- For the design of temporary structures (defined for this chapter as a structure, that will be in place 180 days or less) load combinations in Equations 16-8, 16-9 can be multiplied by a factor of 0.75.
- For the design of temporary structures the Equations 16-10, 16-11, 16-12 can be multiplied by a factor of 0.67.
- For any combination of dead loads with three or more variable loads, these variable loads can be multiplied by a factor of 0.67.
- For the combinations of loads to be used in the design of permanent structures, the load due to lateral earth and ground water pressure shall be multiplied by a factor of 1.
- A site-specific analysis in accordance with Sections 1813.2, 1813.3, and 1813.4. Site specific response shall be evaluated for site peak ground acceleration magnitudes and source characteristics consistent with the design earthquake ground motions.
- A determination of lateral pressures on basement, cellar, and retaining walls due to earthquake motions.
- An assessment of potential consequences of any liquefaction and soil strength loss, including estimation of differential settlement, lateral movement or reduction in foundation soil-bearing capacity, and shall address mitigation measures. Such measures shall be given consideration in the design of the structure and shall include, but are not limited to, ground stabilization, selection of appropriate foundation type and depths, selection of appropriate structural systems to accommodate anticipated displacements or any combination of these measures. Peak ground acceleration shall be determined from a site-specific study taking into account soil amplification effects, as specified in Section 1615.2.
- The presence of defects or the inclination of bedding planes in the rock are of such size and location so as not to affect stability of the foundation.
- The foundation is not designed for bearing pressures exceeding those permitted in Table 1804.2.
- A description of the planned structure
- A plot showing the location of test borings and/or excavations.
- A complete record of the soil sample descriptions.
- A record of the soil profile.
- Elevation of the water table, if encountered.
- Results of in-situ or geophysical testing
- Results of laboratory testing.
- Recommendations for foundation type and design criteria, including but not limited to: bearing capacity of natural or compacted soil, mitigation of the effects of liquefaction (if applicable), differential settlement and varying soil strength; and the effects of adjacent loads.
- Expected total and differential settlement.
- Pile and pier foundation recommendations and installed capacities
- Special design and construction provisions for footings or foundations founded on expansive soils, as necessary.
- Compacted fill material properties and testing in accordance with Section 1803.5.
- Special installation procedures.
- Pier and pile load test requirements.
- Specifications for the preparation of the site prior to placement of compacted fill material.
- Specifications for material to be used as compacted fill.
- Test method to be used to determine the maximum dry density and optimum moisture content of the material to be used as compacted fill.
- Maximum allowable thickness of each lift of compacted fill material.
- Field test method for determining the in-place dry density of the compacted fill.
- Minimum acceptable in-place dry density expressed as a percentage of the maximum dry density determined in accordance with Item 3.
- Number and frequency of field tests required to determine compliance with Item 6.
- Acceptable types of compaction equipment for the specified fill materials.
|CLASS OF MATERIALS
(Notes 1 and 3)
|MAXIMUM ALLOWABLE FOUNDATION
|MAXIMUM ALLOWABLE FOUNDATION
|1. Bedrock (Notes 2 and 7)
1a Hard sound rock—gneiss, diabase, schist
1b Medium hard rock—marble, serpentine
1c Intermediate rock—shale, sandstone
1d Soft rock—weathered rock
|2. Sandy gravel and gravel (GW, GP)
(Notes 3, 4, 8, and 9)
|3. Granular soils (GC, GM, SW, SP,SM, and SC)
(Notes 4, 5, 8, and 9)
|4. Clays (SC, CL, and CH) (Notes 4, 6, 8, and 9)
|5. Silts and silty soils (ML and MH) (Notes 4, 8, and 9)
|See 1804.2.1||See 1804.2.1|
|7. Controlled and uncontrolled fills||See 1804.2.2 or 1804.2.3||See 1804.2.2 or 1804.2.3|
- Where there is doubt as to the applicable classification of a soil stratum, the allowable bearing pressure applicable to the lower class of material to which the given stratum might conform shall apply.
