Experimental Testing of Burglar Resistance of Fenestration
Abstract
Currently, windows and glass facades are increasingly being used as a building envelope. These are elements that are functional and aesthetic, but there is a need to focus on their safety. Windows as a part of protection system are one of the most vulnerable assets, so they need to be addressed. The paper is focused on the experimental investigation of two types of windows that are commonly used in buildings. The subjects of the interests are wooden frame windows and PVC frame windows. In the experiment, burglar resistance was investigate, carried out by dynamic tests with different weights of steel balls dropped from various heights. Results of the experimental measurement pointed to the limit energy glass panels were broken. Windows with safety film were also tested. The measured results were further evaluated
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Transactions of the VSB - Technical university of Ostrava Safety Engineering Series, ISSN 1805-3238 Vol. XIV, No. 2, 2019 1 pp. 1-6, DOI 10.35182/tses-2019-0006 EXPERIMENTAL TESTING OF BURGLAR RESISTANCE OF FENESTRATION Richard JANKURA1, Lucia FIGULI2 1 UniversityofŽilina,FacultyofSecurityEngineering,Žilina,Slovakia,[email protected] 2 UniversityofŽilina,FacultyofSecurityEngineering,Žilina,Slovakia,[email protected] Abstract: Currently,windowsandglassfacadesareincreasinglybeingusedasabuildingenvelope. Theseareelementsthatarefunctionalandaesthetic,butthereisaneedtofocusontheir safety.Windowsasapartofprotectionsystemareoneofthemostvulnerableassets, sotheyneedtobeaddressed.Thepaperisfocusedontheexperimentalinvestigation of two types of windows that are commonly used in buildings. The subjects of theinterestsarewoodenframewindowsandPVCframewindows.Intheexperiment, burglarresistancewasinvestigate,carriedoutbydynamictestswithdifferentweights ofsteelballsdroppedfromvariousheights.Resultsoftheexperimentalmeasurement pointedtothelimitenergyglasspanelswerebroken.Windowswithsafetyfilmwerealso tested.Themeasuredresultswerefurtherevaluated. Keywords: Glasswindows,impacttest,impactresistance,securityglazing,burglarresistance. Research article Introduction Securityofassetsisoneofthemostimportant aspectstobeconsideredintheprotectionofproperty andpeople.Theessentialmatterofprotectingassets is to know their vulnerability. One of the most vulnerable part of the buildings are windows and glassfacadescreatingpartofthebuildingenvelope. Ifwewanttoincreasetheresistanceoftheelements ofprotection,weneedtoidentifytheirresistanceto thenegativephenomenaasburglarattackis.Several standards describe various approaches how to examinetheirresistance.Inconsequencesmentioned standards classify them into several resistance classes according to the different criteria. In this paper,wefocusedonanexperimentalinvestigation of the resistance of two types of windows under dynamic load.The dynamic performance of these systems was performed following the drop ball standard. Windows and glass facades Glassisamaterialwithdifferentapplications.Itis usedinwindows,doors,andbuildingfacades.There aremanyoptionsforselectingitsfunctions(security, functionality). Glass is a brittle material, is weak in stress due to the nature of its atomic structure andtheresultingsusceptibilitytodeficienciesand the inability to resist crack propagation. Glass behavespurelyelasticallyuntilitsuddenlyreaches maximumtensilestrength,unlikestructuralsteels, aluminium alloys, and even reinforced concrete, whichcanadapttoplasticdeformationaftertheyield point. High stressed glass and larger stretched surfaces result in a higher probability of failure. Thus,theglasshasverylittleorifsomedeformation and suddenly fail. In the glass, there is a slow growth of micro-cracks in a permanent or cyclic loadsituation.Oncethecracksreachacriticalsize, the glass may instantly fail. The following figure showsthebehaviourofglass,steelandaluminium alloysundertensilestress(Code,2018). Fig.1Strengthofindividualmaterialsundertensile stress-strain(Code,2018) T ensille stress Steel Aluminium alloy Glass breakage T ensille strain
