July 29, 2010

How to Model a Semi-Rigid Diaphragm in Standalone RISA-3D

In standalone RISA-3D models (those not integrated from RISAFloor), Semi-Rigid diaphragms cannot be directly defined. Only the Rigid diaphragm type is available by default. To create a semi-rigid diaphragm in a standalone RISA-3D model, users must define plate elements manually. If you’re dealing with a complex roof system in RISA-3D, then you probably need to be able to model something that behaves accurately though and not limited to Rigid diaphragm behavior only.

This is the perfect application for Semi-Rigid Diaphragms. A semi-rigid diaphragm is modeled with plates, and requires you to model and submesh the plates appropriately. In order to adequately mesh your plates it is good to be familiar with Plate-Member Interaction. Plates are modeled using General materials, so the first step is to set up a material with the material properties of your diaphragm.

Link: Plate-Member Interaction

Next, model your plates using the specified material, and with an accurate thickness. Be sure to check the Plane Stress option. This makes it so that the plates only have stiffness within their own plane, and as a result won’t add any composite bending strength to the rafters. With an adequate mesh you can get realistic behavior of a roof diaphragm.

Tags: RISA-3D, Plates, Diaphragms, New

June 27, 2023 | RISA-3D

Using the A1085 Database from the Steel Tube Institute in RISA-3D

RISA-3D features the A1085 HSS sections from the Steel Tube Institute. The Steel Tube Institute provides the values for A1085 HSS sections' geometric properties used in RISA-3D. A1085 has very important use applications in the HSS or steel tube industry. Why? A1085 provides an allowable 50 ksi minimum yield stress for all HSS shapes. Because the tolerance is tighter on A1085 HSS shapes, A1085 allows the use of full nominal weld thickness in strength calculations. This gives A1085 HSS shapes greater strength unlike other steel materials which have to use reduction factors such as 0.93. The A1085 material has already been added to the RISA-3D's default materials spreadsheet. The Ry=1.25 and Rt=1.15 default spreadsheet values are also per the Steel Tube Institute. To select the shape from the database, open the Shape Selection window either from the Section Sets spreadsheet or the member Properties section. You can select the AISC or AISC_historic database. Scrolling all the way down to the bottom of the Shape Name box, the shape names change to have _A1085 appending to the end of the names. For information on HSS connections, check out our video here. Efficient Design of HSS Connections…

May 29, 2020 | Shear Connections, New, Steel, RISAConnection

Skewed Shear Connections are Now Available in RISAConnection v12!

RISAConnection Version 12 now supports skewed shear tab connections. With this enhancement, engineers have the option to skew a wide flange, a tapered wide flange or a channel beam with the following supporting members: Wide Flange Column Tapered Wide Flange Column Tube Column Wide Flange Girder To do this, a new Beam Skew option has been added under the Connection Category in the Connection Properties panel. Beams may be skewed left or right in the horizontal plane. Once a skew direction has been selected, you may specify the angle of the skew. The skew angle can be set between 0 and 45 degrees in RISAConnection and will be designed per AISC guidelines. When specifying a skewed connection, additional 2D views become available allowing users to review the connection layout from a top view. Another important consideration when designing skewed connections is the size of the fillet welds. As the skew angle of the beam becomes more acute, two different weld sizes (on either side of the plate) may need to be specified in order to maintain the required capacity. You can modify the fillet weld sizes in the Column or Girder Weld section of the Connection Properties. The program will…

July 28, 2010 | RISA-3D, Plates, New

How Do Plates Connect to Members?

In order to understand the interaction between plates and members it is important that you know the basics of Physical Members and Plate Connectivity. Remember that plates only connect to other elements at their corners, and you will instantly recognize why the model below will not work as intended. In this model there are two plates, defined between members M2, M5, and M9. The moment in all three beams is zero though, because the surface load on the plates goes to their corners, which fall only on the girders and the columns. In order to get a more realistic one-way load distribution to the beams the plates actually need to connect to them (since plates do not connect to anything along their edges). Above is a submeshed model. The moment diagram for member M9 is plotted on the right. As you can see, the plates are only connected to that member at its midspan, so it is being loaded with a single point load right in the middle. This is not realistic for how a slab would load this beam though, and is therefore an inadequate mesh. In order to get that realistic loading we need enough connection points between…