Reinforced Concrete Frame Building Response Comparison among
Structural Analysis Tools
Submitted: August 8th, 2014
REU Student:
Operation Site:
Project PI:
REU Mentors:
Jacob Gould, Rose-Hulman Institute of Technology Undergraduate
University of Illinois at Urbana-Champaign
Dr. Mehrdad Sasani, Associate Professor at Northeastern University
Weslee Walton, Project Coordinator at University of Illinois
Anahid Behrouzi, University of Illinois Graduate Student
Abstract
Hybrid simulation of structures typically involves analytically modelling the overall system and
experimentally testing a limited number of subcomponents. This enables researchers to
capture both the local and global behavior of individual elements and the structure. The Near
Collapse Performance of Existing Reinforced Concrete Buildings (“RC Frames”) project being
conducted at the University of Illinois NEES facility involves a complex OpenSees building model
with three physical reinforced concrete specimens. The goal of the investigation detailed in this
paper evaluates the potential of using SAP2000 and ZEUS-NL structural analysis platforms for
the RC Frames analytical model, and more generally, the practicality of these programs in
hybrid simulation projects with complex structural systems. These tools enable a level of
visualization and user interactivity that make them attractive for the efficient creation of
models. The primary objective was to investigate the consistency of results through these
various structural analysis tools. Additional efforts were made to study the ease of use of each
software package to help inform researchers on the functionalities and shortcomings that exist.
KEYWORDS: Structural Analysis Software, Near-Collapse Performance, Existing Reinforced
Concrete, Shear-Axial Failure, Column Shear Failure, Hybrid Simulation
Page |1
Table of Contents
INTRODUCTION ............................................................................................................................................ 2
LITERATURE REVIEW .................................................................................................................................... 4
THEORY ......................................................................................................................................................... 5
METHODS & CONTRIBUTIONS ..................................................................................................................... 5
SAP2000 RESULTS ......................................................................................................................................... 7
ZEUS NL RESULTS ........................................................................................................................................ 11
SAP2000 PRODUCT REVIEW ....................................................................................................................... 12
ZEUS NL PRODUCT REVIEW........................................................................................................................ 13
CONCLUSION .............................................................................................................................................. 15
FUTURE WORK............................................................................................................................................ 16
ACKNOWLEDGEMENTS .............................................................................................................................. 16
CONTACT INFORMATION ........................................................................................................................... 16
APPENDIX ................................................................................................................................................... 17
REFERENCES ................................................................................................................................................ 26
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INTRODUCTION
Observations from experimental testing and in-field failures of various structures indicate that
pre-1970’s reinforced concrete columns do not have adequate shear reinforcement to resist
seismic loading (Liel, 2008). This problem has been addressed in modern structures through
updates to various design codes, such as ACI318, that include provisions to improve ductility,
and thus, the earthquake resistance of reinforced concrete buildings (Saadatmanesh et al.,
1994). However, many buildings constructed before updates are still in use and pose a potential
safety threat (Alaee and Karihaloo, 2003). Retrofit is necessary to ensure occupants well-being,
additional research attention should be dedicated to investigating the seismic behavior of these
older structures. Beyond understanding global performance of these buildings, it is important
to study the response at the structural component level as single element failure does not
necessarily result in a complete system collapse (Sasani et al., 2010). Therefore, a critical area
of study involves determining which elements require retrofitting to avoid progressive collapse.
At present, these topics are being investigated through the NEES Near Collapse Performance of
Existing Reinforced Concrete Buildings (“RC Frames”) project. The effort led by Dr. Mehrdad
Sasani of Northeastern University and his graduate student Justin Murray consist of hybrid tests
of a prototype building subjected to an earthquake time history that results in extensive
structural damage. The researchers are examining the behavior of a typical ten story office
building designed in accordance with ACI318-63, pictured in Figure 1 and 2, after one or more
of the structural columns have failed. The RC Frames project involved simulations where the
overall structure is modelled in OpenSees and three columns are tested experimentally first at
the one-tenth and then the full scale. These columns are located at A1 and B1 in Figure 1 on the
first story and B1 on the second story.