- The tabulated values of allowable bearing pressures apply only for massive rocks or for sedimentary or foliated rocks, where the strata are level or nearly so, and then only if the area has ample lateral support. Tilted strata and their relation to nearby slopes or excavations shall receive special consideration. The tabulated values for Class 1a materials (hard sound rock) may be increased by 25 percent provided the geotechnical engineer performs additional tests and/or analyses substantiating the increase
- For intermediate conditions, values of allowable bearing pressure shall be estimated by interpolation between indicated extremes.
- Footing embedment in soils shall be in accordance with Section 1805.2 and the width of the loaded area not less than 2 feet (610mm), unless analysis demonstrates that the proposed construction will have a minimum factor of safety of 2.0 against shear failure of the soil.
- Estimates of settlements shall govern the allowable bearing value, subject to the maximums given in this table, and as provided in Section 1804.2.
- The bearing capacity of clay soils shall be established on the basis of the strength of such soils as determined by field or laboratory tests and shall provide a factor of safety against failure of the soil of not less than 2.0 computed on the basis of a recognized procedure of soils analysis, shall account for probable settlements of the building and shall not exceed the tabulated maximum values.
- Increases in allowable bearing pressure due to embedment of the foundation. The allowable bearing values for intermediate to hard rock shall apply where the loaded area is on the surface of sound rock. Where the loaded area is below the adjacent rock surface and is fully confined by the adjacent rock mass and provided that the rock mass has not been shattered by blasting or otherwise is or has been rendered unsound, these values may be increased 10 percent of the base value for each 1 foot (0.3 meters) of embedment below the surface of the adjacent rock surface in excess of 1 foot (0.3 meters), but shall not exceed 200 percent of the val ues.
- The allowable bearing values for soils of Classes 2,3,4, and5 determined in accordance with Notes three, four and five above, shall apply where the loaded area is embedded 4 feet (1219 mm) or less in the bearing stratum. Where the loaded area is embedded more than 4 feet (1219 mm) below the adjacent surface of the bearing stratum, and is fully confined by the weight of the adjacent soil, these values may be increased 5 percent of the base value for each 1-foot (305mm) additional embedment, but shall not exceed twice the values. Increases in allowable bearing pressure due to embedment shall not apply to soft rock, clays, silts and soils of Classes 6 and 7.
- The allowable bearing values for soils of Classes 2, 3, 4, and 5 determined in accordance with this table and the notes thereto, may be increased up to one - third where the density of the bearing stratum below the bottom of the footings increases with depth and is not underlain by materials of a lower allowable bearing pressure. Such allowable bearing values shall be demonstrated by a recognized means of analysis that the probable settlement of the foundation due to compression, and/or consolidation does not exceed acceptable limits for the proposed building.
- The maximum toe pressure for eccentrically loaded footings may exceed the allowable bearing value by up to 25 percent if it is demonstrated that the heel of the footing is not subjected to tension.
- Area to be filled shall be stripped of all organic materials, rubbish and debris.
- Fill shall not be placed when frozen or on frozen or saturated subgrade.
- The engineer, or the engineer's representative, shall approve the subgrade prior to fill placement.
- Fill material shall consist of well graded sand, gravel, crushed rock, recycled concrete aggregate, or a mixture of these, or equivalent materials with a maximum of 10 percent passing the #200 sieve, as determined from the percent passing the #4 sieve.
- Fill shall be placed and compacted in lifts, not exceeding 12 inches (305 millimeters), at its optimum moisture content, plus or minus two percent, and to not less than a density of ninety-five percent of the optimum density as determined by ASTM D 1557.
- Fill density shall be verified by in-place tests made on each lift.
- The allowable bearing value of controlled fill shall be limited to 3 tons per square foot (383 kPa) providing the underlying soil is not weaker than the controlled fill.
- The soil within the building area shall be explored using test pits at every column. All test pits shall extend to depths equal to the smaller width of the footing and at least one test pit shall penetrate at least 8 feet (2438 mm) below the level of the bottom of the proposed footings. All test pits shall be backfilled with properly compacted fill. Borings may be used in lieu of test pits, provided that continuous samples of at least 3 inches (76 mm) in diameter are recovered.
- The building area shall be additionally explored using one standard boring for every twenty-five hundred square foot (232.3 m2) of building footprint area. These borings shall be carried to a depth sufficient to penetrate into natural ground, but not less than 20 feet (6096 mm) below grade.
