Chemical speciation effects on the volumetric properties of aqueous sulfuric acid solutions

Densities of fifteen aqueous solutions of sulfuric acid (H2SO4) have been measured by vibrating-tube densimetry at solute molalities (m) from (0.01 to 3.0) mol·kg−1 over the temperature range 293.15 ≤ T/K ≤ 343.15. These data have been used to calculate the corresponding apparent molar volumes Vϕ(H2SO4,aq), which represent a significant expansion of the volumetric database for this industrially-important acid. At 298.15 K the present results agree well with literature data, notably with the century-old values given in the 1926 International Critical Tables. At other temperatures, where comparisons are possible agreement with the present Vϕ values is also very satisfactory. Consistent with earlier studies, Vϕ(H2SO4,aq) was found to exhibit an abnormally-large decrease at low concentrations (m ≤ 0.1 mol·kg−1). This effect is consistent with a change in the chemical speciation of H2SO4(aq), from an essentially 1:1 electrolyte (H+(aq) + HSO4− (aq)) at higher concentrations to a predominantly 1:2 electrolyte (2H+(aq) + SO42− (aq)) in dilute solutions. The Vϕ values were modelled using variants of Young’s rule and the Pitzer formalism. Combination of these results with literature values for the standard volume V°(SO42−,aq) enabled estimation of V°(HSO4−,aq) and the standard volume change, ΔrV°, for the first protonation of the sulfate ion (H+(aq) + SO42−(aq) → HSO4−(aq)) as functions of temperature. It is shown that V°(HSO4−,aq) is sensitive to the value of the first protonation constant and probably cannot be determined to better than ± 0.3 cm3·mol−1 at present

Chemical speciation effects on the volumetric properties of aqueous sulfuric acid solutions

Densities of fifteen aqueous solutions of sulfuric acid (H2SO4) have been measured by vibrating-tube densimetry at solute molalities (m) from (0.01 to 3.0) mol·kg−1 over the temperature range 293.15 ≤ T/K ≤ 343.15. These data have been used to calculate the corresponding apparent molar volumes Vϕ(H2SO4,aq), which represent a significant expansion of the volumetric database for this industrially-important acid. At 298.15 K the present results agree well with literature data, notably with the century-old values given in the 1926 International Critical Tables. At other temperatures, where comparisons are possible agreement with the present Vϕ values is also very satisfactory. Consistent with earlier studies, Vϕ(H2SO4,aq) was found to exhibit an abnormally-large decrease at low concentrations (m ≤ 0.1 mol·kg−1). This effect is consistent with a change in the chemical speciation of H2SO4(aq), from an essentially 1:1 electrolyte (H+(aq) + HSO4− (aq)) at higher concentrations to a predominantly 1:2 electrolyte (2H+(aq) + SO42− (aq)) in dilute solutions. The Vϕ values were modelled using variants of Young’s rule and the Pitzer formalism. Combination of these results with literature values for the standard volume V°(SO42−,aq) enabled estimation of V°(HSO4−,aq) and the standard volume change, ΔrV°, for the first protonation of the sulfate ion (H+(aq) + SO42−(aq) → HSO4−(aq)) as functions of temperature. It is shown that V°(HSO4−,aq) is sensitive to the value of the first protonation constant and probably cannot be determined to better than ± 0.3 cm3·mol−1 at present

Diagnosis / Intervention criteria in damaged slabs by severe corrosion of prestressed joists

This research defines diagnosis criteria in R/C one-way slabs with severe corrosion at the lower prestressed reinforcement of the joists and proposes specific actuation criteria and constructive recommendations to increase the safety. The corrosion of this reinforcement is the most common damage in building structures, and the use of aluminous cement in the precast joists can aggravate the corrosion. The usual cases of entire residential buildings with different degrees of damage and with a few or all joists affected in a slab have been simulated. ACI-318 is used as an acceptance criterion for existing structures in the simulations, and a ratio between the ultimate load and the service load is defined as valuation coefficient. By this way, the residual safety for a damaged structure is known. Results are in accordance with the extensive experience in real intervention cases, which often still have high safety reserves.Vercher Sanchis, JM.; Gil Benso, E.; Mas Tomas, MDLA.; Lerma Elvira, C. (2013). Diagnosis / Intervention criteria in damaged slabs by severe corrosion of prestressed joists. Journal of Performance of Constructed Facilities. (04014040). doi:10.1061/(ASCE)CF.1943-5509.0000515S0401404

