1. Introduction

An 11-storey office is being built in Reading with full-height glass walls on all floors. On the top floor, the wall is set back from the edge of the building to create the terrace space at the top floor. The glass wall will be created using a conventional capped glazing system with storey-height glazing units. The edge of the terrace will be protected by a cantilever glass balustrade. For the following, glass has to be recommended and the priority of the recommendations is safety:

1. Wall of the office, general.

2. Wall of the office, at the terrace.

3. Balustrade at the edge of the terrace.

This report will help the developer understand why and what type of glass has to be used, what factors are being considered and what tests or regulations are required to minimise the risk.

1. Assumptions

Some conditions are assumed, which are as follows: • The capped system used is the Stick system; the system’s outer surface is flush with the outer wall of the building and has no structural load on glass. • The priority is the minimise the risk or maximise safety. Other factors like building operation, condition for construction and demolition, building performance in terms of energy conservation/acoustics/sustainability/light and last security for manual attackers/explosion/bullets are the least considered. • The glass used will be soda-lime-silicate glass. • The terrace area has less than 1500m of free space. • The balustrade is free-standing and the handrail is continuous and round in shape. So, the glass is supported at the bottom and top. • The terrace area is for office events to which employees are invited with their families and on a usual day, it is an area for rejuvenation (canteen, play area for table sports like table tennis, foosball etc). On Fridays, it’s a drinking area after working hours. • The maximum wind load is 2 Kpa and the glass size is less than 5m diagonally. • The balustrade is 200mm inside the edge of the wall. • There are no glass roofs or canopy so snow load won’t be considered. • The height of the balustrade is 1100mm. • No financial risk i.e., the client should be able to change the glass in the future with the same glass or so. • The same type of glass for the façade is to be used as different glass has different colours and it’s not acceptable for the aesthetics of the building. • There is no building nearby so the incident solar radiation is increased as a result of the reflection from other building surfaces. 3. Discussion/Explanation

• Glass for the wall (1 to 10 stories) Laminated heat-strengthened glass with PVB (Poly Vinyl Butyral) interlayer can be used. The reason for using it is because of its random breakage pattern. On failure, the glass breaks into large pieces as it has less surface compression and being laminated glass the pieces won’t fall off place. Since the glass is supported by all sides and large pieces are formed, post-failure performance can also be achieved. In comparison with laminated toughened glass, it is less expensive and has better post-failure performance Using laminated toughened glass has its drawback, they are: o It’s more expensive. o Nickel Sulphide inclusion can take place and heat-soaked toughened glass is more expensive than toughened glass. o On breakage, the glass breaks into small pieces and keeps falling off until the glass is replaced, which might cause minor injuries to pedestrians. o On failure the laminated toughened glass has less performance as it breaks into small pieces which leads to lower strength in comparison with Laminated heat-strengthened glass. o On failure, the glass has to be replaced as soon as possible, where Laminated heat-strengthened glass gives an ample amount of time. Single toughened or heat-strength glass can’t be used as it will be much thicker than laminated glass for the same strength and on failure, the glass will just fall off its place causing injuries, in case of heat-strengthened glass the injuries cause will be more dangerous as a large chunk of glass will fall. Another considerable glass type is PVB laminated glass with one lit being toughened and another heat-strengthened. This type of glass has better post-failure performance than laminated toughened glass but poor performance than the laminated heat-strengthened glass on failure the toughened glass is likely to fall off and only the heat-strengthened glass will act to perform after the failure because of its breakage pattern. Before the failure, this type of glass will have more strength than laminated heat-strengthened glass as toughened glass is stronger. • Glass for the terrace I suggest using laminated heat-strengthened glass from floors 1st to 10th, I recommend using the same glass here. The reason for the same is if we use different glass, it would have a different colour from the rest of the building, on failure the glass will stay in its place and will protect the employees from the wind, rain etc and it will give us a good enough time to replace it, unlike toughened glass. If a different colour is not the concern; then toughened glass would be the best choice, it has better heat resistance than any laminated glass available as the interlayer will catch fire and melt causing the glass to fail. It is comparatively cheaper in cost but toughened glass will be thicker than laminated heat-strengthened glass for the same strength. The toughened glass is safe to use as upon failure the glass would shatter into small pieces and minimalizing the injury and there is no possibility of the broken glass falling on the street. • Glass for the Balustrade My recommendation is SentryGlas. The glass would be a sandwich of toughened glasses with an interlayer of SentryGlas. SentryGlas is known for post-failure performance, even on failure, the glass performs better than other products like toughened glass or laminated glass with other interlayers. The glass stays in place, the risk of glass falling is next to no and glass gives enough strength to perform its duty. Unlike PVB or EVA, the SentryGlas (SGP) has [1]: At the same thickness, the SGP bearing capacity is twice that of PVB; under the same load and thickness, the bending deflection of SGP is one-quarter of PVB;  At the same thickness, the SGP has a tear strength of 5 times that of PVB and can be bonded to the glass in the case of tearing without causing the entire glass to fall.  SGP is colourless and transparent, anti-ultraviolet. After long-term sun and rain, it is not easy to turn yellow, and the yellowing coefficient is less than 1.5. However, the yellowing coefficient of PVB interlayer film is 6~12. Therefore, SGP is the darling of ultra-white laminated glass.

