Schematic Designs

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These designs seek to create expressive interior spaces within the logics of conventional systems. They contain various combinations of the construction logic promises defined in a previous post, keyed in the diagram below.

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Automated Jigging

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Automated Jig Table at Huskey Truss

In a truss manufacturing facility, jigging is the process of locating pucks along the tracks of a jigging table where truss members will be held in place for assembly. Traditionally, each puck is located by hand with tape and a chalk line based on shop drawing measurements. This system lends itself well to the creation of many identical trusses but becomes quite labor intensive (and as a result, sometimes cost prohibitive) to create multiple unique trusses.

Automated jigging tables were first introduced in the late 1980s, but have been very slow to catch on. Now computerized, some jig systems can even be controlled alongside other manufacturing operations in programs such as MiTek’s JigSet and MVP mentioned in a previous post.

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Joint Puck Possibilities (Image: http://www.mitek-us.com)

The increased production capacity permitted with auto-jig systems can significantly impact cost, potentially expanding design possibilities for small budget projects. MiTek claims that their automated jigging system, MatchPoint, can lower the build time for a truss by 50-60% and with nearly 100% accuracy, positioning pucks within 1/32”. Jigging setup via computer command takes 30 seconds on average, and the combined process of jigging and building takes 3-5 minutes.

Wall Panels

In areas of demand, truss manufacturers are able to produce wall panels, or framed walls which are pre-fabricated in the plant and erected on-site. Often mistaken for manufactured and modular units, wall panel construction delivers a quality similar to that of conventional framing with higher material and labor efficiency. The main difference between wall panels and conventional framing is the location of assembly.

wall-panel-comparison-diagramMost truss manufacturers are unable to supply wall panels due to lack of demand, a reflection of quality misconceptions and a reluctance from framers to construct. Because on-site construction time for wall panels is low, regional markets exist in areas with strong labor unions. Todd Snyder of MiTek suggests that the decreased construction time should be an incentive for framers, enabling them to take on more projects in the same amount of time.

Another difference when building with panels is a shift in liability. Wall panel manufacturers use software programs to calculate loads and use lumber optimally. As a result, the liability for error in the framed walls falls on the panel manufacturer and not the framer. In fact, the framer is considered an “installer” because the panels are pre-framed. At Huskey Truss in Murfreesboro, TN, lumber is cut, framed, and sheathed at different workstations, each equipped with drawings. Thus, inaccuracies are likely to be caught by one of the workstations prior to the panels leaving the facility.

Some manufacturing facilities employ their own framers to maximize labor efficiency. In times of slow business or bad weather, wall panels can be constructed within the facility, keeping people employed and jobs on schedule. Wall panel construction can also offer increased quality control because of the jig capabilities within the facility. Scrap lumber which would typically be thrown in the dumpster in on-site construction can be repurposed within the facility for floor trusses or other building components. Jackie Crutcher at Huskey Truss says a project typically requiring 4-5 dumpsters can require as few as 1-2 when framed with wall panels.

Panels can arrive at the site as frames only with sheathing bundled separately or pre-sheathed. As mentioned in a previous article, drivers delivering the panels are often equipped with instructions for locating bundles in the area of the site where they will be erected.

MiTek’s Software & Workflow

A previous post explained the workflow at Brown Truss Company, a local plate truss manufacturer using the OnLine Plus software for design and manual saws and jigging for production. OnLine Plus is provided by MiTek, an engineered product supplier for the building components industry. Kevin Brown expressed his plans to transition to MiTek’s more advanced softwares in the future, which prompted us to communicate with MiTek directly.

MiTek’s software suite can be divided into three umbrellas: OnLine Plus, Sapphire, and MiTek. OnLine Plus offers a 2D platform for truss design and engineering. As BIM becomes the standard in architecture and engineering firms, MiTek plans to discontinue updates for OnLine Plus to encourage transition to their other software, Sapphire, which offers a 3-dimensional platform. The Sapphire and MiTek softwares work back and forth to design and ensure the structural viability of trusses within a 3D model. A range of supporting programs aid in truss production and even on-site assembly.