- The fill shall be composed of material that is free of voids and free of extensive inclusions of mud, organic materials such as paper, wood, garbage, cans, or metallic objects, and debris.
- The allowable soil bearing pressure on satisfactory uncontrolled fill material shall not exceed two tons per square foot (192 kPa). One-and two-family dwellings may be founded on satisfactory uncontrolled fill provided the dwelling site has been explored using at least one test pit, penetrating at least 8 feet (2438 mm) below the level of the bottom of the proposed footings, and that the fill has been found to be composed of material that is free of voids and generally free of mud, organic materials such as paper, garbage, cans, or metallic objects, and debris. Test pits shall be backfilled with properly compacted fill.
- Extending a minimum of 4 feet (1219 mm) below grade;
- Constructing in accordance with ASCE-32; or
- Erecting on solid rock.
- All load-bearing walls shall be placed on continuous concrete footings bonded integrally with the exterior wall footings.
- The minimum actual thickness of a load-bearing masonry wall shall not be less than 4 inches (102 mm) nominal or 35/8 inches (92 mm) actual thickness, and shall be bonded integrally with piers spaced 6 feet (1829 mm) on center (o.c.).
- Piers shall be constructed in accordance with Chapter 21 and the following:
- The unsupported height of the masonry piers shall not exceed 10 times their least dimension.
- Where structural clay tile or hollow concrete masonry units are used for piers supporting beams and girders, the cellular spaces shall be filled solidly with concrete or Type M or S mortar.
Exception: Unfilled hollow piers are permitted where the unsupported height of the pier is not more than four times its least dimension.
- The maximum height of a 4-inch (102mm) load-bearing masonry foundation wall supporting wood frame walls and floors shall not be more than 4 feet (1219 mm) in height.
- The unbalanced fill for 4-inch (102 mm) foundation walls shall not exceed 24 inches (610 mm) for solid masonry, nor 12 inches (305mm) for hollow masonry.
- Group R or U occupancies of light-framed construction and two stories or less in height are permitted to use concrete with a specified compressive strength of not less than 2,500 psi (17.2 MPa) at 28 days.
- One- and two-family dwellings not more than three stories in height are not required to comply with the provisions of ACI 318, Sections 21.10.1 to 21.10.3.
Piles supporting walls shall be driven alternately in lines spaced at least 1 foot (305 mm) apart and located symmetrically under the center of gravity of the wall load carried, unless effective measures are taken to provide for eccentricity and lateral forces, or the wall piles are adequately braced to provide for lateral stability. A single row of piles without lateral bracing is permitted for one- and two-family dwellings and lightweight construction not exceeding two stories or 35 feet (10 668 mm) in height, provided the centers of the piles are located within the width of the foundation wall.
- Spacing of piles shall provide for adequate distribution of the load on the pile group to the supporting soil. In no case shall the minimum center-to-center spacing of piles be less than 24 inches (610 mm) nor less than the following for the specific types of piling indicated in this chapter.
- Minimum spacing between enlarged base concrete piles shall be 4 feet 6 inches (1372 mm), center to center except that where the shafts of such piles are cased for their full length, this spacing may be reduced to 3 feet 6 inches (1067 mm). Where a question exists as to possible damage to adjacent previously driven piles, these minimums shall be increased. Minimum center-to-center spacing of piles at the bearing level shall be at least two and one half times the outside diameter of the shell.
- Unless special measures are taken to assure that piles will penetrate sufficiently to meet the requirements of 1808.2.8 without interfering with or intersecting each other, the minimum center to center spacing of piles shall be twice the average diameter of the butt for round piles, one and three quarters times the diagonal for rectangular piles; or, for taper piles, twice the diameter at a level two thirds of the pile length measured up from the tip.
- In cases of practical difficulty, the spacing of new piles from existing piles under an adjacent building may be less than the above values provided that the requirements relating to minimum embedment and pile interference are satisfied and that the soil under the proposed and existing buildings is not overloaded by the closer pile grouping.
- The capacity of the pile as a structural member.
- The allowable bearing pressure on soil strata underlying the pile tips.
- The resistance to penetration of the piles, including resistance to driving, resistance to jacking, the rate of penetration, or other equivalent criteria.
- The capacity as indicated by load test, where load tests are required.
- The maximum loads prescribed in Section 1808.2.8.1.3.
