ANALYSIS AND DESIGN OF VERTICAL VESSEL FOUNDATION
ANALYSIS AND DESIGN OF VERTICAL VESSELFOUNDATIONA thesisSubmitted byJAGAJYOTI PANDA (109CE0168)M.S.SRIKANTH (109CE0462)In partial fulfillment of the requirementsFor the award of the degree ofBACHELOR OF TECHNOLOGYinCIVIL ENGINEERINGDepartme nt of Civil EngineeringNational Institute of Technology RourkelaOrissa -769008, IndiaMay 20131
CERTIFICATEThis is to certify that this report entitled, “Analysis and design of ve rtical vessel foundation”submitted by Jagajyoti Panda (109CE0168) and M.S.Srikanth (109CE0462) in partialfulfillment of the requirement for the award of Bachelor of Technology Degree in CivilEngineering at National Institute of Technology, Rourkela is an authentic work carried out bythem under my supervision.To the best of my knowledge, the matter embodied in this report has not been submitted to anyother university/institute for the award of any degree or diploma.Date:Prof. Pradip SarkarDepartment of Civil Engineering(Research Guide)2
ACKNOWLWDGEMENTWe would like to give our deepest appreciation and gratitude to Prof. Pradip Sarkar, for hisinvaluable guidance, constructive criticism and encouragement during the course of this project.Grateful acknowledgement is made to all the staff and faculty members of Civil EngineeringDepartment, National Institute of Technology, Rourkela for their encouragement. I would alsolike to extend my sincere thanks to my M.Tech senior Mr. K.Venkateswara Rao for his help. Inspite of numerous citations above, the author accepts full responsibility for the content thatfollows.Jagajyoti Panda and M.S.Srikanth3
ABSTRACTKEYWORDS: vertical vessel, anchor bolts, octagonal footing, spectral acceleration,fundamental period, butt weld, dowel bars, soil stiffness, resonance.Vertical vessels are massive structures used in oil industries which store oil and different fluids.Due to the massiveness of the structure and pedestal considerations, an octagonal foundation isdesigned in place of a simple rectangular footing. The design includes analyzing of loads fromsuperstructure, design of base plate and foundation bolt, design of pedestal and footing. Thedesign of pile is not considered in the present study. The main objective of the study is toevaluate the manual method of design procedure. The same footing is modeled in differentcommercial finite element software. Performance of the designed foundation as obtained fromthe finite element analysis is then compared with that obtained from manual calculations.Maximum moment obtained from the software for the given support forces are found to behigher than those calculated manually according to Process Industry Practices guideline.Therefore, the design process outlined in PIP underestimates the bending moment demand as perthe present study. However the present study is based on one typical case study. There is aprovision for repeating this study taking into consideration a large number of foundations withvarying parameters to arrive at a more comprehensive conclusion.4
TABLE OF CONTENTSTITLEPAGE NO.CERTIFICATE2ACKNOWLWDGEMENT3ABSTRACT4TABLE OF CONTENTS5LIST OF TABLES9LIST OF FIGURES10NOTATIONS11CHAPTER 1: INTRODUCTION1.1 Background131.2 Objectives131.3 Scope of Work131.4 Organization of Thesis14CHAPTER 2: LITERATURE REVIEW2.1 General152.2 Identification of load cases152.2.1 Vertical loads152.2.2 Horizontal loads152.2.3 Live loads165
2.2.4 Eccentric loads162.3 Other design considerations16CHAPTER 3: ANALYSIS OF STEEL SUPERSTRUCTURE3.1 Wind load analysis173.2 Seismic load analysis213.3 Fundamental period of the chimney233.4 Check for resonance24CHAPTER 4: MANUAL CALCULATION4.1 General254.2 Material properties254.2.1 Superstructure264.3 Bolt and pedestal design264.4 Footing design294.5 Check for stability314.6 Calculation of section modulus of octagonal foundation324.7 Check for soil bearing324.8 Reinforcement334.9 One way shear check334.10 Punching shear check34CHAPTER 5 : FE ANALYSIS AND DESIGN5.1 General356
