Assessment of Highway Bridge Upgrading by Dynamic Testing and Finite-Element Model Updating

The Land Transport Authority of Singapore has a continuing program of highway bridge upgrading for refurbishing and strengthening bridges to allow for increasing vehicle traffic and increasing axle loads. One subject of this program has been a short-span bridge taking a busy main road across a coastal inlet near a major port facility. Experiment-based structural assessments of the bridge were conducted before and after upgrading works including strengthening. Each assessment exercise comprised three separate components: (1) a strain and acceleration monitoring exercise lasting approximately one month; (2) a full-scale dynamic test carried out in a single day without closing the bridge; and (3) a finite-element model updating exercise to identify structural parameters and mechanisms. This paper presents the dynamic testing and the modal analysis used to identify the vibration properties and the quantification of the effectiveness of the upgrading through the subsequent model updating. Before and after upgrade, similar sets of vibration modes were identified, resembling those of an orthotropic plate with relatively weak transverse bending stiffness. Conversion of bearings from nominal simple supports to nominal full fixity was shown via model updating to be the principal cause of natural frequency increases of up to 50%. The utility of the combined experimental and analytical process in direct identification of structural properties has been proven, and the procedure can be applied to other structures and their capacity assessments.     

Theory and application of Agricultural Innovation Platforms for improved irrigation scheme management in Southern Africa

Abstract

Many small-scale irrigation systems are characterized by low yields and deteriorating infrastructure. Interventions often erroneously focus on increasing yields and rehabilitating infrastructure. Small-scale irrigation systems have many of the characteristics of complex socio-ecological systems, with many different actors and numerous interconnected subsystems. However, the limited interaction between the different subsystems and their agents prevents learning and the emergence of more beneficial outcomes. This article reports on using Agricultural Innovation Platforms to create an environment in which irrigation scheme actors can engage, experiment, learn and build adaptive capacity to increase market-related offtake and move out of poverty.     

M?ssbauer and Electrical Studies of Mn x Co1?x Fe2O4 Compounds Prepared via Glycothermal Route

Manganese-cobalt ferrite powders (Mn _x Co_1?x Fe₂O₄ with x varying from 0.0 to?0.6) have been produced by glycothermal process from pure metal chlorides. Single phase cubic spinel structure and nanophase structure of the as-synthesized samples were confirmed by X-ray diffraction (XRD) and by transmission electron microscope (TEM). The results show that the produced powders have grain sizes in the range 7 to 13?nm. Fe-57 M?ssbauer spectra for as-synthesized and for annealed samples at 700???C (in Ar atmosphere for 1?hour) are found to be similar. No significant changes in the spectra are observed across the composition range studied. The variations of grain sizes, lattice parameters, and M?ssbauer parameters as a function of composition have also been investigated. Bulk samples in the form of pellets were also produced from the as-synthesized compounds for resistivity measurements. The temperature dependence of the electrical resistivity for the samples sintered at 1050???C were studied using the four-probe method, from room temperature to about 110???C in a PID controlled oven. Two possible mechanisms for resistivity involving T ^?1/2 and T ^?1 dependences are investigated.     

Relaxation characteristics of cement mortar subjected to tensile strain

Tensile relaxation characteristics are important for the crack resistance of concrete members subjected to restrained contraction, for example bonded overlays and patch repairs. In the experimental research discussed in this paper, relaxation characteristics were measured for mortar specimens subjected to constant strain which corresponded to stresses close to the tensile strength of the mortar. Relaxation was found to relieve a considerable portion of tensile stresses. Ultimate relaxation values ranged from 20 to 45%, depending on w/c ratio and specimen age. As expected, a decrease in specimen age and an increase in w/c ratio resulted in increasing relaxation values. The rate of stress decay was found to be rapid, with approximately 80% of the ultimate relaxation occurring in the first 12?h after loading. A basic equation for the prediction of time development of relaxation is proposed and future research needs are discussed.     

