Chapter 14.36
SEISMIC HAZARD IDENTIFICATION PROGRAM FOR UNREINFORCED MASONRY BUILDINGS
Sections:
14.36.040 Building owner notification.
14.36.060 Engineering reports.
14.36.080 City review of engineering reports and letters of intent.
14.36.090 Building tenant notification.
14.36.110 Progress reports to city council.
Appendix A Engineering Standards.
Appendix B Format for Engineering Reports.
* Code reviser’s note: Ordinance 13-89 adds the provisions of this chapter as Chapter 14.35. The chapter has been editorially renumbered to prevent duplication of numbering.
14.36.010 Purpose.
It is generally acknowledged that the city of Half Moon Bay is located in a geographic area of high seismic risk, due to its proximity to the San Andreas fault, and may reasonably be expected to experience moderate to severe ground shaking in the event of a significant local earthquake. Such ground shaking could result in serious injury or loss of life due to damage or collapse of buildings. Historically unreinforced masonry buildings have been shown to be especially vulnerable. The purpose of this chapter is to promote public safety by identifying those buildings in the city of Half Moon Bay which exhibit structural deficiencies in their capacities for earthquake resistance, and by determining the severity and extent of those deficiencies in relation to their potential for causing injury or loss of life. (Ord. 13-89 §1(part), 1989).
14.36.020 Definitions.
For purposes of this chapter the following definitions apply:
A. “Civil engineer or structural engineer” means a licensed civil or structural engineer registered by the state of California pursuant to the rules and regulations of Title 16, Chapter 5, of the California Administrative Code.
B. “Uniform Building Code (UBC)” is as published by the International Conference of Building Officials, Whittier, California, as adopted by the city of Half Moon Bay.
C. “Unreinforced masonry (URM) building” means any building containing walls and/or columns constructed wholly or partially of masonry without at least fifty percent of the reinforcement required by the latest edition of the UBC, adopted by reference by the city of Half Moon Bay, and includes:
1. Unreinforced brick masonry;
2. Unreinforced concrete masonry;
3. Hollow clay tile;
4. Adobe or unburned clay masonry;
5. Stone masonry.
D. “Risk categories” are defined as follows:
1. “Essential building” means any building housing a hospital or other medical facility having surgery or emergency treatment areas; fire or police stations; municipal government disaster operation and communication centers.
2. “High risk building” means any building not classified as an essential building, having an occupant load of one hundred persons or more.
3. “Medium risk building” means any building not classified as an essential building, having an occupant load of twenty persons or more.
4. “Low risk building” means any building, not classified as an essential building, having an occupant load of less than twenty persons.
E. Other terms are as defined in the 1985 edition of the UBC. (Ord. 13-89 §1(part), 1989).
14.36.030 Scope of program.
Owners of all URM buildings in the city of Half Moon Bay, except as exempted below, shall be required to have an engineering report submitted to the city’s building department, to determine the existence, nature, extent and severity of structural deficiencies in their buildings’ capacities for earthquake resistance which could result in damage or collapse with possible injury or loss of life.
A. Exempted Buildings. The following buildings are exempted from complying with this chapter:
1. Residential buildings with five or fewer dwelling units.
2. Warehouses or similar structures not used for human habitation, except for warehouses or structures housing emergency services equipment or supplies.
3. Buildings which have already been structurally upgraded in substantial accordance with either the 1973, or later, edition of the UBC. (Ord. 13-89 §1(part), 1989).
14.36.040 Building owner notification.
Owners of buildings which have been identified as being included in the scope of this program shall be notified within six months of the enactment of this chapter by the building department of the city of Half Moon Bay that each such building has been included in the city’s list of potentially hazardous URM buildings, and is required to have an engineering report submitted to the city. (Ord. 13-89 §1(part), 1989).
14.36.050 Recording.
At the time of building owner notification, the building official shall file with office of the county recorder a certificate stating that the subject building falls within the scope of this chapter, has been included in the city’s list of potentially hazardous URM buildings, and is required to comply with the provisions contained herein. At such later time as each such identified building has either been determined as excludable from the city’s list by further investigation, or has undergone mitigation of its hazards to the satisfaction of the building official, the building official shall then file with the office of the county recorder a certificate stating that the building has been removed from the potentially hazardous classification. (Ord. 13-89 §1(part), 1989).
