This document provides information on blast resistant design of structures. It discusses the objectives of blast resistance, types of blast resistant structures, and outlines the basic design process. The design process involves calculating blast loads, determining member properties, modeling the structure, selecting trial member sections, performing dynamic analysis using single-degree-of-freedom or multi-degree-of-freedom methods, checking deformation criteria, designing connections, and designing foundations. Dynamic analysis methods like equivalent static method, SDOF, and MDOF are described for evaluating structural response to blast loads.

1. Prepared by: Mithun Pal
Civil/Structural Engineer
March 05, 2013
Prepared by: Mithun Pal
Civil/Structural Engineer
March 05, 2013
BP-WND Project – Blast Resistant Design
Single Degree of Freedom System (SDOF)

2. Blast Resistant Design
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 CONTENTSCONTENTS
o Introduction
o Objective of Blast Resistance Design
o Types of Blast Resistance Structures
o Design Process Diagram
o Basic Design Information
o Design Process
o References

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 INTRODUCTIONINTRODUCTION
• Explosion is a phenomenon associate with sudden release of energy
causing shock wave or pressure wave.
 TYPES OF EXPLOSIONTYPES OF EXPLOSION
• Nuclear Explosion
• Chemical High Explosive
• Accidental Explosions
 TYPES OF EXPLOSION IN PETROCHEMICAL FACILITIESTYPES OF EXPLOSION IN PETROCHEMICAL FACILITIES
• Vapor Cloud Explosion (VCE)
• Pressure Vessel Explosion
• Condensate Phase Explosion
• Dust Explosion

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 OBJECTIVE OF BLAST RESISTANT DESIGNOBJECTIVE OF BLAST RESISTANT DESIGN
• Personal safety
• Controlled shutdown
• Financial consideration
 TYPE OF STRUCTURESTYPE OF STRUCTURES
Types of Construction
Side-on Overpressure
(Pso)
Remarks
Conventional Construction
Buildings designed for
D+L+W/E
Pso < 1.0psi
With minor enhancement on windows,
connections
Enhanced Pre-engineering
Metal Buildings
1.0< Pso < 3 psi
Steel frame with cold-formed steel panels on
girts & purlins
Reinforced Masonry Clad
Buildings
Pso order of 3 psi
Steel/RC frame w/ reinforced masonry exterior
walls
Metal Clad Buildings Pso order of 3 psi Conventional "stick-built" design.
Precast Concrete Buildings Pso order of 7 to 10 psi
Ductile connections are an important
consideration.
Cast-in-place Concrete
Buildings
Pso > 7psi Shear walls with steel/concrete frames.

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PROCESS DIAGRAMPROCESS DIAGRAM

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 BASIC INFORMATIONBASIC INFORMATION
• Client Specification
• Plot Plan and ELP
• Architectural Drawings
• System Vulnerability and Safety Requirements
 DESIGN PROCESSDESIGN PROCESS
• Step 1: Load Calculation
• Step 2: Determination of Member Properties
• Step 3: Model Representation
• Step 4: Trial Member Section
• Step 5: Dynamic Analysis
• Step 6: Deformation Criteria Check
• Step 7: Connection Design
• Step 8: Foundation Design
Note: Damage level determined by Owners.

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o FRONT WALLFRONT WALL
• OVERPRESSURE RESULTING FROM INCIDENTAL
PRESSURE, Pso
1. From Client Specification
2. From Fig 2-7 & 2-8 for
of UFC 3-340-02
3
W
R
Z =
Z=Scaled Distance
R=Radial Distance from Charge
W=Charge Weight
 LOAD CALCULATIONLOAD CALCULATION

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• PEAK DYNAMIC WIND PRESSURE, qso
2
022.0 soo Pq ≈ psi (Ref Eq 3.4 of ASCE for Blast Design)
• REFLECTED PRESSURE, Pr
sorr PCP = (Ref Eq 3.2 of ASCE for Blast Design)
Cr is reflection coefficient
Cr = (2+0.05Pso) (Ref Eq 3.3 of ASCE for Blast Design)
Where Pso is in psi and this equation is for blast wave reflection of 00
.
Ref Fig 3-2 of ASCE for Blast Design for other values
• STAGNATION PRESSURE, Ps
Ps = Pso+Cdqo (Ref Eq 3.7 of ASCE for Blast Design)
Cd is drag coefficient which depends on shape and orientation of
the obstruction surface. For rectangular building, drag coefficient
may be taken as +1.0 for front wall and -0.4 for side and rear walls
and for roof

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FRONT WALL LOADING
• DURATION OF POSITIVE PHASE, td
td also may be provided in client specification
so
w
d
P
I
t
2
=
• IMPULSE, Iw
Measure to define the ability of blast wave to do damage.
From Fig 2-7 & 2-8 for of UFC 3-340-02
Or, by the eqn,
3
W
R
Z =
∫=
dt
w dttPI
0
)(

