OPTIMISATION OF THICKNESS OF FIBRE REINFORCED POLYMER SHEETS FOR STRENGTHENING REINFORCED CONCRETE BEAMS WITH FLEXURAL DEFICIENCY

The use of Fiber Reinforced Polymer (FRP) is becoming a widely accepted solution for repairing and strengthening of deteriorated reinforced concrete members, to restore their load carrying capacities. One of the major concerns in the use of FRP is its cost. This therefore calls for the use of efficient and cost effective design approach. Design efficiency in terms of cost can be achieved through optimisation. In the present paper, Generalized Reduced Gradient (GRG) optimisation technique was employed to optimize the strengthening cost of a simply supported reinforced concrete beam strengthened with Fibre Reinforced Polymer (FRP). Optimum design charts for the considered problem were presented. The results showed that considerable savings in thickness can be achieved using FRP of high modulus of elasticity. For example at very high capacity reduction say 70% (kc = 0.3), the required FRP thicknesses for FRP with elastic moduli of 25GPa, 50GPa, 75GPa, 100GPa, 125GPa and 150GPa are respectively equal to 2.5mm, 1.75mm, 0.75mm, 0.6mm, 0.5mm and 0.4mm.  http://dx.doi.org/10.4314/njt.v36i1.

DEVELOPED PROBABILISTIC REDUCTION FACTORS FOR LOPHIRA ALATA (EKKI) TIMBER JOISTS SUBJECTED TO CREEP-RUPTURE

Wood experiences a significant loss of strength and stiffness when loaded over period of time. This phenomenon is known as creep-rupture. Several models were developed for the estimation of the reduction of load carrying capacity of timber with time. In this paper, the results of time dependent structural reliability analysis of timber joist produced with Lophiraalata (Ekki) timber specie was presented. Three load duration models were considered in the study, namely: The Model proposed by Wood, Gerhards model, and Nielsen. The timber joist was designed in accordance with the Eurocode 5. The uncertainties in all the basic design variables were fully accommodated in the time dependent reliability analysis. The entire process was implemented using a developed MATLAB program employing First Order Reliability Method (FORM). Time dependent mathematical models for modification of safety index to account for the effect of load duration were proposed. The use of both Gerhards and Nielsen model, for the design of Lophiraalata timber members was recommended.  http://dx.doi.org/10.4314/njt.v36i1.

Probabilistic Evaluation of Eurocode 5 Fire Design Criteria of a Timber Portal Frame

Structural reliability analysis for a three-hinge timber portal frame subjected to fire was undertaken. Eight modes of failure were identified for the frame and limit state function was formulated for each failure mode. The limit state functions were based on the Eurocode 5 design criteria. Uncertainties in the timber material properties were generated from laboratory test results performed on five commonly used timber species in Nigeria, namely Alstonia boonei (Ahun), Triplochiton Scleroxylon (Obeche), Terminalia Ivorensis (Idigbo), Terminalia superba (Afara) and Lophira Alata (Ekki). Uncertainties in loading and geometrical properties were obtained from international references. The limit state functions were evaluated using nonlinear constrained optimization technique. The optimization was executed using Genetic Algorithms(GA) based First Order Reliability Method (FORM) algorithm, through a developed computer programme in MATLAB. The results indicated that, the predominant mode of failure for a three-hinged timber portal frame in fire is the failure of the rafter-column connection that resulted to least safety levels for all the considered fire exposure times. Also, it was observed that at the critical mode of failure the portal frame can sustain fire for up to 50 minutes before failure, however, the target safety index of 3.8 recommended in the Eurocode can only be achieved at fire exposure time less than or equal to 25 minutes.http://dx.doi.org/10.4314/njt.v34i1.

EFFECT OF UNCERTAINTY ON THE FATIGUE RELIABILITY OF REINFORCED CONCRETE BRIDGE DECK UNDER HIGH STRESS LOADS

The deterioration of reinforced concrete bridge deck that has been damaged as a result of load action can affect the durability, safety and function of the structure. In this paper, a reliability time-variant fatigue analysis and uncertainty effect on the serviceability of reinforced concrete bridge deck was carried out. A simply supported 15m bridge deck was specifically used for the investigation. Mathematical models were developed and the uncertainties in structural resistance, applied loadings as well as the structural components were accommodated using probabilistic method. The limit state functions were evaluated using the First Order Reliability Algorithm and the entire process was implemented using a developed MATLAB program called Rayswit.m. Failure in the deck shear region gave the most critical effect with a reliability index range of 6.95 to -12.38 when compared to flexure region with an index of 8.58 to -10.53. http://dx.doi.org/10.4314/njt.v35i3.

