The Sixteenth World Conference on Earthquake Engineering (16WCEE) is a quadrennial event providing a unique opportunity for academia, building code experts, design/building professionals, earthquake engineering professionals to share the latest advances in earthquake science, best practices for outreach and education, building science and code advancement, and policy initiatives that improve resiliency.

D. J. Wald(1), K. Lin(2), C.A. Kircher(3), K. Jaiswal(4), N. Luco(5), L. Turner(6), D. Slosky(7)

(1) Supervisory Research Geophysicist, U.S. Geological Survey, wald@usgs.gov

(2) Research Geophysicist, U.S. Geological Survey, klin@usgs.gov

(3) Principle, Kircher & Associates Consulting Engineers, CAkircher@aol.com

(4) Research Civil Engineer, U.S. Geological Survey, kjaiswal@usgs.gov

(5) Research Civil Engineer, U.S. Geological Survey, nluco@usgs.gov

(6) Bridge Engineer, California Department of Transportation, nluco@usgs.gov

(7) Developer, U.S. Geological Survey under contract to Synergetics, Inc., dslosky@usgs.gov

Abstract

The ShakeCast system is an openly available, near real-time post-earthquake information management system. ShakeCast is widely used by public and private emergency planners and responders, lifeline utility operators and transportation engineers to automatically receive and process ShakeMap products for situational awareness, inspection priority, or damage assessment of their own infrastructure or building portfolios. The success of ShakeCast to date and its broad, critical-user base mandates improved software usability and functionality, including improved engineering-based damage and loss functions. In order to make the software more accessible to novice users—while still utilizing advanced users’ technical and engineering background—we have developed a “ShakeCast Workbook”, a well documented, Excel spreadsheet-based user interface that allows users to input notification and inventory data and export XML files requisite for operating the ShakeCast system. Users will be able to select structure based on a minimum set of user-specified facility (building location, size, height, use, construction age, etc.). “Expert” users will be able to import user-modified structural response properties into facility inventory associated with the HAZUS Advanced Engineering Building Modules (AEBM). The goal of the ShakeCast system is to provide simplified real-time potential impact and inspection metrics (i.e., green, yellow, orange and red priority ratings) to allow users to institute customized earthquake response protocols. Previously, fragilities were approximated using individual ShakeMap intensity measures (IMs, specifically PGA and 0.3 and 1s spectral accelerations) for each facility but we are now performing capacity-spectrum damage state calculations using a more robust characterization of spectral deamnd.We are also developing methods for the direct import of ShakeMap’s multi-period spectra in lieu of the assumed three-domain design spectrum (at 0.3s for constant acceleration; 1s or 3s for constant velocity and constant displacement at very long response periods). As part of ongoing ShakeCast research and development, we will also explore the use of ShakeMap IM uncertainty estimates and evaluate the assumption of employing multiple response spectral damping values rather than the single 5%-damped value currently employed. Developing and incorporating advanced fragility assignments into the ShakeCast Workbook requires related software modifications and database improvements; these enhancements are part of an extensive rewrite of the ShakeCast application.

Keywords: ShakeCast; ShakeMap; HAZUS, earthquake response; critical infrastructure; critical facilities

1. Introduction

The ShakeCast® system is an openly available, near–real-time post-earthquake information management system. ShakeCast is widely used by public and private emergency planners and responders, lifeline utility operators and transportation engineers [1] to automatically receive and process ShakeMap products for situational awareness, inspection priority, or damage assessment of their own infrastructure. The success of ShakeCast to date and its broad, critical-user base mandates improved software usability and functionality, including improved engineering-based damage and loss functions. As a distributed software application, ShakeCast can be either installed “in-house” within a user’s network and their physical or virtual operating systems, or more commonly, by running an “instance” of the ShakeCast software as a cloud-hosted service after cloning the system disc image provided by U.S. Geological Survey (USGS).

