| Rigid End Zones
|
Whether or not to consider the effects of rigid end
zones is declared in the
Rigid End Zone
box. You may choose to ignore these effects by clicking
the
Ignore Effects option button. If you choose
to include the effects and click on the
Include Effects option, you can either type
a percent reduction (between 0 and 100%) in the
Reduction % field or accept the default
value of 0%. See the
RAM Frame manual for further
discussion of Rigid End Zones.
|
| Member Force Output
|
There are two choices where the member force output
is displayed: at the face of the joint, or at the center line of the joint.
This choice is made by clicking one of the option buttons in the
Member Force Output group.
Note: If Rigid End
Zone effects are included, the Member Forces will always be output at the face
of the joints.
|
| AISC 360
|
An option to
Use Reduced Stiffness for Steel Member is
available. The engineer should select this option if it is intended to use the
AISC 360 design code. The program does not iterate to determine the correct
value of τb, so the engineer either
specifies 1.0 or some other value. Although technically τb is distinct for each load combination for
each member, the program uses the specified value on all members. Also, the
program does not provide an Assign command to assign different
τb values to different members, nor
does it use a different stiffness for each different load combination. Note
that the program uses the reduced stiffness for all load cases. The flexural
stiffness of frame members (whose flexural stiffness is considered to
contribute to the lateral stability of the structure) is modified according to
Eq (A-7-2) . Note that if a lateral member is pinned at either end, this
modification is not applied. The axial stiffness is also modified according to
Eq. (A-7-3) in AISC 360-05, Appendix 7. Also note that the modification is only
applied to steel members.
|
| Response Spectra Analysis
|
| Setting | Description |
|---|
| Consider Sign for Analysis Results
|
Analysis results related to a dynamic load
case (i.e., response spectra analysis) are obtained after modal contributions
from each dynamic mode are combined according to CQC or SRSS. Thus, all results
(displacements, reactions or member forces etc...) always have a positive sign.
In some cases, the sign of analysis results is required (examples are for
design of foundations, load combinations with dynamic load cases, etc...).
Therefore,
RAM Frame includes a method to
assign signs to the displacements, reactions, or member forces calculated from
a dynamic analysis. The following equation is used so that the sign from the
most predominant modes for each dynamic analysis result is used as the sign of
the response. In the following equation, the computation is carried out for
"N" mode shapes, and ϕi is ith mode shape value of any
dynamic quantities (member force or displacements, etc...).
In order to consider the sign of dynamic
analysis results, this box is needed to be checked. Note that once this option
is checked, it is applied to all dynamic analysis load cases.
|
| Include nodal Mass in Z-Direction
|
For semirigid diaphragms, diaphragms mass as
well as mass from members and loads are handled in such a way that the total
mass is distributed to mesh points. Hence, the program creates nodal masses and
assign them to nodes. By default, nodal mass is defined for X- and Y-direction.
If one wants to include nodal mass in Z-direction, the option
Include nodal mass in Z-direction
should be check out.
|
|
| Eigenvalue Analysis
|
For the calculation of structural periods and modes,
there are three methods provided in the program: Subspace iteration,
Arnoldi/Lanczos eigenvalue solution and (Load Dependent) Ritz Vectors.
The subspace iteration solution is the default
choice in the program. This solution calculates natural modes (i.e. Eigen
vectors) and frequencies of an undamped free vibration system. These natural
modes and frequencies are the exact modes and frequencies and they provide
excellent information about dynamic characteristics of the system.
The Arnoldi/Lanczos Eigenvalue solution also
calculates exact natural models (i.e., Eigen vectors) and frequencies and it is
much faster than other two solutions and consumes significantly less memory.
For large models, this solution is recommended.
It should be noted that both the Lanczos solution
and Subspace solution produce the same results.
Solution with the Ritz Vectors is an approximate
solution to Eigen vectors but it produces results that are the same or nearly
the same as the Eigen Vectors if enough number of Ritz Vectors are included.
