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May 2017
Gallatin County Law and Justice Center -
ASCE 41-13 - Tier 3 Systematic Evaluation
and Retrofit Alternatives
Tier 3 Systematic Evaluation and Retrofit Alternatives Report
5/5/2017 Page 1 of 25
Job Number: 0939-03817
Tier 3 Systematic Evaluation and Retrofit
Alternatives Report
Prepared For:
Gallatin County
311 West Main Street
Bozeman, MT 59715
May 2017
Prepared By:
Stahly Engineering & Associates
851 Bridger Dr., Suite #1
Bozeman, MT 59715
Phone: (406) 522-8594
Written By: Theron Thompson, P.E.
Senior Engineer
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1 Facility/Structure Description
The current Law and Justice Center was originally built in 1962 as the Holy
Rosary Parish High School. The original facility was remodeled in 1979 to
renovate it into the Gallatin County Law and Justice Center. The facility was
again remodeled in 1993 to revamp the existing gym into court rooms and office
space for the Bozeman Police Department and the Gallatin County Sherriff’s
Department.
The facility is composed of three main areas which were used to develop the
study (See Figure 1). Area A is the northern portion of the original main building
consisting of offices and a court room. Area B is the south portion of the original
main building and contains the main entry, office space, locker rooms and
restrooms. Area C is comprised of the original gym which was renovated to add
court rooms and office space for the Police and Sheriff’s Departments.
Figure 1 – Building Areas
Area A is constructed of a three-story concrete frame structure with concrete
joists, beams and slabs. The lateral system is a combination of concrete
moment frames and concrete frames with masonry infill panels. The original
lateral structural system was concrete frames with masonry infill panels, but the
later renovations removed a majority of the infill panels, leaving a concrete frame
structure.
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Area B is much like Area A, with the exception that fewer of the masonry infill
panels were removed and a concrete shear wall was added in the 1993
renovation. See Appendix A for drawings indicating the alterations to the original
structure.
Area C is comprised of numerous lateral systems. The majority of the original
masonry shear wall system in the north and south walls was removed during the
1993 renovation. It was replaced with concrete shear walls at the eastern
corners of the building. The renovation also included adding an upper floor
which is laterally supported by light gage steel stud walls with plywood sheathing.
These walls are supported on a rigid concrete deck which is laterally supported
by the concrete shear walls and two steel braced frames. Again, see Appendix A
for drawings indicating the alterations to the original structure. The lateral system
for Area C in the north-south direction is comprised of glulam arch moment
frames. The frames were repaired and strengthened during the 1993 renovation.
2 Performance Objectives and Seismic Hazards
For an ASCE 41-13 evaluation the Basic Performance Objective can be selected
as either the Basic Performance Objective for Existing Buildings (BPOE) or the
Basic Performance Objective Equivalent to New Building Standards (BPON).
The BPOE performance objective accepts performance less than what the
current ASCE 7 requires, but considers the shorter remaining life span than a
new building. It also recognizes the increased cost of achieving the higher level
of performance.
Although a reduced cost may be realized with the BPOE performance level, for a
Risk Category III or IV such as an essential facility, the BPOE is not appropriate.
Therefore the BPON performance objective was selected for this evaluation.
This requires that the existing structure be evaluated for the Basic Safety
Earthquake (BSE) 1 for use with the BPON performance objective (BSE-1N).
This is equivalent to the design, 5% damped, spectral response accelerations
required by ASCE 7 for new buildings.
The target building performance levels evaluated were the Immediate Occupancy
(S-1) and the Life Safety (S-3). The Immediate Occupancy performance level is
defined as the post-earthquake damage state in which a structure remains safe
to occupy and essentially retains its pre-earthquake strength and stiffness. The
Immediate Occupancy level is similar to a new building designed with current
codes as an essential facility. A Life Safety performance level is defined as the
post-earthquake damage state in which a structure has damaged components
but retains a margin against the onset of partial or total collapse.
The Level of Seismicity for the geographical location is classified as “High
Seismicity”. See Appendix B for the seismic information for this Tier 3
evaluation.
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3 ASCE 41-13 Tier 3 Systematic Evaluation
The purpose of this study is to complete an ASCE 41-13, “Seismic Evaluation
and Retrofit of Existing Buildings”, Tier 3 Systematic Evaluation which includes
an analysis of the entire building. Analysis procedures were selected per ASCE
41-13 requirements and the building components were evaluated per the defined
acceptance criteria for capacities and behavior.