In order to make the software more accessible to novice users—while still utilizing advanced users’ technical and engineering background—we have developed a “ShakeCast Workbook”, a well documented, Excel spreadsheet-based user interface. The Workbook allows users to input notification and inventory data and export XML files requisite for operating the ShakeCast system. Users will be able to select structure types from a pre-established library of various facility types (i.e., buildings, bridges and other structures) based on a minimum set of user-specified facility (e.g., building location, size, height, use, construction age, etc.). A new versión of the Workbook contains “default” values of building properties based on these minimum data, as well “improved” values of building properties based on additional building information provided by advanced users. Additional building information includes, for example, identification of structural irregularities which can significantly affect building perfomance. Further, “expert” users can develop and import user-created facility types and associated building properties into facility inventories.

The goal of the ShakeCast system is to provide simplified(i.e., green, yellow, orange and red levels), near–real-time damage and inspection metrics in order to facilitate users’ inspection priorities and protocols. To date, fragilities have been approximated using individual ShakeMap intensity measures (IMs; specifically PGA and 0.3 and 1s spectral accelerations) for each facility rather than performing iterative calculations. We have extended this strategy by supplementing the existing ShakeCast Workbook by allowing more advanced structural characteristics for ShakeCast fragility calculations, an approach based on the methods of HAZUS [2] as described in the next section.We have also been considering options for multi-period spectra in lieu of the assumed three-domain design-anchored spectrum (0.3s marking constant acceleration; 1s delimiting the constant-velocity to constant- displacement transition). For example, we note that the Kathmandu KATNP record from the 2015 Gorkha, Nepal earthquake provided a reminder of the potential significant inaccuracy of such anchoring: Despite having a relatively low PGA (0.18g), KATNP had much higher peak response accelerations of 0.5g at periods of 4–5s. With the usually-assumed spectral shape, larger long-period spectral response values cannot be accomodated. HAZUS methods would be modified to incorporate multi-period spectra. At this time, discrete values of damage and loss are calculated as a function of spectral demand defined by 0.3s, 1s and 3s spectral accelerations.

As part of our research and development, we will also explore the use of ShakeMap IM uncertainty estimates and evaluate the assumption of employing multiple response spectral damping values rather than the single 5%-damped value currently employed. Developing and incorporating advanced fragility assignments into the ShakeCast Workbook requires related software modifications and database improvements; these enhancements are part of an extensive rewrite of the ShakeCast application. In the following sections, the engineering-based approaches for determining damage state (or inspection priorities) are outlined, the ShakeCast Workbook spreadsheet aimed at facilitating users’ data management is described, and ongoing developments, including ShakeCast software re-engineering, are detailed. Some recent relevant improvements to the ShakeMap system are also introduced.

2. Background on HAZUS and Related Applications

The methods for calculating building damage and loss of the ShakeCast Workbook are based on the HAZUS earthquake loss estimation technology, originally developed in the 1990s by the Federal Emergency Management Agency for estimating earthquake impacts on large regions [2, 3]. The HAZUS technology is very broad in nature, estimating damage and loss to buildings, critical facilities, utility and transportation lifelines caused by ground shaking, ground failure and other (induced) hazards such as fire following. Regional loss estimation precludes modeling of individual buildings (e.g., there are over 2 million individual buildings in Los Angeles County). Rather, aggregate estimates of damage and loss are made for each combination of model building type (i.e., structural system of the building) and building use (i.e., occupancy) by census tract. Model building type (MBT), defined in terms of construction material, (e.g., wood, steel, etc.), height (low-rise, mid-rise and high-rise) and seismic design level (based on design vintage), influences the calculation of peak building response during an earthquake and the associated damage to the structure, nonstructural systems and building contents. Building occupancy, defined by the residential, commercial or industrial use of the building, influences the calculation of economic, functional and social losses (e.g., the nonstructural systems and contents of a hospital are very different and would cost much more to replace or repair than those of a warehouse).

The ShakeCast Workbook relies largely on the methods of the HAZUS Advanced Engineering Building Module (AEBM) Manual [3] for calculating damage and loss to specific buildings (e.g., a portfolio of buildings). While based on the same concepts, model building types and occupancies as the basic methods of HAZUS [2], the HAZUS AEBM anticipates that users will have better, building-specific, information. Among other refinememts of the basic methods of HAZUS, the HAZUS AEBM uses the actual height (number of stories) of each building to improve the calculation of peak building response [4]. Of particular significance, the HAZUS AEBM allows “expert” users to develop building-specific properties based on “engineering” data, such as calculations of structural strength and building inspections to identify structural deficiencies. The HAZUS AEBM methods have been adapted for seismic risk assessment of Veterans Administration (VA) hospital buildings [4] and safety evaluation of older California hospital buildings by Office of Statewide Health Planning and Development (OSHPD) [5]. In the VA and OSHPD applications, “engineering” data are based detailed building evaluation criteria that may now be found in ASCE 41-13 [6].

