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Rebecca Dick
Structural Option
Dr. Memari
Spring 2012 Senior Thesis
April 4, 2012
Blast Design and Analysis
National Business Park- Building 300
300 Sentinel Drive
Annapolis Junction, MD, 20701
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Acknowledgments
A very special thank you Dr. John O. Hallquist, President, Livermore Software Technology Corporation
(LSTC), and Marsha J. Victory, President, FEA Information Inc, for providing me access to the LS-DYNA
finite element software for free for my senior thesis and to Gunther Blankenhorn and Todd P Slavik for
the invaluable technical support and troubleshooting they provided.Additional thanks to Michael Baker, Jr., Inc. for the use of National Business Park- Building 300,
especially Mr. Erik Spicker.
Special Thanks to:
My Family:
Thank you to my dad for always answering my questions for the last five years. Thank you to my mom
for listening to me complain all the time and putting up with my breakdowns. Thank you to my brother
for giving me academic competition.
Penn State Faculty:
Dr. Memari
Dr. Hanagan
Dr. Parfitt
Ryan Solnosky
My Friends:
Brian Rose
Dave Tran
Mike Kostick
Ryan Blatz
Liz Kimble
Rob Livorio
RJ Fazio
The past five years have been a blast and I couldn’t have made it through without you guys. You’ve kept
me as close to sane as any AE can be through all the crazy projects, late night study sessions, and post-
exam celebrations. I will always love you guys!
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Table of ContentsAcknowledgments ......................................................................................................................................... 2
Special Thanks to: ................................................................................................................................. 2
Executive Summary ....................................................................................................................................... 6
National Business Park- Building 300 ............................................................................................................ 8
Structural Background .................................................................................................................................. 9
Foundations .............................................................................................................................................. 9
Floors....................................................................................................................................................... 12
Load Path ............................................................................................................................................ 12
Columns .................................................................................................................................................. 13
Lateral System ......................................................................................................................................... 14
Load Path ............................................................................................................................................ 15
Impact of Lateral System on Calculations ........................................................................................... 16
Design Codes ............................................................................................................................................... 17
Material Properties ..................................................................................................................................... 18
Original Design ........................................................................................................................................ 18
Reinforcement: ................................................................................................................................... 18
Structural Steel: .................................................................................................................................. 18
Metal Deck: ......................................................................................................................................... 18
Concrete: ............................................................................................................................................. 18
Blast Redesign ......................................................................................................................................... 19
Reinforcement: ................................................................................................................................... 19
Structural Steel: .................................................................................................................................. 19
Metal Deck: ......................................................................................................................................... 19
Concrete: ............................................................................................................................................. 19
Gravity Loads............................................................................................................................................... 20
Dead Load ............................................................................................................................................... 20
Live Load ................................................................................................................................................. 20
Snow Load ............................................................................................................................................... 20
Structural Proposal ..................................................................................................................................... 21
Blast Design ................................................................................................................................................. 22
Procedure .................................................................................................................................................... 23
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Blast Load Determination ........................................................................................................................... 24
Column Design ............................................................................................................................................ 28
Beam Design ............................................................................................................................................... 30
Girder Design .............................................................................................................................................. 32
Slab Design .................................................................................................................................................. 33
Moment Connection Design ....................................................................................................................... 36
Final Design ................................................................................................................................................. 39
LS-DYNA Modeling ...................................................................................................................................... 40
Comparison of Results ................................................................................................................................ 44
Additional Comments and Conclusion ........................................................................................................ 48
Lateral System Implications .................................................................................................................... 48
Effects on Foundations ........................................................................................................................... 48
MAE Requirements ..................................................................................................................................... 49
Breadth Topic I: Site Redesign .................................................................................................................... 50
Breadth Topic II: Façade Redesign and Heat Transfer ................................................................................ 54
Façade Design ......................................................................................................................................... 55
Heat Transfer .......................................................................................................................................... 57
Cost Estimates ............................................................................................................................................. 61
Conclusion ................................................................................................................................................... 63
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Executive Summary
National Business Park- Building 300 is a seven story office building located in Annapolis Junction,
Maryland. It was designed in 2007 and construction was completed in 2009. The structure of NBP-300
is composed of a composite steel system and utilizes four eccentrically braced frames for the lateral
system located at the core of the building.
National Business Park- Building 300 was not designed to resist blast, and therefore, were an attack
made on the building, heavy structural damage would likely result. For this reason, it will be assumed
that NBP-300 will be redesigned as a high risk building for terroristic threats, and as such would be
required to meet certain criteria for blast loading. Designing for interior blast has many challenges, as
well as many solutions. There is no clear “cookie-cutter” method to designing for blast, which makes it
one of the most intriguing and interesting new topics of study. Blast design isn’t new per say, but in the
realm of structural design, it has only be in consideration for the last 50 years or so. Although
progressive collapse is a major issue when designing for blast, the scope of this redesign will be limitedto strength factors only due to time restraints, and redundancy of design will be ignored.
A specific situation has been created for the design. It can be assumed that the greatest threat in terms
of explosives will be a briefcase sizes device detonated in the interior of the lobby on the second floor.
The UFC -340-02 documents outlining blast requirements were used to identify threat levels, design site
security, and find blast loads. The blast load from this situation was calculated and a typical bay located
at the lobby location was designed to withstand the blast loading found. Additionally, the façade of
NBP-300 was redesigned to allow venting of the interior during the blast. The large percentage of glass
currently on the façade could potentially be harmful to occupants when the façade fails.
LS-DYNA Blast Modeling software was used to analyze a critical portion of the original and redesigned
structure. A comparative study was completed where the assumed explosive for this situation was
detonated in the original LS-DYNA model and the redesigned LS-DYNA model. The intent was to
minimize structural damage as much as economically possible through this redesign. By comparing the
original structure to the redesign it became apparent that the redesign was highly conservative, but
overall, withstood the blast load and incurred very little damage.
In addition to the blast design and analysis, a site redesign was completed. Also, a façade breadth was
completed, including a façade redesign with anchored “blowout panel” and a heat transfer study of the
new façade.
MAE coursework was incorporated into several aspects of the redesign for NBP-300, including building
modeling techniques (AE 597A), a moment connection design (AE534), and a façade design (AE542).
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Going into this thesis design, the following goals were set forth and achieved:
Design a typical beam, girder, column, moment connection, and floor system
Use a finite element analysis software (LS-DYNA Blast) to model the effects of blast in theoriginal structure and redesigned structure, and compare the results
Show that designs using hand calculations are overly conservative
Redesign the site of NBP-300 to mitigate large exterior blasts
Redesign the façade of NBP-300 to allow venting of the interior during an interior explosion
Calculate heat transfer through the new façade and determine if the new design is acceptable
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National Business Park- Building 300
National Business Park- Building 300 is an office building located in an industrial park in Annapolis
Junction, Maryland. Owned by COPT, the seven story office building, which has an additional
mechanical penthouse on the roof, was designed in 2007 and construction was completed in 2009. As
part of an industrial park, the architecture was intended to complement the existing offices in the
surrounding area. Shown below in Figures 1 and 2 is the building footprint of National Business Park-
Building 300 and a satellite view of the building, respectively.
