Structural Engineering and Materials

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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.
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.
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.
Curtain Beam Strip Analysis
Moen, Cristopher D.; Janas, Matthew (2011-04-01)
A beam strip model based on an Euler-Bernoulli elastica solution is implemented in a freely available wind analysis computer program for metal building vehicular access doors to calculate door jamb forces and curtain deflections considering jamb and framing flexibility. The software is provided to support analysis-based vehicular access door design for metal buildings. Existing access door curtain and jamb design approaches are viable for rigid door jambs. However it was shown with experiments that wind-lock forces decrease and door out-of-plane deflection increases when the door jamb and framing are more flexible, for example, in the case of typical cold-formed steel framing details where a C-section jamb is discretely braced by wall girts.
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.
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.
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.
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.
Energy Dissipation for Cold Formed Steel Connections
Haus, Andreas (2014-02-18)
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.
Experimental Evaluation of a Vehicular Access Door Subjected to Hurricane Force Wind Pressures
Gao, Tian; Moen, Cristopher D. (Virginia Polytechnic Institute and State University, 2009-11-01)
This report presents findings on the behavior of a typical rolling sheet vehicular access door under a hurricane force wind pressure. The objectives are to quantify the structural behavior of a rolling sheet vehicular access door and the attached frame under both positive pressure (pushing the door into the building) and negative pressure (suction pulling the door away from the building), including the direct measurement of the catenary forces in the wind locks with strain gauges. The results will be used to optimize existing design methods for a rolling sheet vehicular access door and the supporting door frame.
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.
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.
Flexural Capacity Prediction Method for an Open Web Joist Laterally Braced by a Standing Seam Roof System
Cronin, Luke; Moen, Cristopher D. (Virginia Polytechnic Institute and State University, 2012-04-01)
A new strength prediction approach is presented for open web joists partially braced by a standing seam roof. The approach employs the existing AISC column curve to calculate top chord flexural buckling capacity using the top chord critical elastic buckling load. Recently derived buckling load equations are presented that account for lateral stiffness provided by the roof and the parabolically varying axial load from a uniform vertical pressure along the span. A new hybrid experimental-computational protocol is introduced for approximating standing seam roof lateral stiffness for systems without and with intermediate bridging. The strength prediction approach is demonstrated to be accurate for a small set of experiments, however a larger scale validation effort is still needed.
Flexural Strength of Exterior Metal Building Wall Assemblies with Rigid Insulation
Gao, Tian (Virginia Polytechnic Institute and State University, 2011-08-01)
The goal of this research study is to observe and quantify the influence of rigid board insulation on through-fastened girt capacity. Rotational restraint tests are performed to study local rotational stiffness at the flange-insulation contact point. Vacuum box tests on through-fastened wall systems are conducted to explore the effect of insulation thickness on the R-factor. The results will be used to support new code language in AISI S100-07 D6.1 that accommodate capacity prediction of metal building wall systems with rigid board insulation.
Historical Survey, Structural Analysis, and Load Testing of the Ironto Wayside Footbridge
Huffman, Elaine; Moen, Cristopher D. (Virginia Polytechnic Institute and State University, 2012-01-27)
A structural study examines the oldest remaining metal bridge in the Commonwealth of Virginia, a wrought iron bowstring arch-truss, designed and manufactured by the King Iron Bridge Company. Finite element analysis is used to evaluate interaction between arch and truss, and the results are compared to field measurements from a live load test. The study reveals that diagonal truss elements decrease arch bending by distributing concentrated vertical loads along the arch toward the abutments in a way consistent with that of modern network arch bridges. With truss diagonals absent, vertical bridge deck deflection doubles. Underslung portal frames provide lateral stiffness to the arch, an innovation that accommodated a shallow arch profile conducive to transportation and erection.
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.
Out-of-Plane Web Deformation and Relative Arch Movement of Hybrid-Composite Beams Based on Photogrammetry
Mascaro, Margret Grace; Moen, Cristopher D. (2012-07-27)
Recently invented by John R. Hillman, Hybrid-Composite Beams (HCBs) are a new approach to structural design that incorporate four materials in such a way as to maximize the efficiency of each material. A concrete arch serves as the main compression reinforcement, with steel strands tying the arch and carrying tension forces. The space between the arch and the steel is filled with stiff, lightweight foam. A Fiber Reinforced Plastic (FRP) box encases the system and adds shear reinforcement. The Virginia Department of Transportation is interested in using HCBs in bridges and funded a project at Virginia Tech to better understand the behavior of the beams. Close-range photogrammetry was incorporated into the project to detect out-of-plane movement of the FRP web and movement of the arch within the FRP shell due to applied loads. The individual beam underwent two phases of testing, the first of which occurred prior to the concrete arch being placed in the beam. The second phase took place after the arch cured. A total of 22 photosets were taken of the beam, four during Phase I and 18 during Phase II. The results of the FRP web study indicate that beam is flexible laterally and prone to lateral displacement when not connected to a larger bridge system. Significant movement of the arch within the FRP shell was detected demonstrating sinusoidal behavior along the edge of the arch and restrained movement at the center of the arch.
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.

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