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Sabouri-Ghomi S.,K. N. Toosi University of Technology | Ahouri E.,K. N. Toosi University of Technology | Sajadi R.,K. N. Toosi University of Technology | Alavi M.,Finele Consulting Engineers | And 2 more authors.
Journal of Constructional Steel Research | Year: 2012

Openings in steel plate shear walls (SPSWs) in buildings are provided for architectural reasons as well as for access requirements. Despite the reduction of stiffness and strength in panels with an opening being well-understood, further studies are essential in order to determine both the mechanism and the degree of this degradation, as well as its dependency on the location and the size of the opening. To accomplish this aim, a non-linear finite element analysis is used in this paper to study the behaviour of both stiffened and unstiffened SPSWs with a single rectangular opening. The size and location of the opening are varied from model to model in order to determine their influences on the stiffness and strength of the system. Based on the results obtained, the strength and stiffness degradation of unstiffened panels are affected adversely by the location of the opening. In contrast, the re-location of an opening of a specific size within the panel area in stiffened panels does not appear to influence this degradation, so that the stiffness and strength deterioration are not a function of the location of the opening. As expected, both stiffened and unstiffened panels experience a progressive reduction in their stiffness and strength with an increase of the size of the opening. It is demonstrated further that with an increase in the opening ratio (width to height), the energy absorbed by the system arising from seismic loading considerations in both stiffened and unstiffened SPSWs show a linearly decreasing trend; this trend being less stiff for stiffened panels. Unstiffened SPSWs with a central opening experience the least energy absorption. It is also shown that the absorption of energy is substantially higher in stiffened panels when compared with their otherwise identical, but unstiffened, counterparts. © 2012 Elsevier Ltd. All rights reserved. Source


Lee W.K.,Forell Elsesser Engineers Inc. | Billington S.L.,Stanford University
Earthquake Engineering and Structural Dynamics | Year: 2011

Highway bridges in highly seismic regions can sustain considerable residual displacements in their columns following large earthquakes. These residual displacements are an important measure of post-earthquake functionality, and often determine whether or not a bridge remains usable following an earthquake. In this study, a self-centering system is considered that makes use of unbonded, post-tensioned steel tendons to provide a restoring force to bridge columns to mitigate the problem of residual displacements. To evaluate the proposed system, a code-conforming, case-study bridge structure is analyzed both with conventional reinforced concrete columns and with self-centering, post-tensioned columns using a formalized performance-based earthquake engineering (PBEE) framework. The PBEE analysis allows for a quantitative comparison of the relative performance of the two systems in terms of engineering parameters such as peak drift ratio as well as more readily understood metrics such as expected repair costs and downtime. The self-centering column system is found to undergo similar peak displacements to the conventional system, but sustains lower residual displacements under large earthquakes, resulting in similar expected repair costs but significantly lower expected downtimes. © 2010 John Wiley & Sons, Ltd. Source


Cooke R.J.,Forell Elsesser Engineers Inc. | Kanvinde A.M.,University of California at Davis
Journal of Constructional Steel Research | Year: 2015

Finite element (FE) simulations used to characterize extreme limit states in steel structures require the calibration of numerous parameters. Calibration of these models for large strains (greater than 0.3 or so) cannot be performed using stress-strain curves on standard tests, since the stress state in these tests becomes non-homogenous due to necking or buckling which occur at lower strains. As a result, calibration is often performed by matching load-displacement curves of calibration specimens to those obtained through complementary FE simulations. In these situations, multiple parameter sets produce strain fields that match the measured load-displacement response, resulting in non-unique parameter fits. A series of 2400 FE simulations with 4 specimen geometries, 300 material parameters sets, and 2 loading histories indicates that multiple trial parameter sets produce excellent load-displacement match with the true material response, implying that the method is highly susceptible to non-unique fitting. All simulations use the Armstrong and Frederick constitutive model with a von Mises yield surface. The impact of non-unique fitting is assessed through FE simulations based on parameter sets that show excellent load-displacement match with calibration specimens. It is determined that the non-uniqueness does not significantly affect the prediction of peak force. However, it severely impacts the accuracy in prediction of internal plastic strains, with errors as large as 50% with respect to the true material. This has serious implications for FE simulation used to characterize extreme, strain-based limit states such as fracture. Strategies for mitigation of this inaccuracy are presented, along with limitations of the study. © 2015 Elsevier Ltd. All rights reserved. Source


Kanvinde A.M.,University of California at Davis | Marshall K.S.,Structural Integrity Associates | Grilli D.A.,University of California at Davis | Bomba G.,Forell Elsesser Engineers Inc.
Journal of Structural Engineering (United States) | Year: 2015

The earthquake on February 22, 2011, in Christchurch, New Zealand, resulted in the first documented field fractures of links in eccentrically braced frames (EBFs). A comprehensive forensic analysis of these fractures, which occurred in the parking garage of the Christchurch Hospital, is presented. The analysis is based on mechanical and spectrochemical testing and three-dimensional (3D) scanning of procured physical samples of the fractured links. The analysis features nonlinear time history simulations to characterize deformation demands and continuum finite-element simulations to determine the capacities based on a sophisticated fracture mechanics model. The exercise represents a multiscale end-to-end simulation of the system and provides insight regarding the observed fractures. The analysis reveals the inherent challenges in determining the proximate cause of the fractures because the fractures occurred because of a confluence of several interacting factors, primarily the intensity of shaking (several times the intensity that was expected during a design-level event) and the frame geometry, which severely amplified the imposed demands. In addition, the fractured links also suffered from an erection (fit-up) error, in which the link stiffener was not located (as specified) directly above the brace flange, producing a severe strain concentration. This flaw significantly reduced the deformation capacity; however, the simulation of hypothetical scenarios indicates that, even with this flaw, the links would (with high likelihood) have survived a design-level event. Strategies for mitigation include stricter tolerances for stiffener location, consideration of frame geometry to reduce amplification of rotation, and enhancement of the seismic hazard used for design. The limitations of the study are outlined. © 2014 American Society of Civil Engineers. Source


Zareian F.,University of California at Irvine | Sampere C.,Forell Elsesser Engineers Inc. | Sandoval V.,Engineering Simulation and Scientific Software | McCormick D.L.,Simpson Gumpertz and Heger | And 2 more authors.
Earthquake Spectra | Year: 2012

This paper summarizes the EERI reconnaissance team findings on damage to the Chilean wine industry after the 27 February 2010 Offshore Maule Earthquake. Wine production is one of the major industries in Chile, with an annual production of approximately one million metric tons. It is estimated that the total loss to the wine industry is over 125 million liters, with infrastructure damage estimated as high as US$430. Most of the damage was concentrated in older wineries with collapse of adobe walls and timber roofs or ribbed brick vaults. Damage to steel fermentation tanks was widespread among all wineries visited with the severity of such damage depending on the type of tank anchorage. Local buckling of legs in legged tanks or excessive movement followed by the tank falling off the support pad led to toppling that ruptured piping or valves. Stacked barrels, stored bottles of wine, and production lines were also damaged. © 2012, Earthquake Engineering Research Institute. Source

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