NBP-300 is a 212,019 gross square foot, 116.92’ tall, composite steel framed building that utilizes braced
frames for its lateral system. Foundations consist of strip and spread footings, but since the first story is
only a partial floor plan, and is sub-grade at a few locations, footings are located below both the first
and second stories at their respective locations. The façade system is composed of a glass and precast
concrete curtain wall that is tied into the structural system at each floor level.
Figure 1: NBP-300 Footprint on Site Figure 2: Satellite View of NBP-300 provided by
Courtesy of Baker and Associates ©Google Maps, 2011
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Structural Background
Foundations
Since the first floor is only a partial floor and the grading on the site is such that the second floor is at
ground level at the main entrance, foundations occur below both the first and second floors at the
respective areas where no preceding floor exists below. Figure 3, on the following page, outlines the
area of the partial first floor. Figure 4, also on the following page, provides more detail by showing a
section cut in the North-South direction, which shows the partial first floor and the slab on grade and
foundations on the second floor. Additionally, two side of the first floor will be supported by basement
walls. These walls are reinforced with #7 bars at 10” on center, each face, vertically, and #5 bars at 12”
on center, each face, horizontally. These walls will see lateral pressure from soil, which was noted to be
60 psf per foot of depth in the structural notes.
The foundations of NBP-300 consist of strip and spread footings with a 5” slab-on-grade on the partial
first floor and on the second floor where it does not sit over the first floor, and were designed to meetthe suggestions set forth in the geotechnical report prepared by Hillis-Carnes Engineering Associates,
Inc. 6x6 W2.0xW2.0 Welded Wire Fabric was used in all slabs-on-grade. A bearing pressure of 3.5 ksi
was required for all foundations. 4” of compacted backfill meeting AASHTO 57 course aggregate was
also a requirement below the slabs-on-grade.
The strip and spread footings are located around the perimeter of the partial first floor and at the
perimeter locations on the second floor that contain the slab on grade. Additionally, interior columns
are supported by spread footings. These range in size from 8’ square to 19’ square, depending on the
location and the load. The depths of the spread foundations also vary between 24” to 46”. A
5’-0”x5’-0” footing at piers is typical, reinforced with #5@12” on center, each way.
Additionally, the mechanical room on the first floor is sunken 3’ below the standard floor level which
required the foundations to be stepped down at the transition locations.
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Figure 3: Outline of Partial First Floor Plan on Foundations, Courtesy of Baker and Associates
Figure 4: Building section showing partial first floor and slab on grade at second floor,
Courtesy of Baker and Associates
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Floors
NBP-300 was constructed using a composite steel system. For the floors, this entailed the use of
cambered composite beams and girders. A 3 ½” lightweight concrete topping (117 pcf) on 3”x20 gage
metal floor deck, bonding type, was used on each elevated floor for the composite slab, reinforced with
6x6 W2.0xW2.0 welded wire mesh. Additional reinforcement was required over filler beams and girders
along column lines. This additional reinforcement consists of #3 bars at 18” on center, 8’-0” long.
Composite action is obtained through the use of ¾” diameter, 5 ½” long shear studs spaced equally
along beams. See Figure 5, below, for a typical section cut through the composite floor system.
Floor beams vary in size and vary per floor, but are cambered 0”, ¾”, or 1”, depending on the location.
The exterior girders also vary in size, but are not cambered. Beams typically span 35’ at 10’ on-center,
while girders typically span 30” at 35’ on-center.
Load Path
Gravity loads on each floor are transferred from the composite slab to the beams. The load is
then transferred to the girders, which then transfer the load to the columns. The gravity loadsterminate at the foundations at the second level or at the partial first level.
Figure 5: Typical Composite Floor System,
Courtesy of Baker and Associates
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Columns
Wide flange columns are used throughout NBP-300. Although the weight of the columns differs
throughout the building and across floor levels, most wide flanges are W14 and all conform to ASTM A-
992 Grade 50 steel requirements. Splices occur at levels 4 and 6 for most columns. This information is
presented in a column schedule, of which a partial view can be seen in Figure 6, below. At the
penthouse level, square HSS posts are used around the perimeter of the enclosure to support the
penthouse cladding.
Base plates are used to connect the steel columns to the foundations or shear walls located on the first
floor. The base plates vary in size, but conform to ASTM A-36 type steel.
Figure 6: Partial Column Schedule,
Courtesy of Baker and Associates
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Lateral System
The main lateral system used in NBP-300 consists of four different eccentrically braced frames. These
occur at column lines “D”, “E”, “4”, and “11”, each spanning about one full bay (See Figure 9 on the
following page). This provides two lateral bracing frames in each direction. The frame at column line
“D” begins on the first floor, while the other three frames begin on the second floor, supported by
concrete shear walls on the first level. Two wind bracing frames are shown below, in Figures 7 and 8, to
show the difference in height. The shear walls at the base of the three shorter frames are 1’-2” thick
and are reinforced with #7 bars at 10” on center, each way on each face of the wall.
HSS tubes are used for the bracing, and vary in size from frame to frame, but conform to ASTM A-500
Grade C steel and have a yield strength of 46 ksi. All connections in the braced frames are slip-critical.
Shear studs at wind bracing beams occur at 12” on center, and are ¾” in diameter and 5 ½” in length. At
the base plates, an 8x4x3/4 angle at 1’-6” in length is used on each side of the gusset plate to resist
100% of the design shear. Additionally, 7/8” diameter by 8” long shear studs are used at the shear wall
connections for the three elevated braced frames.
Figures 7 and 8: Wind Braced Frames, Courtesy of Baker and Associates
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Figure 9: Location of Braced Frames at Core of building, Courtesy of Baker and Associates
Load Path
As wind lateral forces are applied to NBP-300, they are transferred from the façade to the
composite floor system through bearing connections. From there, the load is transferred from
the floor system to the four braced frames, which travel through the height of the building to
foundations and shear walls on the first and second floor. Where braced frames connect to
shear walls, the load is then resisted by the shear wall and ultimately transferred to the
foundations below.
Ground motion due to seismic loads is resisted by the foundations, first floor shear walls, andbraced frames that run the height of the building. As each floor is seismically loaded, the force
is transferred to the braced frames, which transfers the load to the foundations and shear walls
at the base of the building.
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Impact of Lateral System on Calculations
The lateral system used in the design of NBP-300 consists of four eccentrically braced frames. In
ASCE 7-05, this system provides a Response Modification Coefficient of 7, but since the
structural documents provided for NBP-300 specifically state that seismic resistance was not acontrolling factor in design (see Figure 10 below), an R value of 3 was used instead, to allow
comparison between the calculations presented in this document and the design criteria of NBP-
300. This assumption effected the seismic calculations, namely the value of the seismic
response coefficient. By using R=3, a higher base shear was calculated, making this a
conservative assumption for design. In regards to detailing, this system may be more
complicated and expensive. Eccentrically braced frames are used more in regions with high
seismic activity, but by using an R=3, the stability will be affected during design and will have to
be compensated through other detailing methods.
