Download Damage Assessment of Buildings Affected by the Fort Worth Tornado and more Exams Construction in PDF only on Docsity!
- of Fort Worth Tornado, 28 MarchDamage Survey and Assessment C.W. Letchford, H.S. Norville, and J. BilelloWind Science & Engineering ProgramTexas Tech University Prepared By
- National Institute for Standards and Technology Submitted to August
- Contents 1. Introduction..................................................................................................................... 12. Tornado details................................................................................................................ 13. Documented damage....................................................................................................... 64. Discussion 252.1 Tornado path estimate 12.2 Timing of the tornadoes............................................................................................. 22.3 Radar images of the tornado...................................................................................... 33.1 Summary of damage.................................................................................................. 63.2 Low-rise buildings................................................................................................... 143.3 High-rise buildings 22 Damage Survey and Assessment of Fort Worth Tornadoof March 28,
- Conclusions................................................................................................................... 286. Bibliography 297. Acknowledgements....................................................................................................... 29Appendix A – Photographs............................................................................................... 30Appendix B – Wind speed calculations 44Appendix C – Summary of other inner city tornadoes 454.1 Lower bound wind speed estimates......................................................................... 254.2 Debris source and paths........................................................................................... 264.3 Glazing performance
2.2 Timing of the tornadoes The National Weather Service has given the following timings for the Fort Worth andArlington Tornadoes. 2:53 p.m.: 5:33 p.m.: 6:10 p.m.: 6:11 p.m.: 6:18 p.m.: 6:22 p.m.: 6:25-6:26 p.m.: Tornado watch issued.Severe thunderstorm warning issued.Tornado warning issued after a rotating storm is spotted 5 miles west ofFort Worth sounds emergency sirens. (Sirens are repeated at 6:22, 6:23 andTornado sighted west of Fort Worth, near Castleberry High School.Tornado reported just west of downtown, near Montgomery Ward building onMeacham Field, heading east.6:26.)7th Street. Tornado sweeps through Fort Worth central business district.
6:28 p.m.: 6:37 p.m.: 6:40 p.m.: 7:05 p.m.: 7:07 p.m.: 7:20-7:24 p.m.: 7:26 p.m.: (Sources: National Weather Service, Grand Prairie Fire Department) Tornado dissipates.Tornado indicated at I-35 and Riverside.Tornado warning re-issued.Tornado detected 5 miles west of Arlington Airport, moving east.Tornado observed near I-20 and Collins in Arlington.Tornado dissipates. Tornado touches down in southwest Grand Prairie.
2.3 Radar images of the tornado Figures 2 and 3 show radar images of the Fort Worth Tornado. Figure 2 shows the radialvelocity at the lowest elevation as inferred from the radar.significant convergence of flow towards the supercell and tornado. It is seen that there is
Figure 2. Radial velocity at 0.5 deg elevation angle, at about the time the tornado ishitting the downtown area. (source: NWS)
Figure 4.Church on left.Telegram) Fort Worth tornado approaching Mallick Tower. Significant debris is evident in the flow field. (source: Fort Worth Star- Towers of First Methodist
3. Documented damage The major buildings damaged in the Fort Worth tornado are shown on the map in Figure5, with a more detailed map of the downtown in Figure 6.team surveyed the general damage area on the eastern side of the Trinity River on March30 in two groups, and several buildings were documented in detail.the Trinity River was documented on March 31 as a single team. The damage documentation The western side of
