@phdthesis{Sahellie2015, author = {Sahellie, Samer}, title = {Study on the temperature effect on lap shear adhesive joints in lightweight steel construction}, issn = {1611-5023}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:co1-opus4-35153}, school = {BTU Cottbus - Senftenberg}, year = {2015}, abstract = {In line with the developments in steel industry, the methods of joining steel members have been developed; therefore, the configuration of functional connections with economic and partly-aesthetic advantages has become possible by the use of the known joining methods, which are bolts, rivets and welding. However, these joining methods do not accompany the further developments and requirements needed to construct lightweight connections or to join dissimilar materials or composite constructions. Moreover, the traditional joining methods do not fulfill the increased requirements of the aesthetics of the joints. In the field of steel constructions, structural engineers might use the bonding technique as an alternative method to join the lightweight steel members or as a helpful mean in the bolted or riveted joints in heavyweight steel structures. Despite the advantages of the adhesive bonding technique, the structural designers in the field of steel constructions are still not able to use it in their practical applications because of the doubts regarding the verifiability of bonded steel joints. This is mainly because of the lack of standards for verifying such joints in steel constructions. To facilitate using this technique in steel constructions, hard efforts have to be performed in order to find out the methods of verifications of bonded steel joints. This starts with understanding the behaviour of the adhesive materials as well as their cohesion ability to the steel surfaces over the whole lifetime of the structure and under all possible loading and environmental conditions. Afterward, the mechanical properties of the adhesives have to be presented by their reliable values that take into account all factors and conditions to which the bonded joint is subjected. These values have to be based on the reliability methods and consequently they are guaranteed for the intended lifetime of the designed structure. It is well known that the adhesives, being viscoelastic materials, are very sensitive to several factors such as the environmental effects, mainly temperature and humidity, and the long-term loading. The loss of strength and durability of adhesives materials, due to the mentioned factors, is an essential aspect that has to be determined and to be taken into account of the structural designers during the design process. For example, it is generally proven that the increase of temperature causes a decrease in the elastic (E) and (G) moduli, cohesive and adhesive forces within the joint and maximum stresses which can be carried by the joint. However, there is still a huge lack in describing the degradations of the mechanical properties quantitatively. Similarly, the failure in the adhesives, loaded for long time by a constant stress even less than their short-term strengths, is probable due to the well-known rheological phenomenon of viscoelastic materials which is the creep phenomenon. Moreover, the adhesives will creep at high temperatures faster; hence the failure will happen in a shorter time. Describing the long-term behaviour of the structural adhesives is still modest; therefore, the time-to-failure of bonded steel joints under long-term loading cannot be exactly predicted. This is an essential issue has to be dealt with to fulfill the requirements of employing the adhesive bonding technique in the structural fields including the steel constructions. The efficiency of using adhesive-bonded joints in steel constructions is higher when the adhesives in these joints are loaded in shear. In such shear joints, the lightweight steel members (adherends) are likely to yield before the break within the adhesive layer happens, especially when large bonded areas are used because the developed shear stresses over the most of these areas will be very small. This thesis deals with the temperature influence on the behaviour of two adhesive systems (acrylic and epoxy) and on the capacities of adhesively bonded lap shear joints. The temperature influence is quantitatively described for short-term loading over a service range of temperature from -20 °C to +40 °C. The quantitative description is done by proposing the partial factors and the conversion factors that take the temperature effect into account. This influence is also dealt with for long-term loading to describe the shear creep behaviour of the adhesive materials used. Consequently, the time-to-failure of the bonded lap shear joints due to the creep phenomenon of the adhesives under three applied stresses at room temperature is predicted. Moreover, the estimation of time-to-failure is extended to be used for other shear stress levels. The temperature influence as well as the efficiency of using adhesive-bonded joints in lightweight galvanized steel constructions is also illustrated by giving a practical example of strengthening cold-formed "C" section girders. Comparisons between the two adhesive systems for all cases are given.}, subject = {Bonded steel joints; Temperature effect; Structural adhesives; Short and long-term loading; Shear strength; Geklebte Stahlverbindungen; Temperatureffekt; Strukturelle Klebstoffe; Kurz- und Langzeitverhalten; Schubspannung}, language = {en} }