The HAZUS AEBM methods were also used as the technical basis for a recent update of the rapid visual screening methods of FEMA 154, as described in FEMA 155 [6]. The rapid visual screening methods of FEMA 154, while intentionally not as rigorous as the detailed evalaution criteria of ASCE 41-13, provide a basis to expeditously develop limited building-specific information. The docuemtation of the VA and OSHPD HAZUS applications and FEMA 155 provide values of HAZUS AEBM response and damage parameters for each model building type as a function of the “engineering” data. For example, baseline values of response and damage parmeters are modified for those buildings found (by inspection or analysis) to have a “soft-story” to better reflect the poor performance expected for buildings with this type of significant structural irregularity. The ShakeCast Workbook contains databases of baseline and modified values and of each HAZUS AEBM parameter taken from the documentation of the VA and OSHPD applications and FEMA 155. Baseline values of parameters are used as “default” values for building evaluation when only minimal building information is provided by the user; modified values are used for building evaluation when “engineering data” are provided by the user and these data indicate improvement of “default” values are appropriate.

3. Engineering-based Inspection Priority and Damage Calculations

The default setup of ShakeCast offers users different options for assigning inspection priorities to their facilities and infrastructure, and thus allows different criteria for sending automatic notifications. Inspection priorities are based on assessed damage estimates using ShakeMap ground motion parameters, namely peak horizontal ground acceleration, peak ground velocity, and damped elastic spectral acceleration (0.3, 1.0, and 3-sec periods) as well as Instrumental Intensity [7]. At present, three common approaches are being used to provide users with an indication of damage: HAZUS-based, Intensity-based, and customized damage functions.

Starting with the current ShakeCast (2016 Version 3, or V3) software and later versions, we have implemented building-specific damage functions and inspection prioritizations based on the procedures developed by the HAZUS AEBM. The newly designed ShakeCast AEBM framework utilizes a combination of these measured or estimated ground motion parameters, earthquake source parameters (magnitude and distance), and building capacity information to produce a 4-state discrete output. Herein, we describe the requirements and general procedure for the ShakeCast AEBM framework (Fig.1).

Fig. 1 – ShakeCast Flowchart showing implementation of HAZUS AEBM Methods. Dashed lines indicate loss-related functions and associated output not yet implemented.

There were a number of technical issues to work through when implementing the AEBM framework. As a near real-time earthquake response application, ShakeCast divides the computation framework to two main areas. The ShakeCast AEBM workbook handles building-specific capacity curve parameters and fragility medians as part of the users’ ShakeCast setup and configuration, that is, prior to the occurrence of an earthquake. The posterior part of the ShakeCast AEBM framework takes place after a ShakeMap becomes available for an earthquake in order to generate the demand spectra and to analyze building response.

Implementing ShakeCast facility fragilities is not to be taken lightly. Users can select structure types from a pre-established library of various facility types (i.e., buildings, bridges and other structures) based on a minimum set of user-specified facility (building location, size, height, use, construction age, etc.). The revised ShakeCast Workbook contains “default” values of HAZUS Model Building Types (MBT) based on these minimum data. These defaults can be improved by users who have better information.

This real-time AEBM analysis framework is also compatible with the general HAZUS damage methods defined in the current ShakeCast application. Depending on the quality and completeness of building-specific data provided by the user, ShakeCast supplements default MBT parameters and damage functions in order to take advantage of the new computational framework. It is anticipated and expected that the three tiers of user data and (likely) engineering expertise range from (1) minimal – no engineering expertise, but the ability to select default fragilities or MBT assignments per structure, (2) moderate – e.g., the FEMA 154/155 Rapid Visual Screening [8] procedure, and (3) advanced, specifically ASCE 41 [9] structural engineering data. Alternatively, users can specify generic or custom fragilities in the standard from of its median (alpha) and lognormal standard deviation deviation (beta) values based for any of the ShakeMap intensity metrics.

