Improving flexural ductility of high-strength concrete beams

With the advent of advanced mineral and chemical admixtures, the strength level of concrete has been raised dramatically and high-strength concrete (HSC) is becoming more and more commonly used. However, HSC is generally more brittle than normal strength concrete. In fact, it has been shown that the use of HSC, if not properly controlled, could significantly reduce the flexural ductility of reinforced concrete beams. Herein, it is proposed to compensate for the reduction in flexural ductility owing to the use of HSC by adding compression and confining reinforcements. A parametric study based on complete moment-curvature analysis of beam sections made of different grades of concrete and provided with different amounts of tension, compression and confining reinforcements has been carried out to evaluate the increases in flexural ductility achievable by adding compression and confining reinforcements. From the numerical results, the compression and/or confining reinforcements needed to maintain a consistent level of minimum flexural ductility at all concrete strength levels have been determined and correlated to the concrete strength for direct evaluation in the design of HSC beams.published_or_final_versio

Theoretical study on effect of confinement on flexural ductility of normal and high-strength concrete beams

Compared with normal concrete, high-strength concrete has higher strength but is generally more brittle. Its use in a reinforced concrete structure, if not properly controlled, could lead to an unsustainable reduction in ductility. However, confinement could be provided to improve the ductility of the structure. In this study, the effects of concrete strength and confinement on the flexural ductility of reinforced concrete beams have been evaluated by means of complete moment-curvature analysis of beam sections cast in different concretes and provided with different confinements. The results reveal that the use of high-strength concrete at a constant tension steel ratio would increase the flexural ductility, but at a constant tension to balanced steel ratio would decrease the flexural ductility. In contrast, the provision of confinement would always increase the flexural ductility. It does this in two ways: first, it increases the balanced steel ratio so that, at the same tension steel ratio, the tension to balanced steel ratio is decreased; and second, it increases the residual strength and ductility of the concrete so that, at the same tension to balanced steel ratio, the flexural ductility of the beam section is increased.published_or_final_versio

Design of high-strength concrete beams subjected to small axial loads

In the design of reinforced concrete beams, the effects of small axial loads (axial load ≤ 0% of axial capacity of concrete section) are often ignored or at most only nominally allowed for. Moreover, the existing guidelines given in the various design codes are applicable only to beams cast of normal-strength concrete and designers are left to themselves to decide what to do when high-strength concrete is used. In this study, the effects of small axial loads on the flexural strength and ductility of normal- and high-strength concrete beams have been investigated by complete moment–curvature analysis of beam sections cast of different grades of concrete and subjected to different levels of axial load. The results revealed that the application of a small axial load has the beneficial effect of increasing the flexural strength but also the adverse effect of decreasing the flexural ductility. Based on the numerical results, simple formulae for estimating the effects of small axial loads and guidelines for the design of normal- and high-strength concrete beams subjected to small axial loads have been developed.published_or_final_versio

Ischaemic stroke related to branch artery disease: a missing link?

INTRODUCTION: Clinicians and researchers often classify atherosclerotic cerebral infarctions into large artery atherothrombotic disease (LAD) and small artery lacunar infarction (LACI), but this system of ‘dichotomisation’ cannot account for a substantial proportion of stroke cases. Twenty years ago, a third mechanism for cerebral infarction - branch artery disease (BAD) - was proposed. However, this concept was understudied and still remains an obscure entity. METHODS: Stroke patients admitted under the Neurology Unit of Queen Mary Hospital over a 24- month period were studied retrospectively. Patients with ischaemic stroke presumably due to atherosclerotic disease were classified according to their imaging +/– clinical findings into three groups: LAD, BAD, and LACI. Patients with BAD were further categorised into five BAD stroke syndromes based on radiological criteria. Clinical characteristics, vascular risk factors, results of vascular workup, and outcome among the various stroke subgroups were compared. RESULTS: A total of 720 patients with a diagnosis of stroke were admitted during the study period, including 123 LAD (17% of all stroke patients or 33% of all studied patients), 147 BAD (20% or 40%), and 102 LACI (14% or 27%). Among the BAD patients, the number of cases involving Heubner’s artery, lenticulostriatal arteries, anterior choroidal artery, thalamoperforating/geniculate arteries or paramedian pontine infarction were 0, 47, 45, 15 or 40 (0, 32, 31, 10 or 27%), respectively. Patients with BAD were the youngest among the three groups. As compared to LAD patients, BAD patients had lower NIHSS scores, were less often diabetic, and carotid stenosis was less common, while stenosis of the intracranial arteries were more frequently seen in BAD as compared to LACI patients. Mean follow-up period was 1085 days, and outcome of BAD patients was intermediate between LAD and LACI. Comparison of variables among the BAD stroke syndromes showed that they were a homogenous group of conditions. CONCLUSION: Despite being a rarely applied concept, BAD is the most prevalent subtype of ischaemic stroke in our study. The homogeneity among the BAD syndromes suggests they might represent a distinctive stroke entity. Although patients with BAD and LACI had similar degrees of neurological deficits on presentation, outcome in the former group was significantly worse than the latter.published_or_final_versionThe 15th Medical Research Conference; Department of Medicine, The University of Hong Kong, Hong Kong, 16 January 2010. In Hong Kong Medical Journal, 2010, v. 16 suppl. 1, p. 30, abstract no. 4

