Virginia Tech Structural Engineering and Materials Report Series

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Experimental Testing of a Reinforced Concrete Structural Wall Under Cyclic Loads
This report presents the setup and results of an experimental test focused on the seismic performance of a non-ductile reinforced concrete wall. The specimen was a half-scale representation of the lower stories in an 8-story prototype building, constructed in California between the mid-1950s and early 1960s. The cross-section had a barbell shape, with heavily reinforced end pilasters and very light reinforcement in the web region. The specimen was the first in a series of tests, aimed to investigate the strength and failure modes of existing RC wall construction, and also assess the efficiency of different retrofit techniques (the latter will be considered in subsequent tests). Applying lateral displacement cycles of increasing amplitude led to the gradual accumulation of damage. The specimen failed due to the formation of a localized diagonal crack in the web, followed by rupture of several horizontal bars and, ultimately, a sudden shear-crushing failure at the base of the pilaster. The pilaster region also exhibited buckling of the vertical reinforcing bars and rupture of transverse ties. The failure of the specimen was abrupt, occurring at a drift ratio of 1.31%. Computational simulations conducted for the specimen provided further insights on the damage sequence and failure mechanism.
Survey Related to Edge Details in Concrete-Filled Steel Deck Slabs
Omar Al-Masarani; Kerry Kreitman; Matthew R. Eatherton; W. Samuel Easterling (2024-03-23)
The aim of this survey is to gain insight into the common practices employed by structural engineers regarding the typical edge detail in concrete-filled steel deck floor systems. The survey content, which included questions and figures, was developed based on feedback from design engineers and the AISC Task Committee 5 on composite structures. The survey was advertised to the structural engineering industry through the AISC weekly bulletin email and was open from May to August 2023. The survey results provided valuable perspectives on different practices and typical edge details of structural engineering design firms across the United States from 34 respondents. It showed large scatter in typical edge details related to minimum slab overhang distance, pour stop type used, steel deck termination, pour stop connection and more.
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.
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.
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.
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.
Mechanical Performance of Yellow-Poplar Cross Laminated Timber
Mohamadzadeh, Milad; Hindman, Daniel (2015-12-03)
Cross-laminated timber (CLT) is a structural wood composite material consisting of multi-layers of lumber orthogonal to each other creating massive wood panels. Development of CLT introduced a new concept of using wood in low to midrise buildings as an alternative for concrete and steel. Speed and ease of construction, seismic performance and carbon sequestration are advantages of CLT material. Softwood species have been traditionally used as wood structural materials while hardwood species have not. The purpose of this paper was to examine whether CLT made from fast growing hardwood species can provide sufficient mechanical performance need to be used in structural engineering applications. Yellow-poplar CLT was tested experimentally for stiffness and strength in five-point bending and four-point bending tests, respectively as well as resistance to shear by compression lading and resistance to delamination and the results were compared with American National Standard Institute/APA-The Engineered Wood Association (ANSI/APA) PRG 320-Standard for Performance Rated Cross-Laminated Timber and previous research. Bending stiffness, bending strength and resistance to delamination exceeded the required value in the standard, while wood failure in resistance to shear by compression loading was less than the required value. Shear strength of the yellow-poplar CLT was also greater than CLT produced from softwood species tested in previous research. Acceptable mechanical performance of yellow-poplar CLT confirmed in this research, could be a start point of using hardwood species in CLT structural design.
Rotational and Translational Stiffness Provided by Insulated Metal Panels to Girts and Purlins in Metal Building Wall and Roof Systems
Wu, Haiteng; Moen, Cristopher D. (2016-02-06)
The goal of this study is to quantify the restraint provided by insulated metal panels (IMPs) to girts and purlins in a metal building wall and roof system. These panels are fastened to their support members with screws that are either uniformly spaced across the panel width and penetrate through the entire panel thickness or that fasten through clips concealed within the side joint located at the panel side edges only. Current through-fastened panel design methodology in the American Iron and Steel Institute (AISI) North American Specification for the Design of Cold-Formed Steel Structural Members does not provide guidance for secondary member design when these panels are employed, thus each new IMP product requires costly testing as part of a wall or roof system in a vacuum chamber.
