General approach- Since the analysis procedure is basically numerical, and
since it is based on the finite-element method, it will always be required to
endorse a finer mesh (one with more smaller elements) in order to yield more
accurate results. * In the following, we will adopt a procedure that maintains
that general understanding.

Vertical Loads

  • A story-by-Story analysis under the effect of dead and live loads shall be
    performed using SAP2000, taking into consideration the following:

  • A finer mesh shall be used.

  • Columns shall be includes in the analysis (not as knife-edge supports).

  • Walls loads shall be included as line loads.

  • Design of slabs and beams (under vertical loads) shall be done using the
    results of the analysis

  • Column and wall normal forces due to dead and live loads shall be summed up
    for all stories.

  • Columns and wall moments due to dead and live loads shall be recorded at this

Lateral Load Analysis (The
Etabs File)

  • Build the Etabs model, taking into consideration the following.

  • For columns, use frame elements

  • For walls, use a horizontal mesh of 0.5-0.8ms and a vertical mesh of
    1.2-1.8ms (an element 0.6X1.2 seems appropriate, also may be 0.6X1.75). Don�t
    forgetcompositecolumns (if any). Group sum each wall and each core
    separately (pier forces) are required stories.

  • For slabs include slab limits and openings ignore small openings since they
    add more shell elements. Add beam elements at their locations as frame
    elements. Discretize slab with the finest mesh possible (less than or equal
    2.5 x 2.5m, if) possible. Try to have the mesh as regular as possible All
    points within each horizontal level shall be included in a separate

  • Use reduced stiffness 0.35 for beams and 0.7 for columns and walls, and 0.25
    for slabs.

  • For the dead loads, add dead load as a distributed load. It includes flooring
    and wall weight (A value of 0.3 – 0.5 seems usually reasonable). Include the
    self weight in the dead load. (Including the walls as a line load is an

  • For the live load, add live loads as a distributed load.

  • For the earthquake loads. Use UBC�97 loads in both directions with the
    following options:

  • Include eccentricity 0.05 in each direction.

  • Include Ct

  • First option: Ct = 0.02ft (user-defind)

  • This includes Ta as ct hn ¾ (Eq. 30-8)

  • Second option: Ct = 0.02ft (Program Calculated)

Calculate T using equation from code and compares it with Ta according to Eq.
(30-8). Youhavetoincludedynamicanalysisoption forthisoptiontowork. Otherwise,
program sometimes chooses T wrongly as We recommend using this second option.
Third option: Ta is user-defined as ct hn ¾.There should be a match between
the Eq. (30-8) first and third options.- R = 5.5 (or as per code)

  • Soil type = Sc (or per code)
  • Z = 0.15 (or as per code)
  • These loads are ultimate. To get working loads divide by 1.4For the wind loads
    using BS 6399-95, use the following options!
  • Exposure extents from rigid diaphragm
  • Wind direction Oo (x-direction) and 90 (y-direction)
  • Front Coeff CP = 0.8
  • Rear Coeff CP = 0.3
  • Exposure height: Top STORY & BOT. Story (exclude basements)
  • Include parapets (if any)
  • Effective speed ve (m/sec) = 45 (or as per code)
  • Size effect factor, Ca = 1
  • Dynamic augmentation factor, Cr = 0.25
  • Exposure width (table)         Calculated from diaphragm extents. This wind
    loads option is recommended to be used.

For the wind loads using ASCE7-98, use the following options:

  • Exposure extents from rigid diaphragm
  • Direction angle Oo (x-direction) and 90o (y-direction)
  • Windward Cp = 0.8
  • Leeward Cp = 0.5
  • Exposure height: Top STORY & Bot. STORY (exclude basements)
  • Include parapets (if any)
  • Basic wind speed v= 100 mph
  • Exposure category = C
  • Importance factory, Iw=1
  • Kzt = 1
  • Kd = 0.85
  • Gust factor G = 0.85
  • Exposure width (tables)          calculated form diaphragm extents

For the winds loads using UBC-97, use the following options:

  • Exposure extents from rigid diaphragm
  • Direction angle Oo (x-direction) and 90o (y- direction)
  • Wind ward Cq = 0.8
  • Lee ward Cq = 0.5
  • Exposure height: Top STORY & Bot. STORY (exclude basements)
  • Include parapets (if any)
  • Basic wind speed v= 100 mph
  • Exposure type = C
  • Importance factory, Iw=1
  • Exposure width (tables)          calculated form diaphragm extents.

For the response spectrum, use the following options:

  • UBC�97 response spectrum
  • Damping 5%
  • Scaling factor to equate base shear (may be you first need to run the program
    to get initial base shear values for response spectrum then calculate the
    scale factor)
  • Use Ritz vector.
  • Choose number of modes = 15
  • Use SRSS option for combination of modes.

Also, review these options before you run your file:

  • Mass per unit volume = 0.25 t/m3 (concrete)
  • Weight per unit volume = 2.5t/m3 (concrete)
  • Mass per unit volume = 0.785 t/m2 (Structural Steel)
  • Weight per unit volume = 7.85 t/m3 (Structural Steel)
  • Ec = 140000(fcu)1/2   t/m2  for a given fcu (concrete)
  • Es =  21000  t/m2                                 (Steel)

For the mass source data, use:

  • Mass defined from loads
  • Mass source data
  • Mass lateral lump mass frommass onlyatstories load No   Yes
  • Mass source loads

Load   multiplierDead       1For the P-Delta effect, choose: * Number of iterations  =  2

  • P-Delta load combination = 1.2D + 0.5L

  • It is not recommended to perform a P-Delta analysis, unless a run is done
    without P-Delta to know that everything is ok, since P-Delta run takes more

No load combinations are recommended to be included. No design using Etabs is
also recommended.

Consider reversibility of lateral loads
Results of all loads are working loads, except for earthquake load, which are

Analysis Results & Design

Drift: drift values should not exceed 0.005h for lateral load cases

Slabs: slab design is basically dependent of item �2-vertical loads�. However,
effect of lateral loads should be checked from step �3-lateral load analysis�,
especially in case where framing in based on flat slab behavior, rather than
connecting beams

Beams: Beam design is based on superposition of vl loads from �2-vertical
loads� and lateral loads from �3-lateral load analysis�.

Columns and walls

  • Vertical Loads (working loads)
  • Normal forces: from step �2-vertical loads�. Results of normal forces due to
    D.L and L.L from step �3-lateral load analysis� should be overviewed only,
    since meshing is usually course (wide) and doesn�t produce accurate results
    and may be wall loads were not entered as line loads. Note that normal forces
    in columns and walls intersecting retaining walls drop in value in basements,
    due to interference of retaining walls.
  • Moments: use recorded values in step �2-vertical loads� or from minimum sec
    (as per codes). Results of moments from step �3- lateral load analysis�
    should be overviewed only, since meshing is usually course and doesn�t
    produce accurate results, in addition to other reasons mentioned above.
  • Lateral Loads (working loads)
  • Normal force and moments from �3-lateral load analysis� for max. cases of
    wind, EQ, and response spectrum shall be used for design.
  • Note that EQ forces should be divided by 1.4 in order to be service loads.
  • Use PCA column with pervious service straining actions for column and wall