Steel Building Design Considerations
With the development of our diverse building systems line, the prospective customer is offered more choices in the design, appearance, and value of a building. This enables the customer to select a system that provides the performance characteristics that best meet specific building requirements. Our building systems include:
Gable Symmetrical: A ridged (double slope) building where the ridge of the roof is in the center of the building. This is the type of building that can be configured, priced and ordered online.
Gable Unsymmetrical: A ridged (double slope) building where the ridge of the roof is off-center. This type of building requires a custom quote.
Single Slope: A sloping roof in one plane. The slope is from one sidewall to the opposite sidewall. This type of building requires a custom quote.
Lean-To: Ideally suited to give you that extra space you need alongside your building. The lean-to attaches at or below the eave of your building, and can provide shelter for a variety of uses, from just a covered area to a completely enclosed addition to your building. This type of addition requires a custom quote.
Hybrid Structures: Hybrid structures blend the advantages of metal building system construction with the strength of conventional steel members. Hybrid structures meet heavy loading requirements by providing the most effective design possible – the best of both worlds. The advantages include:
Single source responsibility
Fast, easy construction
The designs and engineering available allows virtually any requirement for hybrid structures, no matter how large or complex. When it comes to large, tough construction jobs, the hybrid building approach provides a cost-conscious alternative.
Crane Buildings: With the end use of metal building systems dominated by the manufacturing and warehousing sector, building cranes become an important element of the structure. We recognize the need to properly integrate the design of the metal building system with the building crane specifications. The building crane is a complex structural system consisting of the crane with trolley and hoist, cranes rails, crane runway beams, structural supports, stops and bumpers.
The cranes typically found in metal building systems include:
We can provide each metal building and crane support system to meet the specific requirements of your project.
Aviation Facilities: Aircraft hangars are individually engineered to meet specific requirements and are flexible enough to satisfy even the most complex aviation need. The hangars may be designed using gable symmetrical, gable unsymmetrical or single slope structural systems.
These cost effective, functional structures have many advantages:
Fast, easy construction
Reduced maintenance costs
Clearspan design provides column-free interiors for wide-open floor space and eave heights that can accommodate today’s larger aircraft. The structures allow for a variety of door options including bi-fold, bi-parting, and stack leaf designs.
By combining the metal building system with conventional exterior materials such as brick, stone, precast concrete, or glass, the structure can be aesthetically appealing while providing the perfect solution to aviation needs.
Construction Material Requirements
Consider some of the key factors that influence the selection of construction materials by the manufacturer, the designer and the user.
STRENGTH is a very important factor.
AVAILABILITY of material influences its selection, cost of material and final in-place cost.
To facilitate design and fabrication, a material must possess a good degree of WORKABILITY.
WEIGHT and BULK become important from a handling and shipping standpoint.
DURABILITY of the finished product is measured in terms of its resistance to wear and destruction from all causes.
Materials must be capable of presenting a pleasing APPEARANCE.
Steel is used extensively in many segments of construction, especially in standard structural members. When you hear a construction worker refer to “red iron,” he or she is talking about steel.
The primary advantage of steel is its strength. The material, as it comes from the mills, has very exacting specifications, enabling engineers to design structures with a high degree of accuracy. In addition, steel is a plentiful and well-accepted material. It has a high degree of workability because it can be cut, welded, shaped, and formed to meet a great variety of needs. Steel can also take a great deal of abuse and wear.
The greatest disadvantage of steel is that it will rust – deteriorate by a process of oxidation – when exposed to the elements. This is prevented, however, by the application of protective finishes and paints.
Although steel will not burn, it is not classified as fireproof because it can become distorted, lose its structural strength, or even melt – depending on the intensity of the heat. Nevertheless, compared to many materials, steel offers a great deal of fire resistance due to the large amount of heat needed to cause it damage.
Fundamental Factors Affecting Building Design
Buildings provide shelter for persons and property. A building must have many desirable characteristics such as an attractive appearance, long life, flexibility of use, and economy. However, its basic requirement must be one of protection.
You might analyze this a step further and really consider two kinds of protection.
One type is protection against forces or loads that may be exerted upon the building. Unless the structure can offer adequate resistance against various loading conditions, the safety of persons and the value of property are endangered. This is where sound design consideration must be given as to the strength of the building and particularly to the structural system.
Another kind of protection is protection against rain, wind, heat, and cold. Any of these can contribute to the discomfort of persons and cause a decrease in the value of contents. The degree of protection against them is determined by the weather tightness and thermal efficiency of a building. These things, of course, greatly influence the design of roofs and walls – also known as the covering system.
