No description available.

The ANSI/AISC 360-10 Appendix-6 provisions provide limited guidance on the bracing requirements for beam-columns. In cases involving point (nodal) or shear panel (relative) lateral bracing only, these provisions simply sum the corresponding strength and stiffness requirements for column and beam bracing. Based on prior research evidence, it is expected that this approach is accurate to conservative when the requirements can be logically added. However, in many practical beam-column bracing situations, the requirements cannot be logically added. This is because of the importance of the brace and transverse load position through the cross-section depth, as well as the fact that both torsional and lateral restraint can be important attributes of the general bracing problem. These attributes of the bracing problem can cause the current beam-column bracing requirement predictions to be unconservative. In addition, limited guidance is available in the broader literature at the current time regarding the appropriate consideration of combined lateral and torsional bracing of I-section beams and beam-columns. Nevertheless, this situation is quite common, particularly for beam-columns, since it is rare that separate and independent lateral bracing systems would be provided for both flanges. More complete guidance is needed for the proper consideration of combined bracing of I-section beams and beam-columns in structural design. This research focuses on a reasonably comprehensive evaluation of the bracing strength and stiffness requirements for doubly-symmetric I-section beams and beam-columns using refined Finite Element Analysis (FEA) test simulation. The research builds on recent simulation studies of the basic bracing behavior of beams subjected to uniform bending. Various cases of beam members subjected to moment gradient are considered first. This is followed by a wide range of studies of beam-column members subjected to constant axial load and uniform bending as well as axial load combined with moment gradient loading. A range of unbraced lengths are considered resulting in different levels of plasticity at the member strength limit states. In addition, various bracing configurations are addressed including point (nodal) lateral, shear panel (relative) lateral, point torsional, combined point lateral and point torsional, and combined shear panel lateral and point torsional bracing.

The objective of this research is to evaluate the stiffness and strength demands on flange braces in metal building systems. This objective is accomplished by a targeted study of the effects of various attributes of metal building systems not fully addressed in existing bracing design procedures. Special emphasis is placed on attributes such as unequal brace spacing and stiffness, end brace point flexibility, nonprismatic member geometry, special requirements at knee joints and the specific configuration of combined girt/purlin, flange diagonal, diaphragm and X bracing systems used in metal building construction. A sub-objective of the research is the demonstration of how virtual test simulation via full nonlinear finite element analysis may be applied to solve a structural engineering research problem that would be difficult to address by any other means. When conducted properly, virtual test simulation can serve as a valuable companion to experimental testing since attributes such as residual stresses and critical geometric imperfections can be controlled precisely and with relative ease in virtual test simulation. Both highly simplified and more complex but relatively rigorous procedures are considered, with the ultimate goal being improved economy and safety of flange stability bracing in metal buildings.

An analytical and numerical investigation is conducted for the lateral torsional buckling analysis of wooden beam with a mid-span lateral brace subjected to symmetrically distributed loading. Two models are developed; one for the case of a rigid brace and another one for the case of a flexible brace. The analytical solutions are based on the principle of stationary potential energy and a Fourier expansion of the buckling displacement fields and bending moments. The validity of both models are verified against 3D finite element analyses in ABAQUS. Where applicable, verifications were also conducted against available solutions from previous studies. Parametric studies were conducted to investigate the effect of geometric and material parameters on the critical moments. The results indicate the presence of two separate groups of potential buckling modes, symmetric and anti-symmetric, with fundamentally different behavioural characteristics. The governing buckling mode is shown to depend on the bracing height, load height and lateral brace stiffness. The study shows that beyond a certain threshold bracing height, the critical moment is governed by the antisymmetric mode of buckling. Also, above a certain optimum bracing stiffness, no increase is observed in the critical moments. The models developed are used to construct a comprehensive database of parametric investigations which are then employed for developing simplified equations for determining the threshold heights, associated critical moments, and optimum stiffness.