- For piles embedded entirely in decomposed rock or granular soils, or in controlled fill materials, the polygon shall be circumscribed at a level located two-thirds of the embedded length of the pile, measured up from the tip.
- For piles penetrating through silts and clays into bearing in decomposed rock or granular soils, the polygon shall be circumscribed at the bottom of the strata of silts or clays.
|TYPE OF PILE||MAXIMUM ALLOWABLE PILE LOAD (TONS)|
|Caisson Piles||No upper limit|
|Open-end pipe (or tube) piles bearing on rock of Class 1a, 1b, or 1c||18-in O.D. and greater 250
14-in to 18-in O.D. 200
12-in to 14-in 150
10-in to 12-in 100
8-in to 10-in 60
|Closed-end pipe (or tube) piles, H-piles, cast-in-place concrete, enlarged base piles,
and precast concrete piles bearing on rock of Class 1a, 1b, or 1c
|Piles (other than timber piles) bearing onsoft rock of Class 1d||80|
|Piles (other than timber piles) that receive their principal support other than by direct
bearing on rock of Class 1a through 1d
|Timber piles bearing on rock of Class 1a through 1d||25|
|Timber piles bearing in suitable soils||40 tons maximum permissible with load test, 30 tons
maximum without load test.
|MINIMUM DRIVING RESISTANCEa, c, d, e|
|Piles Bearing on Soft Rock
|Piles Bearing on Rock
(Class 1a, 1b, and 1c)
|Up to 20||15,000||19||48||5 Blows per 1/4 inch
(Minimum hammer energy
of 15,000 ft. lbs.)
|70 & 80
||19,000||5 Blows per 1/4 inch
(Minimum hammer energy
of 19,000 ft. lbs.)
- Final driving resistance shall be the sum of tabulated values plus resistance exerted by nonbearing materials. The driving resistance of nonbearing materials shall be taken as the resistance experienced by the pile during driving, but which will be dissipated with time and may be approximated as described in Section 1808.2.8.1.5.1.
- The hammer energy indicated is the rated energy.
- Sustained driving resistance. Where piles are to bear in soft rock, the minimum driving resistance shall be maintained for the last 6 inches, unless a higher sustained driving resistance requirement is established by load test. Where piles are to bear in soil Classes 2 through 5, the minimum driving resistance shall be maintained for the last that inches unless load testing demonstrates a requirement for higher sustained driving resistance. No pile needs to be driven to a resistance that penetrates in blows per inch (blows per 25mm) more than twice the resistance indicated in this table, nor beyond the point at which there is no measurable net penetration under the hammer blow.
- The tabulated values assume that the ratio of total weight of pile to weight of striking part of the hammer does not exceed 3.5. If a larger ratio is to be used, or for other conditions for which no values are tabulated, the driving resistance shall be as approved by the commissioner.
- For intermediate values of pile capacity, minimum requirements for driving resistance may be determined by straight line interpolation.
|MINIMUM DRIVING RESISTANCE (BLOWS/IN.)
TO BE ADDED TO DRIVING RESISTANCE
EXERTED BY NONBEARING MATERIALS
(ftilbs.) (Note 2)
|Up to 20||Formula in Note 4 shall apply||7,500-12,000|
|Over 20 to 25||9,000-12,000|
|Over 25 to 30||12,000-16,000
|Greater than 30||15,000-20,000
- The driving resistance exerted by nonbearing materials is the resistance experienced by the pile during driving, but which will be dissipated with time and may be approximated as described in Section 1808.2.8.1.5.1.
- The hammer energy indicated is the rated energy.
- Sustained driving resistance. Where piles are to bear in soil classes, Soft rock, the minimum driving resistance shall be maintained for the last 6 inches, unless a higher sustained driving resistance requirement is established by load test. Where piles are to bear in soil Classes 2 through 5, the minimum driving resistance measured in blows per inch (blows per 25 mm) shall be maintained for the last 12 inches unless load testing demonstrates a requirement for higher sustained driving resistance. No pile need be driven to a resistance that penetrates in blows per inch (blows per 25 mm) more than twice the resistance indicated in this table nor beyond the point at which there is no measurable net penetration under the hammer blow.