Figure 1. Portion of the floor plan
Source. Murray, J. 2014
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Figure 2. AutoCAD representation of office building
Over the course of the Research Experience for Undergraduates (REU) at the University of
Illinois’ George E. Brown Jr. Network for Earthquake Engineering Simulation (NEES) facility,
there was a considerable opportunity to assist with experimental testing portion of the RC
Frames project through sensor installation, calibration, and trouble-shooting as well as other
test preparation tasks. The main research effort outside of this work was evaluating the
potential of a variety of structural analysis software tools to be used in modelling full building
systems for hybrid simulation, such as that shown in Figure 2. The RC Frames research team
currently used a complex OpenSees model that required considerable experience and
understanding to develop, besides the additional effort necessary to run this in parallel with the
physical laboratory test. To address some of these challenges, there was an interest to explore
other publicly or commercially available software options that would provide visualization and
some level of user interactivity to assist in model development. In evaluating the options it was
necessary to determine how results compare in each of the structural analysis platforms to
determine consistency. To achieve these goals, models of the prototype RC Frames structure
were developed, analyzed, and compared for Zeus-NL and SAP2000. Beyond side-by-side
comparisons of analytical simulation results in OpenSees, Zeus-NL, and SAP2000, efforts were
made to study the ease of use of each software package to summarize the unique
functionalities that exist to support model development and shortcomings that may impede it.
Page |4
LITERATURE REVIEW
Over the past several decades, engineers and researchers have been putting a great deal of
effort into understanding how pre-1970s reinforced concrete structures will behave under
seismic loads (Henkhaus et al., 2013; Murray et al., 2013). Numerous simulations have been
focused on various aspects of how reinforced concrete structures under seismic loadings will
fail (Henkhaus et al., 2013; Murray et al., 2013). While much has been learned about failure
modes that occur in reinforced concrete structures, these tests are often complicated in terms
of their loading conditions and data acquisition, and it is difficult to address many of the
research questions related to non-ductile design in an individual test program (Li et al., 2011;
Zhou et al., 2013). Therefore, simulations have been broken up into smaller, more manageable
sub-sets that allow data collection where each portion addresses a specific concern of the
researcher. These test sub-sets include such concerns as loading distribution (Jiang, 2013),
progressive collapse (Mirzaei et al., 2011), and retrofitting of the existing structure (Sasani et
al., 2010).
Analytical simulations have been developed that model a structure after initial damage has
occurred and resulted in partial or complete column removal; this damage may be attributable
to seismic load, explosions, or collisions and result in load redistribution (Levy and Salvadori,
1992) (Sasani et al., 2008). The results of these simulations have brought attention to how we
design our structures (Abruzzo et al., 2006). Column failure can also lead to increases in
bending moments, axial compression, and tension forces. This phenomenon is referred to as
progressive collapse and can be seen in many different events such as the Oklahoma City
bombing in 1995 where a central point of damage eventually led to almost complete collapse of
the structure (Val et al., 2006).
According to Sagiroglu and Sasani, column removal and subsequent load redistribution be easy
to conceptualize, it can be difficult to simulate in a controlled lab setting. In the specific case of
the RC Frames project, four years of extensive preparation was necessary for both the
analytical model and experimental test to capture the behavior researchers wanted to examine.
The ability to model collapse with respect to different failed elements is essential in furthering
the capability of current structural analysis programs such as OpenSees, SAP2000, and Mastan2
that are used for new design and to evaluate existing structures. The objective of the RC Frames
project, as a whole, is to further the ability to predict progressive collapse that results from
column failure. The intended outcome is advanced models that allow engineers to take action
to either retrofit susceptible structures or come up with designs that are not vulnerable to this
type of failure (Sagiroglu and Sasani, 2014).
While the ability to predict this failure is important, it is equally critical to understand effective
methods to retrofit pre-1970s buildings to alleviate issues related to non-ductile structural
systems (Alaee and Karihaloo, 2003). Numerous techniques, such as beam or column isolation,
have been implemented to resolve these problems. However, current solutions are not
regulated by any code (Gould et al., 2006). While there are guidelines that engineers can
reference in designing and detailing retrofits, there is need for codes supported by laboratory
Page |5
research and in-field testing that standardizes the way that the structures are retrofitted (Gould
et al., 2006).