The objectives of this research were to determine the required net lateral restraining force to brace j-webs or j-chords braced by one or more continuous lateral braces (CLB's), and to develop a methodology for permanent bracing design using a combination of lateral and diagonal braces. SAP2000 (CSI, 1995), a finite element analysis program, was used to analyze structural analogs for three sets of truss chords braced by n-CLB's and one or two diagonals, one web braced by one and two CLB's, and j-truss chords braced by n-CLB's. System analogs used to model five eight-foot truss chords braced by three CLB's and one diagonal, six twenty-foot truss chords braced by nine CLB's and two diagonals, and eleven twenty-foot truss chords braced by nine CLB's and two diagonals were analyzed. For each of the three cases analyzed, the chord lumber was assumed to be 2x4 No. 2 Southern Pine (S. Pine) braced by 2x4 STUD Spruce-Pine-Fir (SPF). Chord load levels of 10% to 50% of the allowable compression load parallel-to-grain assuming le/d of 16 were studied. All wood-to-wood brace connections were assumed to be made with 2-16d Common nails. A nonlinear load-displacement function was used to model the behavior of the nail connections. Single member analogs were analyzed that represented web members varying in length from four-feet to twelve-feet braced by one and two CLB's. The web and CLB's were assumed to be 2x4 STUD SPF. The web members were also analyzed assuming 2x6 STUD SPF. Single member analogs were analyzed that represented chord members varying in length from four-feet to forty-feet braced by n-CLB's spaced twenty-four inches on-center. The truss chord was assumed to be No. 2 Southern Pine and the CLB's were assumed to be STUD SPF. The chord size was varied from 2x4 to 2x12 and connections were assumed to consist of 2-16d Common nails. The system analog analysis results were compared to the single member chord analysis results based on the number of truss chords and the diagonal brace configuration. For the three cases studied involving multiple 2x4 chords braced as a unit (and believed to be representative of typical truss construction), the bracing force from the single member analog analysis was a conservative estimate for bracing design purposes. It was concluded that the single member analysis analog yields approximate bracing forces for chords larger than 2x4 and for typical constructions beyond the three cases studied in this research. For analysis and design purposes, a ratio R was defined as the net lateral restraining force per web or chord divided by the axial compressive load in the web or chord. For both 2x4 and 2x6 webs braced with one CLB, the R-value was 2.3% for all web lengths studied. For both 2x4 and 2x6 webs braced with two CLB's, the R-value was 2.8% for all web lengths studied. The web and CLB lumber species did not affect the R-values for the braced webs. Calculated R-values for truss chords, 2x4 up to 2x12, braced by n-CLB's assumed to be spaced two feet on-center for chords four to twelve feet in length ranged from 2.2% to 3.0%, respectively. For chords from sixteen to forty feet in length, R ranged from 3.1% to 2.6%, respectively. The lumber species and grade assumed for the chord and CLB did not affect the R-values for the truss chords. Step-by-step design procedure was developed for determining the net lateral restraining force required for bracing j-chords based on the results of the single member analogs studied. The required total lateral restraining force for j-compression members in a row can be calculated based on the R-value for or the number of CLB's installed at 2 feet on-center, the design axial compression load in the chord, and number of trusses to be braced. / Master of Science

No description available.

The standard grid bracing problem has a nice solution via the brace graph. If we introduce a window by removing an interior vertex of the grid, this solution comletely breaks down. We examine a 6 x 10 unit grid with a 2 x 2 window and provide an optimal solution via the Rigidity Matrix.

Appendix 6 of the ANSI/AISC 360-10 Specification provides methods for assessing the required stiffness and strength for basic bracing of columns and of beams. Substantial evidence exists showing that the Appendix 6 equations provide an accurate characterization of the stability bracing requirements, particularly when various refinements from the AISC Commentary are employed. Nevertheless, the development of these equations is based largely on elastic stability theory and various practical approximations are invoked to make the equations useful for design. Some of the important approximations relate to the handling of member inelasticity as well as the influence of member continuity across brace point locations. To the knowledge of the author, no comprehensive studies have been conducted to date to evaluate the specific nature of these approximations. Furthermore, the current Appendix 6 provisions do not recognize the benefits of combined lateral and torsional bracing. Limited prior research studies have shown substantial reduction in the demands on the individual bracing components by using them in combination. This thesis presents a methodical and comprehensive study of basic beam bracing behavior via refined FEA test simulation. Various point (nodal) lateral, shear panel (relative) lateral, point torsional, combined point lateral and point torsional, and combined shear panel lateral and point torsional bracing cases are studied for representative beams subjected to uniform bending. Detailed comparisons to the current Appendix 6 rules are provided, where applicable, and recommendations for improvements are forwarded. Specific questions addressed in this research are: • What is the effect of inelasticity on the bracing response and requirements? • What is the influence of member continuity across the brace points on the bracing response and requirements? • What are the benefits of combined torsional and lateral bracing when the lateral bracing is placed on the compression flange versus when it is placed on the tension flange.

