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Dongxiao Wu P. Eng. (Alberta, Canada) 
Home >> Tutorial >> Seismic Design for Petrochemical Facilities As Per NBCC 2005
Seismic Design for Petrochemical Facilities As Per
NBCC 2005 ?
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TABLE OF CONTENTS
2.1 Spectral Acceleration S_{a}(T) and
S(T)
2.2 Methods to Determine Site Class
2.3 Determine If Seismic Design Is Required for
Project
4.0 DUCTILTY AND OVERSTRENGTH FACTOR
Case 02 Nonbuilding Structures Similar to
Building
Case 03 Self Supported Vertical Vessel
Case 04 Braced LegSupported Ver Vessel
Case 05?
Self Supported Horizontal Vessel
Case 07 Nonbuilding Structure (Less Than 25% Comb
Wt) Supported by Other Structure
Case 08 & 09 Nonbuilding Structure (More Than
25% Comb Wt) Supported by Other Structure
Design Example 01: Nonbuilding Structure Similar
to Building  Exchanger Structure
Design Example 02: SkirtSupported Vertical
Vessel
Design Example 03: Braced Leg Supported Vertical
Vessel
Design Example 04: SelfSupported Horizontal
Vessel
Design Example 05: Building Structure
Design Example 06: Nonbuilding Structure (>
25% Comb Wt) Supported by Other Structure
This guideline
is intended to be used as supplementary document to NBCC2005 for the seismic
design of petrochemical facilities in Canada, with particular focus on Northern
Alberta Fort McMurray area.
This document
only covers Equivalent Static Force Procedure (ESFP), which is the easiest and
most applicable way to implement seismic design in low seismic zone like Fort
McMurray area.
There is no
provision on seismic design of Nonbuilding Structure in NBCC2005. ASCE 705 Chapter 15 Seismic Design Requirements for
Nonbuilding Structures is referenced for Nonbuilding Structure seismic
design in Canadian location. When ASCE 705 is referenced, NBCC2005 version of
ground motion parameters is used to interpret the ASCE 705 formula. This is
what NBCC2005 recommends in Commentary J page J61, Para. 226.
2.1 Spectral Acceleration S_{a}(T)
and S(T)
S_{a}(T)
?
5%
Damped Spectral Response Acceleration?
?
Based
on Site Class C as per NBCC Table 4.1.8.4.A
?
For
most cities in Canada, S_{a}(T) value can be found in NBCC Appendix C
Table C2
S(T)
?
Design Spectral
Acceleration
?
Modified
from S_{a}(T) by applying F_{a} and F_{v} factors
relating to Site Class?????????? NBCC
4.1.8.4 (6)
?
S(T)
= S_{a}(T)? when specific project
site class is Class C
2.2 Methods to Determine Site Class
Two methods are available to determine Site Class if it?s not
provided by Geotechnical consultant
1.
Average shear wave velocity V_{s} NBCC Table 4.1.8.4A
?
Preferable
way to classify Site Class????????????? NBCC
4.1.8.4 (2)
?
Shear
wave velocity V_{s }?is normally
available in soil report under dynamic machine foundation section
?
Use? V_{s} = SQRT(G/
ρ) = SQRT(Gg /
γ ) to get shear wave velocity if only
shear modulus is provided
2.
SPT N_{60}, for sand site.
Undrained shear strength, s_{u}, for clay site??? NBCC Table 4.1.8.4A
2.3 Determine If Seismic Design Is Required
for Project
From NBCC 4.1.8.1? ?
requirements in this Subsection need not be considered in design if S(0.2), as defined in Sentence
4.1.8.4.(6), is less than or equal to 0.12
Please note it?s S(0.2)<=0.12 , not S_{a}(0.2)
<=0.12
For Fort McMurray, S_{a}(0.2)=0.12
For Site Class C or better, S(0.2) <= S_{a}(0.2)=0.12
?
seismic design is not required
For Site Class D or worst, S(0.2) > S_{a}(0.2)=0.12
?
seismic design is required
For most projects in Fort McMurray, average shear wave
velocity is 200~300 m/s, and the Site Class is Class D.
