Praveen K. Malhotra

Strong-Motion Records for Site-Specific Analysis

A procedure is presented to select and scale strong-motion records for site-specific analysis. The procedure matches records’ smooth response spectra with the site response spectrum by scaling of the acceleration histories. The parameters defining the smooth spectrum of various records are computed and tabulated to allow easy selection of records. Hazard de-aggregation is used to identify closer and distant seismic events, which are simulated by the scaled ground motion histories. The procedure can also be used to obtain ground motion pairs in orthogonal directions for multidimensional dynamic response analyses.

Smooth Spectra of Horizontal and Vertical Ground Motions

An improved method of constructing a smooth-response spectrum from peak values of ground acceleration, velocity, and displacement (pga, pgv, and pgd) is presented. Improved dynamic amplification factors are presented for applying damping adjustments to the spectral accelerations or to backcalculate pga, pgv, and pgd from spectral accelerations. Horizontal-to-vertical spectral ratios are analyzed for rock and soil sites to allow the construction of a vertical design spectrum from a given horizontal design spectrum.

Seismic Design Loads from Site-Specific and Aggregate Hazard Analyses

A significant limitation of site-specific probabilistic seismic hazard analysis (known as PSHA) is usually overlooked. The seismic design loads derived from PSHA can only be expected to control the risk at individual locations (site-specific risk); they cannot be expected to control the risk at multiple locations simultaneously affected by an earthquake (aggregate risk). This article presents a method of calculating the seismic design loads for controlling both the site-specific and the aggregate risks.

Response spectrum of incompatible acceleration, velocity and displacement histories

The ground motions induced by an earthquake are expressed by the histories of acceleration, velocity and displacement. It is generally assumed that the acceleration, velocity and displacement histories contain identical information, i.e. the velocity history is obtained by integration of the acceleration history, and the displacement history is obtained by integration of the velocity history. However, this is not always true. In conventional processing of ground motion histories, additional corrections are applied to the velocity and displacement histories, which are not reflected in the acceleration history. As a result, the three ground motion histories contain slightly different information, or they are not fully compatible with one another. The structural response computed from the acceleration history, therefore, does not correspond to the processed velocity and displacement histories. The purpose of this paper is to underscore the engineering difficulties associated with incompatible histories and to provide a method of computing the response spectrum, which is compatible with the acceleration, velocity and displacement histories. Copyright

Testing Sprinkler-Pipe Seismic-Brace Components

The design codes and standards (e.g., UBC, IBC, NFPA-13) estimate the amplitude of the seismic load in sprinkler-pipe braces, but they do not specify the number of cycles for which this load must be resisted by various components of pipe braces. Because the components can fail in low-cycle fatigue, the number of load cycles must be considered in establishing the strength of the brace components. The first part of this study deals with determining the number of cycles for which a component must resist its rated capacity. Strong-motion records from 18 strongly shaken buildings were incorporated into a low-cycle fatigue model to develop a test criterion for measuring the seismic strength of brace components. In the second part of this study, a series of tests were conducted to gain insight into the cyclic behavior of brace components. Finally, a test protocol was established to measure the seismic strength of brace components. With some modifications, the protocol can be applied to many other nonstructural components.

Earthquake Induced Sloshing in Tanks with Insufficient Freeboard

Earthquake induced sloshing in tanks is caused by long-period ground motions which attenuate slowly with distance. A minimum freeboard is needed to accommodate the sloshing waves. Since freeboard results in unused storage capacity, many tanks lack the required freeboard. As a result, sloshing waves impact the roof, generating additional forces on the roof and tank wall. Tanks have suffered extensive damage due to sloshing waves, but the effect of sloshing waves is usually ignored in seismic design of tanks. This paper presents a simple method of estimating sloshing loads in cone and dome roof tanks.

Seismic Risk and Design Loads

The 2003 International Building Code seismic design procedures do not result in uniform risk throughout the country. A comparison is made between the expected lifetime damage to two identical buildings—one in the western United States and other in the central United States. The seismic design accelerations are the same for these buildings, but the expected lifetime damage is very different. The causes of this difference are discussed in the paper.

Discussion of “NGA-West2 Research Project”

Manuscript Reference: Yousef Bozorgnia, Norman A. Abrahamson, Linda Al Atik, Timothy D. Ancheta, Gail M. Atkinson, Jack W. Baker, Annemarie Baltay, David M. Boore, Kenneth W. Campbell, Brian S.-J. Chiou, Robert Darragh, Steve Day, Jennifer Donahue, Robert W. Graves, Nick Gregor, Thomas Hanks, I. M. Idriss, Ronnie Kamai, Tadahiro Kishida, Albert Kottke, Stephen A. Mahin, Sanaz Rezaeian, Badie Rowshandel, Emel Seyhan, Shrey Shahi, Tom Shantz, Walter Silva, Paul Spudich, Jonathan P. Stewart, Jennie Watson-Lamprey, Kathryn Wooddell, and Robert Youngs, Earthquake Spectra, vol. 30, no. 3 (August 2014): 973–987.

Should Building Codes Target Societal Risk

The purpose of building codes is to reduce the risk to life and property from future hazards. Man-made hazards (e.g., fires and explosions) usually affect single locations. Therefore, they pose risk only to individuals. Natural hazards (e.g., earthquakes, floods, and hurricanes) affect multiple locations; an entire city can be destroyed by an earthquake or a hurricane. Natural hazards pose risk to individuals as well as to the society. Building codes attempt to reduce the risk at individual locations, but should they also target the societal risk from natural hazards?