COMPUTER PROGRAMS IN FOUNDATION ANALYSIS AND DESIGN BASICS AND TUTORIALS

FOUNDATION ANALYSIS COMPUTER PROGRAMS BASIC INFORMATION
What Are Foundation Analysis Computer Programs?

A large number of foundation engineering problems can be efficiently analyzed and/or designed using a digital computer. Particular advantages of using a computer accrue from these features:

1. One is able to try a range of problem variables to obtain a feel for the effect of specifying, or using, a particular set of soil parameters.

2. One can avoid having to use tabulated data or plotted curves, which usually require interpolation and excessive simplification of the foundation model.

3. One can minimize computational errors from these sources:

a. Erroneous key entry when using a calculator. The bad entry is (or should be) output to paper using a computer so the input can be checked.

b. Omission of computational steps. A working computer program usually includes all the design steps. A set of hand computations may not include every step for any number of reasons (forget, not be aware of, carelessness, etc.).

c. Calculator chip malfunction not readily detected except by using two calculators. Computer chips are often internally checked on power-up, or output is so bad that chip errors are visually detected.

4. With output to a printer one has a paper record of the problem for office files without the necessity of transcribing data from intermediate steps. This avoids copy errors such as 83 for 38 and the like.

The major disadvantage of using a computer program is that it is difficult to write a first generation, error-free program of real use in a design office. Program usability tends to increase with each revision (or history) level.

With the current wide availability of computer programs—many, such as those on the included diskette, having a "history"—the advantages gained from program use far exceed any perceived disadvantages.

The author suggests that both geotechnical and foundation engineers should use computer programs whenever possible—and certainly be aware of what computer program(s) each is likely to use for the given project.

This statement is made with full awareness of the possibility of program errors (or "bugs"). Fortunately, most geotechnical software is task-specific so that the possibility of program errors or their not being detected is not so likely as for some of the large finite-element or structural analysis programs that purport to solve a wide range of tasks.

In any case, the author cannot recall a single reported foundation design failure that can be attributed to a bad4 computer program. It should be evident that computer programs vary widely in perceived quality, perceived quality being defined here as problem limitations and "ease of use." Both users and programmers should be aware that it is difficult to predefine the full range of problem parameters likely to be encountered in practice, so nearly any geotechnical program of significant value is likely to have some built-in limitations.

Ease of use is highly subjective and depends more on user familiarity with a program than how easy it really is to use—many users like pulldown menus and graphics whereas others are quite content without these features. As a final comment on computer programs, be aware that although business applications and games usually have a market in the hundreds of thousands, geotechnical programs have a potential market of only a few thousand.

This small market means geotechnical software is likely to be more expensive than other software and, to minimize development costs, it is not likely to have many so-called user-friendly features.

One should routinely check the output from any computer program used for design or analysis. The user is responsible for his or her design since it is impossible to write a computer program with any usefulness that cannot be misused in some manner. Primarily for this reason most computer programs are sold or licensed with a disclaimer making the user responsible.

Fortunately, most computer programs can be written to be somewhat self-checking, either by writing back the input data or by providing output that can be readily identified as correct (or incorrect) if the user understands or knows how to use the program. It should go without saying that, if you do not know much about the specific problem being designed or analyzed, you should first do some preliminary study before using a computer program on it.

FOUNDATION ENGINEERING BASICS AND TUTORIALS

FOUNDATION ENGINEERING BASIC INFORMATION

What Is Foundation Engineering

The title foundation engineer is given to that person who by reason of training and experience is sufficiently versed in scientific principles and engineering judgment (often termed "art") to design a foundation. We might say engineering judgment is the creative part of this design process.

The necessary scientific principles are acquired through formal educational courses in geotechnical (soil mechanics, geology, foundation engineering) and structural (analysis, de-sign in reinforced concrete and steel, etc.) engineering and continued self-study via short courses, professional conferences, journal reading, and the like.

Because of the heterogeneous nature of soil and rock masses, two foundations—even on adjacent construction sites—will seldom be the same except by coincidence. Since every foundation represents at least partly a venture into the unknown, it is of great value to have access to others' solutions obtained from conference presentations, journal papers, and textbook condensations of appropriate literature.

The amalgamation of experience, study of what others have done in somewhat similar situations, and the site-specific geotechnical information to produce an economical, practical, and safe substructure design is application of engineering judgment.

The following steps are the minimum required for designing a foundation:

1.       Locate the site and the position of load. A rough estimate of the foundation load(s) is usually provided by the client or made in-house. Depending on the site or load system complexity, a literature survey may be started to see how others have approached similar problems.

2.       Physically inspect the site for any geological or other evidence that may indicate a potential design problem that will have to be taken into account when making the design or giving a design recommendation. Supplement this inspection with any previously obtained soil data.

3.       Establish the field exploration program and, on the basis of discovery (or what is found in the initial phase), set up the necessary supplemental field testing and any laboratory test program.

4.       Determine the necessary soil design parameters based on integration of test data, scientific principles, and engineering judgment. Simple or complex computer analyses may be involved. For complex problems, compare the recommended data with published literature or engage another geotechnical consultant to give an outside perspective to the results.

5.       Design the foundation using the soil parameters from step 4. The foundation should be economical and be able to be built by the available construction personnel. Take into account practical construction tolerances and local construction practices. Interact closely with all concerned (client, engineers, architect, contractor) so that the substructure system is not excessively overdesigned and risk is kept within acceptable levels. A computer may be used extensively (or not at all) in this step.

The foundation engineer should be experienced in and have participation in all five of the preceding steps. In practice this often is not the case. An independent geotechnical firm specializing in soil exploration, soil testing, design of landfills, embankments, water pollution control, etc. often assigns one of its geotechnical engineers to do steps 1 through 4.

The output of step 4 is given to the client—often a foundation engineer who specializes in the design of the structural elements making up the substructure system. The principal deficiency in this approach is the tendency to treat the design soil parameters—obtained from soil tests of variable quality, heavily supplemented with engineering judgment—as precise numbers whose magnitude is totally inviolable.

Thus, the foundation engineer and geotechnical consultant must work closely together, or at least have frequent conferences as the design progresses. It should be evident that both parties need to appreciate the problems of each other and, particularly, that the foundation design engineer must be aware of the approximate methods used to obtain the soil parameters being used. This understanding can be obtained by each having training in the other's specialty.

To this end, the primary focus of this text will be on analysis and design of the interfacing elements for buildings, machines, and retaining structures and on those soil mechanics principles used to obtain the necessary soil parameters required to accomplish the design. Specific foundation elements to be considered include shallow elements such as footings and mats and deep elements such as piles and drilled piers.