VTechWorks Repository :: Browsing by Author "Easterling, William Samuel"

Browsing by Author "Easterling, William Samuel"

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Active control of floor vibrations
Hanagan, Linda M. (Virginia Tech, 1994-12-15)
The active control of structures is a diverse field of study, with new applications being developed continually. One structural system, which is often not considered a dynamic system, is the floor of a building. In many cases the dynamics of a floor system are neglected in the design phase of a building structure. Occasionally, this omission results in a floor which has dynamic characteristics found to be unacceptable for the intended use of the building. Floor motion of very small amplitudes, often caused by pedestrian movement, is sometimes found objectionable by occupants of the building space. Improving an unacceptable floor system's dynamic characteristics after construction can be disruptive, difficult and costly. In search of alternative repair measures, analytical and experimental research implementing active control techniques was conducted to improve the vibration characteristics of problem floors. Specifically, a control scheme was developed utilizing the measured movement of the floor to compute the input signal to an electromagnetic actuator which, by the movement of the actuator reaction mass, supplies a force that reduces the transient and resonant vibration levels. Included in the analytical component of this research is the development of a mathematical model for a full scale experimental test floor. This model is studied, using a matrix computation software, to evaluate the effectiveness of the control scheme. The experimental component of the research serves two purposes. The first is the verification of the system behavior assumed in the analytical component of the research. The second is the verification of control system effectiveness for various excitations, control gains, and actuator locations on the experimental test floor and six additional floors.
Analysis and Design of Steel Deck-Concrete Composite Slabs
Widjaja, Budi R. (Virginia Tech, 1997-10-15)
As cold-formed steel decks are used in virtually every steel-framed structure for composite slab systems, efforts to develop more efficient composite floor systems continues. Efficient composite floor systems can be obtained by optimally utilizing the materials, which includes the possibility of developing long span composite slab systems. For this purpose, new deck profiles that can have a longer span and better interaction with the concrete slab are investigated. Two new mechanical based methods for predicting composite slab strength and behavior are introduced. They are referred to as the iterative and direct methods. These methods, which accurately account for the contribution of parameters affecting the composite action, are used to predict the strength and behavior of composite slabs. Application of the methods in the analytical and experimental study of strength and behavior of composite slabs in general reveals that more accurate predictions are obtained by these methods compared to those of a modified version of the Steel Deck Institute method (SDI-M). A nonlinear finite element model is also developed to provide additional reference. These methods, which are supported by elemental tests of shear bond and end anchorages, offer an alternative solution to performing a large number of full-scale tests as required for the traditional m-k method. Results from 27 composite slab tests are compared with the analytical methods. Four long span composite slab specimens of 20 ft span length, using two different types of deck profiles, were built and tested experimentally. Without significantly increasing the slab depth and weight compared to those of composite slabs with typical span, it was found that these long span slabs showed good performance under the load tests. Some problems with the vibration behavior were encountered, which are thought to be due to the relatively thin layer of concrete cover above the deck rib. Further study on the use of deeper concrete cover to improve the vibrational behavior is suggested. Finally, resistance factors based on the AISI-LRFD approach were established. The resistance factors for flexural design of composite slab systems were found to be f=0.90 for the SDI-M method and f=0.85 for the direct method.
Analysis of Buckled and Pre-bent Columns Used as Vibration Isolators
Sidbury, Jenny Elizabeth (Virginia Tech, 2003-12-04)
Vibrations resulting from earthquakes, machinery, or unanticipated shocks may be very damaging and costly to structures. To avoid such damage, designers need a structural system that can dissipate the energy caused by these vibrations. Using elastically buckled struts may be a viable means to reduce the harmful effects of unexpected vibrations. Post-buckled struts can support high axial loads and also act as springs in a passive vibration isolation system by absorbing or dissipating the energy caused by external excitation. When a base excitation is applied, the buckled strut may act to reduce the dynamic force transmitted to the system, thus reducing the structural damage to the system. Several models of buckled and pre-bent struts are examined with different combinations of parameters and end conditions. The models include pinned or fixed columns supporting loads above their buckling load, and columns with an initial curvature supporting various loads. The varying parameters include external damping, internal damping, and stiffness. The columns will be subjected to simple harmonic motion applied at the base or to a multi-frequency base excitation. The response of each model is measured by the deflection transmissibility of the supported load over a large range of frequencies. Effective models reduce the motion of the supported load over a large range of frequencies.
