Vector and Scalar IMs in Structural Response Estimation, Part II: Building Demand Assessment

Abstract

The advantages and disadvantages of using scalar and vector ground motion intensity measures (IMs) are discussed for the local, story-level seismic response assessment of three-dimensional (3-D) buildings. Candidate IMs are spectral accelerations, at a single period ( Sa) or averaged over a period range ( Sa avg). Consistent scalar and vector probabilistic seismic hazard analysis results were derived for each IM, as described in the companion paper in this issue ( Kohrangi et al. 2016 ). The response hazard curves were computed for three buildings with reinforced concrete infilled frames using the different IMs as predictors. Among the scalar IMs, Sa avg tends to be the best predictor of both floor accelerations and inter story drift ratios at practically any floor. However, there is an improvement in response estimation efficiency when employing vector IMs, specifically for 3-D buildings subjected to both horizontal components of ground motion. This improvement is shown to be most significant for a tall plan-asymmetric building.

Seismic intensity measures for above‐ground liquid storage tanks

“…As much as the aforementioned IM s may seem useful for the assessment of certain structural systems (eg low and/or mid‐rise frame‐structures respectively), their suitability cannot be taken for granted for the entire range of civil engineering structures. The reason is that individual spectra carry too much variability that cannot always be captured by S a ( T 1 ) or PGA alone; in fact, there are several cases in recent literature where alternative scalar IM s or even complex combinations of them are adopted to adequately represent the seismic input on a given structural system . For instance, the first‐mode inelastic spectral displacement and its combination with higher mode spectral ordinates have been proposed for pulse‐like and non–pulse‐like ground motions, while the geometric mean of the S a ( T 1 ) values along the longitudinal and transverse directions of a 3‐dimensional (3D) moment resisting frame is considered in place of the arbitrary S a ( T 1 ) ground motion component, especially for cases that the fundamental period of the structure does not predominately favour either of the building axes.…”

“…Studies by many researchers have shown that a wide variety of IM s defined according to the general frame of Equation can offer substantial efficiency and sufficiency for building structures …”

“…In view of further improving the accuracy with respect to the MAF estimation, the concept of vector‐valued intensity measures has emerged, offering the ability to better tackle sufficiency and efficiency. There are several examples where vector‐valued IM s may be desirable, such as the case of incorporating higher or “elongated” modes of buildings, or even that of buried pipelines subject to 3D deformation at fault crossings …”

Q-Factor Verification of a 6-Storey Concentrically Braced Frame via the Innoseis Risk-Based Approach

“…Accurate nonlinear models are formed, where both simulated and non-simulated (non-modelled) modes of failure are determined. Incremental Dynamic Analysis [4] is then employed, using an appropriate set of records for European sites, together with a novel intensity measure [5,6] that is designed to retain sufficiency across an entire class.…”

An earthquake-source-based metric for seismic fragility analysis

“…A similar observation is offered in Vargas et al (2013), which uses ordinates of the spectral displacement as intensity measure, but seeks an approach that takes into account the non-linear behaviours of structures. Alternative two-dimensional vector-valued seismic intensity measures were proposed in Baker and Cornell (2006), Baker and Cornell (2005), Tothong and Luco (2007) and Kohrangi et al (2016b). Graphical representations of seismic fragility as functions of vector intensity measures are called fragility surfaces.…”