Temperature Dependent Load Bearing Capacity of Laminated Glass Panes 2010 54 1 11 Influences the Strength of Glass Pane
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Ŕ periodica polytechnica Temperature dependent load bearing Civil Engineering capacity of laminated glass panes 54/1 (2010) 11–22 doi: 10.3311/pp.ci.2010-1.02 Kinga Pankhardt / György L. Balázs web: http://www.pp.bme.hu/ci c Periodica Polytechnica 2010 RESEARCH ARTICLE Received 2009-11-11, accepted 2010-03-30 Abstract An experimental programme with numerous single and lam- inated glass specimens was carried out to study the tempera- ture dependent behaviour of laminated glasses. The difference of load bearing capacities between the laminate manufactured from ordinary float (laminated glass) or tempered glass layers (safety laminated glass) were also studied in four-point bending. Fig. 1. Glass separation wall When glass laminate fractures, the interlayer can keep the frag- ments in place. Different types of interlayer materials, both resin 1 Introduction and foil (type EVA) were studied in safety and non safety lami- Tendency of architecture is to use larger size glass panes or nated glass specimens. Glasses are used not only in the interior to expose it to carry high loads e.g. glass slabs with carry loads but also in exterior places. Therefore, the effect of temperature of cars. Therefore, appropriate laminated glass panes should be of -20˚C, +23˚C and +60˚C were investigated on bending char- selected in order to avoid excessive deflections, and the effect acteristics of glasses. The main influencing factors on the load of temperature – especially at outdoor conditions – has to be bearing capacity and bending characteristics of the glass spec- taken into account to the calculations. Glass is often used as a imens were investigated e.g. tempering, laminating and temper- construction material to create load bearing structures where the ature. bending strength of the material plays an important role in the load bearing capacity. Keywords For safety glazing applications, heat-strengthened or heat- glass laminated glass temperature delamination EVA · · · · · tempered glass should be used. Only the lamination of glass interlayer layers does not make it safe. Therefore, the layers of lami- nated safety glass should be consisting of heat-strengthened or Acknowledgement heat-tempered glass layers. Tempering increases the price of the The authors would like to express thanks to RÁKOSY GLASS glass (about 1.5 times), therefore, sometimes people try to use Ltd. for providing the specimens and for the support to DSC ordinary float glass where the use of heat-strengthened or tem- analysis of plastics to Prof. Dr. V. VARGHA and R. C. BENDE, pered glass would be necessary. Fig. 1 indicates that non-safety Sz. MÁTÉ, BME Department of Plastics and Rubber Technol- glass was used in glass separation wall and the failure stared by ogy. The authors would like to thank to Dr. S. G. NEHME for about 120 panes. The use of float glass in point fixed glazing his intellectual support and would also like to thank to Dr. S. is especially dangerous, because it is not resistant to high stress FEHÉRVÁRI, A. EIPL, M. VARGA, D. DIRICZI, G. KOVÁCS concentrations e.g. which develop around holes [1]. and P. TISZA for their technical support. EN ISO 12543-1:2000 [2] differentiates between laminated Kinga Pankhardt and laminated safety glasses. Laminated safety glass is gener- Department of Civil Engineering, Debrecen University, H-4028 Debrecen, ally used with kind of foil. But for larger sizes and curved shapes Hungary or bent laminated glass is usually available with a resin inter- e-mail: [email protected] layer. The interlayer has two functions [3]: (i) to keep in place György L. Balázs the glass splinters during the fracture process to reduce the risk Department of Construction Materials and Engineering Geology, BME, H-1111 of injury and (ii) to increase residual load bearing capacity. Budapest, Hungary Until recently, some national standards explicitly stipulated e-mail: [email protected] Temperature dependent load bearing capacity of laminated glass panes 2010 54 1 11 influences the strength of glass pane. Therefore, the strains in middle of pane and in the edge regions were also studied. The results of tempered glass specimens were compared to those of non heat treated float glass specimens. 