Abbie B. Liel

Seismic Collapse Safety of Reinforced Concrete Buildings. II: Comparative Assessment of Nonductile and Ductile Moment Frames

This study is the second of two companion papers to examine the seismic collapse safety of reinforced concrete frame buildings, and examines nonductile moment frames that are representative of those built before the mid-1970s in California. The probabilistic assessment relies on nonlinear dynamic simulation of structural response to calculate the collapse risk, accounting for uncertainties in ground-motion characteristics and structural modeling. The evaluation considers a set of archetypical nonductile RC frame structures of varying height that are designed according to the seismic provisions of the 1967 Uniform Building Code. The results indicate that nonductile RC frame structures have a mean annual frequency of collapse ranging from 5 to 14×10-3 at a typical high-seismic California site, which is approximately 40 times higher than corresponding results for modern code-conforming special RC moment frames. These metrics demonstrate the effectiveness of ductile detailing and capacity design requirements,...

Accounting for Ground-Motion Spectral Shape Characteristics in Structural Collapse Assessment through an Adjustment for Epsilon

One of the challenges of assessing structural collapse performance is the appropriate selection of ground motions for use in the nonlinear dynamic collapse simulation. The ground motions should represent characteristics of extreme ground motions that exceed the ground-motion intensities considered in the original building design. For modern buildings in the western United States, ground motions that cause collapse are expected to be rare high-intensity motions associated with a large magnitude earthquake. Recent research has shown that rare high-intensity ground motions have a peaked spectral shape that should be considered in ground-motion selection and scaling. One method to account for this spectral shape effect is through the selection of a set of ground motions that is specific to the buildings fundamental period and the site hazard characteristics. This selection presents a significant challenge when assessing the collapse capacity of a large number of buildings or for developing systematic procedures because it implies the need to assemble specific ground-motion sets for each building. This paper proposes an alternative method, whereby a general set of far-field ground motions is used for collapse simulation, and the resulting collapse capacity is adjusted to account for the spectral shape effects that are not reflected in the ground-motion selection. The simplified method is compared with the more direct record selection strategy, and results of the two approaches show good agreement. DOI: 10.1061/(ASCE)ST.1943-541X.0000103.

Cost-Benefit Evaluation of Seismic Risk Mitigation Alternatives for Older Concrete Frame Buildings

Cost-benefit assessment is used to evaluate the effectiveness of various seismic retrofit strategies to address concerns about earthquake safety and damage to older concrete frame buildings. The benefits of mitigation are quantified in monetary terms by assessing the reductions in risk of building damage (repairs) and occupant fatalities. When evaluated considering repair costs only, the maximum cost of retrofitting that offers a positive rate of return is 10% to 30% of the building replacement value. Since seismic retrofits generally cost more than this, this result suggests that reduced risk of damage and repairs alone does not warrant the expense of retrofitting. However, the added benefits of reduced fatality risks would make retrofitting cost-effective if it costs as much as 60% of the building replacement cost. The cost-benefit approach provides an important tool to evaluate the merits of seismic mitigation in light of competing demands for finite public and private resources.

Using Collapse Risk Assessments to Inform Seismic Safety Policy for Older Concrete Buildings

For many in the engineering community, nonductile concrete buildings are the next priority for seismic safety legislation in California. The history of such policies shows that implementation has been challenged by the high costs of seismic retrofit, opposition from building owners, and difficulty in defining and evaluating seismic safety standards. As a result, seismic legislation for existing buildings has developed in response to major earthquakes, rather than through proactive risk assessment. Advances in performance-based earthquake engineering provide a consistent framework for assessing building collapse risk using nonlinear dynamic analysis. These tools are applied to evaluate the risk of earthquake-induced collapse and fatalities in a representative set of older concrete frames. Results show that nonductile concrete frame buildings are about 35 times more likely to collapse in earthquakes than their modern counterparts. These assessments are used to investigate the impact of policy alternatives for seismic mitigation of nonductile concrete buildings.

SEISMIC PERFORMANCE OF REINFORCED CONCRETE FRAME BUILDINGS IN SOUTHERN CALIFORNIA

This study examines the impact of the ShakeOut earthquake on reinforced concrete (RC) frame structures in Southern California. The assessment uses synthetic ground motions and nonlinear dynamic analysis to evaluate 20 RC frame buildings hypothetically located at 735 sites throughout the region. Results show that older nonductile RC frame structures may collapse at 8% to 32% of the sites analyzed, especially in Palm Springs, Los Angeles, and San Bernardino. Modern code-conforming RC frame structures are predicted to collapse at fewer sites (1–11%), but modern midrise construction may be vulnerable in Los Angeles due to rupture directivity and basin effects. These seismic performance metrics can inform the development of policies for emergency response and for mitigating earthquake-induced collapse of existing RC frame buildings. The study further provides a prototype that can be used in developing future scenario studies that will benefit from ongoing research to improve building and seismological models.

