Home About us Contact
|
Home About us Contact | ||
|
|
||
Concrete Elements (concrete + element)
Selected AbstractsNäherungsweise Spannungsberechnung vorgespannter BetonbauteileBETON- UND STAHLBETONBAU, Issue 2 2007Olaf Mertzsch PD Dr.-Ing. Mit Einführung der DIN 1045-1 (07.2001) erfolgt die Bemessung von Stahlbeton- und Spannbetontragwerken nach einer einheitlichen Berechnungsvorschrift. Hiermit besteht die Möglichkeit einer besseren Auslastung der Konstruktion. Dies hat zur Folge, dass den Nachweisen der Gebrauchstauglichkeit eine größere Bedeutung zukommt. Ziel der nachfolgenden Betrachtungen ist es, wirklichkeitsnahe Berechnungsansätze zur Vorhersage der Beton- und Stahlspannungen abzuleiten. Diese Berechnungsansätze ermöglichen eine einfache Abschätzung der Spannungen und sind auch für Handrechnungen geeignet. Approximate Stress Calculation of prestressed Concrete Elements With the introduction of the DIN 10451 (07.2001) the dimensioning of reinforced concrete- and prestressed concrete constructions are carried out after an uniform calculation regulation. With this arises the possibiltiy of a much better utilization of the construction. But it has also the consequence that the proof of the usability gets much more importance. Aim of the following paper is it, to derive a realistic calculation-modell for the prognoses of the concrete and steel stresses. A simple estimation of stresses shall be made possible by this and it shall be also suitable for a hand-made calculation. [source] Analysis of the behaviour of the structural concrete after the fire at the Windsor Building in MadridFIRE AND MATERIALS, Issue 2 2010E. Menéndez Abstract The analysis of the concrete subjected to high temperatures is usually undertaken by means of tests specifically designed and carried out in the laboratory, or by using theoretical approaches using standardized curves for theoretical fires. An analysis by different techniques has been carried out on structural concrete to real fire of Windsor Building in Madrid, which was severally damaged by a fire in 2005. These techniques are X-ray diffraction, differential thermal and thermogravimetric analysis and backscattered electron microscopy with dispersive X-ray microanalysis. Samples of the concrete were taken from different floors in the building and analyses were carried out at different depths starting from the surface exposed to the fire itself. The analysis allows the damaged area to be limited as well as situating the 500,C isotherm in the concrete element. In accordance with the results obtained, the damage is limited to just a few centimeters from the surface exposed to the fire itself, in spite of its prolonged exposure to the fire. This would justify that the concrete has demonstrated a suitable resistant behaviour. Likewise, it can be deduced from the results obtained that the fire, to which the concrete was subjected, can be qualified as severe. Also, these results can confirm that the calculation hypothesis in the project is correct in relation to the fire resistance exigencies of the concrete. Copyright © 2009 John Wiley & Sons, Ltd. [source] Numerical Model for Biaxial Earthquake Response of Reinforced ConcreteCOMPUTER-AIDED CIVIL AND INFRASTRUCTURE ENGINEERING, Issue 4 2007Cemalettin Dönmez The model is tested using data from two types of experiments with reinforced concrete elements: (1) elements subjected to varying pseudo-static biaxial lateral loads and (2) elements that responded biaxially to simulated earthquake motions. The goal for the model was not only to help determine the absolute maxima for earthquake response but also to enable calculation of the entire waveform, including the ranges of low- and moderate-amplitude response. The comparisons of measured and calculated results and sensitivity of the proposed model to variations in the input parameters are discussed. The output was found to be insensitive to the changes in input parameters related to concrete and sensitive to input parameters related to reinforcing steel. The results of the calculations were tested using experimental data. [source] An efficient three-dimensional solid finite element dynamic analysis of reinforced concrete structuresEARTHQUAKE ENGINEERING AND