The triple threat: Precision, performance, and beauty for entryways

by sadia_badhon | September 26, 2019 11:09 am

by Roger Overend

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When designing building entryways, especially highly visible and heavily trafficked ones, architects and specifiers must successfully achieve precision, performance, and beauty (the triple threat) simultaneously.

While this is no simple task, products are available to meet all three of these requirements. One such product is the balanced door, a true ‘triple threat’ when it comes to creating striking, reliable, and fail-safe entryway systems.

Balanced door basics

The fulcrum is placed at one-third the width of the balanced door, so one-third of the door leaf recesses into the facility when the door is opened. This creates a more balanced pivot point for superior weight distribution. Even though a balanced door’s fulcrum is inset, it offers a similar opening space as conventional butt-, continuous-, and pivot-hinged doors.

The balanced door was invented in 1927 during an era of increasing popularity for skyscrapers and tight-knit construction. This new building trend inspired a need for a more high-profile door with the ability to resist both the external force of whipping winds through narrow streets and the internal stack pressures.

The first commercial balanced door was manufactured in 1932. What the manufacturer did not know then was that some of the balanced door systems that were created in the first few years of production would still be in use after the turn of the millennium, more than 80 years later. It is also likely they did not foresee the advantages (detailed below) balanced doors would offer to the design and functional challenges of today’s architects and specifiers.

Precision

The varied balanced hardware components set balanced doors apart from their conventional counterparts, and allow them to offer the pinnacle of precision. As a unified system, the many parts work together to facilitate nearly effortless door opening with reliable closing.

Components of precision

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Starting from the top, a check and guide channel assembly can be found in the balanced door’s frame header. This component provides a conduit for the elliptical cycle of a balanced door, as well as the capacity to manage closing and latching speeds. These adjustments are achieved through a removable component of the guide channel assembly containing hydraulic fluid and two valves––one capable of adjusting initial closing speed and another for latching speed. These modifications can be made from the underside of the header without having to remove the component based on the facility’s needs, an important consideration to avoid removing large and heavy doors during maintenance. These can be accomplished by a facilities manager or a door installer.

The component working in conjunction with the check and guide assembly, and thereby serving as the door’s fulcrum, is the roller guide located in the door’s top rail. Typically, a door roller guide is cast in a manganese alloy housing for strength, as it absorbs the shock caused by the door’s opening and closing. Contained within the roller guide is a sealed roller bearing that moves back and forth in the underside of the guide channel to help facilitate the door’s elliptical path.

A top pivot bearing is set into the door top rail and contains a steel roller bearing inside. It is joined to the door’s top arm by a heavy-duty stainless steel pivot pin. When the pin engages into the pivot bearing, the top arm is able to support the lateral weight of the door’s top portion.

At the bottom of the door, the lower arm bears the weight, and is therefore thicker and heavier than the top arm. Both arms are welded to the heavy-duty tube shaft running the door’s length. In order to ensure long-term durability, it is important to select a door manufacturer who uses true penetration welds to attach the arms to the shaft, rather than a wedged fit.

The door’s bottom pivot component differs from the top in that its bearing is made of an engineered self-lubricating composite. This is done to minimize corrosion, as the bottom portion is susceptible to corrosives like salt from coastal environments, deicing chemicals, or cleaning solutions.

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Fitting inside the tube shaft is the torsion bar, or closer spring. This torsion bar provides the closing force. The spring is tightened using torsion, as opposed to outdated coil springs, to provide durability and precision in tightening. This durability allows the torsion bar to accommodate very heavy doors, while requiring little user force.

A balanced door’s floor box holds much of the hardware in place, and also receives the door weight transferred from the tube shaft and arm assembly. However, the standard floor box is just 13 mm (½ in.) thick, 100 mm (4 in.) wide, and 178 mm (7 in.) long from interior to exterior. In addition to its weight-bearing and assembling capacities, it also serves as a convenient location for tightening the torsion bar to ensure correct tension. The torsion bar spring can be easily tightened with a wrench, as its top portion is pinned in place to the upper part of the tube shaft. It is important to note the bronze and stainless steel components within the floor box will not move unless being maintained, and therefore remain unharmed by dirt or corrosives. The author recommends contacting a door service company or the manufacturer for direction on maintenance procedures.

