Dynamic Analysis on Staad

2007 ASCE Standard for Seismic Design of Petrochemical FacilitiesSeismic Design of Coker

Structures using ASCE 7-05

D. S. (Stan) Martin P.E.Bechtel Corporation

Oil, Gas, and Chemicals Global Business UnitHouston, Texas

• Growth trend in U.S. and worldwide for Coker projects due to shifting crude oil supply patterns

• Refineries are processing more high sulfur/ low quality crude oil

• Delayed Coking process converts the heavy “bottom of the barrel” components into solid coal-like fuel

• Coke is used for Power Generation, Cement production (Kiln fuel), Exports

Seismic Design of Coker Structures

• Bechtel Corporation has been active in recent growth of Delayed Coking

• Entered Alliance with Conoco in 1994 as exclusive agent for marketing and licensing its process technology for delayed coking

• Recent projects in which seismic loading controlled design of the coker structure

Client Location Code Seismic Criteria

Conoco_Phillips Borger, TX ASCE 7-98 SDC B

PetroCanada Edmonton, Alberta, Canada

NBC (Canada) 1995 Zone 1

HOVENSA St. Croix, USVI UBC-97 Zone 4

Conoco Billings, MT UBC-88 Zone 2B



Concrete Table-Top

Coke Drums(in Pairs)

Steel Drilling Structure

Foundation Mat / Pit


EXAMPLE PROBLEM FOR UPDATED ASCE SEISMIC GUIDELINES FOR PETROCHEMICAL FACILITIES

Coke DrumsDiameter: 23’-6”Base Ring to Upper Seam: 80’-0”Operating Wt (Pair): 4112 kips% of Seismic Mass: 19.5%

El 77’-0”

El 57’-9”

El 27’-0”

El 0’-0”

Table-Top Structure6 Columns w. 8’-0”x 8’-0” Cross SectionColumn Grid: 1 N-S Bay @ 37’-0”

2 E-W Bays @36’-0”Top Level: 7’-0” Thick SlabIntermediate Level: 4’-0” Thick Slab with 8’ wide x 7’ deep beams on Col linesLower Level: 8’wide x 7’ deep beams on Col linesSelf Wt: 14213 kips% of Seismic Mass: 67%

Seismic Design Criteria for Example• Site Class C (Assumed Soil Properties, Chap 20)

• SDS (0.2 sec) = .51g (Section 11.4)

• SD1 (1.0 sec) = .20g (Section 11.4)

• Occupancy Category III (Table 1.1)

• Importance Factor 1.25 (Table11.5.1)

• Seismic Design Category D (Tables 11.6-1 & 11.6.2)


Seismic Analysis and Design


Step 1 - Determine the Fundamental Period of the Structural System• Coupled Model, Fixed Base• Concrete Sections Cracked• Drums Modeled as Linear Elements• Steel Modeled as Weight at Support Points

TN-S: 0.74 seconds

TE-W: 0.69 seconds



Step 2 – Select the Analysis Procedure• Permitted Analytical Procedures listed in Table 12.6-1• Period less than 3.5 Ts (1.37 sec)• Coker Table Top contains Vertical Stiffness (Type 1) and Mass (Type 2) Irregularities as defined in Table 12.3.2

Equivalent Lateral Force Analysis is not permitted.

Modal Response Spectrum Analysis is chosen



Step 3 – Develop the Design Response Spectrum (Section 11.4.5)

Coker Example Response Spectrum

0.00

0.10

0.20

0.30

0.40

0.50

0.60

0.00 1.00 2.00 3.00 4.00 5.00 6.00

Seconds

Acc

eler

atio

n (g

)



Step 4 – Prepare the Analytical Model (Sections 12.7 and 15.3)

Seismic Design of Coker StructuresSeismic Analysis and Design

Step 5 – Process the Dynamic ModelMode No. Freq (Hz) Period

(Sec)X-Spectrum

% ParticipationY-Spectrum

% Participation

1 1.348 0.742 84.74

2 1.443 0.693 85.58

6 2.983 0.335 3.74

7 3.088 0.324 3.02

8 8.475 0.118 6.34

10 8.731 0.115 6.39

TOTALS 94.99 94.82

Mode Shape 1Mode Shape 6Mode Shape 8


Step 6 – Response Spectrum Analysis• Ensure 90% of mass participating• Combine internal modal forces from design response

spectrum using SRSS or CQC• Check base shear for need to scale results upward

Direction Coupled Analysis RSA (V)

ELF(V)

RSA/ELFS(Base Case)

Scaling Required?