Figure 5.damaged. 3.1 Summary of damage The following table summarizes building characteristics and tornado damage surveyed bythe Texas Tech investigators. It is not exhaustive, but is believed to be representative ofnon-domesticmechanism for some specific buildings follows the table. Appendix A shows photographsof typical damage.Johns ManvilleBuilding The Sweet ShopMap of the region affected by the tornado showing the major buildings buildings within this tornado. A detailed discussion of the failure
Montgomery WardWarehouseCalvary TempleChurchN WitherspoonBuilding933 WWeatherfordMallick TowerCash AmericaInternational^ LexingtonPlace Trinity TerraceBank OneHunter PlazaTandy TechnologyCenter^ Tandy Center– Outlet MallUPR
Building Name^ Occupancy^ Location^ ConstructionType
Cladding Damage^ Roof Damage^ StructuralEvidence of DebrisDamageImpact Trinity Terrace^ Retirement1600 TexasSteel and concretecomplex –Sttower, 15 floorsMultipleAbove Groundapartments,Level (AGL)Publicassembly,Parking
Insulating Glass (IG) unitno^ No^ Yes, roofing fromwindows broken, in quite aupstream impactedfew cases only the outeron west facingpane is brokenbalcony windows onW face (~3%)^7
th^ th^ and 15^ levels th^ Cash AmericaOffice –West 7 St^ Steel and concreteInternationalMultipletower, 9 floorstenancyAGLPublic-window andassembly,spandrel glass andParkingtravertine skin atcorners and rooflevel Severe damage to all butMembrane peeled?^ Evidence of suctionNE face with majoroff roof from SEfailure on windowsdamage on that facefaceadjacent to W cornerSW face – already brokenon NE and SE faces.outMostly likely due toNW face ~ 100% lites andoverpressure fromspandrelsdebris impacted NWSE face –and SW faces.Lites ~ 80%Spandrels ~ 35%evidence of suction failureon S corner of SE faceNE face –Lites ~ 35%Spandrels ~ 25% CalvaryChurchWest cornerSteel frame cladTemplecomplex –of Penn &in brick.ChurchPublic5thAuditorium to 3assemblyfloors AGL,steeple to 6 floorsAGL
Brickwork removed fromMembrane peeledYes, plasticYes, S face showssteeple and E & W parts ofoff towards S fromhinges formextensive debristhe auditorium walls andoffice complex toin steelimpact markingparapets. Ground levelwest of church,framing ofwindows broken on W, Sroof sheeting loststeeple.and E (~100%) faces.from auditoriumA/C unit ends up Sth^ across 6^ St OfficeOffice – forSummit,Brick clad 2BuildingleasePenn & Wfloors AGL5th
Bricks peeled off E face,Roof pulled off WW wall fallsDebris markings onW wall falls out extensivewingout, probablywall and Roseglazing damage to E andafter roof iswindow probablyW wallspulled offbroken by impact
Building Name^ Usage^ Location^ ConstructionType
Cladding Damage^ Roof Damage^ StructuralEvidence of DebrisDamageImpact EducationalOffice –South cornerSteel and concreteEmployeesSingleof Penn andto 4 floors AGLCredit Uniontenancy7th
Window failures on SWMembrane peeledno^ Either suctionface and on NE and SEoff on western andremoves rockwall onfaces near E corner,southern corners.SE face or windowExterior insulated finishingA/C units blownbreakage on NE orsystem (EIFS) removedover.SW corners lead tofrom top 2 floors of NWover pressurerd^ face and 2^ floor only, justblowing offabove a podium, on SErockwall.face. Mallick Tower^ Office –BetweenSteel frame to 10MultipleSummit,floors AGL.tenancyFahey,Weatherfordth^ and 5^ St
Severe damage to glazingMembrane peeled?^ Some windows inE facefrom SW cornerthe middle of theLites ~ 45%(from video)eastern face areSpandrels ~ 25%bowed outward –N faceinternal impact?Lites ~ 45%Evidence of suctionSpandrels ~ 70%failure at W end ofW faceN face.Lites ~ 85%Spandrels 100%S face ~ 100% Witherspoon^ AdvertisingWest cornerBrick clad woodAgencyof Lexingtonframe some steel&bracing, 2 floorsWeatherfordAGL, plusundergroundparking
Many windows broken, onPea sized roofingCollapse ofSeveral safety glassW (~20%) and E facesgravel piled upwesterndoors broken and IG~33%).under conicalcorner due tounits blown in onBrick facing collapsed onvortices, membraneinternalwestern sides.western and southernbubbledpressurizationSkylight andwalls. Ties fromblowing outwindow damage onbrickwork to stud wall notSE walleastern side due toeffective.impact
Building Name^ Usage^ Location^ ConstructionType
Cladding Damage^ Roof Damage^ StructuralEvidence of DebrisDamageImpact TandyOffice^ Weatherford6 floors AGL^ ndTechnology^2 , BurnettCenterand Taylor
Window damage on SNone^ None(~2%) and E (3%) faces Tandy CenterOffice^ WeatherfordMostly glass clad– Fort Worthbetween20 floors AGLOutlet SquareThrock-North Towermorton &Taylor
