Management des Windrisikos bei weitgespannten Überdachungen

A number of modern structures characterized by a relevant impact and elegance often coupled with lightness and irregular shapes are dramatically exposed to the wind aerodynamic action, which becomes a key factor in their safety assessment. These structures are involved into a global and complex design process in which players like the environment and social sciences join engineering in order to guarantee an optimal result under several aspects, not the last the economical aspect. In this background, it is not possible trusting into unreliable deterministic considerations, where the over-engineering would assure the result. The attention is now shifted to overall frameworks of Performance-Based Design aimed to specific performance targets and their optimization. In particular, the criteria to ensure the achievement of the results are expressed in terms of risk of failure. This work of thesis presents a general framework for calculating all the possible structural damages and subsequently economic losses after a natural catastrophic event. The framework is adjusted and applied to the specific case study of the covering of the Stadium of Braga in Portugal, where the hazard of a windstorm, the loads that the latter enforces on the covering, the structural response, the resulting damages and other consequences are hierarchically calculated. Particular emphasis, and original contribution of the work, is paid on the evaluation of the dynamic response of the structure. Pressure fluctuations on buildings produced by storms have a complex temporal and spatial organization and their study, keeping under control the whole physical phenomena, is quite difficult. Accordingly, some suitable tools like the orthogonal decomposition are adopted in order to handle the huge amount of data. Moreover a consistent and operative procedure aimed at enhancing the assessment of the aerodynamic wind pressure on the covering is provided. This work addresses a fundamental topic for the risk assessment; the results achieved by the duly application of the framework can be successfully transferred to other actors involved in the management and the governmental processes devoted to natural hazards.Zahlreiche moderne Bauwerke zeichnen sich durch Eleganz, Helligkeit und unregelmäßige Formen aus und sind in extremer Weise aerodynamischen Kräften ausgesetzt, welche eine zentrale Rolle in Sicherheitsanalysen einnehmen. An der Planung derartiger Bauwerke sind viele Fachrichtungen, auch Umwelt- und Sozialwissenschaften, beteiligt, um einen optimalen Bauwerksentwurf zu gewährleisten, wobei nicht zuletzt ökonomische Aspekte von großer Bedeutung sind. Daher ist es oft nicht empfehlenswert, deterministische Verfahren einzusetzen, da diese zur Überdimensionierung von Bauelementen führen können. Stattdessen werden Bauwerke heutzutage zunehmend für verschiedene Gefährdungsstufen bemessen, um die Wirtschaftlichkeit der Baumaßnahme sicher zu stellen und das Versagensrisiko zu bewerten. In der vorliegenden Arbeit wird eine Methodik vorgestellt, mit der alle möglichen strukturellen Schäden eines Bauwerks rechnerisch erfassbar und die damit einhergehenden ökonomischen Schäden abschätzbar sind, die mit einer Naturkatastrophe einhergehen. Die Methodik wird auf die Überdachung des Stadions in Braga, Portugal, angewendet, wobei die Gefahr eines Sturms, die infolge des Sturms induzierten Lasten auf das Bauwerk, die strukturelle Antwort sowie die resultierenden Schäden und weitergehende Konsequenzen berechnet werden. Hierbei findet die Bewertung der dynamischen Antwort des Bauwerks besondere Beachtung, da Druckschwankungen infolge des Sturms komplexe zeitliche und räumliche Verteilungen aufweisen können. Daher werden Verfahren wie die orthogonale Zerlegung angewendet, um den Berechnungsaufwand zu verringern. Ferner wird eine konsistente operative Methode vorgestellt, die eine verbesserte Erfassung des aerodynamischen Winddrucks auf Überdachungen erlaubt. Die Arbeit adressiert eine fundamentale Fragestellung in der Risikobewertung. Die Ergebnisse, die aus der Anwendung der vorgestellten Methodik resultieren, können für alle im Risikomanagement von Naturkatastrophen involvierten Ingenieure und Institutionen von großer Bedeutung sein

Ab initio and electron spectroscopy study of carbonyl derivatives

The bands present in the low ionisation energy region (Ei[less-than-or-eq] 12 eV) of the He I photoelectron spectra, and the low energy resonances of the electron transmission spectra of some substituted carbonyls XC(O)R (X = Et2N, alkyl, EtS and EtO; R = Me and CH2SR) have been assigned to the corresponding molecular orbitals by comparison with the assignments reported for simple related molecules. Fully optimized 3-21G ab initio calculations reproduce the assignment of the spectra and available geometric parameters and therefore have been used to determine the electronic charge distribution among the various atoms and groups in the studied compounds. A combined analysis of the theoretical and experimental data provides a detailed understanding of the electronic interaction among the X, CO and R groups in the molecules studied

Electronic interactions in 2-(ethylsulphonyl) ketones studied by ultraviolet photoelectron spectroscopy

The bands present in the low ionization energy region (EI <= 12 eV) of the (He I and He II) photoelectron spectra of some aromatic (R = NO2C6H4, 4; C6H5, 5; MeOC6H4, 6; n= 1) and aliphatic (R = Me, and n= 1, 2; or 2, 3) ethylsulphonyl ketones, RC(O)(CH2)nSO2Et, have been assigned to the corresponding molecular orbitals by comparison with the assignments reported for simpler related molecules. The comparison has been assisted by the determination of the geometric structure of 6. (by X-ray diffraction) and of the model compounds HC(O)CH2SO2H and p-C6H4C(O)CH2SO2CH3(by semiempirical calculations). Oppositely charged atoms of the carbonyl and ethanesulphonyl groups are separated by distances shorter than the sum of the van der Waals radii, allowing crossed charge-transfer interactions. Low symmetry allows a deep through-space and through-bond mixing among the various group orbitals, as indicated by experimental Ei values and theoretical calculations

