The increased use of metal framing has created a need for computer software for the design of metal trusses and wall framing. Wood truss design software has been used for many years, but because of many differences between wood and steel (strength, available lengths, connection types, etc.), the conversion of wood truss design software to steel truss design software is impractical. AISI has recently published the Design Guide for Cold-Formed Steel Trusses which recommends how metal trusses should be designed. Without the use of sophisticated computer software, it would be extremely difficult and time consuming to analyze a metal truss.
The design of steel trusses are very complex because the analysis has to take into account many aspects such as:
Truss geometry (standard and odd shaped trusses)
Plane frame finite analysis of the top and bottom chord
Possible offset web members
Possible eccentricities between chords and webs
Different type connections
Concentrated, uniform and trapezoidal loads
Multiple load combinations (Dead, Live, Snow, Wind, Seismic)
Different building codes
Permanent lateral bracing
Some architectural building designs have lead to unique truss shapes. Generating the truss geometry for trusses with hip/hip roof intersections, vaulted ceilings, tray ceilings, offset peaks, mechanical openings, etc., can be very time consuming. Analysis programs that are not specifically designed to generate regular and irregular truss shapes can be frustrating to use.
The key to selecting a metal truss computer program is to ensure that all the aspects listed above are addressed. Also a costing module will be required to determine the most economical truss design.
John F. Butts & Associates has developed a finite element truss design and estimating program called TRUSS D&E and released version 1.0 in December 1994. Since then, many upgrades have been added to facilitate different building codes, truss configurations, fasteners, etc. TRUSS D&E takes the complexity out of designing steel trusses. Through a menu input routine, a truss design can be generated in less than 5 minutes. The program can select the most economical design layout and components usage for a specific application. A complete Bill of Materials, list of required construction details and truss cross-section is automatically produced.
TRUSS D&E conforms with all the guidelines recommended in the AISI Design Guide for Cold-Formed Steel Trusses. Additional design criteria is listed in the TRUSS D&E Reference Manual. The reference manual also has over 180 truss connection details. The program will automatically reference the details required for fabrication.
Some unique design features of TRUSS D&E are:
Select either FPS (feet & inches) or Metric (SI) units
Input concentrated loads at any point along the top or bottom chord
Input dead, live, snow, trapezoidal and seismic loads
The User Configured Truss Option can generate any truss shape very quickly with a minimum of effort. All that is required is inputting the bottom and top chord break points and maximum panel spacing.
Truss webs normally meet at a common point. The Offset Diagonal Option separates the web members, thus eliminating connector plates and decreasing fabrication time. TRUSS D&E is the only commercial truss program which offers this option.
Several connection options are available; screws (from #6 to 1/4), rivets, bolts and welding.
Multiple steel member selection. At present there are 7 member libraries to choose from; Dale/Incor, Dietrich, MSMA, MBCI, KMI Framemaker, KMI CZ and AISC.
Merge Libraries - Two libraries can be merged, either member by member or all members.
There are several building codes to select from; ASCE 7, BOCA, SBC, UBC, Canadian, British, French and Australian.
The analysis is performed for seven (7) preset load cases and ten (10) load combinations.
Top and bottom chord permanent lateral bracing is sized and spaced per AISI, AISC and SJI formulate.
Maximum interior and overhang deflections and stiffness ratios are calculated and displayed in tabular form.
Additional internal features:
On-line Help menu's
Error detection routines
Step through menu's
Auto save/recall of project files
Additionally, a complete Bill of Materials (BOM) for the truss components is produced. The BOM would include coil material (if applicable), fasteners, truss member lengths and number required, permanent bracing and connector plates. The BOM eliminates the need to do an extensive material takeoff.
The Truss Cost module will allow the user to easily enter or change cost data for different components of the truss. With the ability to change the cost data, the user has full control of the truss estimate. Also, a Currency Selection Menu allows the user to specify what currency is to be used for the truss estimate; i.e. Dollars, Dinars, Yen, Pounds, etc.
John Butts is president of John F. Butts & Associates, Inc., Colorado Springs, CO. He is a graduate of the University of Colorado with a degree in Architectural Engineering and is a registered engineer in several states. John has authored several structural manuals and computer programs for the design of light-gage (cold formed) metal shapes and structures. The firm specializes in light-gage (cold formed) design nationally and internationally.