Concrete Wall - Seismic Design

Concrete walls can now be designed for seismic design provisions. Here the process is described.

Note:

Seismic Design Rules

Label

The label is the name for the Wall Seismic Design Rule that is called out for a wall panel.

Wall Type

These are the three wall types supported in RISA-3D.

Ordinary

This option adds no extra checks to the wall on top of the regular code checks for a non-seismic consideration per section 18.2.1.6(b). The provisions required to be met are elements not considered in the RISA-3D analysis/design.

Intermediate Precast

This option has provisions specific to wall piers per section 18.5. This Wall Type assumes Seismic Design category D, E or F.

Special

This option has provisions specific to section 18.10.

Shear Force Amplification in ACI 318-19

ACI 318-19 Section 18.10.3.1 requires the special concrete wall to consider the design shear force amplification per Equation (18.10.3.1). RISA calculates the amplification factors Ωv and ωv automatically based on the code provisions. The governing Ωv and ωv values are provided in the wall panel/region Detail Report. These amplification factors are used to calculate the seismic design force Ve. Note that the combined amplification factors shall not exceed 3.0 per Equation (18.10.3.1).

Ωv is calculated per Table 18.10.3.1.2. RISA assumes the lowermost wall panel/region base to be the critical section. In the table, the hwcs refers to the height of the entire structural wall, and lw is the width of a wall panel/region. Mpr is the moment capacity calculated assume steel yield stress is 1.25*fy. The governing combination of Mpr/Mu will be used to calculate Ωv factor. For the wall panel/region at critical section, Mpr and Mu values are reported in the Region result of the Detail Report.

ωv is calculated per Equation (18.10.3.1.3), the number of story above the critical section ns is user-input parameter in Global Model Setting-Seismic Tab:

Pier Design

Pier design is governed by section 18.10.8. Section 18.14 is not considered. This design consideration is applicable to Intermediate Precast and Special shear wall types. To determine whether to perform pier checks we use the pier dimensions from Table R18.10.1. Piers must have vertical edges that meet at a wall edge or opening.

The wall below has four piers.

The program is checking the reinforcement in the piers based on Section 18.10.8.1, which references section 18.7.4, 18.7.5 and 18.7.6. If any of these cases gives a failure we will give red text in the detail report regarding this. Specifically, the program checks:

Coupling Beams

Coupling beam design is governed by section 18.10.7 and is applicable to the Special shear wall type.

Specifically the program checks:

Boundary Elements/Zones

Boundary zone checks are based only on section 18.10.6.3. The program performs a check of the maximum extreme fiber compression stress for the worst-case earthquake load combination. If this value exceeds 0.2*f'c then a boundary zone is required. The program will currently tell you if a boundary zone is required or not.  It will not design for the provisions of the boundary zone.

Reinforcement Limits for Regions

These checks are for regions that are outside of pier locations.

Specifically the program checks:

Spreadsheet Results

Wall Panel Seismic

Coupling Beam/Wall Pier

This column determines whether the output is for a coupling beam or a wall pier.

Region/Pier

This column states the specific region and the associated pier or lintel.

UC Shear In-Plane

There is one main shear code check for either piers (per Section 18.7.6.1.1) or coupling beams (per equation 18.10.7.4). If the load combination that controlled the design used the overstrength seismic forces (meaning it had an Ω factor in the load combination) then the governing load combination will be followed by an asterisk (*).

LC

The governing load combination.

BZ Required?

If No it means there are no boundary elements/zones required. If Yes then boundary elements/zones are required.

Detail Report Results

Wall Summary Report

In this report the program gives a color-coded view of the piers and coupling beams in the wall. In the tables the code checks and reinforcement is reported as well.

Shear Details - Seismic Tab in ACI 318 - 19

When ACI 318-19 code is selected and special concrete shear walls are used in seismic analysis, a new Shear Details - Seismic tab is added next to the regular Shear Details tab. In this tab, the governing Ωv value as well as Mpr, Mu values are presented. The amplified shear demand will be used to calculate the new UC values.

Please note that for each wall panel group (a group of seismic concrete shear walls stacked on each other to resist seismic load), the governing Ωv value is used for all panels in this group. There may be multiple wall panels/regions at the critical location which produces different Ωv values, the program only reports the governing Ωv, Mpr, and Mu values in the detailed reports of each wall panel/region.

Wall Summary Report

In this report the program gives a color-coded view of the piers and coupling beams in the wall. In the tables the code checks and reinforcement is reported as well.

Pier Report

In the pier report the program performs a shear code check and gives results for the reinforcement limits required.

Coupling Beam Report

In the coupling beam report the program defines the shear check based on the diagonal bars and gives overall wall reinforcement checks.