1.
Equivalent Static Force Procedure (ESFP) ????????? NBCC
4.1.8.11
ESFP may be used for structures that
meet any of the following criteria
a)
in cases where I_{E} F_{a}
S_{a}(0.2) is less than 0.35,
b)
regular structures that are less than
60 m in height and have a fundamental period T_{a} < 2s
c)
irregular structures, other than those
that are torsionally sensitive, that are less than 20 m
in height and have T_{a} <
0.5s
In Fort McMurray, for the highest importance category Post
disaster structure, Site Class D, I_{E} F_{a} S_{a}(0.2)
= 1.5x1.3x0.12 = 0.234 < 0.35?
? For Site Class D or better, ESFP can
be used as the seismic analysis method for all structures in Fort McMurray
area.
2.
Modal Response Spectrum Method?????
NBCC 4.1.8.12
Not covered in this guideline.
3.
Time History Method
??????????????? NBCC
4.1.8.12
Not covered in this guideline.
Notes on Equivalent
Static Force Procedure (ESFP)
1.
NBCC2005 4.1.8.11 (3) allow the use of
estimated period for seismic calculation.
Computed structure period via computer
model is not absolutely required.
2.
Most of the time, the computed period
is much longer than estimated one. This is due to the fact that formula for
estimation given by code always leans to the conservative side.
Using computed period instead of
estimated one gives us the advantage to reduce the seismic base shear.
Below is a comparison of S(T) value
based on estimated T_{a} and computed T_{a}, from Example 01.
?
From Example01, Moment Frame
direction, estimated period = 0.91 s, STAAD computed period = 2.43 s
3.
NBCC2005 4.1.8.11 (3)(d) sets the
upper limit? on using longer computed
period, considering that the actual structure may be stiffer than the model in
STAAD. For example, mechanical equipments, pipings, cable trays etc are
conventionally not modeled in STAAD while they may actually contribute to the
stiffness of SFRS system.
NBCC2005 focuses mainly on
residential/commercial buildings, for industrial facilities there are mostly
open structures and less partition wall cases. In high seismic zone, should there
be a demand for reducing seismic force to achieve a an economical design for
industrial structures, engineering judgment is required to identify if this
upper limit is applicable, when the engineer is confident that the computer
model can reflect the actual SFRS stiffness and give an accurate period.
4.
Seismic serviceability check? NBCC 4.1.8.13
?
Storey
drift weighs more important than lateral deflection at top of structure???????? NBCC Commentary J Para 195
?
NBCC
4.1.8.13 (3) specifies storey drift limit 0.025h for normal buildings. 0.025h
is an allowable limit for inelastic storey drift, which is applicable when
seismic force is not reduced by dividing R_{d}xR_{o} factor.
Use R_{d}xR_{o} / I_{E}
to scale up the drift? for
comparison with 0.025h when the drift value is obtained from a model with
seismic load scaled down by I_{E}/(
R_{d}xR_{o}).
4.0 DUCTILTY AND OVERSTRENGTH FACTOR
NBCC Table 4.1.8.9
DuctilityRelated Seismic Force Reduction Factor?????????????????????? R_{d}
OverstrengthRelated Seismic Force Reduction Factor????????????? R_{o}
In high seismic zone, the total seismic load can be more than
20 times of total wind load.
Refer to attached example 01, exchanger structure, site
location: Vancouver
Base shear by seismic =8270 kN, base shear by wind =341 kN? ?????????? 8270/341
= 24.3
It?s almost impractical to design a structure deforming
elastically with seismic lateral load 24 times of wind load.
R_{d}xR_{o} factor is used to reduce the seismic
forces in recognition of the fact that a ductile structure designed based on
the reduced forces is able to dissipate the earthquake energy through inelastic
deformation without collapsing.
Higher Ductility of SFRS
for High Seismic Zone
In high seismic zone, higher ductility of SFRS is more
desirable.
Refer to attached example 01, exchanger structure, site location:
Vancouver
If Ductile SFRS is used, R_{d}xR_{o} =5.0x1.5
for moment frame and R_{d}xR_{o} =4.0x1.5 for eccentrically
braced frame, the seismic force for design can be reduced to? 8270 / (4.0x1.5) = 1378 kN , which is more comparable
to wind load, 341 kN.