Retrofit alternatives were analyzed to determine recommended retrofit methods
to bring the structure into compliance with the selected Performance Objective.
An Opinion of Probable Cost was included to provide the expected cost range for
the selected retrofit methods.
Tier 1 Potential Deficiencies 3.1
The potential deficiencies identified in the previous Tier 1 Structural Screening
are addressed in this evaluation and are as follows:
Area A:
Concrete Moment Frames:
o Possible weak story and soft story
o The shear capacity of the frame members not able to develop the
moment capacity at the ends of the members
o Potential that a strong-beam weak-column exists at the frames
o Shear stress demand in the frame columns exceeds the capacity
o Column axial stress demand exceeds the capacity
o Concrete columns are not adequately doweled into the foundation
o Beam reinforcing is detailed inadequately
o Column tie spacing is inadequate
o Original drawings do not show adequate beam stirrup spacing
o Beam-column joints are not adequately reinforced
o Secondary components within the system do not have the shear
capacity to develop the flexural strength of the components
Masonry Infill Panels:
o Shear stress demand in the infill panel walls exceeds the capacity
of the walls
o Concrete columns are not adequately doweled into the foundation
o Secondary components within the system do not have the shear
capacity to develop the flexural strength of the components
o Wall openings are not adequately reinforced
o Infill wall panels do not meet the aspect ratio requirements
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Area B:
Area B is very similar to Area A and has the same possible deficiencies, except
that less of the masonry infill panels have been removed. Also, the concrete
shear walls that were added create a condition with the concrete frames in which
the frames do not have the shear capacity to develop the flexural capacity,
similar to the infill panels. As well, the coupling beams do not have adequate
reinforcing over means of egress.
Area C:
Concrete shear walls are possibly stressed at a level that exceeds their
capacity.
Due to the main floor being a concrete diaphragm, a rigid diaphragm
analysis should be completed to determine the loads that are resisted by
the concrete shear walls, remaining masonry shear walls, and the steel
braced frames.
Diaphragm connections may not be adequate to transfer the load to the
shear walls.
Secondary components within the system do not have the shear capacity
to develop the flexural strength of the components.
Steel braced frames may be over capacity.
Glued laminated timber arch members and their connections in three-
hinge arch systems will need further analysis to determine if there are any
possible deficiencies.
Seismic Structural Analysis 3.2
The entire structure was analyzed per the procedures outlined in Chapter 6 and 7
of ASCE 41-13, including the material specific requirements of Chapters 8
through 12. Multiple methods were utilized to evaluate the various structural
seismic lateral systems within the facility. The analysis methods utilized within
the specific areas are defined below.
Area A and B:
Area A was analyzed using Linear Static Procedure 2-D models, a Linear Static
Procedure 3-D model and a Linear Dynamic 3-D model. The 2-D models
included the lateral systems in the transverse and longitudinal directions and the
3-D models encompassed the entire Area A structure. The structure of Area A is
similar to Area B; therefore the findings from Area A will be similar to those of
Area B. Because of this, the analysis findings and retrofit analysis for Area A will
be utilized for Area B as well.
Figure 2 shows a representative 2-D longitudinal frame with the expected
deflected shape shown in Figure 3. Figure 4 shows the 3-D model with the
expected deflected shape in Figure 5. Additional models and calculations can be
found in Appendix C.
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Figure 2 – Longitudinal Concrete Frame 2-D Model
Figure 3 – 2-D Model Deflected Shape
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Figure 4 – Area A 3-D Model
Figure 5 – Area A Deflected Shape
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Figure 6 – Area A Member Unity Check
The Linear Static Procedures used the Equivalent Lateral Force method,
whereas the Linear Dynamic Procedure used a modal response method based
on the previously identified BSE-1N spectral response acceleration parameters.
The models were assessed to determine the probable capacity and behavior of
the entire system. The overall findings and recommendations were developed
from the comparative results of the three modeling techniques. See Appendix C
for calculations and results.
Figure 7 - BSE-1N Response Spectrum
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Area C:
Area C was analyzed using a rigid diaphragm analysis to determine load
distribution to the primary lateral load resisting systems with Linear Static 2-D
models for the primary lateral load system. The system included the CMU
masonry shear walls, the steel braced frames and the wood shear walls added
during the 1993 retrofit. See Figures 8 through 11 for the braced frame and arch
models. See Appendix C for calculations and results.
