Code of Massachusetts Regulations
780 CMR - STATE BOARD OF BUILDING REGULATIONS AND STANDARDS
Chapter 16 - Structural Design
Section 1613 - EARTHQUAKE LOADS
Subsection 1613.6 - Alternatives to ASCE 7

Universal Citation: 780 CMR MA Code of Regs 1613.6

Current through Register 1531, September 27, 2024

The provisions of Section 1613.6 shall be permitted as alternatives to the relevant provisions of ASCE 7.

1613.6.1 Assumption of flexible diaphragm. Add the following text at the end of Section 12.3.1.1 of ASCE 7.

Diaphragms constructed of wood structural panels or untopped steel decking shall also be permitted to be idealized as flexible, provided all of the following conditions are met:

1. Toppings of concrete or similar materials are not placed over wood structural panel diaphragms except for nonstructural toppings no greater than 11/2 inches (38 mm) thick.

2. Each line of vertical elements of the seismic-force-resisting system complies with the allowable story drift of Table 12.12-1.

3. Vertical elements of the seismic-force-resisting system are light-frame walls sheathed with wood structural panels rated for shear resistance or steel sheets.

4. Portions of wood structural panel diaphragms that cantilever beyond the vertical elements of the lateral-force-resisting system are designed in accordance with Section 4.2.5.2 of AF & PA SDPWS.

1613.6.2 Additional seismic-force-resisting systems for seismically isolated structures. Add the following exception to the end of Section 17.5.4.2 of ASCE 7:

Exception: For isolated structures designed in accordance with this standard, the Structural System Limitations and the Building Height Limitations in Table 12.2-1 for ordinary steel concentrically braced frames (OCBFs) as defined in Chapter 11 and ordinary moment frames (OMFs) as defined in Chapter 11 are permitted to be taken as 160 feet (48 768 mm) for structures assigned to Seismic Design Category D, E or F, provided that the following conditions are satisfied:

1. The value of RI as defined in Chapter 17 is taken as 1.

2. For OMFs and OCBFs, design is in accordance with AISC 341.

1613.6.3 Automatic sprinkler systems. Automatic sprinkler systems designed and installed in accordance with NFPA 13 shall be deemed to meet the requirements of Section 13.6.8 of ASCE 7.

1613.6.4 Autoclaved aerated concrete (AAC) masonry shear wall design coefficients and system limitations. Add the following text at the end of Section 12.2.1 of ASCE 7:

For ordinary reinforced AAC masonry shear walls used in the seismic-force-resisting system of structures, the response modification factor, R, shall be permitted to be taken as 2, the deflection amplification factor, Cd, shall be permitted to be taken as 2 and the system overstrength factor, [OMEGA]o, shall be permitted to be taken as 21/2. Ordinary reinforced AAC masonry shear walls shall not be limited in height for buildings assigned to Seismic Design Category B, shall be limited in height to 35 feet (10 668 mm) for buildings assigned to Seismic Design Category C and are not permitted for buildings assigned to Seismic Design Categories D, E and F.

For ordinary plain (unreinforced) AAC masonry shear walls used in the seismic-force-resisting system of structures, the response modification factor, R, shall be permitted to be taken as 11/2, the deflection amplification factor, Cd, shall be permitted to be taken as 11/2 and the system overstrength factor,[OMEGA]o, shall be permitted to be taken as 21/2. Ordinary plain (unreinforced) AAC masonry shear walls shall not be limited in height for buildings assigned to Seismic Design Category B and are not permitted for buildings assigned to Seismic Design Categories C, D, E and F.

1613.6.5 Seismic controls for elevators. Seismic switches in accordance with Section 8.4.10 of ASME A17.1 shall be deemed to comply with Section 13.6.10.3 of ASCE 7.

1613.6.6 Steel plate shear wall height limits. Modify Section 12.2.5.4 of ASCE 7 to read as follows:

12.2.5. 4 Increased building height limit for steel- braced frames, special steel plate shear walls and special reinforced concrete shear walls. The height limits in Table 12.2-1 are permitted to be increased from 160 feet (48 768 mm) to 240 feet (75 152 mm) for structures assigned to Seismic Design Category D or E and from 100 feet (30 480 mm) to 160 feet (48 768 mm) for structures assigned to Seismic Design Category F that have steel-braced frames, special steel plate shear walls or special reinforced concrete cast-in-place shear walls and that meet both of the following requirements:
1. The structure shall not have an extreme torsional irregularity as defined in Table 12.2-1 (horizontal structural irregularity Type 1b).

2. The braced frames or shear walls in any one plane shall resist no more than 60 percent of the total seismic forces in each direction, neglecting accidental torsional effects.

1613.6.7 Minimum distance for building separation. All buildings and structures shall be separated from adjoining structures. Separations shall allow for the maximum inelastic response displacement [DELTA]M. [DELTA]M shall be determined at critical locations with consideration for both translational and torsional displacements of the structure using Equation 16-44.

Click to view image (Equation 16-44)

where:

Cd = Deflection amplification factor in Table 12.2-1 of ASCE 7.

[DELTA]max = Maximum displacement defined in Section 12.8.4.3 of ASCE 7.

I = Importance factor in accordance with Section 11.5.1 of ASCE 7.

Adjacent buildings on the same property shall be separated by a distance not less than [DELTA]MT, determined by Equation 16-45.

Click to view image (Equation 16-45)

where:

[DELTA]M!, [DELTA]M2 =The maximum inelastic response displacements of the adjacent buildings in accordance with Equation 16-44.

Where a structure adjoins a property line not common to a public way, the structure shall also be set back from the property line by not less than the maximum inelastic response displacement, [DELTA]M, of that structure.

Exceptions:

1. Smaller separations or property line setbacks shall be permitted when justified by rational analyses.

2. Buildings and structures assigned to Seismic Design Category A, B or C.

1613.6.8 HVAC ductwork with Ip = 1.5. Seismic supports are not required for HVAC ductwork with Ip = 1.5 if either of the following conditions is met for the full length of each duct run:

1. HVAC ducts are suspended from hangers 12 inches (305 mm) or less in length with hangers detailed to avoid significant bending of the hangers and their attachments, or

2. HVAC ducts have a cross-sectional area of less than 6 square feet (0.557 m2)..

Disclaimer: These regulations may not be the most recent version. Massachusetts may have more current or accurate information. We make no warranties or guarantees about the accuracy, completeness, or adequacy of the information contained on this site or the information linked to on the state site. Please check official sources.
This site is protected by reCAPTCHA and the Google Privacy Policy and Terms of Service apply.