14.36.060 Engineering reports.
Owners of identified buildings shall submit engineering reports to the building department of the city of Half Moon Bay as follows:
A. Time Frame. Engineering reports shall be submitted to the city within eighteen months of building owner notification.
B. Authorized Preparers. Engineering reports shall be prepared by civil or structural engineers, as previously defined herein, who are familiar with seismic analysis and design.
C. Purpose. The purpose of each such engineering report shall be to investigate, in a thorough and unambiguous fashion, a building’s structural systems that resist earthquake forces, and to evaluate their adequacy to resist the seismic design forces as specified herein.
D. Engineering Standards. The engineering standards to be used in preparation of engineering reports shall be the 1982, or the most recent version, of the UBC adopted by the city of Half Moon Bay, and the 1985 City of Los Angeles Division 88 Standard for URM Buildings, as modified by Appendix A of this chapter.
E. Format. The format for engineering reports shall be as outlined in Appendix B of this chapter, or other equivalent format approved in writing by the building official. (Ord. 13-89 §1(part), 1989).
14.36.070 Letters of intent.
A letter of intent shall be submitted within ninety days of submittal of each engineering report, and shall describe in general fashion how the building owner intends to approach hazard reduction of his or her building and provide a reasonable time period for achieving hazard reduction. Options available to the building owner for approaching hazard reduction include, but are not limited to, the following:
A. Structural rehabilitation of the building to meet or exceed the seismic provisions of the engineering standards referenced herein.
B. Change in use of the building to a residential or warehouse occupancy exempted from compliance with this chapter, as previously described herein, as may be allowed by other city ordinances.
C. Sale of the building to a new owner, who shall then bear the responsibility of hazard reduction.
D. Vacating the building pending further investigation of possible alternatives.
E. Demolition of the building, or portions thereof, to eliminate the potentially hazardous conditions.
F. Any building which qualifies as “historical property” as determined by an appropriate governmental agency under Section 37602 of the Health and Safety Code shall be retrofitted in accordance with the State Historical Building Code. (Ord. 13-89 §1(part), 1989).
14.36.080 City’s review of engineering reports and letters of intent.
The building department shall review the documents submitted for each identified building for conformance to this chapter. The building department may, at its option, engage the services of consulting civil or structural engineers to assist in evaluation of documents submitted. Costs of each such review shall be recovered by fees assessed upon the building owner at the time of submittal of documents, based upon the time required for review of any structural rehabilitation plans subsequently submitted for building permit purposes for work directly related to compliance with this chapter. Copies of engineering reports submitted shall be available to the public for review at the building department upon request. (Ord. 13-89 §1(part), 1989).
14.36.090 Building tenant notification.
Owners of each identified building shall provide each of their tenants with written notification that a seismic investigation of their building has taken place, and that the engineering report documenting the investigation is available for review at the building department. Such notification shall occur within ninety days of submittal of each engineering report. (Ord. 13-89 §1(part), 1989).
14.36.100 Penalties.
Nonconformance with this chapter is unlawful. Violation constitutes a misdemeanor and is subject to civil prosecution under the laws and ordinances of the city of Half Moon Bay. (Ord. 13-89 §1(part), 1989).
14.36.110 Progress reports to city council.
The building department shall prepare annual progress reports to the city council on the implementation of this chapter. (Ord. 13-89 §1(part), 1989).
14.36.120 Interpretations.
The interpretation of the building official shall prevail on matters relating to the implementation of this chapter. (Ord. 13-89 §1(part), 1989).
APPENDIX A: ENGINEERING STANDARDS
For purposes of preparing engineering reports on URM buildings for the city of Half Moon Bay the following engineering standards shall apply.
(a) Earthquake demand forces shall be equal to seismic design shear values specified in the 1985 edition of the UBC, as modified by Tables A-1 and A-2 of this appendix.
(b) Testing of URM walls utilized to carry vertical loads and seismic forces shall be performed as follows:
1. Mortar joints may be raked, cleaned and pointed with Type S or N mortar (no masonry cements) prior to testing, under the continuous observation of a special inspector as defined in the UBC.
2. Tests may consist of in-place shear tests or core tests. The minimum number of tests shall be two (2) per wall or line of wall elements resisting a common force, or one (1) per fifteen hundred (1500) square feet of wall surface, with a minimum of eight (8) total tests. Exact test or core locations shall be field- determined by the civil or structural engineer responsible for the engineering report.