3D + Time Reconstruction: Designing Optimal Camera Parameters
Helsel, Michelle; Salomon, Abraham Lama; Moen, Cristopher D. (2015-08-01)
Three dimensional plus time reconstructions are an emerging concept in the civil engineering industry. The application possibilities are continuing to develop, resulting in an expansive range of projects. Proper image based modeling should utilize different camera parameters depending on the individual application. Currently, research examining the optimal camera settings for 3D reconstruction quality is limited. Knowing the ideal camera parameters and how each parameter will affect the modeling utilized for image reconstruction settings will improve modeling quality of 3D reconstructions. This paper examines the effective methods for improving reconstruction features based on picture quality. Camera settings tested include depth of field, shutter speed, ISO light sensitivity, resolution, and the number of pictures taken to be utilized in the 3D reconstruction. The variables also incorporate changes in lighting types, as well as material surface reflections. Distinct trends can be identified within the data set with respect to the mentioned variables.
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.
Stiffness and Strength of Single Shear Cold-Formed Steel Screw-Fastened Connections
Pham, Hong S.; Moen, Cristopher D. (2015)
Results are presented from an experimental program on single shear cold-formed steel-to-steel through-fastened screw connections, including documentation of the complete load-deformation response and stiffness degradation. Ply thicknesses from 0.88mm to 2.58mm and screw diameters of 4.17mm to 5.49mm were tested to cover the practical range of applications common to cold-formed steel framing. A custom non-contact optical technique measured steel ply relative displacements and screw tilting angles. Fastener load-deformation response is presented in a format that can be incorporated into codes and standards for system level design calculations that require connection stiffness to quantify load sharing. The simplified multi-linear curves characterized from monotonic responses can also serve as nonlinear springs in cold-formed steel subsystem computational models (e.g., shear wall, floor diaphragm, roof truss) and 3D whole building cold-formed steel structural simulations.
Spectral Matching Program using Broyden Updating
Adekristi, Armen (2015-04-28)
A matlab based program has been written for spectral matching ground motions to a target pseudo-acceleration spectrum using a Broyden algorithm for solving the set of nonlinear equations. This is a time-domain based spectral matching program that builds on the concepts in the RspMatch program.
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.
Crack Detection and Measurement Utilizing Image-Based Reconstruction
Zheng, Paul (2014-06-17)
Image-based reconstruction for automated crack detection has been on the rise for the past decade or so; this new technology can be applicable to many different areas such as laboratory testing, field inspections, construction quality control and quality assurance, and post disaster reconnaissance. An added feature to automated crack detection is the ability to perform digital crack measurements with increased safety. Crack detection during experimental testing may require researchers to mark cracks on the specimens, whereas researchers can take photographs of the specimens from a safe distance and have the reconstructed model digital crack detection. Automated crack detection along with digital crack measurements will increase the quantity of cracks observed and measured. Increased quantity could reduce cost of field inspections by reducing inspection time. Compared to traditional crack measurement techniques such as a crack detection pocket microscope (crack scope) or crack width card (also referred to as a crack width gauge), safety would be less of a concern since photographs for image reconstruction can be taken at a distance rather than having to be directly against the structure; both of these traditional tools can be seen in Figure 1. Safety is a major concern in post disaster reconnaissance; after an event such as an earthquake or tsunami, structures have to be examined to determine the extent of damage. By utilizing image based reconstruction, assessments can be made without placing the inspector or engineer in dangerous situations.
