February 2019

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PhD Dissertation: RESPONSE OF CONCRETE COLUMNS UNDER TEMPERATURE INDUCED TRANSIENT CREEP STRAIN

PhD Dissertation: RESPONSE OF CONCRETE COLUMNS UNDER TEMPERATURE INDUCED TRANSIENT CREEP STRAIN

Event Date/Time: 
February 5, 2019 - 1:00pm
Event Location: 
3546D Engineering Building
Speaker: 
Saleh Mohammad Alogla
PhD Dissertation Defense Presentation

The Department of Civil and Environmental Engineering
Michigan State University

PhD Dissertation Defense
RESPONSE OF CONCRETE COLUMNS UNDER TEMPERATURE INDUCED TRANSIENT CREEP STRAIN

By

Saleh Mohammad Alogla
Tuesday, February 5, 2019 at 1:00 pm 3 pm
3546D Engineering Building
Advisor: Dr.
Venkatesh Kodur

ABSTRACT

Structural members experience significant creep deformations in later stages of fire exposure and are susceptible to failure due to temperature induced creep strains. Fire in a concrete structure can burn for several hours, before extinguished and sectional temperatures on concrete and reinforcing steel can reach above 500°C. At such temperatures, high levels of creep strains can develop in concrete and steel, especially in reinforced concrete columns. However, there is lack of fundamental understanding on the evolution of creep and lack of data on temperature induced creep strains for specific types of concrete. Further, temperature induced creep strains are not fully accounted for in evaluating fire resistance of concrete members even through advanced analysis. 

To overcome current limitations, comprehensive experiments on evolution of transient creep strain are undertaken under various heating, temperature, and loading regimes in different concrete types. Transient creep tests are conducted on four types of concrete; normal strength concrete (NSC), steel fiber reinforced concrete (NSC-SF), high strength concrete (HSC), and high strength concrete with polypropylene fibers (HSC-PP). For measuring creep strain, concrete specimens were subjected to combined effects of heating and mechanical loading in the temperature range between 20°C to 750°C. The test variables include temperature, load level, rate of heating, strength of concrete and presence of fibers in concrete. Data from these tests indicate that transient creep strain constitutes a significant portion of the total strain developed during high-temperature exposure. Data also affirm that temperature range and stress level have significant influence on the magnitude of transient creep strain, specially at temperatures above 500°C and stress levels of 40% or more. However, rate of heating and presence of fibers in concrete have only a moderate influence on the extent of transient creep in concrete. Presence of steel fibers in normal strength concrete slightly reduce the extent of transient creep strain, while the presence of polypropylene fibers in high strength concrete leads to higher transient creep strain. Generated data from experiments is then utilized to propose temperature and stress dependent creep strain relations for four types of concrete. These transient creep strain relations can be implemented in fire resistance evaluation of concrete members.

As part of this study, a three-dimensional finite element based numerical model is developed in ABAQUS to account for temperature induced transient creep in undertaking fire resistance analysis of reinforced concrete (RC) columns. Temperature induced transient creep strains in specific types of concrete and reinforcing steel are explicitly accounted for in this advanced analysis. The model also accounts for temperature induced degradation in concrete and reinforcing steel, and material and geometrical nonlinearities. The validity of the model is established by comparing fire response predictions generated from the model with measured response parameters, namely temperature and deflections, in fire tests on RC columns. Results from the analysis clearly indicate that high-temperature transient creep significantly influence the extent of deformations when the temperatures in concrete exceed 500°C for stress level of 40% or more, and this in turn influences, failure time or fire resistance of RC columns.

The validated model is applied to assess influence of transient creep on fire response of RC columns under different conditions, including different fire scenarios, load level, and number of exposed sides in a column. Results from the numerical studies clearly indicate that severe fire exposure induces higher creep strains in RC columns in much shorter duration than exposure to a standard building fire. Moreover, asymmetric thermal gradients resulting from two or three side fire exposure on a column, can increase transient creep effects and, thus, affect fire resistance. The extent of the developed transient creep in concrete columns under various scenarios of fire exposure is highly dependent on type of concrete. Overall, results from the analysis infer that neglecting transient creep can lead to lower prediction of deformations and, thus, overestimation of fire resistance in RC columns, particularly when subjected to severe fire exposure scenarios, with higher thermal gradients.

02/05/2019 - 1:00pm
 
 
 
 
 
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Models, Data, and Analytical Tools for Water Resources Management

Models, Data, and Analytical Tools for Water Resources Management

Event Date/Time: 
February 21, 2019 - 1:00pm
Event Location: 
3540 Seminar Room EB
Speaker: 
Dr. Andrew Gronewold, Ph. D., P.E.
CEE Seminar

Models, data, and analytical tools for water resources management


 


ABSTRACT:  Dr. Gronewold will present findings from research focused on improving data sets and forecasting tools for hydrologic science and uncertainty assessment.  Specific examples include a novel approach to establishing the statistical basis for the design of a new water quality testing kit currently used in developing countries, and the customization of new land surface hydrology models for the Great Lakes region.  Dr. Gronewold will also discuss his work over the past decade on understanding climatological and hydrological drivers behind changes in Great Lakes water levels.


 


BIO:  Dr. Gronewold is an Associated Professor in the School for Environment and Sustainability at the University of Michigan, where he also holds an adjunct appointment in Civil and Environmental Engineering.  Prior to joining the University, Dr. Gronewold spent nearly a decade leading the hydrology group at the NOAA Great Lakes Environmental Research Laboratory.   Cornerstones of Dr. Gronewold's research include developing an understanding of drivers of variability in the hydrologic cycle at regional scales, with an emphasis on developing models, data sets, and analytical tools for the Laurentian Great Lakes.  Prior to joining NOAA, Dr. Gronewold conducted a post-doctorate fellowship with the USEPA Office of Research and Development.  He received his Bachelor's degree at Cornell University, and spent 7 years in the environmental engineering consulting industry before returning to academia to work on his Ph.D. at Duke University under the guidance of Drs. Ken Reckhow and Robert Wolpert. 

02/21/2019 - 1:00pm
 
 
 
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