Experimental and numerical studies of reinforced concrete stair beams strengthened with steel bars and plates

The bends under sagging moments in a Reinforced Concrete Stair Beam (RCSB) in staircases may be damaged because of improper detailing design or construction; therefore, they need to be strengthened or repaired. The structural behavior of strengthened RCSBs has not been investigated adequately. This paper presents experimental and numerical investigations on the flexural strengthening of RCSBs with bends under sagging moments. Tests on RCSBs were undertaken that were strengthened by using either the Near-Surface Mounted Steel Bars (NSMSBs) or the Externally Bonded Steel Plates (EBSPs). Three steel materials were employed, including Steel Bars (SBs), Steel Sheets (SSs) and Stainless-Steel Plates (SSPs). The test program and outcomes are described in detail of six full-scale strengthened RCSBs loaded up to collapse. A finite element model is developed employing ABAQUS to simulate the performance of the tested RCSBs. It is found that the utilized strengthening techniques effectively enhance both the cracking and ultimate loads in addition to the energy absorption capacity. The agreement between simulations and experiment is good, suggesting that the model of nonlinear finite element analysis can be used with confidence to perform further parametric instigations

Factors affecting the microwave coking of coals and the implications on microwave cavity design

The work carried out in this paper assessed how processing conditions and feedstock affect the quality of the coke produced during microwave coke making. The aim was to gather information that would support the development of an optimised microwave coke making oven. Experiments were carried out in a non-optimised 2450 MHz cylindrical cavity. The effect of treatment time (15–120 min), power input (750 W–4.5 kW) and overall power input (1700–27,200 kWh/t) on a range of coals (semi-bituminous–anthracite) was investigated. Intrinsic reactivity, random reflectance, strength index and dielectric properties of the produced cokes were compared with those of two commercial cokes to assess the degree of coking produced in the microwave system. Overall energy input and coal rank were found to be the major factors determining the degree of coking following microwave treatment. The dependency on coal rank was attributed to the larger amount of volatiles that had to be removed from the lower ranked coals, and the increasing dielectric loss of the organic component of the coal with rank due to increased structural ordering. Longer treatment times at lower powers or shorter treatment times at higher powers are expected to produce the same degree of coking. It was concluded that microwave coke making represents a potential step-change in the coking industry by reducing treatment times by an order of magnitude, introducing flexibility and potentially decreasing the sensitivity to quality requirement in the feedstock. The main challenges to development are the energy requirements (which will need to be significantly reduced in an optimised process) and penetration depth (which will require an innovative reactor design to maximise the advantage of using microwaves). Understanding and quantifying the rapidly changing dielectric properties of the coal and coke materials is vital in addressing both of these challenges

Chemical desulfurization of Turkish Cayirhan lignite with HI using microwave and thermal energy

The purpose of the present work was to investigate the effect of the concentration of HI and reaction time in the chemical desulfurization of Cayirhan lignite in a microwave energy set up and to compare the results with those obtained in a thermal heating system. As the concentration of the HI was increased, the extent of desulfurization was also increased in all the experiments done for all of the samples of lignite. The main difference between the thermal and microwave heating was the extremely short times for desulfurization in the case of microwave experiments. After desulfurization experiments Stotal/C ratio of all of the samples decreased to a lower value than that of the raw lignite which was 0.034. The loss of the sulfur containing bands in the FTIR spectra of the desulfurized lignite showed that the HI treatment was effective in the cleavage of dithioethers and thioetheric groups. Sulfur containing functionalities like thioethers and thiols although usually requiring strong reducing agents could be removed in significant amounts with concentrated hydroiodic acid from the coal matrix. The rapidity of the desulfurization reactions with microwave heating in concentrated HI was probably due to localized superheating which made HI more effective in the reactions such as with thioethers and thiols that normally resisted to cleavage by HI under thermal heating conditions

Ankara'nın alyans evleri

Ankara : İhsan Doğramacı Bilkent Üniversitesi İktisadi, İdari ve Sosyal Bilimler Fakültesi, Tarih Bölümü, 2014.This work is a student project of the The Department of History, Faculty of Economics, Administrative and Social Sciences, İhsan Doğramacı Bilkent University.by Aslan, Mustafa Çağatay

Torsional Improvement of RC Beams Using Various Strengthening Systems

Many structural elements are subjected to a significant torsional moment that affects the structural design and may require strengthening. This paper presents different effective strengthening techniques to enhance the torsional capacity of reinforced concrete (RC) beams. An experimental and numerical investigation was undertaken to evaluate the efficacy of utilizing various strengthening systems. The experimental program included six full-scale RC beams with a cross-section dimension of (150 mm × 300 mm) and a length of 1500 mm, split into one beam without strengthening as a control beam, and six beams strengthened with various materials. The various strengthening materials were wrapped aluminum strips with anchorage bolts, wrapped stainless steel strips with anchorage bolts, wrapped glass fiber reinforcement polymer (GFRP), one layer of wrapped steel wire, and two layers of wrapped steel wire meshes along the beam. The results showed that the ultimate torque of the beam strengthened by wrapped aluminum strips and the beam strengthened by wrapped stainless steel strips was larger than the control beam by about 32% and 40%, respectively, because the strips acted as an external reinforcement. In addition to the strengthening systems, using aluminum strips and stainless steel strips is effective in raising the capacity to a similar degree despite the high cost of the stainless steel strips. The ultimate torque of the beams strengthened by GFRP, one-layered wrapped steel wire meshes, and two-layered wrapped steel wire meshes along the beam is larger than the control beam by about 62%, 118%, and 163%, respectively, in addition to the ultimate angle of twist, which was larger than the control beam by about 53%, 93%, and 126%, respectively. This showed that the strengthening using the two-layered wrapped steel wire meshes along the beam would be very significant in increasing the ultimate torque strength. Moreover, the strengthened beam by two-layered fully wrapped steel wire meshes along the beam developed the highest ductility factor compared to all strengthened beams; in contrast, the beam strengthened by GFRP had less ductility. To verify the outcomes of the experimental tests, a finite-element program, ABAQUS, was performed. Finally, an excellent agreement between the experimental and numerical results was obtained

