Design of torsionally unbalanced structural systems based on code provisions II: Strength distribution

Abstract

SUMMARYThis paper presents the results of an analytical study of the strength distribution of lateral load resisting elements in torsionally unbalanced systems designed based on codified torsional provisions. It is shown that the element strength can be expressed conveniently as the element strength of a similar but torsionally balanced system multiplied by a strength factor. This strength factor depends on three system parameters, namely, the location of the element relative to the centre of rigidity, and the torsional stiffness and eccentricity of the structure. In addition, it depends on the design coefficients of the code specified design eccentricity expressions. The influence of each of these factors on the element strength distribution is discussed. A new set of values for the design coefficients is proposed. By means of examples, it is shown that the proposed torsional provision is an improvement over those suggested in the National Building Code of Canada and the New Zealand code.

Effect of Overstrength on the Seismic Behaviour of Multi-Storey Regularly Asymmetric Buildings

“…Because of such an evidence, large research efforts have been devoted to examining effects of the lateral-torsional coupling on building seismic behaviour (Goel and Chopra, 1990;De Stefano et al, 1993, 1998De Stefano and Rutenberg, 1999) and to developing and proposing design procedures (Goel and Chopra, 1990;Chandler and Duan, 1992;Duan and Chandler, 1992;Tso and Zhu, 1992;Zhu and Tso, 1992; aimed at providing both plan-regular and plan-irregular systems with a similar level of seismic protection. To this purpose, most studies on seismic response of asymmetric structures have analysed response of single-storey models (Goel and Chopra, 1990;Tso and Zhu, 1992;Zhu and Tso, 1992;De Stefano et al, 1993, 1998De Stefano and Rutenberg, 1999; representing the most extreme idealisation of plan irregular buildings. Such models usually consist of a floor deck, rigid in its own plane and supported by massless, axially inextensible vertical resisting elements, characterised by a bi-linear elastic-hardening behaviour.…”

Seismic Vibration Control of 3D Steel Frames with Irregular Plans Using Eccentrically Placed MR Dampers

“…The other voltage dependent parameters in (Equation (18)) are defined as a linear function of the efficient voltage, [55,56] as follows:…”

“…The LQR algorithm has been developed by Kurata et al [57], and widely used in optimum control problems [37][38][39]. The LQR algorithm finds the optimal control force that can be The other voltage dependent parameters in (Equation (18)) are defined as a linear function of the efficient voltage, u [55,56] as follows:…”

Inelastic rotational response of single story lateral load resisting structures

“…Neglecting the accidental eccentricities in the expressions above (due to stiffness uncertainties, possible torsional ground motion and an unfavorable distribution of live load mass), it may be seen that a coefficient , accounts for amplified torsional moments and determines the strength in elements on the flexible side of the structure, while a coefficient is critical for assessing the strength in elements on the stiff side of the structure (Zhu and Tso, 1992). There is however controversy about these coefficients and different country codes (NBCC-1995, UBC-1994, EAK-2000, NZS-1992, EC8-1993 provide different values for them.…”