Credit: elitesafetyglass Here is a video to help you understand the post-failure performance between toughened glass, toughened glass with PVB and toughened glass with SentryGlas. www.youtube.com Since the glass is to be used for Balustrade, we need to make sure that post-failure performance is important. The terrace area might have kids, drunk adults etc. A round handrail should be used as there are chances of keeping a glass or other objects on a flat rail, which can cause an accident of the object toppling over the rail and the object might fall on a pedestrian. The glass should have some caution information on it; could be a strip of film running horizontally on the centre of the glass or the use of frosted inner glass. So that people can notice the glass, especially when ambient light is low; to reduce accidents of running into the glass or so. Another consideration would be PVB laminated glass with one lit being toughened and another heat-strengthened, in comparison with laminated toughened glass the post-failure performance is way better but the pre-failure strength of glass is lower than PVB laminated glass with one lit being toughened and another heat-strengthened. For the same strength as SentryGlas, Toughened glass is thicker and heat-strengthen glass is even thicker but the main issue is that on failure the toughened glass will reduce the strength of the balustrade and falling glass can harm the pedestrian. Toughened laminated glass on failing will become like a foldable material as shown in image 1. This will impact the performance of the balustrade.

Credit: glassonweb The use of laminated toughened glass with an interlayer of PVB and heat-strengthened glass is also possible but it will be thicker than SentryGlas for the same performance and the post-failure performance would be poor. The SentryGlas would be the best for safety but the most expensive of all.

The safety and fire resistance don’t go side by side, one of the other has to be sacrificed or the cost of the façade will be very high. Generally, it’s advised to go for safety and good water sprinklers and other fire retention systems will help with the fire. A single toughened or heat-strengthened glass would perform better against fire than PVB interlayer laminated glass as, in the event of a fire, PVB laminated glass may break and hang loosely from its frame. Softening/melting of interlayer may cause broken laminated glass to continue to fall for a significant period after a fire has been brought under control, and it is a serious hazard to fire-fighters [2]. Single toughened or heat- strengthened glasses are good against fire resistance as their failure due to temperature is more than 1100oF. To increase the fire resistance of glass we can use the following [3]: • Heat Soaked Modified Thermally Toughened Soda Lime Silicate Safety: The tempering process creates high stresses that maintain the integrity of the glass. • Resin Laminated: Integrity is achieved by an intermediate layer based on flame retardant and flame retardant resins. • Modified Toughened-Laminated: The tempering process creates high stresses that maintain the integrity of the glass. • Thermally Toughened Borosilicate Safety: Due to its composition and low thermal expansion, this kind of glass remains intact. • Laminated Intumescent: These have an intumescent interlayer or layers which become opaque and swell when exposed to fire. • Gel Laminated: They also have a layer deposited designed to become opaque and swell when exposed to fire. The above mention glasses or laminates can be installed as add-ons in the last/inside glass. The thickness of PVB plays an important role, the thicker the interlayer stronger the glass (withstand more loads). I would recommend 1.14mm of PVB interlayer or thicker for best performance. Table 1 gives a brief about who is responsible for what. In our case, the client and the design team would be responsible for any kind of safety issues, anything related to design, procurement, maintenance, inspection, repairs, end of life and demolition.

