
September 27, 2018
Using Analysis Offsets in RISA-3D
Have you ever wondered what the Analysis Offset feature does? Let’s take a look at how this feature can be used to model members at top of steel.
If you've ever wondered what it’s like to be an industrial structural engineer, let me paint you a picture: Imagine juggling a dozen problems at once—steel frames, conveyor supports, pipe racks, tank foundations—all while trying to decipher a set of drawings that look like they were faxed from 1997. And, of course, every single solution is needed yesterday. But don’t worry! With the right tools (cough RISA and ADAPT cough), navigating this daily chaos becomes a lot more manageable. So, grab your coffee (black, obviously), and let’s walk through a typical day. 6:30 AM: Morning Coffee & Evaluating Additional Loads The first email of the day: “Can we add another 10,000 lbs of equipment to the mezzanine? What about seismic drift and vibration?” Instead of a lengthy hand calculation, you fire up RISAFloor and check gravity load distribution. Exporting to RISA-3D, you analyze modal frequencies and check if the additional weight will push the structure into an uncomfortable range for human occupancy. Seismic drift is next. A quick response spectrum analysis in RISA-3D confirms that the drift is still within acceptable limits. You send your report with confidence—no major framing changes required. 9:00 AM: Field Issue - Pipe Rack Base…
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Have you ever wondered what the Analysis Offset feature does? Let’s take a look at how this feature can be used to model members at top of steel.
For concrete column members, the load combination producing the maximum shear code check is reported in the Detail Report and corresponding Results spreadsheet. Since concrete is evaluated based on a batch solution, this can be useful when shear governs the design.
There are many different types deflection values calculated by RISA-3D. Let’s take a deeper dive into each.
RISA-3D v16.0.4 introduces an enhancement that will allow for more control over the beam deflection ratio through Deflection Ratio Options. As part of the member properties, you can now designate the ends of single and multi-span beams as a cantilever or supported. This will determine whether the...
RISA-3D v15 now includes automatic drift definitions for diaphragms as well as simplified story drift application. The reported drift results have been updated as well, and are now much more relevant for today’s codes. Drift results will report results in red text when seismic drift exceeds the...
RISAFloor has the ability to assign camber design rules which allow the user more control over which members are cambered. A camber is the slight upward curvature of a steel beam which is used to compensate for deflection. A user can assign a camber directly to a member or set up design rules to...
RISA-3D v14 introduced envelope detail reports for all material members. This means that you can see the enveloped solution (force diagrams and governing code check values) in the detail report for each member when you solve either an Envelope or Batch + Envelope solution type.
After solving a model, you will see in the Member Deflections spreadsheet the following deflection ratios:
The beams in a lateral force resisting system, such as a braced frame or moment frame, typically carry a significant axial force. In the example below (with no diaphragms) the beam (M4) carries a significant axial tension.
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