| Product(s): | RAM Structural System; Ram Concrete | ||
| Version(s): | Various | ||
| Area: | Modeling; Analysis; Design |
Overview
This page addresses common issues and questions specific to concrete beams designed and analyzed in the RAM Concrete Module of RAM Structural System
Slab Self-Weight
For rectangular beams, the portion of the slab that intersects the rectangular beam is included in both the slab self-weight and the beam self-weight. For T-shape beams, this double counting of self-weight does not occur. See RAMSS Gravity Loads [FAQ] for details.
Loading Diagrams (RAM Concrete Analysis - Reports - Beam Load Diagram)
The beam loading diagram displays point and line loads values that are calculated by the program and applied directly to the member by one-way decking or associated with beam self-weight.
The following information is excluded from the reports:
- Magnitudes of supported beam (or column) reactions: These are excluded because the loads are applied as line loads on the supported beams. Force transfer to the supporting beams is completed in the finite element analysis. The program does not analyze these beams separately with point loads as is done in RAM Steel Beam. The location of the supported reactions is shown in the report for convenience. The Load Diagram Report in RAM Steel Beam can be used to report the tributary point load distributed to the beam if one-way decks are used.
- Loads from transfer columns and walls above: Vertical reactions from levels above are collected by the program and applied as loads on levels below. Neither the magnitude or location of these loads are included in the Load Diagram Report.
- Load from two-way decks: For models containing beams and two-way decks, the surface loads are applied as a series of nodal loads at each finite element node. These loads are directed into the framing members and supports based on relative stiffness in the finite element analysis. The program does not perform a yield-line analysis and determine a trapezoidal line load on each beam member. Since a line load is not calculated and placed on a member, the floor load from the two-way deck will not be represented in the Loading Diagram Report. The Beam Load Diagram Report will show the beam self-weight only, since this is the only line load that is calculated by the program and applied directly to the beam.
Deep Beam Design
The ACI code classifies beams with a clear span to depth ratio greater than 4 as deep beams. RAM Concrete Beam can check if beams exceed this ratio. The option to include or exclude this check is found in RAM Concrete Beam – Criteria – Beam Design – Design Checks/Forces tab:
When the option is selected, a design warning is produced when the clear span to depth ratio exceeds the threshold. . RAM Concrete Beam does not design deep beams for flexure and shear; It is the user’s responsibility to design deep beams outside the program.
ACI 318 also requires deep beam checks when a concentrated load is located within twice the member depth from the face of the support. RAM Concrete does not check the location of concentrated loads and will not generate a design warning for this situation.
Torsion Design
RAM Concrete Beam can check the torsion demand to the threshold torsion defined in ACI 318-08 11.5.1. The option to include or exclude this check is found in RAM Concrete Beam – Criteria – Beam Design – Design Checks/Forces tab:
When this option is considered, a design warning will be reported when the beam torsion exceeds the threshold torsion. RAM Concrete Beam does not design the torsion reinforcement; It is the user’s responsibility to design this outside the program. The Beam Design Report will report the maximum factored torsion at each station and the fT*Tc.
Effective Depth
The effective depth that is used in the beam design is based on an assumed cover assigned in RAM Concrete Beam – Criteria – Beam Design – Reinforcement tab.
For the case of 2 layers of reinforcement, It's important to understand that the Criteria - Beam design - Cover to Center of Bars - 2 layers dimension is the assumed distance from the compression face to the centroid of the double layer of reinforcement. It is NOT the location of the 2nd layer. For example, by specifying a dimension of 3.50" the program assumes that the cluster of bars is centered at d = h - 3.5".
If the assumed effective depth is greater than the actual effective depth calculated from the minimum cover and bar sizes, a design warning similar to the following will be displayed:
When this warning occurs, the assumed cover should be increased slightly. This can be done globally for all beams (RAM Concrete Beam – Criteria – Beam Design – Reinforcement tab) or can be assigned beam by beam (RAM Concrete Beam – Assign – Reinforcement Layout).
It would be better if the program allowed the user to specify clear cover and clear spacing between layers, and then calculated exact bar placement and tension reinforcement centroids, but that becomes iterative as bar sizes change and is therefore not how it was implemented.
Pan Joist Design
There are special tools for modeling a generation of pan joists in Ram Modeler. This works best when the edge beams are already sized and where the pan size and joist widths are predefined. For other cases it may be faster to layout beams using the standard beam generation or add off-grid tools. Regardless if concrete beams and modeled as beams or pan joists in the Modeler, they can be designed as joists in Ram Concrete Beam. In order for the special provisions for joists to be used The Design Member Type must first be set to Joist using Assign - Reinforcement Layout...