Washington Administrative Code › Title 51 - Enterprise Services, Department of (Building Code Council) › Chapter 51-50 - State Building Code adoption and amendment of the 2021 edition of the International Building Code › Section 51-50-1615 - Tsunami loads

Current through Register Vol. 24-14, July 15, 2024
1615.1 General.
The design and construction of
				Risk Category III and IV buildings and structures located in the Tsunami Design
				Zones shall be in accordance with Chapter 6 of ASCE 7-22, except as modified by
				this code. Wherever ASCE 7 is referenced herein, it shall refer to ASCE 7-22,
				within the extent of ASCE 7 Chapter 6 and WAC
				51-50-1615.
USER NOTE:
The intent of the Washington state amendments to ASCE 7
						  Chapter 6 (Tsunami Loads and Effects) is to require use of the Washington
						  Tsunami Design Zone maps to determine inundation limits, i.e., when a site is
						  within a tsunami design zone. The Washington state department of natural
						  resources has parameters for tsunami inundation depth and flow velocity
						  available for all of Washington's coastal waters and tidally influenced
						  riverine systems (WA-TDZ). These parameters are required to be used in lieu of
						  ASCE Tsunami Design Geodatabase, and as a basis for comparison in the
						  probabilistic tsunami hazard analysis in this chapter.
1615.2 Modifications to ASCE 7.
The text of
				Chapter 6 of ASCE 7 shall be modified as indicated in this section.
1615.2.1 ASCE 7 Section 6.1.1.
Replace the third
				paragraph of ASCE 7 Section 6.1.1 with the following and remove the associated
				exception:
The Tsunami Design Zone shall be determined using the
				Washington Tsunami Design Zone maps (WA-TDZ). The WA-TDZ maps are available at
https://www.dnr.wa.gov/wa-tdz
.
1615.2.2 ASCE 7 Section 6.1.1.
Add new fifth
				paragraph and user note to ASCE 7 Section 6.1.1 to read as follows:
Whenever a Tsunami Design Zone or Fig. 6.1-1 is referenced in
				ASCE 7 Chapter 6, the WA-TDZ maps shall be used.
USER NOTE:
Tsunami design zone and design parameters may be
						  obtained from the Washington state department of natural resources. See
https://www.dnr.wa.gov/wa-tdz
.
1615.2.3 ASCE 7 Section 6.2.
Modify ASCE 7 Section
				6.2 definitions to read as follows:
ASCE TSUNAMI DESIGN GEODATABASE:
Not
				Adopted.
USER NOTE:
The ASCE tsunami design geodatabase is not adopted for
						  design purposes in Washington state.
MAXIMUM CONSIDERED TSUNAMI:
A probabilistic
				tsunami having a two percent probability of being exceeded in a 50-year period
				or a 2, 475-year mean recurrence, or a deterministic assessment considering the
				maximum tsunami that can reasonably be expected to affect a site.
TSUNAMI DESIGN ZONE MAP:
The Washington Tsunami
				Design Zone maps (WA-TDZ) designating the potential horizontal inundation limit
				of the Maximum Considered Tsunami found at
www.dnr.wa.gov/wa-tdz
.
1615.2.4 ASCE 7 Section 6.2.
Add new definitions
				to ASCE 7 Section 6.2 to read as follows:
WASHINGTON TSUNAMI DESIGN ZONE MAP (WA-TDZ):
The
				Washington department of natural resources maps of potential tsunami inundation
				limits for the Maximum Considered Tsunami, designated as follows:
Columbia River
DOGAMI SP-51 (L1 scenario) adopted by WA DNR
Outer Coast and Strait area Port Townsend
MS 2022-01
MS 2018-03 (partially superseded by MS 2022-01)
Puget Sound
MS 2021-01 (revised 2022)
San Juan Islands
MS 2016-01 (partiallyern superseded on its eastern edge
						  by MS 2021-01)
Southern Washington Coast
MS 2018-01
The Washington state department of natural resources
				geodatabase of design parameters for tsunami inundation depth, flow velocity,
				offshore tsunami amplitude, predominant period, and tsunami design zone maps
				for a maximum considered tsunami is available at the Washington TDZ website
				(
https://www.dnr.wa.gov/wa-tdz
).
1615.2.5 ASCE 7 Section 6.5.1.
Add new second
				paragraph to ASCE 7 Section 6.5.1 to read as follows:
6.5.1 Tsunami Risk Category II and III buildings and
				other structures.
The Maximum Considered Tsunami inundation depth and
				tsunami flow velocity characteristics at a Tsunami Risk Category II or III
				building or other structure shall be determined by the WA-TDZ maps. Those
				parameters shall be used as the Maximum Considered Tsunami inundation depth and
				tsunami flow velocity characteristics in lieu of the Energy Grade Line Analysis
				in Section 6.6.
