Upgrading the Structural Capacity of a Steel Frame using Externally Bonded CFRP Master's Thesis in the International Master's Program Structural Engineering

Externally bonded Carbon Fiber Reinforced Polymer (CFRP) laminates can be an excellent alternative to reinforce degraded elements. The use of this relatively new technique in a proper way with suitable laminates and adhesive for the structure in matter can result in a considerable upgrade of the structural capacity. Benefits of CFRP laminates are their superior mechanical and physical properties. They are also easy to handle and apply, which minimizes the time that the structure has to be out of use. This master thesis investigates how much the collapse load for an A-shaped steel frame can be increased, using externally bonded CFRP. The frame is serving as a pipe support at a nuclear power plant. A hold-up in the production in this kind of facility leads to severe economical consequences, which is why a quick and easy measure to strengthen is of great importance. A final strengthening scheme of CFRP laminates, that increases the collapse load the most, was searched for. The collapse load is defined according to the American design code ASME III – Rules for Construction of Nuclear Power Plants Components. The frame with bonded CFRP was modeled in the finite element programs I-DEAS and ABAQUS, using continuum (solid) plane stress elements. In the field of civil engineering, CFRP laminates are generally used for strengthening members in bending or tension. For this reason, this study had its original focus on cases where the laminates are bonded to the tension flanges. However, the analysis of the unreinforced frame showed that failure was a result of immense shear forces in the web. As a consequence to this, these web areas needed to be reinforced by adding steel plates. The use of steel plates was not part of the original objective, but due to the unexpected behavior of the frame, this measure was considered to be essential in order to justify the use of CFRP in further reinforcing measures. The results obtained from the analysis of the web reinforced frame confirmed that yielding started in the flanges, which motivated a strengthening scheme with CFRP. Applying High-Strength laminates to this web reinforced frame increased the collapse load at the most with 24 %, from 3.52 MN for the unreinforced frame, to 4.63 MN. However, as this thesis was written there was neither any information about laminates subjected to compression, nor limits for allowable stresses in the adhesive layer. This is two essential factors that need to be verified before the success of this strengthening scheme can be confirmed.