Accounting for the effects on residual deformations due to torsional response

Recent developments in performance-based seismic design and assessment approaches have emphasised the importance of properly assessing and limiting the residual (permanent) deformations typically sustained by a structure after a seismic event, even when designed according to current code provisions. In this contribution, the performance-based design framework for residual deformations, previously developed by the authors for 2-D regular structures, is further extended to the behaviour of 3-D irregular (asymmetric in-plan) buildings. The seismic response of a set single storey systems, comprising of seismic resisting frames, and made of alternative materials (concrete or steel), is investigated under uni-directional earthquake loading excitations. Different layouts in plan, leading to either torsionally unrestrained or restrained systems, are considered. Sensitivity analyses are carried out in order to identify the influence of varying levels of torsional restraint on the residual deformations/displacements in the response of a 3-D irregular building, the irregularity being given by an imposed mass eccentricity

Accounting for residual deformation and simple approaches to their mitigation

in oral section of abstracts bookRecent developments in performance-based seismic design and assessment approaches have emphasised the importance of properly assessing and limiting the residual (permanent) deformations, typically sustained by a structure after a seismic event, even when designed according to current code provisions. Recent investigations have led to a proposed Direct Displacement-Based Design (DDBD) approach which includes an explicit consideration of the expected residual deformations accounting for 2-dimensional and MDOF effects. Having estimated the possible residual deformations in a structure, it remains to implement specific design features to reduce them to an acceptable level. Previous studies have identified post-yield stiffness as being critical to residual deformation behaviour, therefore a series of simple approaches are proposed to increase this element and system parameter. These methods do not utilise re-centring post-tensioned technology. First, the effects of changes in material stress-strain behaviour and section design in the primary seismic-resisting system are considered, and then the design and introduction of a secondary elastic frame to act in parallel with the primary system is demonstrated. Using moment-curvature and non-linear time-history analyses, the proposed approaches are shown to be effective at achieving their intended goal of residual deformation reduction

Behaviour of steel plated RC columns subject to lateral loading

The main focus of this paper is to describe the behaviour of RC columns that are retrofitted with an alternative technique to 'jacketing' or wrapping. This new technique consists of attaching steel plates to the flexural faces of a concrete column using bolts. It is envisaged that this technique would be suitable primarily for columns having rectangular cross-sections and in situations where lateral loading induces predominately a single plane of bending (as opposed to biaxial bending). Effectiveness of this new technique has been demonstrated by experimental testing and numerical simulations. This paper studies the mechanism of the new retrofit scheme, how it works, and the behaviour of columns retrofitted using such a scheme, as well as the important parameters that affect the response of the retrofitted columns. This study forms the basis for the design of the plate retrofitting system

Assessment of shear forces on bridge abutments: Simplified method

The conventional application of reduction factors to response spectrum analysis results is inappropriate for the abutment shear forces, which are based on elastic action. On the other hand, adopting the unreduced values from the elastic dynamic analysis does not achieve equilibrium among the abutment shear forces, deck inertia forces, and reduced pier forces. A simplified method is here proposed for the assessment of the shear on the abutments, documented by comparison with response spectrum and time history nonlinear analyses for several bridge configurations. For the analyzed configuration of the bridge with an internal movement joint, the response spectrum analysis underestimates the shear on the abutment for low values of the abutment flexibility and overestimates it when the stiffness of the abutments becomes higher than that of the piers. In all the case studies analyzed, the proposed method approximates the time history results better than the response spectrum

Initial stiffness versus secant stiffness in displacement based design

Displacement-based design (DBD) methods are emerging as a valuable tool for performance based seismic design. A distinguishing feature between the different DBD procedures proposed in recent years is the type of analysis used in the design process. This paper identifies various challenges associated with the application of both initial stiffness and secant stiffness based DBD methods and considers whether one form is more effective than the other. Four of the most recent DBD methods that utilise response spectra are reviewed, two of which are initial stiffness based and two of which are secant stiffness based. Through application of the procedures to various case studies some difficulties associated with their application are identified, and significant differences in design strength are observed. Aspects of the design process that are considered influential to the success of the methods are then examined. Finally, the performance of each procedure is assessed by means of non-linear time history analyses. Despite the differences in strength, the performance assessment indicates that each of the DBD methods ensure design limit states are not exceeded. The results of the study infer that DBD utilising response spectra with either initial stiffness or secant stiffness structural characteristics may be equally effective. The biggest difference between approaches may be related to the ease with which they can be accurately applied to various structural forms. It is emphasised that the key to a successful design will be an appreciation of the assumptions that exist within each method irrespective of the approach adopted