Current Issue : July - September Volume : 2018 Issue Number : 3 Articles : 5 Articles
Hydraulic factors account for a large part of the causes of bridge collapse. Due to the\nnature of the underwater environment, quick and accurate inspection is required when damage\noccurs. In this study, we developed a 2 MHz side scan sonar sensor module and effective operation\ntechnique by improving the limitations of existing sonar. Through field tests, we analyzed the\ncorrelation of factors affecting the resolution of the sonar data such as the angle of survey, the\ndistance from the underwater structure and the water depth. The effect of the distance and the water\ndepth and the structure on the survey angle was 66~82%. We also derived the relationship between\nthese factors as a regression model for effective operating techniques. It is considered that\napplication of the developed 2 MHz side scan sonar and its operation method could contribute to\nprevention of bridge collapses and disasters by quickly and accurately checking the damage of\nbridge substructures due to hydraulic factors....
The bending behavior of T-section beams composed of a glulam web and an upper cross-laminated timber flange was studied. The\ninfluence of two fundamental factors on the bending strength and stiffness was considered: the wood species used for the webs and\npretensioning with unbonded tendons. Sixteen specimens with a 9m span were tested until failure: eight of them were nontensioned\n(4 Picea abies webs and 4 Quercus robur webs) and the other eight were pretensioned using threaded bars with 20mm\ndiameter anchored in plates fixed at the ends of the specimens (4 Picea abies webs and 4 Quercus robur webs). Pretensioning with\nunbonded tendons showed a clear improvement in the load capacity of the specimens with Picea abies webs, while the difference\nwas not significant for the specimens with Quercus robur webs. Considering deflection, pretensioning gave the advantage of an\ninitial precamber but also generated slight variations in the stiffness as a result of increasing the portion of the section that was in\ncompression. The variation in the stiffness depended on the relation between the compressive and tensile moduli of elasticity\nparallel to the grain, and its influence on the deflection was analyzed using a finite element method....
The scope of the paper is to report an investigation on durability of infrastructure concrete\nfor roads and bridges by creating a size and shape-designed pore systems in concrete in order to\nimprove it, especially in terms of freezeââ?¬â??thaw resistance. By means of this experimental laboratory\nstudy, an alternative for usage of air entrainment agents (AEA) in concrete infrastructures was\nfound in the way of using superabsorbent polymer materials (SAPs). The effect of the addition of\nSAPs of different amounts and different types into fresh concrete mix was investigated, including:\ncompressive strength tests, weight loss measurements, visual and microscopic inspections and\nscanning electron microscopy (SEM) analysis. The detrimental strength reduction effect was not\nobserved. The freezeââ?¬â??thaw procedure was varied, using different types of de-icing salts and\nheating/cooling regimes. It can be concluded that an improvement of the freezeââ?¬â??thaw resistance of\nconcrete infrastructure depends on the particle size and optimal amount of SAPs added into concrete\nmix. The addition of 0.26 wt % of dry SAPs into the fresh concrete reference mix led to the significant\ndecrease of scaling up to 43% after 28 freezeââ?¬â??thaw cycles. Both dosage and particle size of the SAPs\nhad a significant impact on the obtained results and the freezeââ?¬â??thaw resistance in this experimental\nlaboratory study....
A research and development project has been conducted aiming to design and produce\nultra-thin concrete shells. In this paper, the first part of the project is described, consisting of an\ninnovative method for shape generation and the consequent production of reduced-scale models\nof the selected geometries. First, the shape generation is explained, consisting of a geometrically\nnonlinear analysis based on the Finite Element Method (FEM) to define the antifunicular of the shell�s\ndeadweight. Next, the scale model production is described, consisting of 3D printing, specifically\ndeveloped to evaluate the aesthetics and visual impact, as well as to study the aerodynamic behaviour\nof the concrete shells in a wind tunnel. The goals and constraints of the method are identified and\na step-by-step guidelines presented, aiming to be used as a reference in future studies. The printed\ngeometry is validated by high-resolution assessment achieved by photogrammetry. The results are\ncompared with the geometry computed through geometric nonlinear finite-element-based analysis,\nand no significant differences are recorded. The method is revealed to be an important tool for\nautomatic shape generation and building scale models of shells. The latter enables the performing\nof wind tunnel tests to obtain pressure coefficients, essential for structural analysis of this type\nof structures....
The fibre utilization efficiency of directionally distributed fibre-reinforced concrete is better than that of randomly distributed\nfibre. However, controlling the fibre direction is difficult, which limits its applications. In this paper, a method in which fibres were\nartificially directed was used to simulate the feasibility of orienting fibres during 3D concrete printing. Based on artificially\ndirected steel fibre-reinforced concrete specimens, the orientation characteristics of directional fibre-reinforced concrete\nspecimens were studied. The differences between the gravity and the boundary effects in ordinary fibre-reinforced concrete and\nartificially directed fibre-reinforced concrete were compared. The average orientation coefficient in randomly distributed fibrereinforced\nconcrete was 0.59, whereas this value in directionally distributed fibre-reinforced concrete was over 0.9. This result\ndemonstrated the feasibility of manually orienting the fibres in steel fibre-reinforced concrete in layer-by-layer casting....
Loading....