For the same number of modes, Ritz Vectors usually provide a better mass
participation and it is computationally faster with almost the same level of
accuracy. The Ritz Vectors method is recommended where the solution with Eigen
Vectors may not reliably capture lateral structural models (for instance,
failing to capture 90 percent mass participation with a reasonable number of
modes) or the Eigen Vectors solution captures irrelevant vertical models due to
vertical vibration of slabs (although those are real modes but they are not
relevant to the structural analysis). The method of Ritz Vectors also has the
advantage of being generally faster. For this reason, use of Ritz Vectors is
also an attractive for very large models.
|
| Diaphragm
|
Check the option to Store forces for diaphragm cross-section
force calculations to calculate diaphragm cross-section
forces at a user-defined location after analysis. If the option is not
selected, no diaphragm cross-section forces are reported.
In addition, diaphragm stresses and internal forces can be displayed on
structure after analysis if the option Store stresses and
internal forces is selected.
|
| P-Delta
|
The P-Delta effect may be considered or ignored. To
consider P-Delta, select the
Yes option. Two options are provided for
P-Delta effects to be considered in analysis:
- Use Mass
Loads: This option uses building mass to calculate P-Delta effects.
It is briefly mass associated with diaphragms. Note that this is the default
method used in the program. If you choose to consider the P-Delta effect, you
can either enter a scale factor between 0 and 10 in the edit box or accept the
default value of 1.
- Use
Gravity Load: Instead of using building mass, this option uses
applied dead, live, roof, and snow loads to calculate P-Delta effects. Note
that different scale factors can be defined for dead, live, roof, and snow load
components.
In either case, the program applies the same method
to calculate P-Delta effects. The only difference is that the former uses
building mass converted to building weights to be used in P-Delta calculations
and the latter uses dead and live loads instead for P-Delta effects.
It should be also noted that P-Delta effects are
not only considered for rigid diaphragms but they are also included for
analysis with semirigid diaphragms. See the
RAM Frame manual for further
discussion on P-Delta.
|
| Analytical Model
|
Lateral walls are automatically meshed by the
program along their heights and lengths. The program generates best possible
mesh configuration for walls and semirigid diaphragms to produce good analysis
results. For most cases, the automatically generated mesh configuration for
walls and diaphragms is good enough. On the other hand, the user may want to
define mesh parameters to obtain an better configuration. It should be known
that very distorted meshes should be avoided before starting analysis. Usually
a mesh composed of elements close to square or rectangular shapes is
preferable. It is always advised to check analysis results.
Semirigid diaphragms are automatically meshed and
their connection with walls, columns, beams and braces are automatically
adjusted by the program. Although penetrations are not considered, any opening
in semirigid diaphragms are considered in generated mesh. The program
internally enforces compatibility between semirigid diaphragms and other
members (columns, beams, walls and braces) and it also computes diaphragm
properties (such as thickness, modulus of elasticity, etc...) for shells
elements that represent meshed diaphragms. Note that forcing compatibility
between members and semirigid diaphragms ensures load transfer from semirigid
diaphragms to these members.
| Setting | Description |
|---|
| Merge Node Tolerance
|
Once meshing walls and semirigid diaphragms
are done, the program generates a finite element model for analysis, which is
basically composed of nodes and elements (columns, beams, braces and shells in
walls and semirigid diaphragms). During this process, it is possible that
several nodes are very close. To have a good (and valid) analytical model,
these nodes are merged to a single node and elements connected to this node are
adjusted accordingly. The
Merge Node Tolerance is used in such
a way that if distance between any 2 (or more) nodes are found to be smaller
than the
Merge Node Tolerance , then they are
treated as a single node (i.e., these close nodes are merged together). Note
that the node tolerance is not only used for nodes generated after meshing
process, but for all nodes in a model (whether there is wall or semirigid
diaphragm).
|
| Mesh Controls
|
The program provides control for
meshing to improve mesh quality:
Max. Distance between Nodes on Mesh
Line allows you
to define the maximum distance between nodes on wall edges and nodes on
semirigid diaphragm edges. Note that the program may generate additional nodes
closer than the typed value, but it is never allowed to be larger than that.