?
Higher Ductility Causes Rigorous
Design Requirements for Connection Detailing
The tradeoff of higher ductility for SFRS, is the steel member
and connection design requirements.
CSA S1609 Clause 27 specifies the requirements for design of
members and connections for all steel SFRS with R_{d} >1.5, with the
exception of Conventional Construction, R_{d}=1.5 R_{o}=1.3 in S1609
27.11
Some direct impacts to structural design, if the SFRS is under
Clause 27 coverage
1.
Limitation on beam and column size,
mainly only Class 1 & 2? section are
allowed
2.
For energy dissipating elements, not
the min yield strength Fy , but the probable yield strength RyFy = 1.1Fy shall
be used, and RyFy shall not be less than 460MPa for HSS or 385MPa for others
sections????????? S1609 27.1.7
3.
S1609 requires that all bracing
connections in SFRS be detailed such that they are significantly stronger than
the probable tensile capacity of bracing members.? S1609 27.5.4.2
Brace connection design to meet such
high capacity is very difficult, considering probable capacity using RyFy =
1.1Fy, and for HSS RyFy shall not be less than 460MPa.????? S1609 27.1.7
4.
The amplification factor U2, to
account the Pdelta effects for structural element in SFRS, is calculated
differently compared to conventional design ? S1609
27.1.8.2
5.
Ductile moment resisting connections
for seismic application must satisfy more rigorous design and detail
requirements. Moment Connection shall be prequalified connections and designed
as per CISC publication Moment
Connections for Seismic Applications2008, which contains design procedure
of three types of prequalified moment resisting connections.
Conventional
Construction for Low and Moderate Seismic Zone
From above we can see that, once SFRS is covered by S1609
Clause 27, the increased complexity of SFRS frame member sizing, frame analysis,
connection design and detailing, steel facbrication and erection is tremendous.
In low and moderate seismic zone, Conventional Construction
is an advantageous design option to waive all provisions in S1609 Clause 27,
except clause 27.11.
In low seismic zone like Fort McMurray, the low ductility of
Conventional Construction SFRS will not cause significant increase to member
size, as the seismic load is normally lower or comparable to wind load, even
using the lower reduction factor R_{d}xR_{o} value of Conventional
Construction.
Refer to attached example 01, exchanger structure, location:
For McMurray
The seismic base shear before applying / (R_{d}xR_{o})
is 823 kN, wind load base shear is 341 kN
With Conventional Construction, design seismic load reduced
to 823 / (R_{d}xR_{o}) = 823 /(1.5x1.3) = 422 kN, which is
already close to wind load 341 kN?
? use of higher ductility SFRS is not
necessary.
In Fort McMurray, always use Conventional Construction, R_{d}xR_{o}
= 1.5x1.3, for all SFRS systems.
Most of petrochemical facilities can be classified as the
following categories:
1.
Building Structure
2.
Nonbuilding Structure Similar to
Building
3.
Nonbuilding Structure Not Similar to
Building
4.
Nonbuilding Structure (Less Than 25%
Comb Wt)? Supported by Other Structure
5.
Nonbuilding Structure (More Than 25%
Comb Wt)? Supported by Other Structure
Classification of Petrochemical Facilities and Applicable Code Provisions
Seismic provision in NBCC2005 is written predominantly to
address residential and commercial building structures. ?It covers the seismic requirements for
Building Structure (clause 4.1.8.11 and table 4.1.8.9) and Nonstructural
Component (clause 4.1.8.17 and table 4.1.8.17), but there is no provision for Nonbuilding
Structure.
Nonbuilding Structure includes many popular petrochemical
facilities, such as all freestanding vertical vessels, flare stacks, all horizontal
vessels, piperacks, exchanger structures, process/equipment modules etc.
?In this guideline,
ASCE 705 Chapter 15 is referenced for seismic design of Nonbuilding Structure.
