1.3 BEAM WEB PENETRATIONS (540 words)

       Beam web penetrations are a way of allowing mechanical ductwork and plumbing lines to pass through structural beams and girders while maintaining a shallow ceiling sandwich and minimum floor-to-floor height. Beams and girders in buildings have, by natural consequence, regions of reserve capacity. The length of the member offers areas that can tolerate the placement of a round, square or rectangular penetration, either concentrically or eccentrically placed (see Figure 14). Concentrically placed penetrations have the centerline of the penetration matching the member depth centerline. Eccentric holes have their centerline either above or below the member depth centerline.

     Depending on the size, location and beam or girder, loading will determine whether the penetration should be reinforced or unreinforced. In some cases, beam and girder penetrations may not be structurally feasible. It is important to fully discuss the size and location of all intended web penetrations early in the project with a qualified structural engineer so that the structural design may proceed and costly field installed penetrations may be avoided. 

       Unreinforced web penetrations are holes cut in the web of the beam or girder with no other material added to strengthen the member, as the member carries the shear and moment forces in the beam satisfactorily. These type of penetrations are the least expensive to provide. Reinforced web penetrations are required in critical structural beams and girders that are heavily loaded and/or have very large penetrations that will compromise the integrity of the member. The material taken away by the penetration may be so significant that the member shears and moments cannot be accommodated by the remaining beam or girder material alone. As a result, reinforcing material must be added.

        Hole reinforcing may consist of horizontal plates, a combination of horizontal and vertical plates or pipe sections for round penetration. This reinforcing is placed on one or both sides of the web. The specific structural member loading, member size, size of penetration and location of penetration will all play a role in determining the amount of reinforcing required. 

       As an aid to the architect in coordinating beam and girder web penetrations with the building ductwork and piping services, the following guidelines are suggested:

• Penetrations through members that have adepth-to-web thickness, d/tw > 75 should be avoided. Domestically available rolled shapes generally fall outside this criterion.
• The ratio of hole length to depth should be limited to 2.5.
• The hole depth must be limited to a maximum of 70 percent of the member depth.
• A minimum 15 percent of the member depth must remain from the edge of the hole to the outside face of the flange.
• Corners of penetrations must be made with a radius of approximately one inch. This must be
• considered in determining the size of penetration to accommodate ductwork and piping services.
• Concentrated loads from beams and column transfers must not be made within the length of the hole.
• Multiple holes should have a minimum two times the hole length between hole edges.
• Beams are to be laterally supported by the floor/roof construction.
• Penetrations in members that are at or near deflection limits or that have sensitive vibrations should be avoided.
• All penetrations must be investigated by a qualified structural engineer to insure the structural integrity of the member.

(Design with Structural Steel - A Guide for Architects)