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• SHOCK WAVE VELOCITY, U
ft/s (Ref Eq 3.5 of ASCE for Blast Design)
5.0
)058.01(1130 SOPU +=
• BLAST WAVE LENGTH, LW
(Ref Eq 3.6 of ASCE for Blast Design)dW UtL =
• STAGNATION TIME, tC
(Ref Eq 3.8 of ASCE for Blast Design)dc t
U
S
t <=
3
S = clear distance, the smaller of BH or BW/2

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o ROOF LOADINGROOF LOADING
• For roof with slope less than 100
shall not experience any
reflected overpressure and shall experience same side-on
overpressure as side wall
(Ref Eq 3.11 of ASCE for Blast Design)
o SIDE WALLSIDE WALL
SIDE WALL AND ROOF LOADING
Effective side-on overpressure
Pa=CePso+Cdqo
Ce=reduction factor on side-on overpressure
with time and distance

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o REAR WALL LOADINGREAR WALL LOADING
•Peak overpressure similar to that of side walls and is calculated by
previous equation
•As its inclusion reduce the overall lateral blast force, many times it
is neglected
o FRAME LOADINGFRAME LOADING
ACTUAL FRAME LOADING
SIMPLIFIED FRAME LOADING

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o SUCTION DUE TO NEGATIVE PHASE PULSESUCTION DUE TO NEGATIVE PHASE PULSE
• Peak value of negative phase pressures are generally small
compared with peak positive overpressure, however durations is
longer.
 DETERMINATION OF MEMBER PROPERTIESDETERMINATION OF MEMBER PROPERTIES
Dynamic yield strength
Fdy=(Fy)(SIF) (DIF)
o STRENGTH INCRESE FACTOR, SIFSTRENGTH INCRESE FACTOR, SIF
• Actual yield strength is higher than the values mentioned in codes
and specification. SIF used to account this condition.
• Refer Appendix 5.A of ASCE for Blast Design for SIF values.
o LOAD COMBINATIONLOAD COMBINATION
U(T) = D+aL+B(t)
U(t) = total applied time dependant load
D=static dead load
L=live load, a=reduction factor to live load
B(t)=time dependant blast load

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o DYNAMIC INCRESE FACTOR, DIFDYNAMIC INCRESE FACTOR, DIF
• Concrete and Steel material experience an increase in strength
due to rapid strain for blast load. For high strain rate greater load is
required for same deformation.
• Refer Appendix 5.A of ASCE for Blast Design for DIF values.

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 MODEL REPRESENTATIONMODEL REPRESENTATION
• Structural member representation
• One-way or two-way action
• Loading distribution for each member
• Connection philosophy
 TRIAL MEMBER SELECTIONTRIAL MEMBER SELECTION
• Dynamic analysis requires trial member sizes
• Nonlinear response properties are calculated from the trial sections
 DYNAMIC ANALYSISDYNAMIC ANALYSIS
• Equivalent Static Method
• Single Degree of Freedom Systems (SDOF)
• Multi-Degree of Freedom System (MDOF)

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o EQUIVALENT STATIC METHODEQUIVALENT STATIC METHOD
• Approximate load, called “equivalent wind” is applied to simulate
dynamic response.
• This is not recommended in ASCE for Blast Loading (Cl: 6.3) and
can only be used when structure is far away from blast source and
blast loading acts like wind gust
o SINGLE DEGREE OF FREEDOM SYSEMS (SDOF)SINGLE DEGREE OF FREEDOM SYSEMS (SDOF)
• For common types of structures like single story frames, cantilever wall, box
like building.
• All structures posses more than one degree of freedom which can be
represented as series of SDOF.
• Approximation of equivalent SDOF for structural components requires
deflected shape and strain energy equivalence between actual structure and
SDOF approximation.

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17 Linear: Mÿ + Ky = F(t) Meÿ + Key = Fe(t)
Bilinear: Mÿ + R = F(t) Meÿ + Re = Fe(t)
(Lesser of Ky or Rm) KLMMÿ + R = F (t)
Me=KMM Fe=KLF Ke=KLK Re=KLR KLM=KM/KL
Actual structure Equivalent SDOF
TYPICAL STRUCTURAL REPRESENTATION OF EQUIVALENT SDOF SYSTEM

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• SINGLE DEGREE OF FREEDOM (SDOF) METHOD
Equivalent Mass of SDOF system: Me
Me = KMM
KM = Equivalent mass/Total actual mass = Me/M
Equivalent Force of SDOF system: Fe
Fe = KLF
KL = Equivalent force/Total actual force = Fe/F
Equivalent Resistance of SDOF system: Re
Re = KLR
R = Lesser of Ky or Rm
Rm is maximum resistance to
blast load

