In today’s market it is important to design your trusses competitively. One way the MiTek 20/20 software helps you design competitively is by giving you many different plate options. These options can help make your quality control easier and also help to design trusses that are easier to build in the shop. We are going to start at the top in plating options and move down explaining each option.
Figure 1. Plating Options Box in MiTek 20/20
• Plate for handling: The first option is Plate for handling. Plate for handling instructs the program to use a set of minimum plate sizes that our engineers feel are appropriate based on the joint type, chord size and truss span. This option can help you to avoid repairs on damaged plates caused by the erection process.
• Use stocked plates only: Selecting the second option Use stocked plates only instructs the program to only use the plates that are checked on in your selected plate inventory. If this option is not checked, then the program will use all the plates that are in your selected inventory to plate the joints on the truss.
• Do not force joint centered plating: When you check the option Do not force joint centered plating the program will use the smallest plate for the joint in question and tell you the exact location of where the plate needs to be on the joint. While this option will lead to smaller plates, it is important that each plate be placed on the joint exactly as stated on the engineering drawing. Not checking this might cause you to spend more money on plates, but save you money on doing repairs if the plates are not positioned correctly. Trusses with off-centered plates will generally take more time to manufacture.
The figure to the right shows the difference in the way the program would plate a joint if Do not force joint centered plating was clicked. Note that the plate is offset in both the x and y dimensions.
• Allow the use of overhang for plating: Allow the use of overhang for plating gives you the option to plate in the top or bottom chord overhangs or past the bearing. This might give you smaller plates but then your customer is not able to remove the overhang with out a repair.
• Include non stock plates in plate editor: The option Include non stock plates in plate editor allows the user to design with plates that are turned off or not in stock while in the Plate Editor.
Figure 3. Shows all the MT20 plates that would be in plate editor when "Include non stock plates in plate options" is turned on.
• Use plumb plate for symmetric peak first: When Use plumb plate for symmetric peak first is clicked on the program with try to use a horizontal or vertical plate at the peak before trying orientations parallel to the chords. With this checked on, the program will jump up to a horizontal high strength plate at the peak before rotating it. With this checked off, you will see a lot of peak plates that are not horizontal or vertical, but they will be smaller.
• Plate parallel to lumber, cuts, horiz, vert: When Plate parallel to lumber, cuts, horiz, vert is checked on the program will only place a plate parallel to lumber cuts, horizontally or vertically. If this is not on the program is allowed to try other plate orientations. This setting generally affects hip joints and keeps the program from using the miter-cut orientations.
• Try a non-centered plate before changing gauges: Next in the options box is Try a non-centered plate before changing gauges. When this is clicked the program will cycle through the first selection of plates before advancing to the next highest gauge. In other words, the program will try each plate positioned in a variety of ways before going to the next gauge plate in your inventory. If you have your plate inventory ordered in the way you would like to use them, typically by cost, you will generally want to have this checked on.
• Block splicing option: The Block splicing option governs the way the program will use splice blocks. A splice block is typically used to increase the steel section plating capacity on small dimensional bottom chord lumber containing exceptionally high tension forces. The Block Splicing Options dialog box gives he user a great deal of control over how splices will be plated. You can choose whether you want to use a block splice at all or to increase the plate gauge before using a block splice. Checking “Plate to extend beyond width of chord” but not “Blocks” will keep the program for using blocks but allow the use of ½” beyond the width of the chord for the steel section.
Figure 4. Block Splicing Options
• Non structural members: The Non structural members option governs the plating of members that are “nonstructural”; i.e. those that are not part of the designed load-bearing components of a truss (an example would be a bottom chord filler on a scissor truss). In cases where separate plating at the heel is not possible, due to limited heel height, this option allows the non-structural member to be plated with the truss with one plate at the heel when Plate as structural is chosen. The program still recognizes that this is a zero force member and puts only a minimal amount of plate on the member.
• No tie plates on ribbon blocks if length less than: When ribbon blocks are present on floor trusses, the program defaults to using a small plate for the attachment. If you would like to use three 10d nails to attach the top of the ribbon block instead of a plate, the maximum ribbon block length should be entered. If the ribbon block length exceeds this length a plate will be used. A note will tell you the requirements for attaching the ribbon block with nails.
