draw diaphragm in risa 3d

Diaphragms

Diaphragms provide lateral load distribution functions, and are necessary for automatic Wind and Seismic load generation. In that location are three primal types of diaphragms in structural modeling:

• Rigid Diaphragms
• Semi-Rigid Diaphragms
• Flexible Diaphragms

Note:

• See the Diaphragms - Assay and Results topic for more than information on flexible diaphragm analysis and design.
• Wall panels can be detached from a diaphragm from the Wall Console Editor.

For additional advice on this topic, please see the RISA Tips & Tricks webpage at risa.com/post/support. Type in Search keywords: Diaphragms.

RISA-3D Rigid Diaphragm	RISAFloor linked with RISA-3D Includes Rigid and Flexible Diaphragms

Rigid Diaphragms

Rigid diaphragms represent a aeroplane of very high rigidity. Rigid diaphragms distribute load to elements which connect to them solely based on the stiffness of the elements. They achieve this by tying all of the nodes within the diaphragm aeroplane together for both translation and rotation, but only within the plane of the diaphragm. This is typical behavior for well-nigh slabs and decks, which aspect vertical loads based on the tributary surface area of their supporting members.

• Older versions of RISA-3D had a diaphragm choice called "Planar". This option was removed due to a lack of real-world applicability to whatever structure.
• There is no rigid diaphragm pattern in the program. This is strictly an analysis tool.
• Sloped rigid diaphragms are not supported. Therefore, rigid diaphragms always exist in a apartment horizontal plane.

Load Attribution

Loads applied within the plane of a diaphragm will exist attributed to all elements which connect to the diaphragm. The amount of load which each chemical element takes is proportional to its stiffness. Diaphragms are capable of both translation and rotation, then the torsional effects of the moment arm between the center of load and the center of rigidity are deemed for. This is besides true for a dynamic mass which is beginning from the center of rigidity.

Because a rigid diaphragm is part of the stiffness matrix, an explicit Center of Rigidity is not calculated or reported. Internally, the program creates a hidden set of rigid links which interconnect all of the nodes in the diaphragm, therefore preserving the diaphragm's rotational degree of freedom (something which traditional nodal slaving is incapable of).

Connectivity

All nodes which fall within the plane of the diaphragm automatically get continued to it. Nodes may be intentionally disconnected from the diaphragm by checking the Disassemble From Diaphragm box in the Node Coordinates spreadsheet. If a boundary condition exists within the airplane of a diaphragm it will act every bit a restraint for all of the nodes connected to the diaphragm.

Rigid Diaphragms must be divers along the Global Axes, therefore they can simply exist in the XY, XZ, or YZ planes. If rigid behavior is desired forth a aeroplane other than these, a semi-rigid diaphragm (fabricated of plates) with a big stiffness value can exist used instead.

Rigid Diaphragm Stiffness

The stiffness of the rigid diaphragm is fix to a unitless value of 1 x 10⁷ by default. This value has been calibrated every bit providing the best behavior for almost models. Information technology can exist adjusted from inside the diaphragms spreadsheet, however adjusting this value is simply recommended in the post-obit circumstances:

1. The lateral stiffness of elements which laissez passer through the diaphragm is sufficiently large to crusade the rigid diaphragm to behave equally a semi-rigid diaphragm (i.e. the translations of the nodes within the diaphragm do not stand for to a uniform rotation nearly i signal). If this is the case, effort a diaphragm stiffness of 1 x 10⁸.
2. The dynamics solver is non converging. In this instance, try reducing the diaphragm stiffness to 1 x 10^{half dozen}, however, be sure to confirm that the diaphragm is not behaving semi-rigidly (run into #1)
3. The program has generated a warning that the sum of the reactions does non equal the full applied load. In the case of points on the diaphragm which have a very close proximity to each other, the stiffness of the internally generated rigid link between them may arroyo the stiffness of a boundary status. If this happens, the model can accept Ghost Reactions, which are points which act as boundary conditions (dumping load out of the model) without any notification. In this case try reducing the diaphragm stiffness to one 10 ten^vi. Even so, be certain to confirm that the diaphragm is not behaving semi-rigidly (meet #ane).