THEORY
The premise of hybrid simulation is that the overall structural system is modelled using a
structural analysis software and a small sub-set of the structural components are physically
tested (Schellenberg et al., 2008). In the case of an earthquake time-history hybrid-simulation a
load step is applied to the analytical structure and the resultant forces and displacements at the
nodes of the physically-modelled specimens become commands to the experimental load
control. In turn, the feedback from the test specimen is utilized as the response of those
elements in the model. In the case of the RC Frames project, the model has been constructed in
OpenSees, and as mentioned earlier is quite complex with considerations for non-linear column
behavior and a high level of element discretization that results in many thousands of nodes.
This type of model becomes very time-intensive to prepare and requires extensive knowledge
of the analysis program as it is completely text-based input.
To increase efficiency and ease of both producing and trouble-shooting models, two structural
analysis platforms with graphical user interfaces are investigated as substitutes for OpenSees in
a complex hybrid simulation such as the RC Frames project; these include Zeus NL and
SAP2000. The former is an open-source program from the University of Illinois Mid-America
Earthquake (MAE) Center used by various academics around the world for earthquake
engineering analyses, the latter is a tool that is used for similar purposes but is prevalent in the
industry setting and has a wide realm of applicability with its continuous software refinements.
The investigation detailed in this paper attempts to validate the results of the Zeus NL and
SAP2000 models by examining the consistency between the two programs and OpenSees;
establishing consistency is seen as the first step in identifying if these are potential stand-ins for
the current analytical model.
METHODS & CONTRIBUTIONS
The most significant portion of effort required for this investigation was developing full-scale
analytical models of the prototype RC Frames building with SAP2000 and Zeus NL: visualization
of these models can be seen in Figures 4 and 5. The ultimate goal was to examine and compare
the predicted failure modes, deflections, and other metrics of global system response resulting
from earthquake loading for the various programs. However, there were shortcomings for each
of the structural analysis tools had that limited the accuracy and effectiveness of the analysis.
For each program, models were generated with as much detail that was permitted by the
available input parameters of the given software. These properties include material
descriptions (concrete compressive strength of 4500 psi, Grade 60 steel for reinforcement),
section geometry (column/beam cross section dimensions; reinforcement size, number, and
location based on provisions from the ACI 318-63), overall structural geometry (bay and story
spacing), static loading (live and dead loads), and earthquake loading based on the Lucerne
Page |6
Station ground motion record from the Landers Earthquake as shown in Figure 3. The original
structure is a ten story office building is based on a survey of typical pre-1970s reinforced
concrete buildings in the San Francisco area. This building has 2 by 6 bay structural layout with
a twenty foot spacing between columns in both directions. The first level of the building is 154
inches tall while the remaining nine levels are 129 inches tall. Each floor consists of a four inch
concrete slab that supports a superimposed 30 lb/ft2 live load and 65 lb/ft2 dead load.
Landers Earthquake
20
Acceleration (in/s2)
10
0
0.00
5.00
10.00
15.00
20.00
25.00
30.00
35.00
40.00
45.00
50.00
-10
-20
-30
Time (sec)
Figure 3. Landers earthquake time-history record
In discussing the models, it is relevant to note that many of the structural elements has rebar
cut-offs along their length which meant that there could be distinct cross-sections with varying
amounts of longitudinal reinforcement over the member. Neither Zeus NL nor SAP2000
program allows the user to incrementally change the longitudinal reinforcement along the
length of a single member. For this reason, each member was divided into three different
sections and reinforcement was placed to correspond to the RC Frames prototype building
design according to the specifications. All other relevant details can be found in the Appendix.
Page |7
Figure 4. Zeus NL model representation
Figure 5. SAP2000 model representation
SAP2000 RESULTS
The first analysis conducted in SAP2000 was a linear, modal timehistory using the previously mentioned Lucerne accelerogram, this
was applied via a base excitation of the structural model in the xdirection. Various response parameters were examined in the time
domain. During this process, efforts were made to ensure that the
results are reasonable by either engineering judgment or quick
calculation; for example, reviewing the deflected shape at various
time stages allowed the author to see if the movement of the
structure followed the expected path.