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o MULTI-DEGREE OF FREEDOM SYSEMS (MDOF)MULTI-DEGREE OF FREEDOM SYSEMS (MDOF)
• Shall be used when structural configuration is complex or significant dynamic
interaction between interconnected member can not be avoided.
• Will require computer analysis.
• Finite element analysis shall be performed.
• Software associated with nonlinear analysis should be used (e.g., ANSYS)
• Due to association of nonlinearity with plasticity, there is possibility of large
displacement. Hence direct time integration (time-pressure / load diagram)
method should be used.
• Available commercial computer programs for dynamic nonlinear finite
element analysis suitable for use in blast resistant design are LS-DYNA,
ABAQUS, ADINA, ANSYS, MSC/NASTRAN and FLEX.

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 DEFORMATION CRITERIA CHECK (RESPONSE)DEFORMATION CRITERIA CHECK (RESPONSE)
• Ductility Ratio
• Hinge Rotation
o DUCTILITY RATIODUCTILITY RATIO
• Ductility Ratio, µ = Maximum deflection / displacement at elastic limit.
• This is a measure of the degree of inelastic response experience by the
member
Peak Load, Fo=BL+DL
Ru=ultimate resistance
(Table 6.1, 6.2 & 6.3 of ASCE for Blast
Design)
td=blast loading duration
tn=period,
e
e
n
K
M
f
t ∏== 2
1

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o HINGE ROTATIONHINGE ROTATION
• It relates maximum deflection to span and indicates the degree of instability
present in the critical areas of the member.
Refer Appendix 5.B of ASCE for Blast Design for allowable deformation limits
Ductility
μ=ym/ye
Resistance – Deflection Curve

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o BUILDING RESPONSE CRITERIA SPECIFIED BY CLIENTBUILDING RESPONSE CRITERIA SPECIFIED BY CLIENT
Low Response : Localized building/component damage.
Building can be used, the cost of repair is moderate.
Medium Response: Widespread building/component damage.
Building should not be occupied until repaired, the cost of repair is
significant .
High Response: Building/component lost structural integrity.
Building should not be used, the total cost of repairs approaches
replacement of building.

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 CONNECTION DESIGNCONNECTION DESIGN
• Plastic hinge developed should be maintained.
• For reinforce concrete design, splices and development lengths must
be provided for the full yield capacities of reinforcement
• For steel design, connections are designed for a capacity somewhat
greater that that of its supported member.
 FOUNDATION DESIGNFOUNDATION DESIGN
• Should be more rigid than conventional structural foundation
• Relative displacement between column and walls need to be
minimized in order to maintain structural integrity. This is accomplished
using grade beams to tie spread footings or pile cap or by using
combined mat foundation.
• Foundation can be analyzed by static analysis and dynamic analysis

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o STATIC ANALYSISSTATIC ANALYSIS
• Typically designed for the peak reactions obtained from the superstructure
dynamic analysis.
• The reactions are treated as simultaneous static load, disregarding any time
phase relationship.
• 80% of ultimate net soil-bearing capacity shall be used for shallow foundation
• 80% of ultimate static pile capacity shall be used for deep foundation
• Followings are factor of safety which shall be used for static analysis as per
ASCE

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o DYNAMIC ANALYSISDYNAMIC ANALYSIS
• Analysis is complex in nature.
• Shall be used when static analysis is giving uneconomical foundation sizes.
 DESIGN PROCEDURE (SDOF APPROACH)DESIGN PROCEDURE (SDOF APPROACH)
Step 1: Determine blast loads
Step 2: Determine dynamic material properties
Step 3: Determine deformation limits
Step 4: Try structural member sizes
Step 5: Compute resistant – Bending and shear
Step 6: Compute SDOF Equivalent System:
a) Compute effective stiffness
b) Compute equivalent mass
c) Compute period of vibration
Step 7: Compute response by chart
a) Determine ductility from chart
b) Compute maximum deflection ym
c) Compute support rotation
d) Check deformation limit
e) Compute support reaction
Step 8: Resize structural component if deformation limit exceeds.

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 REFERENCESREFERENCES
• “Design of Blast Resistant Buildings in Petrochemical
Facilities” First Edition 1997, Second Edition
December 2010
ASCE Task committee
• ARMY TM 5-1300, “Structures to Resist the effects of
accidental Explosions”, November 1990
• ASCE Manual No. 42, Design of Structures to Resist
Nuclear Weapons Effect, 1985
• PIP STC01018, Blast Resistant Building Design
Criteria
• PIP ARS08390, Blast Resistant Door and Frames,
2002
• UFC 3-340-02 Structures to resist the effects of
Accidental Explosions (Dept of Defense USA)

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THANKS!
QUESTIONS ?