How do I design a column reinforcement

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Wide flange beam for HSS pillar torque connections

Hollow Structural Sections (HSS) are efficient members to use in a wide variety of applications, including moment frames. If the beams and columns are HSS members, moment connections can be constructed using the provisions in the American Institute of Steel Construction (AISC) Specification for Structural Steel Buildings Chapter K. The tables in Chapter K cover various connection configurations and indicate the limit states with The applicable force equations. If the beams are wide flange sections and the columns are HSS, there are several options for moment connections and these are discussed in this article.

It is important to remember that the connection to an HSS column is different from the considerations for connecting to the flanges on a wide flange column. The moments in wide flange beam are released to concentrated forces on the jet flanges that have to be transferred into the column. The main difference between an HSS and a wide flanged column is how the forces from the jet flanges are transferred into the crevice trajectories to withstand as shear. In a wide-flanged column, the web (and thus the rigidity) is in the middle of the column flange. In an HSS column, the forces applied to the column surface must be transferred to the side walls, which serve as tracks. Due to the fact that HSS walls are generally thinner and the forces have to be transferred to the side walls, the thickness of the HSS pillar wall becomes a critical consideration for the strength and rigidity of a moment connection between an HSS pillar and a wide flange beam.

With these considerations in mind, the common connection types and recommendations discussed in this article are generally directed to making the concentrated forces from the jet flanges practical as close to the sidewalls of the HSS column. Two general recommendations can be made for all connection configurations. Design the column to eliminate the need for reinforcement at the joint and keep the ratio between column width and beam flange width close to one.

Whenever possible, the connection configuration and the forces applied to the HSS columns should be considered when selecting the column size. Thicker walls and / or narrower column face dimensions can reinforce and stiffen the column wall and remove the need for costly stiffeners or column reinforcement. In simpler terms, it is typically more economical to have heavier pillars than to have reinforced joints. This also applies to connections with wide-flanged columns. There are requirements for the application of concentrated forces on the flanges that may result at the time of stiffening or doubler plates (if the column sheet or flanges are not thick enough). AISC recommends using heavier column sections to avoid costly joint reinforcement.

The second recommendation is to keep the column width and flange width in the optimal ratio. Narrow jet flanges (compared to the width of the column face) concentrate the force on the central part of the HSS wall, making the thickness of the wall more critical.

Five of the most common connection types are discussed in this article, but there are several other viable configurations that are discussed in the Resources. This article will focus on low seismic applications, but there are compounds that are suitable for high seismic applications.

(This article comes fromSteel Tube Institute edit released)

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Wide flange beam in a light frame construction

How did the beam get so big? This was what I had to ask myself when I finished sizing and detailing a steel joist that should fit in the floor joist depth for a flat ceiling. We removed an unreinforced masonry bearing wall and a new one wide flange beam installed to support the existing floor joists as part of a seismic retrofit and remodel. Since the floor joists would have been spliced ‚Äč‚Äčover the existing support wall, it would have been much easier to just fit a new joist under the joists.

The architect didn't want the beam to be installed below the frame as it would stick out too far. The steel structure offers several wide flange profiles that work for a specific load. For this particular design, I could use a W24x55, W16x67, or W14x90. Each has roughly the same strength (section module, Sxx) and stiffness (moment of inertia, Ixx). With no restrictions, you'd pick the lightest section that works. Space constraints that require a flatter beam result in increased beam weight (and cost).

I suggested two solutions for installing the beam in the floor surface and hanging the joists from a nail. One option allowed the steel beam to extend under the floor beam, while the other required a heavier, flatter beam to fit into the room. The owner wanted a flat ceiling and didn't care about the additional cost of the jet, which weighed about 60% more than the optimal jet size.

Regardless of the space constraints for constructing a steel beam, designers must provide a suitable hanger to connect to the steel beam. Simpson Strong-Tie has many matching top flange brackets. The most common are coat hangers that are attached to a wood nailer. Many upper flange brackets can also be welded to the beam. Not every nailer solution is rated for the climb, so choose a hanger that suits your needs.

Installers can also use powder actuated fasteners to connect the hangers instead of welding. Allowable loads for some of our top flange brackets are addressed in a design letter, ITS, MIT, LBV and BA hangers installed on a steel head with powder operated fasteners.

Of course, as with all of our hanging loads, we created these loads by running a lot of tests.

(This article comes fromSimpson Strong-Tie editor released)

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