Figure 10: Response Modification Coefficient Assumption,
Courtesy of Baker and Associates
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Design Codes
National Business Park- Building 300 was designed in 2007 and constructed in 2009. At this point in
time, the following codes were used to complete the design of the project:
International Building Code (IBC) 2003 (with local amendments for Anne Arundel County,
Maryland)
The Life Safety Code, 2006 (NFPA 101)
ASCE 7-02
AISC, 13th Edition
ACI 318-02
AISI Specification for the Design of Light Gage Cold-Formed Structural Steel Members and the
Steel Deck Institute’s Design Requirements
Specifications for Masonry Structures, ACI 530.1/ASCE 6/TMS 602-92
Structural Welding Code, 2006, D1.1
In the redesign, the codes listed below were used to complete the analysis of National Business Park-
Building 300.
International Building Code (IBC) 2009
ASCE 7-05
AISC, 13th Edition
ACI 318-05
Vulcraft 2008 Decking Manual
UFC-340-02
AISC Seismic Design Manual
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Material Properties
Original Design
Reinforcement: Reinforcing Bars ASTM A615, Grade 60
Welded Wire Fabric (WWF) ASTM A-185
Reinforcing Bar Mats ASTM A184
Lap Splices ACI 318
Structural Steel:
Grade 50: ASTM A992, Grade 50, Fy= 50 ksi
HSS Pipes: ASTM A500, Grade C, Fy = 46ksi
Steel Tubes: ASTM A500, Grade B, Fy = 46ksi
All other steel: ASTM A 36, Fy = 36 ksi
Bolts: ASTM A325, with threads included in shear planes, ¾”
or 7/8” diameter
Shear Studs: ¾” diameter x 5” long, uniformly spaced at 24”
maximum
Metal Deck:
Floors: 3”x20 gage, bonding type
Roof: 3”x22 gage
Concrete:
Minimum Concrete Compressive Strengths (f'c)
Member 28 Day Strength (psi)
Elevated Slabs 3500
Slab-on-Grade 3500
Walls, Piers, and Grade Beams 4000
Interior Concrete Topping 3500
Concrete Exposed to Freezing 4500Grout 3000
All Other Concrete 3000
Table 1: Minimum Concrete Compressive Strengths
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Blast Redesign
The following material properties were used in the redesign:
Reinforcement: Reinforcing Bars ASTM A615, Grade 60
Welded Wire Fabric (WWF) ASTM A-185
Lap Splices ACI 318
Structural Steel:
Grade 50: ASTM A992, Grade 50, Fy= 50 ksi
All other steel: ASTM A572, Grade 50, Fy = 50 ksi
Bolts: ASTM A325, with threads included in shear planes, 1.5”
diameter
Metal Deck: Floors: 3VLI16, composite
Concrete:
Minimum Concrete Compressive Strengths (f'c)
Member 28 Day Strength (psi)
Elevated Slabs 4000
Slab-on-Grade 4000
Walls, Piers, and Grade Beams 4000
Interior Concrete Topping 4000
Concrete Exposed to Freezing 4000
Table 2: Minimum Concrete Compressive Strengths
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Gravity LoadsUsing IBC 200, ASCE 7-05, and estimation, the dead, live, and snow loads were calculated for NBP-300.
Tables 2, 3, and 4 that follow show the loads used for the analysis presented in this paper compared to
the loads used in the original design of NBP-300.
Dead Load
Superimposed Dead Loads
Area Design Load
Floors 15 psf
Roofs 15 psf
MEP 20 psf
Table 3: Superimposed Dead Loads
Live Load
Live Loads
Area Design Load ASCE 7-05 Load
Floors (including partition load) 100 psf 80 + 20 psf
Mechanical Room 125 psf -
Elevator Machine Room 150 psf -
Penthouse Floor 150 psf -
Stairs 100 psf 100 psf
Slab-on-Grade 150 psf -
Screen Enclosure and Roof Area 60 psf 60 psf
Table 4: Live Loads
Note: (-) signifies that there was no recommended value from ASCE 7-05 for the specified loading
condition and the design load was assumed to be correct.
Snow Load
Snow LoadsLoad Type Design Load ASCE 7-05 Load
Roof Snow Load 20 17.5
Drift Load Not available 81.94
Table 5: Snow Loads
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Structural Proposal
National Business Park-300 was designed initially as a typical office building. For the purpose of this
thesis, it will be assumed that National Business Park- Building 300 will be designed as a Federal office
building with the potential to be a target of terrorism. This means that, to protect the life and safety of
the occupants of NBP-300, it will be required to be designed for blast loading.
The first step in designing for blast is to determine the type and level of threat expected. It was decided
that the site would be redesigned and the security of the site increased to eliminate a vehicular
explosion from being the controlling blast load. It was then determined that the controlling load would
be a small-device, and that it most likely would be an interior explosion.
Using these specific design constraints, a typical bay of National Business Park- Building 300 was
redesigned to withstand the blast load. This includes the design of a column, a beam, a girder, and the
floor slab. A typical moment connection will also be discussed. Due to time constraints, progressive
collapse and a lateral system analysis were not completed, but would be investigated in depth if given
more time.
The intent of this redesign is to show a difference in the amount of structural damage between a
building designed for blast and a building not designed for blast, and to determine the effectiveness of
minimizing structural damage using blast design and analysis. This thesis will also look at the
effectiveness of modeling only critical sections of a building designed for blast. This will be achieved
through the use of LS-DYNA Blast Modeling software, a finite element analysis program. Comparisons
between the two structures and their reactions to an explosive event will be discussed in detail, and
through design and analysis, it will be shown that the linear elastic method is highly conservative.
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Blast Design
Until the 1960’s, blast design was reserved for facilities where accidental or chemical explosions could
occur. Blast design was not considered for ordinary structures. In the 1960’s, though, design guides for
blast started to emerge, mostly for buildings with the potential for chemical explosions. In today’s
world, terrorism is an unfortunate reality, and designing for the safety of the occupants in high risk
structures has become more important. After the Oklahoma City bombing in 1995, blast design gained
significant popularity as a design consideration for life safety. Since 9-11, blast design has become a
well-sought after design not only for federal and military building, but other high risk buildings such as
hospitals, banks, and international business buildings, to name a few, and is an issue of life safety.
Blast design has to take into consideration both impact loads from the initial wave front of the blast, and
additional time-dependent pressures, which can occur due to thermal effects behind the wave front.
Reflected pressures must be taken into account as well as ventilation to relieve built up pressures in
confined explosions. In some cases, shrapnel from the explosive container may act as a projectile, andcould cause serious damage, such as breaching.
Much of blast design is based on the members behaving plastically. Therefore, there are strict limits on
their ductility ratios and support rotations. The ductility ratio is “an approximate measure of plastic
strain based on the assumption that the curvature in the maximum moment regions increase
proportionally with deflection after yielding and plane sections remain plane,” as stated in the
“Handbook for Blast Resistant Design of Buildings.” The limit on the ductility ratio makes sure the
member’s plastic deflections are within the allowable range. The limit on the support rotation
maintains that tension membrane action that may develop in a member will be limited so as not to
cause connection failures.