3. For each in-place shear test, the bed joints of the outer wythe of the masonry shall be tested in shear by laterally displacing a single brick relative to the adjacent bricks in that wythe. The opposite head joint of the brick to be tested shall be removed and cleaned prior to testing. The minimum quality mortar in eighty percent (80%) of the shear tests shall not be less than the total of thirty (30) psi plus the axial stress in the wall at the point of the test. The shear stress shall be based on the gross area of both bed joints and shall be that at which movement of the brick is first observed.
4. For each core test, the mortar joint of the outer wythe of the masonry core shall be tested in shear by placing the circular core section in a compression testing machine with the mortar bed joint rotated fifteen (15) degrees from the axis of applied load. The mortar joint tested in shear shall have an average ultimate stress of twenty (20) psi based on the gross area. The average shall be obtained from the total number of cores made. If test specimens cannot be made from the cores taken, the shear value shall be reported as zero (0).
5. Five percent (5%) of existing wall anchors utilized to resist pull-out forces shall be tested, with a minimum of four (4) tests per roof or floor, consisting of two (2) tests at walls perpendicular to framing and two (2) tests at walls parallel to framing. The test apparatus shall be supported on the masonry wall at a minimum distance of the wall thickness from the anchor tested. The rod anchor shall be given a preload of three hundred (300) pounds prior to establishing a datum for recording elongation. The tension test load reported shall be recorded at one-eighth inch relative movement of the anchor and the adjacent masonry surface. Results of all tests shall be reported. The report shall include the test results as related to wall thickness and joist orientation. The allowable resistance value of the existing anchors shall be forty (40) percent of the average of those tested anchors having the same wall thickness and joist orientation.
6. All testing agencies and inspectors shall be approved in writing by the Building Official. Testing results and field observation reports shall be included in the engineering reports submitted to the Building Department.
Allowable height-to-thickness ratios for tested walls are given in Table A-3 of this appendix. Allowable stresses for tested walls are given in Table A-4 of this appendix.
(c) Capacities of existing materials other than the URM walls themselves may be assumed as indicated in Table A-4 of this appendix.
(d) The capacity/demand ratio (factor of safety) for each element of the seismic force-resisting system shall equal or exceed one (1.0). Any element for which this ratio is less than one shall be considered deficient.
(e) The fifty percent (50%) increase in the seismic force factor for shear walls specified in Section 2407(h)4F of the 1985 edition of the UBC may be omitted in the computation of seismic loads to existing shear walls.
(f) URM shall not be considered to have tensile stress capacity. However, tension due to out-of-plane seismic forces applied to URM walls may be neglected for walls within the height-to-thickness ratios specified in Table A-3 of this appendix. Tensile fiber stresses due to bending under seismic forces may be reduced by the full direct axial stress due to vertical dead loads.
(g) URM walls found to be deficient may be permitted to remain in place provided that they are anchored as required for veneer by Section 3006 of the 1985 edition of the UBC.
(h) Wood shear walls shall not be permitted to resist seismic forces imparted by concrete or masonry in buildings over two (2) stories in height.
