The tensile strength: The most fundamental mechanical characteristics of concrete

Concrete is an inhomogeneous building material. It has a considerable and reliable compressive strength and a relative low tensile strength which can be even exhausted locally under unfortunate conditions. It is quite obvious that the concrete tensile strength was always reprehended as the most unreliable concrete property. A simple relationship between tensile- and compressive strength is introduced. The mechanical background of the relation tensile- to compressive strength in case of ‘normal’ and high strength concretes is elucidated. Mechanical bond, too, relies completely on the tensile strength. In the design of structural concrete members the tension fields are more characteristic than the compression fields. Effective concrete strengths are not successful. Tensile strength can be applied as ‘yield condition’ for the lower bound solution in the theory of plasticity. The paper intends to contribute to the acceptance of the tensile strength as the more fundamental concrete characteristics.

Lower Bound Solution of Foundation Bearing Capacity beneath Strip Footing Based on Parabolic Mohr Failure Criterion

The static allowable stress field of foundation under strip foundation is constructed by means of stress columns, and the calculation method of the lower bound foundation bearing capacity based on the two-parameter parabolic Mohr yield criterion is proposed. Moreover, the influence of the amount of stress columns and material mechanical parameters on the lower bound bearing capacity is analyzed. The results show that a better solution can be obtained by optimizing the static allowable stress field. However, the improvement of lower bound solution might be inefficient if the stress column amount is large enough. The stresses of the superimposition area show a reduction with the improvement of stress field; on the other hand, the superposed stresses are enhanced ever faster as the involved stress column increases. The tensile-compressive strength ratio has a moderate effect on the lower bound solution. Finally, the reliability of the proposed method is verified by some rock foundation loading tests.

Lower-Bound Solution of Foundation-Bearing Capacity under Circular Uniformly Distributed Load

The semispatial static allowable stress field was constructed by three-dimensional stress columns, and the analytical lower-bound solution of bearing capacity of Mohr–Coulomb foundation beneath circular uniformly distributed load was put forward for the first time. The influence of the amount of stress columns and soil shear strength parameters on the lower-bound solution of the foundation-bearing capacity is analyzed. The research showed that (1) when the number of stress columns is more than 9 (n > 4) and the friction angle is less than 30°, the relative error between the lower-bound solution of the bearing capacity and exact solution is less than 6.6%, (2) the suggested analytical solution is applicable for common clayey materials; thus, the application scope of the analytical lower-bound solution is further expanded, and (3) the influence of cohesion on bearing capacity is linear. However, with the increase of the friction angle, the bearing capacity increases faster and faster under all cohesion levels. The correctness and effectiveness of the proposed method were verified by literature comparison.

USING THE STRESS-WAVE THEORY TO DETERMINE THE BEARING CAPACITY OF PILES

High strain dynamic pile testing is usual practice, and has many benefits that make its use highly attractive. However, it requires careful preparation, specific equipment, attention to detail and testing engineer skill to properly perform these tests. Engineer skills for testing largely determines the non-proliferation of the method in Russia. Without of understanding wave equation analyses, the test engineer may not realize when results are valid, or when capacity results may be only a lower bound. It is widely known that the capacity of driven piles may change with time after installation and for that reason restrike tests are generally recommended. It is also generally stated that the set per blow should be at least 2 mm, or otherwise the dynamic test may only yield a lower bound solution. To confirm or refute these recommendations, an analysis of the existing test database was conducted, as well as an analysis of the tests performed at the Perm region facilities. The article presents the conclusions of this analysis and practical recommendations.

A Combination of Singular Cell-Based Smoothed Radial Point Interpolation Method and FEM in Solving Fracture Problem

The singular cell-based smoothed radial point interpolation method (CS-RPIM) has been previously proposed and shown good performance in solving fracture problems. Motivated from the fact that CS-RPIM performs over softly by providing an upper bound solution and the finite element method (FEM) is overly stiff by providing a lower bound solution, this work proposes a combination of singular CS-RPIM and FEM with a correlation coefficient [Formula: see text], and [Formula: see text] has been recommended through intensive numerical studies. Several numerical examples have been studied and the proposed method has been found perform quite well from both stress intensity factors and strain energy.

Metal drawing goodness degree to which the Hollomon equation applies

In order to establish the cold wire drawing production, the CuNi2Si alloy passes schedule were examined by the Duckfield and Ermanok methods in two wire drawing versions: with the diamond die with an angle of 9o and the tungsten carbide die with an angle of 7o . Experiments confirmed that the CuNi2Si alloy can be successfully transformed to the wire with the diameter of 0.2 mm with properties enabling its practical application. The experimental results and the control group showed that the theoretical methods of the upper and lower bound solution can determine the values of the relevant cold wire drawing factors for the CuNi2Si alloy to which Hollomon curve applies.

Lower-Bound Solution Algorithm for Equilibrium Signal-Setting Problem

The equilibrium signal-setting problem is stated and subsequently formulated as a continuous equilibrium network design problem. The bilevel formulation is nonconvex and therefore cannot be solved for global optima by using descent solution algorithms. Therefore, a lower bound using a system optimal flow pattern is proposed that will be quite tight in both uncongested and highly congested network traffic situations. A solution algorithm based on the standard steepest-descent method is proposed for the lower-bound problem. Performance of the solution algorithm on a network problem is reported.

Upper and Lower Bounds for Incipient Failure in a Body Under Gravitational Loading

Recent numerical work has investigated incipient failure of yield stress materials under gravitational loading, for both the rectangular block and cylinder geometries [Chamberlain et al.; 2001, Int. J. Mech. Sci. 43(3):793-815, 2002, Int. J. Mech. Sci. 44(8):1779-1800]. While the rectangular block solution is exact, the cylinder solutions give lower bounds on the height of incipient failure. Consequently, we construct upper bound solutions for the height of incipient failure of a cylinder under gravitational loading. This closes the cylinder problem and quantifies the accuracy of the Haar-Karman hypothesis used in slip-line analysis. For completeness, we also give a simple lower bound solution for the cylinder, as well as upper and lower bound solutions for the two-dimensional rectangular block. These results have the advantage of being analytical, in contrast to the previous purely numerical results.