Seismic Earth Pressures on Deep Stiff Walls

Abstract

Experimental and numerical studies of the seismic response of a deep, stiff basement structure were motivated by the fact that the current seismic design methodologies based on the work of Wood (1973) and Ostadan (2005) predict very large dynamic forces in areas of high seismicity. The experimental program consisted of a geotechnical centrifuge model with a basement structure embedded in cohesionless backfill. The numerical analyses sought to replicate the results of the centrifuge experiment and to validate the use of numerical analyses for the prediction of expected behavior. Overall, the results of this study show that the Mononobe-Okabe method of analysis provides a reasonable estimate of the expected response of stiff basement structures provided depth-averaged design accelerations are considered. IntroductionThe introduction of more stringent seismic design provisions in recent updates of design codes, e.g. IBC 2012 and FEMA 750, has increased the demand on seismic design of retaining walls and basement structures and, hence, there is a need for appropriate analysis and design methodology. While not all codes are prescriptive in specifying a particular methodology, the most commonly recommended analyses for non-yielding or "rigid" walls (e.g., embedded structures and basement walls) are based on an elastic solution developed by Wood (1973). More recently, Ostadan (2005) proposed a simplified method that has the Mononobe-Okabe (M-O) method, based on work by Okabe (1924) and Mononobe & Matsuo (1929), as a lower bound and the Wood (1973) solution as an upper bound, which can be as much as 2 to 2.5 times greater than the M-O method. The principal problem for a designer is that at high design accelerations, > 0.5 g, these methods predict very large dynamic forces for non-yielding walls, which appear unrealistic in view of actual experience in recent earthquakes.

Comparing Eurocode 8-5 and AASHTO methods for earth pressure analysis against centrifuge tests, finite elements, and the Generalized Coefficients of Earth Pressure

“…The last decades, a great number of experimental, numerical, and analytical studies [14,15,[24][25][26][27][16][17][18][19][20][21][22][23] point that the Mononobe-Okabe method yields conservative active earth pressure values and excessively conservative values for PGA values greater than 0.4g. Some authorities have already recognized the conservatism of the Mononobe-Okabe method adopting as standard design practice the use of a reduction coefficient for the expected PGA; in this respect, AASHTO [7] considers a horizontal seismic coefficient equal to half PGA.…”

Comparing Eurocode 8-5 and AASHTO methods for earth pressure analysis against centrifuge tests, finite elements, and the Generalized Coefficients of Earth Pressure

“…The last decades, a great number of experimental, numerical, and analytical studies [14][15][16][17][18][19][20][21][22][23][24][25][26][27] point that the Mononobe-Okabe method yields conservative active earth pressure values and excessively conservative values for PGA values greater than 0.4g. Some authorities have already recognized the conservatism of the Mononobe-Okabe method adopting as standard design practice the use of a reduction coefficient for the expected PGA; in this respect, AASHTO…”

Simplified solution for seismic earth pressures exerted on flexible walls

“…Ground surface motions for each study were obtained and interpreted to obtain PGV and T m . Accelerometer data by Wagner and Sitar (2016) and Candia et al (2016) were filtered prior to the data being curated and made publicly available (Candia et al, 2011; Wagner and Sitar, 2013), so that no further data processing was required aside from integrating acceleration in time to compute PGV , and applying the Rathje et al (2004) procedure to compute T m . Raw acceleration recordings for the dataset by Hushmand et al (2016) were filtered and baseline corrected prior to computing PGV and T m .…”

“…We would like to thank Shideh Dashti and Ashkaan Hushmand for sharing data presented in Hushmand et al (2016), Farhang Ostadan for sharing data presented in Ostadan (2005), and Professor Sitar and his research group for publishing the experimental data described by Candia et al (2011) and Wagner and Sitar (2013) via DesignSafe (Rathje et al, 2017). This work benefited from review and feedback from the Building Seismic Safety Council (BSSC) Provisions Update Committee, and especially Issue Team 7 comprised of Stephen Harris, CB Crouse, Gyimah Kasali, Bruce Kutter, Armin Masroor, Ian McFarlane, Bob Pekelnicky, and the second author.…”