• Split heel plate before changing gauge: On some shallow sloped trusses the program may require an exceptionally long length of plate to cover the scarf joint properly. If the Split heel plate before changing gauge option is checked the program will use two plates, if needed, at the heel before cycling to the next gauge plate. The maximum length of plate size the program will use is dependent upon you plate inventory.
Figure 5. Shows how the program will split the plate on heels when the Split heel plate before changing gauge option is checked
• Number of plates before not showing label: Next you can select the number of plates that are the same size that a truss should label before the program suppresses their labels. The program will add a note stating what the plate size is assumed to be if not shown. This allows you to see the truss with less clutter, both onscreen and in print.
• TPI/QC Fabrication Tol. (%): In preparation for the new ANSI/TPI 1-2007 requirements, TPI has allowed for the change from using the Cq factor to using this Fabrication Tolerance as the measure for how much of a reduction a design will use on the grip value for plating to account for defects. Prior to version 7.0, the Truss Manufacturer selected their Cq value, which in most cases was set to either 1.0 or 1.25 (taking into account 20% or 0% defects, respectively). In version after 7.0, the TPI/QC Fabrication Tol. (%) is now used to put in the desired % defect area. So, instead of inputting a Cq factor of 1.00, you will now enter a percentage from 0 to 20 for the TPI/QC Fabrication Tol. (%) in the plate options dialog box. Once again, the input value represents how much grip reduction (% defect Area) the user wants to use in their Quality Control Plan. For floor trusses this value would range from 0 to 11. Note: The setting “Use Existing Materials” prevents the changes in Fabrication Tolerance values from being applied. Any changes to these values will only be applied when you start the analysis from the beginning using Analyze Redesign.
Figure 6. New TPI QC Fabrication Tol (%) starting in version 7.0
• Flat plate TPI QC fabrication tol (%): This option only applies to floor trusses and the value you enter should typically be the same as you use for roof trusses, as this value is for the plates applied to the wide face of floor truss splices.
• Incremental Decrease of Fabrication Tol. (%): Let’s say you have the TPI/QC Fabrication Tol.(%) set to 20% and you have set Incremental Decrease of Fabrication Tol. (%) to 4%. In this situation the program will run the plating routine at 20% reduction and if it cannot plate a joint, then it will reduce the Fab Tol. by increments of 4% until the plate works (as close to 20% without failure to plate). This gives you the opportunity to have a plate with the most available defects without having a joint that will not plate.
• To reduce critical joints, try to limit JSI below: The To reduce critical joints, try to limit JSI below option enables the software to automatically increase the plate size when the joint stress index (JSI) value is above the value you enter. The typical values range from .80 to 1.00 for roof and floor. By entering 0.80, you will have less critical joints (those that require inspection) but you will have larger plates on the joints that would have otherwise required inspection.
• Plating tolerance:
Plating tolerance is the amount (in sixteenths of an inch) that a connector plate may be moved from its specified position and still pass quality control. A value of 4 indicates that the plate can be shifted up to one-quarter of an inch in any direction and the plate will still pass. Figure 7. The box around the green box shows the plating tolerance.
• TPI QC plate rotational tolerance (degrees): The TPI QC plate rotational tolerance (degrees) is the amount that a connector plate can be rotated from its specified position and still pass quality control. 10 percent is the recommended value in ANSI TPI 1 and the software will add a note on the drawings if a value of less than 10 is used in a design.
• Max plate length at heel before split plate: The Max plate length at heel before split plate option uses two separate plates at the heels when a single plate is required to be longer than the value entered in the box. In other words, if you enter at value of 10400, then if a plate larger than 16” is required, the program will use two separate plates instead of using one long plate.
• Use T-Plates: The next option allows you to choose if you want to use T-Plates for your top chord bearing trusses that would otherwise fail the top chord bearing reaction limit. If a T-plate will work geometrically, it will increase the reaction limit to 2400 pounds.
