A repair was made to the second floor laundry room floor to stop floor vibrations from occurring when the clothes drier was running. The vibration was noticeable in the second floor laundry room and to people watching television in the first floor family room below the laundry room.
The repair was designed and installed by the author, a Winchester resident and a Licensed Kentucky Structural Engineer and is described as follows.
The second floor joists were originally designed for the correct design loads and deflection limits. An acceptable amount of floor bounce could be felt by the author when walking across the floor. The floor vibrated to a level unacceptable to the author when the clothes drier was operating.
Summary of repair method
Three threaded steel hanger rods were hung from a spreader beam in the roof attic. The hanger rods extended down from the attic through a small space in a pocket door frame to a support saddle that was installed beneath two second floor joists. These two wood joists were supporting most of the weight of the clothes drier.
View the following photo slide show to see the installation procedure.
1. Construct a spreader beam made of two wood two by twelves, separated by a three quarter inch thick wood spacer. The length of the spreader beam is long enough to be supported by four roof rafters. The spreader beam was designed to be stiff enough so that the four rafters would each carry some load from the hanger rods. A cursory structural analysis was performed by the author to determine that the rafters could support the added load.
2. Hang the spreader beam beneath the four supporting rafters and connect the spreader beam to each of the four rafters with a steel angle iron and steel bolts.
3. Obtain one half inch diameter threaded rods that are short enough to bring into the attic and work with.
4. Hang three rods through the three quarter inch center space in the spreader beam, supporting the threaded rod on top of the spreader beam with steel bearing plates.
5. Drill three holes in the top of the wall top plate that houses the pocket door below. Locate the three holes so that the installed rods will not interfere with the operation of the pocket door.
6. Remove a small piece of second floor ceiling drywall to expose the two second floor joists that are going to be supported by the new steel hanger rods.
6. Splice the short lengths of the threaded steel hanger rods with coupling nuts as the rods are are lowered through the pocket door frame until they extend near the bottom of the second floor joists.
7. Obtain a one half inch thick steel bottom bearing plate eighteen inches in length to support the two floor joists. Drill three holes in the plate to accept the three hanger rods.
8. Notch the bottom of the two joists one half inch deep to accept the steel bearing plate.
9. Install the bearing plate on the three hanger rods to the bottom of the two joists with steel hex nuts.
10. Tighten the nuts on the threaded rods until the threaded rods are snug but not supporting all of the floor weight. The threaded rods are intended to function as a shock absorber, supporting a small amount of the floor weight and not the entire weight of the floor.
11. Replace the small piece of second floor drywall that was removed to install the steel bearing plate.
The installation was completed and successfully performed as intended, reducing floor vibrations to a level that was barely perceptible.
This project demonstrates that a substantial effective structural repair can be installed in an existing house without requiring extensive demolition or repair to finish wall, floor and ceiling finish surfaces.
Contact your engineer
If improperly installed, structural members may be over-loaded. This repair was made to a twenty year old house, so most or all of the long term creep deflection in the wood members has already occurred. Creep deflection is the continuing deflection occurring in wood flexural members as they age. If this repair was made to a brand new structure, the threaded rods might continue to be subjected to unintended additional floor load as the new floor joists experience most of their creep within their first few years. Contact a structural engineer for design assistance if you do not feel qualified to perform the necessary structural calculations for the project.
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