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Showing 1-5 of 202 Abstracts search results

Document: 

SP348

Date: 

March 19, 2021

Publication:

Symposium Papers

Volume:

348

Abstract:

Sponsors: Sponsored by ACI Committee 351 Editor: Carl A. Nelson This special publication grew out of the Technical Session entitled “Application of ACI 351-C Report on Dynamic Foundations,” held at the ACI Spring 2019 Convention in Québec City, Québec. Following this event, Committee 351 decided to undertake a special publication with contributions from those session participants willing to develop their presentations into full-length papers. Three papers included in the current publication were contributed by these presenters and their coauthors, with six additional papers provided by others. All but one of the papers deal with the subject matter of ACI 351.3—Foundations for Dynamic Equipment—updated in 2018. The one exception (the paper of Wang and Fang on wind turbine foundations) provides valuable information to engineers dealing with a lack of consistent design criteria among various codes for reinforced concrete foundations subjected to high-cycle fatigue loads. I would like to thank the members of ACI Committee 351 for their support, in particular the current main Committee and Subcommittee C Chairpersons Susan Isble and Dr. Mukti L. Das, respectively. I also wish to express my gratitude to the authors for their perseverance through the difficult circumstances of 2020, and to the reviewers who generously contributed their time and expertise to this publication. Last, but not least, I want to thank my wife Cindy for tolerating me (and the growing piles of paper) over the past several months as the deadline approached. Carl A. Nelson On behalf of ACI Committee 351 Minneapolis, December 2020


Document: 

SP-348_07

Date: 

March 1, 2021

Author(s):

Pericles C. Stivaros and Pablo A. Bruno

Publication:

Symposium Papers

Volume:

348

Abstract:

This paper presents a case study involving the structural analysis and design of an elevated foundation plinth to support multiple pieces of rotating machines with different operating weights and speeds. The equipment is used to operate a high-speed balancing testing facility for turbines and rotors that are located within an adjacent testing chamber. This project comprised of several layout and design challenges, including vibration and resonance concerns, effects of multiple operating frequencies, plinth shape, and pile foundation effects. Major concern was to maintain the high precision and strict tolerance limitations required by the high-speed balancing operations. Elevated machine foundations integral with other structures possess many natural frequencies, both locally and globally. The traditional design rules-of-thumb are not adequate for analyzing and designing elevated machine foundations. A computer-based finite element analysis method is required to identify the multiple natural frequencies of a complicated foundation structure. The strength design of a machine foundation can become very challenging when trying to implement code requirements that are mostly applicable to building elements and not to massive concrete foundations. This study recognizes the need for the development of a design standard to include special design requirements for mass concrete machine foundations.


Document: 

SP-348_05

Date: 

March 1, 2021

Author(s):

O.S. Ali Ahmed

Publication:

Symposium Papers

Volume:

348

Abstract:

Dynamic pile group effect can either increase or decrease the response of pile-supported structures. This paper presents the results of a three-dimensional finite element model of the pile-to-pile interaction that considers the effect of the surrounding soil to determine the dynamic stiffness and damping for vertical end bearing pile groups subjected to vertical harmonic loading. The results were generated for a wide range of the dimensionless frequency parameter (ao) for a 9x9-pile group with three different spacings: 2-, 4-, and 6-pile diameter. Both the stiffness and the damping showed an oscillatory behavior with the dimensionless frequency parameter ao, as well as with the soil shear modulus. Also, the group efficiency was determined as a function of the pile spacing and the soil shear modulus. The efficiency factor for the stiffness can be as high as 1.15 and as low as 0.7 and for the damping as high as 3.75 and as low as 0.4 as a function of the dimensionless frequency parameter ao.


Document: 

SP-348_09

Date: 

March 1, 2021

Author(s):

Xuan Wang and Shu-jin Fang

Publication:

Symposium Papers

Volume:

348

Abstract:

One of major challenges for the US wind industry is the lack of consistent fatigue design criteria. ASCE/AWEA RP2011 recommends several design codes for fatigue analysis of land-based wind turbine support structures. However, it does not provide discussions on the differences and limitations of these codes. The purpose of this paper is to present our findings on the application of fatigue design codes including Model Code 2010 (MC10), Eurocode 2 (EC2), Det Norske Veritas (DNV), and ACI 215. Comparison of the design results from using these codes/standards are summarized. Due to lack of consistency in the design standards, evaluation results may vary greatly, which can be confusing and inconclusive at times. In addition, this study shows that there will be significant differences on fatigue design adequacy depending on which analysis method is used: the average sectional method or finite element method, the two principal methods used to analyze fatigue. A number of suggestions and critical comments are also provided in this paper for helping development of more consistent fatigue analysis and design criteria for wind turbine foundations.


Document: 

SP-348_04

Date: 

March 1, 2021

Author(s):

O. S. Ali Ahmed and Damon G. Reigles

Publication:

Symposium Papers

Volume:

348

Abstract:

This paper discusses the factors that affect the dynamic response of machine foundation systems, which include (1) the soil dynamic properties, (2) the geometric properties of the foundation, (3) mass of the machine and foundation, and (4) the amplitude and frequency of the applied dynamic loads. The primary objective in any machine foundation design is to limit the foundation response below a specific amplitude threshold. A foundation response exceeding this limit may adversely affect the performance of the machine and damage the machine internals, resulting in costly repairs and lost revenue. Also, the excessive vibrations may result in structural degradation of the foundation, additional excitation stresses on the machine, and increase the compressor unbalance loading. This paper presents dynamic analysis results of a four-cylinder compressor foundation originally designed without consideration for soil-foundation interaction and suffering from excessive vibration. The foundation block supports a 4-cylinder Dresser-Rand compressor, suction and discharge bottles, a crank, and a driving motor with a total weight of approximately 300 kip (1334 kN). A three-dimensional, finite element model representing the soil–foundation system was developed to determine the dynamic characteristics and assess the foundation response under applied dynamic loading from the compressor crank. Results showed that the response of the soil-foundation system is governed by the response of the individual support piers (blocks) and not the global foundation response. This paper also provides a recommended modification to the foundation geometry to reduce the effect of the individual piers' local modes and enhance the foundation dynamic performance.


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