The deflected-shape envelope of the structure for the Lucerne
ground motion is shown in Figure 6 to the right. From the
deformed shape, several observations can be made. First, the
magnitude of the absolute deflection of the nodes at the top of the
building are much higher than the lower nodes. Second, the lower
levels have the highest inter-story drift. This observation may be
explained by the effect of the masses at the top of the structure:
the top levels will not want to translate relative to each other and
will move more as a unit. The lower levels, however, are very close
Figure 6. Deflected
shape envelope
Page |8
to the excitation input location at the base and will be affected almost regardless of the
presence of mass. One final observation from the deflected shape is the behavior of the fixed
supports at the base of the structure. The rotations near the fixed base supports are quite large
and it seems that the system may have experienced a leaning-column failure. Examination of
the rotations near the base at various time steps during the earthquake record show that there
is otherwise very low rotation compared to that seen in the deflected envelope. Other rigid
connections throughout the building seem to also show limited rotations through the timehistory.
Comparison of SAP2000 time-history results to the OpenSees model (Murray, J 2014) involved
deflection of individual members: Column A1 for the first floor, and Columns B1 on the first and
second floor (Figure 7 and 8). Above are the time-displacement graphs created by OpenSees for
the 1st and 2nd floor. second floor (Figure 7 and 8). Above are the time-displacement graphs
1st Floor X-Displacement
3.5
X-Displacement (in)
3
2.5
2
1.5
1
0.5
0
-0.5 0
5
-1
10
15
Time (sec)
Figure 7. 1st floor OpenSees X-displacements
2nd Floor X-Displacement
6
X-Displacement (in)
5
4
3
2
1
0
-1
-2
0
5
10
15
Time (sec)
Figure 8. 2nd floor OpenSees X-displacements
Page |9
created by OpenSees for the 1st and 2nd floor. Figure 7 and 8). Above are the time-displacement
Similarly the same time-deflection graph was developed by SAP2000 and these results were
compared and differences were noted in the data and graphical representations. Below, Figures
9 and 10, are the graphs of the SAP2000 deflections in the x and y directions.
SAP2000 X-Displacements
of the Center Columns
X-Displacement (in)
4
2
0
-2
0
10
20
30
40
50
-4
-6
-8
Time (sec)
2nd Floor
1st Floor
Figure 9. X-displacement of 1st and 2nd level columns
SAP2000 Y-Displacements
of the Center Columns
Y-Displacement (in)
0.05
0.03
0.01
-0.01 0
10
20
30
40
50
-0.03
-0.05
Time (sec)
1st Floor
2nd Floor - interior
2nd Floor - exterior
Figure 10. Y-Displacement of 1st and 2nd level columns
Once the data was collected the author evaluated whether the results could be accepted as
reasonable response to the input ground motion. The time-acceleration graph shows the
highest acceleration around the same time as the peak X-displacements. It should also be noted
that the ground motion is in the x-direction seems fitting that the deflection in the y-direction is
minimal. The only node that is showing deflection in the y-direction is the exterior column that
will experience more stresses than the center columns during the ground motions; however,
P a g e | 10
this value is still very small. Figure 11 below shows output from OpenSees and SAP2000 for the
absolute values of the X-displacements to show relative magnitude of displacements compared
to the original position.
1st Floor Absolute X-Displacements
4.5
X-Displacement (in)
4
3.5
3
2.5
2
OpenSees
1.5
SAP2000
1
0.5
0
8
10
12
14
16
Time (sec)
Figure 11. X-displacement comparisons
From Figure 11, it can be seen that the SAP2000 model tends to yield much larger displacement
values than OpenSees by about 20 – 25%. One cause for this difference might be a potential
reduction factor in the earthquake record in OpenSees. The graduate researcher indicated a
factor was used to reduce the magnitude of the seismic activity to diminish the damage to the
structure. If this reduction factor is only accounted for in the OpenSees model, then two
programs seem logical.
However, while the magnitude of the deflections may make sense, the time-shift in the location
of peaks must be explained. As can be seen from above the graph, OpenSees tends to have
deflection peaks about one second later than the SAP2000 model. This difference could be
explained by reasons such as a variance in mass distribution or inconsistency with connection
details between models.
