Effect of Different Factors on the Service Life of Concrete Structures in Chloride Environments: A Parametric Study – Part One

This paper presents a comprehensive parametric study to determine the effect of different factors on the service life of reinforced concrete structures in chloride-laden environment. A model for corrosion initiation is selected and solved numerically by Finite Element Method for one-dimensional diffusion problem. It has been found that increase in water to cement ratio by 12.5%-50% in range of 0.20-0.40reduces the service life by 8%-35%, and by 7.35%-30.5% for the range 0.40-0.60. Also, the increase in concrete cover in the range of 20-35 mm by 14%-42%increases the service life by 8.1%-25.8%, and in the range of 35-60 mm by 7.7%-21.8%.Regarding mineral admixtures, the addition of fly ash and blast-furnace slag resulted in enhances the service life by 8%-70.7% due to increase of age factor by 25%-200%. Moreover,the addition of silica fume by 5%-15% increases the service life by 25.5%-80.6%.Finally, the rise of temperature by 25%-75% reduces the service life by 6.45%-18.7%, and the reduction of relative humidity by 25%-50% increases the life by 21.2%-89%. These values are based on a conservative approach and tend to guide the practice engineer on how these parameters affect service life of concrete structures

Effect of Different Factors on the Service Life of Concrete Structures in Chloride Environment: A Parametric Study - Part Two

In this paper, the effect of different factors on the service life of reinforced concrete structures in marine environments is investigated through a parametric study. The considered case for the study was the two- dimensional diffusion problem. By solving the selected model for corrosion initiation by Finite Element Method, it has been concluded that, corrosion initiates at corner bars before side bars. Also, concrete elements subjected to two-dimensional diffusion are more susceptible to corrosion initiation than elements subjected to one-dimensional diffusion. Moreover, increase in water to cement ratio by 12.5%-50% in range 0.20-0.40 reduces the service life by 6.2%-31%, and by 5.3%-16.9% for the range 0.40-0.60. And, the increase in concrete cover in the range of 20-40 mm by 12.5% - 50% increases the service life by 5.1%-18.8%, and in the range of 35-60 mm by 2.9%-10.3%. The addition of fly ash and blast-furnace slag increased the service life by 6.35%-69.7% due to increase of age factor by 25%-200%. Furthermore, the addition of silica fume by 5%-15% increases the service life by 21.7%-81.2%. Regarding the environmental factors, increasing of temperature by 25%-75% reduces service life by 4.7%-12.75%, and reducing of relative humidity by 25%-50% increases the life by 17.5%-90.4%.are also given

Synthesis, Characterization and Biological Evaluation of some New Thieno[2,3-d]Pyrimidine Derivatives

10-Oxo-4,6,7,8,9,10-hexahydroprazolo[1,5-a][1]benzothieno[2,3-d]pyrimidine-3-carbaldehyde (2) was prepared by Vilsmeier-Haack reaction of 3-amino-2-methyl-5,6,7,8-tetrahydro[1]benzothieno[2,3-d]pyrimidin-4(3H)-one (1). Reaction of carbaldehyde derivative 2 with malononitrile afforded arylidene malononitrile 3. Cyclization of the latter compound with thiourea yielded pyrimidinethione 4. Interaction of carbaldehyde derivative 2 in presence of thiourea with keto- compounds such as ethyl acetoacetate, or acetylacetone, or dimedone or ethyl cyanoacetate gave pyrimidine derivatives 5-8. Hydrazinolysis of carbaldehyde derivative 2 gave the hydrazone 9. Reaction of the latter with phenyl isothiocyanate afforded thiosemicarbazone 10, which underwent cyclization with oxalyl chloride to give thioxoimidazolidinedione 11. Condensation of compound 2 with thiosemicarbazide furnished thiosemicarbazone derivative 12. Reaction of compound 2 with aminopyrazolone in the presence of an acid and/or a base afforded pyrazolones 13 and 14. Treatment of carbaldehyde derivative 2 with cyanoacetohydrazide gave acrylohydrazide 15. Interaction of the latter with carbon disulfide yielded mercaptooxadiazole 16.  Condensation of compound 2 with acetylpyridazinone 17 produced chalcone 18. Reaction of  compound 18 with malononitrile in pyridine gave cyanopyran 19, while its reaction with malononitrile in presence of ammonium acetate in ethanol yielded cyanopyridine 20. Structures of the newly synthesized products have been deduced on the basis of elemental analysis and spectral data. The synthesized compounds were screened for their antimicrobial activity.Â