If you were to ask an engineer to design a structure of a certain size, he/she would first have to know what loads would be imposed upon the building – their type and magnitude. Only with this basic information will he/she be able to design a building that will meet the prospective customer’s exact needs for loading conditions, it is important that you have a basic understanding of design loading.
A load is a force exerted upon a structure or one of its members. There are many different kinds of loads that must be taken into consideration in various situations, but only those that are of prime importance will be covered at this time.
Dead Load: The weight of the metal building system, such as roof, framing, and covering members.
Live Load : Any temporary load imposed on a building that is not wind load, snow load, seismic load or dead load. A few examples of a live load are workers, equipment, and materials.
Snow Load : The vertical load induced by the weight of snow, assumed to act on the horizontal projection of the roof of the structure.
(Note: Very wet snow 6″ deep is equal to one inch of water. One inch of water on a square foot of surface weighs five pounds.)
Wind Load: The forces imposed by the wind blowing from any direction.
Seismic Load: The load or loads acting in any direction on a structural system due to the action of an earthquake.
Auxiliary Loads: All dynamic live loads such as cranes and material handling systems.
Collateral Load : The weight of additional permanent materials, other than the weight of the metal building system, such as sprinklers, mechanical and electrical systems, and ceilings.
Resistance of Material to Forces
Loading has been defined as a force exerted on a building. Such forces, in turn, are transmitted through joints and connections to individual parts or components. This eventually leads to a consideration of the properties of materials to resist forces in order to provide the engineer with a basis for subsequent design calculations.
Stress:The force acting on a member divided by its area.
Tension: Stresses acting away from each other that produce a uniform stretching of a member.
Compression: Stresses acting toward each other that causes a member to compress.
Shear: Stress that tends to keep two adjoining planes of a material from sliding on each other under two equal and parallel forces acting in opposite directions.
For an illustration of a few of these terms, take a simple rubber eraser and draw evenly spaced straight lines across its width.
By grasping the eraser in both hands and pulling apart, you are exerting tension on the eraser. Its resistance to breaking is its internal resistance. This is indicated by the widening of the spaces between the lines drawn on the eraser.
Using the eraser again, grasp it in both hands and push towards the center of the eraser . Notice how the lines tend to become closer to each other. This is compression. The internal resistance of the eraser prevents its parts from being pushed together.
As an example of both tension and compression, grasp the eraser in both hands and bend it (Figure D). Notice that the top part of the eraser is stretching and is in tension, while the bottom part of the eraser is pushing together and is in compression.
Any structure placed on a foundation causes a load to be imposed on that foundation. All buildings have these loads imposed by the columns on the foundation. These loads are called column reactions.
Column reactions are often expressed using the term “kip.” A kip is a commonly used engineering term for 1,000 pounds, derived from the contraction of the words Kilo (1,000) and Pound.
Framing structures exert a load on a foundation both vertically and horizontally. The vertical load is the result of the dead weight of the structure, and other loads such as snow on the roof, wind loads, crane loads, or seismic loads.
The horizontal load is the result of wind loads or seismic loads, and also produces the tendency of the base of rigid frame columns to spread apart under vertical load.
A third type of load arises from framing systems, which have fixed base columns. A streetlight or a flag poll is a common example of a fixed base column. When this type of column is subjected to wind loads, the foundation of such columns must be designed to resist the wind’s effort to overturn them. This overturning force is called a moment.
Engineers usually express the overturning moment as “foot-kips”. As an example, assume that the wind load against the wall of the building creates an effective force of 2,000 pounds against the top of a 12′ column.
The resulting moment at the base would be an overturning force or moment of 24 -ft- kips (2,000 Pounds or 2 kips x 12 feet = 24 -ft- kips).
You do not need to understand the total engineering involved, but you should know that the loads exist, and how they are expressed. You’ll find these loads shown on the anchor bolt drawings.
Regardless of the type of load or where it is exerted on a rigid frame building, it is always transferred from part to part down to the foundation.
Assume, for example, a man standing on the roof. His weight is directly on the panels, but this load is transmitted through the panels to the purlins – the closest purlins taking the greatest part of the load. The purlins transfer the load to the rafter, the rafter to the column, then the column to the foundation.
The load at the base of the column will be a vertical load and also a horizontal thrust or “side kick”. These horizontal thrusts can become very sizeable figures and must be taken into consideration when designing foundations for rigid frame buildings.