Following the time-history analysis, a model analysis was completed in SAP2000 to identify the
primary mode shapes of the structure and periods associated with these modes. Using a ruleof-thumb provided by Anahid Berhouzi, that the period of the structure in seconds will be
number of stories divided by ten, it was the impression that the period would be around one
second. After the analysis was performed, the periods were obtained which can be seen in
table 1 below. However, these results were not the original values obtained. When the analysis
was first performed, the fundamental period was on the order of nearly a minute. This value
was deemed far too high for the height, mass, and the input motions of the prototype structure
and an investigation was necessary. The author determined when masses were defined only in
the z-direction, the time periods seemed far more feasible rather than when masses were
defined in all directions that produced very high period values. For this reason, the values
P a g e | 11
obtained using masses in the z-direction only are displayed. These results will be later
compared to the Zeus NL modal results.
Table 1. SAP2000 modal period values
Modal Period Values
Period (sec)
Mode 1
1.513
Mode 2
1.388
Mode 3
1.238
Mode 4
0.471
ZEUS NL RESULTS
Creation of the Zeus NL model was challenging, and many of the
obstacles which the author encountered are detailed in the “Zeus NL
Product Review” section. The results obtained from this program are
limited to a modal analysis as there was difficulty in successfully
completing a complete time-history analysis due to issues with
convergence. While the problem was investigated, a solution was
never discovered before the completion of this paper. However, Zeus
NL did complete an Eigenvalue analysis and provided periods
associated with the first ten modes of the structure which are
summarized in Table 2 to the right.
At first glance the user may notice that these values are much higher
than the rough estimate for the fundamental period of one second.
The user can also see from Table 3 below that the values are also
significantly higher than the SAP2000 values calculated.
Table 2. Zeus NL
modal period values
Mode Zeus NL (sec)
1
3.191022
2.614617
2
3
2.580735
4
1.216076
5
1.033148
6
1.005096
7
0.969186
8
0.883982
9
0.728860
10
0.683270
Table 3. Zeus NL and SAP2000 modal differences
Mode 1
Mode 2
Mode 3
Mode 4
Modal Period Differences
Zeus NL (sec) SAP2000 (sec) Percent Difference
3.19102
1.513
110.86
2.61462
1.388
88.42
2.58074
1.238
108.47
1.21608
0.471
158.06
Because of rather large percent differences between the period of the fundamental mode in
Zeus NL and SAP2000 as well as the rule-of-thumb calculation, and the fact that the program
would not complete a time-history analysis, it can be inferred that the error is in the Zeus NL
rather than SAP2000 model. It is believed that a user or programing error occurred to interrupt
P a g e | 12
the analysis so that it produced invalid data for the model that was attempting to be analyzed.
It is important to note, that while Zeus NL did not provide near the value anticipated, it should
be assumed that the program produced the proper period time for the model that was created
and that it is the model likely needs modification to improve accuracy.
SAP2000 PRODUCT REVIEW
When creating the model of the prototype RC Frames building in SAP2000, the author
discovered that the most tasks necessary to define the structural model could all be done with
minimal effort or after some
amount of investigation of
resources including the CSI
website and online software
discussion forums. When defining
the section properties for each
member, selecting the location of
the rebar was relatively simple for
columns because the program
gives the user the capability to set
the clear cover, longitudinal bar
size number and size in each
direction, and stirrup size and
spacing. The SAP2000 section
property definition enables the
user to select the “other”
property type which opens the
“Section Designer”, in Figure 12.
This allows the user to create the
column shape, rebar location and
size, and many other properties
with great flexibility. While this
operation is very powerful, the
creation of multiple members can
be very time intensive. The reason
for this is because clear cover and
number of bars cannot be
assigned up-front, rather each bar
must manually be inserted and
Figure 12. Section designer
adjusted individually on a
Cartesian coordinate system. When the user selects a row or group of rebar, after left clicking, a
table appears that shows the shared properties of all selected items. The table appears to be
modifiable which can be very useful so the user can place multiple items in a line or change the
size or material in a single action. However this function does not appear to be fully functional
P a g e | 13
because once a property is changes, no update occurs in the interactive graphical user interface
or table of bar locations.
Another difficulty that comes with SAP2000 is the addition of time dependent earthquake
loading to the structural model. Initially to load a time-history activity, the user must create a
new function. After the new function is defined, a load case must be created to model the
previously defined function. Once the system has been run with the loaded function along with
dead load, live load, and other applied loads, results given over time may be difficult to obtain
and record. To perform this action, the user will need to go to time plots and select the
property that is desired to be observed. The default of the program is to observe the property
over time; however, both axis can be changed to various properties. Once these properties are
displayed, the user has the option to export them into a text file for further data interpretation.