NUMERICAL INVESTIGATION OF THE PERFORMANCE OF INSULATED FRP-STRENGTHENED REINFORCED CONCRETE BEAMS IN FIRE

Fiber reinforced polymers (FRP) have been widely used in retrofitting and strengthening of deteriorated or deficient reinforced concrete (RC) elements. A major concern about those systems is their performance under elevated temperature which limits the application of FRP for strengthening requirements. Fire protection of the strengthening FRP system can be made by applying an external coating layer of a thermal resisting material. In order to predict the fire performance of such insulated FRP-strengthened members and their efficiency, experimental investigations are required to be carried out for such elements under realistic fire conditions, which requires time and cost. This paper presents numerical modelling of RC beams strengthened with externally bonded FRP and insulated by a fire protection layer under elevated temperature specified by standard fire tests. The nonlinear time domain transient thermal-stress finite element analysis is performed using the general purpose software ANSYS 12.1 in order to study the heat transfer mechanism and deformation within the beam for fire conditions initiating at the bottom side of the beam. The finite element model accounts for the variation in thermal and mechanical parameters of the constituent materials such as concrete, steel reinforcement bars, FRP and insulation material with temperature. Application is made on an FRP-strengthened and insulated RC T-beam which has been experimentally tested in the published literature in order to verify the adopted modelling procedure. The obtained numerical results are in good agreement with the experimental results regarding the temperature distribution across the beam and mid-span deflection. The presented procedure thus provides an economical and effective tool to investigate the effectiveness of fire insulation layers when subjected to high temperatures and to design thermal protection layers for FRP strengthening systems that satisfy fire resistance requirements specified in building codes and standards

A Comparative Study of Prediction Techniques for Supersonic Missile Aerodynamic Coefficients / Loai A. El-Mahdy … [et al.]

Evaluating the aerodynamic coefficients of flying vehicles such as missiles is a key step in their design and development procedures. In practice, the aerodynamic coefficients can be estimated using experimental measurements, numerical simulations, or using empirical and semi-empirical engineering tools. In the present paper, these three approaches are compared in the context of examining the aerodynamic coefficients of a fin-stabilized tactical missile. Supersonic flight conditions up to Mach 4 at incidence up to 18 degrees are considered. Lift and drag coefficients as well as the centre of pressure locations based on the three approaches are compared. The flow features around the missile are explored based on the numerical simulations

Impact of opioid-free analgesia on pain severity and patient satisfaction after discharge from surgery: multispecialty, prospective cohort study in 25 countries

Background: Balancing opioid stewardship and the need for adequate analgesia following discharge after surgery is challenging. This study aimed to compare the outcomes for patients discharged with opioid versus opioid-free analgesia after common surgical procedures.Methods: This international, multicentre, prospective cohort study collected data from patients undergoing common acute and elective general surgical, urological, gynaecological, and orthopaedic procedures. The primary outcomes were patient-reported time in severe pain measured on a numerical analogue scale from 0 to 100% and patient-reported satisfaction with pain relief during the first week following discharge. Data were collected by in-hospital chart review and patient telephone interview 1 week after discharge.Results: The study recruited 4273 patients from 144 centres in 25 countries; 1311 patients (30.7%) were prescribed opioid analgesia at discharge. Patients reported being in severe pain for 10 (i.q.r. 1-30)% of the first week after discharge and rated satisfaction with analgesia as 90 (i.q.r. 80-100) of 100. After adjustment for confounders, opioid analgesia on discharge was independently associated with increased pain severity (risk ratio 1.52, 95% c.i. 1.31 to 1.76; P < 0.001) and re-presentation to healthcare providers owing to side-effects of medication (OR 2.38, 95% c.i. 1.36 to 4.17; P = 0.004), but not with satisfaction with analgesia (beta coefficient 0.92, 95% c.i. -1.52 to 3.36; P = 0.468) compared with opioid-free analgesia. Although opioid prescribing varied greatly between high-income and low- and middle-income countries, patient-reported outcomes did not.Conclusion: Opioid analgesia prescription on surgical discharge is associated with a higher risk of re-presentation owing to side-effects of medication and increased patient-reported pain, but not with changes in patient-reported satisfaction. Opioid-free discharge analgesia should be adopted routinely