- The minimum driving resistance shall be determined by the following formula:
P = 2WhH (S + 0.1) or P = 2E (S + 0.1)
where: p = Allowable pile load in pounds Wp = Weight of pile in pounds. Wh = Weight of striking part of hammer in pounds. H = Actual height of fall of striking part of hammer in feet. E = Rated energy delivered by the hammer per blow in foot/lbs. S = Penetration of pile per blow, in inches, after the pile has been driven to a depth where successive blows produce approximately equal net penetration.The value Wp shall not exceed three times Wh
1808.2.8.1.5.1 Piles Installed by Use of Steam-Powered, Air-Powered, Diesel-Powered or Hydraulic Impact Hammers
- The minimum required driving resistance and the requirements for hammer energies for various types and capacities of piles are given in Tables 1808.2.8.1.5A and 1808.2.8.1.5B. To obtain the required total driving resistance, the indicated driving resistances shall be added to any driving resistance experienced by the pile during installation, but which will be dissipated with time (resistance exerted by nonbearing materials or by materials which are to be excavated). For the purposes of this section, the resistance exerted by nonbearing materials may be approximated as the resistance to penetration of the pile recorded when the pile has penetrated to the bottom of the lowest stratum of nominally unsatisfactory bearing material (Class 6 and uncontrolled fills, but not controlled fill) or to the bottom of the lowest stratum of soft or loose deposits of soils of Class 4 or 5 but only where such strata are completely penetrated by the pile.
- Alternate for similitude method—The requirement for installation of piling to the penetration resistances given in Tables 1808.2.8.1.5A and 1808.2.8.1.5B may be waived where the following six conditions are satisfied:
- The piles bear on, or in, soil of Classes 2 through 5.
- The stratigraphy, as defined by not less than one boring for every 1600 square feet (149 m2) of building area, shall be reasonably uniform or divisible into areas of uniform conditions.
- Regardless of pile type or capacity, one load test, as described in Section 1808.2.8.1.5.3, shall be conducted in each area of uniform conditions, but not less than two typical piles for the entire foundation installation of the building or group of buildings on the site, nor less than one pile for every 15,000 square feet (1394 m2) of pile foundation area shall be load tested.
- Except as permitted by the provisions of paragraph 2.6 below, all building piles within the area of influence of a given load-tested pile of satisfactory performance shall be installed to the same or greater driving resistance as the successful load-tested pile. The same or heavier equipment of the same type that was used to install the load-tested pile shall be used to install all other building piles, and the equipment shall be operated identically. Also, all other piles shall be of the same type, shape, external dimension, and equal or greater cross-section as the load-tested pile. All building piles within the area of influence represented by a given satisfactory load-tested pile shall bear in, or on the same bearing stratum as the load test pile.
- A report by an engineer shall be submitted to the commissioner for review and approval establishing that the soil-bearing pressures do not exceed the values permitted by Table 1804.1 and that the probable differential settlements will not cause stress conditions in the building in excess of those permitted by the provisions of this code.
- Where the structure of the building or the spacing and length of the piling is such as to cause the building and its foundation to act as an essentially rigid body, the building piles may be driven to length and/or penetration into the bearing stratum without regard to penetration resistance, subject to the requirement of paragraph 2.5 above, relating to the submission and approval of a report.
- Comparison piles, as required by the provisions of Item 4 below, shall be installed using an impact hammer and driving resistances corresponding to the proposed pile capacities as determined in paragraph 3 below or to tip elevations and driving resistances as determined by the engineer.
- For each comparison pile, an identical index pile shall be installed by use of the vibratory hammer at a location at least 4 feet (1219 mm), but not more than 6 feet (1829 mm), from each comparison pile. The index piles shall be installed to the same tip elevation as the comparison pile, except that where the comparison piles bear on rock, the index piles shall bear in or on similar material. All driving data for the index pile shall be recorded.
- The index piles shall be load tested in accordance with the provisions of Item 4 of this section. Should the specified load test criteria indicate inadequate capacity of the index piles, steps 1, 2, and 3 shall be repeated using longer, larger or other types of piles.
- All building piles within the area of influence of a given, satisfactorily tested index pile shall be installed to the same or lesser rate of penetration (inches per minute mm per minute) as the successful index pile. The same equipment that was used to install the index pile, identically operated in all aspects, shall be used to install the building piles. All building piles shall be of the same type size and shape as the index pile. All building piles within the area of influence as represented by a given satisfactorily tested index pile shall bear in, or on, the same bearing stratum as the index pile.