A wind load on the sidewall of the rigid frame structure may produce uplift on the main frame as well as horizontal thrusts.
The foundation must be designed to support not only vertical loads, but also the horizontal thrust.
Building code is a set of minimum requirements for construction covering safety and serviceability. This safety involves life, health, fire, and structural stability. Most areas have enforced codes governing construction in the community. They may be administered by a city, county, or state, or by a combination of the three.
Building codes are necessary since their purpose is to benefit the public by helping eliminate unsafe design, poor construction practice, and unsightly buildings.
By the same token, they should be modern and clear. They should also provide for updating. Unfortunately, many communities have codes that are old and obsolete, and fail to recognize the parade of new materials and designs.
A community may originate and write its own codes, but generally it either adopts a recognized building code in its entirety, or modifies it for its specific use.
Here are some authoritative and well-known codes:
THE UNIFORM BUILDING CODE, (UBC) compiled by the International Conference of Building Officials (ICBO). It is prominent on the West Coast and in some areas of the Midwest and South.
THE BOCA BASIC BUILDING CODE (formerly the National Building Code) is administered by Building Officials and Code Administrators International (BOCA International) is primarily used East of the Mississippi and North of Tennessee.
THE STANDARD BUILDING CODE (SBC) covers most of the Gulf Coast states and other Southern areas. Southern Building Code Congress International (SBCCI) sponsors it.
International Building Code (IBC) Over the past several years the three national model building code bodies, SBCCI, BOCA, and ICBO have been working together to produce a single code to be used throughout the United States. The result of their labor is the International Building Code that was published in 2000 as the IBC 2000.
Many other building codes exist, but these are the major ones. An important point is that communities are not compelled to adopt any of these codes. They were compiled by groups of building officials, and are available for adoption by communities either in whole or in part.
From a building design viewpoint, the IBC code has adopted new requirements for live, wind, snow, and seismic loads. The rules for applying and combining these loads are much more complex than in previous codes, and in many cases cause higher loads to be used for designing the building. This can result in higher costs for building foundations as well as for the metal building structure.
There are new load maps in the code for wind load, snow load, and seismic loads. The wind load maps are based on 3-second gust wind loads, unlike the maps in the old codes that were based on sustained wind speeds. This means that the code specified wind speed for the whole country will be higher than before. Also, unlike some earlier codes, it is necessary to specify wind exposure categories and enclosure classifications.
The ground snow load maps in the new code are based on more recently accumulated data, but for most parts of the country the starting snow load values have not changed that much. However, there are new unbalanced snow load equations which drastically increase the roof snow load, especially for snow loads of 20 psf and greater.
The seismic provisions of the new code reflect the latest research for earthquake loads. The new seismic maps measure “Spectral Response Acceleration” for 0.2 and 1.0 seconds. This is a completely new approach to this problem. The IBC seismic equations and maps result in substantially higher imposed loads.
Because of all these changes, you must make sure to use the new load maps whenever you are using the IBC codes. Over time, many areas have responded to unusual storms by increasing the base load to guard against future collapses. Many of the wind and snow load provisions of the new code were written in response to such events.
The snow provisions in the new code, for instance, may result in unbalanced loads more than twice the basic roof snow load, even with no high-low conditions. The minimum wind speed on the maps is now 85 mph, in lieu of the old 70 mph minimum that has been effect for years.
Because of these changes, make sure to determine the values for the wind, snow, and seismic loads for a project only from the new maps. The majority of state and local jurisdictions will likely adopt this code during the next few years.
Codes are complicated and cover many phases of construction and differ from community to community. It is necessary that you become familiar with the codes that are applicable in your area. It is also advisable to discuss the code official’s interpretation of the codes. Interpretations of these codes can vary from official to official.
A building code is not intended to function as a building specification, such as an architect would write for an individual structure. It is a legal document. The purpose of this document does not go beyond the establishment of those minimum design and construction requirements that are essential to, and directly related to, the safety, health, and welfare of the public.
Because of the various properties and characteristics of steel, many factors must be considered when designing both individual members and completed structures. Two organizations have published manuals that provide data and standards on which to base calculations for the design of steel:
AISC – The American Institute of Steel Construction was originated by steel fabricators and is generally concerned with hot rolled shapes and plates.
AISI – The American Iron and Steel Institute was originated by steel producers and is concerned with cold-formed steel structural members.
The Manufacturer’s products, where applicable, are designed in accordance with AISI and AISC specifications. This is a mark of sound design and engineering practices, and contributes to the high quality of our products.