Lateral System Beams

• 21.10.3 (b) Shear Capacity - The beams are designed to meet the larger of the analysis shear load V_u and the limiting shear induced at the end of the beam based on the members nominal moment capacity M_n as outlined in R21.10.3

  Vuel = (M-nl + M+nr)/ln + Vu_max_l and

  Vuel = (M+nl + M-nr)/ln + Vu_max_l

  Vuer = (M-nl + M+nr)/ln + Vu_max_r and

  Vuer = (M+nl + M-nr)/ln + Vu_max_r

  where

  ln	=	Clear span length
  Vu_max	=	End shear from factored gravity loads on beam using the load combo factors selected in the Frame Type dialog box
  M'n	=	Unfactored section negative moment capacity (Φ = 1)

The assumption is made that there is uniformly varying shear in between the ends of the beam. An additional shear diagram is created using the largest V_uel for the left shear and V_uer for right shear which are superimposed onto the shear envelop that was generated from the regular load combinations using the analysis shears. See Figure below - Shear Diagrams.

Shear Diagrams

• 21.10.4.2 Stirrup layout - Stirrups must be provided starting 2 inches from the face of the support to a distance of 2h.

  Stirrup Spacing limits:

  • a. d/4
  • b. 8d_b for the smallest longitudinal bars
  • c. 24d_b of stirrups
  • d. 12 in
• 21.10.4.3 - The remainder of the span must have stirrup spacing of no more than d/2.
• 21.10.4.1 - Positive moment capacity at support face must be larger than 1/3 of the negative moment capacity at that same face.
• 21.10.4.1 - The negative and positive moment strengths at any point along the clear beam span must be at least 1/5 of the maximum moment strength (the greater of either the negative or the positive moment strength) provided at either face.

Beam Design Report

For lateral beams some additional report information is provided to help check the design of IMF members. At the start and end of the span M_n, V_ugravity due to the gravity loading on the single span and final design V_u are reported. If the user is interested in the required shear capacity due to the analysis only without consideration of V_ue, the Frame type should be changed to OMF and the design rerun.

Lateral System Column

• 21.10.2 Design as column or beam - If the largest axial column load from all the design data points on a column with a tie bar pattern group is less than , then a design warning will be generated indicating the column should be designed as a beam.

  Note 1: The option to check the maximum axial load for column design can be turned off by selecting the proper option under the Design Check tab in the Design Criteria dialog.

  Note 2: Columns with spiral reinforcement satisfying ACI 318-99 Eq. 10-6 do not need to satisfy any of the provisions of section 21.10.5. If a spiral reinforced column does not meet Eq. 10-6 a design warning regarding reinforcement ratio is generated.

• 21.10.3 (b) - The column Shear Capacity is required to meet the larger of the analysis shear load Vu and the limiting shear induced at the end of the column based on the members nominal moment capacity Mn as outlined in R21.10.3

  Vuet = (Mnt + Mnb)/ln, Vueb = (Mnt + Mnb)/ln - Major Direction

  Vuet = (Mnt + Mnb)/ln, Vueb = (Mnt + Mnb)/ln - Minor Direction

  It is assumed that there is uniformly varying shear in between the top and bottom of the column. An additional shear diagram is created using the largest V_uet for the top shear and V_ueb for bottom shear superimposed onto the shear envelop that was generated from the regular load combinations using the analysis shears. This is similar in concept to Figure below - Shear Diagrams. M_n is calculated using a reduction factor of 1.0 and the value is based on the design data point that has the correspondingly largest M_n capacity for the major and minor axis.

• 21.10.5.1 – For tie bar pattern groups, ties must be provided at both ends of the member, maximum tie spacing shall not exceed so over a length of l0 measured from the bottom face of the deepest beam where so is the smaller of:

  Tie Spacing limits:

  • e. 8d_b for the smallest longitudinal bars
  • f. 24d_b of ties
  • g. ½ of the smallest cross-sectional dimension of the member
  • h. 12 in

  Where l0 is at least the larger of:

  • a. 1/6 of the clear span,
  • b. Maximum cross-sectional dimension of the member
  • c. 18 inches.
• 21.10.5.4 - Outside of the l_o region tie spacing cannot be larger than 2s_o.

Column Design Report

For lateral columns some additional report information is provided to help check the design of IMF members. M_n, and V_u are reported. If the user is interested in the required shear capacity due to the analysis only, without consideration of V_ue, change the Frame type to OMF and rerun the design.