Seismic Loss and Downtime Assessment of Existing Tall Steel-Framed Buildings and Strategies for Increased Resilience

In areas of high seismicity in the United States, the design of many existing tall buildings followed guidelines that do not provide an explicit understanding of performance during major earthquakes. This paper presents an assessment of the seismic performance of existing tall buildings and strategies for increased resilience for a case study city, San Francisco, where an archetype tall building is designed based on an inventory of the existing tall building stock. A 40-story moment-resisting frame system is selected as a representative tall building. The archetype building is rectangular in plan and represents the state of design and construction practice from the mid-1970s to the mid-1980s. Nonlinear response history analysis (NLRHA) are conducted with ground motions representative of the design earthquake hazard level defined in current building codes, with explicit consideration of near-fault directivity effects. Mean transient interstory drifts and story accelerations under the 10% in 50-year ground motion hazard range from 0.19 to 1.14% and 0.15 to 0.81 g, respectively. In order to influence decision making, performance is reported as the expected consequences in terms of direct economic losses and downtime. Furthermore, to achieve increased levels of resilience, a number of strategies are proposed including seismic improvements to structural and nonstructural systems as well as mitigation measures to minimize impeding factors. Expected direct economic losses for the archetype building are in the order of 34% of building cost and downtime estimates for functional recovery are 87 weeks. The strategies presented in this paper enable up to a 92% reduction in losses and minimize downtime for functional recovery to 1 day or less

How clumpy is my image? Evaluating crowdsourced annotation tasks

13th UK Workshop on Computational Intelligence (UKCI), Guildford, UK, 9-11 September 2013This is the author accepted manuscript. The final version is available from the publisher via the DOI in this record.The use of citizen science to obtain annotations from multiple annotators has been shown to be an effective method for annotating datasets in which computational methods alone are not feasible. The way in which the annotations are obtained is an important consideration which affects the quality of the resulting consensus estimates. In this paper, we examine three separate approaches to obtaining scores for instances rather than merely classifications. To obtain a consensus score annotators were asked to make annotations in one of three paradigms: classification, scoring and ranking. A web-based citizen science experiment is described which implements the three approaches as crowdsourced annotation tasks. The tasks are evaluated in relation to the accuracy and agreement among the participants using both simulated and real-world data from the experiment. The results show a clear difference in performance between the three tasks, with the ranking task obtaining the highest accuracy and agreement among the participants. We show how a simple evolutionary optimiser may be used to improve the performance by reweighting the importance of annotators

Arousal system stimulation and anesthetic state alter visuoparietal connectivity

Cortical information processing is under the precise control of the ascending arousal system (AAS). Anesthesia suppresses cortical arousal that can be mitigated by exogenous stimulation of the AAS. The question remains to what extent cortical information processing is regained by AAS stimulation. We investigate the effect of electrical stimulation of the nucleus Pontis Oralis (PnO), a distinct source of ascending AAS projections, on cortical functional connectivity (FC) and information storage at mild, moderate, and deep anesthesia. Local field potentials (LFPs) recorded previously in the secondary visual cortex (V2) and the adjacent parietal association cortex (PtA) in chronically instrumented unrestrained rats. We hypothesized that PnO stimulation would induce electrocortical arousal accompanied by enhanced FC and active information storage (AIS) implying improved information processing. In fact, stimulation reduced FC in slow oscillations (0.3–2.5 Hz) at low anesthetic level and increased FC at high anesthetic level. These effects were augmented following stimulation suggesting stimulus-induced plasticity. The observed opposite stimulation-anesthetic impact was less clear in the γ-band activity (30–70 Hz). In addition, FC in slow oscillations was more sensitive to stimulation and anesthetic level than FC in γ-band activity which exhibited a rather constant spatial FC structure that was symmetric between specific, topographically related sites in V2 and PtA. Invariant networks were defined as a set of strongly connected electrode channels, which were invariant to experimental conditions. In invariant networks, stimulation decreased AIS and increasing anesthetic level increased AIS. Conversely, in non-invariant (complement) networks, stimulation did not affect AIS at low anesthetic level but increased it at high anesthetic level. The results suggest that arousal stimulation alters cortical FC and information storage as a function of anesthetic level with a prolonged effect beyond the duration of stimulation. The findings help better understand how the arousal system may influence information processing in cortical networks at different levels of anesthesia