Table 1 Credit: CWCT The use of heat-soaked toughened glass instead of any kind of toughened glass I have mentioned in my above report. This will reduce the failure of nickel sulphide inclusion to negligible. Once the glass is heat soaked, the occurrence of inclusion occurs once in every 26,500m2 of 6mm toughened glass, this is an extremely low chance of failure occurring. For heat-soaked toughened glasses we need to follow Standard EN14179-1, Approved Document K and BS6262-4 [4][5] For any glass, we need to check for quality and warranty for the same so that glass performance is up to the mark. I have not considered IGU as its main purpose is to improve the building’s energy performance. IGUs can also be made safer by using laminated glass panes or thick toughened glass. Since we will be using toughened or heat-strengthened glasses, the risk of failure due to thermal stress is very less as the safe temperature to not cause thermal stress is 2000C for toughened glass and 1000C for heat-strengthened glasses [6]. Based on below mentioned Tests and regulations, we will get to know the measurement of glass to be used (based on different loads), what things to consider in case of fire or falling a person etc are as follows: • Impact test: with this test, we will be able to under the breakage of the glass, the impact force, and behaviour at each drop height for each test piece. This shall include whether or not the test piece broke. If the test piece broke, the mode of breakage shall be stated, and whether or not it is following the criteria, type and nominal thickness of the glass product etc for the same, we can refer to CWCT TN 61, BS EN 12600 and BS EN 12150. This goes for all the glasses of the whole office building and balustrades. 2 (B) 2 is the minimum requirement. • BS EN ISO 12543-1,2,3 will give us an understanding of laminated glass and its safety. BS EN 14449:2005 will help us to understand the quality control of the factory and how to keep in check, how to test for ensuring data provided by the factory and test for the effectiveness of lamination process. • Wind load & weather tightness tests and guidance provided by authorities are a must so that we can have the right thickness of the glass to withstand wind resistance. For the same, we can refer to BS 6262-3:2005, CWCT TH03 and TH 09. • CWCT TN69 and TN99 will give us guidance and British standers to make our balustrade safe. These notes will give us the high (1100mm), loads acting, design criteria, deflection limit and impact test. • BS EN 1320 BS 6399-1:1996 For infill panels with continuous supports, the infill panel must comply with the design criteria. • To understand fire, its safety and the regulations related to it we have approved document B. • To understand safety in terms of falling, impact, collision and the regulations related to it we have approved document K. • BS EN 14449:2005 for understanding the thickness of the PVB interlayer. • The use of safety glazing in low-rise buildings is described in approve document N

With the recommendations in my report and complying with the above-mentioned test, guidance and regulations, we will be able to get the right thickness of glasses and interlayer. Will going through the test and regulations, we will see how my recommendations are good to use while ensuring safety and the value of money.

1. Conclusion

Based on my report, I would recommend PVB laminated heat-strengthened glass for the office building in general as they are cheap, have no worries about nickel sulphide inclusion, post-failure performance is best and in terms of safety, performance is great. An alternate would be PVB laminated glass with one lit being toughened and another heat-strengthened. For the terrace, I would PVB laminated heat-strengthened glass just because of the aesthetics of the building and if this is not the case then toughened glass is better as on failure it can shatter into small pieces which reduces the chances of injuries when compared to heat-strengthened glass. For balustrades, I would like SentryGlas should be used. It has the best strength and post-failure performance concerning the all-mentioned glass in this report but it’s the most expensive of all. An alternative would be a PVB laminated glass with one lit being toughened and another heat-strengthened, it has good pre and post-failure performance but is lower than SentryGlas. The only advantage over SentryGlas is that it’s cheaper in cost.