X-ray Diffraction, UV Photoelectron, and ab initio Study of Intramolecular Interactions in β-Carbonyl Sulfones

Information on the geometric and electronic structures of β-carbonylsulfones, XC(O)CH2SO2R (1-10, X = Et2N, EtS, EtO, alkyl and aryl, and R' = alkyl and aryl) are obtained for different pairs of the X and R substituents. The results of the x-ray diffraction and of the PE spectra analyses fully agree with the results of optimized ab initio 3-21G* calculations. The electron charge distribution at various atoms and/or groups is discussed in connection with the other observables. In the compounds studied the CH2-S bond is gauche to the carbonyl group irrespective of the X and R substituents and of the gas or solid phase. This conformation is dictated by the interplay of the electronic interactions between the XC(O) and SO2R groups with two strong non bonded interactions between pairs of oppositely charged atoms. The negatively charged carbonyl oxygen and one of the sulfonyl oxygen atoms lie at distances shorter than the sum of the corresponding van der Waals radii from the positively charged sulfur and carbonyl carbon atoms, respectively. The interaction of the sulfonyl oxygen with the carbonyl carbon atom is the stronger of the two and partially offsets the strong inductive effect of the sulfonyl group. The presence of both through-bond and through-space interactions between the carbonyl and the sulfonyl groups in the ground and ionized states is confirmed by eigenvector analysis and by the shifts in the MO energies with respect to reference compounds. The conformation of compound 5, in solid phase, is in part determined by crystal packing forces

Conformational and Electronic Interaction Studies of some beta-ketosulfoxides

The analysis of the carbonyl I.R. band and the U.V. phoelectron spectroscopic data along with the ab-initio calculations and X-ray diffraction of alfa­ (methylsulfinyl)- and alfa-(phenylsulfinyl)-acetophenones indicated the predominance of the cis rotamers aver the gauche ones

Spectroscopic and theoretical studies of some alpha-ethylsulfinyl ortho-substituted acetophenones

The preferred conformations of the α-ethylsulfinyl ortho-substituted acetophenones X_PhC(O)CH2S(O)Et (X = OMe 1, Me 2, F 3, Cl 4, Br 5, NO2 6) are determined by νCO IR analysis, ab initio HF/6-31G** computations (1-4 and 6) and X-ray diffraction analysis (6). The matching between the IR frequency and intensity of the carbonyl doublet components, in carbon tetrachloride and the results of the calculations indicates that the lower energy component corresponds to the cis2 (anti) conformer for 1, 3-5 and cis2 (syn) for 2. The higher frequency component is related to the gauche3 conformer anti for 3 and syn for 2, 4 and 5, and to the gauche4 (anti) conformer for 1. For 6, gauche conformers correspond to both doublet components. The cis2 conformer population prevails over the gauche one for 1-3 (ca.80%) but not for 4 and 5 (ca.30%). For 6, the lower frequency gauche3 conformer population (85%) is significantly larger than that for the gauche2 one. These trends are discussed in terms of strong stabilising charge transfer and electrostatic interactions between pairs of oppositely charged atoms and their variation with the electronic and steric properties of the X substituent. The X-ray diffraction analysis shows that 6, in the solid state, is in the cis1 conformation which is stabilised through dipole moment coupling and intermolecular hydrogen bonds. In the gas phase and in the crystal, the ortho-nitrophenyl plane is almost perpendicular to the acetyl plane allowing a strong stabilising interaction

Experimental and theoretical study of the intramolecular interactions determining the conformation of β-Carbonyl Sulfoxides

Information on the geometrical and electronic structures of α-methylsulfinylacetophenone, C6H5C(O)CH2S(O)CH3 2, have been obtained from X-ray diffraction analysis, UV photoelectron spectroscopy and ab initio 6-31G** calculations. A comparison of the results with those obtained from the spectra and the computations on α-methylthioacetophenone, C6H5C(O)CH2SCH3 1 and α-methylsulfonylacetophenone, C6H5C(O)CH2SO2CH3 3, together with previous results on β-keto sulfides and β-keto sulfones indicates that the CH2–S(O) bond in 2 is quasi-cis to the carbonyl group in the gas and solid phase, at variance with the other β-carbonyl thioderivatives which adopt a gauche conformation. Eigenvector analysis, electron charge distribution at various atoms and/or groups and geometric parameters indicate that the cis conformation of 2 is stabilized by a strong non-bonded interaction between the negatively charged carbonyl oxygen and the positively charged sulfur atom from which it is separated by a distance (2.8–2.9 Å) much shorter than the sum of the van der Waals radii. The predominant charge transfer interaction in 3 and related sulfones occurs in the opposite direction (OSO2→ CCO). The inversion of the direction of the charge transfer (and the change of the cis/gauche orientation of the thio group) from sulfone to sulfoxide is associated with an increase of electron affinity of the thio group in the latter, and could explain its smaller thermal stability. Ab initio 3-21G* calculations on several conformations of the bis-thioderivatives C6H5C(O)CH(SCH3)S(O)CH3 4, C6H5C(O)CH(SR)SO2R (R = Me 5 and Ph 6) and C6H5C(O)CH(SOCH3)SO2CH3 7, together with X-ray diffraction (4, 6 and 7) and photoelectron spectroscopy (4) analyses confirmed the cis(SOR) and gauche(SR and SO2R) preferred orientation of the thio groups with respect to the carbonyl group as observed in the monosubstituted derivatives. In 4 and 7 the SSO atom is about 30° out of the cis plane [O(1)–C(2)–C(3)]