To adapt the diaphragm stiffness, right-click on the diaphragms spreadsheet and select Set Diaphragm Stiffness. Y'all may likewise modify this value in Model Settings Solution tab Advanced options:

Rigid Diaphragms in a RISA-3D Merely Model

With RISA-3D'due south diaphragm feature, a node tin can exist divers within a given plane as the diaphragm node, and all points in that plane volition be rigidly connected to each other with internal rigid links. Thus, each node volition rotate and interpret as one rigid body and showroom rigid diaphragm behavior. RISA-3D'south rigid diaphragm feature is discussed further in the Diaphragm Modeling Tips section.

Rigid Diaphragms in a Combined RISAFloor/RISA-3D Model

A RISA-3D model that is linked upwards to RISAFloor has an automatic rigid diaphragm analysis and blueprint. Each individual slab/deck polygon is converted to a rigid diaphragm inside RISA-3D. Therefore, information technology is possible to have multiple independent diaphragms at any given flooring acme.

Semi-Rigid Diaphragms

A semi-rigid diaphragm is one which distributes loads based on both the stiffness of elements which connect to it and on the stiffness of the diaphragm itself.

Semi-Rigid Diaphragms in a RISAFloor/RISA-3D Model

The Semi-Rigid diaphragm in RISA-3D will help you distribute the lateral forces based on the stiffness of the slab. When RISA-3D is integrated with RISAFloor the program can create a Semi-Rigid diaphragm automatically. The Semi-Rigid diaphragm is defined in Diaphragm Parameters in a Beam Supported Flooring and the Slab Definitions spreadsheet in a Physical Floor Slab. During the integration between RISAFloor and RISA-3D, the plan creates a mesh of FEA plate elements inside the edges of the slab. The thickness of the plates is defined by the slab/diaphragm defined in RISAFloor. The plate elements are automatically submeshed so that they attach to all vertical elements (columns and walls) as well as any new members or loads added into the RISA-3D model. Below shows an case of a unproblematic L-shaped building with the mesh displayed.For farther brandish data see the Results View Settings - Diaphragms topic.

When the model is in RISA-3D, the mesh size is controlled by the Model Settings - Solution Tab -Semi-Rigid Mesh . For RISAFloor ES models, the slab stiffness can be reduced based on the Icr factor in the RISAFloor Slabs spreadsheet and the Use Cracked Slabs checkbox in the Model Settings in RISA-3D. The Icr slab stiffness only affects the out-of-plane stiffness. For farther information on croaky slabs, see Elevated Slabs - Assay. The elevation of the columns are stock-still to the diaphragm using links to distribute the forces over a 12"x12" surface area rather than a unmarried column node. For farther information come across the Column Meshing department of the help.

• Sloped semi-rigid diaphragms are not supported. Therefore, semi-rigid diaphragms e'er be in a flat horizontal plane.

Semi-Rigid Modeling Tips for Physical Floor Slabs

Lateral Elements: When modeling with a Semi-Rigid diaphragm, information technology's of import to make all columns and walls Lateral. This will bring all the columns and walls into RISA-3D which will support the slab as the vertical loads are practical. In RISA-3D, the program will apply both lateral and vertical loads to the diaphragm for analysis of the lateral organization. This is different than Rigid diaphragms because only the lateral resisting arrangement needs to be transferred into RISA-3D.

Reinforcement Design: RISA-3D will not design the reinforcement for the slab. The reinforcement is designed in RISAFloor and is based on the vertical loads. Still, yous can find forces in the slab in RISA-3D using the tools listed below.

1. Contours: The contours will brandish the global axis forces over the slab.  Run across the Results View Settings - Diaphragms section for further data on display of the contours. The contours can exist used to notice the loftier and depression forces as needed for reinforcement design.
2. Internal Force Summation Tool (IFST): In that location is an IFST Slab tool that allows you to find forces from a point on the submesh to some other indicate on the slab.  This tool can be used to "cut" beyond the slab and will finds forces along the "cutting". This is the aforementioned tool that is used internally in RISAFloor to find Auto-Pattern Cuts within the Design Strips. For further information on this tool, come across the IFST Topic.