Application of the Finite Element Method to the Seismic Design and Analysis of Large Moment End-Plate Connections
Mays, Timothy Wayne (Virginia Tech, 2004-08-12)
Due to problems associated with welded moment connections uncovered after the Northridge earthquake, large bolted connections are becoming a much more attractive alternative for design in seismic regions. However, stringent design requirements established by the AISC Seismic Provisions for Structural Steel Buildings (1997) make current moment end-plate configurations and design procedures inadequate for multi-story buildings. This dissertation first examines and critiques current seismic design philosophies as applied to moment end-plate connections. Next, the finite element method is used to develop much-needed design procedures for large moment end-plate connections, and to improve the understanding of the role of geometric parameters (e.g., bolt pitch and stiffener locations) in the response of these connections. Finally, single-story and multi-story frames incorporating large moment end-plate connections with known moment-rotation characteristics are considered under seismic loading to determine the effectiveness of these systems in dissipating energy caused by the ground motion.
Assessment of Analytical Procedures for Designing Metal Buildings for Wind Drift Serviceability
Bajwa, Maninder Singh (Virginia Tech, 2010-08-03)
While designing metal buildings for wind drift, for simplicity of analysis and design, connection at base of column is considered as pinned which provides no rotational restraint. The actual behavior of the connection however, is partially rigid, that provides some rotational stiffness even in case of single row of bolts. Moreover, using a two-dimensional (planar) structural model for analysis ignores any load distribution provided by roof and wall sheeting. Simulation of true behavior of base connection and diaphragm stiffness can substantially reduce drift caused due to lateral forces thereby lessening the conservatism in traditional design practices. This thesis provides results obtained from full-scale experimental testing and analytical study for a metal building. A full scale load test was conducted to quantify the lateral stiffness of an existing metal building. A static lateral load, consistent in magnitude with the building's design wind pressure, was applied to the knee of a primary frame, and the resulting lateral displacements and column-base rotations for all primary frames were measured. The test procedure was repeated at several locations. The experimentally obtained results were then validated using two-dimensional and three-dimensional analytical models. The three-dimensional models explicitly simulated the primary and secondary framing, roof and wall diaphragms, and column-base stiffness. A couple of approaches have been proposed to model column-base plate connection varying in complexity and accuracy. Once validated, the FE model is utilized to quantify the relative stiffness contributions of the metal building system components to lateral drift. While performing analysis some other parameters were also studied. These consisted of effect of base plate thickness and length of anchor bolts on column-base rigidity. Also, effect of including shear deformations and considering the haunch (column-rafter junction) as rigid were studied. Another small but important part of the paper is comparison of wind pressures obtained using different procedure of ASCE 7-05 with database assisted design pressures. Once these parameters are quantified practical engineering guidelines are developed to incorporate the influence of secondary framing, roof diaphragms, wall cladding, and column-base stiffness and wind loads in metal building design.
Behavior and Strength of Simple and Continuous Span Re-Entrant Composite Slabs
Traver, Thomas Mathew (Virginia Tech, 2002-07-29)
This study investigates the further development of the commercially available re-entrant steel deck profile. The effects of various embossments and continuous construction are investigated through three Series of composite slab load tests. The test specimens in this study were constructed to simulate actual field construction of composite slabs as part of reinforced concrete structures. The results of this experimental study are analyzed using methods given in the ASCE Standard for the Structural Design of Composite Slabs. Recommended design procedures for the improved re-entrant profile are given and various future profile modifications are suggested.