1615.2.6 ASCE 7 Section 6.5.1.1.
Modify the first
				paragraph of ASCE 7 Section 6.5.1.1 to read as follows:
6.5.1.1 Runup evaluation for areas where no map values
				are given.
For Tsunami Risk Category II and III buildings and other
				structures where no mapped inundation limit is shown in the Tsunami Design Zone
				map, the ratio of tsunami runup elevation above Mean High Water Level to
				Offshore Tsunami Amplitude, R/HT, shall be permitted to be determined using the
				surf similarity parameter Xi100, according to Eqs. (6.5-2a, b, c, d, or e) and
				Fig. 6.5-1.
1615.2.7 ASCE 7 Section 6.5.2.
Modify the
				paragraph and the exception, to read as follows:
6.5.2 Tsunami Risk Category IV buildings and other
				structures.
A site-specific Probabilistic Tsunami Hazard Analysis (PTHA)
				shall be performed for Tsunami Risk Category IV buildings and other structures.
				Site-specific velocities determined by site-specific PTHA determined to be less
				than the design flow velocities determined from the WA-TDZ maps shall be
				subject to the limitation in Section 6.7.6.8. Site-specific velocities
				determined to be greater than the WA-TDZ map velocities shall be used.
EXCEPTION:
For structures other than Tsunami Vertical Evacuation
						  Refuge Structures, a site-specific Probabilistic Tsunami Hazard Analysis need
						  not be performed where the inundation depth determined from the WA-TDZ maps is
						  determined to be less than 12 ft (3.66 m) at any point within the location of
						  the Tsunami Risk Category IV structure.
1615.2.8 ASCE 7 Section 6.6.1.
Replace ASCE 7
				Section 6.6.1 to read as follows:
6.6.1 Maximum inundation depth and flow
				velocities.
The maximum inundation depths and flow velocities associated
				with the stages of tsunami flooding are determined by the WA-TDZ maps. Flow
				velocity for design purposes shall not be taken as less than 10 ft/s (3.0 m/s)
				and need not be taken as greater than the lesser of
				1.5(
ghmax
)1/2
				and 50 ft/s (15.2 m/s).
1615.2.9 ASCE 7 Section 6.7.
Replace ASCE 7
				Section 6.7 with the following and add a user note:
When required by Section 6.5, the inundation depths and flow
				velocities shall be determined by site-specific inundation studies complying
				with the requirements of this section. Site-specific analyses shall use an
				integrated generation, propagation, and inundation model that replicates the
				given offshore tsunami waveform amplitude and period from the seismic sources
				given in Section 6.7.2.
USER NOTE:
WA-TDZ maps are based on an integrated generation,
						  propagation, and inundation model replicating waveforms from the seismic
						  sources specific to Washington state. See
https://www.dnr.wa.gov/wa-tdz
.
1615.2.10 ASCE 7 Table 6.7-2.
Modify ASCE 7 Table
				6.7-2 to read as follows:
Table 6.7-2 Maximum Moment Magnitude
Subduction Zone
Moment Magnitude
						  MWmax
Alaskan-Aleutian
9.2
Cascadia
9.0
Chile-Peru
9.5
Izu-Bonin-Mariana
9.0
Kamchatka-Kurile and Japan Trench
9.4
1615.2.11 ASCE 7 Section 6.7.5.1.
Modify ASCE 7
				Section 6.7.5.1 Item 4, Item 5, and Item 6 to read as follows:
6.7.5.1 Offshore tsunami amplitude for distant seismic
				sources.
Offshore tsunami amplitude shall be probabilistically
				determined in accordance with the following:
4. The extent of offshore tsunami amplitude
			 points considered for the site shall include the following:
(a) For outer coast sites, the extent shall
			 include points within at least 40 mi (64.4 km) but not exceeding 50 mi (80.5
			 km) of projected length along the coastline, centered on the site within a
			 tolerance of plus or minus 6 mi (9.7 km);
(b) Reserved;
(c) For sites within bays or inland waterways
			 (such as the Strait of Juan de Fuca), the designated center of the computed
			 offshore tsunami amplitude points shall be taken offshore of the mouth of the
			 bay or waterway centered in accordance with criteria (a) above;
(d) For island locations where the projected
			 width of the island is less than 40 mi (64.4 km), it shall be permitted to
			 consider the extent of offshore tsunami amplitude points corresponding to the
			 projected width of the island. Shorter extents of offshore tsunami amplitude
			 points shall be permitted for island locations, but shall not be less than 10
			 mi (16.1 km);
(e) In addition to the
			 above, the tsunami source development and inundation modeling are subject to an
			 independent peer review by a tsunami modeler approved by the Authority Having
			 Jurisdiction, who shall present a written report to the Authority Having
			 Jurisdiction as to the hazard consistency of the modeling with the requirements
			 of Section 6.7.