Due to the unpredictable nature of blast design, often times it is overly conservative. Sometime,
though, this over conservative nature leads to unreasonable designs or costs. For that reason, structural
elements are allowed to be damaged, as long as collapse is prevented.
The principles of blast design were researched throughout this redesign and will be presented through
calculations, diagrams, tables, and figures throughout this thesis.
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Figure 11: UFC-340-02 Cover Page
Procedure
The first step in designing for blast is to decide what the maximum threat on the building will be during
the life of the building. As stated in earlier section, in this case, it was determined that an interior blast
from a briefcase sized explosive would be the design scenario. To eliminate the possibility of any other
type of blast controlling, both building setback and site control had to be determined. This information
will be presented in the Site Redesign Breadth.
Next, the blast load was determined by using
engineering judgment to estimate the type of
explosives in the blast. In this scenario, C-4 was used to
estimate the blast load. By following the UFC-340-02
(seen to the right in Figure 11) prescribed technique,
blast pressures were determined for the specific
situation set forth in the problem statement.
After determining blast loads, the member designs
were completed. A typical column, an interior beam,
the exterior girder, and the floor slab were designed for
the determined blast pressures. Plasticity was
considered in each design. Additionally, a moment
connection design was investigated.
After the hand calculations were completed for the
member designs, LS-DYNA was used to build a partial
model of NBP-300. A 3 bay by 3 bay by 3 story model of
NBP-300 was built to demonstrate several findings.
Firstly, it was a goal of this thesis to show that since the
stress in structural members decreases significantly as distance from the bay of detonation increases it
is not necessary to show an entire model. The blast forces may not even be significant in bays that are
two or three bays from the initiation of the blast in some cases. Additionally, due to the sophistication
of the LS-DYNA program and the tedious nature of the input, it was deemed not in the scope of this
thesis to build the entire model.
All hand calculations, Excel spreadsheets, tables and figures used in the design process will be presented
in the appendices of this document, and will be referenced in the detailed explanations in each section.
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Figure 12: 3D Blast Wave Projections
Blast Load Determination
Blast loads are pressure waves caused by the rapid
release of energy during a chemical reaction. The
wave propagation is spherical in nature and
dissipates with distance from the blast initiation,
which can be seen in Figure 12 to the right. Although
the spherical nature of a blast wave will cause
differential pressures along the length of certain
elements, such as columns, it can be assumed to be
linear for simplification of design and analysis.
Generally, the design process using a single degreeof freedom method is conservative, so this assumption will still provide a valid design.
The first step of the actual design process in blast design requires that the blast event load be
determined. As C-4 was assumed to be the explosive compound being used in this analysis/redesign, a
determination of a reasonable weight of the explosive needed to be calculated. Since C-4 has properties
similar to clay, it was assumed that about 50 pounds of C-4 could fit inside a large briefcase or small
rolling suitcase. Since NBP-300 is an office building, it was assumed that the explosives would have to
be camouflaged to fit into the everyday environment of the workspace, hence a briefcase or a small
business suitcase.
The weight of C-4 then needed to be converted into equivalent TNT weight. Not a lot of research has
been done with explosives other than TNT to date, so all the tables and charts in the UFC used in blast
design were designed around data collected with TNT testing. Much is known about the explosive
power of this compound, but not of many others. Therefore, the weight of actual explosives assumed in
this scenario had to be converted into equivalent pounds of TNT. The conversion was performed by
dividing the weight of C-4 by the weight conversion factor found in Table 6.1 of “The Handbook for Blast
Resistant Design of Buildings,” and an excerpt from the table can be seen in Figure 13 on the following
page. The equivalent mass for pressure was used since design pressures would be the critical values for
the structural design.
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Figure 13: C-4 Equivalency Conversion Factors, from
“The Handbook for Blast Resistant Design of Buildings”
Figure 14: Simplified Floor Plan of Lobby Area
with members to be designed highlighted
The equivalent weight was found to be 36.5 pounds of TNT.
Next, the scaled distance needed to be found, which is representative of the front of the pressure wave.
The equation was used to find the scaled distance, which equaled to 4.5 ft/lb1/3
assuming a
standoff distance of 15 feet since that would be the average distance of the explosive to the closest
structural elements in the lobby. See Figure 14 below for a simplified floor plan of the lobby area. From
this information the peak incident overpressure value of 50 psi was found using Figure 6.6 of “The
Handbook for Blast Resistant Design of Buildings”, which can be found in Appendix B.
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From these values the peak reflected pressure was found using the UFC figures. Interpolation between
Figures 2-100 and 2-97 provided a peak reflected pressure of 117 psi. Peak reflected pressure is
important in confined explosions because as the wave front encounters barriers, some of the pressures
are reflected off these materials, thereby increasing the pressure created by the blast. This is a critical
component for determining design loads.
Additionally, the value was found similarly by interpolation between Figures 2-149 and 2-146to give a value of 81 psi-ms/lb1/3. These values were then used to find the effective duration of the blast
from the UFC. An effective duration of 4.6ms was calculated.
This is only half of the battle, though. Since it is assumed, for the purpose of this thesis, that the
explosion will be a confined event, the gas pressure must also be calculated to account for the pressure
build up behind the initial front that occurs during an explosion due to the heat released during the
explosion. Gas pressure loading density was calculated by dividing the equivalent weight of TNT by the
free volume of the space. Then, Figure 2-152 of the UFC was used to determine the peak gas pressure.Additionally, the scaled gas impulse was found using Figure 7-15 of “The Handbook for Blast Resistant
Design of Buildings.”
No fragmentation was accounted for in the determination of blast loads because it was assumed that
debris would be negligible. As stated previously, the explosives would likely be contained in a briefcase
or suitcase, which is assumed to disintegrate from tremendous heat and pressure at the initiation of
blast.
A summary of the pressure and impulse design values are summarized in Table 6 on the next page and a
diagram of the bilinear pulse blast loading expected can be seen in Figure 15 on the next page. The full
calculations are provided in Appendix B.
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Figure 15: Peak Reflected Pressure and Peak
Gas Pressure vs. Time
Table 6: Summary of Blast Load Data
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Column Design
In blast design, there are many additional factors that affect the design process as compared to a
simpler design for service loads only. Certain ductility requirements must be met. Additionally, there
are both dynamic increase factors and overstrength factors that have to be considered during design.
The dynamic increase factors account for the increased yield and tensile strengths of steel due to rapid
loading.
The overstrength factor accounts for the fact that steel actually has a higher yield stress than specified
by the AISC. The Department of Defense Explosives Safety Board allows the use of this higher yield
stress in design and analysis.
There is an additional load combination to be checked, also: 1.0B+1.0D+0.25L. Since the controlling
load combination in the original design was 1.2D+1.6L for the gravity system, this was again used as the
controlling gravity load. Both load combinations were checked to determine the overall controlling
design load for the column.