When ASCE 705 is referenced for seismic design in Canadian location, Canadian
version of ground motion parameters in NBCC2005 are used to interpret formulas
in ASCE 705. This is exactly what NBCC2005 suggests in its Commentary J page
J61 Para. 226.
Some of the equipments, such as hor vessel, can be treated as
either Nonstructural Component or Nonbuilding Structure. When a hor vessel is
supported on a steel structure and it?s weight is less than 25% of the combined
weight, it?s a Nonstructural Component and NBCC2005 4.1.8.17 is used to
calculate the base shear, for equipment local support design only. For the
overall structure, NBCC2005 4.1.8.11 is used to calculate the base shear. The
hor vessel weight is considered as part of effective seismic weight in the base
shear calculation and seismic force distribution.
Building structure seismic force shall be designed as per
NBCC 4.1.8.11, with the weight of nonstructural components (Process, HVAC equipment
and Bridge Crane etc) considered as effective seismic weight for base shear
calculation and base shear distribution along vertical direction.
?
25% of roof snow load shall be counted
as effective seismic weight for base shear calculation as per NBCC Commentary J
page J46 note 168
?
All process equipments (piping, tank,
vessel, exchanger, pump, crusher etc) content weight under normal operating
condition shall be counted as effective seismic weight for base shear
calculation as per NBCC Commentary J page J46 note 168
?
For building with crane, only crane
empty weight (bridge+trolley/hoist), excluding lifting weight, shall be counted
as effective seismic weight for base shear calculation as per AISC Design Guide 7: Industrial
BuildingsRoofs to Anchor Rods 2nd Edition 13.6 on page 50
Case 01 Building Structure
Case 02 Nonbuilding Structures Similar
to Building
Nonbuilding Structures Similar to Building seismic force
shall be designed as per NBCC 4.1.8.11, with the weight of nonstructural
components (Process, Mechanical equipments etc) considered as effective seismic
weight for base shear calculation and base shear distribution along vertical
direction.
?
25% of snow load, if there is any,
shall be counted as effective seismic weight for base shear calculation as per
NBCC Commentary J page J46 note 168
?
All process equipments (piping, tank,
vessel, exchanger, pump, crusher etc) content weight under normal operating
condition shall be counted as effective seismic weight for base shear
calculation as per NBCC Commentary J page J46 note 168
?
All Process, Mechanical equipments
supported on a steel/conc structure with its weight less than 25% of the
combined weight, shall be designed as Nonstructural Component and NBCC2005
4.1.8.17, for equipment local support design only. For the overall structure,
NBCC2005 4.1.8.11 is used to calculate the base shear. The equipment weight is
considered as part of effective seismic weight in the base shear calculation
and seismic force distribution.
Case 02 Nonbuilding Structures Similar
to Building
Case 03 Self Supported Vertical Vessel
Case 03 Self Supported Vertical Vessel

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Case 04 Braced LegSupported Ver Vessel
Braced Leg Supported vertical vessel seismic force shall be
designed as per NBCC 4.1.8.11, with the seismic force distributed as per NBCC
4.1.8.11 (6).
?
The
leg brace is normally Tension Only brace which is designed by vendor.
?
The
vendor will provide foundation load, including seismic case, for foundation and
anchor bolt design. The engineer shall always carry on the seismic load calculation
by his own and verify the vendor provided data.
?
The
Braced Leg Supported vertical vessel is more flexible compared to Skirt
Supported vertical vessel. Engineer can use STAAD to get the fundamental
period. Please note that the Tension Only brace makes the support system more
flexible and will generate longer period.
?
Depends
on the shape of the vertical vessel, it can be classified as Sphere type or Cylinder
type. The PSC vessel below is Sphere type vessel, the seismic load can be
applied at mass center. The Deaerator vessel below is the Cylinder type, the
seismic force can be applied as reverse triangle.
?
The
seismic overturn moment to vessel base shall be corrected by multiplying
reduction factor J obtained from NBCC Table 4.1.8.11.? This is due to the fact that the higher mode
forces, F_{t} , make a much smaller contribution to the storey and base
overturn moment.