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MiTek’s Software Suite Design & Management Programs (not showing programs related to business management)

The diagram below explains a workflow which could occur in a relationship between architect and truss manufacturer using MiTek’s software. The architect can submit drawings in two or three-dimensional form, but only models created in AutoCAD Architecture, Autodesk Revit Architecture, Autodesk Revit Structure, and Cadsoft Envisioneer can be directly converted into a file type (MXF) compatible with Sapphire Structure. The software recognizes Revit assemblies within the MXF file, and the assemblies’ properties inform the location of building components which can populate the model automatically in the form of truss profiles and wall panels. Truss profiles are populated with structural webbing in MiTek’s Engineering software. It is best if the architect and truss designer have established the final truss profiles before doing the calculation work in the Engineering software.

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MiTek’s Virtual Plant (MVP) and JigSet are two programs that aid in production management. In plants with automated jigging, JigSet can streamline the process of placing pucks for assembly. MVP allows plant managers to virtually see and organize production activities within the plant, helping to maximize labor and material efficiency. Automated jigging and the use of MVP software is commonly found at higher-end facilities that require the extra efficiency to keep up with orders. Proper use of these tools can significantly impact the cost of a project, especially in the production of multiple unique trusses which would otherwise require hand-adjusting each jig set.

 

A future post will summarize our visit to Huskey Truss, a fully-automated truss manufacturing facility in Middle Tennessee.

 

This post has been edited from the original to reflect a better understanding of the inter-operability between MiTek’s software and Revit.

Construction Logic Promises

This research posits that design opportunities uncommon in small house design are possible with slight manipulation of conventional construction logics (outlined in a previous post). The graphic below illustrates a few of these possibilities.

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Optimized Framing | With precision, optimized framing can be employed to maximize lumber utility.

Exposed/Organic Framing | Uniform load distribution creates opportunities, with proper calculation, for unique compositions within stud walls which can be exposed to the interior.

Angled Sill | An alteration to the standard stud wall as simple as angling the top plate creates new formal possibilities.

Atypical & Asymmetric  Forms | Bottom chords can be angled to rest on walls of different heights, and profile possibilities are diverse in absence of a standardized assumption.

Sectional Manipulation | Interior and exterior profiles  can exist relatively independent from one another, creating opportunities for spatial definition within the ceiling.

Sectional Variability | Variation in sectional manipulation can be used to define multiple interior volumes.

 

 

Techniques to “Help the Framer”

Prefabricated trusses can simplify construction and bridge occasional gaps between designers and builders. Through our research we have come across a few methods which can be employed to “help the framer” install accurately, minimize on-site errors, and save time on repetitive steps (ideally reallocating that time instead on those areas that impact design and craft).

Typically trusses require blocking to brace each other. These can be labor intensive to cut and inconvenient to nail, and they create staggered nailers for the roof sheathing. Kevin Brown of Brown Truss Company often lowers the top chords by 2-1/3” to allow for a continuous bracing member, simplifying the connection of jack trusses and doubling as a consistent nailer. Brown said framing trusses with this technique results in a product where use is “self-explanatory” to the framer. Furthermore, notching at end gables can secure a continuous bracing member or make flush connections for overhangs. Automated saws are becoming more common in truss manufacturing, and notching and marking members for quicker assembly can be achieved with negligible increase in expense.

Brown often includes birdsmouth and plumb cutting on the ends of trusses and extends truss members for overhang framing as part of his services. They create no additional cost to him and save the framers considerable time on site. As part of his services, he also visits sites to ensure bearings and bracing elements are located properly.

 

 

Todd Snyder of MiTek, the software and machinery provider for Brown Truss Company, expressed a strong interest in seeing direct interaction between framers and members of the truss industry for training and general awareness purposes. MiTek helps framers by providing their Sapphire Mobile Viewer for free so framers can view the built structure virtually as if it were already erected on-site. With this software they can locate themselves within the 3D model to compare the design model and the actual construction underway.

Another service that some structural component manufacturers provide relates to bundling and staging. For example, factory cut wall panels can be bundled (as panels or kit of parts), labeled, and then unloaded according to their placement in the design. The delivery driver is equipped with an annotated floor plan, and can unload each bundle (“E01” (East Bundle 01), “E02” (East Bundle 02), etc.) directly to the location on the slab where they will be soon be erected.

Jimmy Pye at Anderson Truss Company uses the term “defensive design” for efforts aimed at preventing or alleviating problems which can arise after the trusses are set. Where possible, truss designers at Anderson locate non-structural members at the interior profile of trusses to accommodate possible ceiling height changes on-site. Another of their practices is upsizing members at critical points in a truss, for example where span may be an issue if not properly installed.