STRUCTURAL DYNAMICS, Issue 2 2006K. V. Spiliopoulos Abstract Most of the finite element analyses of reinforced concrete structures are restricted to two-dimensional elements. Three-dimensional solid elements have rarely been used although nearly all reinforced concrete structures are under a triaxial stress state. In this work, a three-dimensional solid element based on a smeared fixed crack model that has been used in the past mainly for monotonic static loading analysis is extended to cater for dynamic analysis. The only material parameter that needs to be input for this model is the uniaxial compressive strength of concrete. Steel bars are modelled as uniaxial elements and an embedded formulation allows them to have any orientation inside the concrete elements. The proposed strategy for loading or unloading renders a numerical procedure which is stable and efficient. The whole process is applied to two RC frames and compared against existing experiments in the literature. Results show that the proposed approach may adequately be used to predict the dynamic response of a structure. Copyright © 2005 John Wiley & Sons, Ltd. [source] Potential mapping technique for the detection of corrosion in reinforced concrete structures: Investigation of parameters influencing the measurement and determination of the reliability of the methodMATERIALS AND CORROSION/WERKSTOFFE UND KORROSION, Issue 2 2009Y. Schiegg Abstract The potential distribution around a corrosion site in concrete was modeled by means of a simple mathematical model for a rod-shaped anode. Based on these calculations the influencing parameters and the limits of the potential mapping technique were determined. They demonstrate that the location of anodes depends on the anode length, the concrete coverage, and the measuring grid. Moreover small anodes with less than 1 cm length are virtually impossible to localize. Investigations on concrete elements without reinforcing steel showed that heterogeneous water content and chloride distribution can result in potential differences of up to 150 mV on the concrete surface. This effect was related to the streaming potential and the diffusion overpotential in the concrete. In order to determine the reliability of the potential mapping technique in the field application, the concrete on a tunnel wall was removed after the measurement of the potential distribution and the corrosion loss of the steel was determined. It was found that all corrosion sites with more than 2 mm material loss were detected by the potential mapping technique. Only some smaller corrosion sites were not found. Based on this investigation, the applicability of the potential mapping technique for detecting corrosion sites was confirmed. The observed high reliability of the potential mapping technique can be explained by a combination of the heterogeneous wetting of the concrete, the inhomogeneous contamination with chloride, and the macrocell formation. [source] Dispute Resolution and the Politics of Cultural GeneralizationNEGOTIATION JOURNAL, Issue 1 2003David Kahane This essay argues that generalizations about cultural identities and values should play a key role in designing procedures to resolve disputes. Generalizations about cultures are risky given the complexity of memberships and group boundaries, not to mention the power dynamics within and between social groups. But it is important to take the risk: attempts to avoid or transcend culture in resolving disputes pose an even greater danger, of reiterating the understandings of dominant cultural groups under the guise of neutrality. The author explores the "politics of cultural generalization" in theoretical terms, then considers its implications for concrete elements of dispute resolution training and process design. [source] Teilsicherheitsfaktoren für die Berechnung von GroßkraftwerkenBETON- UND STAHLBETONBAU, Issue 7 2010Simon Glowienka Dr.