In the original design, all connections were shear connections. As stated previously, the lateral system
was composed of four eccentrically braced frames, so the columns in the lobby took no lateral load as
they were not part of the original lateral system. Although the redesign requires all connections to be
moment connections, the controlling load combination for blast does not require other lateral loads to
be accounted for due to the probability of having maximum blast load simultaneously with maximum
wind or earthquake loads being very minimal. Therefore, the only lateral load applied to the column
was the blast load.
Another assumption made was that the column would behave plastically during the blast loading. Thisallows the use of higher allowable strength values described previously.
To begin the design, several more assumptions had to be made. Firstly, the column was assumed to be
pinned-pinned. This assumption follows the procedure set forth in the UFC to allow for more simplified
calculations in the linear elastic analysis procedure. Additionally, due to the orientation of the columns
in the bay, it was assumed that only the flange would be loaded during the blast. Realistically, the load
would be distributed to both the web and the flange as it would originate at about a 45 angle to the
flange face.
Finally, it was assumed that the 117 psi peak reflected pressure would be the controlling pressure in this
design. The blast pressures were determined assuming that the explosion would detonate in the center
of the bay at floor level. As stated previously, the relationship between pressure and distance is not
linear, and the closer the blast is to a structural element, the higher the blast and impulse on that
member. Although the space will be fully vented and the reflected pressure is unlikely to ever reach 117
psi, the possibility of the blast being detonated much closer to the column exists. This would inflict the
most stress and have the highest probability of damaging the structure, so the 117 psi was used to
account for the possibility of this situation. This may be conservative, but column failure could result in
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Figure 16: 3D model of typical bay with column called out
progressive collapse of the structure or “pancaking” of floors from above, so it is important to design the
column to withstand a direct blast load.
Once these assumptions were
established, the distributed and axial
loads on the column could be calculated.Then the maximum moment and shear
values were calculated. An unbraced
length of 15’ was used. The dynamic
yield strength was calculated by
multiplying the 50 ksi yield strength by
both the dynamic increase factor for yield
and the overstrength factor to get 71 ksi
yield strength. A preliminary section was
selected based on the required section
modulus, calculated by dividing themaximum moment by the yield strength,
and the requirement that bf /2tf ≤7. A
W14x159 was found to be the smallest
section that met the required 8.64 in3
section modulus and the compact section
criteria.
The W14x159 was then analyzed to
determine if it met all the requirements for blast. This included checking the d/tw ratio, web shear, the
plastic section modulus, plastic moment, plastic axial load, slenderness ratio, allowable axial stress,allowable moment, and the Euler buckling load. Modified interaction equations for blast loading and
plastic behavior were used to account for the combined axial and bending. These calculations can be
found in Appendix C.
It was determined that the member met all the design requirements, and so a W14x159 was used as the
typical column in the final design. Figure 16 above shows a typical column for the redesign.
Additionally, after designing a typical beam and girder, the column was again checked to make sure it
had the capacity for the transferred elastic moment from the moment connections in each frame. It
was determined to be adequate and a W14x159 was used as the column members in the LS-DYNA
model, which will be discussed further in later sections.
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Figure 17: 3D model of typical bay with beams called out
Beam Design
As for the column design, some assumptions
had to be made before jumping right into
the design process. The beam was assumed
to be simply supported with a maximum
support rotation of 2. Additionally, it was
assumed that the blast load would only act
over the width of the flange of the beam.
This system was not designed as a composite
system, so tributary uplift between beams
would not be an issue. Had the system been
designed as a composite system, the uplift
on the floor slab from the blast would be
transferred to the beams, and the beams
would have to be designed to withstand the
larger blast load. Finally, it was assumed
that the pressure-time loading on the beam
would be the most critical. The reason for
this is that the longer duration will have an
overall larger effect on the structure.
Additionally, since the probability of the space reaching 117 psi is minimal it can be considered not to be
the most critical condition.
Two different bay configurations were designed. Initially it was believed that using three infill beams asopposed to two would allow a significant decrease in the weight of the system. Since only the flange of
the beams were assumed to be taking the blast load (not a tributary width of floor slab transferring the
load to the beam as with composite systems), it was believed that a beam with a smaller flange width
would carry less blast load and could therefore be designed as a lighter member. A second design was
also performed using the original bay configuration with two infill beams. In the end, it was realized
that the larger members obtained in the second design with the original beam layout was a much lighter
system even though the beams had to withstand a larger blast load. Figure 17, above, shows the beams
that were designed and the final bay layout using two infill beams equally spaced.
Due to the strict rotational limitations, many iterations of the design process had to be completed. Afterperforming several iterations by hand, an Excel spreadsheet was set up to calculate most of the values,
with the exception of a few values that had to be read from tables in the UFC. An example hand
calculation of the first iteration can be found in Appendix and the Excel spreadsheets for the two
different bay layouts can be found in Appendix D.
To begin the design, both service load combinations and blast load combinations were checked to find
the controlling combination. Blast was found to be the controlling load, again using the combination
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1.0D+0.25L+1.0B. This equation accounts for the direction of the loading, in this case uplift from blast
but gravity loads from the superimposed dead loads, estimated self-weights, and live loads. From the
controlling distributed load, the moment was calculated. Plastic moment capacity was used to
determine the required section modulus for the beam. Additionally, the local buckling requirements
were determined. From these requirements, an initial member was chosen. Plastic moment was
determined to make sure it was less than the plastic moment capacity of the chosen member. The
natural period of vibration was calculated to find the ductility ratio of the beam. Additionally, the strain
rate of the beam was calculated to determine if the DIF originally estimated was accurate. The ductility
ratio and rotation of the member were calculated and compared to the criteria established at the
beginning of the design. Finally, ultimate shear capacity was compared to maximum support shear using
the dynamic shear yield stress.
Several iterations of this process were completed in order to determine that a W 27x161 was the
smallest beam that worked. The ductility ratio of this member was found to be 1.0, which means that
the DIF assumed at the beginning of the design was adequate. This means that the maximum deflection
is expected to be the equivalent elastic deflection. Also, lateral bracing was checked, and was calculatedto be required at every 3 feet along the length of the beam. This requirement will be met by the slab on
deck floor system that will produce an unbraced length of zero across the length of the beam.
Additionally, rebound of the member was checked. Rebound is the reversal of load and deflection that
occurs after the blast wave has passed. The member must have a rebound resistance greater that that
specified in Figure 5-13 of the UFC. This allows the member to remain elastic during the rebound phase.
It was determined that the member had sufficient rebound resistance.
Live load and total load deflections were also checked under service loads only. The beam was found to
be adequate in live load and total load deflections.
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Figure 18: 3D model of typical bay with girders called out
Girder Design
The girder design followed the same design
principles and procedure as the beam design,
differing only in their distribution of loading.
