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Composite Beams (composite + beam)
Selected AbstractsDamage Identification of a Composite Beam Using Finite Element Model UpdatingCOMPUTER-AIDED CIVIL AND INFRASTRUCTURE ENGINEERING, Issue 5 2008B. Moaveni As a payload project attached to a quasi-static test of a full-scale composite beam, a high-quality set of low-amplitude vibration response data was acquired from the beam at various damage levels. The Eigensystem Realization Algorithm was applied to identify the modal parameters (natural frequencies, damping ratios, displacement and macro-strain mode shapes) of the composite beam based on its impulse responses recorded in its undamaged and various damaged states using accelerometers and long-gage fiber Bragg grating strain sensors. These identified modal parameters are then used to identify the damage in the beam through a finite element model updating procedure. The identified damage is consistent with the observed damage in the composite beam. [source] Design of a composite beam using the failure probability-safety factor methodINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 9 2005E. Castillo Abstract The paper shows the practical importance of the failure probability-safety factor method for designing engineering works. The method provides an automatic design tool by optimizing an objective function subject to the standard geometric and code constraints, and two more sets of constraints, that guarantee some given safety factors and failure probability bounds, associated with a given set of failure modes. Since a direct solution of the optimization problem is not possible, the method proceeds as a sequence of three steps: (a) an optimal classical design, based on given safety factors, is done, (b) failure probabilities or bounds of all failure modes are calculated, and (c) safety factors bounds are adjusted. This implies a double safety check that leads to safer structures and designs less prone to wrong or unrealistic probability assumptions, and to excessively small (unsafe) or large (costly) safety factors. Finally, the actual global or combined probabilities of the different failure modes and their correlation are calculated using a Monte Carlo simulation. In addition, a sensitivity analysis is performed. To this end, the optimization problems are transformed into another equivalent ones, in which the data parameters are converted into artificial variables. In this way, some variables of the dual associated problems become the desired sensitivities. The method is illustrated by its application to the design of a composite beam. Copyright 2004 © John Wiley & Sons, Ltd. [source] Cost optimization of composite floors using neural dynamics modelINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN BIOMEDICAL ENGINEERING, Issue 11 2001Hojjat Adeli Abstract The design of composite beams is complicated and highly iterative. Depending on the design parameters a beam can be fully composite or partially composite. In the case of design on the basis of the American Institute of Steel Construction (AISC) Load and Resistance Factor Design (LRFD) one has to consider the plastic deformations. As pointed out by Lorenz, the real advantage of the LRFD code can be realized in the minimum cost design. In this article, we present a general formulation for the cost optimization of composite beams based on the AISC LRFD specifications by including the costs of (a) concrete, (b) steel beam, and (c) shear studs. The problem is formulated as a mixed integer-discrete non-linear programming problem and solved by the recently patented neural dynamics model of Adeli and Park (U.S. patent 5,815,394 issued on September 29, 1998). It is shown that use of the cost optimization algorithm presented in this article results in substantial cost savings. Copyright © 2001 John Wiley & Sons, Ltd. [source] OXYGEN-INHIBITED LAYER IN ADHESION DENTISTRYJOURNAL OF ESTHETIC AND RESTORATIVE DENTISTRY, Issue 5 2004Byoung I. Suh MS ABSTRACT Purpose:: Characteristics of the oxygen-inhibited layer, including bond strength, photoinitiator decomposition, and post-curing degree of conversion, were investigated. Materials and Methods: To investigate shear bond strength, BisCover (Bisco, Inc., Schaumburg, IL, USA) and D/E Resin (Bisco, Inc.) were placed on disks of Renew composite (Bisco, Inc.) and cured both with and without an oxygen-inhibited layer. Light-Bond composite (Reliance Orthodontic, Itasca, IL, USA) was placed in a gelatin capsule and light cured over the cured resin. After soaking in water for 2 hours at 37°C, specimens were sheared to failure using a universal testing machine (Model 4466, Instron Inc., Canton, MA, USA). To investigate microtensile bond strength, composite substrates prepared using Renew A2 composite were light cured either in air or under nitrogen. Light-Core (Bisco, Inc.) was placed on each substrate and light cured. The resulting specimens were sectioned into composite beams and stressed to failure using a microtensile tester (built by Bisco, Inc.). To determine camphorquinone (CQ) decomposition, an experimental CQ resin was placed between two glass plates and irradiated for different time intervals. The absorption spectrum was obtained using a Cary 50 Bio UV-Visible Spectrometer (Varian, Mulgrave, Australia). To explore the degree of conversion, polyester film strips (Mylar, DuPont, Wilmington, DE, USA) coated with the CQ resin were pre-cured in air for different time periods, and then post-cured at low intensity for 5 minutes under nitrogen. A Spectrum 1000FTIR Spectrometer (Perkin Elmer, Norwalk, CT, USA) was used to measure the degree of conversion. Results: Bond strength tests resulted in no significant difference between samples with or without an oxygen-inhibited layer. The oxygen-inhibited layer contained reduced amounts of photoinitiator. The degree of conversion of post-cured oxygen-inhibited layers was lower than that for the control. Conclusion: An oxygen-inhibited layer is not necessary for bonding with composite resin. [source] Einfluß des Kriechens und des Betonschwindens auf das Tragverhalten von Holz-Beton-Verbundbalken , Ein erweiterter Bemessungsvorschlag und dessen AnwendungsgrenzenBAUTECHNIK, Issue 7 2005Jörg Schmidt Dr.