Transactions of the VSB - Technical university of Ostrava Safety Engineering Series, ISSN 1805-3238 Vol. XIV, No. 2, 2019 2 The limit state of glass can be defined as thestatebeyondwhichthestructurenolongermeets therelevantdesigncriteria.Thelimitstatedesignis basedontherequirementofresistance,whichshould begreaterthantheloadeffect.Thisstatementcanbe expressedby(Code,2018): Resistance≥Loadeffect Thestrengthoftheglassvariesgreatlydepending on the particular heat treatment cycle used in its manufacture, resulting in different types of glass. Therearemanyglasses,whichcaninclude(Code, 2018): • Annealedglass(ordinaryFloatglass)-produced bymeltingglassandbreakingintolargefragments withsharpedges. • Heat-strengthened glass - glass that has been heatedaboveitssofteningpointandcooledrapidly to increase its strength. It breaks like annealed glass. • Insulatingglass- itis anassembly consistingof twoormoreglasspanesseparatedbyabarspacing toformacavitybetweentheglasspanes. • Safetyglass-theseareglassorfacadesthatare "break safe", such as laminated or toughened glass. Laminated glass is a safety glass used in construction, architecture, often as building structures (partitions, railings). The structure of theglassisconsistingoftwoormorepiecesofglass bonded by one or more PVB (poly vinyl-butyral) films. If the glass is damaged, the film holds the fragmentstogether(Laminated,2019). Tempered safety glass is specially heat-treated sothatwhenbroken,theglassisbrokenintosmall pieces.Temperedglassisformedbyrapidlycooling the outer surface of the glass. The result is four timesmoreresistanttoimpactthanannealedglass (Guidelines,2013). As already mentioned, each glass (window) has different properties that reflect its resistance. The dynamic response of windows depends on thestrengthandstiffnessoftheglass.Ifadynamic loadisappliedtothewindow,severalfailuresmay occurwhen(Code,2018): • Thetensilestrengthoftheglassisachieved. • The maximum bending deformation (orthemaximumslopeofthedeformationcurve ofthestructure)hasbeenexceeded. • The entire window construction is torn from masonryorotherwallmaterial. Safetyglassmustbemadeofqualitymaterials. Themeasuretheirquality,somestandardsneedto bemettotalkaboutsafetyglasses.Theseglassesare strengthenedtoresistbreakage,oriftheforceapplied is too great, the glass is broken carefully. Safety glasscanbereinforcedintwoways:laminatingor tempering(Which,2019).Weknowasetofseveral standardstodetermine theresistance ofwindows. In the area of security of objects, property, and persons,glass(generalwindowsandglassfacades) isveryimportant. Fenestration and their function inthefieldofsecurity Assetprotectioncanbedefinedasthecomplex ofsecurity,technical,andregimemeasures aimed atimpedinganyadverseeventagainstaprotected assetsandpersons.Theaimistopreventattackson personsandproperty,butalsotopreventviolations of the established regime, peace, and order in the protected area.Asset protection is realized byintegratingforcesandmeansonmultiplelayers ofprotection(Hofreiter,2015).Windowsandglass facadesplayanimportantfunctionintheenvelope protectionofassets.Thislayerofprotectionisone ofthemostimportantbecauseseparatestheexternal spacefromtheinternalenvironment. Physical security is a summary of security measuresimplementedonassetsandbuildings.This protectionaimstoprevententryintothebuilding, to deter and slow down the intruder. It consists of building