Herpes simplex encephalitis: how good are we in diagnosing this condition?

INTRODUCTION: Herpes simplex encephalitis (HSE) is the commonest sporadic infective encephalitis in Hong Kong. Early recognition of HSE, which relies on a high index of suspicion, is important as effective treatment is available. Empirical acyclovir is advocated for all cases of clinically suspected viral encephalitis. Electroencephalography (EEG) is a routine investigation in suspected HSE. METHODS: The EEG database of Neurodiagnostic Unit, Queen Mary Hospital, was reviewed retrospectively. All referrals from April 2006 to March 2009 with a diagnosis of suspected HSE treated with empirical intravenous acyclovir were identified. Their presenting features, imaging and laboratory findings, and final diagnoses were reviewed. RESULTS: During the study period, 60 patients (mean age, 51 years; range, 18-90 years, M:F ratio=13:7) underwent EEG for suspected HSE. Presenting features included fever (n=39), confusion (n=39), impaired consciousness (n=31), focal signs (n=15, seizure in 8), and headache (n=13). All patients underwent brain CT and 45 had MRI. The commonest imaging findings were unrelated old changes (n=20) and normal study (n=16). Lobar inflammation was detected in four patients. EEG was normal, showed diffused abnormalities, or focal/ multifocal abnormalities in 16, 31, or 13 patients, respectively. Lumbar puncture was performed in 59 patients. Total cell count was ≤10×106 /L in 68% of patients and CSF protein was <0.8 g/L in 51% of patients. Polymerase chain reaction for herpes simplex virus was positive in one out of 56 requests. Viral encephalitis was the final diagnosis in three patients (HSE=1, Japanese encephalitis=1, other virus=1). Other common diagnoses included meningitis (n=9), non-CNS sepsis (n=9), psychiatric illnesses (n=8), epileptic seizure (n=6), and acute stroke (n=5). CONCLUSION: Our findings demonstrate that we were exercising a high index of suspicion for diagnosing HSE. Our liberal use of empirical acyclovir was also consistent with the IDSA (Infection Diseases Society of America) recommendations. Despite our low threshold of investigating for HSE, only one case was identified over 3 years, suggesting HSE is an uncommon condition.published_or_final_versionThe 15th Medical Research Conference; Department of Medicine, The University of Hong Kong, Hong Kong, 16 January 2010. In Hong Kong Medical Journal, 2010, v. 16 suppl. 1, p. 29, abstract no. 4

Predicting Mendelian Disease-Causing Non-Synonymous Single Nucleotide Variants in Exome Sequencing Studies

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Brainstem encephalitis in neuromyelitis optica spectrum disorders

Poster: abstract no. 41published_or_final_versionThe 17th Medical Research Conference (MRC), Department of Medicine, the University of Hong Kong, Hong Kong, 14 january 2012. In Hong Kong Medical Journal, 2012, v. 18 suppl. 1, p. 3

AMPK Activators Suppress Cervical Cancer Cell Growth through Inhibition of DVL3 Mediated Wnt/β-Catenin Signaling Activity

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AMPK Activators Suppress Cervical Cancer Cell Growth through Inhibition of DVL3 Mediated Wnt/β-Catenin Signaling Activity

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Cerebral involvement in neuromyelitis optica spectrum disorders among Hong Kong Chinese

published_or_final_versionThe 16th Medical Resarch Conference (MRC), The University of Hong Kong, Hong Kong, China, 22 January 2011. In Hong Kong Medical Journal, 2011, v. 17, suppl. 1, p. 55, abstract no. 8