Tension stiffening in concrete beams. Part 2: Member analysis

Based on finite-element analysis of cracked reinforced concrete beams, a tensile stress block was proposed in part 1 of this paper. Here, the proposed tensile stress block is contrasted with existing ones developed by others to provide an overall review. The proposed tensile stress block is then applied to a section analysis of beams to evaluate the moment-curvature curves of typical beam sections. The section analysis results are compared with available experimental results and empirical curves given in design codes to demonstrate the validity of the tensile stress block. Subsequently, the proposed tensile stress block is applied to member analysis by first dividing the beam member into short segments and then applying section analysis to each segment to evaluate the load- deflection curves of typical beam members. The member analysis results are checked against finite-element analysis results and available experimental results to fine-tune the tensile stress block and verify the accuracy of the finetuned tensile stress block. Such member analysis could be extended to multi-level analysis of frame structures for their full-range load-deflection behaviour at the elastic, post-crack and post-peak states.published_or_final_versio

Tension stiffening in concrete beams. Part 1: FE analysis

Although after cracking, concrete has negligible tension capacity, the intact concrete between cracks within the tension zone of a reinforced concrete beam can still develop significant tensile stresses to contribute to the flexural stiffness of the concrete beam. Such a tension stiffening effect in a flexural member is not quite the same as that in an axial member because the tensile stresses in a cracked flexural member are induced not only by the steel reinforcement-concrete bond but also by the curvature of the flexural member. In this study, the tensile stresses developed in cracked concrete beams are analysed using a finite-element (FE) model that takes into account the non-linear biaxial behaviour of the concrete and the non-linear bond stress-slip behaviour of the steel reinforcement-concrete interface. Based on the numerical results so obtained, a tensile stress block is proposed for section analysis of the moment-curvature curves of reinforced concrete beams at both the uncracked and cracked states. It will be shown in part 2 of this paper that the tensile stress block may also be used for member analysis of the load-deflection curves of concrete beams without resorting to FE analysis.published_or_final_versio

Modelling dowel action of discrete reinforcing bars in cracked concrete structures

AIP Conference Proceedings, vol. 1233 entitled: ISCM II and EPMESC XII : proceedings of the 2nd International Symposium on Computational Mechanics and the 12th International Conference on the Enhancement and Promotion of Computational Methods in Engineering and Science, Hong Kong-Macau, China, 30 November-3 December 2009Dowel action is one of the component actions for shear force transfer in cracked reinforced concrete. In finite element analysis of concrete structures, the use of discrete representation of reinforcing bars is considered advantageous over the smeared representation due to the relative ease of modelling the bond-slip behaviour. However, there is very limited research on how to simulate the dowel action of discrete reinforcing bars. Herein, a numerical model for dowel action of discrete reinforcing bars crossing cracks in concrete is developed. The model features the derivation of dowel stiffness matrix based on beam-on-elastic-foundation theory and the direct assemblage of dowel stiffness into the concrete element stiffness matrices. The dowel action model is incorporated in a nonlinear finite element programme with secant stiffness formulation. Deep beams tested in the literature are analysed and it is found that the incorporation of dowel action model improves the accuracy of analysis. © 2010 American Institute of Physics.published_or_final_versio

Clinical predictors of sputum microbiology in chronic Chinese bronchiectasis

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The relationship between sputum microbial load and inflammatory indices in bronchiectasis

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CT features of advanced lymphoepithelioma-like carcinoma (LELC)

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Erythromycin is highly efficacious in chronic bronchiectasis

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Increase in methicillin-resistant Staphylococcus aureus acquisition rate and change in pathogen pattern associated with an outbreak of severe acute respiratory syndrome

Background. An outbreak of severe acute respiratory syndrome (SARS) occurred in our 22-bed intensive care unit (ICU; Prince of Wales Hospital, Hong Kong, HKSAR, China) from 12 March to 31 May 2003, when only patients with SARS were admitted. This period was characterized by the upgrading of infection control precautions, which included the wearing of gloves and gowns all the time, an extensive use of steroids, and a change in antibiotic prescribing practices. The pattern of endemic pathogenic organisms, the rates of acquisition of methicillin-resistant Staphylococcus aureus (MRSA), and the rates of ventilator-associated pneumonia (VAP) were compared with those of the pre-SARS and post-SARS periods. Methods. Data on pathogenic isolates were obtained from the microbiology department (Prince of Wales Hospital). Data on MRSA acquisition and VAP rates were collected prospectively. MRSA screening was performed for all ICU patients. A case of MRSA carriage was defined as an instance in which MRSA was recovered from any site in a patient, and cases were classified as imported or ICU-acquired if the first MRSA isolate was recovered within 72 h of ICU admission or after 72 h in the ICU, respectively. Results. During the SARS period in the ICU, there was an increase in the rate of isolation of MRSA and Stenotrophomonas and Candida species but a disappearance of Pseudomonas and Klebsiella species. The MRSA acquisition rate was also increased: it was 3.53% (3.53 cases per 100 admissions) during the pre-SARS period, 25.30% during the SARS period, and 2.21% during the post-SARS period (P < .001). The VAP rate was high, at 36.5 episodes per 1000 ventilator-days, and 47% of episodes were caused by MRSA. Conclusions. A SARS outbreak in the ICU led to changes in the pathogen pattern and the MRSA acquisition rate. The data suggest that MRSA cross-transmission may be increased if gloves and gowns are worn all the time.published_or_final_versio

Anti-inflammatory effects of fluticasone in bronchiectasis

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Regional white matter anisotropy and general intelligence in preterm born children: a voxelwise analysis

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