Despite the desired users’ levels noted above, several notable ShakeCast implementations are running that employ only default (typically intensity-based) shaking parameters for determining inspection priorities. When combined with users’ priorities, these ShakeCast instances benefit the users, despite the lack of detailed structural response parameters. Likewise, regulatory criteria have been often used within the ShakeCast framework for coordinating response or for situational awareness [10] rather than specifying or relying on engineering-based damage estimates.

3.1 Building Capacity Curve Parameters and Damage-State Medians

For building-specific damage calculations, users need to provide engineering parameters to define the capacity curve parameters and damage-state medians using the ShakeCast AEBM Workbook. If specified, these building parameters will override the default values for the yield and ultimate capacity control points for the selected MBT. Desired parameters include: the building height, seismic design level, design strength, weight pushover modal factor, height pushover modal factor, higher-mode factor, yield strength to design strength factor, ultimate strength to yield strength factor, ductility ratio, and the inter-story drift ratio for each damage-state. The basic source of the values of default and improved building data are taken primarily from Veterans Administration (VA) Hospital Risk Assessment adaptation of the HAZUS AEBM, for which structural collapse is based on the California Office of Statewide Health Planning and Development (OSHPD) hospital safety assessment adaptation of the HAZUS AEBM.

For buildings with partial list of parameters, default values of code building capacity parameters for each of the 36 generic MBTs are extracted from the values given in Tables 5.4 through 5.6 of the HAZUS-MH Technical Manual for different seismic design level. The computed capacity control points are adjusted for the actual building height instead of the general height category (Low-Rise, Mid-Rise, and High-Rise). The above calculations are computed in both the ShakeCast workbook and during the stage of uploading building inventory to the ShakeCast database, that is during system configuration prior to earthquakes (Fig 1). A similar procedure is applicable to the definition of the damage-state median spectral displacement. The default values of inter-story drift ratio (Table 5.8 of the HAZUS-MH Technical Manual [11]) will be used to compute the median displacement for each damage state, adjusted to the actual building height. Computation of the damage-state beta for each damage state requires additional earthquake parameters and will be evaluated during the processing of a ShakeMap.

3.2 Building Response Parameters

Peak displacement building response is defined by the intersection of demand spectrum and the capacity curve. The demand spectrum is the 5%-damped spectrum of ground shaking at the building site reduced for effective damping above 5% of critical.

3.2.1 ShakeMap-based “three-domain” Response Spectrum

Contrary to the standard HAZUS method, ShakeCast constructs demand spectra using four ShakeMap ground motion parameters (PGA, and PSA at 0.3, 1.0, and 3.0 seconds). With a standardized response spectrum shape of the Probabilistic Earthquake Seismic Hazard (PESH) input, three domain transition periods were defined using the ShakeMap input data. Furthermore, the ShakeMap spectral accelerations do not need to be adjusted for soil amplification effects. The three-domain constant-acceleration, velocity and displacement) response spectra are smoothed near the mid-to-long-period transition period, Ts, and use an improved estimate of long-period level, TL, to match the frequency content of multi-period demand spectra.

3.2.2 Effective Damping and Demand Spectrum

ShakeCast AEBM computed response parameters include elastic damping and degradation () factors that reduce the hysteretic damping and affect intersection capacity and demand. ShakeCast develops an inelastic response (demand) spectrum from the 5%-damped elastic response (ShakeMap input) spectrum. Effective damping, eff, is defined as the total energy dissipated by the building during peak earthquake response and is the sum of an elastic damping term and a hysteretic damping term associated with post-yield inelastic response. Instead of using amplitude-dependent damping reduction factors in HAZUS (RA at periods of constant acceleration and RV at periods of constant velocity), we adopted a model [12] for a damping scaling factor (DSF) that can be used to adjust the 5% damped response spectrum predicated by the ShakeMap input to demand spectrum. The DSF model captures the influence of duration by including both the magnitude and rupture distance (Rrup) variables in the model.

3.3 Performance Point, Damage-State Probabilities, and Uncertainties

The calculation of the performance point (i.e., peak displacement response) is based on the effective damping of the building which is a function of the amplitude of response, building elastic and inelastic response properties and the duration of shaking (estimated using magnitude and Rrup). The performance point was calculated using straight line interpolation between discrete points of demand spectra and capacity curves at the 20 response periods (Fig.2).

