§ 18.08.190. Section 2114 Rock Masonry Retaining Walls, Yard Walls and Fences, added.
International Building Code, 2015 Edition, Section 2114 Rock Masonry Retaining Walls, Yard Walls and Fences, is hereby added to read as follows:
Section 2114 Rock Masonry Retaining Walls, Yard Walls and Fences.
2114.1 General.
1. All retaining rock masonry walls, rock yard walls and rock fences shall be so designed as to withstand any normal and special loading which may be expected for the intended use of the structure and no subsequent change of use shall be permitted without provisions for the additional loading imposed by such new uses. For the purpose of this section, fences are further defined as free-standing structures supporting no vertical weight other than the weight of the materials used in the construction of the fence and resisting no externally applied horizontal loadings other than wind or earthquake forces. Freestanding masonry sign pylons shall be classified as fences.
2. Rock masonry walls used in whole or in part for earth retention, in excess of 24 inches in height, shall be provided with adequate footings of reinforced concrete. Rock walls and fences, which due to inadequate or improper design or deterioration, show indications of becoming unstable or unsafe shall, be considered unsafe. Unsafe walls and fences shall be abated by repair and rehabilitation or by demolition.
3. If a wall is proposed to be built, constructed, or repaired on a common property line, written approval of adjoining property owners must be submitted with the application for a building permit. If the City is the adjoining property owner, written approval of the Zoning Administrator must be requested and submitted with the permit application.
2114.2 Retaining Walls. Permanent excavations with a grade separation exceeding twenty-four (24) inches on a vertical line, as opposed to embankments along the natural angle of repose of the soil material, that are retained with masonry shall have the masonry designed and constructed within the provisions of this chapter. Both residential and non-residential construction shall comply with this section.
2114.2.1 Design and Stability.
1. Walls used to retain more than four (4) feet of earth shall be designed by a registered professional engineer.
2. Walls shall be analyzed as gravity type structures. Native rubble masonry construction spanning between buttresses may be considered as having a flexural tensile/compressive strength of fifteen (15) PSI and an axial compressive strength not to exceed sixty (60) PSI. The effective width (thickness) dimensions for structural strength and stability shall be reduced by six (6) inches unless the wall is constructed utilizing a cast-in-place concrete core to ensure solid construction.
3. Foundation concrete shall be effectively bonded to the supported native stone rubble masonry in order to enable the system to perform as an integral composite unit. Bonding may be accomplished by the use of stones twelve (12) inches or larger in dimension placed in the plastic concrete of the foundation to obtain a minimum of six (6) inch embedment with a six (6) inch projection to bond with the native stone rubble masonry constructed above.
4. Externally applied loadings acting on retaining structures shall be those computed from design conditions but shall be no less than required under Chapter 16 of this Code. Parking areas limited to automobiles and other light vehicles shall require a minimum fifty (50) PSF uniform surcharge loading. A minimum of two hundred fifty (250) PSF uniform surcharge loading or AASHTO Lane Loading (whichever is greater) shall be required for parking areas subject to heavy vehicles.
2114.2.2 Materials.
1. Concrete, reinforcing steel and native stone, shall conform to the requirements of Chapters 19 and 21 of this Code. Structural concrete for foundations shall have a minimum twenty-eight (28) day compressive strength of two thousand five hundred (2500) PSI. Concrete for core fill of gravity retaining walls shall have a minimum twenty-eight (28) day compressive strength of two thousand (2000) PSI.
2. Mortar shall have a minimum twenty-eight (28) day compressive strength, of one thousand eight hundred (1,800) PSI when averaged over three (3) two (2) inch cubes of three (3) three (3) by six (6) inch cylinders in accordance with ASTM C109 or ASTM C780 and shall not contain more than fifteen (15) pounds of ASTM C207, Type S hydrated lime per cubic foot of mortar when mixed by volume. The building official may require submission of test reports confirming compliance with these requirements.
2114.2.3 Construction.
1. Foundations shall bear on native undisturbed soil capable of sustaining the load imparted upon it. Subject to the approval of the building official.
2. Foundation may be built upon mechanically compacted soil (native soils with increased densification or engineered fill materials) upon submittal of evidence that the proposed loadings will be adequately supported.
3. Adequate provisions shall be made to eliminate hydrostatic pressure buildup through the use of a free-draining backfill material over an underground water collection system that will drain through the wall and above the foundation in order to ensure stability of the foundation supporting soil. Random pattern weep holes shall not be considered as sufficient to accomplish required drainage. Retaining structures retaining less than four (4) feet of earth are not required to provide the above drainage system.
4. Foundations must bear a minimum of two (2) feet below finish grade level or one (1) foot into native undisturbed materials satisfactory for bearing (on the low side of the retaining structures) whichever provides the lowest elevation.
2114.2.4 Drawings and Specifications. All structures governed under this section shall be required to submit drawings in accordance with Chapter 18.02 Administrative Code. Such drawings shall include the following:
1. Theoretical calculated soil pressures at the toe and heel of the wall foundation.
2. Factor of safety against horizontal sliding and overturning (tipping) equal to or greater than 1.5.
3. Uniform surcharge loading and soil unit weight used in analysis and design (PCF).
4. Line or strip loadings (PLF) and locations with respect to wall.
5. Assumed unit weight of native stone rubble masonry construction (PCF).
6. Wall thickness and height dimensions with relative positioning for yard wall extensions, retained heights, base widths and foundations.
7. Locations of construction (through-wall) joints, changes in foundation bearing elevations, positioning, extent and construction of underground drainage against the retaining structure.
2114.3 Yard Walls and Fences. Yard walls and fences of masonry materials shall be considered as non-bearing walls and shall be supported either horizontally or vertically by intersecting fences, pilasters, monolithic columns, integral, with the fence construction of sufficient strength and stability to provide the required structural support. The minimum thickness shall be sufficient to resist all normal vertical and horizontal loads applied to the fence.
2114.3.1 Masonry walls over six (6) feet in height shall be designed as a structural wall by a licensed professional engineer and provided with adequate footings. The design will be reviewed by the building official.
2114.3.2 Design and Stability.
1. The unsupported height to thickness (KH/t) or length to thickness (KL/t) shall not exceed 40, where, K=2.0 for cantilevered conditions, and 1.0 for both ends being supported:
H = Height of fence above foundation
L = Horizontal distance between stiffening elements
t = Thickness of fence
2. In native stone rubble masonry walls with "no mortar" finishes, three (3) inches shall be deducted from the thickness of the fence for each face where this finish is used, when computing the minimum thickness for KH/t, KL/t and structural stability requirements.
3. Lateral support (stiffening elements) shall be provided by intersecting fences, pilasters, monolithic columns integral with the fence construction or other vertical members of sufficient strength and stability to provide the required structural support.
4. Masonry fences, including native stone rubble, shall have each wythe through-bonded with native stone rubble masonry having through-bond stones at a maximum spacing of three (3) feet vertically and three (3) feet horizontally.
5. Adequate strength, and stability to resist overturning, and other stresses for externally applied horizontal loads, shall be provided to the satisfaction of the building official and shall conform to accepted engineering design principles. Wind loading and shape factors shall be as set forth in Chapter 12 of this Code.
2114.3.3 Materials.
1. All materials shall be in accordance with Chapter 21.
2. Masonry fences, including native stone rubble, shall be laid in Type M, S, or N mortar.
3. Masonry fences, including native stone rubble, shall be provided with a reinforced concrete foundation in accordance with the approved subdivision design standards of the City.
(Ord. No. 18509 , § 1, 5-31-2016)