Case 04 Braced LegSupported Ver
Vessel
Case 05 ?Self Supported Horizontal Vessel
???????????????????? ??????????????????????????????? Case 05 SelfSupported
Hor Vessel
Case 06 Concrete Base Mounted Pump and
Compressor
Period Estimation
From ASCE Seismic Design Guideline Page 4.A6 Case G
Period of Vibration ? Generalized OneMass Structure
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Case 06 ?Concrete Base Mounted Pump and Compressor
Nonbuilding structure is not covered in NBCC2005, ASCE 705
15.4.2 Rigid Nonbuilding Structures is referenced.
For Concrete Base Mounted Pump and Compressor, the pump and
compressor is more like a rigid block and their own fundamental period is
normally less than 0.06s. As defined by ASCE 705 15.4.2, nonbuilding
structures that have a fundamental period T_{a} < 0.06s is
classified as Rigid Nonbuilding Structure. The base shear shall be
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Case 07 Nonbuilding Structure (Less
Than 25% Comb Wt) Supported by Other Structure
Nonbuilding structures weight is less than 25% of combined
(nonbuilding structures+supporting structure) weight
ASCE 15.3.1
?
For Local Structural Support Design
Nonbuilding structures seismic force
shall be designed as Nonstructural Component as per NBCC 4.1.8.17
?
For Supporting Structure Design
Supporting structure seismic force
shall be designed as Building Structures or Nonbuilding Structures Similar to
Building as per NBCC 4.1.8.11, with the weight of nonbuilding structure
considered as effective seismic weight for base shear calculation and base
shear distribution along vertical direction.
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Case 07 Nonbuilding Structure (Less
Than 25% Comb Wt) Supported by Other Structure
Case 08 & 09 Nonbuilding Structure
(More Than 25% Comb Wt) Supported by Other Structure
Nonbuilding structures weight is greater than 25% of combined
(nonbuilding structures+ supporting structure) weight
ASCE 15.3.2
Case 08 Nonbuilding
Structure (More Than 25% Comb Wt)?
Supported by Other Structure
???????????
???Rigid Nonbuilding Sructures????????????
Nonbuilding structures that have a foundamental period less
than 0.06s are considered as Rigid Nonbuilding Structures?? ASCE 15.3.21
?
Nonbuilding structure shall be
considered as a rigid element with appropriate distribution of its
effective seismic weight
?
R_{d}xR_{o} value of
combined system is permitted to be taken as the supporting structure?s R_{d}xR_{o}
value
?
Supporting structure seismic force
shall be designed as Building Structures or Nonbuilding Structures Similar to
Building as per NBCC 4.1.8.11
Case 08 Nonbuilding Structure (More
Than 25% Comb Wt)? Supported by Other
Structure
????????????????????????????????????????? Rigid
Nonbuilding Structures
Case 09 Nonbuilding
Structure (More Than 25% Comb Wt)?
Supported by Other Structure
??????????????
Nonrigid Nonbuilding Sructures?????
Nonbuilding structures that have a fundamental period greater
than 0.06s are considered as Nonigid Nonbuilding Structures?? ASCE 15.3.22
?
Nonbuilding structure and supporting
structure shall be modeled together in a combined model with appropriate
stiffness and effective seismic weight distribution
?
R_{d}xR_{o} value of
combined system shall be taken as the lesser? R_{d}xR_{o} value of the
nonbuilding structure or the supporting structure
?
The combined structure seismic force
shall be designed as Nonbuilding Structures Similar to Building as per NBCC
4.1.8.11
Case 09 Nonbuilding Structure (More
Than 25% Comb Wt)? Supported by Other
Structure
????????????????????????????????????????
Nonrigid
Nonbuilding Sructures
Design Example 01: Nonbuilding
Structure Similar to Building  Exchanger Structure
Structure
Classification: Case 02 & Case 07
Calculate the seismic force for an exchanger structure
supporting stacked heat exchangers as shown on next page.
Frames along GL1,2,3 are moment frame. Frames along GLA, C
are braced frame. Frame along GLB is unbraced.
Single exchanger shell operating weight 500 kN, each floor
equipment effective seismic weight = 4 x 500 = 2000 kN.