Effects of Cocaine-Kindling on the Expression of NMDA Receptors and Glutamate Levels in Mouse Brain

In the present study we examined the effects of cocaine seizure kindling on the expression of NMDA receptors and levels of extracellular glutamate in mouse brain. Quantitative autoradiography did not reveal any changes in binding of [3H] MK-801 to NMDA receptors in several brain regions. Likewise, in situ hybridization and Western blotting revealed no alteration in expression of the NMDA receptor subunits, NR1 and NR2B. Basal overflow of glutamate in the ventral hippocampus determined by microdialysis in freely moving animals also did not differ between cocaine-kindled and control groups. Perfusion with the selective excitatory amino acid transporter inhibitor, pyrrolidine-2,4-dicarboxylic acid (tPDC, 0.6 mM), increased glutamate overflow confirming transport inhibition. Importantly, KCl-evoked glutamate overflow under tPDC perfusion was significantly higher in cocaine-kindled mice than in control mice. These data suggest that enhancement of depolarization stimulated glutamate release may be one of the mechanisms underlying the development of increased seizure susceptibility after cocaine kindling

Global patient outcomes after elective surgery: prospective cohort study in 27 low-, middle- and high-income countries.

BACKGROUND: As global initiatives increase patient access to surgical treatments, there remains a need to understand the adverse effects of surgery and define appropriate levels of perioperative care. METHODS: We designed a prospective international 7-day cohort study of outcomes following elective adult inpatient surgery in 27 countries. The primary outcome was in-hospital complications. Secondary outcomes were death following a complication (failure to rescue) and death in hospital. Process measures were admission to critical care immediately after surgery or to treat a complication and duration of hospital stay. A single definition of critical care was used for all countries. RESULTS: A total of 474 hospitals in 19 high-, 7 middle- and 1 low-income country were included in the primary analysis. Data included 44 814 patients with a median hospital stay of 4 (range 2-7) days. A total of 7508 patients (16.8%) developed one or more postoperative complication and 207 died (0.5%). The overall mortality among patients who developed complications was 2.8%. Mortality following complications ranged from 2.4% for pulmonary embolism to 43.9% for cardiac arrest. A total of 4360 (9.7%) patients were admitted to a critical care unit as routine immediately after surgery, of whom 2198 (50.4%) developed a complication, with 105 (2.4%) deaths. A total of 1233 patients (16.4%) were admitted to a critical care unit to treat complications, with 119 (9.7%) deaths. Despite lower baseline risk, outcomes were similar in low- and middle-income compared with high-income countries. CONCLUSIONS: Poor patient outcomes are common after inpatient surgery. Global initiatives to increase access to surgical treatments should also address the need for safe perioperative care. STUDY REGISTRATION: ISRCTN5181700

EN 338 Strength Grade and Uncertainty Models of Material Properties for Nigerian Grown Terminalia Superba (White Afara) Timber Specie

In this paper, the EN 338 strength class of Nigerian grown Terminalia superba timber specie was determined. This will enable the utilisation of the specie in the design of timber structures using Eurocode 5. The uncertainty models (mean, coefficients of variation and theoretical distribution models) of the tested specie were also generated. This information is required if structural reliability analysis and design is to be undertaken. The strength classification and the material properties were based on detailed laboratory experiment conducted on samples of the tested timber specie based on EN 408 (2004) and EN 13153-1 (2002). The laboratory data was analysed using an open source statistical computer package, Easyfit (2010) in accordance with EN 384 (2004). Terminalia superba was found to be of strength class D24 according to EN 338 (2009). The statistical analysis revealed that the coefficient of variation of modulus of elasticity is 21%. The coefficient of variations of both the bending strength and density is 19%. It was also found that, the best theoretical distribution models for density is normal distribution, while lognormal distribution was found to be the best distribution model for both bending strength and modulus of elasticity.  Due to the high coefficients of variation of material properties of timber as indicated in this study, it is recommended that EN 338 strength class should include the information on the statistical parameters of timber. With this, the design criteria of timber structures using Eurocode 5 can be enhanced by the use of structural reliability method in order to fully accommodate uncertainties.http://dx.doi.org/10.4314/njt.v34i1.