Section 27-685. Foundation piers

Foundation  piers  shall be designed as
  columns. Reinforced concrete piers shall be designed in accordance  with
  the   provisions   of   reference   standard  RS  10-3.  Reinforced  and
  unreinforced masonry piers shall be  designed  in  accordance  with  the
  provisions  of  reference  standards  RS  10-2 and RS 10-1. Unreinforced
  concrete piers shall be designed in accordance with subdivision  (b)  of
  this section.
    (a)  Lateral  support.  The  equivalent  unbraced  length  of  a  pier
  supported by lateral soil pressure may be  determined  by  a  recognized
  method of elastic analysis. Alternatively, such a pier may be assumed to
  be hinged, but laterally braced at intervals equal to the full height of
  the  pier  or  eight  times  the  least  lateral  dimension of the pier,
  whichever is the lesser value. The provisions of subdivision (e) of this
  section shall apply.
    (b) Unreinforced concrete piers. Where unreinforced concrete piers are
  used, the allowable compressive stress shall not exceed 0.25f'c and  the
  center  of cross section of the pier at any level shall not deviate from
  the line of action of the resultant of all forces (which line of  action
  shall consider the eccentricities due to all loads and moments acting on
  the pier) by an amount more than one-sixtieth of its height or one-tenth
  of  its least lateral dimension and the ratio of the height to the least
  lateral dimension shall not exceed eight. For larger values of the ratio
  of  the  height  to  the  least  lateral  dimensions,  or  for   greater
  eccentricities, piers shall be reinforced.
    (c)  Metal shells. Where piers are encased by a metal shell, the shell
  may be considered as contributing to the structural strength of the pier
  provided that the thickness is one-eighth inch or greater,  and  subject
  to the following requirements:
    (1)   Where  boring  records  or  site  conditions  indicate  possible
  deleterious action on the shell, where  any  portion  of  the  shell  is
  embedded  in  ash,  cinder fill or garbage fill, where the encased piers
  are used for support of chemical plants, piles of coal, or  under  other
  conditions  conducive  to chemical seepage or corrosive action, or where
  the encased piers are used for support of electrical generating  plants,
  the metal shells shall be protected against deterioration by encasement,
  coating, or other device acceptable to the commissioner.
    (2)  The  area  of  the  metal  section of the shell multiplied by the
  efficiency of the horizontal joints shall be  considered  as  equivalent
  vertical reinforcement of the pier. The area of the metal section of the
  shell,  multiplied  by  the  efficiency of the vertical joints, shall be
  considered as equivalent spiral reinforcement of the pier.
    (d) Minimum dimensions. The provisions  of  subdivision  (e)  of  this
  section  shall apply. In addition, the plan dimensions of the pier shall
  not be less than those of the column above. If the  column  above  is  a
  steel  section resting on a base plate, the base plate and pier shall be
  proportioned for allowable bearing pressures as prescribed in  reference
  standards RS 10-1, RS 10-2, and RS 10-3.
    (e)  Filling.  The  provisions  of  subdivisions  (a)  and (d) of this
  section shall apply only where the fill (or backfill) is  placed  around
  the pier as controlled fill, and wherein the level of the fill is raised
  uniformly  around  the  entire  perimeter  of  the  pier. Where the fill
  operation is not controlled the least lateral dimension of a  foundation
  pier  shall be twenty-four inches and the pier shall be proportioned for
  lateral pressure equal to the pressure of a differential height of  fill
  equal  to  five feet, applied simultaneously with the other loads on the
  pier specified in article three of this subchapter.