The structures we design are exposed to various loads, including lateral forces such as wind, earthquakes, and other horizontal impacts, which are particularly challenging for tall buildings. Acting horizontally, these forces test the stability and integrity of structures, making it essential to ensure that buildings can withstand them without excessive movement or damage. In this regard, lateral analysis is a crucial aspect of civil engineering, focused on predicting lateral displacements, internal forces, and overall building performance under such loads.
To withstand lateral forces like wind and earthquakes, structures rely on specific elements designed for stability, strength, and flexibility. These components work together to maintain the building's integrity, control sway, and minimize damage. Shear walls are among the most important elements for resisting lateral forces. In this article, we will demonstrate how to design shear walls in RFEM 6, using the walls of the multi-story building shown in Image 1 as an example.
Designing Shear Walls in RFEM 6 in the Building Model Add-on
The building in Image 1 is a multistory building with shear walls. RFEM 6 offers the Building Model add-on for designing such buildings. This powerful tool allows you to define your building story by story and make various adjustments to the stories as needed. It also supports the integration of shear wall and spandrel elements and enables diaphragm assignment to floors, with multiple diaphragm types available. These elements are crucial for lateral analysis, as they create a cohesive system designed to resist lateral forces effectively.
This text primarily discusses the design of shear walls, specifically those illustrated in Image 1. The three walls span from the ground to the top floor, with two of them (Wall 1 and Wall 2) linked by spandrel elements. Enabling Surface Cells as special objects in the Navigator can be highly beneficial in such scenarios. This functionality allows the program to automatically recognize surface cells, making it easier to differentiate between the shear walls and the spandrel elements that connect them, as illustrated in Image 2.
You can start defining the shear walls by right-clicking on the "Shear Wall" folder in the navigator to open the appropriate window (see Image 3). Begin by selecting the surfaces or surface cells using the input in the top right corner of the window, which can be done graphically. For the first wall, select the four surface cells located to the left of the openings to define a continuous shear wall extending from the base to the top of the structure (see Image 2). Repeat this process for the shear wall on the right side of the opening (Wall 2) and for Wall 3, shown above in Image 1. Note that Wall 3 is defined using surfaces only, as there are no openings.
After defining the walls, you can set the design parameters for each wall individually or select all the walls to apply the same settings to all of them at once. Start by activating the "Generate result sections" option (see Image 3), which enables you to create horizontal sections within the shear wall and display the results, such as summed internal forces, in a table format. Since you are focusing on wall design, make sure also to select “Design Properties”, which allows you to enter the necessary design inputs.
With "Design Properties" enabled, additional tabs become available in the window. These tabs allow you to specify details such as the concrete cover for the shear walls (see Image 4) or to define the longitudinal reinforcement (see Image 5).
Various types of rebar are available for longitudinal reinforcement, including symmetrical, unsymmetrical, uniformly surrounding, line, and single types. In this example, the "uniformly surrounding" type is chosen, with 22 #7 bars placed evenly around Wall 1 and Wall 2 (see Image 5). For Wall 3, however, 40 #7 bars are used due to its larger width.
Similarly to the longitudinal reinforcement, you can define shear reinforcement for the shear walls. You have control over parameters such as stirrup type, material, bar size, diameter, number, and spacing (Image 6). Additionally, you can enable crossties by checking the corresponding box, which will position them across the longitudinal bars. If you prefer to exclude a crosstie at a specific location, simply click on the longitudinal bar to disable it. You can also re-enable the crosstie by clicking the longitudinal bar again.
Design support can be added at the points where the shear wall connects to the slabs/floors (see Image 7). These supports can be configured in the associated window (as shown in Image 8). In this example, both the start and end supports of the shear wall are of the type Concrete, with a width of 10 inches, matching the slab thickness framing into the wall transversely. The design support at the internal nodes should have the same type and thickness, but make sure to select the "Inner support" option to indicate that it is not an end support in this case (see Image 8).
Once the design parameters are configured, you can select the input data for the calculation within the Concrete Design add-on (Image 9). This process involves choosing the design situations to be considered, specifying the limit state type for each, defining the objects to be designed, etc.
The results, including reinforcement details and design ratios for the shear walls, are presented in both tabular and graphical formats, as illustrated in Image 10. This allows you to, for example, graphically overlay the Provided Reinforcement and Required Reinforcement graphically to check if the provided reinforcement exceeds the required amount. If this is not the case, the Not Covered Reinforcement can also be visualized for further assessment.
For design check ratios, in addition to their tabular and graphical representation, detailed information for each design check is available via the corresponding button, offering an in-depth view of the design calculations (Image 11).
