Journal of Structural Engineering & Applied Mechanics
Structural performance of reinforced concrete (RC) structures should be improved due to new design standards, strength reduction, and/or functional changes throughout their service life. To reach a sufficient level of structural performance, the following two options can be considered: reconstruction or strengthening of structures. Although reconstruction has some advantages in terms of using current technological developments, this option can lead to some negative consequences such as interruption of the building's service life, relatively high cost, and sustainability issues. Therefore, strengthening an existing structure mostly stands out as the first choice. The techniques used in strengthening applications can be grouped into two different methods: traditional (addition of new structural members) and non-conventional (seismic base isolation, local retrofitting, and jacketing). Among innovative methods, the fibre-reinforced polymer strengthening method attracts attention due to several advantages including practical applicability, as well as shear and bending capacity increase. Its application to the outer surface of structural members using resin reduces deterioration. Plus, fibres oriented in various directions spread stresses in different directions, therefore, provide effective force distribution. In this study, the effect of carbon fibre reinforced polymer (CFRP) orientation and RC material properties in the strengthening RC beams were investigated using MATLAB software. Accordingly, all stages of the design process are presented for RC beam strengthening considering both flexural and shear effects based on the American Concrete Institute (ACI) 440.2R standard. Through compiling MATLAB code, calculation time reduces, and material characteristics can be obtained more accurately. Plus, using curves obtained by MATLAB coding, shear and bending capacity increases can be observed. According to our findings, the application of one-layer CFRP plate to an RC beam increases the bending capacity by 50.6% and shear capacity by 33.6%. However, as the number of layers increases, the capacity increase rate reduces.
In this study a new repair method, called buckling zone relocation, for buckled steel braces is presented. In this method, buckled zone of the steel brace is wrapped with steel plates to relocate the buckling zone toward the undamaged locations of the brace. Thus, the brace can be reach buckling load again. The effectiveness of the proposed method was experimentally investigated. To do this, 2 tubular brace specimens, each have 2000 mm length and 70×70×3 mm cross section, were subjected to quasi-static cyclic loadings. First specimen were loaded until global buckling and then unloaded to repair with the proposed method. The length of the buckling zone to be repaired with steel plates was determined with finite element analysis. When the repair process completed, the specimen reloaded until collapse. The second specimen was loaded until collapse to be used as reference member. As a result, it was determined that the buckled steel brace tested in this study could been effectively repaired via buckling zone relocation method without any significant decrease in its performance.
The effects of third-order shear deformation theory (TSDT) displacements and advanced nonlinear varied shear correction coefficient on the free vibration frequency of thick functionally graded material (FGM) plates under environment temperature are studied. The nonlinear coefficient term of TSDT displacements is included to derive the advanced equation of nonlinear varied shear correction coefficient for the thick FGM plates. The determinant of the coefficient matrix in dynamic equilibrium differential equations under free vibration can be represented into fully homogeneous equation and the natural frequency can be found. The parametric effects of nonlinear coefficient term of TSDT, environment temperature and FGM power law index on the natural frequency of thick FGM plates are investigated.
Hilal Filiz Öztekin
Mete Onur Kaman
Studies on weight reduction in aviation and space vehicles have gained momentum recently. Thermoplastic matrix composite materials are important alternative materials, especially due to their high specific strength, formability and recyclability. In this study, it is aimed to investigate the mechanical behavior of fiber reinforced thermoplastic composites for different fiber and layer configurations. Thermoplastic composite materials used in the study were produced by lamination technique. In composite production; Glass fiber and carbon-aramid hybrid fabrics were used as fiber, and polyethylene granules were used as matrix. Thermoplastic sheets were obtained by keeping polyethylene granules and woven fibers in the hot press for a certain period of time. The damage behavior of the composite test specimens under tensile load was tested for the number of layers and fiber type. As the number of layers increased, stiffness, damage load and deformations increased in thermoplastic composites. Using hybrid fabric instead of glass as fiber material increased the maximum damage load by 100%.
İpek Yalçın Enis
The purpose of this study is to develop an impact absorber with a core made of sustainable textile waste as an alternative to the conventional honeycomb structure. In this case, the core structure is made of cotton fiber webs recycled from denim waste, and the outer shell is made of polypropylene plates reinforced with carbon, jute, and E-glass woven fabrics. Production of the sandwich structure is carried out using the hot press method. In addition to the fabric types and layer sequences utilized in the outer shell, the geometry of the core structure is altered, and their effect on the drop-weight impact resistance is examined. The prominent results emphasize that the use of high-performance fabrics in the outer shell facing the outer surface increases the impact resistance, and the sizes of the holes to be obtained in the core structure should be optimized in order to be effective in energy absorption. The results reveal that these developed sandwich structures can constitute a promising alternative for the automotive industry.
Tuğçe Sevil Yaman
Plate girders are designed to carry massive loads over large spans. Flanges resist moment and web resists shear forces. Shear strength of steel girders having slender webs is much less than the yielding shear capacity. It is mainly due to the buckling of the web prior to reaching the yield strength of the material. Webs are generally reinforced with transverse stiffeners to increase their buckling strength. Stiffened webs resist shear also after buckling, which is called as post buckling strength. Tension field theories explain the formation of the post buckling strength and predict the stiffened web’s ultimate shear strength. Most design code provisions are set on tension field theories. There exists plenty of tension field theories proposed until today. This paper covers the design shear strength check and design flexural strength check and the stiffeners’ design of a steel girder specimen which was designed intentionally to fail in shear buckling. Analysis and stiffeners’ design were performed according to the provisions for load and resistance factor design (LRFD) in the ANSI/American Institute of Steel Construction (AISC) 360-16 - Specification for Structural Steel Buildings.