Analysis of the residual safety level in R/C slabs with severe joist corrosion

An analysis until the failure on a series of one-way slabs with severe corrosion at the lower reinforcement of the R/C joists is presented. Different positions in the slab and number of damaged joists have been studied, obtaining the residual safety assessment in cases of slabs damaged by flexural failure mechanisms. Since the boundary conditions have proved decisive for obtaining the behavior, the damaged slab has been evaluated as part of the entire building, as precisely as possible, taking into account the different phases of the construction process and deterioration in time, and the complex behavior of concrete, steel and masonry. The results of the proposed methodology are consistent with the pathology of the observed cases. As a result of this study the authors propose practical recommendations to help in making decisions about the magnitude of the intervention, always necessary in this type of pathology.Vercher Sanchis, JM.; Gil Benso, E.; Mas Tomas, MDLA.; Cubel Arjona, FJ. (2014). Analysis of the residual safety level in R/C slabs with severe joist corrosion. Journal of Performance of Constructed Facilities. 1-14. doi:10.1061/(ASCE)CF.1943-5509.0000608S11

Epidemiology of Streptococcus pneumoniae and Staphylococcus aureus colonization in healthy Venezuelan children

Streptococcus pneumoniae and Staphylococcus aureus cause significant morbidity and mortality worldwide. We investigated both the colonization and co-colonization characteristics for these pathogens among 250 healthy children from 2 to 5 years of age in Merida, Venezuela, in 2007. The prevalence of S. pneumoniae colonization, S. aureus colonization, and S. pneumoniae–S. aureus co-colonization was 28%, 56%, and 16%, respectively. Pneumococcal serotypes 6B (14%), 19F (12%), 23F (12%), 15 (9%), 6A (8%), 11 (8%), 23A (6%), and 34 (6%) were the most prevalent. Non-respiratory atopy was a risk factor for S. aureus colonization (p = 0.017). Vaccine serotypes were negatively associated with preceding respiratory infection (p = 0.02) and with S. aureus colonization (p = 0.03). We observed a high prevalence of pneumococcal resistance against trimethoprim–sulfamethoxazole (40%), erythromycin (38%), and penicillin (14%). Semi-quantitative measurement of pneumococcal colonization density showed that children with young siblings and low socioeconomic status were more densely colonized (p = 0.02 and p = 0.02, respectively). In contrast, trimethoprim–sulfamethoxazole- and multidrug-resistant-pneumococci colonized children sparsely (p = 0.03 and p = 0.01, respectively). Our data form an important basis to monitor the future impact of pneumococcal vaccination on bacterial colonization, as well as to recommend a rationalized and restrictive antimicrobial use in our community

