GTSTRUDL calculate resultant forces

GT STRUDL Output and Interpretation
V 3 2.3.7 - 11 Rev D
Table 2.3.7.2-1
GTSTRUDL Input for CALCULATE RESULTANT
FORCES Example Problem
CALC RES CUT ‘A)A’ ELE 31 TO 33, 46, 47 NOD 49 TO 54
CALC RES CUT ‘B)B’ ELE 57 NOD 55, 56
CALC RES CUT ‘H)H’ ELE 31 TO 33, 46, 47, 57 NOD 49 TO 56
CALC RES CUT ‘H2)H2’ NOD 49 TO 56 ELE 28 TO 30, 44, 45, 56
CALCULATE RESULTANT FORCES ALONG CUT ‘L)L’ ELEM 2 TO 23 BY 7, )
26 TO 38 BY 3, NODES 3 TO 75 BY 8
CALC RES CUT ‘L2)L2’ NODES 3 TO 75 BY 8 ELEM 3 TO 75 BY 7, 27 TO 39 BY 3

 

DESIGNING SHEAR WALLS
RESPONSE SPECTRUM EARTHQUAKE ANALYSIS
When designing shear walls that are modeled as finite element meshes, it is often the case that the structural
engineer uses resultant forces (i.e., axial, shear, and bending moment forces) on a free-body section of the wall
for purposes of design calculations. The resultant forces can be obtained from the GTSTRUDL "CALCULATE
RESULTANT" command or from hand calculated static equivalents of the finite element nodal forces along the
free-body cut as output by the GTSTRUDL "LIST ELEMENT FORCE" command. For static analysis results,
this procedure works well.
However, for Response Spectrum Analysis results, the procedure of obtaining correct resultants is more
complicated. Therefore, consider the following:
1. For static analysis, the resultants computed from FE nodal force values output by the LIST ELEMENT
FORCES command are identical to those output by the "CALCULATE RESULTANT" command,
andmay be used for design.
2. For Response Spectrum analysis, the resultants computed from FE nodal force values are the same
as output by the "CALCULATE RESULTANT" command. However, if the free-body cut joints along
which the resultant forces are computed are support joints, the resultants computed from the reaction
values are NOT the same as those computed from the FE nodal force values, and are NOT the same
as output by the "CALCULATE RESULTANT" command.
The reason for this is as follows:
a. FE nodal force values are the result of a specified modal combination over the currently active
modes (e.g., an RMS combination over 10 modes).
b. The CALCULATE RESULTANT command computes the static equivalent resultant of the FE
nodal forces (i.e., the RMS combination over 10 modes).
c. The support reactions are computed from the specified modal combination over the currently
active modes (e.g., an RMS combination of each reaction component over 10 modes). The static
equivalent resultant of RMS'ed reactions, in general, is NOT the same as the static equivalent
resultant of the FE nodal forces.
3. For any one single mode such as Mode 2, if the free-body cut joints along which the resultant forces
are computed are support joints, the resultants computed from the FE nodal force values are identical
to the resultants computed from the reaction values, and both are the same as output by the
"CALCULATE RESULTANT" command.
Now, in order for finite element resultant force calculations to be consistent with the way in which member end
forces, internal member section forces, FE nodal stresses, FE nodal forces, and support reaction components
are computed, the following must be done in order to obtain consistent resultant forces at a free-body cut
through a finite element shear wall:.1. Calculate the FE nodal forces or support reactions on a MODE-BY-MODE basis. For example, if LOAD
1001 is a response spectrum load, and where modes 1, 2, 3, 4, and 5 are the five modes whose mass
participation factors sum to an acceptably large value, the following sequence of commands can be used:
=====================================================