Window breakageNone^ NoSE face (~20%)Mostly near SW cornerSW face (~5%) rd^ Tandy CenterOffice 3 betweenMostly glass clad– Fort WorthThrock-20 floors AGLOutlet Squaremorton &South TowerTaylor Window breakageNone^ NoSE face (~15%)Mostly near SW corner andat ground levelSW face (~95%) Tandy CenterRetail^ Taylor St^ Glass clad to 3– Outletfloors AGLSquare
Significant ~ 50% window?^? breakage on Taylor St Fort WorthLibrary^ Taylor,2 floors AGL^ ndCentral LibraryBurnett, 2^ rd& 3^
Glazing damage on mostSkylights broken, 6? facesA/C unitsdislodged Sundance SqAccommo-N corner of14 floors AGL^ WestdationThrockmortrdon & 3^
Glazing damage on south?^ noneand west facesSE face (~ 50%)S 1/3 portion of SW face(~50%)NW face (0%)NE face (~10%)
BuildingUsage^ Location^ ConstructionNameType
Cladding Damage^ Roof Damage^ StructuralEvidence of DebrisDamageImpact thBank OneOffice Taylor, 4 ,Glass clad to 35th (^) Tower 5 &floors AGLThrock-morton Extensive damage to?^ no^ Many brokenglazingwindowsN chamfer ?NW face (~60%)W chamfer (~100%)SW face (~90%)S chamfer (~40%)SE face (~15%)E chamfer (~20%)NE face (~40%) Union PacificOffice^ Main,Glass clad to 38ResourcesCommerce,floors AGLTower (UPR)6th & 7th
Extensive damage to?^ no^ Yes, only outerglazingpanes broken onNE face (~0%)many IG units on SEN face^ Lites (~1%)faceSpandrels (~10%)NW face Lites (~1%)Spandrels (~5%)SW face Lites (~65%)Here only 30% had bothpanes of IG unit brokenSpandrels (~95%)S face^ Lites (~35%)Spandrels (~25%) City CenterOffice^ Two towersGlass clad to 40Towerson easternfloors AGL& westerncorners ofCommercendand 2^
Each Tower similar with?^ noW face (~8%)S face (~8%)Negligible damage on Nand E faces
3.2 Low-rise buildings Low-rise buildings are defined as being fewer than three stories in height and this class ofbuilding performed the worst in terms of structural damage.discussed in detail here are:The Sweet Shop FactoryThe Sweet Shop Factory lay between Stayton and Harrold Streets, just north of West 6Street.failure and generated a large amount of debris.collapsed state of this building. The debris varied in size and weight from portions of tarcovered roofing insulation to full 20’x 2’ sheets of metal roofing with the formerobserved approximately one-half mile to the SSE on the fifteenth floor of Trinity Terracefacing Fournier Street, just south of West 10observed on the ground on Fournier Street between West 7 • • • • The Sweet Shop Factory buildingJohns Manville Warehouse buildingWitherspoon building933 Weatherford buildingConstructed of tilt-up concrete wall panels, this building suffered catastrophic th Street. Figure 7 shows a schematic of the The larger roofing sheets wereth and West 10 The buildings in this class th Streets and onth
the seventh floor of Trinity Terrace.The postulated failure mechanism is as follows: • • • • • Debris marking on the intact steel building fronting the factory on Stayton Street,indicated that the wind approached the building from the south and west. The 10’high chain mesh fence on the western side of Stayton Street blew over to the east.Roof decking on the southern side and particularly near the western cornerdetached from the roof trusses (as evidenced by upside down roof portions in theadjacent debris and wall panels lying on top of roofing - in particular the southernand western wall panels fell inward (to the north and east respectively) on top ofthe awning that covered the front (western) entrance while the northern walls felloutward (to the north) also on top of roofing.The building had several openings; a front entrance safety glass single door in thesouthern end of the western wall and loading bays in the middle of the northernwall and the eastern end of the southern wall. These openings were sealed as thetornado hit and appeared to remain so during the building’s collapse.not expected that internal pressurization lead to failure of the roofing.The wall panels in the vicinity of the roofing failure were exposed to the fullwindward pressure and the full negative pressure that removed the roofing.Without the diaphragm action of the roof decking, the walls lost their uppersupport and fell. Figure 5 indicates that the western half of the building fell Thus, it is
- • • northwards, while the eastern half fell southwards.The western end wall fell inwards on top of the already collapsed southern wall.The eastern end wall fell outwards onto Harrold Street.An interior wall, which divided the building approximately in half, fell toward theeast.