A final, often overlooked component adding precision to a balanced door is its semi-automatic hold-open device. As its name implies, this part keeps the door ajar without using an external element, like a doorstop. It is located in the bottom rail, and has a tapered foot pin connecting with a hole in the threshold (outside the walking path), allowing the door to remain open at its full 90-degree position. The foot pin is spring-loaded, so that a firm push is the only requirement to disengage the device and close the door.

Performance

When choosing an entry door system, architects and specifiers must consider several criteria to ensure high performance.

Foot traffic

First, anticipate the amount of traffic to the door. If the location of the door subjects it to constant use from foot traffic and exposure to the environment, the door needs to be a solid product highly resistant to deterioration and abuse. Balanced doors have a mechanical advantage—their balanced weight distribution—that allows them to offer long-term material durability.

With a conventional door, the weight is hung off the frame. Over time, screw holes elongate, causing bolts to come loose and the door to pull away from the frame, resulting in sag and drag. With a balanced door, the leaf is not connected to the frame, so the door’s weight is transferred to the bottom arm, down to the floor box, and eventually to the floor, which is much more capable of bearing weight than metal hinges. For this reason, a balanced door system lasts longer than a conventional hinged door assembly.

Conventional entry doors typically last 10 years with general use. Quality balanced doors are constructed in-house and contain parts cast and machined with high-grade materials. Therefore, balanced doors survive the test of time, generally lasting many decades with the oldest installations being 80 years and counting.

Wind and stack action pressure

The door needs to open easily and also remain closed in all conditions. When a balanced door is pulled against the forces of air, its entire surface area is not negatively impacted as it is with a conventional door. The air pressure affects both the strike and hinged sides (on either side of the fulcrum), using some of the force to assist in opening the door.

The same is true when the door closes, allowing for a more efficient closing motion. Balanced door systems facilitate fluid opening and closing, even when strong external wind pressures and internal stack pressures exist, as the door works with, rather than against, these forces. This also ensures doors remain closed (and not flutter) when confronted with uneven air pressure, ultimately reducing a facility’s energy costs.

User-friendly

The arrangement of a balanced door is such that the fulcrum is inset at one-third the width of the door—this allows for large, heavy, and durable doors to be opened with relative ease. A typical entry door has a fulcrum located on its side, which is attached to the frame with hinges, forcing the user to pull the entire weight of the assembly to open. Additionally, the weight of the door leaf hangs on the frame, constantly applying force to both the hinge and frame.

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Finally, if applicable, review the leaf projection of the door to the exterior to prevent it from protruding onto the sidewalk area and possibly obstructing pedestrian traffic. While traditional doors have a circular arc projection, the elliptical swing path of a balanced door reduces door leaf projection by one-third. In many cities, sidewalk space is valuable. If there is heavy foot traffic, a door opening into the flow of traffic can interrupt passersby. Only two-thirds of a balanced door leaf project to the exterior of the building. Many cities, such as New York City, have stringent door projection codes—the balanced door’s reduced leaf projection is especially useful in these situations.

Performance to code compliance

When choosing an appropriate entrance system, it is very critical to follow the American with Disabilities Act (ADA) to not only avoid legal ramifications, but also ensure easy access for everyone. The most updated version of the regulation, the 2010 revised requirements (with a compliance date on or after March 15, 2012), is consistent with the International Building Code (IBC) guidelines.

Among the most pertinent guidelines associated with entry systems is ADA 404.2.3, “Clear Width,” and involves clear opening space. It reads:

Door openings shall provide a clear width of 815 mm [32 in.] minimum. Clear openings of doorways with swinging doors shall be measured between the face of the door and the stop, with the door open 90 degrees. Openings more than 610 mm [24 in.] deep shall provide a clear opening of 915 mm [36 in.] minimum. There shall be no projections into the required clear opening width lower than 865 mm [34 in.] above the finish floor or ground. Projections into
the clear opening width between 865 mm and 2030 mm [80 in.] above the finish floor or ground shall not exceed 100 mm [4 in.].

When considering balanced door manufacturers, it is important to choose one with extensive knowledge about ADA guidelines to ensure the proper measurements are taken into account. For a single door, it is typically possible to meet the 815 mm minimum width requirement, provided the leaf is at least 940 mm (37 in.) with a 1092 mm (43 in.) total frame width. This allows the 102 mm (4 in.) required for balanced hardware, the approximately 25 mm (1 in.) required for door stop material on the opposing side, and the 76-mm (3-in.) door jambs at each side. A pair of doors with a 1981-mm (78-in.) frame (914 mm [36 in.] per door) would also provide an 815-mm opening with one door fully open, bringing in similar opening dimensions to a swing or pivot door.

