Simplified Method of Determining Torsional Stability of the Multi-Storey Reinforced Concrete Buildings

This article proposes a simplified method for determining the elastic radius ratio of the multi-storey reinforced concrete building. The elastic radius ratio is the benchmark parameter of the buildings in determining torsional stability during an earthquake. When buildings are torsionally flexible, the torsional component of seismic response amplifies the overall response of the building. Because of the numbers of simplified assumptions such as the adoption of the single-storey model, much of the published articles have a very limited range of application. Quantifying the interaction of different forces in multi-story non-proportional buildings has been the main challenge of these studies. The proposed “shear and bending combination method” solves this by introducing parameters that can determine the relative influence of individual actions. Moreover, the proposed method applies to buildings with all type of structural systems, having asymmetry, and accidental eccentricity. The method is validated through a parametric study consisting of eighty-one building models and using computer analysis. The proposed method and the research findings of this study are useful in determining the torsional stability of the building, in verifying the results of the computer-based analysis, and in optimizing the structural system in the buildings.

Quantitative assessment of seismic design provisions for buildings with torsional irregularities

ASCE/SEI 7 design requirements for seismic-induced torsion in buildings are evaluated to determine their effectiveness for resisting seismic-induced collapse of torsionally irregular buildings. The ASCE/SEI 7-16 provisions are found to be generally conservative for most torsionally irregular building configurations—exceptions are some buildings that rely heavily on lines of lateral resistance orthogonal to the design earthquake force to resist torsional moments, and also some torsionally flexible buildings designed using modal response spectrum analysis. Modifications to provide better consistency in collapse resistance over a large range of building configurations and degrees of torsional irregularity are recommended. The study also demonstrates that buildings classified as extremely torsionally irregular may not need to be prohibited from Seismic Design Categories E and F, as long as the lateral system is proportioned properly.

Seismic Assessment of Asymmetric Single-storey R/C Buildings by Two New Methodologies: Enforced Displacement-Based and Forced-Based Pushover Procedures

Τwo new documented non-linear static (pushover) procedures on asymmetric single-storey R/C buildings are presented in detail herein, aiming directly at the Near Collapse state. Both procedures apply relative to the “Capable Near Collapse Principal reference system” of the single-storey building. The main objective of the two proposed procedures is to fully consider the coupling between torsional and translational vibrations of the floor-diaphragm under translational seismic excitation of the building’s base. The first pushover procedure, which is a Direct Displacement-Based one, uses floor enforced-displacements as action. In the second pushover procedure, which is a Force-Based one, the floor lateral static forces are applied eccentrically to centre of mass using suitable inelastic design eccentricities (dynamic plus accidental ones). The floor enforced-translations/rotation and the appropriate inelastic dynamic eccentricities used in the two proposed procedures derive from extensive parametric non-linear response history analysis and are given by figures or equations. In order to clarify in detail and evaluate the new pushover procedures, a torsionally-flexible, double-asymmetric, single-storey R/C building is seismically assessed. The validation of both procedures relative to the results of non-linear response history analysis shows that both predict with safety the in-plan displacements of the building.

Self-Excited Torsional Oscillations under Locked-Wheel Braking: Analysis and Experiments

ABSTRACT This paper analyzes the effect of tire/vehicle parameters, specifically of tire/suspension torsional stiffnesses, on the stability of self-excited tire torsional oscillations during locked-wheel braking events. Using a torsionally flexible tire-wheel model and a dynamic tire-ground friction model, two system models for tire oscillations are considered: with suspension torsional compliance included in one but excluded in the other. Bifurcation analysis is conducted on both systems to derive the effect of tire/vehicle parameters on the stability. For the system without suspension torsional compliance, it is highlighted that the primary cause of unstable self-excited oscillations is the “Stribeck” effect in tire-ground friction. Based on the parameters obtained experimentally, the bifurcation surface of vehicle velocity with respect to tire/suspension torsional stiffness is also given. The effect of tire/suspension torsional stiffness to the stability of tire torsional oscillation is qualitatively validated via comparisons between locked-wheel braking simulations and experiments with tires with different torsional stiffnesses.

On the Stability of Tire Torsional Oscillations Under Locked-Wheel Braking

This paper deals with the stability of self-excited tire torsional oscillations during locked-wheel braking events. Using a combination of torsionally flexible tire-wheel model and a dynamic tire-ground friction model, it is highlighted that the primary cause of unstable oscillations is the ‘Stribeck’ effect in tire-ground friction. It is also shown analytically that when suspension torsional compliances are negligible, the bifurcation parameters for the local torsional instability include forward speed, normal load and tire radius. In the presence of significant suspension torsional compliance, it is shown that the stability is also affected by suspension torsional stiffness and damping. Furthermore, the tire torsional stiffness becomes an important bifurcation parameter only in the presence of significant suspension compliance. This analysis gives useful insights for the selection of tire sidewall stiffness ranges and their proper matching with targeted vehicle suspensions at the design stage.

Seismic Response of Steel Buildings with Different Structural Typology

This study investigates the influence of the in-plan structural layout on the seismic response of symmetric and asymmetric steel structures. A five-storey steel frame building was used as reference structure and two different structural systems were employed to represent torsional stiff and torsional flexible structures. Accurate numerical models of the different typologies of structures were developed and both nonlinear static and dynamic analyses under bi-directional ground motion were carried out. The influence of axial force-bending moment interaction in columns in the two main directions and second order effects were taken into account in the numerical analyses. The results of the numerical investigations on symmetric structures showed that the reduction of the number of moment resisting connections may lead to an increase of the structural damage. Asymmetric variants of the investigated structures were created by assuming different mass eccentricities in each of the two main directions and extensive parametric studies were performed. For the torsionally flexible building, the influence of ground motion intensity was very strong. A transition from torsionally flexible to torsionally stiff behaviour in the weaker direction of the initially torsionally flexible structure was observed for severe seismic actions. The change of the stiffness of the structure in one direction due to high levels of plastic deformations affected the structural response in the orthogonal direction. Torsional effects decreased in case of severe seismic excitations and high levels of plastic deformations. The reduction of torsional effects observed for low seismic actions on the stiff side of torsionally stiff buildings disappeared under strong seismic excitations.