DESIGN PROBLEMS OF ANCHORING OF ABOVEGROUND STEEL TANKS

Transcription

1 УНИВЕРСИТЕТ ПО АРХИТЕКТУРА, СТРОИТЕЛСТВО И ГЕОДЕЗИЯ Трети национален симпозиум по стоманени, дървени и комбинирани конструкции септември 2010 DESIGN PROBLEMS OF ANCHORING OF ABOVEGROUND STEEL TANKS Lyubomir A. Zdravkov 1 Keywords: abovegroud steel tak, achor, achor s chair, radial deflectio, stress Research area: steel structures SUMMARY Abovegroud steel taks are spatial sheet structures. The loads which impact o them are self-weight, sow, wid, earthquake, overpressure ad vacuum. Whe the earthquake, overpressure ad wid loads have high values, it is possible that the tak overtur or goig to slide. To elimiate the threat from free movig, the steel facilities are ofte achored to the foudatio. This solutio is ot recommedable, ad i stadards [1] ad [2] it is positioed o the last place. Despite the stadard s recommedatios whe the coditios of exploitatio are strait ad/or extreme, the steel vertical taks must be achored. Because of it, the developig of ew specific details is eeded o the purpose to miimize their ufavourable effects. 1. Itroductio The achorig of steel taks has a purpose to prevet their movemets out of the positio accordig to the project. I geeral this movemet ca be divided i the followig mai groups: - Tak s upliftig; - Tak s overturig; - Horizotal movemet ( slidig ) of the tak. I the first two groups of movemets the achors bear tesio forces. Whe the tak slides the achors work agaist shearig. The type of the effort determies how the achor s chairs shall be costructed (Fig.1) This type of the chair prevets the radial deflectios of the shell. This leads to the chage i the stress strai state i the shell i the fields close to achor s chairs. The curret research of the taks i which achor bolts, respectively chairs (Fig.2), must bear tesio ad shearig forces, has the followig purpose: - to check how the stress-strai state chages i the shell i the zoes of achor s chairs; - to check whether the achor bolts are beded whe the tak is beig filled ad cosecutive shell s deformatio; - what is the ifluece of the iteral stiffeig rig. 1 Lyubomir A. Zdravkov, PhD, Civil Egieer, UACEG, Sofia 1046, 1 Hristo Smiresky str., floor. 7 office 733, [email protected]

2 Fig. 1. Type of achor s chair depedig o forces i bolts 1. Tak's shell 2. Plate 3. Tak s bottom 4. Superior plate 5. Achor bolt 6. Vertical ribs 7. Iferior plate 8. Stiffeig rig I some cases achor bolts bear tesio ad shearig forces ad this case imposes the relevat details of their chairs (Fig.2) Fig. 2. Achor bolts for tesio ad shearig forces, ad their chair 1. Tak shell 2 Plate 3. Tak s bottom 4. Superior plate 5. Achor bolt 6. Vertical ribs 7. Iferior plate 8. Stiffeig rig

3 2. Research of the ifluece of achor s chairs The ifluece of the achor s chairs shall be researched for the tak T003, i La Reuio. The tak have the followig parameters (Table 1): Table 1. Tak Т003, i La Reuio Idex Descriptio 1 Mai dimesios 1.1 Nomial volume - V V = 630 m Iteral diameter - D D = mm 1.3 Shell height - H s H = mm 1.4 Roof - Type Self-supportig coe 2 Liquid ( product ) 2.1 Name water 2.2 Desity - ρ kg/m Temperature t 0 C - miimum workig - maximum workig mi t = C max t = C 2.4 Overpressure - p 0 p 0 = 1,00 kpa 2.5 Vacuum - p v p v = 0,50kPa 2.6 Maximum level of the fillig H t = mm accordig to the project 3 Coditios of the site 3.1 Sow - S o 3.2 Wid - w w m = 34 m/s 3.3 Seismic zoe - E VIII th zoe, k c = 0, Geological soil structure Accordig to the geological report 4 Additioal data 4.1 Material used for bottom, shell ad S235J0 accordig to EN roof 4.2 Achorig 16 pieces М Mode of costructio Sheet by sheet 4.4 Productio powder - g p o 4.5 Thermal isulatio - g t o A software product SAP 2000 Noliear was used for the aalysis. It was used to create several 3D tak s models. Achor s chairs which must bear tesio ad shearig forces i bolts are icluded also (Fig.3). I these models the bottom, shell, roof, achor s chairs ad stiffeig rigs o the shell were iserted as shell elemets ad achor bolts are frame elemets.