By and large, the concrete panels remained intact upon falling, but the three fillet-weldedjoints (~4” long at 6’ spacing) up each side between adjacent panels failed.would have occurred after the loss of the roof and during the fall of the wall.concrete wall panels had similar short fillet welds at their bases and some of theseshowed significant corrosion.metal plate set into the top of the concrete wall panels.connection failed once the walls began to fall.trusses were removed intact, as evidenced by the upside down trusses toward the middleof the building.Nine staff, members of the cleaning crew, were lucky to escape with their lives.had attempted to move away from the southwest corner, which was fortunate, as thiscorner collapsed inwards. The upper cords of the roof trusses were tack welded to a Some cases failed as the roofing and It is anticipated that this This failure TheyThe
Figure 7. Schematic of damage to Sweet Shop Factory.Stayton St Harrold St
MetalbuildingundamagedConcrete wallpanels 24’x24’x5” Internal wallalsocollapsesOriginal flooroutline144’x408’ N Adjacentbuildings Front entrance& awningChain mesh fence Indicates roofingfound upside downor under collapsedwall panels
Figure 8. Schematic of damage to Johns Manville Warehouse 17
N Railway line andloading dock Adjacent buildings,largely undamaged 1 large bay gable roofoverhanging loadingdocks to south andwestStayton St Roof line –open beneathFlat roofed 2-story officebuilding Sweet Shop Factory,totally collapsed3 bay gable roofoverhangingloading dock to theeast Harrold St
Witherspoon buildingThe Witherspoon building is a two-story L-shaped structure occupying the southwesternside of Lexington, between Weatherford and Belknap Streets.schematic of the damage to the building.of the southwest corner including removal of the brick cladding on the southeast face andcollapse of the roof over the southwest corner.damage to glazing on both western and eastern facing walls as well as east facingskylights.the river some one-quarter mile to the west.someparticularly at the western and northern extremities of the arms of the L.failure mechanism is as follows: • • protectionDebris breaks windows on the interior of the L particularly on the northwest facenear the western corner, from whence the tornado approached.this was the glass-strewn drawing office, which occupied the western end of thesecond floor.outward, rather than blown inward.This debris damage on the positive pressure face led to a high internal pressurewhich, when combined with suction on the Weatherford Street (southeastern) The building was very exposed to the west with no structures between it and from In addition a north-facing skylight had glass and framing sucked that direction but This building suffered major structural failure notSome trees in the interior of the L afforded In addition, there was significant debrissufficient to prevent Figure 9 shows a The evidence for debrisThe postulated damage
The building had only two occupants at the time of the tornado, and they were able totake refuge in the basement parking area. The drawing office was severely damaged, andmany offices on the northern wing had significant glass debris, although surprisinglylittle other damage was evident.^ •^ •^ •^ face, lead to failure of the cavity brick wall.The external brick wall and parapet fell into Weatherford Street and also from thesouthwestern face. The brick ties in some cases did not attach to the stud framingbut only to the rockwall sheeting.The loss of cladding lead to loss of support for the roof in the southwestern cornerand subsequent collapse of the roof.There was almost complete breakage of skylight windows on the eastern facealong with two highly recessed windows, also on the eastern face.indicate that wind approached the building from this direction at one stage duringthe passage of the tornado.unit failed. The inner panes were safety glass, and although some showed impactmarkings, the building envelope was not penetrated here.^ In all cases only the outer pane of the double glazed^ This would