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“Defensive Design” (grey indicates non-structural elements)

A common practice is to include with the trusses a Dos and Don’ts list or other instructions for proper assembly. One common instruction on this list is to lift trusses with a spreader bar to prevent straining the members. The practice of lifting a truss at its peak, a common installation error, can warp the members and compromise its structural integrity. Improper handling is frequent enough that some manufacturers like Huskey Truss overplate their trusses to compensate, consequently adding material that would otherwise not be necessary.

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Spreader Bar Truss Installation

These proactive techniques simplify, speed up, and control the quality of the installation process, but they rarely alter the framing expense which is gauged by square foot rather than installation time. As installation expense begins to reflect the continuing technological advancements in the truss manufacturing industry, truss design opportunities should become increasingly more accessible in affordable and market rate housing.

Construction Logics: Trusses & Frames

Truss and light wood frame construction methods are considered “conventional” in affordable housing design. They are systems which follow a certain logic, are associated with certain standards, and have over time become a standard themselves. Below we have defined the inherent logics in these systems in preparation to challenge their limitations.

 

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Light Wood Frame Logics

On-Site Fabrication & Adjustment | Light wood structures are easily fabricated on site with dimensional lumber. Stud walls are created in sections and tilted up into place. Member spacing is determined on site.
Pros: Requires simple tools, low skill labor, and can adapt to changes during construction
Cons: Inefficient use of materials, limited spatial complexity

Consistent Sill Plate | The uniformity and orthogonality typical in light wood construction allow for relatively easy and quick assembly. Having no variation in sill height minimizes chance for errors.
Pros: Allows for repetition, minimizing mistakes and lowering assembly cost and time
Cons: Limits design capabilities

Redundancy | Structural loads are distributed amongst repetitive studs spaced 16” or 24” apart. The system over-compensates for the roof load, allowing for on-site flexibilty, openings within the stud walls, and a larger margin of error in construction.
Pros: Can absorb more construction errors and allows for imprecision
Cons: Causes waste, inefficient material use

Flexibility | The system’s redundancy enables on-site flexibility. Wall openings can occur in most locations within the system, even if it means overcompensating for structural loads on occasion.
Pros: The system can adapt to many types of wall openings
Cons: Low precision, often the flexibility is enabled by inefficient use of materials

Imprecision | Redundancy within the system allows for imprecision. The result is shorter construction time and lower skill level required.
Pros: Shorter construction time, lower skill level required
Cons: Causes waste, limits design capabilities

 

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Truss Logics

Off-Site Fabrication | Truss manufacturers design, cut, and assemble trusses according to the length and slope requested. Because they are assembled off-site they are limited by truck dimenisons and regulations. [federal law: overall vehicle width 8’6”; most states limit height from 13’6” – 14’6”; trailer length 48’].
Pros: High level of precision
Cons: Standardized design options

Consistent Sill Plate | The level sill plate and 90 degree connection make field assembly quick and repetitive.
Pros: Quick assembly
Cons: No interior height variation, limits design flexibility

Redundancy | It is common to maintain a consistent truss design throughout. However, to achieve intersecting or hipped roofs, trusses can overlap each other or be cut to a portion of their size.
Pros: Consistency, flexibility within limits
Cons: Causes waste

Roof Profile Assumptions/Expectations | Tradition, inherited construction practices, and standardized production methods have created expectations and assumptions for truss profiles and significantly constribute to the sustained popularity of certain designs.
Pros: Common roof styles can be achieved easily and constructed quickly
Cons: Limits design flexibility and creativity

Large Span Structures | Trusses are intended to span large distances, requiring fewer loadbearing walls. This creates opportunities for extending overhangs or carving outdoor spaces. The zig-zagging truss members allow long spans but prevent attic space from being occupiable.
Pros: Fewer loadbearing walls are needed, system lends to overhangs
Cons: No allowable attic space

Brown Truss Visit

On 31 August we visited Brown Truss Company, a plate truss manufacturing facility in Maryville, TN. We spoke with Kevin Brown, manager of the family business, who stated at the beginning of our conversation that for Brown Truss every order is a custom order. Rarely does he encounter a request that he cannot design and fabricate, as long as it meets structural requirements.