Crack Detection and Measurement Utilizing Image-Based Reconstruction
Zheng, Paul (2014-06-16)
Image-based reconstruction for automated crack detection has been on the rise for the past decade or so; this new technology can be applicable to many different areas such as laboratory testing, field inspections, construction quality control and quality assurance, and post disaster reconnaissance. An added feature to automated crack detection is the ability to perform digital crack measurements with increased safety. Crack detection during experimental testing may require researchers to mark cracks on the specimens, whereas researchers can take photographs of the specimens from a safe distance and have the reconstructed model digital crack detection. Automated crack detection along with digital crack measurements will increase the quantity of cracks observed and measured. Increased quantity could reduce cost of field inspections by reducing inspection time. Compared to traditional crack measurement techniques such as a crack detection pocket microscope (crack-scope) or crack width card (also referred to as a crack width gauge), safety would be less of a concern since photographs for image reconstruction can be taken at a distance rather than having to be directly against the structure. Safety is a major concern in post disaster reconnaissance; after an event such as an earthquake or tsunami, structures have to be examined to determine the extent of damage. By utilizing image based reconstruction, assessments can be made without placing the inspector or engineer in dangerous situations.
Energy Dissipation for Cold Formed Steel Connections
Haus, Andreas (2014-02-18)
Elastic Buckling of Cold Formed Steel Beams with Unstiffened Holes
von der Heyden, Aaron; Moen, Cristopher D. (2011-04-01)
Critical elastic buckling analyses for cold-formed steel beams with unstiffened holes are performed in this assignment. The beam dimensions, boundary and loading conditions for the conducted simulations are based on experiments conducted by A. Schudlich [14]. Critical buckling moments for local, distortional and global buckling are calculated on the one hand by using the finite element method and on the other hand by employing the simplified methods for deriving critical elastic buckling parameters for coldformed steel provided by the American Iron and Steel Institute’s Direct Strength Method (DSM) [1]. The results of both analyses have been compared in order to validate the DSM simplified methods. Also beams without holes are considered in this assignment as well as all beams with holes are also simulated without holes included. With comparing the results of members without holes to those members with holes, the influence of unstiffened holes can be obtained.
Distortional Buckling Experiments on Cold-Formed Steel Joists with Unstiffened Holes
Schudlich, Anna; von der Heyden, Aaron; Moen, Cristopher D. (2011-09-01)
Experiments were conducted on cold-formed steel C-section joists with rectangular unstiffened web holes. The presence of holes decreased joist capacity and amplified distortional buckling deformation. Distortional buckling was accompanied by unstiffened strip buckling of the compressed web. When hole depth approached the web depth, sudden flexural buckling of the compressed flange at the hole was observed. Forthcoming direct strength method equations for joists with holes accurately predicted flexural capacity when web hole depth equaled two-thirds the web depth, and was unconservative for larger web holes.
Experimental Investigation of the Multiple Row Extended 1/2 End-Plate Moment Connection
Sumner, Emmett A.; Murray, Thomas M. (2001-12-01)
End-plate moment connections are widely used by the low-rise metal building industry to provide the rigid connections necessary in gable frames. There are numerous end-plate moment connection configurations. The multiple row extended 1/2 (MRE 112) end-plate moment connection configuration is the focus of this investigation. The MRE 1/2 end-plate moment connection has three rows of bolts at the tension flange, one row located outside the beam flange and two rows located inside the beam flange. Six MRE 1/2 end-plate moment connection tests were conducted at the Virginia Tech Structures and Materials Laboratory. The purpose of the tests was to investigate the moment strength of the connections and to validate the current design procedures. Details of the connection design, test set-up, testing procedure, and test results are presented within this report. It is concluded that the current design procedures, presented in the forthcoming AISC Steel Design Guide 16, Flush and Extended Multiple Row Moment End-Plate Connections (Murray and Shoemaker, 2002), conservatively predict the strength of MRE 112 end-plate moment connections. The strength predictions are adequate for MRE 1/2 end-plate connections utilizing A325 or A490 bolts with a standard or a large inner pitch distance.

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