While the capability certainly exists for a time-history, steps necessary to provide the input
ground motion and extract the desired nodal or element results can be tedious.
ZEUS NL PRODUCT REVIEW
As previously stated, Zeus NL is an open-source user interface developed by University of
Illinois at Urbana-Champaign by a team of professors and graduate students at the MAE Center.
With that being said, Zeus does not have the resources CSI has to produce structural analysis
programs such as SAP2000 with support materials and updates. Even with these limitations,
Zeus NL does have the capabilities and potential to be a useful program in earthquake analyses
structures.
The first issue the author encountered, similar to that in SAP2000, was the placement of
longitudinal reinforcement in beams due to vertical asymmetry of the section. In principle
defining rebar location should be a relatively simple action where the user indicates where the
reinforcement is in the upper
right quadrant of the rectangular
cross-section as described in
Figure 13, and then that rebar
layout was reflected over the
remaining three quadrants about
the center of the column. The
author determined that different
size and/or number of
reinforcement could not be
placed on the top versus bottom
of the cross-section because the
Figure 13. Rebar placement note
program assumes that it is doubly
symmetric. The author initially tried using other, non-rectangular sections to see if it was
possible to account for the singly symmetric layout of reinforcement. The most effective
attempt to achieve this was by selecting a T-Beam section that allows the user to reflect the
reinforcement about the vertical axis only. Also slight modifications need to be made to the
P a g e | 14
overall beam dimensions to satisfy constraints placed on the T-beam definition. This means the
user will create the flange a very small increment wider, for example 0.10 mm, than the web to
satisfy the programs requirements that the flange must be larger than the web. By using this
input method for the reinforcement definition, the geometry of the member has not changed
by any appreciable amount and will result in a nearly insignificant change the analysis results.
Another helpful feature of this program is its Data Entry Table shown in Figure 14. By using this
feature, the user is able to copy and paste data points from another program such as Excel into
Zeus NL. For example the user can enter the material name, material type, and material
properties into the same row on
Excel and then copy-paste into
Zeus. The reason that this feature
is so helpful is because manually
entering in properties such as
nodes or element connectivity
can be time consuming but can be
shortened by using the built in
functions in Excel. That being said,
Figure 14. Date entry table
a good understanding of Excel is
highly recommended before trying to use this program. However, one downside to using this
function of Zeus NL is the fact that when certain types of data points are entered, the program
does not immediately recognize them as acceptable property entries. The user will then have to
double-click and then press “ok” on each data point to tell the program to utilize these values.
This problem can become troublesome when a user is defining hundreds of nodes or elements,
and has to complete this step for each of the entries.
While the Data Entry Table is useful, it is not always the best option for creating properties such
as connecting nodes to make an element. One of the more obvious flaws of the program is the
limited amount of interaction the visualization created beside the data tables are with one
another and the user. In SAP2000, the user can choose to draw a line and then click on two
separate nodes, and an element will be created. The same programs will also show changes in
geometries such as when the user changes the number of reinforcement bars in a beam or size
of the beam. When the user enters a property in Zeus NL, there is visual indication that the
entry was successful. Being able to interact with the visualization by selecting elements and
real-time updating would be a major step for this program to becoming more effective
structural analysis modelling tool.
One of the reasons that interaction in the visualization would be helpful is because the display
options for this program are not user friendly. For example, if the user is trying to connect to
nodes to create an element, there is an option to show all node names for the structure. If the
user has created hundreds of nodes, nodes cannot be identified one from another because the
labels are as close together as shown in Figure 15. The user may think that using the zoom,
P a g e | 15
rotate, or pan features may help and to some
extent they do. However, their helpfulness is
limited because of a few reasons. The first major
reason is the fact that the user cannot rotate the
full 360˚ because it stops after turning only 90˚in
any direction. By limiting our field of vision with
these constraints, the user can only use 1/8 of the
total view. While a seemingly simple issue of
visibility, this can create complications when
developing a model with thousands of nodes that
need to be connected with elements of assigned
masses.