Semi-Rigid Modeling Tips for Beam Supported Floors

Vertical Loads: The semi-rigid diaphragm has self weight and out-of-aeroplane stiffness. Internally, the plates are modeled as normal so that in that location is stiffness out-of-aeroplane. The diaphragm is used for out-of-plane and in-plane load distribution.

Diaphragm Material:The Semi-Rigid diaphragm material uses the Full general Materials.  In that location are a list of default General Materials, nevertheless you can add to this list to lucifer your diaphragm. See Materials for further information on creating your own Full general Cloth.

Diaphragm Thickness:The Semi-Rigid diaphragm thickness should be selected based on the gauge stiffness yous expect from the slab or deck for lateral loading. The semi-rigid diaphragm is modeled using isotropic plates. Therefore, there is no association with the deck management for the semi-rigid diaphragms. If your diaphragm is truely one-way, you may consider using a Flexible diaphragm.

Semi-Rigid Diaphragms for RISA-3D Only Models

RISA-3D does not have the power to automatically define a Semi-Rigid diaphragm. Notwithstanding, Semi-Rigid diaphragms tin be represented in the model using plates.

A semi-rigid diaphragm is modeled with plates, and requires y'all to model and submesh the plates appropriately. In order to adequately mesh your plates it is expert to exist familiar with Plate-Fellow member Interaction. Plates are modeled using full general materials, then the first stride is to set up a material with the fabric properties of your diaphragm.

Next, model your plates using the specified cloth, and with an accurate thickness. Be sure to cheque the "Plane Stress" choice. This makes it so that the plates simply have stiffness inside their own airplane, and every bit a event won't add any composite angle forcefulness to the beams in the plane of the diaphragm.

• When meshing a floor diaphragm effectually members, yous desire to make sure that the corners of your plates meet at members. Otherwise, when applying surface loads to plates, the members will non see that load.

Flexible Diaphragms

Flexible diaphragms distribute loads to elements which connect to them solely based on the tributary surface area of the element within the plane of the diaphragm.

Flexible Diaphragms in a RISA-3D Only Model

The diaphragm feature in RISA-3D cannot exist used to create a flexible diaphragm. To consider a flexible diaphragm in RISA-3D there are a couple of options. The main option is to manually calculate how much strength is going to each frame or shear wall in the lateral organization and use that load directly to those elements as a point or distributed load. Some other option is to essentially use a semi-rigid path to use plates with an equivalent thickness and material properties every bit your diaphragm. You may cull a very small equivalent thickness which will yet exist semi-rigid, simply much closer to flexible than rigid.

Flexible Diaphragms in a Combined RISAFloor/RISA-3D Model

A flexible diaphragm can exist divers in a combined RISAFloor/RISA-3D model. For wood diaphragms, the program volition really design the sheathing and nail spacing, incorporating the code specified pattern tables from the NDS/IBC. See the Diaphragms - Assay & Results topic for more information on how the pattern works and how loads are attributed both for wind and seismic loads. The diaphragm can be defined as flexible when drawing the deck edge or from the Diaphragms spreadsheet.

• Flexible diaphragms cannot be defined on an elevated slab flooring.

Flexible diaphragms inside RISAFloor/RISA-3D are used solely as load-attribution devices, and practise not exist as elements within the stiffness matrix, unlike rigid or semi-rigid diaphragms. Flexible diaphragms take no stiffness, and are incapable of transferring load from one chemical element inside them to another. Thus, members that do not have lateral resistance out of airplane are susceptible to stability issues. To increase stability in a model with a flexible diaphragm it may be necessary to add small springs in the out-of-plane directions on the frames at the tops of the columns. This volition stabilize the members while generally having a minimal event on the assay of the model.