DYNAMIC ANALYSIS EIGENSOLUTION
LIST DYNAMIC PARTICIPATION FACTORS
PERFORM RESPONSE SPECTRUM ANALYSIS
COMPUTE RESPONSE SPECTRUM DISPLACEMENTS FORCES -
STRESSES REACTIONS MODAL COMBINATIONS RMS
CREATE PSEUDO STATIC LOAD 3001 'MODE 1 RESULTS' -
FROM MODE 1 OF LOAD 1001 $ X-DIRECTION
CREATE PSEUDO STATIC LOAD 3002 'MODE 2 RESULTS' -
FROM MODE 2 OF LOAD 1001 $ X-DIRECTION
CREATE PSEUDO STATIC LOAD 3003 'MODE 3 RESULTS' -
FROM MODE 3 OF LOAD 1001 $ X-DIRECTION
CREATE PSEUDO STATIC LOAD 3004 'MODE 4 RESULTS' -
FROM MODE 4 OF LOAD 1001 $ X-DIRECTION
CREATE PSEUDO STATIC LOAD 3005 'MODE 5 RESULTS' -
FROM MODE 5 OF LOAD 1001 $ X-DIRECTION
OUTPUT MODAL CONTRIBUTIONS ON
LIST RESPONSE SPECTRUM REACTIONS MODAL COMB RMS
OUTPUT MODAL CONTRIBUTIONS OFF
LOAD LIST 3001 TO 3005
LIST REACTIONS
LIST ELEMENT FORCES ELEMENTS 1 2
CALCULATE RESULTANT CUT 1 JOINTS 1 2 3 ELEMENTS 1 2
=====================================================
2. For the static equivalent resultants of the FE nodal forces, or of the support reaction components, along
some free-body cut, compute the desired modal combination (e.g., an RMS combination) of the modal
resultants from EACH of the Loads 3001 TO 3005 (i.e., each of these loads contain the mode response for
EACH of modes 1 to 5 respectively) by hand or by using a spreadsheet. This modal combination of the modal
resultants is consistent with the same calculation procedure used to compute modal combinations for member
end forces, member section forces, etc.
The following two pages contain the GTSTRUDL commands for a very simple example of a static and response
spectrum analysis of a shear wall..STRUDL
UNITS INCH SECONDS CYCLES
STORE RESPONSE SPECTRUM ACCELERATION LINEAR VS PERIOD LINEAR 'RS-Job-1'
$ THE 0% CRITICAL DAMPING CURVE
DAMPING RATIO 0.0 FACTOR 386.08 $ G = 386.08 IN/SEC**2
0.156,0.01 0.66,0.1 0.68,0.2 0.66,0.3 0.6,0.4 0.5,0.5 -0.42,0.6
0.34,0.7 0.3,0.8 0.26,0.9 0.22,1.0 0.2,1.1 -0.18,1.2
0.16,1.3 0.147,1.4 0.138,1.5 0.125,1.6 0.119,1.7
0.108,1.8 0.1,1.9 0.098,2.0 0.09,2.1 0.084,2.2 0.08,2.3 -0.079,2.4
0.075,2.5 0.07,2.6 0.069,2.7 0.065,2.8 0.062,2.9 -0.06,3.0
END RESPONSE SPECTRUM
UNITS KIPS INCH
GEN 3 JOI ID 1 1 X LIST 0 40 100
REP 3 ID 3 Y 100
STATUS SUPP JOI 1 2 3
TYPE PLATE
GENERATE 2 ELEMENTS ID 1 1 F 1 1 T 2 1 T 5 1 T 4 1
REPEAT 2 ID 2 F 3
ELEMENT PROPERTIES
EXISTING TYPE 'SBHQ6' THICK 10.
MATERIAL CONCRETE
LOAD 1
JOINT LOADS
10 FORCE X 100
QUERY
STIFFNESS ANALYSIS
$ SPECIFY THE DYNAMIC RESPONSE SPECTRUM INDEPENDENT LOADING CONDITION
$ USING THE ABOVE RESPONSE SPECTRUM CURVES
RESPONSE SPECTRUM LOAD 1001 'RESPONSE SPECTRUM: TRANSLATION X-DIRECTION'
SUPPORT ACCELERATION
TRANSLATION X 1.0 FILE 'RS-Job-1'
END OF RESPONSE SPECTRUM LOAD
INERTIA OF JOINTS LUMPED
INERTIA OF JOINTS FROM LOAD 1
DAMPING RATIOS 0.0 10
$ ------------------------------------------
$ PERFORM DYNAMIC EIGENSOLUTION ANALYSIS FOR
$ 10 FREQUENCIES AND MODE SHAPES
$ ------------------------------------------.EIGEN PARAMETERS
NUMBER OF MODES 10
SOLVE USING GTLANCZOS
PRINT MAX
END
DYNAMIC ANALYSIS EIGENSOLUTION
LIST DYNAMIC PARTICIPATION FACTORS
PERFORM RESPONSE SPECTRUM ANALYSIS
COMPUTE RESPONSE SPECTRUM DISPLACEMENTS FORCES STRESSES REACTIONS -
MODAL COMBINATIONS RMS
CREATE PSEUDO STATIC LOAD 2001 'RMS RESULTS' FROM RMS OF LOAD 1001 $ X-DIRECTION
CREATE PSEUDO STATIC LOAD 2002 'MODE 2 RESULTS' FROM MODE 2 OF LOAD 1001
OUTPUT MODAL CONTRIBUTIONS ON
LIST RESPONSE SPECTRUM REACTIONS MODAL COMB RMS
OUTPUT MODAL CONTRIBUTIONS OFF
LOAD LIST 1 2001 2002
LIST REACTIONS
LIST SUM REACTIONS
LIST ELEMENT FORCES ELEMENTS 1 2
CALCULATE RESULTANT CUT 1 JOINTS 1 2 3 ELEMENTS 1 2
CINPUT