NONLINEAR FINITE ELEMENT ANALYSIS OF INSULATED FRP STRENGTHENED REINFORCED CONCRETE COLUMNS SUBJECTED TO FIRE

In recent decades, Fiber Reinforced Polymers (FRP) have shown tremendous potential for retrofitting or repairing existing deficient or damaged concrete structural elements due to their superior properties such as high strength, corrosion resistance and ease of application. However, concern arises about the vulnerability of FRP material to combustion under fire condition, since they are usually applied to the exterior surface of structural members. Damage of the FRP strengthening layer due to high temperature is likely to decrease the load carrying capacity of the columns and threaten the safety of the structure. This paper presents numerical investigation of the behaviour of reinforced concrete (RC) columns strengthened with FRP sheets and insulated by a thermal resisting coating under service load and fire conditions. The finite element numerical modelling and nonlinear analysis are made using the nonlinear finite element analysis software ANSYS 12.1 [1]. The numerical model is verified for several FRP confined and insulated RC columns that have been experimentally tested under service load and standard fire tests in the published literature. The obtained numerical results are in good agreement with the experimental ones regarding the temperature distribution and axial deformation response. Consequently, the presented modelling gives an economic tool to investigate the behaviour of loaded FRP strengthened RC columns under high temperatures occurring in case of fire, if the modelling is verified against experimental works. Furthermore, the model can be used to design thermal protection layers for FRP strengthened RC columns to fulfill fire resistance requirements specified in building codes and standards

NUMERICAL INVESTIGATION OF FRP-STRENGTHENED REINFORCED CONCRETE BEAMS AT HIGH TEMPERATURES

Fiber reinforced polymers (FRP) strengthening systems are mainly used to retrofit existing and deficient structural members. The performance of such strengthened structures at elevated temperatures is a critical issue that threatens the safety of the structure. Published research includes experimental testing of reinforced concrete (R.C) beams strengthened using FRP and subjected to fire tests. However, there is a need for numerical tools that simulate the performance of these FRP-strengthened elements in case of fire. This research work presents numerical modelling and nonlinear analysis conducted to assess the performance of reinforced concrete beams strengthened with externally bonded carbon FRP sheets when subjected to standard fire conditions. Finite element model using the general purpose software ANSYS 12.1 is developed and validated with experimental results published in the literature by other researchers.The developed finite element model achieved good correlation with the experimental results. Further, application of the validated finite element model is extended into a parametric study to explore the influence of different variables on the performance of the FRP system when subjected to fire. Different aggregate types, moisture contents, concrete cover thickness, insulation material types and insulation material thickness are included in the study. The developed finite element model is thus regarded a valid and economical alternative to experiments for prediction of the performance of FRP strengthened and insulated R.C beams under fire conditions. Additionally, it can be used for estimation of the fire rating of such structures as well as for design of adequate fire protection layers

APPLICATION OF AEM IN PROGRESSIVE COLLAPSE DYNAMICS ANALYSIS OF R.C. STRUCTURES

The Finite Element Method (FEM) and the other numerical strategies are viably actualized in linear and non-linear analysis of structures. Recently, a new displacement based on Applied Element Method (AEM) has been developed. It is applicable for static and dynamic for both linear and non-linear analysis of framed and continuum structures. In AEM, the structural member is partitioned into virtual elements connected through normal and shear springs representing stresses and strains of certain portion of structure. FEM assumes the material as continuous and can indicate highly stressed region of structure, however it is difficult to model separation of element unless crack location is known. The main advantage of AEM is that it can track the structural collapse behavior going through all phases of the application of loads. In the current research, the application of AEM is illustrated through a non-linear dynamic analysis. Progressive collapse simulation is conducted using Extreme Loading for Structures software (ELS), which follows the AEM. The experimental and analytical works carried by Park et al. [17 and 28] for 1/5 scaled 3 and 5 stories reinforced concrete structures are used for verification. Good matching between the experimental and numerical results has been obtained using ELS. Therefore, it can be confirmed that ELS is capable in simulating the structures’ behavior up to collapse. Furthermore, a study has been made to investigate the effect of considering the floor slabs on progressive collapse. The results show that considering slab in progressive collapse analysis of multistory buildings is important as neglecting the slabs’ contribution leads to incorrect simulation and uneconomic design