Ceiling Diaphragm (Sloped Roofs)

When a flexible diaphragm is applied to a sloped roof in RISAFloor, a setting exists to specify whether a ceiling diaphragm is present.

The load attribution for the flexible diaphragm will occur only for Lateral Members from RISAFloor when a ceiling diaphragm is not specified. This is illustrated above where the lateral load follows the rafters. When a ceiling diaphragm is specified, it is necessary to draw in collector beams at the ceiling height and then that the load can be carried directly the columns or walls at the base of the sloped members. With a ceiling diaphragm, the sloped members will not experience any lateral load directly. Note that the same total amount of lateral force will exist applied regardless of this setting. This only controls whether the lateral load is applied to the sloped members, or in a horizontal apartment aeroplane.

Diaphragms Spreadsheet - General Tab

The Diaphragms Spreadsheet contains diaphragm data and may be accessed by selecting Diaphragms on the Spreadsheets bill of fare nether Information Entry. Alternatively, it can be accessed by clicking the push button on the Data Entry Toolbar.

For RISA-3D models at that place are two different versions of the Diaphragms spreadsheet. One version is for models which take been created in RISA-3D, the other is for models which are linked to RISAFloor.

RISA-3D Simply

Node Label defines the primarynode for the diaphragm. For diaphragms in the ZX plane, the diaphragm will be created at the Y-coordinate of the specified node. Similarly, XY diaphragms will utilize the node's Z coordinate, and YZ diaphragms will use the node'due south X coordinate.

When the Inactive box is checked the diaphragm will exist ignored past the program. This is a convenient way to disable diaphragms without deleting them.

You may designate any floor level as a No Current of air / Drift (i.eastward. mezzanine) level in order to omit it from the generated wind load calculation and the drift calculations.

• Previous versions of RISA-3D had a Blazon field that had a Membrane and Planar option. The Planar pick has been removed and all diaphragms are Membrane. Only the in-plane rigidity is in play and not the out-of-plane rigidity.
• In that location are not semi-rigid or flexible options for RISA-3D as a standalone program.

RISA-3D Linked With RISAFloor

Pinnacle displays the pinnacle of the diaphragm. This is the same tiptop every bit the floor which the diaphragm was created on.

Mass displays the dynamic mass tributary to the diaphragm. This mass is used to calculate seismic forces for both static and response spectra methods.

Mass MOI displays the dynamic mass moment of inertia of the diaphragm. This moment of inertia is used to calculate seismic forces for response spectra assay.

Center of Mass displays the X and Z coordinates of the middle of mass of each diaphragm. This is the location at which static (equivalent lateral force) seismic loads are applied for each diaphragm.

Eccentricities are the percent of length/width of the diaphragm which are used to place "accidental eccentric" seismic loads for each diaphragm. This only applies to the static (equivalent lateral force) procedure. See ASCE 7-16, Department 12.viii.4.2 for more information.

When the Inactive box is checked, the diaphragm will be ignored by the plan. This is a convenient mode to disable diaphragms without deleting them.

Y'all may designate whatsoever floor level equally a No Wind/ Drift (i.due east. mezzanine) level in society to omit it from the generated wind load calculation and the drift calculations.

Diaphragm displays the diaphragm label. This label is used for the naming of Diaphragm Regions.

Type specifies whether the diaphragm is Rigid (Membrane) or Flexible for a Axle Supported Floor or Rigid (Membrane) or Semi-Rigid for Concrete Floor Slab. If a diaphragm has been defined as Flexible within RISAFloor it tin be toggled between Rigid and Flexible in RISA-3D.

Region lists the diaphragm regions for each diaphragm. Diaphragm regions are used for the blueprint of wood flexible diaphragms, and are as well useful for explicitly defining how flexible load attribution is to be performed.

Design Rule specifies the Design Dominion which is assigned to each region. Only the data on the Diaphragms tab of the Design Rules Spreadsheet is considered.

SGAF is the specific gravity adjustment factor for the blueprint of wood flexible diaphragms. For more data meet AF&PA NDS SDPWS, Table A4.ii, Note 2. This value defaults to 1. Even so, it should be manually changed if the framing supporting the wood flexible diaphragm is non Douglas Fir-Larch or Southern Pine.