5.2 FE analysis based on STAAD Pro365.2.1 3-d view of the pedestal and footing365.2.2 Staad generated mesh of pedestal and footing375.2.3 Load cases details385.2.4 Staad pro results385.3 STAAD foundation395.4 Design40CHAPTER 6 : RESULTS AND DISCUSSIONS6.1 General426.2 Design results: data on sub-structure426.2.1 Pedestal426.2.2 Anchor bolt426.2.3 Footing436.3 Plaxis Analysis436.4 Discussions44CHAPTER 7: SUMMARY AND CONCLUSION7.1 Summary457.2 Conclusions457.3 Scope for Future Work45REFERENCES467
LIST OF TABLESTITLEPAGE NO.Table 1: Details of the superstructure25Table 2: Modeling parameters for STAAD P ro35Table 3: Material properties35Table 4: Plate Contour39Table 5: Node reaction summary39Table 6: Pedestal data of vertical vessel42Table 7: Anchor bolt data42Table 8: Footing data43Table 9: Soil parameters438
LIST OF FIGURESTITLEPAGE NO.Fig. 1 : Plan of pedestal and foundation31Fig. 2 : Graph for calculation of L diag of octagonal footing32Fig. 3 : STAAD Model of pedestal and footing36Fig. 4 : Plate Model37Fig. 5 : Base force and Moment38Fig. 6 : STAAD Foundation Model40Fig. 7 : Plaxis model439
NOTATIONSd0Diameter of anchor boltBCDBolt circle diameterDpedDiameter of pedestalh efDepth of embedmentMpedOverturning moment at the base of the pedestalFuMax. tension in reinforcing barαStrength reduction factor in rebarh footDepth of footingAfootArea of footingSRStability RatioAstArea of steel reinforcementDC DDowel circle diameterSBCSafe bearing capacityEsElastic modulus of steel 2 x105 MPaEcModulus of elasticity of concretefydDesign yield strengthfyYield strength of structural steelfck28 day characteristic strength of concreteVbBasic wind speed10
rcRadius of gyrationIMoment of InertiaIeffEffective moment of inertiaMBending moment acting on a section at service loadMuUltimate moment of resistanceTTensionCtCoefficient depending upon slenderness ratiokSlenderness ratioVcrCritical velocityVdDesign wind speedXUDepth of neutral axisb edge anchor Edge distance of anchor boltM pedOverturning moment at the base of pedestalndNumber of dowelsh footDepth of the footing11
CHAPTER 1INTRODUCTION1.1BACKGROUNDVertical vessels find their application usually in oil and gas industries. They contain a number oftrays which are designed for mixing between a rising gas and a falling liquid. The vessel issimilar to a horizontal drum that comprises of two dished heads, one at the top and one at thebottom. It is supported by a skirt which is welded to the bottom head. Skirt is a cylindrical steelshell which rests on the reinforced concrete foundation.It is due to the massive structure and large capacities of the vessels for which octagonalfoundations are preferred. The monopoles are also designed with octagonal foundationsunderneath. The design includes analyzing of loads from superstructure, design of base plate andfoundation bolt, design of pedestal and footing. The design of pile is kept outside the scope ofthe study.1.2OBJECTIVESPrior to defining the specific objectives of the present study, a detailed literature review wastaken up. This is discussed in detail in the next chapter. The main objectives of the present studyhave been presented as follows.1. Analyze and Design vertical vessel foundation using manual calculation available inliterature.2. Model and analyse the foundation using FEM3. Evaluate the Manual Method of designing vessel foundation1.3 SCOPE OF WORK1. The design includes following items: Analysis of loading on the foundation. Design of foundation bolt. Design of pedestal and footing.12
2. The foundation is designed as a soil supported one i.e. as a shallow foundation.3. Design of pile is kept outside the scope of the study1.4ORGANISATION OF THESISChapter 1 has presented the background, objective and scope of the present study.Chapter 2 starts with a description of various load cases and different design considerations to betaken into account for foundation design.Chapter 3 deals with the analysis of the vessel superstructure.Chapter 4 discusses the manual calculation of design of anchor bolts, pedestal and the footingusing the available literatures.Chapter 5 shows the design results of the octagonal footing by manual calculation and with thehelp of finite element software.Finally chapter 6 presents summary, significant conclusions from this study and future scope ofresearch in the area.13
