Evaluation of Ultimate Strength of Reinforced Concrete Beams Strengthened with FRP Sheets under Torsion

The ultimate torque of reinforced concrete (RC) members strengthened with fiber reinforced polymer (FRP) sheets does not only depend on the torque of RC members, but also on the FRP contribution to the torque. For structural design, predicting the accurate torsional capacity of the strengthened beams is considerably important. Three existing models for calculating the ultimate torsional moment of RC beams and two existing models for computing the FRP contribution to the ultimate torque are described and combined. Based on an experimental database collected from existing literature, six combinations were discussed and evaluated from the calculative values compared with the experimental results. The comparison shows that the combination of ACI 318 and fib Bulletin 14 models (Group 2), as well as Chinese and Ghobarah models (Group 6), can reasonably and accurately predict the ultimate torque of beams strengthened with FRP sheet. Furthermore, the ultimate torque of six boxsection beams strengthened with fully wrapping or U-wrap calculated by the Group 6 shows closely to the experimental results

Prediction of Optimal Design and Deflection of Space Structures Using Neural Networks

The main aim of the present work is to determine the optimal design and maximum deflection of double layer grids spending low computational cost using neural networks. The design variables of the optimization problem are cross-sectional area of the elements as well as the length of the span and height of the structures. In this paper, a number of double layer grids with various random values of length and height are selected and optimized by simultaneous perturbation stochastic approximation algorithm. Then, radial basis function (RBF) and generalized regression (GR) neural networks are trained to predict the optimal design and maximum deflection of the structures. The numerical results demonstrate the efficiency of the proposed methodology

Effectiveness of repair method using hybrid fiber reinforced polymer fabric on concrete-filled double skin steel tubular columns exposed to fire

Concrete-filled double skin steel tubular (CFDST) columns were often used in outdoor construction where fire is not a main concern. Therefore, this series of research deals with behaviour of CFDST columns after fire exposure, residual strength and method of repairing fire-damaged columns. This particular paper focused on the effectiveness of Hybrid Fiber Reinforced Polymer (FRP) repairing method. Total of 42 specimens were casted and 36 of the specimens were exposed to ASTM E-119 until the temperature of 600˚C. After that, the temperature was kept constant for 60 and 90 minutes. Out of 36 specimens that were exposed to fire, 24 of the specimens were repaired with FRP using hand lay-up method. All of the specimens (control, heated unrepaired and heated repaired) were subjected to concentric axial loading. It was found that by using Hybrid FRP, the ultimate strength at failure of repaired specimens greatly increased when compared to fire-damaged specimens to the extent of exceeding the control specimens. In addition, FRP is also effectively confined thinner outer steel tube than thicker outer steel tube. However, the effectiveness of Hybrid FRP repair method depends on several factor such as thickness of outer steel tube and maximum exposure time

Concrete-filled double skin steel tubular column with hybrid fibre reinforced polymer post fire repair