2.1 Test parameters and test programme Test parameters of laminated glass specimens were the fol- lowing [9]: Constants: test arrangement, width and length, thickness, rate • of loading (20 mm/min), edgework. Variables: number of glass layers: two or three, type of lam- Fig. 2. Effect of ambient temperature on the temperature of an insulating • window glazing [6] inate (non safety or safety laminate), type of interlayer mate- rial (resin or EVA foil or without interlayer), temperature of specimens. the composition of the interlayer, usually within the standard definition of laminated glass. As a result, interlayer materials Tests were based on glass panes with a thickness of 6 mm. The are not explicitly specified for composition or fields of applica- chosen thickness allows the study of large deflections of the tion e.g. use in commercial or public buildings in outdoor or glass specimens in bending. Single glass specimens with thick- indoor conditions. The new European standards (EN 356:1999 ness of 12 and 19 mm were also investigated, to compare the [4]) also focus on performance (e.g. tensile strength, ultimate monolithic upper layered limit of 2 6 mm and of 3 6 mm lam- × × elongation) rather than composition. As a result, those foil and inated glass specimens. To determine the lower layered limit, resin interlayer materials or others are acceptable, which are de- laminated glasses layers without use of interlayer material (with termined to be acceptable for use in laminated glass by the man- use of only spacer at the edges) were tested. ufacturer of interlayer materials. The schematic diagram of the test programme for laminated When using laminated glass on external surfaces (facades, glass specimens is illustrated in Fig. 3. roofing, etc.), the temperature can reach about 60˚C in summer Simplified symbols were used in this paper to distinguish the or -20˚C in winter [5]. Fig. 2 indicates the change of tempera- studied specimens, these are e.g. E_2_R. The meaning of the ture of an insulating glass in summer and in winter, calculated symbols are as follows: at first place is the type of glass: (E_) with Helios software [6], when the room temperature is regu- tempered, (F_) float; at the second place is the number of applied lated and it is +20˚C. In case of an insulating glass unit the outer glass layers (_2_,_3_); at third place is the type of interlayer glass layer is more affected by the temperature of the environ- material (_R) resin, (_F) EVA foil, or (_D) non bonded glass ment. The question araises – especially in the case of load bear- layers. In the case of single glasses the used symbols indicate ing glass constructions exposed to a wide range of temperatures the type of glass and the nominal thickness e.g. E_12 mm means (depends on the climatic region of the countries) – how the tem- single layer tempered glass with nominal thickness of 12 mm. perature affects the load bearing capacity of single or laminated Interlayer materials used in laminated glasses were resin (cast glasses. in place, unsaturated polyester resin based on ortho-phthalic The aims were to study the bending characteristics of lami- acid with stryrol content, pre-accelerated, light stabilised) and nated soda lime silicate glasses including: force and deflections, EVA (ethyl-vinyl-acetate) foil. While PVB (polyvinyl-butyral) strains in two different regions as well as the residual load bear- foil is widely used in laminated glass, EVA foil is a new gener- ing capacity. ation of foils (product of Bridgestone). EVA interlayer was first used in Hungary in 2005 by Rákosy Glass Ltd. 2 Materials and test programme The main properties of the tested interlayer materials in more An experimental programme was carried out to analyse the details are summarised in [9]. The glass transition tempera- load bearing capacity of single and laminated glass panes. Spec- ture and melting temperature ranges were not available for cured imens were tested in four-point bending. Specimens were manu- resin. These data were only available for EVA foil. In order to factured from soda-lime silicate float glass with polished edges. determine the glass transition- and melting temperature ranges, Tempering induces a pre-determined amount of stress into the DSC (Differential Scanning Calorimetric) tests were carried out glass. ASTM C1048-85:1985 defines the required surface and at Faculty of Chemical Technology and Biotechnology, Depart- also edge compression stresses. Required compressive stress for ment of Plastics and Rubber Technology, BME. The determined 2 heat tempered glass is at least 69 N/mm on the surface and at glass transition temperature, Tg, was -42 to -38˚C and melting 2 least 67 N/mm at the edges [7]. In the case of tempered glass, temperature, Tm, was +109˚C (80˚C to 140˚C) for cured resin. the stress must first exceed the built-in compression stresses be- The average values were determined for each test combina- fore tension develops [8]. The influence of edge strength also tion from at least three measurements in the case of laminated 12 Per. Pol. Civil Eng. Kinga Pankhardt / György L. Balázs Fig. 3. Schematic diagram of test programme for laminated specimens [9, 10] Fig. 5. Test of laminated safety glass specimen Fig. 4. Test method for four-point bending (EN 1288-3:2000 [11]) where, 1.: specimen: 1100 360 mm, 2.: bending roller, 3.: supporting roller, 4.: rubber × strips (3 mm thick, according to ISO 48 [12]), 5.: self-designed transducer, 6.: custom-made insulation (40 mm thick), Ls : 1000 mm, Lb: 200 mm, h: thickness of the specimen (6 mm, 12 mm, 19 mm or 2 6, 3 6 mm) [9].