N-S 5296 k 6186 k 0.86 no

E-W 5710 k 6623 k 0.86 no


Step 7 – Select a Structural System for the Concrete Table Top (1of 3)

• Considered a NBS similar to Buildings• Available systems listed in Table 15.4-1• For SDC D, the following moment frame systems are permitted;

Lateral Force Resisting System R Height Limitations Detailing Requirements

Ordinary Reinforced Concrete Moment Frame (OMF)

0.8 50 ft ACI 318, excluding Chapter 21

Intermediate Reinforced Concrete Moment Frame (IMF)

0.8 No limit ACI 318, including Chapter 21

Intermediate Reinforced Concrete Moment Frame (IMF)

3.0 50 ft (Discussion Follows)

ACI 318, including Chapter 21

Special Reinforced Concrete Moment Frame (SMF)

8.0 No limit ACI 318, including Chapter 21ASCE 7 Section 14.2.2.6


Step 7 – Select a Structural System for the Concrete Table Top (2 of 3)

• SMF (R=8) not recommended– Damage to structure, equipment and piping systems from even moderate Seismic Event could

affect plant operations– Structure likely to maintain a significant degree of original stiffness after reinforcement yielding

due to massive member proportions. This could result in serious under-design and disguise approach of push-over limit

• IMF (R=0.8 when Ht>50ft)– Cost Penalty for Overdesign and Detailing– Seismic loads in higher design categories will control member sizes and pile on even more seismic

mass


Step 7 – Select a Structural System for the Concrete Table Top (3 of 3)

SDC Structural System

(Recommended)

R Detailing

Requirements

A & B OMF 3 Exclude ACI Chapter 21

C IMF 3 Include ACI Chapter 21

D, E, F IMF ** 3 Include ACI Chapter 21

All Coke Drums 3 Welded steel with special detailing

** Outside of current ASCE Ht Limitation of 50 ft. Task Committee believes OK for oversize petrochemical structures, but requires comprehensive analysis and approval of Owner and permitting authority


Step 8 – Develop Load Combinations• DL(1.2) + LL(1.0) + EL(1.0)• DL (.9) + E(1.0)• EL includes

– 100% primary direction lateral load – 30% perpendicular direction lateral load

– 20% of DL x SDS in vertical direction

– Accidental Torsion– Redundancy Factor of 1.3 applied to lateral loads


Step 9 – Post Processing (1 of 2)

• Drift in Concrete Table-Top

Level Max Computed Story Drift Allowable Story Drift

N-S E-W (per Table 12.12.1)

73.5’ - 54.25’ 0.83” 0.68” 2.66”

54.25’ - 23.5’ 2.30” 1.99” 4.26”

23.5’ – 0’ 1.32” 1.20” 3.25”


Step 9 – Post Processing (2 of 2)

• Member Forces and Capacities

Bending Check at Elev 73.5’ E-W Moment in Slab at Elev 73.5’


Step 10 – Develop Design Details

#4 TIE SETS SPACED @ 11" (TYP) 7 TIES PER SET

NO LAP SPLICES IN N-S BEAMSPANLAP SPLICE E-W BEAM ATMIDSPAN (2 LOCATIONS)

2"

EXTEND COLUMNTRANSVERSEREINFORCEMENTTO TOP OF JOINT

#4 TIE SETSSPACED @ 11"

DETAIL AT TOP OFCOLUMNS

8'-0"

7'-0

"

BEAM CROSS SECTION

18-11's

18-11's

2-11's

2-11's

2-11's

2-11's

8'-0"

8'-0

"

68 - #11 BARS

#4 TIES

COLUMN CROSS SECTION

Seismic Design of Coker StructuresStep 11 – Design Nonbuilding Structures

supported by the Table-Top• Coke Drums

• Steel Drilling Structure– Seismic loading (Fp) from Chapter 13

– Design as Ordinary Concentrically Braced Frame with R=1.5

– OCBF does not have height limitations or detailing requirements

– Higher seismic loading typically not problem as wind governs design

– Seismic loading from the RSA of the combined model– R=3 for skirt-supported elevated vessels provided special detailing

requirements met– Loads usable for drum design and anchorage to table-top


QUESTIONS AND ANSWERS

Dynamic Analysis on Staad

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