elements (walls, ceilings...), which are complemented by structural parts. Among thestructuralpartswecaninclude(Mach,2010): • doorsandtheircomponents, • windowsandtheircomponents, • bars,blinds,roll-top. Windows and glass facades are often used in buildings. Often they become places, used by perpetrators to enter into the assets. Therefore, their functionisnotonlytolightentheindividualspaces of the buildings, but also to secure the building envelopesufficiently.Aburglarcanuseseveralways tobreaktheglass.Onepossibilityistobreakglass withanobject(stone)oratool(hammer).Another wayistobreakaglassbyusingitsstrength(shoulder punch,leg).Thestandardthatdealswithburglary resistance of windows classifies several sets of toolstoovercomethewindow.Inpractice,crowbar, hammer,axarethemostcommonlyusedtoolsfor breakingwindows.Basedontheirresistance,their passive safety can be determined (Zvaková and Kavický,2016).Inmanycases,theirresistanceis pp. 1-6, DOI 10.35182/tses-2019-0006
Transactions of the VSB - Technical university of Ostrava Safety Engineering Series, ISSN 1805-3238 Vol. XIV, No. 2, 2019 3 definedbyasetofstandards.Relevantstandardsare describedinthefollowing. Standards concerned with the resistance of glass and windows One of the most essential standards analysing theresistanceofthestructuralglassisEN12600 Glass in Building - Pendulum test - Impact test method and classification for flat glass. It used to test the strength of safety glass for application in buildings. The standard defines safety glass as glass which must have passed an impact test and eithermustnotbreakormustbreaksafely.Theglass issubjected toa testwhere rubbertiresweighing 50kgarereleasedintotheglasspaneatdifferent heights.Three-digitratingsaregiventotheglass, e.g.3B2or3C1dependingonthelimitedheightof thependulumthetypeofruptureofdamagedglass (EN12600). The standard classifies tests into three major resistance classes (Tab. 1). The first number representstheheightclassfromwhichthependulum droppedwhentheglasswasnotbrokenorbroken intosmall fragments.Thesecond letterrepresents thetypeofbreakagemode.Thethirdlettershallbe givenforaheightclassinwhichtheglassdoesnot breakordoesnotallowpenetration(Which,2019). Tab.1ResistanceclassesaccordingtoEN12600 (ŠubrtandPetrtyl,2019) Theeffectoftheimpactorissimilartotheperson hittingtheglasswiththeshoulder.Thisclassification iscomplementedbythetypesofinfringementwhich are(ŠubrtandPetrtyl,2019): • TypeA-numerouscracksappear,formingseparate fragments with sharp edges, some of which are large, • TypeB-numerouscracksappear,butfragments arejoinedandnotseparated;(failuremodetypical ofcoatedandlaminatedglass), • TypeC-disintegrationoccurs,resultinginalarge number of small particles that are relatively harmless(toughenedglass). The following figure (Fig. 2) shows the test equipment,wherewecanalsoseewherethedrop heightismeasured. Fig.2Standardmeasurementscheme (EN12600,2017) Another important standard dealing with theresistanceofglass,respectivelyofwindowsis EN356Glassinbuilding-Securityglazing-Testing and classification of resistance against manual attack. This standard classifies individual glasses into 8 levels. In the testing process, the glass is subjectedtoseveralteststodetermineitsstrength. The standard divides windows into two classes dependingontypeoftest,(ŠubrtandPetrtyl,2019): • P1AtoP5A, • P6BtoP8B. Inthefirst5levels,thetestisbasedonthedrop oftheball.Thetestiscarriedoutusingasteelball withthemassof4.11kgforclassesP1AtoP5Aand anaxeforclassesP6BtoP8B.Theballisdroppedon thetestsampleseveraltimesfromdifferentdefined heightsaccordingto theresistance class.Theball shallnotpenetratetheglassforthetestitemtopass theexamination.Specificationsforthesetestlevels aresummarisedbelow. Classification Drop height [mm] 3 190 2450 1 1200 1524 mm minimum 914 mm minimum Alternate means of bracing frame, use one brace at each vertical member 914 mm minimum Concrete wall, steel beam, or other sturdy construction Bolt securely to floor Test specimen Stranded steel cable approx 3 mm in diameter Maximum 12.7 mm when impactor is hanging free Center line of test specimen 1524 mm minimum Dr op Height pp. 1-6, DOI 10.35182/tses-2019-0006