A second pertinent consideration for ADA responsibility is opening force requirement. The Act does not have guidelines for opening force for exterior doors because it would be too inhibiting. Exterior doors are often large and heavy, and also have panic or latching devices, which must function properly. ADA does not limit the use of such devices with a strict guideline, but does pose an advisory in section 404.2.9, “Door and Gate Opening Force,” which reads:

The maximum force pertains to the continuous application of force necessary to fully open a door, not the initial force needed to overcome the inertia of the door. It does not apply to the force required to retract bolts or to disengage other devices used to keep the door in a closed position.

Although ADA does not universally require power operation functionality on entry systems, some cities (e.g. Chicago) need at least one power-operated entry on every new public building. Therefore, it is important to choose a balanced door manufacturer with the ability to make power-operated balanced doors. If power operation is desired, it must be a low-energy, power-operated door complying with the American National Standards Institute (ANSI) A 156.19, Power-assist and Low-energy Power-operated Doors.

Beauty

Since its invention in 1927, balanced door assemblies have graced the entrances of well-known museums, libraries, government facilities, flagship retail entrances, and corporate headquarters. From the Art Institute of Chicago and the Smithsonian buildings in Washington, D.C., to World Trade Center and the Empire State Building, balanced doors have been specified for high-profile projects because of their sheer craftsmanship and beauty.

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The door, frame, and balanced hardware create the complete assembly. The anatomy of a balanced door has been crafted to produce a ‘marquee’ entrance system.

Doors and framing are available in several materials (and finishes), including bronze, stainless steel, aluminum, wood, and glass. They are made in one of two ways depending on the material chosen. The types of glass stops used will depend on the construction method. For instance, bronze and stainless steel are formed-up giving more flexibility in the design and allowing pocket stops to be used if it is desired. Whereas, aluminum is extruded and has more limitations on design, resulting in the use of applied stops.

Balanced door leaves are available as stile and rail (when the door structure is metal) or tempered glass (when the structure is glass)—either with or without a stile. In any of the door types, full top and bottom rails are required to accommodate the balanced hardware.

Formed-up stile and rail door construction includes minimum-sized 70-mm (3-in.) stiles and top rails, bottom rails that are at least 152-mm (6-in.) tall (though 254 mm [10 in.] is required for ADA compliance), and a corner-welded internal subframe for rigidity. Door material is minimum 2.3-mm (³/₃₂-in.) thick with internal and external parts made of the same material. For bronze and stainless steel assemblies, spot-welding directly through the door face creates a unitized superstructure.

Quality balanced doors are built and pre-hung at the manufacturing location, allowing any adjustments to be made so operation is honed to perfection. This process allows for easy installation and is useful for renovation applications where the building must remain accessible.

Custom balanced door manufacturers can produce doors with multiple combinations of materials, sizes, and designs. These manufacturers can also incorporate sidelites and transoms around the doors, but it is recommended architects and designers work with a curtain wall or storefront manufacturer to achieve a unified aesthetic between the door system and surrounding building area.

Extruded aluminum balanced doors are a budget option similar in structural appearance to formed stainless steel or bronze versions. Aluminum extrusions are used in place of the formed metal. Aluminum material is available in an almost limitless number of architectural paint finishes, as well as traditional anodized finishes. While dissimilar metal corrosion between frame and internal machinery metals is not a concern for stainless steel, there is some electrolysis between bronze and aluminum over a long period of time if the doors are not periodically cleaned or there is a lot of salt buildup.

If balanced doors are used and panic hardware is required, the latter shall be a type of push pad not extending more than one-half the width of the door measured from the latch side. Balanced doors are configured this way to meet the National Fire Protection Association (NFPA) 101, Life Safety Code.

Conclusion

A superior entryway in every way with precision, performance, and beauty, balanced door systems are an investment lasting a lifetime, or more. They can be a suitable fit for any application in new construction, renovation, or retrofit, and they always leave a lasting impression.

Roger Overend is the CEO of Ellison Bronze. Throughout his 36-year career at Ellison, Overend has held a variety of roles, most recently as vice-president of operations. He is familiar with the varied aspects of balanced door production. Today, he oversees all aspects of project management, engineering, and fabrication, while working with customers to meet delivery requirements. He can be reached at roverend@ellisonbronze.com[6].

Source URL: https://www.constructionspecifier.com/the-triple-threat-precision-performance-and-beauty-for-entryways/

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