CHAPTER 2LITERATURE REVIEW2.1GENERALIn this section a general study on the different type of loads and load combinations is carried outusing the STE03350 - Vertical Vessel Foundation Design guide and various other literaturesavailable. The most relevant literature available on the study of different load cases has beenreviewed and presented in this Chapter.2.2IDENTIFICATION OF LOAD CASESDifferent loads are taken into account while analyzing the superstructure i.e. the various verticalloads, the horizontal wind loads and the eccentric loads.2.2.1 VERTICAL LOADSStructure dead load- It is the sum of weights of the pedestal, footing and the overburdensoil. Erection dead load- It is the fabricated weight of the vessel taken from the certified vesseldrawing. Empty dead load- It is the load coming from the trays, insulations, piping, attachmentstaken from the drawings. Test dead load- It is the load coming from the empty weight of the vessel and that of thetest fluid (usually water) required for hydrostatic test. Operating dead load- It is the weight of the empty vessel plus the weight of the operatingfluid during service conditions.2.2.2 HORIZONTAL LOADSWind load- It is the wind pressure acting on the surface of the vessel, piping and otherattachments of the vessel.14
Seismic load- The horizontal earthquake load is applied 100 % in one direction and 30 %on the orthogonal direction.2.2.3LIVE LOADSLive loads are taken into account as per STE03350 - Vertical Vessel Foundation Designguidelines. Live loads would not typically control the design of the foundation.2.2.4ECCENTRIC LOADSEccentric vessel loads must be taken into account which is caused by large pipes and boilers.2.3OTHER DESIGN CONSIDERATIONS To check stability of structure against stability and overturning. To check soil bearing pressures not exceeding the ultimate bearing capacity of the soil. Anchor bolt design to be carried out.15
CHAPTER 3ANALYSIS OF STEEL SUPERSTRUCTURE3.1WIND LOAD ANALYSISCalculation of static wind load is based on IS 875 Part 3: 1987 considering the vessel as generalstructure with mean probable design life of 50 years.Risk factor (k1) 1As vessel is to be located on a level ground, k3 1and considering vessel site to be located on sea coast terrain, category 1 is considered for thewind load calculation.Since the vessel is 21.6m high, the size class structure is considered as class B.Assuming the highest average wind speed in the site isV max 20 km/hr 6.556 m/sBasic wind speed as per Fig 1. IS 875 Part 3 is V b 39 m/sWind load on the vessel will be increased due to the presence of platform, ladder and otherfittings (5 % increase in the wind load)For computing wind loads and design of the chimney, the total height of the vessel is dividedinto 3 parts.Part 1 (21.6m – 20m)Diameter of the vessel d1 1.3mConsidering k2 factor in this height rangeLateral wind load P1 0.243 10 kN16
Moment due to the wind force at the base and part1M1 (h-20)dh 19.5 kNmShell thickness of the vessel T 1 0.4mSection modulus Z 1 πd2 T/4 0.5 m3Bending stress at the extreme fiber of the shell at 30m level fmo1 1.05 M1 / Z 1 18 MpaMax tensile stress 40 MPaf t1 f allow,T (hence okay)Part 2 ( 20m – 12m)It is located at a height of 12m to 20m from the ground.Considering K2 factor in this height range,P 2a 11.23 kNP 2 11.23 2.43 13.66 kNMoment due to the wind force at the base of part-2 (at 16m)M 2a d (h-12) dh 20.31 kNm17