Behavior and Strength of Welded Stud Shear Connectors
Rambo-Roddenberry, Michelle (Virginia Tech, 2002-04-08)
The behavior and strength of welded shear studs are subjects of ongoing study. In recent years, research has shown that the American Institute of Steel Construction (AISC) specification equations for shear stud strength are unconservative for studs placed in deck with ribs transverse to the steel beam. Twenty-four solid slab push-out tests, 93 composite slab push-out tests, and bare stud tests were performed to study the effects on stud strength of friction, normal load, position of studs in the ribs of steel deck, concrete strength, and stud properties. Stud diameters ranged from 3/8 in. to 7/8 in., deck heights ranged from 2 in. to 6 in., and both single and pairs of studs were tested. The push-out test results from this study were combined with other studies to propose a new stud strength prediction model. Three new beam tests were performed to study the effect of the stud position in the ribs of the steel deck. The results of these tests, along with 61 other beam tests, were used to verify the new stud strength prediction model. A reliability study was performed to determine resistance factors for stud strength and beam strength.
Behavior of Connection with Beam Bearing on Bottom Flange of Girder
Lee, Wey-Jen (Virginia Tech, 2001-09-20)
An analytical investigation was conducted to study the behavior of a bottom flange bearing beam-to girder connection subjected to patch loading. This connection would be useful with deep deck (thickness greater than 3 in.) composite slabs as well as with commonly used deck where floor-to-floor height needs to be minimized. Five girder specimens were loaded until yielding during the initial phase of the research. The analysis section consists of the yield line theory and finite element study that were used to develop a model to predict the collapse loads of the girder sections. These results from the model were then compared to the experimental loads. A design procedure utilizing the proposed model and future work recommendations are then presented.
Behavior of Diagonal Knee Moment End-Plate Connections
Italiano, Vincenza M. (Virginia Tech, 2001-05-03)
An experimental and analytical investigation was conducted to study the behavior of diagonal knee moment end-plate connections and a multiple row extended moment end-plate connection. Diagonal knee moment end-plate connections differ from typical moment end-plate connections because of the large pitch distance required between the top flange and first row of tension bolts. The large pitch distance is outside of the geometric parameters of all previous research. Design solutions are presented for five moment end-plate connections with provisions added to accommodate these parameters. The analytical investigation focused on the limit states of end-plate yielding and bolt rupture. Yield-line analysis was used to predicted end-plate yielding and a simplified Kennedy method proposed by Borgsmiller and Murray (1995) was used to predict bolt rupture including and excluding prying forces. An experimental investigation was conducted to verify the design solutions. Five knee area specimens and one plate girder specimen were tested in this study. The analytical and experimental results are analyzed and compared. For the test specimens that failed in the connection, the predicted results proved to be conservative. Recommendations are presented at the end of the study as well as sample calculations.
Behavior of three-span braced columns with equal and unequal spans
Yang, Yu-Wen (Virginia Tech, 1993)
Columns with three spans separated by elastic braces are analyzed. The influences of translational and rotational resistance at the braces, various end conditions, and the bracing locations for the perfect columns with equal and unequal spans subjected to uniform and nonuniform axial load are investigated. For imperfect columns with equal or unequal spans subjected to uniform compression, the effects of various end conditions at the top and various initial deflections are studied. "Ideal stiffness" and "full bracing" only exist for these columns with equal spans and translational restraints with identical spring stiffness at the braces. Rotational restraints at the braces or at the ends improve the load-carrying capacity of the column. For the imperfect column, three types of initial deflection on the columns with equal and unequal spans and various end conditions at the top are analyzed. Based on a linear elastic analysis, the bracing force induced by a cubic initial deflection for a three-span column often exceeds 20/0 of the axial load. The violation of this rule of thumb in practice is readily revealed. Design curves for the effect of the bracing stiffness on the deflection ratio and bracing force percentage are created for the determination of bracing requirements.