- Dial extensometer gages shall provide readings to the nearest 0.001 inch (0.025 mm). Electrical transducers may be used to make settlement observations provided that backup measurements are made utilizing dial extensometers as described herein at sufficient times to validate the transducer readings. The total test load shall remain in place until the rate of settlement does not exceed 0.012 inches (0.305 mm) over a time period of 12 hours. The total load shall be removed in decrements not exceeding 25 percent of the total load at 1 hour intervals or longer.In addition to observations required by ASTM D 1143, settlement observations shall be performed at 1/2 minute, 1-minute, 2-minute and 4-minute intervals after application of each load increment, and 24 hours after the entire test load has been removed.
- Any temporary supporting capacity that the soil might provide to the pile during a load test, but which would be dissipated with time, shall be eliminated by casing off or by other suitable means, such as increasing the total test load to account for such temporary capacity.
- Fifty-percent of the applied load causing a net settlement of the pile of not more than one 1/100 of 1 inch per ton (0.25mm per 8.9 kN) of applied load. Net settlement in this paragraph is defined as gross settlement due to the total test load minus the rebound after removing 100 percent of the test load.
- Fifty-percent of the applied load causing a net settlement of the pile of 3/4 inch (19mm). Net settlement in this paragraph is defined as the gross settlement due to the total test load less the amount of elastic shortening in the pile section due to total test load. The elastic shortening shall be calculated as if the pile is designed as an end-bearing pile or as a friction pile. Alternatively, the net settlement may be measured directly using a telltale or other suitable instrumentation.
The final load increment shall remain in place for a total of not less than 24 hours; single test piles shall be subjected to cyclical loading or suitably instrumented with telltales and strain gauges so that the movements of the pile tip and butt may be independently determined and load transfer to the soil evaluated. A complete record demonstrating satisfactory performance of the test shall be submitted to the commissioner.
- Construction of a foundation for a building utilizing piles of more than one type or capacity; or
- Modification of an existing foundation by the addition of piles of a type or capacity other than those of the existing piling; or
- Construction or modification of a foundation utilizing different methods or more than one method of installation, or using different types or capacities of equipment (such as different types of hammers having markedly different striking energies or speeds); or
- Support of part of a building on piles and part on footings.
- A soils investigation in accordance with Section 1802.
- Pier or pile load tests in accordance with Section 1808.2.8.3, regardless of the load supported by the pier or pile. The design and installation of the pier or pile foundation shall be under the direct supervision of an engineer knowledgeable in the field of soil mechanics and pier or pile foundations who shall certify to the commissioner that the piers or piles as installed satisfy the design criteria.
- Untreated timber piles shall not be used unless the top level of the pile is below the permanent water table. The permanent water table level shall not be assumed higher than the invert level of sewer, drain, or subsurface structure in the adjacent streets, nor higher than the water level at the site resulting from the lowest drawdown of wells or sumps, but in no case shall untreated timber piles be used where the cut-off level is less than 10 feet (3048 mm) below the adjacent legal grade. Where treated piles are required, preservative treatment shall consist of impregnation with creosote or a creosote solution or CCA treatment. For piles entirely embedded below grade, a pentachlorophenal solution may be used. Treatment shall be in accordance with all requirements of the AWPA standards and as specified in Section 1809.1.2.
- Piles installed in ash or garbage fills, cinder fills, and piles that are free-standing in or near a seawater environment, or that are used for the support of chemical plants, coal piles and piles under similar conditions of chemical seepage or aggressive action, or that are used for support of electrical generating plants, shall be investigated regarding the need for special protective treatment. Where special protective treatment is indicated by the engineer, such piles shall be protected against deterioration by encasement, coating, or other device acceptable to the engineer.
- Group R or U occupancies of light-framed construction and two stories or less in height are permitted to use concrete with a specified compressive strength of not less than 2,500 psi (17.2 MPa) at 28 days.
- Detached one- and two-family dwellings of light-frame construction and two stories or less in height are not required to comply with the provisions of ACI 318, Section 21.10.4.
