Reply to the discussion by R.D. Watts on "Proposed Canadian code provisions for seismic design of elements of structures, nonstructural components, and equipment"

Abstract

It is true that only a few deaths have been reported from failures of nonstructural components during earthquakes. However, a large percentage of people requiring medical treatment in emergency rooms following an earthquake have injuries resulting from movement and falling of nonstructural components. In public places, failure of nonstructural components such as ceilings leads to panic because of the perception that “the building is falling down”. This has caused serious injuries due to crushing and trampling under foot. The nonstructural components section of the earthquake provisions seeks to address these issues of life safety and public safety. In this, the proposed provisions of the Canadian code are consistent with seismic code provisions throughout the world. The cost data referred to by Mr. Watts are not supported by cost data assembled by the author over the past ten years. In response to Mr. Watts’ specific comments: 1) The code provisions require that the importance factor for nonstructural components shall be as a minimum the value of the importance factor used for the structure. There will be cases when it will be appropriate for the nonstructural components to be designed for a higher importance factor than the structure, and the designer is free to use judgement to do this. 2) The distribution and amplitude of forces applied to nonstructural components in buildings is based on empirical data and studies of structural dynamics. Briefly, it is expected that a single-storey building will have a shorter period than a four-storey building. The onestorey building will be designed for a higher percentage of base shear, and it is expected that the forces at the roof of the one-storey building will be higher than the first floor of the four-storey building. 3) Usually the common elements, such as ceiling and pipe restraints in a multi-storey building are designed for the maximum force levels at the top of the building. The connection details are kept the same throughout the building. There is very little difference in costs for these connections over the practical range of forces. The simplicity of design greatly reduces the chance of errors. For large pieces of equipment or architectural components, the difference in cost of seismic restraint from the top to the bottom of the building can be significant. The code provisions enable the designer to take advantage of this.