Effect of alcohol pretreatment in conjunction with atmospheric pressure plasmas on hydrophobizing ramie fiber surfaces

To improve interfacial adhesion between hydrophilic cellulose fiber and hydrophobic polymer matrix, ramie fibers were pretreated with isopropanol and n-butanol and then plasma treated using an atmospheric pressure plasma apparatus. For the plasma-treated fibers, the scanning electron microscopy shows increased surface roughness and the X-ray photoelectron spectroscopy analysis shows a significant increase of C–C bond in isopropanol-pretreated group, whereas for n-butanol-pretreated group the raise of C=O bonds is most noticeable. For both alcohol-pretreated and plasma-treated groups, the water contact angles increase significantly. Microbond pull-out test shows interfacial shear strengths of fiber/polypropylene (PP) samples increase by 47 and 34%, respectively, for the two groups compared with the control. Therefore, it can be concluded that the reaction between both alcohols and cellulose induced by plasma can indeed create a fiber surface with increased roughness and decreased polarity, and thus is more compatible to PP.     

Behaviour of RC beams corroded under sustained service loads

This paper presents the results of an experimental study conducted to characterize the structural behaviour of reinforced concrete beams corroded whilst subjected to constant sustained service loads. Corrosion of tensile steel bars was induced by an accelerated corrosion process using a 5% solution of NaCl and a constant impressed current. Four RC beams were tested, each with a width of 153 mm, a depth of 254 mm and a length of 3000 mm. Beams were tested whilst under a load equivalent to 1%, 8% and 12% of the ultimate load. Longitudinal tensile and compressive strains were monitored during the corrosion process and used to determine the variation of the depth of the neutral axis, the curvature and the second moment of area of beams with the time of electrolysis. The results indicate that the longitudinal strains, the depth of the neutral axis and the curvature of beams depend on both the level of corrosion and the applied service load whilst the second moment of area is mostly influenced by the level of corrosion.     

Resistance and Resilience by Informal Traders in Bulawayo,Zimbabwe: Beyond Weapons of the Weak

Based on Bulawayo, the second largest city in Zimbabwe, this paper shows that the growth of urban informality can be explained by shifts in the Zimbabwean economy. These shifts include the corporatist socialist ideology phase (1980–1989), the era of neoliberal economic policies (1990–1997) and the return to restrictionism and reign of predatory politics (1998–present). Instead of triggering economic growth, these changes led to falling industrial production and declining levels of growth, leading to unemployment. This provided a fertile ground for the growth of the informal sector, such as informal street traders (informal traders). Utilising a qualitative study of 200 informal street traders in Bulawayo, who were purposively sampled between June and December 2013, the paper argues that the presence of such traders in Bulawayo is a form of both covert and overt resistance to the local and central government. Such a response by the informal traders highlights resistance and resilience, first to the economic crisis and secondly to the local and central government, which failed to meet their employment needs. This resistance has taken surreptitious forms, such as dodging municipality police patrols or staying hidden from the regulatory regimes (weapons of the weak), but has also graduated beyond this, taking the form of open defiance of and resorting to legal means to fight the regulatory regimes (beyond weapons of the weak). In this way, the paper offers a nuanced analysis of the enduring presence of street traders in a setting where there is a vibrant and repressive regulatory regime. Further, because urban informality is an integral part of urbanisation in the Global South, there is need for strategies that progressively integrate these economic actors.     

The Effect of Annealing Temperature on the Magnetic Properties of Mn x Co1?x Fe2O4 Ferrites Nanoparticles

Mn _x Co_1?x Fe₂O₄ ferrites compounds (0??x??0.6) have been synthesized by a glycol-thermal method from high-purity metals chlorides. Single phase spinel structure of the nanoparticles has been confirmed by X-ray diffraction (XRD) and transmission electron microscopy (TEM) measurements. The diameters of the as-prepared powders were estimated from XRD and TEM and were found to be in the range: 7 to 13?nm. Room temperature magnetizations were obtained using a vibrating sample magnetometer (VSM) on the as-prepared samples and on samples annealed at 500 and 700?°C. The variation of coercive fields, saturation and remnant magnetizations as a function of composition (x) and grain size have been investigated. ⁵⁷Co M?ssbauer spectra for as-prepared samples were also measured at different temperatures (27, 100, and 200?°C). Significant changes in magnetization properties and M?ssbauer parameters are observed across the composition range studied. The variation of coercive fields and saturation magnetizations appear to critically depend on the particle sizes as the compounds evolve from single domain to multidomain structure.