Figure 8 – Braced Frame Unity Check
Figure 9 – Braced Frame Deflected Shape
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Figure 10 – Glulam Arch Model
Figure 11 – Glulam Arch Deflected Shape
4 Tier 3 Systematic Evaluation Findings
The capacities for the building structural system and individual members were
computed using the methods described above. These results were then
compared to the seismic demands using the Acceptance Criteria as defined in
ASCE 41-13. The acceptance criterion includes variables for the Knowledge
factor and a modification factor to account for the expected ductility at the
selected Performance Level.
The Knowledge factor accounts for the uncertainty in the properties of the
building members. The Knowledge factor for this evaluation was 0.9, due to
gathering material properties from the design drawings only and not conducting
tests to verify the in situ properties. See Appendix C for calculations and results.
Area A and B 4.1
The overall condition of Area A is generally good. The building was inspected
and shows little sign of settlement or deterioration. Although the condition of the
building is good, Area A has numerous seismic deficiencies. The lateral seismic
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force resisting system was found to be highly deficient and with the past
renovations has been compromised with the removal of the masonry infill panels.
The analysis of the different systems generally shows that the members will be
overstressed due to the seismic loads. The structural members were not
detailed in a manner that is acceptable under current design methodology to be
earthquake-resistant and therefore will not behave in a ductile inelastic manner
during an extreme event. Improper dowel lengths, hook lengths and lap splice
lengths can also cause a sudden pull-out failure. Due to the lack of ductility
provided by the lateral force resisting system, the structure has a high risk of
failing in a sudden brittle manner which can cause collapse.
The current design philosophy per ACI 318 is for cast-in-place concrete
structures to act in the nonlinear range with decreased stiffness and greater
energy dissipation, without significant loss of strength. Therefore the system will
retain a substantial portion of its strength into the inelastic range under load and
displacement reversals. This is accomplished by utilizing confining reinforcing
steel such as hoops, ties and stirrups. Lap splices must be of adequate length
and also located in specific locations. The existing structure has inadequate
reinforcing to provide the required concrete confinement and will likely have a
brittle failure.
The specific deficiencies for Area A and B area as follows:
Concrete Moment Frames
Concrete column shear strength is inadequate for columns in tension
The shear capacity of the beams is unable to develop the required
moment capacity. Therefore a brittle failure may occur.
Weak Column-Strong Beam – The moment capacity of many of the
beams is greater than the capacity of the columns.
The column reinforcing is doweled into the foundation but is inadequate to
develop the tensile capacity required. A pull out failure could occur.
The beam top longitudinal reinforcing is not continuous throughout the
frame.
The column tie spacing exceeds d/4.
The majority of the frame beams do not have stirrup reinforcing.
Beam-column joints do not have ties spaced at d/2.
Many of the beams do not have ties at the joint locations.
The secondary components do not meet the reinforcing requirements as
well.
Concrete Shear Walls
The secondary components do not have the shear capacity to develop the
flexural strength and do not meet the reinforcing requirements.
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The coupling beams do not have stirrup reinforcing spaced at d/2.
Concrete Frames with Masonry Infill Panels
The shear stress in the unreinforced masonry infill panels exceeds the
capacity.
The concrete column reinforcing is doweled into the foundation but is
inadequate to develop the tensile capacity required.
The openings in the infill panels do not have trim reinforcing on all sides.
The unreinforced panels do not have the required capacity for out-of-plane
loading.
Area C 4.2
The overall condition of Area C is also generally good. Although the condition of
the building is good, Area C also has numerous deficiencies. The main
deficiency with the differing systems is inadequate strength for the required loads
causing overstressed members.
The specific deficiencies for Area C area as follows:
Concrete Shear Walls
The shear stress in the concrete shear walls exceeds the capacity.
The chord connections to transfer the seismic load to the concrete shear
walls do not meet the required capacity.
Steel Braced Frames
For the Immediate Occupancy performance level, the brace effective area
is less than the brace gross area.
Wood and Light Gauge Steel Shear Walls
The shear stress in the shear walls exceeds the capacity.
Glulam Arches
The glulam arches are overstressed due to the combination of axial load
and bending.
