Awnings 

General Design Considerations for Awnings

The major elements of an awning-system design are:

Purpose

What is the functional objective of the awning - shading, weather protection, identification, or aesthetics?

Style, Configuration, Color

Most awnings and canopies consist of fabric stretched over and secured to a fixed metal frame that is secured by laces or screws. These frames may be welded, bolted or otherwise connected. Other awnings and canopies that consist of individual fabric panels can be stapled to a groove in the face of an extrudedaluminum, fixed-frame element. Still other awnings and canopies consist of rollers and lateral arms that can be retracted manually or automatically.

The Awning Division has adopted standard names for awning and canopy styles. Standard names (with accompanying designs) for awnings and canopy styles are:

Elongated dome

Dome

Rounded entrance canopy

Concave

Quarter round convex

Lateral/arm retractable

Traditional

It should be noted, however, that the possible combinations of styles, configurations, and colors are limitless.

Size and Fit

The size of an awning is determined by its length, width and projection from the building to which it is attached. Other aspects of size include clear height (underneath), rise (pitch) of roof and post or rafter spacing. These features are usually important to those involved in the planning and review process.

The fit of an awning is determined by the interfacing of its frame with other connecting structures (most often a building, but frequently the ground or a concrete slab on the ground). In the case of a building, it is important to coordinate the appropriate parts of the awning frame with structural members in the building so that loads are transmitted properly.

Economy

The economy most directly affects customers and awning contractors. It is clear that an awning system should not have to meet the same code requirements as a high-rise building. However, in most cases, a code does strictly apply. In rare cases when it is not expressly required, there is still a moral and legal obligation to install an awning that can withstand any foreseeable loads.

To develop an economical awning system, the designer must understand how to arrange, size and connect structural members so that the foreseeable loads will be transmitted to its supports while incorporating safety factors, without overengineering the system.

The awning industry and building and code officials should develop a working relationship to better understand each others' needs. In addition, the industry members' active involvement in implementing code changes is very important. The objectives should be to assure public safety and to avoid needless, expensive over-design.

Sound economical design does not necessarily result in the lowest first cost.

Safety: Egress and Fire

Except in rare cases, this is not a significant issue with modem awning and canopy systems. In most cases, frame materials are non-combustible, and fabrics are flame -retardant. However, this point should be ascertained whenever appropriate, such as for enclosed walkway canopies and enclosed patio canopies. The answer is not necessarily to require fire doors and sprinklers for these systems. But the building official does have the right (indeed the obligation) to design systems that provide an open, safe and quick exit to the outside.

Stability

The average designer may have a concept of how beams and posts work structurally. But to design a safe structure, one must fully understand stability issues. A structure comprised of simple beams mounted on the top of simple posts is inherently unstable. This means that the structure is susceptible to falling down because of the number, arrangement and method of connection of the members.

Common post and beam structures, such as pole barns, are rendered stable by the addition of siding, roofing, "X"- bracing and fixed cantilevered footings.

Fabric has no in-plane stiffness; therefore, it does not replace, in an awning or canopy, the function that siding or roofing performs as in a pole barn. This inplane stiffness, which is instrumental to the development of stability, can usually be supplied by triangulation of structural members.

Examples of triangulation are demonstrated as follows:

The important lesson to learn here is that substituting larger beams or posts for smaller ones doesn't solve the problem of instability.

Anchorage

This involves the location, style and strength of connections from the awning or canopy to the building or to its foundations.

Proper design of this element assumes a recognition of the amount of force occurring, and the direction in which this force acts, at the connection at the time that the maximum design load occurs on the frame.

Most common types of connections involve bolt-through, expansion anchors, wood lag screws and adhesive anchors.

Bolt-through connections are preferable, when the are feasible, because the bolt and the nut are manufactured to controlled specifications, and there is a wealth of data on the strength provided by such a connection. Such connections are not generally subject to site questions that are often associated with other types.

Expansion anchors are used to fasten awnings to concrete surfaces. They develop their essential strength by pressing hard against the side of the drilled hole in which they are set. This pressure results in high frictional resistance to pull-out. While these kinds of anchors have been in successful use for a long time and may be well-manufactured, their use requires more good judgement than the use of a simple bolt-through solution. Obviously, when fastening to concrete surfaces, expansion anchors may be the only practical choice.

Wood lag screws are tapered to a point and do not utilize nuts. These are not as sound as bolt-through connections because they are subject to pulling out as the wood surrounding their threads crumbles or chips. Their strength, then, is proportional to the hardness of the wood in which they are embedded. In many awning applica-tions that require fastening to wood fram-ing, bolt-through connections are not possi-ble and wood lag screws may be the best available option.

Adhesive anchors have been made available in recent years to provide the awning installer a way to address field situations in which the preceding anchor types are not suitable. Examples of such conditions are veneer brick surfaces and fasteners located close to corners, where the high pressures associated with expansion anchors will raise the risk of being pulled out. Adhesive anchors are bonded directly to the substrate by filling an oversized drilled hole, which contains the threaded fastener, with an epoxy adhesive. This system does not rely on pressure. A certain amount of cure time may be required before the anchor can be loaded.

Strength

After a stable configuration has been established for an awning design frame, members should be chosen for a strength consistent with the amount and type of stress imposed on them. The most common types of stress are tension, compression, bending and shear.

A common misconception about awnings is that they are safe as long as they don't fall down. All code and engineering standards have long required that a safe design use members that are 1.67 to 2 times stronger than the yield strength required to satisfy the actual design stress. The yield strength is the strength at which the material no longer fully recovers to its original shape when the load is removed; the yield strength is usually significantly lower than the ultimate strength. Thus, it can be immediately recognized that a "safe" structure is stressed well below its breaking strength when it is exposed to its maximum design load.

Drainage & Ponding

Provisions must be made to drain water off an awning or canopy. Fundamentally, this involves establishing a steep enough pitch, properly spaced bows or rafters, as well as maintaining a taut fabric, so that draining water or melting snow cannot cause the fabric to sag and collect water on the surface. Lack of proper attention to this detail can result in potentially large gravity forces on the frame and anchors.

Graphics

The overall success of a commercial awning may hinge on the design of its graphics. Local codes and ordinances may dictate the size and other characteristics of this feature.

Fixed vs. Moveable

A fixed awning's frame cannot be deployed from a stowed position and vice versa. A moveable awning can be stowed against the building to which it is attached The standard lateral arm/retractable awnings and horizontal bow awnings are examples of a moveable awning.

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