TORSION EFFECTS IN BUILDING SEISMIC PERFORMANCE

The paper considers torsion effects that occur during the building response to seismic action. Computation and parametric analysis are conducted for various values of building eccentricity induced by mass and stiffness variation. Such a model accounts for the actual dynamic effect of accidental eccentricity, usually considered in building design by quasi-static value of the torsion moment. Two types of models are employed to explore dynamic parameters of the building. The models are formed using Wolfram Mathematica software in which the mass and stiffness properties are parametrically related to the basic dynamic characteristics of the building. The commercial software package CSI ETABS ver.17 is used for validation of the model. Seismic performance of the building is evaluated, and the results of the parametric analysis are presented using the shear forces and torsion moment. The analysis showed that the nature of eccentricity has a major influence on distribution of seismic forces due to the torsion.

Study on Limit Load of Orthotropic Cylindrical Pipe Under Different Combined Load Conditions

In engineering, many pressure pipes are made of steels with good plasticity, which are subject to internal pressure, axial force, shear force, bending moment, torsion moment or their combined loads. The plastic limit load is an important indicator of the load capacity of pressure pipe. According to Hill yield function, the theoretical solutions of limit load of orthotropic cylindrical pipe under various combined loads under internal pressure, axial force, shear force, torsion moment, and bending moment have been derived on the basis of elastic perfectly plastic constitutive model. The effects of radial stress on different combined limit loads of cylindrical pipe are explored and these results show that the radial stress should be considered about the limit load calculation especially for thick-walled cylindrical pipe. The interactions of various load combination are analyzed in detail and drawn with the interaction curves. For isotropic cylindrical pipe, the limit load increases with the yield strength. For the orthotropic cylindrical pipe, the limit loads of cylindrical pipe under axial force, bending moment, shear force, and torsion moment without internal pressure are only related to the axial yield strength. The limit bending moment is mainly dependent on the axial yield strength when internal pressure is lower, while the impact of the circumferential yield strength of orthotropic cylindrical pipe is obvious when internal pressure is some higher. When the axial yield strength of orthotropic cylindrical pipe is the same, the circumferential yield strength can enhance the limit axial load, limit torsion moment, and limit shear load. Under the different load conditions including internal pressure, bending moment, axial force, shear force, and torsion moment or their combined loads, the relation of limit bending moment with yield strength ratio is diverse, which is decide by the load combination, the circumferential yield strength, and the axial yield strength.

Stress Intensity Factor and Crack Opening Area of Circumferentially-Cracked Pipe Under Torsion Moment

The deterministic leak-before-break (LBB) analysis and probabilistic fracture mechanics (PFM) assessment are two primary approaches for demonstrating extremely low probability of rupture of pressurized piping in the nuclear energy industry. Both stress intensity factor (SIF) and crack opening area (COA) are key components to the LBB and PFM assessments. Most of the studies and engineering practices focus on the SIF and COA due to axial tension, bending moment and internal pressure while limited investigations target on these parameters caused by torsion moment. The objective of this study is to perform three-dimensional finite element analyses (3D FEA) to determine both SIF and COA for through-wall circumferential cracks in the pipe under bending or torsion moment. A range of normalized crack lengths (i.e. θ/π = 1/18 to 4/9) and three pipe radius over thickness ratios (i.e. Rm/t = 5, 10 and 25) are considered. Empirical solutions of the SIF for torsion loading as functions of crack geometry are developed. Comparisons for SIF regarding combined bending and torsion moments evaluated using code-specified solutions are presented. Finally, the COAs regarding the two loading modes are discussed. Such study is expected to be useful for both deterministic LBB analysis and PFM assessment of pressurized pipes.

Biomechanical Aspects of the Spine of Women with High Heels, Pain and Their Influencing Factors - A Cross-Sectional Study.

Purpose: High heels have been a fashion mainstay for women for 100s of years despite the well-known fact that wearing them often causes pain in the feet, legs and back. The cause of this pain is complex and the root cause of it has not been determined because a study exploring the biomechanical effects on the vertebral torsion moment on wearers has not been undertaken. Methods: Using video raster stereography, 140 women were measured while in bare foot and while wearing high heels. The collected parameters formed the basis for biomechanical model calculation in order to make more accurate statements about the torsion moment and muscle strength. In addition, a multivariate regression analysis was carried out to evaluate influence factors on pain that occurred while wearing high heels. Results: One hundred and thirty-six women (97 %) aged 18 to 79 years finished the study. The comparison between the measurement points showed a significant difference in the torsion moment. In the regression analysis, the heel height and the frequency of wearing high heels were significant factors influencing the occurrence of pain. Conclusions: Wearing high heels is associated with changes in the posture parameters. The torsion moment is reduced but it does not influence the development of pain which is mainly affected by the height of the heels and the frequency of wearing high heels. In the present study especially, the wearer’s feet were affected.

