Analysis

Select Criteria > Analysis to display the analysis criteria dialog box. Analysis criteria allow you control over the analytical model that is created, as well as the number of load cases that are generated. These criteria also control the quantity of forces that are extracted for the design modes as described below. For detailed technical information refer to the technical chapter of this manual.

Setting

Description

Analysis Stations

An analysis station is a single location along the length of a beam at which forces are calculated for consideration in the beam design mode (see Section 3.5.2). You can control the number of stations along each concrete beam. These stations are also the locations at which the design checks will be performed. The larger the number of stations the more forces are saved and checked in design for each beam.

The number of stations on any span will be based on the controlling of the two criteria in this frame (see example below). For beams spanning between columns, the stations are always calculated based on the clear length (face-to-face of columns). For beams supported on girders the stations are calculated based in the center-to-center span length.

Minimum number of stations per beam : Specify the minimum number of stations per span of each physical beam. For a cantilever beam the cantilever and back-span are considered separate spans for the purposes of these criteria.

Maximum spacing between stations : Specify the maximum spacing you want between any two adjacent stations.

Example

Minimum number of stations per beam = 10

Maximum spacing between adjacent stations = 12" (250mm)

Resulting number of stations on the cantilever
English: maximum( 10, 72"/12" + 1 ) = 10
SI: maximum (10, 1800mm/250mm + 1) = 10

Resulting number of stations on the back-span
English: maximum( 10, 288"/12" + 1 ) = 25
SI: maximum( 10, 9000mm/250mm + 1 ) = 37

For the cantilever span the minimum number of stations controls the number of stations, for the back-span the maximum spacing criteria controls the number of stations.

The number of stations will have an effect on the force diagrams produced as illustrated in figure below.

Rigid End Zones

Whether or not to consider the effects of rigid end zones is declared in the Rigid End Zone box. The engineer may choose to ignore these effects by clicking the Ignore Effects option button. To include the effects, click the Include Effects option and either enter a percent reduction (between 0 and 100%) in the edit box or accept the default value of 0%. The percentage provided reduces the rigid end zone from the full length (full length is considered to be half the column dimension in the direction of the beam). See the Chapter 3 for more information on Rigid End Zones.

Beam Torsion Stiffness

There are several references that indicate that concrete members will typically exhibit significantly less torsional stiffness than might be calculated using the full cross sectional properties (see Material Properties For more information on the references). In RAM Concrete the torsional stiffness J is calculated based on the dimensions of the web of the beam (not including flange overhangs).

The torsional stiffness of the beam can then be reduced on a beam-by-beam basis based on the torsion cracked factor assigned to the member in the RAM Modeler OR the engineer can select to reduce the torsion stiffness for all concrete beams by the magnitude specified in this dialog. Note if using the value specified in this dialog the gross member torsion stiffness will be multiplied by (1.0 - Specified reduction %) to determine the final beam torsion stiffness. Note that for all other stiffness properties (flexure and axial stiffness) the cracked factor assigned to the both beams and columns in the Modeler are considered to reduce the associated stiffness value.

The loading criteria directly relates to the number of load cases that are generated by the program and applied to the analysis of each story. Note that the larger the number of load cases the longer the analysis time.

Skip load the live load on beam line beams : Select this option to skip load the live load on beams that have assigned beam line numbers. (See Assign Beam Lines for a description of beam lines.) When selected, the program creates one load case per unique live load type (storage, reducible, un-reducible and partition) per beam span. Dead load and Roof live load are not skip-loaded. Also, for beam lines in the two way regions only live loads applied directly to the beams is considered for skip loads.

Skip load the live load on non-beam line beams : Select this option to skip load the live load on beams that do not have beam line numbers. This option can be selected to obtain skip loaded concrete column forces where the concrete column supports beams without beam line numbers. Selecting this option could increase the number of load cases generated (and hence increase the analysis time).

Consider Live Load Reduction : Select this option to have the live load reduction applied to the forces calculated from each span. The program calculates a live load reduction factor for each live load type (roof, reducible and storage) on each member (beam and column). Refer to the RAM Steel manual for a description of the different load types (reducible, unreducible, storage, roof and partition).

The analysis is performed for each live load type independently (i.e. different load cases) if this option is selected. This is to allow the program to reduce the resulting member forces by its corresponding live load reduction value before combining. Where no live load reduction is to be considered all live load types on a beam span can be applied in a single load case for analysis, and no reduction is made to the resulting forces. Refer to the technical chapter for details on how live load reduction is calculated.

Consider Load Polygons as Load Cases on Two-way deck (for pattern loading) : Select this option to skip-load the surface live loads on two-way regions. When selected, the program creates one load case per unique live load type (storage, reducible and un-reducible) per surface load polygon. Dead load and Roof live load are not skip-loaded. Also, if there are any partition surface live loads they are treated similar to un-reducible live load by the program and they show up in un-reducible live load component.

Example

All loads are live loads and beam self wt (dead load) is also applied. The table below shows the number of load cases that will be generated based on the user-selected skip load and live load reduction criteria.

Number of load cases generated (based on the user-selected criteria)

Skip load beam Lines	Consider Live Load Reduct.	DL^a	LL^b roof	LL reduce.	LL unred.	LL Storage	Total
Yes	Yes	1	1	2^c	2	2	8
No	Yes	1	1	1^d	1^d	1^d	5
Yes	No	1	1	2^e	0	0	4
No	No	1	1	0	1^f	0	3

a. Never skip load dead load
b. Never skip load roof live loads
c. Both LL reducible loads applied in one load case per span
d. Each live load type is its own load case to allow for live load reduction to be considered. (see Gravity Design Forces for more information on Design Forces)
e. All live load types applied in one load case per span as LL reduction is not being considered
f. All live loads from all spans are in one load case as no skip loading or live load reduction is being considered.