Assume each floor has 20m long 20? dia pipes to be counted
for effective seismic weight.
Structure importance category = High as the exchanger
contains flamable hydrocarbon content.
Calculate seismic force for the following scenarios:
1.
Site in Fort McMurray, Site D, ?Use SFRS R_{d}xR_{o} of Conventional
Construction (CC)
Use Equivalent Static Force Procedure
?
Seismic
force calc for overall structure steel design
?
Seismic
force calc for local structure steel support design (exchanger support)
?
Compare
wind and seismic force, with the R_{d}xR_{o} value of
Conventional Construction and Moderately Ductility
2.
Site in Vancouver, Site D, Use SFRS R_{d}xR_{o}
of Ductile (D) and Moderately Ductility (MD)
Use Equivalent Static Force Procedure
From STAAD output, braced frame in NS direction T_{a}=0.66s,
moment frame in EW direction T_{a}=2.43s
Example 01 Exchanger Structure
Wind Load Calc for
Overall Structure
To simplify the calc and for comparison purpose only, use the
wind load on enclosed structure for a quick check
Wind load pressure 1/50 yr q=0.35 kPa, C_{f}=1.3, C_{e}=1.10,
C_{g}=2.0, I_{w}=1.15
Wind load base shear = I_{w} x C_{f} x q x C_{g}
x C_{e} x A =1.15 x 1.3 x 0.35 x 2.0 x 1.1 x 12.6 x 23.5 = 341 kN
Seismic Base Shear for
Overall Structure Design
Location: Fort McMurray
????? Location: Fort
McMurray?? ??????????????? Site Class: Site D
SFRS 
Base Shear Ve
before Ve / (R_{d}xR_{o}) 
Base Shear SFRS CC
Ve / (1.5x1.3) 
Base Shear SFRS MD
Ve / (3.0x1.3) 
kN 
kN 
kN 

Moment Frame 
328 
168 
84 
Braced Frame 
823 
422 
211 
From above seismic base shear calc, we can find that, in low
seismic zone such as Fort McMurray area, using Conventional Construction (CC) is
good enough to bring the lateral seismic force down to a magnitude comparable
to wind load, 341 kN.
From CSA S1609 clause 27.11.1 Conventional construction R_{d}=1.5
, R_{o}=1.3
? the requirement of clauses 27.1 to
27.10 and 27.12 shall not apply to these systems.
In low or moderate seismic zone, using a higher R_{d}xR_{o}
modification factor is not necessary as it will trade the convenience of
nonseismic connection design for nothing. With the use of response reduction
factor R_{d}xR_{o} under Conventional Construction, the seismic
load is already comparable to wind load, and in many cases, seismic load is actually
lower than wind load.

NOTES 
It?s incorrect to conceive that in Fort McMurray area the
wind load will govern structural design and the seismic load is negligible
compared to wind load. In this case the seismic load for braced frame, 422 kN,
is bigger than the wind load,
341 kN. One may argue that the wind load still govern when
it goes to the load combination considering wind load factor of 1.4, and
seismic load factor of 1.0, but actually in many cases the seismic load will
govern in the design of petrochemical structures in Fort McMurray area.
Location: Vancouver
????? Location: Vancouver??????? ??????????????? Site
Class: Site D
SFRS 
Base Shear Ve
before Ve / (R_{d}xR_{o}) 
Base Shear SFRS CC
Ve / (1.5x1.3) 
Base Shear SFRS MD
Ve / (3.0x1.3) 
Base Shear SFRS D
Ve / (4.0x1.5) 
kN 
kN 
kN 
kN 

Moment Frame 
4185 
2146 
1073 
698 
Braced Frame 
8270 
4241 
2121 
1378 
From above seismic base shear calc, we can find that, in high
seismic zone such as Vancouver, using higher modification factor of R_{d}xR_{o}
is absolutely necessary, otherwise the huge seismic lateral load, 8270 / 341 = 24
times of wind load in this case, will create an impractical structural design.