4 Fig. 3. Numerical 3D model All the tak s parts are joied with their geometrical characteristic (thickess). All elemets are made from structural steel S235 which mechaical characteristics are show i stadard EN Whole bottom of the tak, icluded also the iferior plates o chairs protruded out as a cosole, is cosidered as plate o the elastic base with the bed s coefficiet k b = 200 MN/m 3. It is assured that the bottom shall bear oly pressure s forces. The detachmet of the bottom e.g. slidig ad overturig of the tak shall be avoided by 16 achors positioed at equal distace aroud the shell, thread M39, made from steel S355. All these achor bolts have pi joits with the upper plate ad are fixed to the foudatio. Achors shall ot bear pressure s forces. Several umerical models were created iitially, i which achor bolts were joited to the bottom (fig.2) e.g. it is ot possible for the bottom to expad or to shrik as a result of temperatures differeces. I these models it is accepted that all steel elemets are additioally loaded with heat. The differece i temperature is equal to Δt = 25 0 C. Desig load combiatio is: g. γfg, sup + T. γft (1) where: g is the characteristic value of its self-weight; T - resulted iside forces whe it acts a additioal temperate load Δt = 25 0 C; γ Fg,sup = 1,35 particular coefficiet for loadig from its self-weight; γ Ft = 1,5 particular coefficiet for loadig from temporary loads. Resulted shearig forces which are caused i the achor bolts as a result from the upper loadig combiatio (1) are show o the Table 2: Table 2. Shearig forces i the achor bolts Iteral stiffeig rig Shearig forces i the achor, kn o 402,84-6х50 401,88-3х ,09-6х ,21 As result, shearig forces i the achors caused by heat loads, exceed their bearig capacity. Because of it i the achor's chair ad / or i the bottom it is formed a oval opeig which assures free expadig or shrikig of the bottom. Later ew research models were created accordig to which the achor bolts are ot coected to the bottom. The bottom ca freely slide from the temperature differeces. These ew models have oly oe

5 differece betwee them ad it is the presece ad measures of the stiffeig rig i the iteral side of the shell. The imposed loads i the 3D models are: G its self-weight of the steel costructio; W a loadig by stored product i the tak; P over pressure; V uder pressure (vacuum); W i wid pressure o the tak. 3. Results Deformatios i the tak s shell (Fig. 4) are a sure sig that the achor s chairs, costructed o this way, which shall bear tesio ad shearig forces are a obstacle for the free movig of the tak. This leads to the chage i stress strai state e i the tak (Fig. 5). Fig. 4. Deformatio i the tak s shell Фиг.5. Mai stresses i the shell ad achor's chairs Radial deflectio of the shell ad its mai stresses are reported i the 3D research models for oe ad the same poit i the tak.

6 Table 3. Radial deflectio of the shell, mm rig Betwee the chairs I the chairs G + W a + P G + V G + W i + P G + W a + P G + V G + W i + P o 1,94 0,16-1,16 0,14-0,23 1,1-6х50 1,57 0,1-0,83 0,4-0,15 0,67-3х100 1,32 0,01-0,46 0,61-0,09 0,39-6х100 1,19 0,01-0,34 0,6-0,07 0,27 Deflectio + it is o the outside directio Deflectio - е it is o the iside directio toward the tak ceter Table 4. Mai stresses i the shell, kn/cm 2 rig Betwee the chairs I the chairs G + W a + P G + V G + W i + P G + W a + P G + V G + W i + P o 10,83 0,187 0,62 2,78 0,09 2,12-6х50 9,94 0,124 0,88 2,5 0,04 3,24-3х100 9,88 0,056 0,97 2,86 0,43 4,41-6х100 9,49-0,087 1,09 2,83 0,51 4,9 Table 5. Shearig forces i the achor bolts Rig Bedig momet М, kn.m Cuttig efforts Q, kn G + W a + P G + V G + W i + P G + W a + P G + V G + W i + P o 0,27 0,16 0,84 4,7 2,1 17,27-6х50 0,4 0,11 0,58 3,95 1,82 16,77-3х100 0,49 0,08 0,43 3,24 1,64 16,5-6х100 0,49 0,061 0,48 3,37 1,57 16,39 4. Coclusio The achor s chair costructed o this way does ot permit the radial deflectio i the shell. This leads to the chages i the stress - strai state i the shell ad i the area of the achor s chair. Whe the movemet of the chair ad the pick of the achor bolts are oe ad the same, there are additioal bedig momets M ad shearig forces Q i the bolts. Because of it achors shall move freely i their upper ed ad for this purpose oval opeigs are doe. Importat iflueces have also ad the geometric characteristics of the stiffeig rigs put iside. The stiffeig rigs with bigger momet of iertia shall cause: Decrease of radial deflectio ad mai stresses i the shell betwee the chairs; Icrease of radial deflectio ad mai stresses i the shell i the chairs area; Icrease of the bedig momet М i the achor bolt by the loadig combiatio G + W a + P LITERATURE 1. API Std 650, Welded Steel Taks for Oil Storage, Eleveth Editio, Jue EN 14015:2004, Specificatio for the desig ad maufacture of site built, vertical, cylidrical, flatbottomed, above groud, welded, steel taks for the storage of liquids at ambiet temperature ad above, November 2004.