1. Introduction

An 11-storey office is being built in Reading with full-height glass walls on all floors. On the top floor, the wall is set back from the edge of the building to create the terrace space at the top floor. The glass wall will be created using a conventional capped glazing system with storey-height glazing units. The edge of the terrace will be protected by a cantilever glass balustrade. For the following, glass has to be recommended and the priority of the recommendations is safety:

1. Wall of the office, general.

2. Wall of the office, at the terrace.

3. Balustrade at the edge of the terrace.

This report will help the developer understand why and what type of glass has to be used, what factors are being considered and what tests or regulations are required to minimise the risk.

1. Assumptions

Some conditions are assumed, which are as follows: • The capped system used is the Stick system; the system’s outer surface is flush with the outer wall of the building and has no structural load on glass. • The priority is the minimise the risk or maximise safety. Other factors like building operation, condition for construction and demolition, building performance in terms of energy conservation/acoustics/sustainability/light and last security for manual attackers/explosion/bullets are the least considered. • The glass used will be soda-lime-silicate glass. • The terrace area has less than 1500m of free space. • The balustrade is free-standing and the handrail is continuous and round in shape. So, the glass is supported at the bottom and top. • The terrace area is for office events to which employees are invited with their families and on a usual day, it is an area for rejuvenation (canteen, play area for table sports like table tennis, foosball etc). On Fridays, it’s a drinking area after working hours. • The maximum wind load is 2 Kpa and the glass size is less than 5m diagonally. • The balustrade is 200mm inside the edge of the wall. • There are no glass roofs or canopy so snow load won’t be considered. • The height of the balustrade is 1100mm. • No financial risk i.e., the client should be able to change the glass in the future with the same glass or so. • The same type of glass for the façade is to be used as different glass has different colours and it’s not acceptable for the aesthetics of the building. • There is no building nearby so the incident solar radiation is increased as a result of the reflection from other building surfaces. 3. Discussion/Explanation

• Glass for the wall (1 to 10 stories) Laminated heat-strengthened glass with PVB (Poly Vinyl Butyral) interlayer can be used. The reason for using it is because of its random breakage pattern. On failure, the glass breaks into large pieces as it has less surface compression and being laminated glass the pieces won’t fall off place. Since the glass is supported by all sides and large pieces are formed, post-failure performance can also be achieved. In comparison with laminated toughened glass, it is less expensive and has better post-failure performance Using laminated toughened glass has its drawback, they are: o It’s more expensive. o Nickel Sulphide inclusion can take place and heat-soaked toughened glass is more expensive than toughened glass. o On breakage, the glass breaks into small pieces and keeps falling off until the glass is replaced, which might cause minor injuries to pedestrians. o On failure the laminated toughened glass has less performance as it breaks into small pieces which leads to lower strength in comparison with Laminated heat-strengthened glass. o On failure, the glass has to be replaced as soon as possible, where Laminated heat-strengthened glass gives an ample amount of time. Single toughened or heat-strength glass can’t be used as it will be much thicker than laminated glass for the same strength and on failure, the glass will just fall off its place causing injuries, in case of heat-strengthened glass the injuries cause will be more dangerous as a large chunk of glass will fall. Another considerable glass type is PVB laminated glass with one lit being toughened and another heat-strengthened. This type of glass has better post-failure performance than laminated toughened glass but poor performance than the laminated heat-strengthened glass on failure the toughened glass is likely to fall off and only the heat-strengthened glass will act to perform after the failure because of its breakage pattern. Before the failure, this type of glass will have more strength than laminated heat-strengthened glass as toughened glass is stronger. • Glass for the terrace I suggest using laminated heat-strengthened glass from floors 1st to 10th, I recommend using the same glass here. The reason for the same is if we use different glass, it would have a different colour from the rest of the building, on failure the glass will stay in its place and will protect the employees from the wind, rain etc and it will give us a good enough time to replace it, unlike toughened glass. If a different colour is not the concern; then toughened glass would be the best choice, it has better heat resistance than any laminated glass available as the interlayer will catch fire and melt causing the glass to fail. It is comparatively cheaper in cost but toughened glass will be thicker than laminated heat-strengthened glass for the same strength. The toughened glass is safe to use as upon failure the glass would shatter into small pieces and minimalizing the injury and there is no possibility of the broken glass falling on the street. • Glass for the Balustrade My recommendation is SentryGlas. The glass would be a sandwich of toughened glasses with an interlayer of SentryGlas. SentryGlas is known for post-failure performance, even on failure, the glass performs better than other products like toughened glass or laminated glass with other interlayers. The glass stays in place, the risk of glass falling is next to no and glass gives enough strength to perform its duty. Unlike PVB or EVA, the SentryGlas (SGP) has [1]: At the same thickness, the SGP bearing capacity is twice that of PVB; under the same load and thickness, the bending deflection of SGP is one-quarter of PVB;  At the same thickness, the SGP has a tear strength of 5 times that of PVB and can be bonded to the glass in the case of tearing without causing the entire glass to fall.  SGP is colourless and transparent, anti-ultraviolet. After long-term sun and rain, it is not easy to turn yellow, and the yellowing coefficient is less than 1.5. However, the yellowing coefficient of PVB interlayer film is 6~12. Therefore, SGP is the darling of ultra-white laminated glass.