The upper level which was added in 1993 is supported with wood sheathing on
light gauge studs in the north-south direction. Shear walls were not added in the
east-west direction, and it is consequently not adequately supported for lateral
loads in that direction. Shear walls, moment frames or braced frames need to be
constructed to accommodate the loads in that orthogonal direction.
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5 Retrofit Alternatives and Recommendations
Area A and B 5.1
There are numerous retrofit options for the deficiencies of Area A and B. FEMA
547 “Techniques for the Seismic Rehabilitation of Existing Buildings” discusses
the alternatives available for retrofitting common structural systems. It provides
common techniques to mitigate specific deficiencies in various model building
types. Chapters 12 and 15 of the FEMA publication have been included in
Appendix D for the concrete moment frame and infill panel systems.
Rehabilitation can be completed by strengthening the existing elements, adding
new elements such as shear walls and bracing, or a combination of both. The
retrofit method will also be designed to increase the ductility of the structure and
ensure that the connection strength of the diaphragms to the vertical lateral force
resisting systems is adequate.
The strengthening of the concrete elements and masonry infill panels can be
completed by reinforced concrete jacketing, steel plate bonding and jacketing or
Fiber Reinforced Polymer (FRP) jacketing (See Figures 12 - 16).
Figure 12 – Jacketing of Concrete Column
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Figure 13 – Jacketing of Concrete Beam and Column
Figure 14 – Steel Jacketing
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Figure 15 – FRP Jacketing of Column
Figure 16 – FRP Jacketing of Beam
Elements can be added to the structure such as new concrete shear walls,
moment frames or braced frames (See Photos 17 – 20). These elements are
integrated into the structure to increase the strength and ductility.
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Figure 17 – Retrofit Concrete Shear Wall
Figure 18 – Steel Moment Frame Retrofit
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Figure 19 – Retrofit Braced Frame – Exterior
Figure 20 – Retrofit Braced Frame - Interior
Jacketing is the least intrusive manner of retrofitting the structure, as it uses the
existing elements and only increases their size. The approach of adding lateral
elements can be more intrusive and affect the overall use of the building. The
added shear walls, moment frames, or braced frames can interfere with the
existing use of the facility. The current use of the facility requires open areas for
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court rooms and offices and thus adding structural elements may compromise
the usage of the facility.
Area C 5.2
The main deficiencies in the gym area would require adding additional concrete
shear walls, strengthening the glulam arches, strengthening the existing wood
shear walls and adding shear walls, moment frames or braced frames in the
east-west direction. These retrofits would be less invasive then those of Areas A
and B, but will still require significant rehabilitation.
Recommendations 5.3
It is recommended that the lateral force resisting system of Area A and B be
retrofitted with a reinforced concrete jacketing or reinforced shotcrete jacketing.
This has generally been proven to be an adequate repair at a lesser cost than
other alternatives. The masonry infill panels are also recommended to be
strengthened with reinforced concrete jacketing or reinforced shotcrete.
The FRP jacketing is also a potential retrofit option, but should be researched
further to determine the cost efficiency. The FRP option is superior in the aspect
that it will not increase the mass and weight of the structure.
It is recommended that Area C be retrofitted by adding additional concrete shear
walls to the exterior and strengthening the diaphragm chord connections to the
concrete shear walls. The glulam arches should be strengthened using steel
members and additional moment frames should be added to support the upper
level in the east-west direction. The wood shear walls will also require
strengthening by additional nailing and revised holdowns.
6 Opinion of Probable Cost
An Opinion of Probable Cost was completed to determine the cost range for the
required structural retrofitting of the facility. This was completed based on a
square foot cost. Costs were developed using FEMA-156 and data from past
evaluations completed in Portland, Oregon and California. It should be noted
that these costs are for the structural portion of the retrofit only and do not
include any costs for mechanical, electrical, plumbing or other miscellaneous
items.
FEMA-156 “Typical Costs for Seismic Rehabilitation of Existing Buildings”
provides structural rehabilitation costs compiled from data collected from a total
of 2088 retrofit projects. The square foot costs were normalized to 1993 dollars
for the State of Missouri to represent a national average. The square foot costs
were developed based on the FEMA Building Type, level of seismicity and size of
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project for the Life Safety performance objective. The 1993 cost values for this
report were normalized to 2017 dollars.