M 2b d (h-12) dh 45.2 kNmM 2 65.55 kNmSection modulus at this level is 0.5 m3Bending stress at the extreme fiber of the vessel at 12m level isf mo2 1.05 M 2 / Z 2 137.65 KN/ m2Max tensile stress f t3 f mo3 28.9 Mpa 212 MpaPart 3 ( 0m-12m)Part 3 is located at a height of 0m to 12m from the ground.d 1.3mconsidering K 2 factor, lateral wind forceP a 2.55 kNP b 12.5 kNShear force due to wind force at the base 12.5 2.55 13.66 28.7 kN18
Moment due to the wind force at the base of the part 3,Ma d (h-0) dh 47.9 kNmMb d (h-0) dh 180 kNmMc d (h-0) dh 28.13 kNmM d d (h-0) dh 90.62 kNmM 3 346.65 kNmZ 0.5 m3 ( at level of 0m )Bending stress at the extreme fiber of the vessel at 0m levelfmo3 1.05 346.68/ 0.5 72.8 MPaMax tensile stress f t3 72.8 MPa 212 MPa19
3.2SEISMIC LOAD ANALYSISMaximum Spectral acceleration value corresponding to the above periods considering 2%damping and soft soil site,Sa 0.75 9.81Importance factor for Steel stack (I) 1.5Response Reduction factor (Rf) 2Zone factor 0.10Design Horizontal acceleration spectrum value (Ah) (Z/2) (Sa/9.81) / (Rf/I) 0.281Design base shear (Vb) Ah Wt 43.2KNMaximum Shear Stress at the base (F sh eq) Vb /(π d T) 0.264 10 MPacalculation of design momentDenominator 2 h2 dh 2dhdh 4.307 105 KN.m21. Moment due to Seismic at the 20m levelMsesmic (2.Vb.(h-20)dh)/denominator 31.48KNBending stress due to Seismic force at 20m level (fsmo ) M/Z 62.9MPaIncrease of 33.33% in allowable stress is allowable stress is allowed for Earthquake loadFallow,seis 1.33 fallow 115.7MPa(Therefore safe)20
2. Moment due to Seismic at the 12m level2Mseismic tor 412.4MPaBending Stress due to seismic force at 12m level (fsmo ) M/Z 100.569MPaIncrease of 33.33% in allowable stress is allowable stress is allowed for Earthquake loadFallow,seis 1.33 fallow 115.7MPa(Therefore safe)3. Moment due to Seismic at the 0m level2Mseismic .Vb.(h-0).dh)/Denominator 2.Vb.(h-0).dh)/Denominator 2.Vb.(h-0).dh)/Denominator 812.53 KN-mBending Stress due to seismic force at 0m level (fsmo ) M/Z 5.254 10 MPaIncrease of 33.33% in allowable stress is allowable stress is allowed for Earthquake load Fallow,seis 1.33 fallow 115.7MPa3.3(Therefore safe)FUNDAMENTAL PERIOD OF THE VESSELFundamental period of vibration for this chimney is calculated as per IS 1893 Part 4 to check thevessel design against dynamic load.Area of c/s at base of the vessel A base πd base .T sh21
0.163 10 m2Radius of gyration at the base of the shell rc (dbase/2) (1/2)1/2 0.45mSlenderness ratio k ht /rc 46.96Coefficient depending upon slenderness ratio C t 1.8k 84.52Weight of superstructure 128.23 KN/mWeight of platform, ladder Wp 0.2 Ws 25.6 KNTotal weight of vessel (Wt ) Ws Wp 153.94 KNModulus of elasticity (Es ) 2 105 N/m2The fundamental period for vibration Tn C t (Wt.Ht/ Es.Abase g)1/2 2.72 s3.4CHECK FOR RESONANCEFundamental period of vibration for the vessel Tn 2.72 sFundamental frequency of vibration f 1/ Tn 3.68 10-1 HzCritical velocity Vcr 5 d f 2.3897 m/sBasic wind speed Vb 39 m/sDesign wind speed V d k1 k2 k3 Vb 43.68 m/s22
Velocity range for resonance :V resonance UL 0.8 V d 34.944 m/sV resonance LL 0.33 V d 14.414 m/sAs critical velocity doesn’t lie within this range of resonance limit,the vessel need not bechecked for the resonance.23
CHAPTER 4MANUAL CALCULATION4.1GENERALUsing the available literature, the foundation is analyzed and designed manually. Theassumptions, procedure and logic have been discussed in this Chapter.4.2MATERIAL PROPERTIESYield stress of the structural steel: f y 415MPaModulus of elasticity of the material of the material of structural shell: Es 2 105 MPaMass density of the structural steel: 78.5 kN/m3Assume Imposed load and wt. of Platform, access ladder 20% of the self- weight of thechimney shella. Max. permissible stress in tensionF allow tension 0.6fy 250MPa(IS 800-2007)Considering efficiency of Butt weld: 0.85Allowable tensile stress: f allow.T 0.85 250 212MPab. Max. permissible stress in shearFallowable Shearc. 0.4fy 160MPaMax. permissible stress in compression is a function ofh level Effective Height for consideration of bucklingD Mean diameter of the vessel at the level of considerable heightT Thickness at the level consideration24
