Driven Concrete Pile Foundation Monitoring with Embedded Data Collector System
Florida Department of Transportation (FDOT) sponsored research performed at the University of Florida resulted in developing a wireless monitoring and real time static capacity estimate technology for driven piles. This new technology, Embedded Data Collector (EDC), uses two levels of instrumentation, embedded in the body of precast prestressed concrete piles near the head and tip. Strain and acceleration measurements obtained at these instrumentation levels during driving are sent wirelessly to a receiver in the field, and analyzed in real time to provide the operator with estimates of static capacity, stresses in the pile, transfer energy, damping factor, stroke height, and other relevant parameters used to evaluate the pile driving process and the driving system. The EDC system is currently undergoing phase one of a two phase field evaluation program planned by the FDOT to determine the level of reliability that can be anticipated by its use. The first phase consists of monitoring piles with EDC instrumentation and concurrently monitoring them with the Pile Driving Analyzer (PDA), given that there is ample data supporting the reliability of PDA. Measurements of strain and particle acceleration converted to force and velocity traces can then be compared between the two systems, along with the corresponding calculated magnitude of downward and upward traveling stress waves as they move along the pile at any point in time. Selected hammer blows recorded by PDA equipment are analyzed by means of signal matching software (CAPWAP) and the estimated static skin, end bearing, and total resistance obtained are compared against EDC static resistance predictions. The second phase of the evaluation will compare EDC estimates of static capacity against instrumented static load test results. The purpose of this paper, is only to present a summary of results obtained thus far in phase one, and compares EDC estimates of static capacity results with those from PDA and CAPWAP.
Embedded data collector (EDC) evaluation, phase II - comparison with instrumented static load tests.
A total of 139 piles and 213,000 hammer blows were compared between the Embedded Data Collector (EDC), the Pile Driving Analyzer (PDA), and the CAse Pile Wave Analysis Program (CAPWAP) along with SmartPile Review versions (3.6, 3.72, 3.73, 3.76 and 3.76.1). Fixed EDC/PDA ratio was consistent (0.89 to 0.97) for all version numbers, with little variability (max coefficient of variation (CV) = 0.17); UF EDC/PDA ratio was slightly unconservative (1.12) for earlier versions (3.6), but conservative (0.89 to 0.93) for later releases, with little variability (max CV = 0.18); Top pile compressive stresses, CSX (EDC/PDA), were consistent (0.91 to 0.93) for all versions, with little variability (max CV = 0.09); Bottom pile compressive stresses, CSB (EDC/PDA), ranged from 0.77 for earlier version (3.6), but quickly stabilized at 0.74 for all subsequent versions (3.72-3.761), with maximum variability (CV = 0.25); Pile tension stress, TSX (EDC/PDA), was slightly unconservative (1.2) for earlier versions (3.6), but was conservative (0.87 to 0.90) for all later releases, with max variability (CV = 0.29); UF EDC/CAPWAP total capacity ratio varied from 1.0 (ver 3.6) to 0.89 (ver 3.761), with R2 = 0.89; UF EDC/CAPWAP skin friction ratio varied from 0.78 to 1.04, with R2 = 0.57; UF EDC/CAPWAP tip resistance ratio varied from 0.85 to 0.93, with R2 = 0.76. A total of 12 static pile test were collected in Florida and Louisiana. From the 12 piles, a total of 17 independent measurements (i.e., total, skin, and tip capacities) were recorded. EDC and SmartPile had a bias or ʎ (ratio of measured/predicted) of 0.96, CVR, of 0.258 for combined (total, tip and skin) resistances. Using ASHTO, 2012, the Load and Resistance Factor Design (LRFD) Φ was determined to be 0.65, for a reliability, β, of 2.33. CAPWAP had a bias, ʎ, of 0.91, CVR = 0.311, and LRFD Φ = 0.54 for β=2.33 with inclusion of side friction and tip resistance.
HYPERGOLIC REACTION MECHANISMS OF CATALYTICALLY PROMOTED FUELS WITH ROCKET GRADE HYDROGEN PEROXIDE
Abstract The coupling of the physical and chemical processes controlling the ignition delays (τ ign ) of hypergolic propellants complicates the direct analysis of the transient ignition processes. The transport properties of both the propellants and the ambient gas, and the heat of vaporization and reaction affect τ ign and must be considered experimentally. Furthermore, since hypergolic ignition occurs, by definition, on contact, the mechanics of initial contact and subsequent mixing can affect τ ign and must also be considered. Experimental results from a study of the hypergolic ignition of a catalytically promoted fuel with rocket grade hydrogen peroxide (RGHP) are presented. Statistical analysis of the experimental data was conducted to evaluate the relative effects of RGHP concentration, initial ambient pressure, and the ambient gas on τ ign . At RGHP concentrations of less than 92% in water, stable ignition was difficult to achieve. At sufficiently high Lewis number, an oscillatory ignition process is observed. A phenomenological model comprising mixing, RGHP decomposition, fuel heating and vaporization, and auto-ignition is presented and compared to the experimental results.