The FEMA-156 cost values were then compared to recent studies completed in
Portland, Oregon and California. The FEMA Life Safety level costs were as
follows:
Level of Seismicity 1993 S.F. Cost 2017 S.F. Cost
Very High Seismicity $25.04 $31.83
High Seismicity $18.89 $42.19
“Portland’s Unreinforced Masonry Seismic Retrofit Project” report by Walt
McMonies and Lane Powell was also reviewed for cost data on similar projects.
There findings for hard costs were $35 to $40 per square foot for Life Safety and
$63 to $74 for Immediate Occupancy. They also recommended adding $30 per
square foot for soft costs.
A report was also completed by David Bell of PJHM Architects, Inc. on “How to
Evaluate Buildings and Determine Retrofit Costs”. In the report the California
Division of the State Architect recommends $60 per square foot for retrofit.
FEMA’s normalized costs adjusted to the Immediate Occupancy level align with
the recommendations of the other reports, therefore $60 per square foot plus $30
per square foot for soft costs were used. The cost of $40/SF and $30/SF were
used for the Life Safety level to align with the normalized FEMA values. The
level of retrofit required for Area C will be less than Areas A and B, thus a
decreased cost was used in that area.
With the use of the above values, overall project costs were developed for the
Life Safety and Immediate Occupancy levels. The Opinion of Probable Costs
can be seen in Figures 21 and 22. Although the cost estimates indicate a
specific cost, at this level of the evaluation they should be viewed as approximate
ranges. Thus, the cost estimate for the Life Safety retrofit should be considered
in the range of $5.5M and $7M and the Immediate Occupancy would be in the
range of $7m and $8.5M.
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Figure – 21 – Life Safety Retrofit Opinion of Probable Cost
Figure 22 – Immediate Occupancy Opinion of Probable Cost
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7 Tier 3 Evaluation Summary
The ASCE 41-13 Tier 3 Systematic Evaluation for the Law and Justice Building
clearly identified numerous seismic deficiencies for the structure. Many of the
deficiencies were related to inadequate strength and lack of ductility due to
insufficient reinforcing details. This applied to the concrete moment frames,
concrete moment frames with masonry infill panels, concrete shear walls, light
gauge steel shear walls and glulam arches. There were also deficiencies
identified with diaphragm connections and steel braced frame net areas.
It is recommended that the lateral force resisting system of Area A and B be
retrofitted with a reinforced concrete jacketing or reinforced shotcrete jacketing.
The masonry infill panels are also recommended to be strengthened with
reinforced concrete jacketing or reinforced shotcrete. FRP jacketing is also a
potential retrofit option, but should be researched further to determine the cost
efficiency.
It is recommended that Area C be retrofitted by adding additional concrete shear
walls to the exterior and strengthening the diaphragm chord connections to the
concrete shear walls. The glulam arches should be strengthened using steel
members and additional moment frames should be added to support the upper
level in the east-west direction. The wood shear walls will also require
strengthening by additional nailing and revised holdowns.
With the use of the previously defined retrofit values, overall project costs were
developed for the Life Safety and Immediate Occupancy levels. The cost
estimate for the Life Safety retrofit should be considered in the range of $5.5M
and $7M and the Immediate Occupancy would be in the range of $7m and
$8.5M.
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Appendix A – Building Structural Alterations
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Appendix B – Tier 3 Seismic Information
www.seaeng.com Engineers and Land Surveyors
851 Bridger Drive, Suite 1, Bozeman, MT 59715 | phone: 406-522-8594 | fax: 406-522-9528
L:\0901-0950\0939-Gallatin County\-03817 L&J Structural Study\Phase 2\Study and Report\L&J - Tier 3 -
Systematic Evalaution Phase.docx 3
May 2017
Law and Justice Center – Tier 3 – Systematic Evaluation Phase
ASCE-41-13
Risk Category: IV – Essential Facility
Performance Objective (Section 2.2): Immediate Occupancy Performance Level (1-B)
Building Performance Level: S-1, N-A
Seismic Hazard: BSE-1N
Level of Seismicity: High – SDC D
Building Type:
Area A (north half of the west wing): C1, C3 and C3a
Area B (south half of the west wing): C1, C2, C3, and C3a
Area C (east wing – original gymnasium): C2, C2a, C3, C3a, S2, S2a and W2
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Appendix C – ASCE 41 Tier 3 Evaluation Calculations
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Appendix D – FEMA 547 Information