Concrete beam subjected to shear and torsion: a comparison between the Brazilian Standard Code NBR 6118, ACI and AASHTO Provisions

Most of torsion studies available are relative to pure torsion, arising from the exclusive application of a torsion moment in a concrete beam. This situation, however, is only possible in laboratories. In practice, the vast majority of twisted beams are subjected to the combination of shear forces and torsion, which gives rise to a more complex state of stress to be analyzed. The purpose of this paper is to present the provisions of the ACI 318/2014 Codes, AASHTO and ABNT NBR 6118: 2014 related to shear and torsion, and compare some results with experimental data from Rahal & Collins[3]. It is shown that if the recommended value of 45º is used for θ, the ACI 318/2014 provisions for shear-torsion interaction give similar results compared to ABNT NBR6118: 2014, but these results are very conservative. If the lower limit of 30º is used, the results obtained using both codes departs, and less consistent results are obtained. This paper concludes that using the recommended value of 36º obtained with the AASHTO provisions, some consistent and more accurate results are obtained.

The Influence of the Deformation Nonlinearity on Stress Concentration in Cylindrical Shells with Holes under Torsion

Circular cylindrical shells, application of which is widely widespread in a space-rocket technique and aircraft building, often have cutouts on the surface on structural and technological terms. The feature of the stress-strain state, when a circular hole is introduced into the shell, is the appearance of stress concentration zones, in which stress can be increased in many times. The linear static analysis often used for determination of maximal stresses in such elements of constructions does not reflect character of stresses change with increasing of the external loading. The results of Finite-Elements nonlinear static analysis of the stresses concentration caused by the hole presence depending on the size of torsion moment increasing from zero to the maximal values are presented in this article. The parametric analysis for the wide range of shells lengths and hole radii is carried out, at which different combinations the dependences of stresses concentration factor (SCF) on the value of torsion moment on all range of loading are defined. It is shown that the stresses fields, unlike the linear model of deformation, transform in the loading process. SCF obtained by taking into account the geometrical nonlinearity of deformation depends not only on the geometrical parameters of the considered sample, but also on the level of loading. There are two types of behavior of SCF dependence on the loading level and on the structure parameters. The SCF increases continuously in the first half of loading range. In the second half in case of the small holes the monotonous growth proceeds to the maximal values, and for the large holes ‒ SCF can fall at load increasing, and sometimes has the repeated areas of intensive growth in the pre-ultimate state.

Limit Load Solutions of the Orthotropic Thick-Walled Pipe Subjected to Internal Pressure, Bending Moment and Torsion Moment

Based on the Hill yield criterion, the analytical solutions of the limit load of orthotropic thick-walled pipes under pure internal pressure, bending moment and torsion are given respectively. The simplified Mises analytical solution and finite element results of limit load for isotropic thick-walled pipe are obtained. The solution verifies the reliability of the analytical solution. The paper discusses the difference of limit load of isotropic and orthotropic pipes under the conditions of pure internal pressure, pure bending moment and pure torsion moment. It is concluded that the influence of material anisotropy on the limit load is significant. The limit load of pipe under pure internal pressure is mainly determined by circumferential yield strength, pure bending is only related to axial yield strength and pure torsion moment is related to the yield strength in the 45° direction and radial yield strength.

Design With SADSF Method and Analyses of Elastic Properties of Torsion-Loaded Double-Tee Section With Torsional Box

The work presents the results of preliminary strength design of a thin-walled structure based on double-tee section loaded with a torsion moment. One of the solutions to this problem is considered, in which the torsional box is introduced in the central part. Then, one constructs a series of solution variants that differ in the torsional box length. In the design one uses the method of statically admissible discontinuous stress fields (SADSF) assuming the condition of equalized equivalent stress in the limit state. The work is complemented with elastic FEM analyses of one of the solution variants. Using this example, one shows good load-carrying properties of structures designed with the SADSF method, and proves that they could be several times better than the properties of structures designed with traditional or intuitive ways.