CONSTRUCTION FIXINGS
One of the most important changes that was implemented in EN 1992-4 is the application of a product dependent reduction factor explicitly taking into account the behavior of bonded anchors under sustained loading.” Major changes for the design of adhesive anchors under sustained loading
One of the most important changes that was implemented in EN 1992-4 is the application of a product dependent reduction factor explicitly taking into account the behavior of bonded anchors under sustained loading (ψ°sus). Based on the suggested reduction factor in the EN 1992-4, for cases where no specific information is provided for a product in e.g an ETA, the applicable bond strength is reduced up to 40% depending on the ratio of sustained action to the sum of the total actions. If in this case the percentage of sustained load is larger than 60% of the sum of the total load acting on the anchorage, the reduction factor ψ°sus needs to be applied to account for the decrease of the bond strength under sustained loading. Applications with 100% sustained load suffer the maximum reduction of 40% of the bond strength whereas for applications with less than 60% sustained load no reduction becomes effective. The current value of the above mentioned reduction factor ψ°sus (ψ°sus = 0.6) given in EN 1992-4 considers the decrease of the bond strength of adhesive anchors due to sustained loading when the concrete temperature in the region of the fastener is at 43°C during a total time period of 10 years within the service life. The factor shall be applied for cracked and non-cracked concrete, as well as for all temperature ranges, although there is no guidance available in EN 1992-4 for maximum long-term temperatures higher than 43°C. The problem with this change is the fact, that under distinct circumstances (applications with primary sustained tension loading) a reduction of the resistance of up to 40% may occur (depending on the loading situation). This may cause significant confusion for consumers and structural engineers, as a considerable difference in design results will occur depending on the applied design code EN 1992-4 or EOTA TR029 or CEN/TS 1992-4. These differences may also occur in design situations with alternative mortars of several manufacturers (depending on the utilised design provisions in the ETA Assessment Documents). CFE (Construction Fixings Europe) therefore recommends proactively informing the customers and structural engineers about the upcoming changes. In the opinion of CFE the current state of the art shall always be applied for the design of post installed fastenings, which means after its publication, EN 1992-4 is quasi mandatory for future projects.
138 FASTENER + FIXING MAGAZINE // ISSUE 113 SEPTEMBER 2018
Literature
1. EN1992-4: ‘Eurocode 2: — Design of concrete structures – Part 4: Design of fastenings for use in concrete’, CEN/ TC 250, 2017. 2. European Organisation of Technical Approvals (EOTA): ETAG 001- Guideline for European Technical Approvals – Metal anchors for use in concrete, Edition 1997. 3. European Organisation of Technical Approvals (EOTA): TR029 – Design of bonded anchors, 2007. 4. European Organisation of Technical Approvals (EOTA): TR045 – Design of metal anchors for use in concrete under seismic action, 2013. 5. European Organisation of Technical Approvals (EOTA): TR047 – Design of anchor channels, 2015. 6. European Organisation of Technical Approvals (EOTA): TR050 – Calculation methods for the Performance of anchor channels under fatigue loading, 2015. 7. CEN/ TS 1992-4: Design of fastenings for use in concrete, CEN, Brussels, 2009. 8. Sippel T., Ignatiadis A.: Design of fastenings for use in concrete construction: New EN1992-4- current status, commentary and background, Proceedings of 3d international Symposium on Connections between Steel and Concrete, Stuttgart, Germany, 2017. 9. Fuchs W., Eligehausen R., Hofmann J.: EN1992-4 – The long route to a European standard for fastening to concrete, Proceedings of 3d international Symposium on Connections between Steel and Concrete, Stuttgart, Germany, 2017. 10. European Organisation of Technical Approvals (EOTA): TR055- Design of fastenings based on EAD 33 0232, EAD 33 049 and EAD 330747, 2018.