Ductility of wide-beam RC frames as lateral resisting system

[EN] Some Mediterranean seismic codes consider wide-beam reinforced concrete moment resisting frames (WBF) as horizontal load carrying systems that cannot guarantee high ductility performances. Conversely, Eurocode 8 allows High Ductility Class (DCH) design for such structural systems. Code prescriptions related to WBF are systematically investigated. In particular, lesson learnt for previous earthquakes, historical reasons, and experimental and numerical studies underpinning specific prescriptions on wide beams in worldwide seismic codes are discussed. Local and global ductility of WBF are then analytically investigated through (1) a parametric study on chord rotations of wide beams with respect to that of deep beams, and (2) a spectral-based comparison of WBF with conventional reinforced concrete moment resisting frames (i.e. with deep beams). Results show that the set of prescriptions given by modern seismic codes provides sufficient ductility to WBF designed in DCH. In fact, global capacity of WBF relies more on the lateral stiffness of the frames and on the overstrength of columns rather than on the local ductility of wide beams, which is systematically lower with respect to that of deep beams.Gómez-Martínez, F.; Alonso Durá, A.; De Luca, F.; Verderame, GM. (2016). Ductility of wide-beam RC frames as lateral resisting system. Bulletin of Earthquake Engineering. 14(6):1545-1569. doi:10.1007/s10518-016-9891-xS15451569146ACI (1989) Building code requirements for reinforced concrete (ACI 318-89). ACI Committee 318, American Concrete Institute, Farmington Hills, Michigan, USAACI (2008) Building code requirements for structural concrete (ACI 318-08) and commentary (318-08). ACI Committee 318, American Concrete Institute, Farmington Hills, Michigan, USAACI-ASCE (1991) Recommendations for design of beam-column connections in monolithic reinforced concrete structures (ACI 352R-91). Joint ACI-ASCE Committee 352, American Concrete Institute, Farmington Hills, Michigan, USAACI-ASCE (2002) Recommendations for design of beam-column connections in monolithic reinforced concrete structures (ACI 352R-02). Joint ACI-ASCE Committee 352, American Concrete Institute, Farmington Hills, Michigan, USAArslan MH, Korkmaz HH (2007) What is to be learned from damage and failure of reinforced concrete structures during recent earthquakes in Turkey? Eng Fail Anal 14(1):1–22ASCE (2007) Seismic Rehabilitation of Existing Buildings, ASCE/SEI 41-06. American Society of Civil Engineers, RestonASCE (2010) Minimum Design Loads for Building and Other Structures, ASCE/SEI 7-10. American Society of Civil Engineers, RestonBenavent-Climent A (2007) Seismic behavior of RC side beam-column connections under dynamic loading. J Earthquake Eng 11:493–511Benavent-Climent A, Zahran R (2010) An energy-based procedure for the assessment of seismic capacity of existing frames: application to RC wide beam systems in Spain. Soil Dyn Earthq Eng 30:354–367Benavent-Climent A, Cahís X, Zahran R (2009) Exterior wide beam-column connections in existing RC frames subjected to lateral earthquake loads. Eng Struct 31:1414–1424Benavent-Climent A, Cahís X, Vico JM (2010) Interior wide beam-column connections in existing RC frames subjected to lateral earthquake loading. Bull Earthq Eng 8:401–420BHRC (2004) Iranian Code of Practice for Seismic Resistant Design of Buildings. Standard Nº 2800, 3rd edn. Building and Housing Research Center, TehranBorzi B, Elnashai AS (2000) Refined force reduction factors for seismic design. Eng Struct 22:1244–1260Borzi B, Pinho R, Crowley H (2008) Simplified pushover-based vulnerability analysis for large-scale assessment of RC buildings. 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Informes de la Construcción 66(533):e008 (in Spanish)Domínguez D, López-Almansa F, Benavent-Climent A (2016) Would RC wide-beam buildings in Spain have survived Lorca earthquake (11-05-2011)? Eng Struct 108:134–154Dönmez C (2013) Seismic Performance of Wide-Beam Infill-Joist Block RC Frames in Turkey. J Perform Constr Facil 29(1):04014026Fadwa I, Ali TA, Nazih E, Sara M (2014) Reinforced concrete wide and conventional beam-column connections subjected to lateral load. Eng Struct 76:34–48Fardis MN (2009) Seismic design, assessment and retrofitting of concrete, Buildings edn. Springer, LondonGentry TR, Wight JK (1992) Reinforced concrete wide beam-column connections under earthquake-type loading. Report no. UMCEE 92-12. Department of Civil and Environmental Engineering, University of Michigan, Ann Arbor, Michigan, USAGómez-Martínez F (2015) FAST simplified vulnerability approach for seismic assessment of infilled RC MRF buildings and its application to the 2011 Lorca (Spain) earthquake. Ph.D. Thesis, Polytechnic University of Valencia, SpainGómez-Martínez F, Pérez García A, De Luca F, Verderame GM (2015a) Comportamiento de los edificios de HA con tabiquería durante el sismo de Lorca de 2011: aplicación del método FAST. Informes de la Construcción 67(537):e065 (in Spanish)Gómez-Martínez F, Pérez-García A, Alonso Durá A, Martínez Boquera A, Verderame GM (2015b) Eficacia de la norma NCSE-02 a la luz de los daños e intervenciones tras el sismo de Lorca de 2011. In: Proceedings of Congreso Internacional sobre Intervención en Obras Arquitectónicas tras Sismo: L’Aquila (2009), Lorca (2011) y Emilia Romagna (2012), May 13–14, Murcia, Spain (in Spanish)Gómez-Martínez F, Verderame GM, De Luca F, Pérez-García A, Alonso-Durá, A (2015c). High ductility seismic performances of wide-beam RC frames. In; XVI Convegno ANIDIS. September 13–17, L'Aquila, ItalyHawkins NM, Mitchell D (1979) Progressive collapse of flat plate structures. 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