Återbruk av konstruktionsstål – Regelverk, provningsmetoder och utmattningslivslängd

Sammanfattning

Steel is one of the most common construction materials in the building industry and has high potential for reuse. Despite this, very little reuse of structural steel is currently taking place in Sweden. Only 11 percent of all steel in Europe is reused, while 88 percent is recycled. Steel production accounts for approximately 7 percent of global carbon dioxide emissions, and reuse of steel is the most effective method to reduce climate impact compared to traditional recycling through melting. The aim of this study is to investigate how Swedish building regulations affect the reuse of structural steel, to identify testing methods for reused structural steel to meet strength requirements, and to identify methods for estimating the remaining fatigue life of reused steel structures. A literature study has been conducted together with complementary interviews. The results show that Swedish building regulations both enable and hinder the reuse of structural steel. Enabling occurs through SS-EN 1090-2, section 5.1, which allows the use of non-standardized products provided certain properties are specified. Hindering factors include the requirements for CE marking and performance declarations, which are difficult to fulfill for reused components lacking original documentation. The interviews confirm that the issue of responsibility is central, while new steel comes with manufacturer guarantees, the full risk for reused material falls on the individual designer. Four well-established testing procedures (A-D) exist to ensure compliance with strength requirements, adapted according to available documentation. Procedure A (original documentation available) requires only non-destructive hardness testing. Procedure B (type 1 steel, manufactured from 1970 onwards, known provenance) combines non-destructive testing on all components with destructive testing on the component exhibiting the lowest hardness value. Procedure C (type 2 steel, manufactured before 1970) requires destructive testing on at least three components per test unit (lowest hardness, highest hardness, and one randomly selected), followed by statistical evaluation. Procedure D (unknown provenance) requires destructive testing on every single component. Key testing methods include UCI hardness testing, tensile testing, impact testing, and chemical composition analysis. The UCI method has a margin of error of up to ±85 MPa. Regarding remaining fatigue life, several scientifically validated methods exist: S-N curves (suitable when documentation exists), fracture mechanics based on Paris' law (useful when cracks have initiated or load history is unknown), probabilistic methods such as VMEA and Monte Carlo (handling uncertainties), non-destructive testing such as thermography, where validation tests show an average difference of less than 5 percentage points, numerical crack propagation with an average ratio between predicted and experimental fatigue life of 1.149, multiaxial fatigue analysis where 80 percent of test data for several steel grades falls within a scatter band of factor 3, as well as combined stepwise procedures. However, none of these methods are currently standardized in applicable regulations, which highlights the need for further research and development in this field. It is concluded that the reuse of structural steel is technically possible within the framework of current regulations, but practical obstacles remain. Procedures A-D provide a clear and adaptable path for verifying strength properties, and several scientific methods are available for assessing remaining fatigue life. However, for reuse to be scaled up, clearer harmonized rules at the European level, standardization of fatigue life assessment methods, and incentives addressing responsibility and cost issues are required.