- Section 184.108.40.206(a) of ACI 318 shall not apply to concrete piles.
- In the case of uplift, the lesser of the nominal tensile strength of the longitudinal reinforcement in a concrete pile, or the nominal tensile strength of a steel pile, or the pile uplift soil nominal strength factored by 1.3 or the axial tension force resulting from the load combinations of Section 1605.4.
- In the case of rotational restraint, the lesser of the axial and shear forces, and moments resulting from the load combinations of Section 1605.4 or development of the full axial, bending and shear nominal strength of the pile.
- For piles having a diameter of 16 inches (406 mm) or less, wire shall not be smaller than 0.22 inch (5.6 mm) (No. 5 gage).
- For piles having a diameter of more than 16 inches (406 mm) and less than 20 inches (508 mm), wire shall not be smaller than 0.238 inch (6 mm) (No. 4 gage).
- For piles having a diameter of 20 inches (508 mm) and larger, wire shall not be smaller than 1/4 inch (6.4 mm) round or 0.259 inch (6.6 mm) (No. 3 gage).
|f'c||=||Specified compressive strength of concrete, psi (MPa)|
|fyh||=||Yield strength of spiral reinforcement ≤ 85,000 psi (586 MPa).|
|ρs||=||Spiral reinforcement index (vol. spiral/vol. core).|
- Requirements in ACI 318, Chapter 21, do not apply, unless specifically referenced.
- Where the total pile length in the soil is 35 feet (10 668 mm) or less, the lateral transverse reinforcement in the ductile region shall occur through the length of the pile. Where the pile length exceeds 35 feet (10 668 mm), the ductile pile region shall be taken as the greater of 35 feet (10 668 mm) or the distance from the underside of the pile cap to the point of zero curvature plus three times the least pile dimension.
- In the ductile region, the center-to-center spacing of the spirals or hoop reinforcement shall not exceed one-fifth of the least pile dimension, six times the diameter of the longitudinal strand, or 8 inches (203 mm), whichever is smaller.
- Circular spiral reinforcement shall be spliced by lapping one full turn and bending the end of the spiral to a 90-degree hook or by use of a mechanical or welded splice complying with Sec. 12.14.3 of ACI 318.
- Where the transverse reinforcement consists of circular spirals, the volumetric ratio of spiral transverse reinforcement in the ductile region shall comply with the following:
ρs = 0.25 (f'c/fyh)(Ag/ Ach — 1.0) [0.5 + 1.4P / (f'cAg)] (Equation 18-5)
but not less than:
ρs = 0.14 (f'c/fyh)[ 0.5 + 1.4P / (f'cAg)] (Equation 18-6)
and need not exceed:
ρs = 0.021 (Equation 18-7)
Ag = Pile cross-sectional area, square inches(mm2). Ach = Core area defined by spiral outside diameter, square inches (mm2). f'c = Specified compressive strength of concrete, psi (MPa) fyh = Yield strength of spiral reinforcement< 85,000 psi (586 MPa). P = Axial load on pile, pounds (kN), as determined from Equations 16-5 and 16-6. ρs = Volumetric ratio (vol. spiral/ vol. core).
- When transverse reinforcement consists of rectangular hoops and cross ties, the total cross-sectional area of lateral transverse reinforcement in the ductile region with spacings, and perpendicular to dimension, hc, shall conform to:
Ash = 0.3shc (f'c/fyh)(Ag/Ach — 1.0)[0.5 + 1.4P/(f'cAg)] (Equation 18-8)
but not less than:
Ash = 0.12shc (f'c/fyh)[0.5 + 1.4P/(f'cAg)] (Equation 18-9)
fyh = 70,000 psi (483 MPa). hc = Cross-sectional dimension of pile core measured center to center of hoop reinforcement, inch (mm). s = Spacing of transverse reinforcement measured along length of pile, inch (mm). Ash = Cross-sectional area of tranverse reinforcement, square inches (mm2) f'c = Specified compressive strength of concrete, psi (MPa).
The hoops and cross ties shall,be,equivalent to deformed bars not less than No.3 in size. Rectangular hoop ends shall terminate at a corner with seismic hooks.
Outside of the length of the pile requiring transverse confinement reinforcing, the spiral or hoop reinforcing with a volumetric ratio not less than one-half of that required for transverse confinement reinforcing shall be provided.