4.2.1SUPERSTRUCTURE DATATable 1: Details of the superstructureOUTER DIAMETER1.7 mTHICKNESS0.4 mHEIGHT21.6mMATERIALSTEELERECTION WEIGHT470 KNEMPTY WEIGHT350 KNOPERATIONAL WEIGHT790 KNWIND LOAD48 KN4.3 BOLT AND PEDESTAL DESIGNDiameter of bolt 45 mmACI 318 requires anchors that will be torqued should have a minimum edge distance of 6d 0b edge anchor 6 d0 6 45 0.27mBolt circle diameter (BCD) Diameter of vessel (0.12 2) 1.7 0.24 1.94mConcrete pedestal supporting the vertical vessel shall be sized according to the following:It should be greater than d1 and d2 whered1 BCD 7 in25
d2 BCD 8d0d1 and d2 come out to be 2.12m and 2.3m. We have assumed the dimension of pedestal to be2.48m which satisfies both the conditions being greater than d 1 and d2 .D ped reqd 2.48m 1.5m(hence foundation is octagonal in shape)Min. embedment depth h ef 12d0 12 0.045 0.54mLet us assume h ef as 1mAccording to ACI 318, min. embedment depth above ground level h proj-ped 0.3mDepth of pedestal larger should be larger than h ef h proj-ped 1.3mDepth of pedestal considered h pedestal 1.6mUnit weight of reinforced cement concrete 25 KN/m3Weight of pedestal 25 5.092 1.6 1 204 KNTotal weight of the pedestal and the vessel 414 KNTotal overturning moment at pedestal base M ped M base F h 866.8 KNUltimate overturning moment 1.6 M ped 1.6 866.8 1386.88 kNmDowels should be provided when the height of pedestal exceeds 1.5m.Assuming no of dowels n d 40Dowel circle diameter DCD d ped – 6in 0.248 10 – 6in26
2.32mTotal downward force F y W ped 210 204 414 KNMax tension in reinforcing bar F u [4Mu ped /n DCD – 0.9(F y W ped)/n ] 5.046 10 KNStrength reduction factor for reinforcing bar α 0.9Therefore the area reqd for each of the dowels As reqd F u /α f ys 50.46 103 / 0.9 415 135.10 mm2Dowel size to be used 16mmAs provided π 162 /4 201.062 mm2Spacing between dowel bars π DCD / n π 2.32 / 40 0.182mThe pedestal shall have a reinforcing grid of 16mm diameter @ 180 mm c/c each way to preventpotential concrete cracking.Provide tie 12mm tie set (2 tie per set) @ 300 mm c/cConsidering the bolts are of ductile steel, strength reduction factor for the anchor 0.75 (fortension)As Indian code doesn’t have specific requirement for design of anchor bolts, ACI 318:2005 isfollowed for the anchor bolt design.Diameter of bolt (assumed) d0 45mmYield strength of the bolt f y bolt 400 MPaTensile strength of bolt f t 0.6 40027
240 MPaTension capacity of each bolt R t 0.8 π d0 2 f t / 4 305.362 KNBCD 1.94mLet number of bolts required (support moment increased by 50 % from stability consideration)be n bn b reqd [4M base 1.25 1.5/(R t BCD)] - [0.7 P base/ R t ] [4 790 1.25 1.5/ (305.362 1.94)] – [0.7 Pbase /Rt ] 9.52We have provided 18 bolts. (okay)4.4FOOTING DESIGNFooting having least dimension across sides that is equal to greater than 2m shall be octagonal inshape. Assuming a trial depth of the footing h foot 0.4mTotal overturning moment at the footing base M base V base h footing 790 48 (1.6 0.4) 886 kNm 150 kN/m2Taking allowable gross soil bearing pressureDiameter D 2.6[M footing /SBC]1/3 2.6 [886/150]1/3 4.7 mProviding a trial diameter d footing 6mSide of foundation 2.485 mArea of footing A foot 8 0.5 3 2.485 2.982 10 m2Footing weight W foot A foot h foot 2528
29.82 0.4 25 298.2 KNUnit weight of wet soil 18 KN / m3Weight of the soil (A foot – A ped)(h ped – h proj-ped) 18 578.448 KNWeight of the pedestal 204 KNTotal weight of vessel, pedestal, soil and footing W P base W soil W ped W foot 210 578.448 204 298.2 1290.648 KNWater
Skirt is a cylindrical steel shell which rests on the reinforced concrete foundation. It is due to the massive structure and large capacities of the vessels for which octagonal foundations are preferred. . Analyze and Design vertical vessel foundation using manual calculation available in literature. 2. Model and analyse the foundation using FEM
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