NYCAC

Article 7 - DISTRIBUTION OF LOADS¶

Section 27-578¶

Section 27-578

  §  27-578  Distribution  of  vertical  loads. Distribution of vertical
loads to supporting members shall  be  determined  on  the  basis  of  a
recognized  method  of  elastic  analysis  or  system of coefficients of
approximation.  Elastic or inelastic displacements of supports shall  be
considered  and,  for  the  distribution  of  dead loads, the modulus of
elasticity of concrete or  composition  sections  shall  be  reduced  to
consider  plastic  flow. Secondary effects, due to warping of the floors
shall be considered.

Section 27-579¶

Section 27-579

  §  27-579  Distribution  of horizontal loads. The following provisions
shall apply to superstructure framing  only,  and  shall  not  apply  to
structures wherein horizontal loads are transmitted to the foundation by
stay-cables,  arches,  non-rectangular frames, or by frames, trusses, or
shear walls not oriented in vertical planes.
  (a) Distribution of horizontal loads to vertical frames,  trusses  and
shear  walls. Horizontal loads on the superstructure shall be assumed to
be distributed to vertical frames, trusses, and shear walls by floor and
roof systems acting as horizontal  diaphragms.  The  proportion  of  the
total horizontal load to be resisted by any given vertical frame, truss,
or  shear  wall  shall  be determined on the basis of relative rigidity,
considering the eccentricity of the applied load  with  respect  to  the
center  of  resistance  of  the  frames,  trusses,  or  shear walls. For
vertical trusses, web deformations shall be considered in evaluating the
rigidity.
  (b) Distribution of horizontal  loads  within  rigid  frames  of  tier
buildings.
  (1)  ASSUMPTIONS.  The  distribution  of horizontal loads within rigid
frames of tier buildings may be determined on the basis of a  recognized
method  of  elastic analysis or, subject to limitations in paragraph two
of this subdivision, may be predicated on one or more of  the  following
simplifying assumptions:
  a.  Points  of inflection in beams or columns are at their midspan and
midheight, respectively. The story shear is distributed to  the  columns
in proportion to their stiffnesses.
  b.  The  change  in  length  of  columns  due  to axial effects of the
horizontal loads may be neglected.
  c. Vertical column loads due to horizontal forces  are  taken  by  the
exterior  columns  only, or are resisted by the columns in proportion to
the column distances from the neutral axis of the bent.
  (2) LIMITATIONS.
  a. For buildings over three hundred feet  in  height,  the  change  in
length of the columns, due to the effects of the horizontal loads, shall
be evaluated or the framing proportioned to produce regular movements of
the  successive joints at each floor so that warping of the floor system
may be neglected.
  b. Simplifying assumptions used in design shall be subject to approval
by  the  commissioner  for  any   of   the   following   conditions   or
circumstances:
  1.  For  buildings  over three hundred feet in height or for buildings
with a height-width ratio greater than five.
  2. At two-story entrances or intermediate floors.
  3. Where offsets in the building occur.
  4. Where transfer columns occur.
  5. In any similar circumstances of irregularities  or  discontinuities
in the framing.
  (c)  Distribution  of load in self-relieving construction. The framing
of self-relieving construction may be  proportioned  on  the  assumption
that  connections  are  fully  rigid in resisting moments due to lateral
load and that any larger moments due to the gravity loads or  due  to  a
combination of gravity and lateral loads will be relieved by deformation
of the connection material, provided that:
  (1)  The  fasteners  shall  be  capable  of developing the full moment
capacity of the connection at the allowable unit stress  established  in
subchapter ten of this chapter.
  (2)  The  connection  shall  be capable of resisting the moment due to
lateral load, and the shear due to lateral load plus vertical load,  all

at  the  allowable  unit  stresses established in subchapter ten of this
chapter.
  (3)   The   framing  and  the  building  are  within  the  limitations
established in subparagraph b of paragraph two  of  subdivision  (b)  of
this section.
  (4)   The  connections  shall  be  detailed  to  permit  the  required
deformations without fracture, and their capacity to so  function  shall
be verified by test or other means.
  (d)   Structural  walls  and  partitions.  Walls  and  partitions,  if
specifically designed to resist the applied forces, may be considered as
contributing to the resistance or rigidity of the structure with  regard
to horizontal loads.