- The flange projections shall not exceed 14 times the minimum thickness of metal in either the flange or the web and the flange widths shall not be less than 80 percent of the depth of the section.
- The nominal depth in the direction of the web shall not be less than 8 inches (203 mm).
- Flanges and web shall have a minimum nominal thickness of 3/8 inch (9.5 mm).
Where grout is placed by pumping through a hollow-stem auger, the auger shall be permitted to rotate in a clockwise direction during withdrawal. An initial head of grout shall be established and maintained on the auger flights before withdrawal. The auger shall be withdrawn in a continuous manner in increments of about 12 inches (305 mm) each. Grout pumping pressures shall be measured and maintained high enough at all times to offset hydrostatic and lateral earth pressures. Grout volumes shall be measured to ensure that the volume of grout placed in each pile is equal to or greater than the theoretical volume of the hole created by the auger. Where the installation process of any pile is interrupted or a loss of grout pressure occurs, the pile shall be re-drilled to 5 feet (1524 mm) below the elevation of the tip of the auger when the installation was interrupted or grout pressure was lost and reformed. Augered cast-in-place piles shall not be installed within six pile diameters center to center of a pile filled with concrete or grout less than 12 hours old, unless approved by the engineer. The level at which return of the grout occurs during withdrawal shall be recorded. If the grout level in any completed pile drops during installation of an adjacent pile, the pile shall be replaced. The installation shall be performed under the direct supervision of the engineer. The engineer shall certify to the commissioner that the piles were installed in compliance with the approved construction documents.
Reinforcement shall conform to the requirements of Sections 1810.1.2.1 and 1810.1.2.2.
- Isolated piers supporting posts of Group R-3 and U occupancies not exceeding two stories of light-frame construction are permitted to be reinforced as required by rational analysis but not less than a minimum of one No. 4 bar, without ties or spirals, when detailed so the pier is not subject to lateral loads and the soil is determined to be of adequate stiffness.
- Isolated piers supporting posts and bracing from decks and patios appurtenant to Group R-3 and U occupancies not exceeding two stories of light-frame construction are permitted to be reinforced as required by rational analysis but not less than one No. 4 bar, without ties or spirals, when the lateral load, E, to the top of the pier does not exceed 200 pounds (890 N) and the soil is determined to be of adequate stiffness.
- Piers supporting the concrete foundation wall of Group R-3 and U occupancies not exceeding two stories of light-frame construction are permitted to be reinforced as required by rational analysis but not less than two No. 4 bars, without ties or spirals, when it can be shown the concrete pier will not rupture when designed for the maximum seismic load, Em, and the soil is determined to be of adequate stiffness.
- Closed ties or spirals where required by Section 1810.1.2.2 are permitted to be limited to the top 3 feet (914 mm) of the piers 10 feet (3048 mm) or less in depth supporting Group R-3 and U occupancies of Seismic Design Category D, not exceeding two stories of light-frame construction.
- Non-cohesive soils below ground water table and less than 50 feet (15 240 mm) below the ground surface shall be considered to have potential for liquefaction.
- The potential for liquefaction on level ground shall be determined on the basis of the Structural Occupancy Categories associated with the uncorrected Standard Penetration Resistance (N) at the site, as defined in Figure 1813.1, or a site specific analysis performed by an engineer with specific expertise in the evaluation of liquefaction.
- The calculated cyclic shear demand is equal to or less than 75 percent of the calculated cyclic shear strength for Structural Occupancy Category I, II, and III structures.
- The calculated cyclic shear demand is equal to or less than 85 percent of the calculated cyclic shear strength for Structural Occupancy Category IV structures.
- Liquefiable soils shall be considered to have no passive (lateral) resistance or bearing capacity value during an earthquake, unless shown otherwise by accepted methods of analysis. The engineer shall submit an analysis for review and approval by the commissioner, demonstrating that the proposed construction is safe against the effects of soil liquefaction.
- Where liquefiable soils are present in sloped ground or over sloped non-liquefiable substrata and where lateral displacement is possible, the engineer shall submit a stability analysis for review and approval by the commissioner, demonstrating that the proposed construction is safe against failure of the soil and that the effect of potential lateral displacements are acceptable.