The interior girder was designed using point
loads from the reaction values from the
second scenario of the beam design. This
meant that there were two point loads
equally spaced along the length of the beam
with combined uplift and gravity, and a
distributed uplift blast load acting on the
bottom flange of the girder. Again, time-
pressure loading was determined to be the
more critical design pressure as it occurs
over a much longer period of time, relatively,
than the peak incident pressure. This design
may be conservative for the exterior beam,
but will be used for simplicity of design.
Again, plastic moment capacity was used to determine the required section modulus for the beam.
Additionally, the local buckling requirements were determined. From these requirements, an initial
member was chosen. A W30 x116 was chosen as a trial member. The following checks were performed
on the member to find if it met the blast requirements:
Plastic moment capacity must be greater than member plastic moment.
The strain rate of the girder was calculated to determine if the DIF originally estimated was
accurate.
The ductility ratio and rotation of the member were calculated and compared to the criteria
established at the beginning of the design.
Finally, ultimate shear capacity was compared to maximum support shear using the dynamic
shear yield stress.
Rebound resistance of the member must be greater than the required resistance.
Since the W30x116 met the specified requirements, it was chosen as the most economical member for
the design. An additional check for deflection under gravity loads only was performed. Both live load
deflection and dead load deflection were found to be less than the allowable deflections. The final
member chosen for the design was the W30x116. Figure 18, above, locates the girders that were
designed.
Hand calculations for the girder design can be found in Appendix E.
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Slab Design
Initially, it was intended to design a slab on deck for the redesign. After a few initial calculations,
though, it became evident that the capacity of such a slab would not be enough to withstand the time-
pressure loading caused by the explosion. At this point, it was decided that a two-way slab on shored
form deck could be designed to satisfy the requirements instead.
It was chosen to design the slab as a Type II Slab as defined by the UFC. This means that rebound
reinforcement will not be required because damage will be allowed and accepted in the slab if rebound
does occur. Therefore, rebound calculations were not performed on the slab, as they were unnecessary.
The slab, needing to withstand a significant uplift force without intermediate supports, was designed
with two-way reinforcement at the top. Being the more critical force on the slab, this reinforcement
was also used on the bottom of the slab to provide the same amount of resistance if the blast were from
above. Calculations for the two-way slab on shored deck form can be found in Appendix F. The design
yielded a 16.5” concrete slab on shored form deck held in place by shear studs. This was not designed
as a composite system, though, so the shear studs are intended only for holding the slab in place. Figure
19 on the next page shows a detailed section of the slab.
Although this slab design provides a solution, there are some problems. This slab is 10” deeper than the
original system. This means that the ceiling height on each floor may have to be decreased in order to
fit all the mechanical, electrical, and telecom equipment, especially since the girders and beams
remained at nearly the same depth as designed originally. Reducing the ceiling height to less than 9’
may make the space feel very crowded and cramped, which would be unpleasant for the occupants.
The other solution would be to increase the building height by 10” per floor, which would result in an
overall building height increase of 70”. This would add significant cost to the building, and would likely
be upsetting to the owner.
The system also does not provide the required lateral bracing for the beams. Although lateral bracing
can be provided by other means than a floor slab, it will add additional cost to the design. Utilizing the
floor slab as lateral bracing for the beams is the most common method of providing stability to beams
due to the economy of the design. Therefore, this would be an inefficient design in that respect, as well.
In addition to the issue of system depth, there are the issues of constructability and reasonable
solutions. A slab with a depth of 16.5” seems highly conservative for a floor system for day to day loads.
There is a lot of extra weight and cost to this system as compared to a traditional slab on deck. Manytimes, it is not economical to design slabs for blast. There are rarely solutions that are both cost
effective and provide complete safety to the occupants. For this reason, it is suggested that the
redesign utilize a composite slab on deck system. Damage will most certainly occur, including but not
limited to cracking and spalling of concrete and possible breach. As stated previously, damage is
allowed as long as collapse does not occur.
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After further research into slab design, it was determined that since the space would be vented at 5 psi,
this pressure could be used to design a floor system. This allowed a second look into slab on deck
systems. A composite deck with slab was designed, and it was found that a 3VLI16 with a 4.5” topping
would provide adequate strength for the gravity system. These calculations can also be found in
Appendix F. This gives a total system depth of 7.5”, which is only a 1” increase in system depth from the
original. A 1” decrease in the ceiling cavity depth should not be an issue with coordinating the MEP.
Additionally, this system will be much less costly, both in materials cost and labor. Overall, this system
provides an alternative solution if damage is not considered to be an issue.
Additionally, further investigation into Aluminum Foam Composite Sandwich Panels , lightweight
sandwich panels composed of aluminum foam cores, could be utilized. This innovative material takes
advantage of the high stiffness and high compressive strains of aluminum foams. Large deformations of
the sandwich panels give them the ability to absorb high quantities of energy. Placed underneath the
slab on deck system, this material could possibly provide the necessary energy dissipation to mitigate
structural failures thinner floor systems. Cost data was not looked into for this system, so no
recommendations can be made on the economy of the system as a whole. With more time, researchinto this new discovery would have been completed, and a design capitalizing on this technology may
have been possible.
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Figure 19: Two-Way Slab on Shored Form Deck Detail
Figure 20: 3VLI16 Slab on Deck Diagram taken from Vulcraft
2008 Cut Sheet
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Moment Connection Design
A typical moment connection at the exterior of the building between a beam and a column was
designed as part of the MAE requirement for thesis. Figure 21 above shows the location of the moment
connection at the exterior of the building. This is important to note because the columns at the interior
may need to be upsized to meet the strong column- weak beam requirements. With more time, an
interior connection between two beams and a column would have been investigated.
In this design, the moment connection must allow the beam to develop its full plasticity. That said, the
overstrength factors that are present in the beam calculations are not accounted for in the connection.
This is because it is necessary for the connection to be designed to develop the full strength of the
connecting members.
It was decided to use seismically prequalified connections in this design. This is because seismic
detailing has many of the same requirements as blast design. Additionally, the design can be
significantly simplified using the prequalified connections specified in the AISC Seismic Design Manual.
The column must have a higher plastic moment capacity than the beam in both situations, providing a
strong column- weak beam connection. In this type of framing, the intention is to have failure occur in
the beam before the column, since column failure could lead to pancaking of floors and ultimately
building collapse. This also helps distribute the inelastic deformations to the rest of the structure.
Another similarity is that member rotation is limited to .04 radians. Since the beam was designed for
this limit, the prequalified connections could be utilized for the design. Finally, seismic design using
prequalified connections ensures that ductile limit states will control, which is the objective in blast
design.
Figure 21: 3D model of typical bay with connection location called out
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One difference to note between seismic connection design and blast connection design is that there are
different compact section requirements. The AISC Seismic Design Manual specifies the limiting ratios for
seismically compact sections. These differ somewhat from the blast requirements for compact sections.
The blast requirements were met in the design of the column, and therefore engineering judgment was
used to follow those requirements rather than the seismic requirements. Additionally, the seismically
compact limiting ratios only apply to members of seismic load resisting systems, which this is not.
