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International Concrete Abstracts Portal

Showing 1-5 of 259 Abstracts search results

Document: 

SP-347_14

Date: 

March 1, 2021

Author(s):

Seong Ryong Ahn and Thomas H.-K. Kang

Publication:

Symposium Papers

Volume:

347

Abstract:

Impact resistance of concrete panels has been researched since the 19th century. Studies therein primarily focused on conventionally reinforced concrete and steel fiber-reinforced concrete. Little research on the impact resistance of prestressed concrete exists. This paper investigated the impact resistance of prestressed concrete panels subject to hard and soft/hollow projectiles and under an assortment of prestressing levels. Damage mode, velocity change, impact force, and internal energy were measured and analyzed. A total of twelve finite element analyses, which considered high strain rate effects, were performed, as well as preliminary analyses with different mesh sizes. It is observed that level of prestressing tends to improve perforation resistance of concrete panels. Additionally, large deformation at soft projectiles occurred during impact, consuming the greater internal energy of the projectiles, unlike hard projectiles. As a result, soft projectiles caused a smaller degree of local failure on the concrete panels than hard projectiles with the same mass and velocity.


Document: 

SP-347_13

Date: 

March 1, 2021

Author(s):

Girum Urgessa and Robert Sobeski

Publication:

Symposium Papers

Volume:

347

Abstract:

This paper presents qualitative and quantitative assessment of material flow response during projectile penetration of concrete targets using outputs from the finite element analysis. The assessment included two parts. First, the movement of the comminuted concrete was analyzed by examining the normal expansion of meshless particles using NECM (Normal Expansion Comparison Methodology). Second, the expansion of finite element nodes adjacent to meshless particles was analyzed by observing direction cosines and velocity profiles of the nodes using SECM (Spherical Expansion Comparison Methodology). This assessment is important to re-examine simplified assumptions used in analytical penetration depth equations that were developed without providing adequate insight into material flow.


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.


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.


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