O trabalho analisa as forças atuantes no contraventamento de treliças triangulares de coberturas de madeira por meio de modelos numéricos computacionais. Os modelos foram confeccionados no sistema de análise estrutural Strap e consideram o funcionamento do contraventamento na estrutura tridimensional. Os valores máximos das forças obtidas nos modelos tridimensionais foram comparados aos valores mínimos indicados pelo método de estimativa da NBR 7190 (1997), este, baseado na instabilidade lateral do elemento contraventado. Os valores dos modelos tridimensionais também foram comparados aos métodos do Eurocode 5, da norma sul-africana SABS 0163 e aos valores propostos por Underwood (2000), por apresentarem formulação semelhante ao da NBR 7190 (1997). Os modelos representam galpões usuais na prática, com dimensões variando de 12 a 24 metros de vão; 24 a 96 metros de comprimento; 3, 4 e 6 metros de altura do pilar. Foram analisados para os tipos de treliça Howe e Pratt, para as classes de madeira C30 e C50 e para os tipos de telhas fibrocimento, metálicas e cerâmicas, materiais mais utilizados no Brasil. Os resultados mostram que as forças atuantes no contraventamento dos modelos tridimensionais são superiores aos valores obtidos pelo método da NBR 7190 (1997) e que valores obtidos pelos métodos propostos pelo Eurocode 5 e por Underwood (2000) apresentam-se mais seguros diante do funcionamento global da estrutura. / This work analyzes the forces acting on the bracing bars of triangular timber trusses by computational numerical models. The models are produced in the system of structural analysis Strap and consider the operation of bracing in the three-dimensional structure. The maximum forces obtained in the three-dimensional models are compared to the minimum values indicated by the estimation method of the NBR 7190 (1997), which is based on the lateral instability of the braced element. The values of three-dimensional models are also compared to the methods of Eurocode 5, the South African standard SABS 0163 and the values proposed by Underwood (2000). The models represent sheds with usual dimensions ranging from 12 to 24 meters wide, 24 to 96 feet long, and pillar 3, 4 and 6 meters tall. Are analyzed the Pratt and Howe types of truss, the timber classes C30 and C50 and the types of tiles: cement, metal and ceramics, materials most used in Brazil. The results show that the forces acting on the bracing of the three-dimensional models are greater than those obtained by the NBR 7190 (1997) and values obtained by methods proposed by the Eurocode 5 and Underwood (2000) provides more insurance on the overall functioning structure.

This thesis presents the development and validation of a high ductility seismic resistant steel brace connector called the Yielding Brace System (YBS) that improves the earthquake performance of steel braced frame buildings. The connector is comprised of two steel castings which dissipate seismic energy through flexural yielding of specially designed triangular yielding fingers. In this body of work, the need for such a system is presented along with a summary of previously developed steel castings for enhanced earthquake performance of building structures. The development of the YBS concept is then discussed in detail and equations are developed to predict the elastic and plastic response of a YBS connector based on the geometry of the yielding fingers. The low-cycle fatigue life of the cast steel material used for the yielding elements of the YBS is characterized based on the results of several cyclic, small-scale yielding fingers tests and a low-cycle fatigue life prediction model is derived. Following this, the design of a prototype connector for the second storey brace of a fictitious six storey sample building located in Los Angeles is presented. This design is conducted using the low-cycle fatigue prediction model, the response prediction equations and non-linear finite element analysis. Results of four full-scale prototype tests are then presented. Two of the tests are axial tests of the device alone, while the other two are full-scale braced frame tests. Finally, the design of a 12-storey sample building is presented. This building design is then evaluated via non-linear time-history analysis using the FEMA P-695 methodology. The results from these analyses are then discussed and compared to a similar study conducted on the same building designed with buckling restrained braces. This work shows that the Yielding Brace System is a highly ductile, seismic resistant brace that can be used as an alternative to the buckling restrained brace with the potential to provide a stiffer structure with increased ductility.