Torsion (mechanics) | EPFL Graph Search

In the field of solid mechanics, torsion is the twisting of an object due to an applied torque. Torsion is expressed in either the pascal (Pa), an SI unit for newtons per square metre, or in pounds per square inch (psi) while torque is expressed in newton metres (N·m) or foot-pound force (ft·lbf). In sections perpendicular to the torque axis, the resultant shear stress in this section is perpendicular to the radius. In non-circular cross-sections, twisting is accompanied by a distortion called warping, in which transverse sections do not remain plane. For shafts of uniform cross-section unrestrained against warping, the torsion is: : T = \frac{J_\text{T}}{r} \tau= \frac{J_\text{T}}{\ell} G \varphi where:

T is the applied torque or moment of torsion in Nm.
\tau (tau) is the maximum shear stress at the outer surface
JT is the torsion constant for the section. For circular rods, and tubes with constant wall thickness, it is equal to the polar moment of

RC U-shaped walls subjected to in-plane, diagonal, and torsional loading: New experimental findings

Katrin Beyer, Ryan Hoult

Although reinforced concrete U-shaped walls are popular in construction practice internationally, there is a paucity of experimental research investigating the seismic performance of such salient elements. The present paper summarizes an experimental campaign on two slender U-shaped reinforced concrete walls detailed with a single-layer of reinforcement. State-of-the-art instrumentation was used to capture the three-dimensional displacement field of the wall surfaces using digital image correlation techniques. Experimental findings are presented, including strain profiles, equivalent plastic hinge lengths, longitudinal strains at the base, cracking distributions and widths, and out-of-plane deformations. Approximately half of the yielding zone length was found to be equal to the equivalent plastic hinge lengths, which were found to decrease as a function of drift. The longitudinal strains at the base of these walls showed some shear lag effects when subjected to in-plane or diagonal loading. For most directions of loading, the largest crack widths were found to be associated with flexural-shear or shear cracks. When subjected to a pure torque, the vertical strain distribution at the base of the wall correlated with the theoretical distribution for an open section governed by warping torsion. The out-of plane deformations were primarily concentrated within a small region towards the ends of the flanges prior to the local buckling failures that were observed experimentally.

ELSEVIER SCI LTD2021

Reduced-order Models for Simulating Coupled Geometric Instabilities in Steel Beam-columns Under Inelastic Cyclic Straining

Alexander Riley Hartloper

Numerical models that can simulate coupled geometric instabilities in steel beam-columns are required for the seismic assessment of certain steel moment-resisting frames. Reliably simulating coupled instabilities requires that the steel material is precisely characterized under inelastic cyclic straining. Full continuum finite element (CFE) models can be used in this context, however, reduced order models are preferred for building-level simulations because of their lower computational cost. Concentrated plasticity models are a typical reduced order approach, although findings from recent full-scale experiments conducted on steel beam-columns have highlighted their limitations in simulating component behavior. The aim of this thesis is to propose accurate reduced-order simulation models for steel beam-column components to simulate coupled buckling at a diminished computational expense compared to full CFE approaches. This goal is achieved by using component macro models that couple CFEs in critical regions with beam-column elements elsewhere. The specific objectives related to the aim of this thesis are to: (i) advance the state-of-the-art in constitutive modeling for structural steels subjected to earthquake-induced inelastic straining; (ii) develop an efficient method of coupling beam-column and CFE domains that incorporates torsion-warping; and (iii) develop general recommendations for modeling wide flange beam-column components subjected to inelastic cyclic straining using the macro model. This thesis developed a constitutive model for mild structural steels to improve upon the initial yield behavior of a classic metal plasticity model by accounting for the discontinuous yielding phenomenon. Constitutive model calibration methodologies were developed using constrained optimization for the cases when the material's cyclic behavior is known and when it is unknown. Simulated geometric instabilities were shown to be sensitive to the constitutive model's input parameters in steel beam-columns of particular geometries subjected to multiaxis loading. Coupling methods that included torsion-warping were developed using multipoint constraint equations. Findings indicate that including torsion-warping in the coupling formulation is critical for steel beam-columns that are susceptible to coupled local and lateral-torsional instabilities. The proposed macro model is efficient for the investigated range of steel beam-columns: it reduces computational cost metrics in benchmark CFE analyses by around 50 %. It is also accurate, as the average error between benchmark CFE and macro model analyses is only 3 %. The advances in material modeling made by this thesis can be used to reduce the uncertainty in steel component simulations. This enables analysts to better comprehend component behavior through simulations and improves simulation-assisted design. Component models that explicitly simulate geometric instabilities and material inelastic behavior at lower computational costs are important in probabilistic assessments and uncertainty quantification. They may be especially useful, for example, in benchmarking concentrated plasticity models and in the process of developing new structural systems.

EPFL2021

Ultra low cycle fatigue of welded steel joints under multiaxial loading

Albano António De Abreu E Presa De Castro E Sousa, Alain Nussbaumer

Ultra low cycle fatigue (ULCF) is a phenomenon that can be summarily defined as the deterioration of material properties under high amplitude cyclic loading, under which failure is reached typically within ten to twenty cycles. This phenomenon is observed in extreme loading scenarios such as earthquakes or exceptional winds where large cyclic strains are expected. Particularly sensitive are structural components that are designed to absorb the loading’s energy through plastic dissipation, like moment or shear links in eccentrically braced frames. The demands on such components can vary significantly throughout its duration due to their variable multi-directional nature and, as such, it is important to assess the resistance of structural joints under multiaxial states. This paper will present an experimental campaign done on a welded high strength steel (S770QL) tube to plate joint. This joint was submitted to high cyclic bending, pure torsional and combined proportional bending and torsional loadings. Weld profile and strain measurements at the weld toe were performed using digital image correlation (DIC). An analysis of more than sixty test results will be presented so as to provide an adequate resistance model for ULCF life estimations.

CRC Press/Balkema2016

Reduced-order Models for Simulating Coupled Geometric Instabilities in Steel Beam-columns Under Inelastic Cyclic Straining

Alexander Riley Hartloper

EPFL2021