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Modulus of Elasticity Impact on Equivalent Top-Loading Curves from Bi-Directional Static Load Tests
The bi-directional static load test (“BDSLT”) is widely used to test the geotechnical resistance of deep foundations. Many, if not all, of these tests are performed on instrumented drilled foundations where applied loads, strains, and displacements are measured during the load test. After the test is completed, the measured data are analyzed to determine required parameters for construction of the equivalent top-loading (“ETL”) curve. One of the main parameters used for the data-reduction process is the drilled foundation’s composite-section elastic modulus, E. This parameter directly impacts the foundation’s computed internal forces, ETL curve, and elastic compression. Several published methods have presented graphical and theoretical expressions to aid determination of a foundation’s elastic modulus, whether a composite-section modulus, or the modulus of concrete/grout. This paper presents a review of these methods, and explores the impact of each outcome on the BDSLT results. Two concrete unconfined compressive strengths were considered to analyze the results of a BDSLT on a 72-inch-diameter drilled shaft. The concrete elastic modulus was determined from a method prescribed by the American Concrete Institute (“ACI”), and the composite-section elastic modulus was determined using the tangent modulus (“TM”) method. Parametric studies were performed using load-transfer (t-z) analyses to investigate the effect of different moduli of elasticity on the t-z curves and the constructed ETL. Results of analysis showed that a given displacement of 2 inches and a 12 to 16 percent difference in axial rigidity, resulted in a 550 to 1,200 kips difference in predicted load determined using the ETL curve. Similarly, a given load of 6,000 kips and same percentage change in the axial rigidity, resulted in 0.5 inch to 1.18 inches change in displacement.
Modulus of Elasticity Impact on Equivalent Top-Loading Curves from Bi-Directional Static Load Tests
The bi-directional static load test (“BDSLT”) is widely used to test the geotechnical resistance of deep foundations. Many, if not all, of these tests are performed on instrumented drilled foundations where applied loads, strains, and displacements are measured during the load test. After the test is completed, the measured data are analyzed to determine required parameters for construction of the equivalent top-loading (“ETL”) curve. One of the main parameters used for the data-reduction process is the drilled foundation’s composite-section elastic modulus, E. This parameter directly impacts the foundation’s computed internal forces, ETL curve, and elastic compression. Several published methods have presented graphical and theoretical expressions to aid determination of a foundation’s elastic modulus, whether a composite-section modulus, or the modulus of concrete/grout. This paper presents a review of these methods, and explores the impact of each outcome on the BDSLT results. Two concrete unconfined compressive strengths were considered to analyze the results of a BDSLT on a 72-inch-diameter drilled shaft. The concrete elastic modulus was determined from a method prescribed by the American Concrete Institute (“ACI”), and the composite-section elastic modulus was determined using the tangent modulus (“TM”) method. Parametric studies were performed using load-transfer (t-z) analyses to investigate the effect of different moduli of elasticity on the t-z curves and the constructed ETL. Results of analysis showed that a given displacement of 2 inches and a 12 to 16 percent difference in axial rigidity, resulted in a 550 to 1,200 kips difference in predicted load determined using the ETL curve. Similarly, a given load of 6,000 kips and same percentage change in the axial rigidity, resulted in 0.5 inch to 1.18 inches change in displacement.
Modulus of Elasticity Impact on Equivalent Top-Loading Curves from Bi-Directional Static Load Tests
Moghaddam, Rozbeh B. (author) / Komurka, Van E. (author)
Eighth International Conference on Case Histories in Geotechnical Engineering ; 2019 ; Philadelphia, Pennsylvania
Geo-Congress 2019 ; 178-188
2019-03-21
Conference paper
Electronic Resource
English
Modulus of Elasticity Impact on Equivalent Top-Loading Curves from Bi-Directional Static Load Tests
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