The concrete-filled double skin steel tubular (CFDST) column is becoming more popular nowadays due to its superior performance compared to conventional composite column and concrete-filled steel tubular (CFST) column. However, the use of this type of column is still limited to outdoor construction such as bridge piers and transmission towers where fire is not the main concern. Moreover, existing research studies on the CFDST column only focused on fire performance, and limited research studies can be found on the residual strength of theCFDSTcolumn. Residual strength can be used to determine the most suitable repair method needed in order to retrofit the column. Therefore, this study aims to study the effect of different parameters on the residual strength of the CFDST column. Among discussed parameters are the thickness of the outer steel tube (t0) and fire exposure time. In addition, this study also aims to determine the effectiveness of the repair method using Single and Hybrid fiber-reinforced polymer (FRP) of fire-damaged CFDST columns. CFDST columns were heated in accordance with ASTM E119-11: Standard Test Methods for Fire Tests of Building Construction and Materials until the temperature reached 600 °C. Afterwards, the temperature was kept constant for two different durations, i.e., 60 and 90 mins. The specimen was then left to cool down to room temperature inside the furnace before itwas taken out and repaired by Single and Hybrid FRP. The specimens were categorized into the following three groups: (1) unheated or control specimens, (2) heated and unrepaired specimens and (3) heated and repaired specimens. All specimens were subjected to axial compression loading until failure. The first and second category specimens failed by local outward buckling of outer steel tube, crushing of concrete and local buckling of inner steel tube, whereas specimens in the third category failed by rupture of FRP followed by similar local buckling and concrete crushing as those observed in first and second category specimens. Ultimate strength, secant stiffness and Ductility Index (DI) decreased as the temperature of the specimen increased. The loss in secant stiffness of thinner CFDST specimens exposed to 60 mins of fire exposure time is similar to thicker CFDST specimens exposed to 90 mins of fire exposure time regardless of their diameter. In addition, CFDST specimens exposed to 90 mins of fire exposure time were more ductile than control specimen. RSI and secant stiffness increased with the increase in fire exposure time. Interestingly, the highest RSI achieved is only 22% whichmeans the specimens were still able to carry more than 70% of their initial load after being exposed to 90 mins of fire exposure timewith only 3mmthickness of outer steel tube. Repairing the fire-damaged CFDST columns with Single and Hybrid FRP is proven to improve the ultimate compressive strength significantly. The increment in ultimate compressive strength is more pronounced in the specimen with Hybrid FRP and thinner outer steel tube. The secant stiffness and Ductility Index (DI) of repaired specimens were, however, not able to be restored to those of the control specimen

Physicomechanical assessments and heavy metals’ leaching potential of modified asphalt binders incorporating crumb rubber and tin slag powders

Industrial solid waste has been widely used as an alternative additive for bituminous material modification. This study aims to evaluate the basic properties and quantify the leaching potential of modified asphalt binders incorporating crumb rubber powder (CRP) from waste tires and tin slag (TS) for a local smelting company. Three percentages of CRP and TS, at 5, 10, and 15%, were considered. The conventional asphalt binder (PEN 60/70), CRP, and TS-based modified asphalt binders were analyzed for toxicity, softening point, penetration value, elastic recovery, torsional recovery (TR), and coatability index. The findings indicated that the addition of the waste materials led to no significant heavy metal content in the asphalt binder mix. Moreover, the basic and physical properties of the asphalt binders were also improved by 5, 10, and 15% of the waste, respectively. However, TS waste exhibited limited effects on all the parameters and had a 5% optimum dosage. The modified binders’ results showed that the CRP modified asphalt binders had fewer heavy metals and responded more to elastic recovery and coatability

研究解説 : Recent Developments in the Field of Bifurcation Analysis

This is a review paper about research works in the field of bifurcation analysis of geometrically nonlinear single-parameter conservative elastic structures. Only problems involving simple bifurcation point are treated. After a brief introduction, general theory of elastic stablity based on energy concept is first described. Direct and indirect methods for detecting bifurcation points and various path-switching strategies are then explained in the following two sections respectively. Lastly, a concluding remark about the present status of research activities regarding bifurcation analysis is given

Full Length Research Paper Proposed Algorithm for Warp Direction Checking in Tensioned Fabric Structures

Abstract. Mesh generation of tensioned fabric structure is needed before form-finding. The sequence of defining the mesh of a surface must ensure that the warp and fill direction of the fabric material used in the model is properly represented due to orthotropic nature of fabric material. Therefore, the checking of orientation of mesh is essential because the orientation of element nodes directly affects the direction of material axes. The manual checking of orientation of mesh is not sufficient to give the accurate and precise result and it is time-consuming. There is no such research to index and search for orientation of mesh specially. Procedure for changing node numbering sequence of elements in a mesh of FE model for initial assumed shape has been proposed in order to obtain a correct warp direction in elements. Results show that the proposed algorithm for warp direction checking can achieve substantially accurate classification