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Seismic Base Shear for Exchanger
Support Design
In this part the equipment is taken as a Nonstructural
Component and its seismic force is calculated as per NBCC 4.1.8.17.
This seismic force is used for the design of local equipment
support only (steel support for exchangers).
The exchangers sitting on top of structure (EL23.500) get the
biggest seismic response as the acceleration increases with the height of
structure. This effect is caputured by the height factor, newly introduced in
NBCC2005, A_{x} = 1 + 2h_{x} / h_{n}
For equipments at foundation level A_{x} = 1.0, and A_{x}
= 3.0 for equipments sitting at roof level.
????? Location: Fort
McMurray?? ??????????????? Site Class: Site D
Lateral Load Type 
Transverse Direction 
Longitudinal Direction 
kN 
kN 

Wind 
18 
4 
Seismic 
122 
243 
From above we find that, for local equipment support design,
the seismic load is much bigger than the wind load if the equipment is located
on a higher elevation above grade. This is mainly due to the dynamic amplifying
effect (Ar =2.5) for big mass sitting on a flexible supporting structure.

NOTES 
It?s incorrect to conceive that in Fort McMurray area the
wind load will govern structural design and the seismic load is negligible
compared to wind load. In this case the seismic load can be 243/4 = 61 times
bigger than the wind load.
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Design Example 02: SkirtSupported
Vertical Vessel
Structure
Classification: Case 03
Calculate the seismic force for a skirtsupported vertical
vessel
Vessel diameter = 7.189 m??????????????
Vessel height = 12.400 m
Vessel shell thickness = 0.25 in
Vessel empty weight = 221 kN
Vessel operating weight = 3793 kN
Vessel hydrotest weight = 5055 kN
Site location : Fort McMurray
Site class : Class D
Structure importance category : Normal

NOTES 
It?s incorrect to conceive that in Fort McMurray area the
wind load will govern structural design and the seismic load is negligible
compared to wind load. In this case
seismic base shear is 131.5 kN? vs wind base shear 71.9 kN
seismic overturn moment is 1087.0 kNm? vs wind overturn moment 499.9 kNm
In this case, the overturn moment caused by seismic is 2
times of the overturn moment caused by wind. This is mainly due to the reverse
triangle distribution of seismic load.
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Design Example 03: Braced Leg
Supported Vertical Vessel
Structure
Classification: Case 04
Calculate the seismic force for a bracedleg supported PSC
vessel. The PSC vessel is supported by 10 x OD=1450mm wall thk =27mm steel
column equally spaced at 22.5m diameter circle. ?The 3D support frame is braced by 25 dia steel
tension only rod. Vessel empty weight = 13810 kN , operating weight = 183710 kN
Site location : Fort McMurray ???????????? Site class : Class D??????????? Structure
importance category : Normal
The PSC vessel is a cone shape, diameter varies from 0m to
32m along the 30m vessel height. To simplify the wind load calculation, assume
it?s a dia=16m H=30m cylinder vessel, which gives the same projection area for
wind load calc.
BracedLeg Supported PSC Vessel
Use Master/Slave to define the top support plane as a rigid
diaphragm. Use the central node as a master node, the central node needs not to
be physically connecting to the surrounding nodes.
STAAD Model : Rigid Diaphragm and
Tension Only Brace
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NOTES 
It?s incorrect to conceive that in Fort McMurray area the
wind load will govern structural design and the seismic load is negligible
compared to wind load. In this case
seismic base shear is 771.6 kN? vs wind base shear 319.0 kN
seismic overturn moment is 10416.4 kNm? vs wind overturn moment 5335.9 kNm
In this case, the overturn moment caused by seismic is 2.0
times of the overturn moment caused by wind. This is mainly due to
?
T_{a}
>0.7s causing F_{t} >0
?
Vessel
mass center is located at a higher elevation
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Design Example 04: SelfSupported
Horizontal Vessel
Structure
Classification: Case 05
Calculate the seismic force for a selfsupported horizontal
vessel
Vessel diameter OD= 3.683 m???????? Insulation
thk = 50mm??????