Punching Shear Behavior of Slabs Made from Different Types of Concrete Internally Reinforced with SHCC-Filled Steel Tubes

The punching shear failure of reinforced concrete (RC) flat slabs is an undesirable type of failure, as it is sudden and brittle. This paper presents an experimental and numerical study to explore the behavior of flat slabs made of different types of concrete under the influence of punching shear. Experimental tests were carried out on four groups of flat slabs, each group representing a different type of concrete: ordinary normal concrete (NC), high-strength concrete (HSC), strain-hardening cementitious composite concrete (SHCC), and ultra-high-performance fiber concrete (UHPFC). Each group consisted of six slabs, one representing an unreinforced control slab other than the reinforcement of the bottom mesh, and the others representing slabs internally reinforced with SHCC-filled steel tubes and high-strength bolts. An analytical equation was used to predict the punching shear capacity of slabs internally reinforced using steel assemblies. A numerical model was proposed using the ABAQUS program, and was validated by comparing its results with our experimental results. Finally, a case study was performed on large-scale slabs. The results showed that using steel assemblies inside NC slabs increased the slab’s punching shear capacity but does not completely prevent punching shear failure. Internally unreinforced slabs made of UHPFC and SHCC were able to avoid punching shear failure and collapse in a ductile bending pattern due to the high compressive and tensile strength of these types of concrete. The proposed analytical method succeeded in predicting the collapse load of slabs reinforced with steel assemblies with a difference not exceeding 9%

Torsional Improvement of RC Beams Using Various Strengthening Systems

Many structural elements are subjected to a significant torsional moment that affects the structural design and may require strengthening. This paper presents different effective strengthening techniques to enhance the torsional capacity of reinforced concrete (RC) beams. An experimental and numerical investigation was undertaken to evaluate the efficacy of utilizing various strengthening systems. The experimental program included six full-scale RC beams with a cross-section dimension of (150 mm × 300 mm) and a length of 1500 mm, split into one beam without strengthening as a control beam, and six beams strengthened with various materials. The various strengthening materials were wrapped aluminum strips with anchorage bolts, wrapped stainless steel strips with anchorage bolts, wrapped glass fiber reinforcement polymer (GFRP), one layer of wrapped steel wire, and two layers of wrapped steel wire meshes along the beam. The results showed that the ultimate torque of the beam strengthened by wrapped aluminum strips and the beam strengthened by wrapped stainless steel strips was larger than the control beam by about 32% and 40%, respectively, because the strips acted as an external reinforcement. In addition to the strengthening systems, using aluminum strips and stainless steel strips is effective in raising the capacity to a similar degree despite the high cost of the stainless steel strips. The ultimate torque of the beams strengthened by GFRP, one-layered wrapped steel wire meshes, and two-layered wrapped steel wire meshes along the beam is larger than the control beam by about 62%, 118%, and 163%, respectively, in addition to the ultimate angle of twist, which was larger than the control beam by about 53%, 93%, and 126%, respectively. This showed that the strengthening using the two-layered wrapped steel wire meshes along the beam would be very significant in increasing the ultimate torque strength. Moreover, the strengthened beam by two-layered fully wrapped steel wire meshes along the beam developed the highest ductility factor compared to all strengthened beams; in contrast, the beam strengthened by GFRP had less ductility. To verify the outcomes of the experimental tests, a finite-element program, ABAQUS, was performed. Finally, an excellent agreement between the experimental and numerical results was obtained

Theoretical derivation for reaction rate constants of H abstraction from thiophenol by the H/O radical pool

Reaction and activation energy barriers are calculated for the H abstraction reactions (C 6H 5SH+X →C 6H 5S+XH, X=H, OH and HO 2) at the BB1K/GTLarge level of theory. The corresponding reactions with H 2S and CH 3SH are also investigated using the G3B3 and CBS-QB3 methods in order to demonstrate the accuracy of BB1K functional in finding activation barriers for hydrogen atom transfer reactions. Arrhenius parameters for the title reactions are fitted in the temperature range of 300K-2000K. The calculated reaction enthalpies are in good agreement with their corresponding experimental reaction enthalpies. It is found that H abstraction by OH radicals from the thiophenol molecule proceed in a much slower rate in reference to the analogous phenol molecule. ΔfH298o of thiophenoxy radical is calculated to be 63.3kcal/mol. Kinetic parameters presented herein should be useful in describing the decomposition rate of thiophenol; i.e., one of the major aromatic sulfur carriers, at high temperatures