• For data about the Wood Diaphragms tab see the Diaphragms - Analysis and Results topic.

Diaphragm Modeling Tips

Modeling a Rigid Diaphragm in RISA-3D

In the Diaphragms spreadsheet, enter the node in the Node Label column that the diaphragm volition exist defined by. Designate the Plane the diaphragm will act.

Internally, the Rigid Diaphragm ties all nodes at that elevation together with Rigid links.

To view the diaphragm, click the Toggle Brandish of Diaphragms push button . This allows y'all to visually see the location of the diaphragms. Inactive diaphragms will not show up graphically.

From here the Wind and Seismic load generators can be run.

Centric Load Limitation

Members in the plane of the diaphragm will take no axial load attributed to them. This is because the internal rigid links that are created to achieve rigid beliefs take the unabridged load. In these cases, the axial loads in these members volition need to be considered exterior of the program.

Openings in a RISA-3D Only Model

If there are openings inside the divers diaphragm, where portions of the structure are non rigidly continued, information technology is possible to disconnect those locations from the diaphragm in the Node Coordinates spreadsheet.

Use of Rigid Diaphragms with the Acme of Member Showtime

Never use Top of Member Offsets with the diaphragm feature. This combination will almost surely make the forces in the member incorrect. This is because a Vierendeel-blazon truss is created, where the internal rigid links created by the diaphragm feature acts every bit a superlative flange and the member acts as the bottom flange. What at present is drawn every bit a single fellow member has multiple internal members influencing these forces.

Partial Diaphragms in a RISA-3D Only Model

There may exist times when you want to model a partial diaphragm, i.east., a diaphragm that extends over simply a portion of a floor or plane.  For case, allow'southward say you are trying to model a floor that is composed of a relatively rigid section (thick concrete slab) and a relatively flexible section (corrugated steel decking).  You lot would like a way to model a rigid diaphragm for just the rigid portion of the floor.

To attain this, you may specify that a node or group of nodes be detached from the diaphragm.  This may be accomplished by selecting the Disassemble from Diaphragm option in the Node Coordinates spreadsheet or click a node and specify it in the Coordinates dialog.

Another way this can be done is to offset the elevations of the nodes that comprise the rigid floor section so that they are all a picayune college or a piddling lower than the surrounding floor.  The offset but needs to exist slightly larger than the Merge Tolerance, since this is the tolerance for other nodes to be on the same aeroplane as the primarynode.  This works considering the rigid diaphragm characteristic will only rigidly connect nodes that are at the same elevation as the chiefnode.  The other nodes, which are on the flexible portion of the floor and are at present at a different summit than the primarynode, will not be incorporated into the diaphragm. This can also be used for a "twin belfry" situation where you desire each tower to act independently of the other.

Fractional Diaphragms in a Combined RISAFloor/RISA-3D Model

For buildings where a flexible diaphragm and rigid diaphragm occur on the aforementioned floor you can model the diaphragms using separate slab edges. This will require a gap between the framing of the two diaphragms even so, such that load will not automatically be shared between the diaphragms.

Below is a screenshot of the gap for case:

Sloped Roof Flexible Diaphragms (RISAFloor/RISA-3D Integration)

The flexible diaphragms at sloped roofs require members that are in the horizontal aeroplane to aspect load to. These members must exist at the base roof meridian. For that reason, in the example below, the program reports "Loads are not attributed for Diaphragm". In the direction perpendicular to the ridge, there are no members for the plan to aspect the wall wind loads to, so no loads are attributed to the diaphragm at all in that direction.

To correct this issue, but draw horizontal bracing in the structure which can option upwards the load and transmit it to the master lateral force resisting system.

For additional advice on this topic, delight see the RISA Tips & Tricks webpage at risa.com/mail/support. Blazon in Search keywords: Sloped Roofs.

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Source: https://risa.com/risahelp/risa3d/Content/3D_2D_Only_Topics/Diaphragms.htm