Kernel reconstruction for delayed neural field equations

Understanding the neural field activity for realistic living systems is a challenging task in contemporary neuroscience. Neural fields have been studied and developed theoretically and numerically with considerable success over the past four decades. However, to make effective use of such models, we need to identify their constituents in practical systems. This includes the determination of model parameters and in particular the reconstruction of the underlying effective connectivity in biological tissues. In this work, we provide an integral equation approach to the reconstruction of the neural connectivity in the case where the neural activity is governed by a delay neural field equation. As preparation, we study the solution of the direct problem based on the Banach fixed point theorem. Then we reformulate the inverse problem into a family of integral equations of the first kind. This equation will be vector valued when several neural activity trajectories are taken as input for the inverse problem. We employ spectral regularization techniques for its stable solution. A sensitivity analysis of the regularized kernel reconstruction with respect to the input signal u is carried out, investigating the Frechet differentiability of the kernel with respect to the signal. Finally, we use numerical examples to show the feasibility of the approach for kernel reconstruction, including numerical sensitivity tests, which show that the integral equation approach is a very stable and promising approach for practical computational neuroscience

Seismic Loss and Downtime Estimates of Existing Tall Buildings and Strategies for Increased Resilience

Tall buildings play an important role in the socio-economic activity of major metropolitan areas. The resilience of these structures is critical to ensure a successful recovery after major disasters. Events such as the Canterbury earthquake in 2011 have highlighted the impact of poor performing buildings on the business continuity of downtown districts, where tall buildings are typically clustered together. Following the 2011 earthquake, Christchurch’s Central Business District (CBD) red zone covered a significant area of the city and more than 60% of the businesses were displaced (CERC 2012). Until the introduction of Performance Based Seismic Design (PBSD) in the 1990s, buildings were designed using conventional building codes, which follow a prescriptive force-based approach based on the first mode translational response of the structure (FEMA 2006). Researchers and engineers have raised concerns that the prescriptive approach of building codes is not suitable for tall building design due to the significant contribution of higher mode effects (PEER 2010a). As a result of these shortcomings, several jurisdictions in areas of high seismicity throughout the Unites States (e.g. Los Angeles and San Francisco) have adopted a PBSD approach for the design of new tall buildings. While new designs follow a more adequate approach, little is known about the seismic performance of older existing tall buildings that were designed prior to the adoption of PBSD (Almufti et al. 2012). This paper presents an assessment of the seismic performance of existing tall buildings in a case study city, San Francisco, where an archetype tall building is designed based on an inventory of the existing tall building stock. Non-Linear Response History Analysis (NLRHA) are conducted with ground motions representative of the design earthquake hazard level defined in current building codes, with explicit consideration of near-fault directivity effects. In order to influence decision making, performance is reported as the expected consequences in terms of direct economic losses and downtime. Once the performance of the archetype building is assessed, a range of structural and nonstructural enhancements are explored for enhanced performance as well as mitigation measures for increased resilience. Expected direct economic losses for the archetype building are in the order of 34% of building cost and downtime estimates for functional recovery are 87 weeks. The strategies presented in this paper enable up to a 92% reduction in losses and minimize downtime for functional recovery to 1 day

Risk-based seismic performance assessment of existing tall steel-framed buildings in San Francisco

This study presents the results of a risk-based seismic performance assessment of an archetype tall building representative of the existing tall building stock in San Francisco, CA. The archetype tall building, selected based on an inventory of existing tall buildings, is a 40- storey Moment Resisting Frame (MRF) representative of design and construction practice from the 1970-s to the mid-1980s. A Multiple Stripe Analysis (MSA) was conducted at 8 different intensity levels ranging from frequent to very rare seismic events, i.e. from 85% to 1% probability of exceedance in 50 years. Non-Linear Response History Analyses (NLRHA) were conducted with ground motions representative of each intensity level considered. The results of the NLRHA results were used to assess the probability of earthquake losses, considering collapse potential and the probability of the building deemed irreparable due to permanent residual drifts in the structure. Based on the MSA results, the collapse fragility of the structure, assumed to follow a lognormal cumulative distribution expressed as a function of spectral acceleration at the fundamental period of the structure (T=5 seconds), has an estimated median of 0.15g and a dispersion of 0.30. A number of loss metrics were developed for the archetype building including: a loss function, which provides the annual frequency of exceeding a certain value of loss, e.g. the expected 500 year loss equals $53M or 39$0.6M or 0.46% of the building replacement cost; and loss exceedance rates, e.g. a loss of 10% building replacement cost or $13.5M has an exceedance rate of 95 years. The use of these results to benchmark the performance of the archetype tall building against the design intent in current building codes and to assess the impact of structural retrofit or other building enhancements is discussed