Lateral System Beams

Geometric Properties Check

• 21.3.1.2 - Beam clear span must be no less than 4 times effective depth.
• 21.3.1.3 - Beam width to depth ratio must not be less than 0.30.
• 21.3.1.4 - Beam width must be no less than a) 10 inches and b) More than the width of the narrowest supporting member plus 1½ times the depth of the beam.

Flexural Reinforcement Design

• 21.3.2.1 - A minimum of 2 bars continuous top and bottom are required in all spans. Maximum and Minimum reinforcement ratios are set to:

  r > 200 bw d / fy same as ACI eq 10-3 r ≤ 0.025

  Note: It is the user's responsibility to set the option for 2 top bars continuous in the detailing defaults dialog.
• 21.3.2.2 - Positive moment strength at a face is checked to be greater than or equal to 1/2 of the negative moment strength at that same face.
• 21.3.2.2 - The negative and positive moment strengths at any point along the beam must be at least 1/4 of the maximum moment strength (the greater of either the negative or the positive moment strength) provided at either face.
• 21.5.4.2 - Development Lengths for normal weight concrete shall not be less than:
  1. 8d_b
  2. 6 in.
  3. $\frac{f_y{d}_b}{65\sqrt{{f^{\prime }}_c}}$
  For lightweight concrete:

  1. 10d_b
  2. 7.5 in.
  3. $1.25\frac{f_y{d}_b}{65\sqrt{{f^{\prime }}_c}}$
• 21.3.2.3 -At splice locations transverse reinforcement must be provided with spacing equal to the smaller of d/4 or 4 in. Even though the optimization process tries to locate the splice near the center of the span the design/analyze process does not check the remainder of the provisions of section 21.3.2.3.

For Bottom bars the development length is multiplied by 2.5 and for top reinforcement it is multiplied by 3.5. Note 1 - 21.5.4.3 is not implemented. Note 2 - It is the engineer's responsibility to set the Lap Splice type to Class B in the Detailing Defaults for Lateral beams.

Shear Design

• 21.3.4 - The beam shear capacity is designed to meet the larger of the analysis factored shear load V_u as well as the limiting shear induced at the end of the beam based on the members probable moment capacity M_pr as outlined in ACI R21.3.4.1

  Vel = (M-prl + M-prr)/ln + Vu_max_l and

  Ver = (M+prl + M-prr)/ln + Vu_max_l

  Ver = (M+prl + M-prr)/ln + Vu_max_r and

  Ver = (M+prl + M-prr)/ln + Vu_max_r

  where

  V	=	Unfactored gravity shear at the ends of the member
  Mpr	=	$A_s(1.25f_y)(d-\frac{a}{2})$
  a	=	$\frac{A_s\left(1.25f_y\right)}{0.85{f^{\prime }}_{c}b}$

  The program assumes that there is uniformly varying shear in between V_el and V_er. An additional shear diagram is created using the largest V_el for the left shear and V_er for right shear which are superimposed onto the shear envelop that was generated from the regular load combinations using the analysis shears. See Figure 5‑6 - Shear Diagrams. Note: Φ = 1 for the calculation of M_n.

• 21.3.4.2 - When the new required shear capacity V_u > V_e / 2 and Axial load < A_g F'_c / 20 then the full shear in the section must be resisted by the shear reinforcement Vs.
  Note: This design constraint may produce two similar shear bar sets in the same beam spans with different shear capacities even though the transverse reinforcement bar size and spacing are identical. This is due to the fact that the capacity for one segment may include the concrete shear capacity because Vu is small enough and for the other segment it will not include the concrete shear capacity because Vu is too large.
• 21.3.3.1 a) and 21.3.3.2 - Hoops must be provided starting 2 inches from the face of the support to a distance of 2h.
  Stirrup Spacing limits:

  1. d/4
  2. 8d_b for the smallest longitudinal bars
  3. 24d_b of stirrups
  4. 12 in.
• 21.3.3.4 - The remainder of the span must have hoops spacing of no more than d/2.

Beam Design Report

The reported information for SMF is similar to that reported for IMF. The only difference is that V_e instead of V_u is reported.