Archive for the ‘Design Methods’ Category

A Second Chance: LRFD for Micropiles Webinar

If you missed the last one, there is another ASCE Continuing Education webinar coming up on LRFD for Geotechnical Engineering Features: Micropile Foundations. The date is advertised as Friday, July 29, 2011 at 11:30AM to 1:00PM. You get the best bang for your buck if you register and make it available to a group because for one registration fee, you can have an unlimited number of people from your organization attend at your site. I have seen this webinar and it is worthwhile if you are new to AASHTO LRFD Design for Micropiles or if you just want to get a bunch of geotechnical engineers together on a Friday to have fun talking about Micropiles. I know of one group that registered an entire local ASCE Geotechnical Chapter for it.

Find out more and register for the event HERE. The webinar description is below:

This webinar focuses on micropile foundations. Micropile foundations are often a technically sound and cost-effective foundation choice where a deep foundation solution is appropriate based on site conditions, applied loads and project schedule and performance requirements. The Load and Resistance Factor Design (LRFD) platform offers a rational framework for consideration of micropile foundation systems. The webinar will use the American Association of State Highway and Transportation Officials (AASHTO) LRFD Bridge and Structures Specifications as a basis for the technical content. The webinar will include discussion on the terminology and construction of micropiles. It will also focus on topics such as: identification of limit states and resistance factors, axial compression and uplift resistance of a single micropile, estimation of grout-ground bond resistance and tip resistance, and group efficiency factors for evaluation of axial resistance of micropiles in groups. It is assumed that the participant has a basic working knowledge of design and construction of deep foundations.

LRFD vs SLD for Micropiles Comparison

Load and Resistance Factor Design (LRFD) is the predominant design method utilized today for reinforced concrete and structural steel, and is the primary focus of the relatively new AASHTO LRFD Bridge Design Specifications. Historically, micropile design has been performed mainly with Service Load Design (SLD) and Allowable Stress Design (ASD) methodologies and most of the design manuals and specifications in existence prior to 2008 were based on SLD and ASD concepts. The AASHTO LRFD Bridge Design Specifications document offers the most comprehensive LRFD guidance for geotechnical engineering features in the United States (and maybe the World) today. The use of this LRFD design specification is mandated by the majority of State DOTs for use in designing highway bridges and highway structures governed by it. The AASHTO LRFD specification adopted a micropile design section in 2008.

In recent DFI / ADSC Micropile Seminars, there have been a number of questions regarding the proper use of LRFD for micropiles. On May 4, 2011, at the DFI / ADSC Micropile Seminar in Little Rock, AR, I will give a presentation that will cover the fundamentals of LRFD as it applies to micropiles, and will provide a comparison with SLD methodology. We will work through an example analysis problem where we will see how every aspect of micropile axial design compares between SLD and LRFD. We will be looking specifically at FHWA and IBC Service Load Design compared to AASHTO LRFD design. This covers pretty much all the current bases for mainstream micropile design. I have never seen this type of comparison presented so don’t miss out.

Register HERE. Hope to see you in Little Rock!

LRFD for Micropiles Webinar

There has been a lot of interest recently for Load and Resistance Factor Design (LRFD) guidance for Micropiles. The American Society of Civil Engineers (ASCE) is offering a webinar entitled Load and Resistance Factor Design (LRFD) for Geotechnical Engineering Features: Micro Pile Foundations. Information on the webinar can be obtained here. LRFD Methodology for this webinar is based on the approach used in the AASHTO LRFD Bridge Design Specifications which is probably the most extensive LRFD Specification applicable to geotechnical and foundation applications in existence today. I attended the first presentation of this webinar and found it to be helpful in understanding LRFD concepts as they relate specifically to micropiles within the framework of AASHTO LRFD Methodology.  The presenter for the pilot presentation of the webinar was Jerry DiMaggio. Jerry has been an instrumental figure in the implementation of LRFD methodology to foundation applications for FHWA and AASHTO and is extremely knowledgeable on the topic. The ASCE website lists the date for the next webinar as March 3, 2011.

Also of interest in terms of LRFD for Micropiles will be the upcoming DFI / ADSC Micropile Seminar in Little Rock, AR on May 3-4, 2011. I will be giving a presentation on LRFD Design of Micropiles on Day 2 of the Seminar. Be sure to check the DFI website for more information and I hope to see you in Little Rock!

LRFD and Micropile Design

The DFI / ADSC Joint Micropile Committee has formed a task force to look at how LRFD design approaches should be applied relative to Micropile Design. Currently, the vast majority of micropile designs are performed using Service Load or Allowable Stress Design in accordance with either FHWA or IBC allowable stresses. AASHTO has adopted an LRFD Design Section for micropiles as well as PennDOT. However, it is not clear how the LRFD design approach stacks up relative to current industry practice. Initial experience with the AASHTO LRFD approach would indicate that it is somewhat more conservative than Allowable Stress design and that it lacks a testing methodology that is consistent with LRFD philosophy. The committee welcomes your input on this topic in our effort to make recommendations for the best way to implement LRFD in Micropile Design and Construction.

Categories: Design Methods