Characterizing the Load-Deformation Behavior of Steel Deck Diaphragms using Past Test Data
O'Brien, Patrick Emmet (Virginia Tech, 2017-08-07)
Recent research has identified that current code level seismic demands used for diaphragm design are considerably lower than demands in real structures during a seismic event. However, historical data has shown that steel deck diaphragms, common to steel framed buildings, perform exceptionally well during earthquake events. A new alternative diaphragm design procedure in ASCE 7-16 increases diaphragm seismic demand to better represent expected demands. The resulting elastic design forces from this method are reduced by a diaphragm design force reduction factor, Rs, to account for the ductility of the diaphragm system. Currently, there exist no provisions for Rs factors for steel deck diaphragms. This research was therefore initiated to understand inelastic steel deck diaphragm behavior and calculate Rs factors. A review of the literature showed that a large number of experimental programs have been performed to obtain the in-plane load-deformation behavior of steel deck diaphragms. To unify review of these diaphragm tests and their relevant results, a database of over 750 tested specimens was created. A subset of 108 specimens with post-peak, inelastic behavior was identified for the characterization of diaphragm behavior and ductility. A new recommended method for predicting shear strength and stiffness for steel deck diaphragms with structural concrete fill is proposed along with an appropriate resistance factor. Diaphragm system level ductility and overstrength are estimated based on subassemblage test results and Rs factors are then calculated based on these parameters. The effects of certain variables such as deck thickness and fastener spacing on diaphragm ductility are explored.
Classification of end plate connections with application to gable frames
Banerjee, Gautam (Virginia Tech, 1990-02-18)
In this study, connection classification system is developed on the basis of previous classifications. Further, flexible connections are modeled by matrix displacement method. The effect of flexible connections are studied on gable frames. Firstly, flush end-plate connections with single row of bolts at the tension flange, are classified. The classification system was developed in this study. End plate connections whose moment-rotation curves are known arc classified on the basis of moments as FR (fully restrained) and PR (partially restrained) connections. Further, the connections are also classified by entering a plot with coordinates - Ratio of Moment at the connection and plastic moment and ratio of corresponding rotation and rotation at plastic moment. Depending on the location the connection can be classified. Secondly, for connections, the rotational stiffness is determined from the moment rotation curves and used in the computer code to implement flexible connections. The effect is studied on gable frames. For the loading and frame used there is not much variation in moments at the flexible joints due to connection flexibility and hence flush end plate connections can be used in gable frames effectively
Computer Program for the Analysis of Loads on Buildings Using the ASCE 7-93 Standard Minimum Design Loads on Buildings and Other Structures
Browning, Stephen E. (Virginia Tech, 1998-04-27)
A computer program for the analysis of loads on buildings is developed. The program determines wind loads, earthquake loads, and snow loads according to the ASCE 7-93 Standard Minimum Design Loads for Buildings and Other Structures (ASCE 7-93). The program is developed using the object-oriented programming methodology and runs on the Microsoft Windows 95 graphical environment. It is a valuable and useful tool for determining loads on buildings.
Connection limit states design teaching aid
Kerr, Robert A. (Virginia Tech, 1994-07-15)
Steel connection design is one area in structural steel design courses that is not always thoroughly addressed. This report attempts to address this area of steel design at a basic level. Its purpose is to be used as a teaching aid for a structural steel design course, and to familiarize students with connection design and its associated strength limit states. Limit states for steel connection design have been covered using both AISC ASD and LRFD Specifications. However, all included connection design examples used only LRFD limit states. Wherever possible all limit state calculations are accompanied by printouts from a knowledge-based expert system, CONXPRT. Typical building connection limit states are covered by way of an accompanying steel structure, which includes many of the connections, in order for students to receive an adequate grasp of both simple framing and moment connections. The purpose of this steel "sculpture" is to actively reinforce the students' understanding of the basic building connections seen in industry today.