Design Inputs | Determinants for plate roof truss designs include bearing points, vault locations, lengths, and pitches. Brown Truss typically receives roof pitch(es), basic 2D floor plans with locations for rooflines and transitions, and perhaps a 3D image. 3D models, when shared, are valued and clarify design intent, especially where unique conditions occur.

Technology | Brown Truss uses the OnLine Plus software by MiTek to design plate trusses. The program rationalizes load distributions and structural capabilities of various dimensional lumber sizes, allowing a truss profile to be populated with appropriate webbing members and gusset plates. Brown Truss typically designs trusses such that members are as similar and repetitive as possible to decrease cutting labor related to saw adjustment. The process above does not require a structural engineer’s input beyond what is included with MiTek’s services. If the engineered software allows Kevin Brown to create a digital truss, then it inherently meets the structural requirements (municipalities vary in their requirements for engineering stamps and state-level approvals). OnLine Plus software is used to generate fabrication drawings, and Brown Truss prints these for use in the factory – manual setting of saw blades for cutting and manual jigging of truss profiles for layout.

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Designing with OnLine Plus (image: http://www.mitek-us.com)

Brown Truss’s machinery currently requires manual re-adjustment of saw blades. This can increase labor costs for orders involving many different angles. However, during our factory tour, Kevin Brown pointed out a new saw that will soon be configured to auto-adjust its saw blade angle by interfacing directly with the truss design software. Computer-controlled automation of saw blade angles will speed up cutting processes and increase accuracy. Though Brown Truss’s current plans for automation do not extend to its jigging tables, a future post will look into automated jigging. Brown Truss’s future plans do include transition to another MiTek software product, Sapphire, in order to take advantage of increased 3D design capabilities.

Cost Drivers | Labor and materials (lumber and plates) are the two main factors determining cost. Labor costs typically reflect the amount of additional time that will be required to reset the saws and create new configurations; however, this will likely decrease as saws become more automated. The heel height of the truss often determines the amount of cost increase due to its positive relationship with lumber usage. For example, if the interior vaulting requested is a low enough pitch, the heel height may not be affected, and the increase in both lumber and cost is insignificant. A request requiring a higher heel height will require more lumber and thus raise the cost.

“Helping the Framer” | Watch for our next post discussing ways that plate truss design anticipates installation accuracy and efficiency.

Sauter Timber Visit

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Hundegger machine at Sauter Timber (image: http://www.sautertimber.com)

On 23 August we visited a local timber company, Sauter Timber in Rockwood, TN. Although Sauter specializes in cuts and joinery for heavy timber construction, similar machinery can be used to cut light wood members ready for installation. We spoke with Reinhard Sauter and inquired specifically about the possibilities for and limits to light wood precut packages.

While Sauter has at times experimented with the production of light wood framing components at his facility and occasionally produces some light wood components as infill for the heavy timber packages he provides, the expense and complexity of his robotic saw and lack of significant demand make this market segment unattractive for him. He did note, however, that the same company that manufactures his robotic saw, Hundegger, also makes a simpler version, known as a Speed Cut, that is well suited to the production of light wood members. Using HSBCad software (other options include SEMA and Cadwork) allows manufacturers to translate designer’s 3D files directly into manufacturing data ready for production. The software recognizes the need for additional framing members at wall openings, adjusts its output to the requested member spacing, and includes parameters for building codes. It currently cannot rationalize organic forms, but Sauter believes that the technology is coming soon. Sauter is confident that this technology could (and should) alter light wood construction standards, but he has seen little willingness from contractors and framers to make the change.

Identifying Precedents

The following are design precedents organized by the strategies they employ which are relevant to our research. The strategies include: expressive framing, space-saving, and affordable design.

 

 

Expressive Framing Strategies | Exposed Structure

These projects embrace unique expression opportunities through exposed structure. Projecting structure to the exterior, exposing structure in the interior, and designing innately expressive structural systems are all strategies valuable to our study.

 

 

Expressive Framing Strategies | Truss Profile Manipulation

These projects use truss profile manipulation to create unique volumes and views.

 

 

Space Saving Strategies | Covered Outdoor Space

These projects use covered outdoor spaces as both cost and space-saving strategies in expressive ways.

 

 

Affordable Design | Sectional Manipulation

These projects utilize common forms and construction methods, achieving design expression through strategic interior planning.

 

 

Affordable Design

These are examples of affordable houses incorporating expressive framing.