Building fragility curves are in the format of lognormal probability functions that describe the probability of reaching, or exceeding, structural damage states, given median estimates of spectral response in spectral displacement. These curves take into account the variability and uncertainty associated with capacity curve properties, damage states and ground shaking. Fragility curves define boundaries between damage states among Slight, Moderate, Extensive and Complete damage states. For a given value of spectral displacement response, discrete damage-state probabilities are calculated as the difference of the cumulative probabilities of reaching, or exceeding, successive damage states. The probabilities of a building reaching or exceeding the various damage levels at a given response level sum to 100%.

HAZUS building fragility functions employ lognormal standard deviation parameters, referrred to as “betas”. The HAZUS betas describe the total uncertainty of the fragility-curve damage states. The current implementation in ShakeCast accepts three sources of variability associated with the capacity curve, the demand spectrum, and the discrete threshold of each damage state. A pre-populated set of damage-state beta’s have been included as default for users to select appropriate values of variability for their structural system. Kircher [13] developed ShakeMap-specific betas for HAZUS-MH based on analyses of several loss-data rich California earthquakes, as a reflection of overall reduced uncertainty of ShakeMap data-constrained shaking estimates compared with HAZUS defaults. Kircher [13] further recommended that revised betas be employed for earthquakes with significant impact (MMI>VI or PGA>0.2 g), specifically when ShakeMap (peak-component motions [7]) maps are used in loss estimation.

However, substantial efforts to quantify and provide frequency-dependent ground motion uncertainties as a function of ShakeMap grid location have been that consider uncertainty contributions of nearby seismic station and macroseismic data, inference of the fault location, and the GMPEs employed in shaking estimates developed [14, 15]. Thus, the propagation of these grid-based ShakeMap uncertainties into site-specific HAZUS-based loss calculations is now possible. We can employ both the upper bounds of the damage as well as capacity curves to evaluation the uncertainty in the building performance (Fig.2), and these values can be reported out if so desired by the user. The convolution process that combines the contributions from the demand spectrum and the building capacity is non-trivial. Instead, ShakeCast uses a simple strategy that accounts for the upper and lower bounds of both demand spectrum and capacity curves to estimate the total uncertainty range of individual facility damage states (Fig.2).

Fig. 2 – HAZUS-MH (AEBM) performance point calculation and intersection of upper and lower bound demand and capacity curves.

4. ShakeCast Inventory Workbook

The ShakeCast Inventory Workbook is a collection of Excel® spreadsheets used to bridge the gap between users’ data and the ShakeCast application (Fig.3). It allows users to collect their facility, notification group, and user information in a single location. Once the data have been collected, a customized function generates a master XML file that contains all the information needed for the user’s ShakeCast instance. Data are validated as they are entered into the workbook and malformed data is not exported. This ensures that data with the potential to corrupt the ShakeCast database will not be uploaded to the application.

The Workbook also serves as a stepping-stone between versions 2-4 of ShakeCast. It has the ability to import CSV and configuration files, which were used to upload data to V2. CSV files containing facility data can be exported from V2 and imported to the inventory workbook. This workbook will remain compatible with future versions of ShakeCast to ensure installations of new software will be hassle free.

4.1 ShakeCast HAZUS AEBM Spreadsheet

A revision to the Workbook is being developed in the form of a spreadsheet specifically designed for the inclusion of building-specific HAZUS AEBM structural parameters. This spreadsheet will be completely separable from the rest of the workbook, allowing users with the required information to take advantage of the AEBM without distracting users with less detailed inventories.

4.2 Model Building Types (MBT) Parameters

A Workbook lookup table is currently used to store MBT information. This table is editable by advanced users to allow for access to customize MBTs. New MBTs can also be created with user-defined fragilities. For the users’ convenience, fragility values can be changed on a case-by-case basis as well.

4.3 Advanced Engineering Building Model (AEBM) Parameters

The Workbook also provides tables of default values of the various (and numerous) HAZUS parameters compiled primarily from the VA seismic risk application of the HAZUS AEBM and FEMA 155, and provides documentation of HAZUS AEBM parameter references and/or methods used to develop parameters (not given in directly in the References).