A sensitivity study of parameters used in shrinkage and creep prediction models

Over the last 15 years, there have been numerous models put forward for the prediction of the time-dependent behaviour of concrete and consequently concrete structures. The development of these models from a number of different sources has meant that the engineer now has a choice to make when undertaking creep and shrinkage prediction and it is difficult to know which is best suited for this purpose. Some are considerably more complex than others requiring greater amounts of input focusing on material data, concrete properties, environmental conditions, specimen geometry and loading conditions. The study reported here focuses on the sensitivity to change, in both the short term and over time, of the individual parameters that comprise the input and whether one model is more appropriate in any given situation. It has been found that for each model certain parameters are more sensitive than others. It is suggested that for any given model, the parameters that do not reflect the expected behaviour when changed counterbalance each other, cancelling out any errors. This further suggests that when deciding on which model to use when predicting shrinkage and creep strains it is prudent to look at the specific conditions that prevail, assess the relevant input parameters for which data are available, assess the sensitivity level of each of these parameters and then make a decision as to the most appropriate model to use

Long-term stress relaxation behavior of predrawn poly(ethylene terephthalate)

Research has been carried out with the aim of better understanding the relevant properties of materials to be used in a new self-healing cementitious composite material system. In a previous study, the buildup of stress in a heat-activated restrained predrawn poly(ethylene terephthalate) (PET) specimen was investigated. In the current study, the long-term stress relaxation behavior of such a restrained specimen has been explored so that its potential for use in the new material system can be better understood. The work includes an experimental study in which the stress in a number of PET specimens, restrained against longitudinal shrinkage, was measured during the initial heat activation and cooling phases, and then monitored for a further 6 months. These data were used to quantify the stress relaxation of the specimen and to inform the development of a new one-dimensional numerical model to simulate the thermomechanical behavior of this material. This model is shown to be able to reproduce the observed short- and long-term experimental behavior with good accuracy

Numerical simulation of the long-term behaviour of a self-healing concrete beam vs standard reinforced concrete

Research on the self-healing cementitious composite material system named LatConX is presented, with predictions made as to the effectiveness of the system in limiting crack widths in concrete beams subjected to sustained loads. A layered beam numerical model for the transient thermo-mechanical behaviour of reinforced concrete has been developed and coupled to a previously published numerical model for transient thermo-mechanical behaviour of a shape memory polymer. The combined model has been validated by comparison with experimental data. Finally, the model is used to predict ten-year crack widths in standard reinforced concrete beams, and in beams employing the LatConX system. These results indicate that the LatConX system has the potential to reduce crack widths by up to 65% when compared with an identical beam without the LatConX system

Experimental investigation of adhesive-based self-healing of cementitious materials

This paper presents the results of a series of self-healing experiments conducted on reinforced mortar beams containing adhesive-filled glass reservoirs. An overview of the findings of the preliminary investigation stage of experiments is given in addition to the results of a parametric study which investigates the effect of the level of reinforcement and loading rate on the amount of self-healing. Results show that both primary and secondary healing occurs during the first and second loading cycles respectively. Qualitative results also show clear evidence of the occurrence of crack-healing following the first loading cycle and new crack formation during the second loading cycle. The long-term motivation for this work is to provide data suitable for the development of a numerical material model for the autonomic healing process in cementitious materials

A shape memory polymer concrete crack closure system activated by electrical current

YesThe presence of cracks has a negative impact on the durability of concrete by providing paths for corrosive materials to the embedded steel reinforcement. Cracks in concrete can be closed using shape memory polymers (SMP) which produce a compressive stress across the crack faces. This stress has been previously found to enhance the load recovery associated with autogenous selfhealing. This paper details the experiments undertaken to incorporate SMP tendons containing polyethylene terephthalate (PET) filaments into reinforced and unreinforced 500 × 100 × 100 mm structural concrete beam samples. These tendons are activated via an electrical supply using a nickelchrome resistance wire heating system. The set-up, methodology and results of restrained shrinkage stress and crack closure experiments are explained. Crack closure of up to 85% in unreinforced beams and 26%–39% in reinforced beams is measured using crack-mouth opening displacement, microscope and digital image correlation equipment. Conclusions are made as to the effectiveness of the system and its potential for application within industry.EPSRC for their funding of the Materials for Life (M4L) project (EP/K026631/1) and Costain Group PLC for industrial sponsorship of the project and autho

Chikungunya as a cause of acute febrile illness in southern Sri Lanka

10.1371/journal.pone.0082259PLoS ONE812-POLN

Endemic Venezuelan Equine Encephalitis in Northern Peru

Since Venezuelan equine encephalitis virus (VEEV) was isolated in Peru in 1942, >70 isolates have been obtained from mosquitoes, humans, and sylvatic mammals primarily in the Amazon region. To investigate genetic relationships among the Peru VEEV isolates and between the Peru isolates and other VEEV strains, a fragment of the PE2 gene was amplified and analyzed by single-stranded conformation polymorphism. Representatives of seven genotypes underwent sequencing and phylogenetic analysis. The results identified four VEE complex lineages that cocirculate in the Amazon region: subtypes ID (Panama and Colombia/Venezuela genotypes), IIIC, and a new, proposed subtype IIID, which was isolated from a febrile human, mosquitoes, and spiny rats. Both ID lineages and the IIID subtype are associated with febrile human illness. Most of the subtype ID isolates belonged to the Panama genotype, but the Colombia/Venezuela genotype, which is phylogenetically related to epizootic strains, also continues to circulate in the Amazon basin

A Simple Genetic Architecture Underlies Morphological Variation in Dogs

The largest genetic study to date of morphology in domestic dogs identifies genes controlling nearly 100 morphological traits and identifies important trends in phenotypic variation within this species