Deep Deck and Cellular Deck Diaphragm Strength and Stiffness Evaluation
Bagwell, Jonathan (Virginia Tech, 2007-06-13)
Twenty cantilever diaphragm tests were performed in the Structures and Materials Laboratory at Virginia Tech. The tests included both deep deck and cellular deck profiles with varying structural and side-lap connections. The tests were conducted with three different structural connections: screws, pins and welds and two different side-lap connections: screws and button punch. The tests were conducted and both load and deflection of the diaphragms were recorded. The current International Code Council, ICC, evaluation procedure shows that there are two different methods for measuring diaphragm deflection. The first method was by measuring specific corner displacements and making corrections to remove any rigid body motion. The second method is by measuring the deflection of the diagonals of the diaphragm. In this study both measurements were taken to do a comparison of the results that were obtained. Both strength and stiffness values were calculated based on the Steel Deck Institute (SDI) Diaphragm Design Manual (2004) and modifications described by Luttrell (2005). The paper by Luttrell (2005) only recommends modifications for the calculation of diaphragm stiffness. The data obtained from the tests were compared to the SDI calculations to distinguish any noticeable trends. Modifications are recommended regarding diaphragm strength and further research is suggested to create a better stiffness prediction of diaphragms.
Design and Behavior of Composite Steel-Concrete Flexural Members with a Focus on Shear Connectors
Mujagic, Ubejd (Virginia Tech, 2004-04-06)
This study consists of three self-standing parts, each dealing with a different aspect of design of composite steel-concrete flexural members. The first part deals with a new type of shear connection in composite joists. Composite steel-concrete flexural members have increasingly become popular in design and construction of floor systems, structural frames, and bridges. A particularly popular system features composite trusses (joists) that can span large lengths and provide empty web space for installation of typical utility conduits. One of the prominent problems with respect to composite joists has been the installation of welded shear connection due to demanding welding requirements and the need for significant welding equipment at the job site. This part of the study presents a new type of shear connection developed at Virginia Tech— standoff screws. Results of experimental and analytical research are presented, as well as the development of a recommended design methodology. The second part deals with reliability of composite beams. Constant research advances in the field of composite steel-concrete beam design have resulted in numerous enhancements and changes to the American design practice, embodied in the composite construction provisions of the AISC Specification (AISC 1999). Results of a comprehensive reliability study of composite beams are presented. The study considers specification changes since the original reliability study by Galambos et al. (1976), considers a larger database of experimental data, and analyses recent proposals for changes in design of shear connection. Comparison of three different design methods is presented based on a study of 15,064 composite beam cases. A method to consider effect of degree of shear connection on strength reduction factor is proposed. Finally, while basic analysis theories between the two are similar, requirements for determining the strength of composite beams in Eurocode 4 (CEN 1992) and 1999 AISC Specification (AISC 1999) differ in many respects. This is particularly true when considering the design of shear connections. This part of the dissertation explores those differences through a comparative step-by-step discussion of major design aspects, and accompanying numerical example. Several shortcomings of 1999 AISC Specification are identified and adjustments proposed.
Design of a multi-span plate girder highway bridge using LRFD bridge specifications
Easter, Scott F. (Virginia Tech, 1993-12-05)
The design of the superstructure of a multi-span plate girder bridge was performed using the new AASHTOILRFD bridge specifications. The bridge was composed of three continuous spans of 100'-120'-100' designed to carry interstate traffic over a relatively wide river. The roadway width was 44'-0" and the girder spacing was 8'- 0". The design was composite in both the positive and negative moment regions. The report includes a review of the loading criteria for the new specifications which are relevant to the project. Comparisons are made between the current 1992 AASHTO requirements and the new AASHTOILRFD requirements. The project includes a detailed analysis of the loads and the moment and shear envelopes. Finally, the design, in accordance with the new specifications, is presented along with drawings and conclusions.
