Abstract in English:Abstract The interfacial stress in a carbon fiber-reinforced polymer (CFRP) plate for strengthening the top flange of a box-girder bridge was theoretically investigated. According to the force analysis results of the box-girder structure, the most unfavorable force area was selected for modeling analysis. Using the simplified beam model, a CFRP plate-concrete interfacial-stress calculation model was derived, and the closed-form solution of the calculation model was obtained. Equivalent simplified test specimens were designed according to the box-girder structure to verify the reliability of the theoretical model. Then, four-point bending tests of the sample were performed. In these tests, the debonding failure modes and strain in the CFRP plate were examined. The CFRP plate-concrete interfacial stress was calculated according to the strain data of the CFRP plate in the experimental tests. Then compared the experimental results with the theoretical results. Furthermore, the corresponding interfacial stresses were calculated and compared according to the different load levels specified in the code. A series of theoretical and experimental comparisons were performed to verify the reliability of the proposed CFRP-concrete interfacial stress closed-form solution model.
Abstract in English:Abstract The influence of single and multiple imperfection cases on the load carrying capacity of mild steel cone subjected to axial compression was considered through numerical simulation in the current paper. Three different imperfection techniques were considered, which are: i) uneven axial length (sinusoidal/square waves), ii) crack, and iii) single load indentation (SLI) imperfection. Abaqus 6.19 FE was used to carry out the numerical simulation. The axial compressive load was applied at the small radius of the cone. Results showed that the buckling load of axially compressed mild steel cone depends on the imperfection approach implemented. The buckling load of cones were seen to be heavily affected by uneven axial length imperfection for both single and multiple imperfection. Also, the effect of multiple imperfection is more noticeable at higher r1/t.
Abstract in English:Abstract In this study, we have investigated the impacts of hazardous earthquakes on the Nusretiye Clock Tower which is one of the historical heritages located in the city of İstanbul. We analyzed the seismicity of the region and performed nonlinear dynamic analyses under real and artificial ground motion data set to contribute to protecting this cultural heritage and its transmission to future generations. To calculate the seismicity parameters (b- values, a- values, Magnitude of completeness) of the region, we have collected a current catalogue in the Marmara region whose coordinate range is 260-310 E longitudes and 400-420 N latitudes. The current catalogue is constructed from 15 April 1905 to 31 December 2020. A complete set of 29223 earthquakes of Md ≥ 1 obtained from Bogazici University, Kandilli Observatory and Earthquake Research Institute, Regional Earthquake-Tsunami Monitoring Center. In the light of the nonlinear dynamic analysis results, masonry tower is significantly vulnerable to suffer strong damage or collapse in an earthquake with a return period of 2475 years.
Abstract in English:Abstract The objective of this study is to investigate a hybrid reinforcement method for concrete beams, which consists of steel rebars and HDPE (high-density polyethylene) uniaxial geogrids, by developing an experimental comparative investigation between utilizing different grades and layers of HDPE uniaxial geogrids as the primary reinforcement or as extra reinforcement to the steel rebars. The experiments for this investigation included 24 reinforced concrete beams in order to provide rich data for the flexural behavior analysis and design approach. For a detailed analysis, strain gauges were connected to steel rebars and HDPE uniaxial geogrids. Analysis of the results shows that the hybrid reinforcement method using steel rebars and HDPE uniaxial geogrids provided greater benefits (such as energy absorption capacity, ductility index, ultimate load, and steel-yield load) and more effective utilization (such as better flexural performance, lower deformation values corresponding to the steel-yield load, and greater benefits to cost ratios) than utilizing HDPE uniaxial geogrids as the primary reinforcement or utilizing the conventional reinforcement of steel rebars. Simple design equations were added to calculate the flexural bending capacity, the necessary HDPE uniaxial geogrids’ grade, and the number of layers utilizing the HDPE uniaxial geogrids as the primary reinforcement or as extra reinforcement to the steel rebars.
Abstract in English:Abstract A simple unified set of displacement and velocity approximations is presented to express various two-stage composite time integration schemes. Based on the unified approximations, two novel sets of optimized parameters are newly proposed for the implicit composite schemes to enhance the capability of conserving total energy. Two special cases of the unified approximations are also considered to overcome some shortcomings of the existing schemes. Besides, the newly proposed unified set of approximations can include many of the existing composite time integration schemes. To be specific, both implicit and explicit composite schemes can be expressed by using the unified set of approximations. Thus, both implicit and explicit types of composite schemes can be selected from the unified set by simply changing algorithmic parameters. To demonstrate advantageous features of the proposed unified set of approximations, various numerical examples are solved, and results are analyzed.
