Load and Resistance Factor Design (LRFD) for Deep Foundations (2004) / Chapter Skim
Currently Skimming:
Pages 14-32
The Chapter Skim interface presents what we've algorithmically identified as the most significant single chunk of text within every page in the chapter.
Select key terms on the right to highlight them within pages of the chapter.
From page 14... ...
2.1.2 Major Findings 2.1.2.1 Design Methodology Averaging the responses for driven piles and drilled shafts, about 90% of the respondents used ASD, 35% used AASHTO Load Factor Design (LFD) , and 28% used AASHTO Load and Resistance Factors Design (LRFD)
|
From page 15... ...
2. The most common dynamic methods used for capacity evaluation of driven piles included the following: • Wave Equation Analysis using the program GRLWEAP (GRL Engineers, Inc.
|
From page 16... ...
, and the Louisiana Transportation Research Center. 2.2.4 Driven Pile Database -- Dynamic Analysis The PD/LT2000 database contains information related to 210 driven piles that have been statically load tested to failure and dynamically monitored during driving and/or restrike (403 analyzed measurements)
|
From page 17... ...
needs to be accounted for when evaluating the resistance factor to be used for field static load tests. Pile Types Geographical Location Soil Types Soil Inertia Type of Data Pile Capacities Pile Type No.
|
From page 18... ...
It is common, however, for example in the Northeast region of the United States, to design and build high-capacity drilled shafts (10 MN and more) , often as an alternative to a large group of small-capacity driven piles.
|
From page 19... ...
2.5 DRIVEN PILES -- DYNAMIC ANALYSIS METHODS 2.5.1 Overview Prior to detailed analyses leading to the determination of resistance factors, two components must be established: (1) the Statistics for the Ratio between Drilled Shaft Capacity of Different Interpretation Methods and the Representative Capacity Davisson DeBeer Shape of Curve FHWA # mx σx # mx σx # mx σx # mx σx 47 0.862 0.17 39 0.908 0.11 36 0.956 0.09 40 0.999 0.13 Notes: # = no.
|
From page 20... ...
. The WEAP analysis is evaluated in this study as a dynamic method for pile capacity prediction, using WEAP default input values and the pile's driving resistance at EOD compared to the static load test results.
|
From page 21... ...
that is assumed to be associated with soil type. The influence of this factor on predicted static capacity depends on the stress wave reflected from the pile's tip, hence on the driving resistance.
|
From page 22... ...
2.5.3 The Controlling Parameters 2.5.3.1 Overview Preliminary examination of the parameters controlling the performance of the dynamic analyses was carried out prior to a final detailed evaluation of these methods, leading to the calculation of appropriate resistance factors. Such examination influenced the subcategorization of the dynamic methods (according to the important controlling parameters)
|
From page 23... ...
So il Ty pe Gravelly Sand Sandy Gravel Clayey Sand Clay Silty Clay Sandy Clay Clayey Silt Silt Sandy Silt Silty Sand Sand Gravel Rock Till 1 sec/m = 0.3048 sec/f t 3.048 Figure 8. Soil type at the pile's tip versus Smith tip damping coefficients used in CAPWAP for 372 PD/LT2000 pile-cases.
|
From page 24... ...
2.5.3.3 The Effect of Time on Tested Capacity Penetration of piles into fine-grained soils causes compression and disturbance, resulting in soil strength during driving So il Ty pe Clay Silty Clay Sandy Clay Clayey Silt Silt Sandy Silt Clayey Sand Silty Sand Sand Gravelly Sand Sandy Gravel Gravel Rock Till -1.86 -5.04 -2.25 7.04 1.51 1.56 2.22no. of cases = 290 -1.5 0.0 1.5-1.00 -0.50 0.50 1.00 Case Damping Coeff icient, Jc Figure 10.
|
From page 25... ...
Soil Acceleration/Driving Resistance. The energy loss through the work performed by the displaced soil mass at the tip is directly related to the acceleration of this mass.
|
From page 26... ...
, with the mean and standard deviation of each group graphed as a point and an error bar against the mid point blow count of the interval. For example, for driving resistance between 0 and 8BP10cm there were 42 case histories with a mean of 2.506 and a standard deviation of 2.217 plotted at the center of the interval, i.e., at 4BP10cm.
|
From page 27... ...
. The probability of failure represents the probability for the condition at which the resistance multiplied by the resistance factors will be less than the load multiplied by the load factors.
|
From page 28... ...
Wirsching (1984) estimated the safety index, or β values, implied by the API specifications (American Petroleum Institute, 1989)
|
From page 29... ...
, a fact contributing to the reliability of pile foundations, which rarely fail. These facts, while recognized, cannot be considered when assigning a target reliability value until more data are available and relevant load factors can be directly developed for foundations.
|
From page 30... ...
2.8 INVESTIGATION OF THE RESISTANCE FACTORS 2.8.1 Initial Resistance Factors Calculations The factors were evaluated using FORM (First Order Reliability Method) with dead load (DL)
|
From page 31... ...
is lower than 1 (overprediction) , while the bias of the dynamic methods is greater than one (underprediction)
|
From page 32... ...
; alternatively, design methods need to be chosen based on their COV. This measure of efficiency needs to accompany prescribed resistance factors in order to avoid a misconception of the existence of a correlation between the economy of a design method and high resistance factors when compared to others.
|
Key Terms
This material may be derived from roughly machine-read images, and so is provided only to facilitate research.
More
information on Chapter Skim is available.