The design of the connection followed the requirements for Special Moment Frames, which are defined
as frames “expected to withstand significant inelastic deformations…” in the AISC Seismic Design
Manual since the members in blast design are expected to withstand the large inelastic deformations
that may occur as a result of blast loading.
The guidelines for prequalified connections design was used, which can be found in the specifications of
the AISC Seismic Design Manual. The beam limitations in section 5.3.1 of the specification for the AISC
Seismic Design Manual were met in accordance with the blast design requirements. Additionally, all
column limitations in section 5.3.2 were met. Additional requirements in Table 6.1 were metthroughout the design process.
Finally, the beam-column relationship requirements of sections 9.6 and 5.4 of the specification were
met. The overstrength factor used in seismic design for this calculation should not be used in blast
calculations. It was determined that the plastic capacity of the column was greater than the plastic
capacity of the beam, and therefore met the requirements for a strong column- weak beam connection.
To begin the actual design, a prequalified connection was chosen. Based on the large expected plastic
moments, an Eight-Bolt Stiffened connection was chosen, or 8ES. Next, a “dog-bone,” otherwise known
as a reduced beam section, was added to the beam to ensure that a plastic hinge occurs in the beam
and not at the connection. The reduced beam section was sized according to AISC design requirements.
The reduced beam section modulus, reduced beam shear, and the expected plastic capacity upon yield
were then calculated.
Next, the end plate and bolts were designed. It was found that shear yield in the plate controlled the
plate design. The plate was determined to be a 2.25” thick plate. The bolts were determined to be 1.5”
A325N bolts.
On the column side, it was determined that stiffeners would be required. Web crippling was
determined to be the controlling limit state, and stiffener plates were designed accordingly. It was
determined that a 1.5” thick stiffener plate was required at the top and bottom beam flange locations.
The same stiffener was used in both locations to account for load reversal during rebound of the beam.
Full penetration groove welds were determined to be required at all welded locations. It is noted that
this is quite costly, but it is also understood that this is the unfortunate downside to blast design.
Figure 22 on the following page shows a side and top view detail of the exterior moment connection.
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Figure 22: 8ES Moment Connection Detail
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Figure 23: Partial Floor Plan of Final Design with Members Labeled
Final Design
Figure 23 below shows a portion a floor plan of the redesigned structure with members labeled. This
was used for the LS-DYNA Redesign model, which will be discussed in later sections.
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LS-DYNA Modeling
LS-DYNA Blast is a finite element analysis software used for modeling and analyzing blast events.
Although not created specifically for use in the building industry, it can be used to model a building
structure to determine member reactions during a blast event. In this thesis, LS-DYNA computer
modeling and analysis will be used to meet the AE597A MAE requirements.
A partial model of NBP-300 was created in LS-DYNA to compare the results using a blast modeling
software to the hand calculations performed in the first half of the structural depth. A partial model, as
opposed to the model of the entire building was used for several reasons. Firstly, blast loads decrease
significantly with increasing distance from the origin. By building a partial model, it can be shown that
members as close as one to two bays away from the blast really don’t see much stress. Therefore, it can
be accurately assumed that a partial model will provide adequate stress-strain data. A full model would
be required for a lateral analysis though.
Second, each member had to be created individually in a text file as opposed to the user interface. This
made the process of building the model very tedious and time consuming. The scope of this thesis did
not allow for that in-depth of a modeling study.
Finally, since LS-DYNA is a finite element analysis software full of dynamic analysis equations and coding,
the run time for large, complicated models increases drastically as compared to smaller less complicated
models. In order to run several iterations, this time issue had to be taken into account.
The model was created using a base keycard file. This file has preset “cards” which are recognized
commands for the LS-DYNA programming. This is where the blast load is defined using the
*LOAD_BLAST card. The equivalent weight of TNT, the (x,y,z) location of the blast initiation, and thedelay time between the start of the model and the blast initiation were identified to define the blast.
This keyword takes into account incident pressures and reflected pressures.
The first member, a W14x159 was created in the user interface using a block mesh command (BMESH).
Figure 24 on the next page shows an example of the mesh for the beam. Initially a rectangular section
was created using five indices in the x-direction, 5 indices in the y-direction, and 6 indices in the z-
direction. The distances between indices in each direction were entered to develop the outline of the
cross section of a W-flange. Finally, material was removed from the square on either side of the
outlined web to create the W-flange shape. This created the “I” shape used for wide flanges. Then the
dimensions for the web and flanges were defined and a height was given to the column.
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Each member was created using this process. In the cases where beams framed into girders, copes were
created by adding more indices in the x-direction and z-direction, and then subtracting out the space
where the cope was required. A standard 3” cope was used and every location required for simplicity.
Once one member was created in the user interface, the file was saved, and then the text file for that
column was opened. From here, each member was created using the format from the first member.
The model was checked periodically during the text input to make sure that the geometry created was
accurate. A sample of this text is available in Appendix H.
The floor slab was created using the block mesh command again. Individual quadrants were created
and restrained at interfaces with one another. Cutouts were created at the column corners. This can
also be seen in the sample text file.
Fixed end moment connections at the ends of the beams and girders were modeled using the
*CONTACT_TIED_SURFACE_TO_SURFACE_CONSTRAINED_OFFSET option.
Once the model was built and the *LOAD_BLAST card was defined, the model was run. The blast was
defined to detonate at 2.5ms into the run time of the model. This process was repeated for the
redesigned structure using the blast members.
Figures 25 through 28 on the following pages show several isometric snapshots from the LS-DYNA
output model, including the frame, the frame with slab, and a connection detail.
Figure 24: View of Block Mesh used in LS-DYNA with Indices
Labeled in “I” and “j” directions
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Figure 25: Isometric view of structural elements of partial LS-
DYNA Model (slab not shown)
Figure 26: Isometric view of structural elements of partial LS-
DYNA Model (slab shown)
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Figure 27: Isometric view of underside of structural elements
of partial LS-DYNA Model (slab shown)
Figure 28: Close-up of Connection in LS-DYNA model
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Comparison of Results
The results of the LS-DYNA model revealed a lot about the blast design process. It showed that the
stresses are lower than expected in the redesign, and that the hand calculations may be too
conservative. Plastic strain was never reached in the redesign, so the members should not yield.
Spikes in stresses and strains occur as pressures are reflected back into the structure, causing the
stresses in the members to build. This is more noticeable in the redesigned structure since it would be
stiffer, and therefore would have a less flexible response to the blast load.
Von Mises stresses were compared to the allowable stresses for the structural steel in dynamic loading.
Von Mises stresses are calculated using the following equation:
This defines a stress plane based on stresses in the 1st, 2nd, and 3rd principle stresses. Within this plane,
stresses are below allowable. Outside the plane, yield occurs. The Von Mises stresses obtained from
the LS-DYNA output should be below the dynamic yield stresses of the structural steel, and were
compared to determine the effectiveness of the redesign. In the original structure, the stresses are well
below dynamic yield. Additionally, in the model designed for blast, we can see that no failures occur, as
the stresses are below dynamic yield stress, or 71,000 psi. This can be seen in Graphs 1 and 2 on the
following page.