Transactions of the VSB - Technical university of Ostrava Safety Engineering Series, ISSN 1805-3238 Vol. XIV, No. 2, 2019 4 Experimental testing of windows under dynamic load Abovementionedstandardshavebeendescribed according to determinacy of the window panes resistance, the impactor of a certain weight or droppedballtest.Inbothcases,wearetalkingabout thesafetyorsecurityglass,havingitsqualityand thickness. In our experiment, we focused mainly on commercially used window systems. These were,inparticular,wooden-framewindowstypical from the 1960s produced in Czechoslovakia and stillinuse.Thesecondsampleconsistedofplastic framewindows,currentlyused.Theexperimentwas focusedondeterminationofthedynamicresistance ofglasswindows. Weperformedaseriesofdynamicexperiments, carriedout inalaboratory attheFaculty ofCivil Engineeringofthe Universityof Žilina.Windows were fixed in the testing frame. Commercially used window systems were investigated during the experiment. Particular attention was paid to the sensitivity of their impact on the type and propertiesofthe supportframe.Theglass sample to be tested consists of annealed glass for both windows. Annealed glass is the basic product intheformofaglasssheetthroughthefloatprocess. This glass breaks into large jagged shards and is relatively susceptible to impact. The window that hasbeentestedisclassifiedintheRC1resistance class and the resistances of glass requirements are not specified. The window is defined against windloadinclassC4.Thismeansthatawindof 1600Padoesnotcausetheframetodeformmore than1/300ofitslength.Glasspanesareplacedin thewindowframeandsealedwithpermanentlyflexible two-component sealant with excellent mechanical properties.Thenominalglassthicknesswas3mm for wooden samples and 4 mm for samples with PVCframes.Intermsofglasssize,dimensionsare definedfromtheoverallsizeofthewindowsamples andframesused.Theglasssurfaceforthewooden frame windows was 1.22 x 1.05 m and 0.81 x 0.97mforthePVCframewindows.Themounting ofthewoodenframewindowintheteststructureis showninthefollowingfigure(Fig.3). Dynamic load testing was performed with various impactors. These were two steel balls withanominalweightof2.644kgand4.571kg, which were dropped from different drop heights (i.e. the horizontal distance between the centre ofthewindowandtheball).Amongotherthings, the acceleration was measured in each test using a sensor located at the bottom of the glass (from therightandbottomedgesatadistanceof0.2m). Tab. 2 Resistance classes according to EN 356 (ŠubrtandPetrtyl,2019) ThelastthreelevelsoftheEN356testarebased on an axe test. These are permanent attacks with atool(theaxe)againsttheglass.Thetestincludes a hydraulically driven hammerhead with a size of 40 mm and a weight of 2 kg, used to attacks theglass.Theintentionistocuta400x400mmhole intheglassandtheproductisclassifiedaccording tothenumberofstrikesneededtoreachthispoint (Which, 2019). Individual window categories are recommendedforspecificbuildingtypes.According tothe"SafeandSecurityGlass"theimpactenergy shown in Table 3 is developed for each class of resistance(EN356Specs). Tab. 3 Impact energy for resistance categories accordingtoEN356(Which,2019) In addition to the aforementioned standards, the resistance of glass apertures can also be classifiedintermsoftheirresistancetowindloads and the resistance against