-Ing. In diesem Beitrag werden die Auswirkungen des Kriechens und des Betonschwindens auf das Tragverhalten der Verbundkonstruktion untersucht. Dabei wird die zeitliche Veränderung der Werkstoffeigenschaften in einem FE-Modell erfaßt. Insbesondere die Berücksichtigung des Verhaltens von jungem Beton führt zu signifikanten Veränderungen des Tragverhaltens im Vergleich zu Verbundkonstruktionen mit vereinfacht konstant angenommenen elastischen Betoneigenschaften. Außerdem wird der Einfluß der Dauer und des Entlastungsprozesses einer temporären Montageunterstützung untersucht, um praxisrelevante Handlungsempfehlungen zu gewinnen. Der um die Verminderung des Tragvermögens infolge Betonschwindens erweiterte Bemessungsvorschlag erlaubt hingegen eine wirtschaftliche Bemessung und gewährleistet ein ausreichendes Sicherheitsniveau zum Versagenszustand. Effects of creep and concrete shrinkage on the load-carrying behaviour of timber/concrete composite beams , an extended design proposal and its limitations. In this paper, the effects of creep and shrinkage with respect to the load-carrying behaviour are studied. In particular, the behaviour of green concrete causes significant changes compared to structures with the simplified assumption of constant elastic material properties. Furthermore, the influence of the duration and the procedure of unloading of a temporary assembly support are investigated to obtain practicable advices. The design proposal, which is extended to take the decrease of load-carrying capacity due to concrete shrinkage into account, permits an economical design and guarantees a constant safety zone to the ultimate state. [source] Bemessungsvorschlag für Holz/Beton-Verbundbalken unter Beachtung abgestufter VerbindungsmittelabständeBAUTECHNIK, Issue 3 2004Jörg Schmidt Dr.-Ing. Die Abstände der Verbindungsmittel von Holz/Beton-Verbundbalken werden i. allg. vorrangig aus Kostengründen entsprechend dem Querkraftverlauf abgestuft. Das Tragvermögen gemäß Bemessungsgrundlagen nach DIN 1052 bzw. EC 5 mit linear ermittelten Schnittgrößen (Näherungsverfahren/,-Verfahren) wird gegenüber Balken ohne die o. g. Abstufung deutlich reduziert. Da das tatsächliche Last-Verformungsverhalten jedoch deutliche Nichtlinearitäten aufweist und die Verbundsteifigkeit hinsichtlich des Tragvermögens nur einen geringen Einfluß besitzt, wird in diesem Beitrag der Einfluß der Abstufung der Verbindungsmittelabstände auf das Tragverhalten von Verbundbalken mittels nichtlinearer FE-Analysen untersucht. Im Ergebnis ist festzustellen, daß der Sicherheitsabstand zwischen Gebrauchslast gemäß E DIN 1052 und Versagenslastniveau mit zunehmendem Abstufungsgrad zunimmt, weil das tatsächliche Tragvermögen weniger , als durch das derzeitige Bemessungsmodell unterstellt , reduziert wird. Somit weisen also die Systeme, deren Verbinderabstände mehrmals abgestuft sind, den größten Sicherheitsabstand auf, könnten also noch wirtschaftlicher bemessen werden. Deshalb wird im Ergebnis der Untersuchungen ein neuer Bemessungsvorschlag unterbreitet und verifiziert, der die Nichtlinearitäten berücksichtigt, einen gleichmäßigen Sicherheitsabstand zum Versagenslastniveau gewährleistet und eine deutlich wirtschaftlichere Bemessung erlaubt. Design proposal for timber/concrete composite beams with graded connnector distances. The distance of connections of timber/concrete composite beams is often graded for economical reasons according the shear force distribution. The load-carrying capacity of composite beams according to DIN 1052 respectively E DIN 1052 with internal forces, which are linearly determined, (,-procedure) are clearly reduced compared to beams without graded distances of connectors. The actual load-bearing behaviour distinctly shows non-linearities. The influence of the gradations of the connectors on the load-bearing behaviour of composite beams is investigated, because the influence of the stiffness of connections on the load-bearing capacity of composite beams is small. The paper presents a comparison between failure loads determined by FE-analysis and the working loads according to the current design rule. It is shown that the decrease of load-bearing capacity is smaller than assumed by current code of practice. Structures with several different distances of connections have the largest safety-factor. These systems can more economically be designed. As the result of the investigations, a new design proposal is presented, which takes non-linearities into account and guarantees a constant safety-zone between failure load and working load. These proposal permits an economic design of timber/concrete composite beams. [source] | ||||||||||