Figure 29 (pages 46-47) shows several still pictures of the blast wave propagation through the structure.
As stated previously, the blast was detonated at 2.5ms into the model. Significant stresses aren’t
immediately felt by the members, though. It takes several more milliseconds for the blast wave to
induce stresses in the members. Additionally, it can be seen that the pressure distribution over the
members is not equal. The base of the column sees the pressure wave many milliseconds before the
top of the column. In the hand calculations, it was assumed that the pressure would be evenly
distributed along the beam. In reality, this would not be the case, and so the member may be overly
conservative in its design. This is true of other members in the bay as well, such as the beams, which
would see the blast load at the center of the span before either of the ends.
In addition to checking the stresses in the members, the pressure from the blast was checked. It was
found that the pressures from the blast were very close to what was calculated by hand. This data waspresented in the “Blast Load Determination” section previously. The maximum pressure was found to
be 147 psi, which occurred at 7 ms. The blast was detonated at 2.5 ms into the analysis. This drops off
quickly and remains between 22 psi and 15 psi between 14 ms and 20 ms. This is very close to the 117
peak pressure and 21 gas overpressure that was found through hand calculations. On the following
pages a progression of still images from the pressure analysis video obtained from LS-DYNA output can
be seen.
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Graph 1: Stress in Original Structure
Graph 2: Stress in Blast Designed Structure
19116
-5000
0
5000
10000
15000
20000
25000
0 5 10 15 20 25
V o n M i s e s S t r e s s ( p s i )
Time (ms)
Stress over Time
Columns
Beams b/t
ColumnsInfill Beams
Girders
Slab
-10000
0
10000
20000
30000
40000
50000
60000
70000
0 5 10 15 20 25
V o
n M i s e s S t r e s s ( p s i )
Time (ms)
Stress over Time
Columns
Beams b/t
Columns
Infill Beams
Girders
Slab
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Figure 29: Blast Pressure Progression
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Additional Comments and Conclusion
Lateral System Implications
The redesign of NBP-300 will likely have several implications to the lateral system. Originally, as stated
previously, the lateral system was composed of four eccentrically braced frames. Of the changes made
during blast design, one of the most important to note is that moment frames would be utilized.
Moment frames can provide more ductility than the present eccentrically braced frames in the building,
which would help distribute the large amount of energy and pressure produced by the blast.
With the increased weight of the structure, the seismic lateral loads would increase, and produce a
larger design load in both directions. Seismic load controlled the design in the east-west direction
originally, and would remain the controlling design load. In the north-south direction, though, wind
loads controlled the lateral design, so this would need to be checked to determine if that were still true.Seismic loading may control in the redesign due to the incredible amount of weight added to the
structure.
A further look into how ground shock affects the building’s foundations would be the next step to
determine additional strength requirements for the foundations. This is another area where additional
research and design could yield some interesting results, but as it was not in the scope of work for this
thesis, redesign of the foundations was not performed.
Effects on Foundations
As stated previously, the redesign adds tremendous weight to the structure. This means that the
current foundations may not be large enough or strong enough to support the additional weight.
Additionally, the lateral loads would increase, so overturning moments in the foundations would have to
be rechecked. Finally, due to ground shock from blast, the slab on grade may need additional strength.
A further look into how ground shock affects the building’s foundations would be then next step to
determine additional strength requirements for the foundations. This is another area where additional
research and design could yield some interesting results, but as it was not in the scope of work for this
thesis, redesign of the foundations was not performed.
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MAE Requirements
As an MAE student, certain masters’ courses were utilized in this thesis redesign. Overall, three masters’
courses were used throughout this thesis. A moment connection was designed using the information
taught in AE 534. Computer modeling was used to model and analyze the original and redesigned
structure, using material and information from AE 597A. Finally, AE 542 information on building façade
systems and glazing was utilized to complete a façade redesign.
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Breadth Topic I: Site Redesign
To redesign the site of NBP-300 several aspects of the site had to be taken into consideration. There
was originally parking located on-site, as well as truck access for garbage collection and delivery drop-
offs. Several pedestrian access points existed on multiple sides of the lot. Waste water management
also had to be considered during any modification to the site. Native plants and materials to the region
were researched. Any plants, trees, or shrubs that were to be planted had to be able to grow in the
climate and soil conditions present for the NBP-300 site. Figure 30 below shows a comparison between
the original site and the redesigned site.
Firstly, all on-site parking was eliminated. This negates the possibility of a car being used as an explosive
at a close range to the building. It will be assumed that the parking structure to the north-east of the
NBP-300 lot has the capacity to take on parking load eliminated from the site. Additionally, this lot will
also require a security system to prevent it from becoming a hazard.
The site was also expanded to meet the setback requirement of 400 ft. This means that at any point on
the building, the closest vehicular access way must be at least 400 ft away. Since there was only one
road running in front of NBP-300, the building could easily be moved further back on the site. The
driveway at the top of the site will remain, but will be for deliveries only and will have a security
checkpoint. The problem with moving the building back on the site is that this will add to the cost of the
project. An additional 80,856 square feet, or 1.86 acres would be required to meet the setback rule.
This is about a 50% increase from the original size. The cost benefit tradeoff makes this purchase worth
the money. If no setback is maintained, then the structure would be required to be designed for other,
possibly higher, blast loads.
An important change to the waste-water management had to be made. The distance to the main hook-
up was increased with the increase in setback. Fortunately, a clear path between the main run and the
building was able to be maintained, and so this wasn’t seen as a critical issue in the redesign.
The other issue that had to be dealt with is the grading of the site. Since NBP-300 has a partial
basement that is exposed at one side, it was preferable to keep this architecture undisturbed. After
looking at the site grading from the original CAD file, it was determined that the site slopes gradually
away from the back side of the building toward the east. Ultimately, it was not seen as an issue for the
architectural integrity or constructability of the building.
Site access for delivery trucks and maintenance vehicles was maintained, but moved. A gated accessroad to the north of the site leads to the loading dock at the northwest corner of the building. This
provides a security checkpoint for any vehicle entering the site, and meets the blast requirements for
site security. The road loops around to provide both entrance and exit points from site. There is a
spacious turn around area and parking area for any vehicle that may require such. The road maintains
at minimum a 24’width to provide adequate space for trucks.
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Next, a perimeter wall was designed to surround the site of NBP-300. This consisted of an 8’ high cast in
place concrete wall. The wall was sized for wind loads and overturning moments. Foundations were
sized up to a standard size rather than using the actual calculated sizes, as they were too small for the
wall size. A CAD drawing of the wall can be seen in Figure 31 on the following page. In front of the wall,decorative boulders will be used to protect the wall from vehicular impact.
More sidewalks and patio areas were added to the site to form a friendlier environment for the
occupants. There are three circular paths with bench seating connected by curved paths. This provides
a nice outdoor walking space for the occupants. Additionally, there is an outdoor patio with tables,
chairs, and umbrellas for those occupants who may wish to eat outside. Birch trees were chosen to line
the perimeter wall to obscure the view o