The
Geometry Tolerance is mostly used in
geometry calculation as a threshold tolerance. This should not be confused with
a merge (close) node tolerance (which is explained below). Examples are as
follows: it is used as a tolerance to check a node is on a line or to check a
point is inside a polygon, etc...
You can generate coarse or fine mesh by
usually setting
Max. Distance between Nodes on Mesh
Line. Usually, a coarse mesh gives conservative results since the
walls and diaphragms are stiffer. A finer mesh leads to more flexible walls and
diaphragms, which leads better results but it may significantly increase
analysis time. A good balance should be provided before starting analysis.
Note that
Max. Distance between Nodes on Mesh
Line does not only affect meshes for walls, but also it affects
generated meshes for diaphragms.
|
|
| Wall Element
|
You can include out-of-plane stiffness of walls during analysis by checking this
box. If not checked, stiffness matrix for wall's out-of-plane direction is
not considered. Otherwise, the program calculates stiffness matrix for
wall's out-of-plane direction during analysis. Note that this option is
applied to all wall segments in the model. Another option is
provided to release rotational fixity at wall foundation nodes. If it is
checked, the program releases rotational fixity at wall foundation
nodes, and then very week rotational springs are added at these nodes to
prevent any instability. Analysis Log report provides further
information about these foundation nodes. Note that this is only applied
for foundation nodes under walls. If this option is not checked, wall
foundation nodes are assumed to be fixed.
Also included is an option to store wall stresses and internal forces for
analyzed load cases. If this option is checked, wall stresses and
internal forces are stored during analysis. This information can be
displayed on structure (See ). In addition, wall stresses are available in shear wall
module
| Setting | Description |
|---|
| Include Rigid Link at Fixed Beam-to-Wall Locations |
Modeling of coupling beams for shear walls can be
carried out by using either frame (beam) elements or shell
(wall) elements. For deep coupling beams, it is recommended to
use shell elements , which captures shear dominated behavior
very well. For slender coupling beams, a beam element may be
sufficient to capture bending action. On the other hand, for
moderately deep coupling beams, using beam element alone may not
be sufficient to capture both shear and bending actions. In
these cases, it is recommended to use Include Rigid
Link at Fixed Beam-to-Wall Locations option. If
this option is selected, the program internally provides a rigid
link at the location where a coupling beam frames into a shear
wall. This kind of modeling provides a better load transfer
between the beam and the wall. It should be noted that the rigid
link is only functionally for the load transfer between the wall
and the beam (otherwise, it does not alter stiffness of the wall
or the beam). |
|
| Solver Type
|
Several types of solvers are offered in the program.
Basically they are categorized in two flavors:
in-core and
out-of-core solvers. With
in-core solvers , the global building
stiffness matrix is assembled, stored and solved in the physical memory (RAM)
of the computer. As long as there is enough memory available for the solution
of the models, this choice always gives the best performance\solution time.
However, for very large models, the
in-core solver might run into out-of-memory
errors. If this is the case, it is suggested to switch to
out-of-core solver . With the
out-of-core solver , the program assembles
stores and solves building stiffness matrix using files that are stored on
hard-drive of the computer. Thus, it involves repeated access to hard drive,
which may substantially increase analysis time. It is always recommended that
models should be first run with the
in-core solvers and if an out-of-memory
error is detected, then the
out-of-core should be used.
More specifically, the program includes
direct and
direct-sparse
solvers. The first is suitable for moderate size
problems where as the latter is for all types of models. Note that the
sparse solvers are substantially faster
solvers thus it is highly recommended for large models. Note that both types
(direct and
direct-sparse) include in-core and
out-of-core versions.
If a sparse-solver type is
selected, further options are provided:
Use Single CPU Core or
Use All Available CPU Cores. The former is
intended for computers with old operating systems or with single core system or
for a user who does not want to allocate all cores for the program's use. The
latter utilizes all available cores.
Note that no matter what solver type is used, they
all lead to the same analysis results.
|
| Buckling Restraint Braces
|
When this option is selected, the program excludes
buckling restrained braces when running analysis for gravity load cases. They
are reinstated for other load cases (seismic, wind, dynamic, etc.).
|