Abstract in English:Abstract Wind effects on tensile fabric structures (TFS) are not extensively investigated. Available studies consider simplified TFS support conditions and comparisons between static and dynamic analyses are lacking. The response of a double hypar TFS under varying wind speed is carried out by using fluid-structure interaction (FSI). Realistic support conditions are considered. The double hypar geometry is determined through form-finding. Computational fluid dynamics (CFD) is the basis to perform dynamic analysis to propose pressure coefficients useful for design. Differences between dynamic and static analyses are assessed. It is found that the stresses in the fabric and axial forces in the supports are significantly different for each type of analysis, which cannot be captured by simplified uniform uplift wind and snow loadings. Static analysis using pressure coefficients leads to differences of up to 17.3% for stresses in the fabric, 10.5% for the compressive force in the masts and 33.5% for the tensile force in the cables, compared to a FSI analysis. Results give further insight into the wind response of realistic TFSs.
Abstract in English:Abstract Limited initiation energy or external stimulation may cause incomplete detonation in a warhead. At present, there is no quantitative method to characterize the energy release of a warhead charge for incomplete detonation such as explosion and deflagration. We propose a method based on average fragment quality to characterize the energy released by a warhead charge. The theoretical study shows that the average fragment quality after warhead initiation is inversely proportional to the initial fragment velocity. The relationship between the average fragment quality and explosive energy release is established and verified by experiment. This relation can be used to determine the charge energy released after warhead initiation. It provides a theoretical basis for optimizing efficiency of charge energy use in high-energy conventional damage technology and warhead design, and provides a quantitative method for evaluating insensitive ammunition.
Abstract in English:Abstract In this study, we investigated the preconsolidation pressure (P C) of sedimentary soft rock and its relationship with brittle-ductile transition (BDT) pressure. We proposed a generalized preconsolidation pressure (P G) suitable for both soil and sedimentary soft rock, which is defined in terms of the yield stress of the initial sediment structure under confined lateral compression. We then explored the digenetic effect on P G using 24 sediment types. Next, P G and BDT pressure were verified using confined compression and conventional triaxial tests, respectively, on red-bed soft rock in the Dingxi region of China. Finally, we discussed the BDT mechanism and analyzed the relationship between the two characteristic pressures for a given initial yield surface considered structural strength. We found that the relationship was dependent on the strength parameters, the initial structural strength, and the coefficient of earth pressure at rest. The findings of this study will have a significant impact on the determination of BDT pressure of sedimentary rock in future studies.
Abstract in English:Abstract This paper focuses on the wall reinforcement design of toroidal shells with openings. Five 304 stainless steel test models were manufactured, and geometric measurements, three-dimensional scanning, and hydrostatic tests were carried out. The scanning models were established according to the measured geometrical imperfections. Linear buckling analysis (LBA), geometrically and materially nonlinear analysis (GMNA), and geometrically and materially nonlinear analysis with imperfections (GMNIA) were used for numerical simulations. The test results were in good agreement with the numerical analysis results, and an effective finite element method was obtained. Finally, 51 numerical simulations were established to study the influence of the size, number, and shape of openings on the buckling load performance of the toroidal shell with openings.
Abstract in English:Abstract There is no doubt that concrete is one of the most consumed materials all over the world. It is a composite mix widely used for constructing structures and infrastructures to sustain environmentally induced stresses such as thermal and seismic. As the mainstream of construction industry is tended to find out feasible solutions, Roller Compacted Concrete (RCC) was introduced to play an essential role in the development of dams and pavements, where over 550 RCC dams were created by the end of 2012. In fact, this material has the same basic constituents of conventional concrete with a zero-slump and a significant difference in the placing process. The majority of available studies in the literature are composed of numerical investigations to assess the thermal and seismic behavior of RCC dams and to provide a clear view on how to improve its performance under various loading conditions. This paper summarizes and compares the general conclusions of recent works on evaluating the structural performance of RCC dams.