Electrical computers: arithmetic processing and calculating – Electrical digital calculating computer – Having specialized input
Reexamination Certificate
1998-11-13
2001-09-25
Malzahn, David H. (Department: 2121)
Electrical computers: arithmetic processing and calculating
Electrical digital calculating computer
Having specialized input
C708S167000
Reexamination Certificate
active
06295544
ABSTRACT:
TECHNICAL FIELD
The present invention relates to the field of building technology, and, in particular, to the determination of specifications for wooden structural supports.
BACKGROUND OF THE INVENTION
The use of wooden structural supports as building components is common, particularly in the western United States. Common wooden structural supports include rafters, joists, beams, and headers (beams built-up from multiple layers of lumber). There are many factors to be considered in designing a structure using wooden supports. Among the factors are the size of the structural supports, i.e., thickness and width, and the span across which they extend. The required size depends upon the loads placed upon the structural supports, the type and grade of wood used, and the span of the structural supports. Conversely, the permissible span will depend upon the loads, the type and grade of the wood, and the size of tie structural supports. Building codes, which may specify, for example, a minimum factor of safety or a maximum designed deflection, are also a factor in determining the design and type of wood used in structural supports.
A designer can predetermine and fix several of these factors and then calculate the remaining design parameters. For example, a designer can decide tie loads that will be supported, the type and grade of the wood used, the size of the supports, and the maximum deflection permitted, then determine the maximum span possible under those conditions. Alternatively, the designer can specify a predetermined load, grade and type of wood, maximum permitted deflection, and span, then calculate the size of supports required.
Calculation of any of the above factors typically requires the use of tabulated data for the different grades and species of wood. Tabulated data of this sort is based on empirical test results obtained in accordance with ASTM standards D2555 and D245 for clear wood and ASTM D1990 for full size test specimens. For western U.S. species of wood tables are published by Western Wood Products Association, Portland, Oreg., in the
WWPA Western Lumber Product Use Manual
and by the American Forest and Paper Association, Washington, D.C., in the
AF
&
PA National Design Specification Supplement.
Because of the various combinations of wood types, grades, and use constraints, a large number of tables are required. Because of the complexity of the calculations and the tables, design calculations are difficult to perform in the field, for example, at a construction site.
Sophisticated computer programs for use with a general purpose personal computer or minicomputer exist for the designer of wooden structures. Such programs are typically rather complex and require the user to have a detailed knowledge of the engineering of structural designs. Furthermore, the physical size of the personal computers required to operate these computer programs is prohibitive of the use of these programs at a construction site.
SUMMARY OF THE INVENTION
An object of the invention is, therefore, to provide a method and an apparatus to allow a user on a construction site to compute sizes and spans of wooden structural supports, such as beams, headers, joints and rafters, that are comprised of various species of wood and subject to uniformly distributed loads.
Another object of the invention is to provide such a method and an apparatus that prompts the user with leading questions and that provides feedback to the user to simplify the input of information needed to compute the size or span of the structural support.
These and other objects of the invention are accomplished by a convenient hand-held calculator. The calculator includes a program stored in association with a processor. The program executes on the processor to compute building requirements for wooden structural supports, including beams, headers, joists, and rafters. The program defines a procedure for acquiring information that establishes premises on which to base the computations. A compact display is coupled to the processor to provide the user with a constant reminder of the user-defined and calculator-generated premises upon which the computations will be made and to provide a means for displaying the computed result.
The program includes a series of input prompts that lead the user through a natural sequence for obtaining the required information. The input prompts are displayed on the compact display in the form of questions or options. When the user is prompted for a numerical value input, the display indicates the expected units of the numerical value and a proposed numeric value. The proposed numeric value can then be approved by pressing an enter key of the calculator or changed by entering the desired value using numeric keys of the calculator. Certain other information or options are entered or selected by pressing a dedicated key in response to the prompt. For example, the user is given the option of computing either a span or a size of the structural support by a prompt that displays “SIZE?SPAN?.” In response to the “SIZE?SPAN?” prompt, the user may direct the program to compute the size by pressing a dedicated SIZE key or to compute the span by pressing a dedicated SPAN key. Yet another type of prompt requires a user to choose from a limited number of available options. When multiple options are available, the user may scroll though the options using one or more dedicated scroll keys of the calculator then choose the desired option by pressing the enter key.
After the user has input the necessary information and options, the calculator automatically computes a desired specification result based upon the parameters and a series of equations. The specification result is then displayed on the compact display. The user can then stop or continue the execution of the program to view the ratios of stresses under the user-specified conditions to the corresponding allowable stresses. Spans and sizes computed by the calculator are normalized by the program to provide results that correspond to commercially available sizes of wooden structural supports or lumber. For expert users, the calculator includes a dedicated SET OPTIONS key that activates a subroutine for changing certain adjustment modifiers used by the program to calculate the results. Although the invention leads users easily through the design process, the user should have a basic knowledge of engineering principals and the assumptions that go into the structural calculations.
The calculator also includes a dedicated calculator key for switching between a program mode in which the program executes and a calculator mode in which the calculator operates as a simple arithmetic calculator. Arithmetic function keys labeled ÷, ×, −, +, and = are provided, along with the numeric keys, for operation in calculator mode.
Additional objects and advantages of this invention will be apparent from the following detailed description of preferred embodiments thereof which proceeds with reference to the accompanying drawings.
REFERENCES:
patent: 4463438 (1984-07-01), Zatezalo et al.
patent: 4744044 (1988-05-01), Stover et al.
patent: 5042006 (1991-08-01), Flohrer
patent: 5138566 (1992-08-01), Comforti
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Malzahn David H.
Stoel Rives LLP
Western Wood Products Association
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