|
RISK CATEGORY |
ZIKCS |
ZIS |
|---|---|---|
|
Essential Building |
0.186 |
1.50 |
|
High Risk Building |
0.133 |
1.00 |
|
Medium Risk Building |
0.100 |
0.75 |
|
Low Risk Building |
0.100 |
0.75 |
|
Note: “ZIKCS” factors apply to whole buildings; “ZIS” factors apply to parts of buildings. |
||
|
BUILDING PART |
Cp |
DIRECTION OF FORCE |
|---|---|---|
|
Walls (interior and exterior, bearing and non-bearing) |
0.20 |
Perpendicular to flat surface |
|
Towers, tanks, racks, chimneys, smokestacks, penthouses, equipment, machinery (including contents) |
0.20 |
Any |
|
Cantilevered walls |
1.00 |
Perpendicular to flat surface |
|
Connections for exterior panels or elements |
2.00 |
Any |
|
Roof and floor diagrams |
0.12* |
In place |
|
*0.16 for medium and low risk buildings. |
||
|
WALL LOCATION |
h/t |
|---|---|
|
One-Story Buildings |
13 |
|
First Story of Multi-Story Buildings |
15 |
|
Uppermost Story of Multi-Story Buildings |
9 |
|
All Others |
13 |
|
80% OF TEST RESULTS IN PSI NOT LESS THAN |
AVERAGE TEST RESULTS OF CORES IN PSI |
SEISMIC IN-PLANE SHEAR BASED ON GROSS AREA* |
|---|---|---|
|
30 plus axial stress |
20 |
3 psi |
|
40 plus axial stress |
27 |
4 psi |
|
50 plus axial stress |
33 |
5 psi |
|
100 plus axial stress |
67+ |
10 psi maximum |
|
*Allowable shear stress may be increased by addition of 10% of the axial stress due to the weight of the wall directly above. |
||
|
MATERIAL/CONFIGURATION |
CAPACITY |
|||
|---|---|---|---|---|
|
1. |
Horizontal wood diaphragms |
|
||
|
|
a. |
Roofs |
|
|
|
|
|
1) |
Straight sheathing |
100 plf (2) |
|
|
|
2) |
Straight sheathing with plaster applied to rafters |
150 plf |
|
|
|
3) |
Diagonal sheathing |
400 plf |
|
|
b. |
Floors |
|
|
|
|
|
1) |
Straight tongue-and-groove sheathing |
150 plf |
|
|
|
2) |
Straight tongue-and-groove sheathing with plaster applied to joists |
200 plf |
|
|
|
3) |
Straight sheathing and finished wood flooring |
300 plf |
|
|
|
4) |
Diagonal sheathing and finished wood flooring |
450 plf |
|
2. |
Shear walls: wood stud walls with lath and plaster |
100 plf each side |
||
|
3. |
Plain concrete footings |
f’c = 1500 psi (3) (unless otherwise shown by tests) |
||
|
4. |
Douglas fir wood |
Per 1985 UBC for D.F. No. 1 |
||
|
5. |
Reinforcing steel |
ft = 18,000 psi |
||
|
6. |
Structural steel |
ft = 20,000 psi |
||
|
|
|
|
|
|
|
(1) Materials must be in good condition. |
||||
|
(2) “plf” = pounds per linear foot, seismic shear. |
||||
|
(3) “psi” = pounds per square inch. |
||||
|
(4) Stress increases for combined loading permitted. |
||||
(Ord. 13-89 §1(part), 1989).
APPENDIX B: FORMAT FOR ENGINEERING REPORTS
Engineering reports on URM buildings in the City of Half Moon Bay shall incorporate the following format:
I. DATA SHEET
This sheet contains general information about the building, including its address, use/occupancy, date of original construction, dates of any subsequent structural alterations, names and addresses of the building’s designers, if known, building area, number of stories, and occupancy load calculations.
II. BUILDING DESCRIPTION
A. Configuration. Include descriptions of the building’s size, shape, arrangements of structural elements, any irregularities or discontinuities, non-structural elements (appendages, parapets, facades), and adjacent buildings if relevant.
B. Materials. Indicate types, ages and present-day observed conditions.
C. Site Geology. Provide information as required by the Building Official for any special site or soil conditions, landslide activity or earthquake fault proximity.
III. PLANS OF EXISTING CONSTRUCTION
The following plans shall be included, to the degree of detail required to adequately show the seismic integrity of existing conditions.
A. Site Plan
B. Roof Plan
C. Floor Plan (for each level)
D. Roof Framing Plan
E. Floor Framing Plan (for each level)
F. Foundation Plan
G. Exterior Elevations
H. Wall Elevations (of any interior URM walls)
I. Structural Building Section(s)
J. Structural Details (as needed)
IV. CALCULATIONS TO CHECK EXISTING CONSTRUCTION
Structural calculations shall include the following:
A. Derivation of earthquake demand (seismic design) forces and their distribution to resisting elements and connections.
B. Capacities of existing resisting elements and connections. Include materials testing results.
C. Capacity/demand ratios (factors of safety) for existing elements and connections.
V. CONCLUSIONS AND RECOMMENDATIONS
Describe areas found by analysis to be deficient in their ability to withstand prescribed seismic forces. Discuss in general terms the alternatives available for mitigation of these inadequacies, and the engineer’s recommendations for most suitable solutions.
NOTE: Each engineering report shall bear the signature and professional registration number, including its expiration date, of the responsible civil or structural engineer.
(Ord. 13-89 §1(part), 1989).