented). The motivation of this project was to understand the design review process as it typically exists in structural engineering firms. Topics included the review process, time spent on review, common errors caught during reviews, and improvements suggested by study participants. Interviews were performed with 22 individuals from 16 structural engineering firms across the country. The study concluded that approximately 70% of firms have a formal internal design review process. A baseline process was established to occur before each submission to a client while each firm added their own unique practices to the process. Some practices, such as process scalability and the inclusion of design charrettes were mentioned by employees of multiple firms. Firms completing building design typically spent 5% of project hours on design review, however most employee suggestions related to expanding the time allowed for review or using it more efficiently. These factors alone cannot be used to indicate the quality of a design review, but the results of this paper may inform on different design review practices across the industry and aid firms in evaluating and improving their individual processes.
Topology Optimization to Resist Buckling
Avecillas, Javier; Eatherton, Matthew R. (2019-07-15)
A topology optimization algorithm to control out-of-plane buckling in shear-acting structural fuses is provided. The optimization procedure uses a genetic algorithm written in Matlab to find the distribution of material that facilitates considerable yielding before buckling in shear-acting structural fuses. Users will need to obtain a copy of the finite element software FEAP to use this topology optimization routine.
Workshop Report: Development of FRP Retrofit Guidelines for Deficient Reinforced Concrete Horizontal Lateral Force Resisting Systems
Dhakal, Pratiksha; Hutton, Hunter; Eatherton, Matthew R.; Jacques, Eric (2022-01-01)
This report presents a summary of the “Development of FRP Retrofit Guidelines for Deficient Reinforced Concrete Horizontal Lateral Force Resisting Systems” workshop held virtually on 17 August 2021. The meeting was a part of the research initiative led by Virginia Polytechnic Institute and State University involving the use of externally bonded fiber-reinforced polymer (FRP) in strengthening deficient horizontal lateral force resisting systems (hLFRS) in older reinforced concrete buildings. The meeting was attended by the research team from the university and an advisory panel comprising engineers, practitioners, and producers. The meeting included a presentation from the research team and brainstorming sessions in which the advisory panel provided their insights into the issues and gaps put forward. The discussions were centered around the three primary research tasks – development of preliminary design approach, experimental evaluation of hLFRS diaphragm shear strengthening, and preparation of design recommendations. The majority of discussions were directly related to the first task. The discussion sessions addressed gaps in areas such as current design procedure, inadequate diaphragm shear capacity, axial tension strengthening, axial compression strengthening, joint strengthening, anchorages, and detailing issues based on the experience of using FRP for diaphragm strengthening. The panel shared consensus that there is a lack of adequate guidelines for the design and detailing of FRP strengthening of deficient hLFRS. Despite the lack of provisions, there exist the widespread application of the FRP for strengthening. In the present scenario, several designs and analysis approaches have been followed by engineers for the retrofit design, force-controlled and displacement-controlled, beam analogy, strut and tie methods, finite element analysis. Further, in the design process, the FRP fibers are treated as reinforcing steel and are mainly unidirectional except at locations of high shear transfer; Carbon FRP fibers are preferred over other types. The limit of 0.0015 on the FRP design strain would be reasonable. Owing to the lack of design expressions for flexural or shear strengthening concrete diaphragms developed for beams, slabs, and walls are adopted even though they do not accurately represent the behavior of diaphragms. The FRP can be laid orthogonally or diagonally depending on the contribution of existing steel. FRP anchors and embedded steel anchors bolted to steel plates are used for anchorage purposes which should be provided at areas of high stress concentration and termination points. For anchorage design, it was recommended to compare anchors between different manufacturers however, as a result of lack of test data at a scale that remotely simulates the size and magnitude of forces being developed, there still exist inconsistencies in the detailing of anchors. The meeting successfully provided recommendations and expert opinions on the diaphragm strengthening using FRP. The issues discussed and the expertise provided by the panel shall be incorporated into the research process.
Yield Line Patterns for End-Plate Moment Connections
Eatherton, Matthew R.; Nguyen, Trai N.; Murray, Thomas M. (2021-12-31)
The purpose of this report is to summarize the yield line patterns and associated yield line parameters for end-plate moment connections. Both the end-plate yield line patterns and the column side yield line patterns are provided. For each yield line parameter, either the derivation is given or details about how the yield line parameter was obtained from one of the other derived yield line parameters is described.

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