-Ing. Normen, Vorschriften, Richtlinien; Berechnungs- und Bemessungsverfahren Abstract Die Baustrukturen von Großkraftwerken werden in Deutschland u. a. auf Basis der VGB-Richtlinie R 602 U berechnet und bemessen. In dieser Richtlinie sind unter Berücksichtigung der Besonderheiten des Großkraftwerksbaus Einwirkungen und Teilsicherheitsfaktoren definiert. Während die Lasten auf diese Randbedingungen abgestimmt wurden, hat man die Teilsicherheitsfaktoren auf der Lastseite aus der DIN 1055-100 entnommen und lediglich die Kombinationsbeiwerte angepasst. Diese Sicherheitsbeiwerte tragen jedoch den speziellen Randbedingungen eines Kraftwerks oder Schwerindustriebaus nur bedingt Rechnung. Im Rahmen des Beitrags werden die Teilsicherheitsbeiwerte auf der Einwirkungsseite , insbesondere für das Konstruktionseigengewicht , für die Bemessung von Stahlbetonteilen vor diesem Hintergrund kritisch diskutiert und ein optimierter, wissenschaftlich abgesicherter Vorschlag unterbreitet. Partial Safety Factors for the Design of Power Plants In Germany power plants are designed in accordance to VGB regulation R 602 U. In this code load actions and partial safety factors are applied taking the special characteristics of power plants into consideration. The actions are defined regarding these circumstances, however the safety coefficients are assumed according to DIN 1055-100 and only the combination coefficients are adjusted. However it has to be recognized that the partial safety factors in DIN 1055-100 are calibrated for building constructions and thus do not consider the specialities of power plants in an adequate manner. In this paper the partial safety factors for the design of power plants and other heavy industry buildings are discussed for structural concrete elements and a scientific based optimized approach for the safety factor for dead load is presented. [source] Versuche zur Tragfähigkeit von Ankerplatten mit einbetonierten Kopfbolzendübeln in schmalen StahlbetonstützenBETON- UND STAHLBETONBAU, Issue 6 2010Stephan Fromknecht Dr.-Ing. Versuche; Befestigung Abstract Müssen große Lasten von Stahl- in Betonbauteile eingebracht werden, sind Ankerplattendetails mit aufgeschweißten Kopfbolzendübeln oft praktikable Lösungen. Dies gilt auch für die Befestigung von Stahlträgern an Stützen aus Stahlbeton. Hier können die Ankerplatten z. B. bauseits an der Schalung befestigt und mit dem Ortbeton einbetoniert werden. Die Dimensionierung dieser Einbauteile kann, wie auch die Berechnung von nachträglich installierten Befestigungsmitteln, derzeit nach Europäischen Technischen Zulassungen (ETA) erfolgen. Im Unterschied zu nachträglich installierten Befestigungen ist für die Ankerplatte mit einbetonierten Kopfbolzendübeln eine rechnerische Nutzung der Tragfähigkeit der Bewehrung möglich. Allerdings führen die diesbezüglichen Regelungen , im Vergleich zu den in den Versuchen ermittelten Tragfähigkeiten , rechnerisch zu stark eingeschränkten Tragfähigkeiten. Dies beruht einerseits auf der Reduktion der Tragfähigkeit wegen geringer Randabstände und andererseits auf der stark eingeschränkten Nutzbarkeit der Bewehrung. Im folgenden Beitrag werden Versuchsergebnisse vorgestellt, welche den Einfluss der Betondruckfestigkeit, der Verankerungslänge, der Lastexzentrizität sowie der Bewehrungsmenge und -position auf das Versagensgeschehen und die Tragfähigkeit zeigen. Results of Experimental Investigations on the Load-Bearing Capacity of Steel Anchor Plates with in Concrete Encased Headed Studs in Reinforced Narrow Concrete Columns Anchor plates with welded shear studs are often used to transfer high loads from steel to reinforced concrete elements. This is for example the case for the fixation of steel beams to reinforced concrete columns. The anchor plates are fixed on site on the formwork and cast in-place in the concrete. The design is calculated according to European Technical Approvals like the design of post-installed anchors. In contrast to post-installed fastenings, the utilisation of the reinforcement of in concrete encased headed studs is theoretically possible. But the regulations of the ETAs lead to great reductions in the analysed load-bearing capacities compared to the capacities, obtained in tests. These tests have been conducted to investigate the load bearing behaviour and failure modes of anchor plates, especially in narrow reinforced concrete columns. In the following article the results of the experimental investigations are presented, which show the influence of concrete compression strength, shear stud length, load eccentricity as well as amount and position of reinforcement. [source] Zur Ermittlung der Normalkraft-Verlängerung und Moment-Krümmung-Beziehungen der Stahlbetonbauteile im Grenzzustand der GebrauchstauglichkeiBETON- UND STAHLBETONBAU, Issue 8 2009Eugen Du, ulescu Dr.