Design of moment end-plate connections for seismic loading
Meng, Ronald L. (Virginia Tech, 1996)
Analytical and experimental research into the seismic response of four-bolt extended moment end-plate connections was conducted. Full-scale connections, ranging in size from moderate to large, were designed, fabricated and tested under cyclic loading until connection failure was observed. The design procedures for minimum end-plate thickness were developed from yield-line theory with prying forces included in the bolt tension forces. Stiffened end-plates, four-bolt wide connections and shimmed end-plate connections were valiations of the four-bolt connection tested. A325 and A490 bolts with internal strain gauges were employed to record and analyze bolt tension forces. Test results demonstrate that the design approach is satisfactory, but several aspects of connection response not previously observed nor reported were encountered. When weld access holes were present in an extended end-plate connection, excessive 3-D stresses developed in the hole region, causing a brittle fracture of the beam flange. In the absence of weld access holes, ductile failure occurred, evidenced by local buckling of the beam flanges and plastic hinge formation. These two responses or failures were exhibited by all connection sizes. The use of end-plate stifieners appeared to provide sufficient stress reduction, as ductile failures were observed in all stiffened, extended end-plate connection tests with weld access holes. Grade 50 steel, four-bolt end-plate connections with built-up beam sections were also tested and demonstrated that inadequate weld strength exists in the beam web-toflange welds. Prior to fracture in these welds, the connections responded in a ductile manner with local beam flange buckling. In conjunction with the full-scale testing, finite element models were created for several connection sizes. When actual material properties of the steel and bolts were modeled, an excellent correlation of test data and the model was noted. When weld access holes were introduced in the models, an increase of flange strain in the hole region was noted. Although not conclusive nor comprehensive for every connection configuration, the four-bolt design appears satisfactory to survive seismic activity. Further research should provide answers to other configurations and eventually provide an acceptable alternative beam-to-column connection for high seismic areas.
Development of Finite Element Modeling Mesh Generation and Analysis Software for Light Wood Frame Houses
Pathak, Rakesh (Virginia Tech, 2004-10-25)
This thesis presents the development of an automatic mesh generator, named WoodFrameMesh, using object oriented C++. The program developed is capable of generating complete finite element models of wooden houses incorporating frames, linear links, springs, nodal loads and restraints at the desired locations. The finite element mesh generated by the program may be triangular or quadrilateral. The triangular mesh can be generated over any arbitrary domain with multiple openings and line constraints. The program implements the advancing front method for triangulation as discussed by Lee and Hobbs. The difference is made by implementing the algorithm using object oriented concepts and the extensive use of the powerful C++ Standard Template Library (STL). Quadrilateral mesh generation is limited to simple quadrilateral domains with no openings or constraint lines. A simple structured technique is implemented to generate the quadrilateral mesh. The amount of time spent in manual generation of the complete finite element model of wooden houses has been considerably reduced by automating the modeling process. Overall, the use of object oriented design has facilitated the code development and has provided a platform for further additions. The program relies on the use of STL as it provides dynamic data structures, algorithms for storage, searching, sorting, etc. Efficiency of the program is improved by the use of the in-built features in STL instead of developing new code. Analysis of the finite element models generated by the automatic mesh generator is performed using SAP 2000 and WoodFrameSolver. WoodFrameSolver is a finite element analysis engine for WoodFrameMesh, which was developed at Virginia Tech by a group of graduate students (including the author) and professors as a separate project. A chapter discussing the WoodFrameSolver architecture, its extensibility features and its verification is also presented in this thesis. The solver performance and accuracy are similar to those of SAP 2000, which was chosen as the benchmark for testing the analysis results.
Development of Membrane, Plate and Flat Shell Elements in Java
Kansara, Kaushalkumar (Virginia Tech, 2004-05-03)
The development of triangular and quadrilateral membrane, plate and shell elements in Java using the object oriented programming technique is presented. The membrane elements developed are the constant strain triangle (CST) element and the four node isoparametric quadrilateral membrane element. The plate bending elements developed are the discrete Kirchoff triangular (DKT) element and discrete Kirchoff quadrilateral (DKQ) element. The flat shell elements are developed by super imposing the stiffness of the membrane element and plate bending element. A finite element analysis program is also developed to check the accuracy of the developed elements. The program is developed using the object oriented programming approach as an alternative to traditional procedural programming. Several test structures are analyzed using the developed program for each developed element and the results are compared with those obtained from the commercial finite element analysis program SAP 2000. The results indicate that all elements give accurate displacements. However, there were significant differences in stresses for the shell elements, which can be attributable to the approximate approach in these elements to model the drilling degree of freedom.

Browsing by Author "Easterling, William Samuel"

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