bullet attack. Separated groupofdynamicaltestingaretestingofwindows forblastresistance.Testprocedureofthewindow systemsreactiontoashockwaveloadisdescribed in(Zvakova,2016).Inthepresentpaper,however, wedealwiththeresistanceofglassusingadropball only. Resistance category Examination P1A Dropheight1500mm+3strikes ofaxeintriangle P2A Dropheight3000mm+3strikes ofaxeintriangle P3A Dropheight6000mm+3strikes ofaxeintriangle P4A Dropheight9000mm+3strikes ofaxeintriangle P5A Dropheight9000mm+3x3 strikesofaxeintriangle P6B From30to50strikesofaxe P7B From51to70strikesofaxe P8B Over70strikesofaxe Resistance category Height of dropped [mm] Impact energy [J] Glass thickness [mm] P1A 1 500 62 6.8 P2A 3 000 123 8.8 P3A 6 000 247 9.1 P4A 9 000 370 9.5 P5A 9 000 370 10.3 pp. 1-6, DOI 10.35182/tses-2019-0006
Transactions of the VSB - Technical university of Ostrava Safety Engineering Series, ISSN 1805-3238 Vol. XIV, No. 2, 2019 5 Thefollowingtableshowstheindividualresults for the sample types, the ball mass and the drop heightfromwhichtheyweretriggered. Tab.4Dynamicimpactmeasurementresults (Figuli,2019) Thetableshowstheindividualimpactdistances at which the glass pane of the window has been damaged.Lookingatthewooden-framewindows, itcanbesaidthat2sampleswerebrokenatnearly equaldistances.Anothersamplewasdamagedquite soon,whatcouldbeduetoseveralfactors(frame stiffness,environmentaleffectsonthewindow,etc.) ComparedtoawindowthathadaPVCframe,itcan beseenthatitcanwithstandmoreenergy. Discussion The results of the measurements showed theenergythattheindividualsamplescanwithstand. To confirm the impact resistance, it is advisable to perform several measurements on such PVC Windows.ComparedtoEN356,thetestedsamples areconsiderablymoreresistance.Thisismainlydue tothethicknessoftheglassesthatareusedtested in the standard and our test. For future measurements, the durability of woodenandPVCwindowsunderdynamicloading usingsafetyfilmwillbeinvestigated.Theeffectof thefilmonincreasingtheresistanceofwindowswill be evaluated. Besides it is possible to investigate fragmentsofglassbreakageinindividualdamage. Conclusion Thepaperwasfocusedonaseriesofexperiments on the impact of a steel ball on a glass pane, toestimatetheburglarresistance.Duringthetests woodenframeandPVCframewindowswereused. The results pointed to the limit impact energy. The results show that the wooden windows used in the 1960s could not resist as much energy as aplasticwindow.Thestudyispartofanongoing project that will include analytical and numerical analysesoftheexaminedsystems. Anothersignificantdevicewasahigh-speedcamera (FASTEC TS31000SC4256 Imaging), which was used to examine the speed of the incident ball basedonslowmotion.Thehigh-speedcamerahas a resolution of 1280 x 1024 and 725 frame per second.Ithasamultimediadisplayand4hourbattery life.Themeasurementschemeandthelocationof thedevicesareshownbelow(Fig.4). Fig.3Woodenwindowinthetestframe Fig.4Arrangementofthesampleand themeasuringinstruments During the experiment, 3 windows with awoodenframeand1withaPVCframewereused. Varioussizesofsteelball(2.644kgand4.571kg) wereusedinthetest,whichgraduallystartedfrom defineddistances.Eachmeasurementwasrecorded with a high-speed camera and an accelerometer sensor.Individualdropheightswereincreaseduntil theglasspanelwasdamage.Subsequently,thetotal impactenergyvalueswereevaluated.Thesevalues were calculated according to equation (1) using slow-motionrecordingsfromahigh-speedcamera: (1) 2 1 2 E mv= Window frame Ball mass [kg] Impact horizontal distance [m] Impact velocity [m/s] Energy [J] Wood 2.644 1.30 2.42 7.72 Wood 2.644 0.90 1.60 3.36 Wood 2.644 1.40 2.59 8.90 PVC 4.571 1.50 2.94 19.75 pp. 1-6, DOI 10.35182/tses-2019-0006
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