-Ing. Berechnungs- und Bemessungsverfahren; Normen, Vorschriften, Richtlinien Abstract Die Nachweise zur Begrenzung der Verformungen von Stahlbetonbauteilen sind infolge der Verwendung von Baustoffen höherer Festigkeiten immer wichtiger geworden, oft sogar maßgebend. Eine Verdopplung der Betondruckfestigkeit eines normalen Betons ruft eine etwa 20%ige Erhöhung des Ec -Moduls hervor aber keine des Betonstahls, da Es konstant ist. Dies und die dementsprechend schlanker gewordenen Stahlbetonbauteile führen zu größeren Verformungen , Verlängerungen, Durchbiegungen und/oder Verdrehungen , die deren Verhalten beeinträchtigen können. Die für die Ermittlung der Verformungen benötigten "Normalkraft-mittlere Dehnungslinien", bzw. "Moment-mittlere Krümmungslinien" werden erläutert. About the Calculation of Displacements of Reinforced Concrete Members in the Serviceability Limit State The verification of reinforced concrete elements for the purpose of limiting deformations has become increasingly important, often even decisive, as a result of the use of higher strength materials. A doubling of the compressive strength of a normal concrete causes an increase of about 20% in the Ec -module, and none of reinforcing steel, because Es is constant. This and, accordingly, the slender reinforced concrete elements lead to larger deformations , elongations, deflections and/or rotations , which may affect their behaviour. The determination of "axial tensile force , mean strain diagrams", respectively "bending moment , mean curvature diagrams", needed for the calculation of the displacements, is explained. [source] Verformungsvorhersage von vorgespannten und nicht vorgespannten BetonbauteilenBETON- UND STAHLBETONBAU, Issue 6 2009Wolfgang Krüger Prof. Dr.-Ing. habil. Baustoffe; Berechnungs- und Bemessungsverfahren; Spannbeton Abstract Wie vergleichende Untersuchungen zeigen, führt eine Begrenzung der Verformung auf der Grundlage des Schlankheitsnachweises, wie er nach DIN 1045-1 bei Stahlbetonbauteilen möglich ist, nicht immer zu dem gewünschten Erfolg. In diesen Fällen und bei Spannbetonkonstruktionen ist grundsätzlich ein Nachweis der Verformungen erforderlich. Ausgehend von allgemeinen Betrachtungen zum Nachweis der Bauteilverformungen, werden wesentliche materialseitige Einflüsse auf die Verformungsvorhersage diskutiert. Es wird deutlich, dass eine genaue Berechnung der Verformung nur bedingt möglich ist. Im Anschluss wird für die tägliche Berechnungspraxis ein Näherungsansatz zur Vorhersage der Verformung bewehrter Betonbauteile formuliert. Im Rahmen von vergleichenden Betrachtungen wird die Genauigkeit des entwickelten Näherungsansatzes abgeschätzt. Hierbei zeigt sich eine gute baupraktische Übereinstimmung zwischen komplexen Berechnungen und dem vereinfachten Berechnungsansatz. Deformation Forecast of Prestressed and Non-Prestressed Concrete Members Comparative investigations have shown that the limitation of deformation, based on a permitted slenderness ratio as possible according to DIN 1045-1 for reinforced concrete elements, do not always achieve the desired success. An exact calculation of the structure deformation is absolutely necessary for prestressed components and in the case of a non-accomplished slenderness proof for reinforced concrete members. In this paper significant material influences of the deformation forecast will be discussed, proceeding from universal views of the component deformation proof. It will be clear, that an exact deformation calculation is only restricted possible. An approximation procedure for practical use to the forecast of deformations of reinforced and prestressed concrete structures will be formulated, afterwards. The accuracy of this developed approximation procedure will be estimated with the aid of comparative studies. At this, the results of the simplified formulation correlate well with the values of complex, numeric investigations in a range of practical use. [source] | ||||||||||