Collapse Risk of Buildings in the Pacific Northwest Region due to Subduction Earthquakes

Subduction earthquakes similar to the 2011 Japan and 2010 Chile events will occur in the future in the Cascadia subduction zone in the Pacific Northwest. In this paper, nonlinear dynamic analyses are carried out on 24 buildings designed according to outdated and modern building codes for the cities of Seattle, Washington, and Portland, Oregon. The results indicate that the median collapse capacity of the ductile (post-1970) buildings is approximately 40% less when subjected to ground motions from subduction, as compared to crustal earthquakes. Buildings are more susceptible to earthquake-induced collapse when shaken by subduction records (as compared to crustal records of the same intensity) because the subduction motions tend to be longer in duration due to their larger magnitude and the greater source-to-site distance. As a result, subduction earthquakes are shown to contribute to the majority of the collapse risk of the buildings analyzed.

A life-cycle framework for integrating green building and hazard-resistant design: examining the seismic impacts of buildings with green roofs

Abstract Building design and performance are increasingly being scrutinised from perspectives of both sustainability and hazard resistance. However, the approaches taken to consider these perspectives are disconnected; green building rating systems do not consider hazard resistance in their assessments, while performance-based engineering methods have tended to neglect consideration of environmental impacts. This study presents a framework to assess a building’s life-cycle performance in terms of social, environmental and economic impacts using probabilistic approaches, considering the possible occurrence of an earthquake or other extreme event. The framework is illustrated through a case study of an office building in Los Angeles, designed with and without different types of vegetated (green) roofs, and at risk from varying earthquake hazard scenarios. The case study results demonstrate trade-offs between upfront building costs, material choices, hazard resistance and environmental impact.

A Comparative Evaluation of Probabilistic Regional Seismic Loss Assessment Methods Using Scenario Case Studies

This study compares current and developing probabilistic regional (portfolio) loss assessment methods. These comparisons are carried out for two scenario earthquake events. Of particular interest are: the impact of directly considering building responses versus basing losses on ground motion intensity; identifying best practices for predicting collapsed buildings; and examining the sensitivity of loss assessments to other methodological decisions related to building stock classification and exposure and key sources of uncertainty. On the basis of the identified strengths and weaknesses of the different regional loss assessment techniques, high-end and simplified methods are recommended for computing probabilistic regional seismic losses.

Information Deficits and Community Disaster Resilience

AbstractInformation infrastructures facilitate communication between community stakeholders through a combination of organizational, technological, and human systems and processes. These systems an...

Ground‐Motion Prediction Equations for Arias Intensity, Cumulative Absolute Velocity, and Peak Incremental Ground Velocity for Rock Sites in Different Tectonic EnvironmentsGMPEs for IA, CAV, and Peak Incremental Ground Velocity for Rock Sites

7 Assistant Professor, Department of Civil, Environ. & Archit. Engrg, Univ. of Colorado Boulder, 1111 8 Engrg Dr. ECOT 514, Boulder, CO, 80309; e-mail: shideh.dashti@colorado.edu 9 10 11 Associate Professor, Department of Civil, Environ. & Archit. Engrg, Univ. of Colorado Boulder, 1111 12 Engrg Dr. ECOT 517, Boulder, CO, 80309; e-mail: abbie.liel@colorado.edu 13 14 Research Professor, Department of Civil, Environ. & Archit. Engrg, Univ. of Colorado Boulder, 1111 15 Engrg Dr. ECOT 441, Boulder, CO, 80309; e-mail: keith.porter@colorado.edu 16 17 18 Research Associate, Department of Civil, Environ. & Archit. Engrg, Univ. of Colorado Boulder, 1111 19 Engrg Dr. ECOT 441, Boulder, CO, 80309; e-mail: zana.karimi@colorado.edu 20 21 22 Professor, Department of Civil & Nat. Res. Engrg., University of Canterbury, Private Bag 4800, Ilam, 23 Christchurch, New Zealand, 8040; e-mail: brendon.bradley@canterbury.ac.nz 24