A workflow for designing punching shear checks with user-defined shear stud reinforcement (User SSR) was added in RAM Concept 2024 (v24.00.00).
This article summarizes the modeling workflow and describes how User SSR affects the RAM Concept analysis and design calculations.
Defining User SSR
Unlike user-defined longitudinal reinforcement, User SSR groups and individual, user-defined stud rails cannot be directly drawn or modeled on the Reinforcement Layer. User SSR can only be created by changing the properties of previously designed Program SSR and converting them to User SSR. After the conversion, SSR properties like stud spacing and number of studs can be modified by the user.
The steps below outline the workflow:
- Run calculations in model with punching checks to produce Program SSR groups that are designed and detailed by RAM Concept.
- Open a plan on the Reinforcement Layer that displays the Program SSR, select one or more SSR groups, and view its properties (Edit menu > Selection Properties or click Selection Properties using the right-click menu).
- In the object properties dialog, change the Designed By selection to User. After this change, the following object properties may be modified:
- SSR System – the assigned SSR System from the Material table
- First Stud Spacing – the spacing to the first stud on each rail
- Typical Stud Spacing – the spacing of studs after the first stud on each rail
- Max Studs/Rail – the maximum number of studs on each rail
- Click OK to close the dialog after making any desired property changes.
- Note that the User SSR group is displayed in orange (similar to user-defined longitudinal reinforcement) to differentiate it from Program SSR groups, which are displayed in gray.
- Run calculations to check the punching shear design with the User SSR
Figure 1 - User SSR Group and Property Dialog
Note that User SSR can also be changed back to Program SSR, but this has no value since RAM Concept removes all program reinforcement, including Program SSR, before subsequent calculations are run.
Analyzing and Designing Models with User SSR
During the design calculations, only a final design check is completed at punching checks with User SSR. If the provided User SSR does not satisfy the punching shear design requirements, a design failure is indicated for the punching check. Additional program rails are never added to User SSR to achieve the required capacity or satisfy code specified spacing requirements.
After the initial creation of User SSR, model geometry changes, such as size or location changes to slab edges or slab openings), can create SSR configurations that would not be detailed by RAM Concept with Program SSR. RAM Concept is designed to flag problem User SSR configurations with errors or warnings issued during the analysis. It also completes rigorous transverse rail spacing checks based on the selected design code requirements to ensure that the User SSR configuration is valid. Refer to the Error and Warning and SSR Transverse Spacing Check sections below for more information.
SSR Transverse Rail Spacing Checks
Design codes do not provide clear guidance for calculating the transverse rail spacing for all possible SSR configurations, especially those with irregular geometry. RAM Concept adopts a rational and proprietary calculation method that can be applied to all punching shear section geometries and SSR designs.
In RAM Concept, transverse spacings are calculated using the line segments that form the stud perimeters of the SSR design. The transverse rail spacings are determined from the lengths of these line segments. See Figure 2 for an illustration of the peripheral lines of stud for a sample SSR design. In the figure, each of the white-dashed line segments that connect two adjacent studs are stud perimeter segments.
Figure 2 - Peripheral Lines of Studs for a SSR Design
The critical punching shear sections are considered during the transverse spacing calculations. The calculation method is designed to automatically exclude any punching shear sections that do not require reinforcement (USR <1). Ineffective regions around and within the punching shear section that do not contribute to punching shear strength are also considered in the calculations. Refer to the RAM Concept manual for more information on these aspects.
Program Errors and Warnings
The following conditions are flagged with errors and warnings during the calculations:
- User SSR with transverse rail spacing exceeding design code limits
- User SSR not located at a punching check
- User SSR includes one or more rails that were previously trimmed due to floor geometry but can now be fully extended to match the other rails due to geometry changes
A commentary on each of these errors and warnings follows:
A punching check at (x,y) has one or more shear stud rails that may exceed code transverse spacing limits
This warning occurs when the calculated transverse rail spacing in a SSR design exceeds the design code limit. The transverse spacing failures are reported in the Punching Check Auditor and can be displayed on screen using the Display Warnings Tool (see Figure 3). In some cases, the warning may be ignored based on engineering judgment. For punching checks with User SSR, the warning can often be eliminated by deleting the User SSR and re-running the calculations so that a new Program SSR group is detailed by the program.
Figure 3 - User SSR Group with Excess Transverse Rail Spacing Displayed using Display Warning Tool
User SSR at (x,y) is not located at a punching check and is ignored in the design checks
This warning occurs when User SSR is defined but not associated with a punching check. The User SSR at the identified location is ignored in the design calculations but is included in the quantities listed in the Estimate report. If designed, the warning can be eliminated by deleting the identified User SSR.
One or more rails in User SSR at (x,y) are not fully extended to the critical section and may not be fully effective
This error occurs when User SSR includes one or more rails that were previously trimmed due to floor geometry but can now be fully extended to match the other rails due to geometry changes. For example, this error would be produced for the User SSR design shown in Figure 1 if the slab openings were deleted and the calculations were re-un. Figure 4 below shows the resulting User geometry and the cut-off punching shear section that RAM Concept would use if the error is ignored.
This error can be resolved by deleting the User SSR and re-running the calculations so that a new Program SSR is detailed by the program. The Program SSR can then be changed back to User SSR and its properties can be modified as required.
Figure 4 - User Configuration with Possible Ineffective Stud Rails