SKELETON FRAMING METHOD IN STRUCTURES BASICS AND TUTORIALS

SKELETON FRAMING BASIC INFORMATION
What Is Skeleton Framing?


In skeleton framing all the gravity loadings of the structure, including the walls are supported by the steel framework. Such walls are termed non bearing or curtain walls. This system made the skyscraper possible.

Steel, being so much stronger than all forms of masonry, is capable of sustaining far greater load in a given space, thus obstructing less of the floor area in performing its function. With columns properly spaced to provide support for the beams spanning between them, there is no limit to the floor and roof area that can be constructed with this type of framing, merely by duplicating the details for a single bay.

Erected tier upon tier, this type of framing can be built to any desired height. Fabricators refer to this type of construction as ‘‘beam and column.’’ A typical arrangement is illustrated in Fig. 7.8.

The spandrel beams, marked B1 in Fig. 7.8, are located in or under the wall so as to reduce eccentricity caused by wall loads. Figure 7.9 shows two methods for connecting to the spandrel beam the shelf angle that supports the outer course of masonry over window openings 6 ft or more in width.

In order that the masonry contractor may proceed expeditiously with the work, these shelf angles must be in
alignment with the face of the building and at the proper elevation to match a masonry joint. The connection of the angles to the spandrel beams is made by bolting; shims are provided to make the adjustments for line and elevation.

Figure 7.9a illustrates a typical connection arrangement when the outstanding leg of the shelf angle is about 3 in or less below the bottom flange of the spandrel beam; Fig. 7.9b illustrates the corresponding arrangement when the outstanding leg of the shelf angle is more than about 3 in below the bottom flange of the spandrel
beam.

In the cases represented by Fig. 7.9b, the shelf angles are usually shipped attached to the spandrel beam. If the distance from the bottom flange to the horizontal leg of the shelf angle is greater than 10 in, a hanger may be required.

In some cases, as over door openings, the accurate adjustment features provided by Fig. 7.9a and b may not be needed. It may then be more economical to simplify the detail, as shown in Fig. 7.9c. The elevation and alignment will then conform to the permissible tolerances associated with the steel framework.

WALL BEARING FRAMING BASICS AND TUTORIALS

WALL BEARING FRAMING METHODS BASIC INFORMATION
What Is Wall Bearing Framing Method?


Probably the oldest and commonest type of framing, wall-bearing (not to be confused with bearing-wall construction), occurs whenever a wall of a building, interior or exterior, is used to support ends of main structural elements carrying roof or floor loads.

The walls must be strong enough to carry the reaction from the supported members and thick enough to ensure stability against any horizontal forces that may be imposed. Such construction often is limited to relatively low structures, because load-bearing walls become massive in tall structures. Nevertheless, a wall bearing system may be advantageous for tall buildings when designed with reinforcing steel.

A common application of wall-bearing construction may be found in many single-family homes. A steel beam, usually 8 or 10 in deep, is used to carry the interior walls and floor loads across the basement with no intermediate supports, the ends of the beam being supported on the foundation walls. The relatively shallow
beam depth affords maximum headroom for the span. In some cases, the spans may be so large that an intermediate support becomes necessary to minimize deflection.

Usually a steel pipe column serves this purpose. Another example of wall-bearing framing is the member used to support masonry over windows, doors, and other openings in a wall. Such members, called lintels, may be a steel angle section (commonly used for brick walls in residences) or, on longer spans and for heavier walls, a fabricated assembly.

A variety of frequently used types is shown in Fig. 7.6. In types b, c, and e, a continuous plate is used to close the bottom, or soffit, of the lintel, and to join the load-carrying beams and channels into a single shipping unit.

The gap between the toes of the channel flanges in type d may be covered by a door frame or window trim, to be installed later. Pipe and bolt separators are used to hold the two channels together to form a single member for handling.

Bearing Plates. Because of low allowable pressures on masonry, bearing plates (sometimes called masonry plates) are usually required under the ends of all beams that rest on masonry walls, as illustrated in Fig. 7.7.

Even when the pressure on the wall under a member is such that an area no greater than the contact portion
of the member itself is required, wall plates are sometimes prescribed, if the member is of such weight that it must be set by the steel erector. The plates, shipped loose and in advance of steel erection, are then set by the mason to provide a satisfactory seat at the proper elevation.

Anchors. The beams are usually anchored to the masonry. Government anchors, as illustrated in Fig. 7.7, are generally preferred.

Nonresidential Uses. Another common application for the wall-bearing system is in one-story commercial and light industrial-type construction. The masonry side walls support the roof system, which may be rolled beams, open-web joists, or light trusses.

Clear spans of moderate size are usually economical, but for longer spans (probably over 40 ft), wall thickness and size of buttresses (pilasters) must be built to certain specified minimum proportions commensurate with the span—a requirement of building codes to assure stability. Therefore, the economical aspect should be carefully investigated.

It may cost less to introduce steel columns and keep wall size to the minimum permissable. On the other hand, it may be feasible to reduce the span by introducing intermediate columns and still retain the wall-bearing system for the outer end reactions.

Planning for Erection. One disadvantage of wall-bearing construction needs emphasizing: Before steel can be set by the iron workers, the masonry must be built up to the proper elevation to receive it. When these elevations vary, as is the case at the end of a pitched or arched roof, then it may be necessary to proceed in alternate stages, progress of erection being interrupted by the work that must be performed by the masons, and vice versa.

The necessary timing to avoid delays is seldom obtained. A few columns or an additional rigid frame at the end of a building may cost less than using trades to fit an intermittent and expensive schedule. Remember, too, that labor-union regulations may prevent the trades from handling any material other than that belonging to their own craft.

An economical rule may well be: Lay out the work so that the erector and iron workers can place and connect all the steel work in one continuous operation.