Strength of SIFCON- Ferrocement One-Way Ribbed Slabs Contain Steel Fibers

Slurry infiltrated fiber concrete” composites (SIFCON) are a novel type of concrete with improved strength, ductility, and crack resistance. In this study, infiltrating fibers (SIFCON) were used to reinforce of specimens of ferrocement one way ribbed slabs. The laboratory work consists of cast and testing of eight specimens with dimensions of 750 mm in length, 500 mm in width and 50 mm in depth. These samples have the same wire mesh reinforcement and the same shape as the ferrocement slabs. Two reference ferrocement slab without ribs contains SIFCON and six ferrocement slabs with ribs contains SIFCON. The variables were the volumetric ratio of fibers in the ribs, which were (2, 4 and 6)% and type of steel fiber (hook-end and hybrid fiber). Hybrid fibers contain two type of steel fiber (hook-end and micro steel fiber) with equal ratio. All samples were tested under line load up to failure with mid deflections for each test with simple supported. The results of the test showed that the presence of steel fibers in the ferrocement ribs, for both types of steel fibers, improves the resistance to the final loads and the ability to reduce deflection and increases the ductility and stiffness significantly.

Stress analysis on the irregular surface of visco-porous piezoelectric half-space subjected to a moving load

Response of moving load over a surface is an intriguing problem of mechanics to determine the stability and strength of a structure. Owing to this the present theoretical framework is devoted to find the stresses and electrical displacements of an irregular visco-porous piezoelectric half-space originated due to a uniformly moving line load. Expressions for normal stress, shear stress and electrical displacements have been derived in closed form. Effect of irregularity depth, irregularity factors and frictional coefficient on the stresses and electrical displacements are delineated graphically. Numerical demonstration of procured results is interpreted by means of graphs for two different materials, namely PZT-5A and PZT-7. A comparative study emphasising various irregularity (parabolic, rectangular and no irregularity) is among the salient features of the study.

Electrical DebtRank Algorithm–Based Identification of Vulnerable Transmission Lines in Power Systems

With the increase of complexity of the power system structure and operation mode, the risk of large-scale power outage accidents rises, which urgently need an accuracy algorithm for identifying vulnerabilities and mitigating risks. Aiming at this, the improved DebtRank (DR) algorithm is modified to adapt to the property of the power systems. The overloading state of the transmission lines plays a notable role of stable operation of the power systems. An electrical DR algorithm is proposed to incorporate the overloading state to the identification of vulnerable lines in the power systems in this article. First, a dual model of power system topology is established, the nodes of which represent the lines in the power systems. Then, besides the normal state and failure state having been considered, the definition of the overloading state is also added, and the line load and network topology are considered in the electrical DR algorithm to identify vulnerable lines. Finally, the correctness and reasonability of the vulnerable lines of the power systems identified by the electrical DR algorithm are proved by the comparative analysis of cascade failure simulation, showing its better advantages in vulnerability assessment of power systems.

Parabolic tendons in prestressed concrete - how accurate are equivalent loads?

The mechanical effects of a parabolic tendon can be modeled replacing the tendon by external loads applied to the concrete. The intensity of these loads depends on the prestressing force P and curvature of the tendons. These two factors are also interrelated because the losses of prestress vary with the curvature. The structural analysis can be simplified by approximating that the line load against the tendon, able to maintain the initial parabolic form of the tendon and called equivalent load, is constant, perpendicular to the centroidal axis of the beam and equal to P/R where R is the radius of curvature of the parabola at its vertex. This approximation is one of the key issues in the textbooks but normally not properly justified. In this paper, the mathematical background for the approximation is formulated. Some typical tendon layouts are analyzed to evaluate the approximation error. The error proved to be insignificant for simple beams. For cantilever and continuous beams more accurate methods in the final design are recommended.

Tribologische Charakterisierung von Polymerfasern unter Trockenreibung, Mischreibung und Hydrodynamik mittels einer optimierten Pin-on-Disc-Prüfmethode

Based on the conventional pin-on-disc test method, a tribology test rig was adapted and optimized regarding its ability to characterize polymer fibers. The method is explained and first applications in the field of tribological characterization of single fibers are presented. The test sequence to investigate the polymer fibers (diameters of only a few 100 µm) is generated in such a way that data can be recorded continuously as a function of time in the wear range from a few 10 µm to several 100 µm even during the first few minutes. The test mode starts by applying line load and dynamically progresses to area load by changing the contact area during the measurement. It is shown that single fibers can be characterized with respect to their friction and wear properties in different tribological systems. The dependence of the wear rates of fiber material, surface roughness of the counter bodies and lubrication rates is presented.

Influence of Tension Stiffening and Cracked Shear Modulus Models on Non-Linear Analysis of High Strength Fibrous Reinforced Concrete Slabs

In the present study, new models are proposed for tension stiffening and cracked shear modulus to study their effect on the response of the slab. These models are used in the nonlinear analysis of High Strength Steel Fiber Reinforced Concrete (HSSFRC) slabs. The suggested models have multiple shapes depending on the curvature factor, these models are compared with the well-known formulas used in previous studies and great agreements are achieved. The Serendipity “eight-node” element type has been adopted for representing the concrete and layered approach is used to simulate the concrete elements and a smeared layer approach is used to represent the steel reinforcement. The concrete compression behavior is modeled using strain hardening plasticity method, the first two stress invariants of the yield condition is used. For finite element analysis, a computer program coded in Fortran 90 is developed and used for performing nonlinear analysis on the slabs. In order to check the validity of the current models, many actual results for testing slabs “in the laboratory” are compared with the results from the present study and a great agreement is achieved. All studied slabs were simply supported from four sides and loaded with concentrated load at the middle of the slab, but slab S5 is simply supported by two opposite parallel sides with line load parallel to the supports at the middle of the span of the slab. For the curvature factors (Bt, Bg) it is found that the values (Bt =0.005-0.5, Bg =0.001-0.05) give the best simulation for the slab. The effect of tension stiffening model is more than the effect of cracked shear modulus model and there is an interaction between tension stiffening and cracked shear modulus models.

Fourier Integral Transformation Method for Solving Two Dimensional Elasticity Problems in Plane Strain Using Love Stress Functions

The Fourier integral method was used in this work to determine the stress fields in a two dimensional (2D) elastic soil mass of semi-infinite extent subject to line and strip loads of uniform intensity acting on the boundary. The two dimensional plane strain problem was formulated using stress-based method. The Fourier integral was used to transform the biharmonic stress compatibility equation to a fourth order linear ordinary differential equation (ODE) in terms of the stress function. The ODE was solved subject to the boundedness condition to obtain the bounded stress function. Cartesian stress components were obtained using the Love stress functions. Application of the stress boundary conditions for the case of line load of uniform intensity and the cases of uniformly distributed load on a strip of finite width gave the respective unknown constants of the Love stress functions; and hence the complete determination of the Cartesian stress components for the two cases considered. Inversion of the Fourier integral expressions obtained for the normal and shear stresses in the Fourier parameter gave respective expressions for the normal and shear stress fields for line and finite strip loads of finite width in the physical domain variables. The results obtained agreed with the results from previous studies which used displacement based methods.