Vessel length = 20.700 m???????????????? Vessel
saddle distance = 16.535 m
Vessel empty weight = 533 kN
Vessel operating weight = 2317 kN
Site location : Fort McMurray
Site class : Class D
Structure importance category : Normal

NOTES 
It?s incorrect to conceive that in Fort McMurray area the
wind load will govern structural design and the seismic load is negligible
compared to wind load. In this case
For lateral load on vessel longitudinal direction
seismic base shear is 80.3 kN?
vs wind base shear 13.1 kN
seismic overturn moment is 157.4 kNm? vs wind overturn moment 20.1 kNm
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Design Example 05: Building Structure
Structure
Classification: Case 01
Calculate the seismic force for a pump house building
Building span = 11.1 m????????????????????? Building
total length = 33.37m????????? Roof slope
= 1:12
Building eave height = 7.94m?????????? Crane
runway height = 5.32m
Building has a 18 tonne overhead crane
Crane bridge wt = 8600kg???????????????? Trolley
+ hoist? wt = 1365kg??????????????
Site location : Fort McMurray
Site class : Class D
Structure importance category : Normal
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Design Example 06: Nonbuilding
Structure (> 25% Comb Wt) Supported by Other Structure
Structure
Classification: Case 09
Calculate the seismic force for a vertical surge drum
supported by a steel frame table top.


Vessel diameter D= 7.550 m = 24.770
ft???????
Vessel height H= 33.150 m = 108.760 ft
Vessel shell thickness t = 25.4mm = 1 in
Vessel empty weight = 2243 kN = 504675 lb
Vessel operating weight=20081kN = 4518225 lb
Vessel hydrotest weight=15938 kN= 3586050 lb
Site location : Fort McMurray
Site class : Class D
Vessel content is flammable hydrocarbon
Structure importance category : High 
Determine If Vessel Is
Rigid Nonbuilding Structure
Vessel linear weight W = 4518225 lb / 108.760 ft = 41543.1
lb/ft
Vessel fundamental period???
_{}?= 0.527 s >>
0.06 s?
? the vessel is a flexible Nonbuilding
Structure
Determine If Nonbuilding
Structure Wt Is More Than 25% of Comb Wt
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Vessel Support Steel Frame
Determine R_{d}xR_{o}
Value
R_{d}xR_{o} value of combined system shall be
taken as the lesser? R_{d}xR_{o}
value of the nonbuilding structure or the supporting structure
? Use R_{d}xR_{o} =
1.5x1.3 as Conventional Construction
Modeling Techniques In STAAD
1.
Model the vertical vessel as seven
segments of beam element, break the 33.15m into?
6x5m + 1x3.15m =33.15m
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Define Vessel Support Base as Rigid
Diaphragm 
Apply Vessel Content Mass As Linear
Load 
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NOTES 
It?s incorrect to conceive that in Fort McMurray area the
wind load will govern structural design and the seismic load is negligible
compared to wind load. In this case
seismic base shear is 766 kN?
vs wind base shear 279 kN ??? 766 /
279 = 2.7 times
seismic overturn moment is 15072 kNm? vs wind overturn moment 4620 kNm?? 15072 / 4620 = 3.3 times
It?s also risky to assume that the vendors? calculation will
take care of the seismic design. The vendor?s seismic calculation always
assumes the vessel base is fixed, as the vendor never has intension to get the
boundary condition of support structure. In this case, when vessel weight
exceeds 25% of combined weight, the vessel and supporting structure shall be
modeled together in a combined model to get the accurate response of
seismic load.
Anchor Bolt Anchor Reinforcement Supplementary Reinforcement ACI 31808 ACI31808 Appendix D ACI 34906 CSAA23.304 CSAA23.304 Annex D CSAA23.304 (R2010) ACI 349.2R07 ACI 355.3R11 ACI31808 D.5.2.9 ACI31808 RD.5.2.9 ACI31808 D.6.2.9 ACI31808 RD.6.2.9 Anchor Bolt Blowout Anchor Bolt Breakout Anchor Bolt Pryout Anchor Bolt Pullout Anchor Bolt Shear Anchor Bolt Moment Anchor Bolt Tension Anchor Bolt Tensile
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