LATERAL FORCE RESISTING SYSTEM

Abstract

A moment frame is formed with two vertical T-shaped posts connected by several cross members secured perpendicular to the two posts forming a ladder-like frame. The cross members are formed of hot rolled steel and are permanently welded to cutouts in the posts. The top of the moment frame is attached to the building structure using any suitable mounting components. The base or bottom of the moment frame is attached to the foundation, or floor using any suitable mounting components.

Description

RELATED APPLICATIONS

This application claims priority from copending U.S. Provisional Patent Application 61/930,374 filed Jan. 22, 2014.

FIELD OF THE INVENTIONS

The inventions relate generally to the field of building construction and in particular to structural framing elements for building construction.

BACKGROUND OF THE INVENTIONS

Buildings are subjected to many forces. Among the most significant are gravity, wind, and seismic forces. Gravity is a vertically acting force, wind and seismic forces are primarily lateral (horizontal). Many buildings use shearwall diaphragms columns and other structural elements to resist lateral loads. Conventional shear resistive building elements are formed by the application of one or more types of sheathing such as, plywood, fiberboard, particleboard, and or drywall (gypsum board), to the inside or outside or both sides of a wall frame. The sheathing is fastened to the wall frame at many points creating a shearwall diaphragm or panel. Many suitable fasteners are available and nails are commonly used and will be referred to hereafter. The sheathed shearwall panel is used to conduct the lateral force acting on the frame of the building to the foundation.

Another misconception among the designers of conventional buildings is the illusion that stiffer is better where lateral force resistance is desired. For example, in some buildings the lateral force resistance is provided by steel I-beams or rigid steel trusses secured in the foundation. In an earthquake the very stiff I-beams and trusses experience catastrophic failure leading to building collapse.

Conventional manufacturers of wood and metal shear resistive building components continue to add elements and stiffness to their products to try and eliminate ductility or flex in their products. As a result, most conventional manufactured shear resistive building components experience catastrophic failure when developing their maximum shear resistance.

SUMMARY

The devices and methods described below provide for a moment frame having two vertical T-shaped posts connected by several cross members secured perpendicular to the two posts forming a ladder-like frame. The cross members are formed of hot rolled steel and are permanently welded into cutouts in the posts. The top of the moment frame is attached to the building structure using any suitable mounting components. The base or bottom of the moment frame is attached to the foundation, or floor using any suitable mounting components.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a front view of a steel moment frame.

FIG. 2 is a cross section of the steel moment frame of FIG. 1 taken along A-A.

FIG. 3 is a front view of a post from the steel moment frame of FIG. 1.

DETAILED DESCRIPTION OF THE INVENTIONS

FIG. 1 illustrates moment frame 10 which includes first post 11 and second post 12 which are connected together by cross members 13. First post 11 and second post 12 have a “T” cross section as illustrated in FIG. 2. Post webs 11W and 12W may be notched to accommodate the cross members as shown in FIG. 3. Cross members or bars such as cross members 13 are preferentially inserted and welded into notches 14 to keep the frame symmetric and thus reduce the amount of weld needed because cross members 13 are locked in by compression instead of placing the welds in shear. Cross members 13 may be attached to post webs 11W and 12W using any suitable technique. Any suitable cross section of cross members 13 may be used such as solid, hollow, tube, round, square, rectangle, “I” or “C” shaped. Naturally rectangular shapes are prone to compression side buckling and cross member needs to have sufficiently thick walls to keep the wall from bulking or collapsing. The closer the plastic modulus of the cross members matches the elastic modulus the less the backbone will curve in the transition from elastic to plastic. A reduced section could be used to insure a more precise bending location.

The components of moment frame 10 may be formed of any suitable ductile metal. For example, cross members 13 may be formed of hot rolled steel to improve ductility of the moment frame. If the shear value of the cross members is held constant the moment frame or panel will be stiffer the larger the cross member or bar so long as web 11W of the post can take the moment of the cross member. Likewise, moment frame 10 will be stiffer with hot rolled metal as apposed to a higher strength formation. Typically hot rolled has enough strain capacity that one can design this system as a simple cantilever column and size the cross members or bars to resist the shear.

Any suitable moment connections can be made first end 10T or second end 10B to create a stiffer system. Other column sections could be used instead of a “T”. A “T” shaped post represents an efficient use of the metal but if there is a significant dead load on the post then either thickening the “T” section or going to a closed section such as a tube may be necessary. Typically the post should be designed to stay elastic. If the post starts to buckle a more pinched hysteresis will occur. Any suitable shape connector 15 may be secured to first end 10T for attaching the panel to most any framing condition.

While the preferred embodiments of the devices and methods have been described in reference to the environment in which they were developed, they are merely illustrative of the principles of the inventions. The elements of the various embodiments may be incorporated into each of the other species to obtain the benefits of those elements in combination with such other species, and the various beneficial features may be employed in embodiments alone or in combination with each other. Other embodiments and configurations may be devised without departing from the spirit of the inventions and the scope of the appended claims.

Claims

1. A moment frame comprising:

two coplanar vertical side members, each vertical side member having an inside web and an outside surface;

a plurality of lateral force resisting members secured to the inside webs between the vertical side members forming a plurality of generally rectangular openings therebetween, wherein the lateral force resisting members control rigidity and resist lateral forces applied to the structural frame; and

a plurality of holdown attachment points on the outside surface of each vertical side member.

2. The moment frame of claim 1 wherein the plurality of lateral force members are generally right circular cylinders formed of hot rolled steel.