Credit: elitesafetyglass Here is a video to help you understand the post-failure performance between toughened glass, toughened glass with PVB and toughened glass with SentryGlas. www.youtube.com Since the glass is to be used for Balustrade, we need to make sure that post-failure performance is important. The terrace area might have kids, drunk adults etc. A round handrail should be used as there are chances of keeping a glass or other objects on a flat rail, which can cause an accident of the object toppling over the rail and the object might fall on a pedestrian. The glass should have some caution information on it; could be a strip of film running horizontally on the centre of the glass or the use of frosted inner glass. So that people can notice the glass, especially when ambient light is low; to reduce accidents of running into the glass or so. Another consideration would be PVB laminated glass with one lit being toughened and another heat-strengthened, in comparison with laminated toughened glass the post-failure performance is way better but the pre-failure strength of glass is lower than PVB laminated glass with one lit being toughened and another heat-strengthened. For the same strength as SentryGlas, Toughened glass is thicker and heat-strengthen glass is even thicker but the main issue is that on failure the toughened glass will reduce the strength of the balustrade and falling glass can harm the pedestrian. Toughened laminated glass on failing will become like a foldable material as shown in image 1. This will impact the performance of the balustrade.

Credit: glassonweb The use of laminated toughened glass with an interlayer of PVB and heat-strengthened glass is also possible but it will be thicker than SentryGlas for the same performance and the post-failure performance would be poor. The SentryGlas would be the best for safety but the most expensive of all.

The safety and fire resistance don’t go side by side, one of the other has to be sacrificed or the cost of the façade will be very high. Generally, it’s advised to go for safety and good water sprinklers and other fire retention systems will help with the fire. A single toughened or heat-strengthened glass would perform better against fire than PVB interlayer laminated glass as, in the event of a fire, PVB laminated glass may break and hang loosely from its frame. Softening/melting of interlayer may cause broken laminated glass to continue to fall for a significant period after a fire has been brought under control, and it is a serious hazard to fire-fighters [2]. Single toughened or heat- strengthened glasses are good against fire resistance as their failure due to temperature is more than 1100oF. To increase the fire resistance of glass we can use the following [3]: • Heat Soaked Modified Thermally Toughened Soda Lime Silicate Safety: The tempering process creates high stresses that maintain the integrity of the glass. • Resin Laminated: Integrity is achieved by an intermediate layer based on flame retardant and flame retardant resins. • Modified Toughened-Laminated: The tempering process creates high stresses that maintain the integrity of the glass. • Thermally Toughened Borosilicate Safety: Due to its composition and low thermal expansion, this kind of glass remains intact. • Laminated Intumescent: These have an intumescent interlayer or layers which become opaque and swell when exposed to fire. • Gel Laminated: They also have a layer deposited designed to become opaque and swell when exposed to fire. The above mention glasses or laminates can be installed as add-ons in the last/inside glass. The thickness of PVB plays an important role, the thicker the interlayer stronger the glass (withstand more loads). I would recommend 1.14mm of PVB interlayer or thicker for best performance. Table 1 gives a brief about who is responsible for what. In our case, the client and the design team would be responsible for any kind of safety issues, anything related to design, procurement, maintenance, inspection, repairs, end of life and demolition.