Analysis Constraints

Several options are available to control finite element model that is created in the RAM Concrete Gravity Analysis.

Setting	Description
Pin base of concrete gravity columns	The analysis of each story (per ACI318-02 8.8.3, BS8110 3.2.1.2.1, AS 3600, EN 1992) fixes the ends of the concrete columns above and below each story that is analyzed. However, you can choose to pin (release) the gravity concrete columns where they are at the foundation. This option will result in less rotational stiffness than would otherwise be calculated at the joints above these columns.
Pin base of column on Transfer Member	The engineer has the option of considering the base of a gravity column as pinned (released) when it sits on transfer beam or wall. Selecting this option will consider the gravity concrete column pinned at its base in this situation.
Pin Top of Concrete Gravity Columns	A column that is continuous at its top that has gravity beams that are pinned and supported on the column will induce bending moments in the top of the column due to the eccentricity between the beam end positions and the column centroid (refer to the Technical Section for more information). To remove any moment being induced in the top of the column the engineer can select this option to pin the top of the gravity columns (for bending). Note that if all the members framing into the column are also released for flexure a situation of instability could arise. At least one member must provide stiffness in each of the six degrees of freedom to prevent an instability.
Remove Rigid Diaphragm Constraint on Sloped Floors	The rigid diaphragm constraint is applied in a horizontal plane even for a sloped floor. For members not located in the horizontal plane of a floor the rigid diaphragm constraint may introduce unrealistic bending moments and torsion forces. Note that this behavior is not a program error but rather an inherent finite element limitation of applying a horizontal rigid diaphragm constraint to nodes not located in the plane of the diaphragm. This option is provided to remove the horizontal rigid diaphragm constraint on the floor for sloped diaphragms. When selected if any node in a diaphragm (single slab edge) is not located at the elevation of the story then none of the nodes in that diaphragm will be constrained (slaved to a master node).
Ignore wall stiffness above story	This option may be selected to ignore the stiffness of the walls at the level above. This selection will result in a more flexible analysis.
Include Out-of-Plane Stiffness for One-Way Decks in Hybrid Slabs	This option may be selected to include the out-of-plane stiffness for one-way decks in hybrid slabs. The default selection is always yes.

Hanger Column Load Iteration

Convergence Tolerance (% Change)

This convergence tolerance value is used to determine the termination of hanging column load iteration. The load iteration is performed to achieve convergence in the load coming through hanging column from level below to the level above. The smaller this tolerance gets the program may take more number of iterations to converge. The default value of this tolerance is set to 5%.

Speed

Setting

Description

Save Results for display purposes

An option is available in RAM Concrete Analysis to allow you to speed up the analysis if desired. By selecting Save results for display purposes (the default) the program will save all display results and will not experience any difference in speed or functionality over previous versions. If unselected the program will not save display results during the analysis. That is, the program will not save member forces, reactions etc that were used to allow you to view the results of the analysis on the screen. The design forces are still saved and all reports as well as the column and beam design modules will function as before. However, there will be no on-screen display available through the Process > Results menu command. This option should significantly increase the time to complete the analysis particularly for structures with significant number of load cases.

Design

Setting	Description
Consider slenderness (Option in ACI Only, Always applies to BS8110, CP 65)	Per ACI318-02 ( 10.12, 10.13(.5) ), BS8110 3.8.3 column forces must be increased where a slender column exists. By selecting this option column slenderness will be checked and where necessary column forces will be magnified. The engineer should ensure that beams on slender columns have sufficient capacity to resist the required increase in end moments.

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 direct solver. With the out-of-core solver, the program assembles stores and solves building stiffness matrix using files that are stored on the hard-drive of the computer. Thus, it involves repeated access to the hard drive, which may substantially increase analysis time. It is always recommended that models should first be run with the in-core solvers and if an out-of-memory error is detected, then the out-of-core should be used. Also, one should note that the results remain unchanged whatever solver is used in the analysis.

Setting	Description
Use In-Core Direct Solver	User may select this option for a moderate size problem.
Use Out-of-Core Direct Solver	While not a common occurrence should a large model experience an out-out-of-memory error during analysis the engineer can select this option to activate the use of the out-of-core solver. As mentioned this solver will utilize the hard drive in its solution process so while it may be a little slower it will be able to effectively analyze larger structures.
Use In-Core Sparse Solver	User may select this option for all types of problems. This is the fastest solver in the library if the required RAM is available for usage.
Use Out-of-Core Sparse Solver	This solver provides another out of core option to be used when the model runs out of memory. This solver is substantially faster than the out-of-core direct solver.

Analytical Model

Setting

Description

Merge Node Tolerance

This value is used to set a tolerance for merging close nodes after the mesh is generated. Any two nodes closer than this specified tolerance is assumed to be the same node and they are merged.

Mesh Controls

Setting	Description
Maximum Distance Allowed between Nodes	This option allows you to define the maximum distance between nodes in slab decks and walls. Note that the program may generate some nodes closer than user entered value, but it is never allowed to be larger than that.
Geometric Tolerance	This value is used to set a tolerance for geometric calculations. This tolerance is required while performing various geometric computations prior to meshing i.e. finding if the point is inside a polygon or point is same as another point etc.
Hard Node Density Factor	This factor is used to determine mesh density around hard nodes which are always located inside slab decks. A hard node is defined as a node where a column, beam or a wall is attached. For most cases, a value of 1.0 is a good estimate to obtain relatively good mesh density around hard nodes.