An increased number of occupant complaints about excessive vibrations in wood-based floors, particularly in those with long spans and large open spaces, or cementitious toppings, are being received. This is both surprising and confusing because the design of these “unsatisfactory floors” conforms to the building codes. A review of the design procedures already in the building codes and those proposed in the literature indicates that they have limited application to wood-based floors of certain classes.
To bridge the gaps in the design procedures already adopted in the building codes and those proposed in the literature, Forintek has conducted a research project to develop and implement a new vibration-controlled design procedure for a broad range of wood-based floor systems. The specific aims of this research project are:
1) To develop a design procedure to control vibrations in a broad range of wood-based floors. This design procedure should include calculation methods to determine 1 kN static deflection and fundamental natural frequency, recommendations for design values for properties of floor components, a vibration-controlled design criterion calibrated to the calculation methods and the recommended design values and test protocols to determine properties which are not currently available in codes and publications.
2) To make a proposal to the code committee for adoption of the new general design procedure to control vibrations in a broad range of wood-based floors. The proposal should also include an impact study of the new design procedure on current floor spans.
To reach these objectives, several tasks have been identified and performed. These tasks include:
1) Development of simplified calculation methods to determine 1 kN static deflection and fundamental natural frequency;
2) Development of test protocols to determine the rotational stiffness of bridging/blocking-to-joist connections required by the simplified calculation methods;
3) Recommendations for the design values of mechanical properties of floor components;
4) Proposed methods for determining bending and shear stiffness of wood trusses;
5) Validation of the calculation procedure including the calculation methods and proposed design values;
6) Formulation of a new design criterion using computed 1 kN static deflections and fundamental natural frequencies of the floors in Forintek’s field survey database;
7) Study of the sensitivity of the new design procedure to various construction parameters for a broad range of spans;
8) Study of the impact of the new design procedure on current spans for a broad range of wood floor systems;
9) Formation of a project Task Group;
10) Preparation of a code implementation proposal.
To date, tasks 1-9 have been completed. The simple calculation methods along with the approaches for lateral bracing (bridging, blocking, strapping, strong-back and ceiling), cementitious topping, and wood panel overlay were validated using a database consisting of 91 laboratory tested floors. The simplified calculation methods were implemented into an Excel file ready for distributing to the wood industry.
Two forms for a tentative design criterion were formulated using the combinations of computed 1 kN static deflection and fundamental natural frequency, or computed 1 kN static deflection, fundamental natural frequency and area mass. The tentative design criterion was validated using a database consisting of 106 field floors. The database includes the floors with the most common construction parameters encountered in practice and a board range of span coverage from 10 feet to 44 feet. Floor acceptance rated by the new design criterion was well matched with the occupants’ ratings.
The preliminary impact study on 10” and 18” wood I-joist floors, and 2x6”, 2x10”, and 2x12” solid sawn lumber joists floors revealed that for floors having spans shorter than 16 feet, the vibration-controlled spans allowed by the new design procedure were comparable with the spans allowed by the Part-9 criterion or CCMC provision. For long-span floors, the new design procedure provided more rational spans than those provided by the CCMC provision. The new design procedure showed great potential to properly address such unresolved issues as long span, bridging/blocking/strapping/strong-backs, topping, etc in current design procedures in the codes and in the literature.
A CWC/Forintek Task Group (TG) was formed to review the progress and to facilitate implementation of the final recommendations and obtain code recognition of the new design procedure to control vibrations in a broad range of wood-based floors. The TG is composed of representatives from proprietary product manufacturers, CCMC and CWC and floor research scientists. Dr. Chui of the University of New Brunswick chairs the TG. It is expected that TG members will assist in conducting full-scale studies of the impact of the new tentative design procedure on their current floor spans, and in finalising the procedure, making a collective proposal to the code committee to consider for adoption.
At present, it can be concluded that the new design procedure shows the potential to provide rational solutions for vibration-controlled spans for a broad range of wood-based floor systems. The new design procedure shows the potential to resolve issues in current floor design such as long spans, overestimated spans of floors with various types of lateral bracing or with cementitious topping. The approach proposed to account for the contribution from installation of bridging/blocking type of discontinuous lateral bracing provides freedom for the innovation of new types of bridging/blocking systems.