Table 1 Credit: CWCT The use of heat-soaked toughened glass instead of any kind of toughened glass I have mentioned in my above report. This will reduce the failure of nickel sulphide inclusion to negligible. Once the glass is heat soaked, the occurrence of inclusion occurs once in every 26,500m2 of 6mm toughened glass, this is an extremely low chance of failure occurring. For heat-soaked toughened glasses we need to follow Standard EN14179-1, Approved Document K and BS6262-4 [4][5] For any glass, we need to check for quality and warranty for the same so that glass performance is up to the mark. I have not considered IGU as its main purpose is to improve the building’s energy performance. IGUs can also be made safer by using laminated glass panes or thick toughened glass. Since we will be using toughened or heat-strengthened glasses, the risk of failure due to thermal stress is very less as the safe temperature to not cause thermal stress is 2000C for toughened glass and 1000C for heat-strengthened glasses [6]. Based on below mentioned Tests and regulations, we will get to know the measurement of glass to be used (based on different loads), what things to consider in case of fire or falling a person etc are as follows: • Impact test: with this test, we will be able to under the breakage of the glass, the impact force, and behaviour at each drop height for each test piece. This shall include whether or not the test piece broke. If the test piece broke, the mode of breakage shall be stated, and whether or not it is following the criteria, type and nominal thickness of the glass product etc for the same, we can refer to CWCT TN 61, BS EN 12600 and BS EN 12150. This goes for all the glasses of the whole office building and balustrades. 2 (B) 2 is the minimum requirement. • BS EN ISO 12543-1,2,3 will give us an understanding of laminated glass and its safety. BS EN 14449:2005 will help us to understand the quality control of the factory and how to keep in check, how to test for ensuring data provided by the factory and test for the effectiveness of lamination process. • Wind load & weather tightness tests and guidance provided by authorities are a must so that we can have the right thickness of the glass to withstand wind resistance. For the same, we can refer to BS 6262-3:2005, CWCT TH03 and TH 09. • CWCT TN69 and TN99 will give us guidance and British standers to make our balustrade safe. These notes will give us the high (1100mm), loads acting, design criteria, deflection limit and impact test. • BS EN 1320 BS 6399-1:1996 For infill panels with continuous supports, the infill panel must comply with the design criteria. • To understand fire, its safety and the regulations related to it we have approved document B. • To understand safety in terms of falling, impact, collision and the regulations related to it we have approved document K. • BS EN 14449:2005 for understanding the thickness of the PVB interlayer. • The use of safety glazing in low-rise buildings is described in approve document N

With the recommendations in my report and complying with the above-mentioned test, guidance and regulations, we will be able to get the right thickness of glasses and interlayer. Will going through the test and regulations, we will see how my recommendations are good to use while ensuring safety and the value of money.

1. Conclusion

Based on my report, I would recommend PVB laminated heat-strengthened glass for the office building in general as they are cheap, have no worries about nickel sulphide inclusion, post-failure performance is best and in terms of safety, performance is great. An alternate would be PVB laminated glass with one lit being toughened and another heat-strengthened. For the terrace, I would PVB laminated heat-strengthened glass just because of the aesthetics of the building and if this is not the case then toughened glass is better as on failure it can shatter into small pieces which reduces the chances of injuries when compared to heat-strengthened glass. For balustrades, I would like SentryGlas should be used. It has the best strength and post-failure performance concerning the all-mentioned glass in this report but it’s the most expensive of all. An alternative would be a PVB laminated glass with one lit being toughened and another heat-strengthened, it has good pre and post-failure performance but is lower than SentryGlas. The only advantage over SentryGlas is that it’s cheaper in cost.