The final major limitation identified model
Figure 15. Node locations are
creation is the process of placing loads on the
very close together
structure. One important detail that seems to
have been omitted from the User’s Manual was whether the model includes self-weight of the
members or not. The program also has no way to place evenly distributed line or area loads
upon a selected section, which is a major problem considering modern structural design
involves distributed live and dead loads superimposed on each floor of a building. Despite this
shortcoming in Zeus NL, a solution can be obtained if the distributed loads are turned into point
loads placed at the column lines. For our particular solution, the slab and loads were placed on
the top of each column based on tributary width and load paths, with the assumption that selfweight is not included.
While some of these methods that were employed to develop the Zeus NL model may not be
the most accurate or practical, ultimately it must be considered that this tool is a work-inprocess developed by a small team of engineering faculty and students. Zeus NL does have the
makings to be a great program, but improvements must be made in the computing power,
interaction with the model, and rebar placement along with others before it is considered for
wide-spread application for analysis and certainly to produce the types of complex models
utilized in hybrid analysis.
CONCLUSION
With the use of hybrid simulation, researchers can now perform work much more efficiently
and effectively than ever before because of the integration of software into simulations. While
improving the usage of time and resources is a great step forward, using hybrid simulation
creates new issues for researchers. By implementing Zeus NL and SAP2000, researchers will
now have more options to turn to for their research tools. As stated in this paper, both of these
programs could streamline the process of hybrid simulation. By implementing these programs
into the researcher’s toolbox, different capabilities will be explored and implemented for
different simulations. The issues discussed in this paper about the programs should be
P a g e | 16
addresses as well as further investigation be taken to discover the full potential of these
programs.
FUTURE WORK
No model is ever a perfect representation of the actual structure constructed; however, steps
can be made to improve the model and reduce errors as much as possible. Therefore, the
future work will be to improve upon the models created for this paper. SAP2000 has many
options that can be explored to help model ground conditions and joint connectivity among
others in a more accurate manner than done previously. As stated previously Zeus NL could not
perform a time-history analysis; therefore, the first step to be completed would be to create a
working model. Once the model is functional, then the user will compare the results of the
other programs stated in this paper to see the consistency of results. After that is completed,
other avenue will be explored to make the model as similar as can be to the actual structure.
It is also desired to use these programs in a hybrid simulation alongside fellow REU, Mitch
Knapp’s work in VecTor 2. These programs will interact through UI-SimCor allowing a hybrid
simulation to be completed. Once these results have been collected, it will be desired to
compare these results to the tests being conducted on Near-Collapse Performance of Existing
Reinforced Concrete Structures.
ACKNOWLEDGEMENTS
I would like to thank Dr. Mehrdad Sasani and Justin Murray for allowing me to work alongside
them in this research project. Special thanks should also be extended towards mentors Weslee
Walton, Anahid Behrouzi, and Do Soo Moon for their support throughout this project as well as
fellow REU participant Mitch Knapp. I would finally like to thank the University of Illinois at
Urbana-Champaign, the NEES REU Program who provides funding through Operation award
number CMMI-0927178, and the National Science Foundation which funds this research project
through Grant Number EEC-1263155.
CONTACT INFORMATION
If you have questions about testing procedure, results, or any other topic discussed in this
paper please do not hesitate to contact anyone from the below list.
- Dr. Mehrdad Sasani, Associate Professor at Northeastern University, sasani@neu.edu
- Jacob Gould, Student at Rose-Hulman Institute of Technology, gouldjh36@gmail.com
- Justin Murray, Graduate Student at Northeastern University,
murray.jus@husky.neu.edu
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APPENDIX
Figure 16. Member locations
Table 3. Section properties
Material/Construction Notes
f'c
4500 psi
fy
60 ksi
slab thickness
4 in
Clear Cover
2.5 in
Table 4. Building dimensions
Office Building Dimensions
Bays (2 x 6)
20 feet
154
Story Height (1st Floor)
inches
129
Story Height (2nd - 10th Floor) inches
* distances are node to node
Table 5. Stirrup information
Stirrup Spacing
Columns
16 in
Beams
16 in
Stirrup Size
Columns
#3
Beams
#3
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Figure 17. Column and beam detailing
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Longitudinal Spandrel Interior Parts are same as Longitudinal Spandrel Exterior
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Transverse Spandrel Exterior is the same as Transvers Spandrel Interior
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