• Sq in. saved before using non-centered plate: The option Sq in. saved before using non-centered plate tells the program to allow a centered plate to be 50 sq. in. larger than a non-centered plate before the program will use the non-centered plate on the truss design. If you reduce this number, you will get more non-symmetrical plates. This will reduce the sizes of some of your plate, but your manufacturing group will have to be more concerned with plate placement. You may find that you are saving on plate costs, but increasing your manufacturing cost.
• Plate truss symmetrically: We all know how easy it is to put a truss up backwards in the field when there are only slight differences like overhangs and splices. Plate truss symmetrically allows you to select if you want the program to plate the trusses symmetrically when there are different overhangs, different splices or both. Plating the truss symmetrically can make things easier and quicker in the field and save on having to do repairs in the future for truss installed backwards.
Figure 8. Plate truss symmetrically options.
• Use stack plates over end bearing: Use stack plates over end bearing allows the user to plate the area above the bearing on a top chord bearing truss to add support to the area. Turning on this feature in plate options would typically add a plate above the bearing to strengthen the chord and tie them together.
Figure 9. Shear plate added when Use stack plates over end bearing is checked
• Allow custom joint center and plate locations: Allow custom joint center and plate locations gives the user the ability to set custom joint center and plate locations for particular joints. To set this up the user must go into setup\manufacture\materials\plates, check the advanced box and then click on Custom Joint Locs.
Figure 10. Customer Joint Settings Option in MiTek 20/20
• Add hinge shear plate on BEH18A and BEH18D joints and Center BEH18A and BEH18D hinge plate on joints: The next two options are for when you are using hinge cap trusses. The first option is Add hinge shear plate on BEH18A and BEH18D joints. When you enter “1” the program will add a small shear plate on one face perpendicular to hinge plate; if “0” is entered the program will not add the plate. The Center BEH18A and BEH18D hinge plate on joints option centers the hinge plates on the centerline of the chords. See MiTek Article Eliminate the Headaches of Piggy-Back Trusses located under the Technical Articles on the MiTek website for more information about hinge cap trusses.
• Plate even if overstressed and Allow overlapping plates: Plate even if overstressed causes the program to plate the truss even if the Lumber stress is over the maximum CSI of 1.00 or other design problems exist. Allow overlapping plates allows the program to plate the truss with plates that overlap each other. You would never want to leave these two options turned on, but they can help you at times to see what changes you may want to make to a truss design.
• Allow perimeter violations: Allow perimeter violations allows the plate to stick into an attic room, a chase or outside the profile of the truss based on settings under the Perimeter violations tab of setup\manufacture\materials\plates\joints types dialog.
Figure 11. Plating Joint Types Option in MiTek 20/20
• Use minimum plate size for all joints on truss(es): Use minimum plate size for all joints on truss(es) allows you to enter the minimum size plates that the program will use, whether it be on all the trusses or only gable end trusses. This option can save you time on a particular job if the owner is requiring a minimum size plate to be used.
• JackRabbit: The JackRabbiT option sets the requirements for building jack trusses with the JackRabbiT machine.
• Use plate to increase bearing capacity (TPI2007): If you manually modify a plate in the program to be within 1/4” of the bearing, then the Use plate to increase bearing capacity (TPI2007) option can be used to add capacity to the truss to resist crushing perpendicular to the grain at that bearing location. This feature helps lower required bearing sizes by using the plate. When this is checked on the program will not automatically place the plate over the bearing. This is something the user has to do manually.
• Use solid bar tension values for plate over splice: The Use solid bar tension values for plate over splice option uses a higher steel tension value for the plate if there is only metal over the splice, i.e. no slots over the splice. This can help to get smaller plates, but it is very important that the plate be placed as specified, otherwise a repair might be required. We recommend this option only be used when a splice joint is otherwise unplateable and not as a default setting, but it can be used to reduce plate sizes or gauge if you are willing to meet the quality criteria which may be significantly more stringent.
Figure 12. Two new options for TPI 2007
Now that you are an expert in the Plating Options that are available, you can be confident that you are designing trusses as competitively as you want to be. You can compare your saving from reduced plate sizes against your needs for quality control, ease/cost of manufacturing, and handling requirement. If you have any questions or if any of this information is not clear, please call your MiTek Engineer for further assistance.