Strenghtening and seismic retrofitting
- Consulting in the field of earthquake protection, especially for masonry buildings.
- Empa develops new methods of retrofitting in cooperation with industrial partners. Empa accompanies the development of new materials and methods from the initial concept to a commercial product.
- Empa performs laboratory and field tests on retrofitted structures to verify safety and serviceability by applying static and dynamic loads.
- Empa consults building owners and engineers about materials and techniques for retrofitting of struc-tures such as bridges and buildings.
- Empa monitors retrofitted civil structures.
Contact: Prof. Dr. Masoud Motavalli, Dr. Christoph Czaderski
RESEARCH AND DEVELOPMENT
TULCOEMPA – Strengthening of a prestressed concrete road bridge with prestressed CFRP strips
In collaboration with the Technical University of Lodz (Poland) a retrofitting concept for a prestressed concrete road bridge is elaborated.
The strengthening was realized with prestressed CFRP strips anchored with the ‘gradient anchorage’ developed at Empa.
A special anchorage device previously developed in the framework of an industrial R&D project was applied for the first time on a bridge construction. Two large-scale girders were built 1:1 at Empa laboratory according to the original elements and was used for static load testing for demonstrating the higher bearing capacity of the retrofitted structure.
Partner / Financing: www.tulcoempa.com
Contact: Dr. Christoph Czaderski, Prof. Dr. Masoud Motavalli
Strengthening of reinforced concrete members by prestressed, externally bonded reinforcement with gradient anchorage
The aim and motivation for this PhD work was to better understand the bond behaviour of prestressed CFRP strips in the region of the gradient anchorage.
Detailed insights in the structural behaviour of CFRP strips that were glued on a concrete surface were found in lap-shear, prestress force release and beam tests. Full-field displacements measurements were performed by using an optical 3D image correlation measurement system.
Contact: Dr. Christoph Czaderski
Temperature stability of externally bonded carbon fiber reinforced polymer (CFRP) strips for strengthen of reinforced concrete structures
CFRP strips can be used to strengthen highway concrete bridges. However, during the asphalt application epoxy resin temperatures up to 80°C and from sunshine temperatures up to 50-60°C might occur. In this project, the temperature resistance as well as the bond durability of externally bonded CFRP strips on concrete substrate by means of beam tests is investigated. The strips will be analyzed at initially unstressed and at prestressed state. The photo shows a long-term loading test at Empa with a continuous monitoring of the CFRP strip strains and outside temperature.
The motivation of the investigation is mainly the idea of a more spread use of the material in bridge construction as a retrofitting technique for decks. The project is supported from the Swiss Federal roads office FEDRO.
Contact: Dr. Christoph Czaderski
Strengthening of metallic members using CFRP laminates
The most commonly used structural metals are steel, cast irons and wrought irons. The effect of CFRP strengthening on static, buckling and fatigue behavior of structural metallic members is investigated. Furthermore, details about fatigue strengthening of riveted girders of 120-year-old metallic railway bridge in Switzerland using pre-stressed un-bonded CFRP laminates are described. The advantages of the new un-bonded retrofit system are: applicable to unsmooth (e.g., riveted or corroded) surfaces, fast on-site installation (i.e., no glue and surface preparation), no damage on metallic member (no weld, hole or grinding) and adjustable CFRP pre-stress level. Furthermore, the system can be easily disassembled and removed from the girder, which makes it suitable to be used as a temporary or permanent retrofit solution particularly for historical bridges.
More details about projects related to steel strengthening: see hereContact: Dr. Elyas Ghafoori, Prof. Dr. Masoud Motavalli
Seismic retrofitting of unreinforced masonry using post-tensioning
Many existing buildings worldwide are made of unreinforced masonry with very little resistance to horizontal loading. An efficient way of improving their seismic behaviour is retrofitting by post-tensioning. The additional vertical load increases the horizontal resistance considerably but can also reduce the deformation capacity, which is an important parameter in displacement-based design.
The goal of this project is to find the optimal application of post-tensioning and to develop corresponding design rules.
Contact: Dr. Benedikt Weber