Sungmin Yoon

Calibration of Resistance Factors for Axially Loaded Concrete Piles Driven into Soft Soils

The evaluation of axial load resistance of piles driven into soft Louisiana soils based on reliability theory is presented. Forty-two square precast, prestressed, concrete piles that were tested to failure were included in the investigation. The predictions of pile resistances were based on static analysis (α-method for clay and Nordlund method for sand) and three cone penetration test (CPT) direct methods: the Schmertmann, De Ruiter–Beringen, and Bustamante–Gianeselli methods. In addition, dynamic measurements with signal matching analysis of pile resistances using CAPWAP, which is based on the measured force and velocity signals obtained near the pile top during driving, were evaluated. The Davisson and modified Davisson interpretation methods were used to determine the measured ultimate load-carrying resistances from pile load tests. The predicted ultimate pile resistances obtained by using the different prediction methods were compared with the measured resistances determined from pile load tests. Statistical analyses were carried out to evaluate the capability of the prediction design methods to estimate the measured ultimate pile resistance of driven piles. The results showed that the static method overpredicted the pile resistance, whereas the dynamic measurement with signal matching analysis (CAPWAP end-of-driving and 14-day beginning-of-restrike) underpredicted the pile resistance. Of the three direct CPT methods, the De Ruiter–Beringen method was the most consistent prediction method with the lowest coefficient of variation. Reliability-based analyses, by using the first-order, second-moment method, also were conducted to calibrate the resistance factors (φ) for the investigated pile design methods. The resistance factors for different design methods were determined and compared with AASHTO recommendation values. The calibration showed that De Ruiter–Beringen method has a higher resistance factor (φDe Ruiter = 0.64) than the other two CPT methods.

Implementation of LRFD of Drilled Shafts in Louisiana

This paper presents reliability-based analyses for the calibration of resistance factor for axially loaded drilled shafts. A total of 16 cases of drilled-shaft load tests were collected from the Louisiana Department of Transportation and Development (LADOTD) archives. Only 11 out of the 16 cases met the Federal Highway Administration (FHwA) failure criterion. Because of the limited number of available drilled- shaft cases in Louisiana, additional 15 drilled-shaft cases were collected from a neighboring state, Mississippi, which has subsurface soil conditions similar to Louisiana soils. A database of 26 drilled shafts representing the typical design practice in Louisiana was created for a statistical reliability analysis. Predictions of load-settlement behavior of drilled shafts from soil borings were determined using the FHwA design method through the SHAFT computer program. Measured drilled-shaft axial nominal resistance was determined from either the Osterberg cell (O-cell) test or the conventional top-down static load test. Statistical analyses were performed to compare the predicted ultimate drilled-shaft nominal axial resistance and the measured nominal resistance. Results show that the selected design method underestimates the measured drilled-shaft resistance by an average of 17%. The Monte Carlo-simulation method was selected to perform the LRFD calibration under strength I limit state. Total resistance factors for different reliability indexes (β) were determined and compared with those available in literature. The LRFD calibration showed that the FHwA design method has a resistance factor (ϕ) of 0.60 at a target reliability index (βT) of 3.0. DOI: 10.1061/(ASCE)IS.1943-555X.0000084.

Development of a Substructure Instrumentation System at the New I-10 Twin Span Bridge and Its Use to Investigate the Lateral Behavior of Batter Piles

Recent advances in sensor and smart material technology can be used to provide real-time data for structural health monitoring of bridges. This paper describes a substructure instrumentation system that was installed at a selected pier of the new I-10 Twin Span Bridge over Lake Pontchartrain in Louisiana. The system was designed for both short-term and long-term health monitoring of the bridge. The monitoring system includes instrumenting eight piles with inclinometers and strain gages, and instrumenting the pile cap with corrosion meters, water pressure cells, tiltmeters and accelerometers. A lateral load test was designed and conducted to investigate the lateral behavior of the pier and to assess the validity of the analysis method used to design the batter pile foundations using the FB-MultiPier software. Two high strength steel strand tendons were used to impose about 1900 kips of lateral load. An automated survey station with prisms monitored the horizontal movements of the pier caps and bents. The strains and deformations within the foundation piles were measured using the inclinometers and strain gages. The results showed that the success rate of train gages and inclinometer sensors instrumentations were about 70%. A comparison of results from the lateral load tests with those from the FB-MultiPier software analyses showed that the software analyses had much higher conservative values compared to the measured values. These variations between measured and predicted values demonstrate the need to evaluate the applicability of the FB-MultiPier system for the design and analysis of batter pile group-cap systems. The soils’ p-y curves at different depths were also backcalculated from the derived soil reaction and lateral deformation profiles at different load increments.

Evaluation of Axial Load Capacity of Driven Piles in Soft Soils using CPT and Static Analysis Methods

This paper presents the comparison of axial load capacity of friction piles driven into soft Louisiana soils predicted using different CPT methods and static analysis. Thirty square Precast-Prestressed-Concrete (PPC) piles were investigated in this study. Since Louisiana soils are mainly consists of clay and silty clay deposits, the side friction (Qs) dominates the total ultimate bearing capacity (Qult) compared to the end bearing capacity (Qb). The axial capacities of the investigated piles were predicted using three direct CPT methods: Schmertmann method, Bustamante and Gianeselli (LCPC) method, and De Ruiter and Beringen method. The static analysis was also conducted to predict the ultimate bearing capacities of selected piles using �-method and Nordlund method. The predicted bearing capacities were compared with the measured bearing capacities from static load tests at field. Davisson interpretation criterion was used to determine the measured ultimate bearing capacity of the investigated piles. The analysis shows that the average method is the preferred method when CPT pile capacity is used.