Masonry Magazine February 1993 Page. 14
How Seismic Code Provisions Affect Use of Joint Reinforcement
The new seismic design provisions being published by the model codes regulating most of the construction east of the Rockies will have an effect on the way new masonry buildings are built and will also affect the renovation of existing masonry buildings.
Seismic design provisions for masonry reinforcement have existed in building codes, particularly those based on the Uniform Building Code, for many years. Recently, as a result of work done by the Building Seismic Safety Council (BSSC) for the Federal Emergency Management Agency (FEMA), new earthquake design provisions are being implemented in areas that traditionally did not consider seismic risk or design.
The map shown in Figure 1 indicates contours of Effective Peak Velocity Related Ground Acceleration. This is a new measure for seismic risk and replaces the Seismic Zones with which some may be familiar. This new contour map is designed to be used with the Seismic Hazard Exposure Groups shown and described in Table 1. Once this data is established a Seismic Performance Category can be determined from Table 2.
Seismic Performance Categories are used to define specific design requirements for different building types in different geographical areas.
By MARIO CA J. CATANI, P.E. President, Dur-O-Wal, Incorporated
Table 3 summarizes some of the specific design requirements related to the various Seismic Performance Categories, with a detailed description following.
Seismic Performance Category A
All buildings built in the green shaded area of the seismic map shown in Figure 1 fall into this category regardless of their occupancy or use. There are no special horizontal steel reinforcement requirements. The use of joint reinforcement is recommended for concrete masonry in conjunction with control joints to control cracking.
Seismic Performance Category B
All buildings built in the yellow shaded area of the seismic map shown in Figure 1 fall into this category except those which are designated as buildings in Seismic Hazard Exposure Group III, i.e. fire, rescue and police stations; surgical facilities etc. There are no special horizontal steel reinforcement requirements for the buildings in this category.
By reviewing the map it can be seen that most of the country east of the Rockies is in the green or yellow shaded area and as a result almost all buildings constructed in these areas will fall under Category A or B and require no special horizontal reinforcement.
Seismic Performance Category C
This category includes all buildings built in the brown shaded area of the map shown in Figure 1 plus those buildings falling in Seismic Hazard Group III which are built in the yellow shaded area and buildings falling in Seismic Hazard Group I built in the blue shaded area. Special reinforcement required by the ACI 530-88/ASCE 5-88 is listed below.
1. Vertical reinforcement of at least 0.20 in. in cross sectional area shall be provided continuously from support to support at each corner, at each side ach side of each opening and at the ends of walls. Horizontal reinforcement not less than 0.20 in.2 in cross section area (1-4 bar or 2-3 bars) shall be provided: (a) at the bottom and top of wall openings and shall extend not less than 24 in. nor 40 bar diameters past the opening. (b) continuously at structurally connected roof and floor levels and the top of walls, (c) at the bottom of the wall or in the top of the foundations when doweled to the wall, (d) at maximum spacing of 10 feet unless uniformly distributed joint reinforcement is provided. Reinforcement at the top and bottom of openings when used in determining the maximum spacing specified in Item No. d above shall be continuous in the wall.
2. Where head joints in successive
14 MASONRY-JANUARY/FEBRUARY, 1993
TABLE 1
SEISMIC HAZARD EXPOSURE GROUP
| GROUP | DESCRIPTION | EXAMPLE |
|---|---|---|
| I | All buildings except those shown below. | |
| II | Buildings which have a substantial public hazard due to occupancy or use. | Assembly buildings with over 300 people Educational buildings with over 250 people |
| III | Buildings which are required for post- earthquake recovery | Rescue, fire and police stations Institutions with surgi- cal facilities |
NOTE: The description and examples given above are only excerpts from model building codes. Consult the appropriate model code for the complete listing of occupancies covered.