Combining existing independent seismic reinforcing methods for clay brick masonry

Abstract

In the last decades induced earthquakes are taking place more frequently in Groningen. This is due to gas extraction form the soil. Buildings are damaged by the earthquakes and building collapse is possible in the near future. Houses in Groningen are commonly build up out of single leaf masonry cavity walls and are not designed for earthquake loads. Oosterhof Holman and SealteQ Group have designed a masonry reinforcing method that is called Quake-Shield. Quake-Shield is an unique reinforcing method and consists out of a combination of two existing independent seismic reinforcing measures. These two existing independent seismic reinforcing measures are: NSM FRP strips and an EB FRP layer. Carbon strips are placed in vertical grooves in the masonry which are filled with a ductile adhesive to bond the strips to the masonry (NSM FRP strips). A polymer or cementitious base layer with an embedded polymer or carbon mesh is attached to one side of the masonry on the outer surface (EB FRP layer). Both reinforcing measures increase stiffness, strength and ductility of the masonry. These three factors result in an increase in earthquake energy absorption and dissipation of the masonry. Which is important when reinforcing houses and buildings to prevent collapse due to earthquake loads. In this project a FEM model is made based on a three point bend test (out-of-plane bending) performed on Quake-Shield reinforced masonry samples. The FEM model is used to develop knowledge about the effect of combining two existing independent seismic reinforcing measures as used in the Quake-Shield masonry reinforcing method. The FEM model is a 3D model with a simplified micro-model approach for the masonry. The bricks are solid elements, the reinforcing materials are shell elements and the mortar and the ductile adhesive are interface elements. The bond-slip behaviour of the ductile adhesive has a significant contribution in the behaviour of Quake-Shield reinforced masonry. The mechanical properties of the ductile adhesive determines mainly the pre and post peak behaviour of the reinforced masonry. Providing gradually decline in load bearing capacity after the peak load. The EB FRP layer has a significant contribution to the reinforced masonry in the displacement range from the initiation of the first crack in the masonry till the onset of yielding of the EB FRP layer. In this range the EB FRP layer is the dominant reinforcing measure. After yielding of the EB FRP layer the NSM CFRP strip becomes the most dominant of the two. The EB FRP layer also provides cohesion between the individual bricks, keeping the masonry wall together after severe cracking has taken place. The FEM model is also used for a configuration analysis to research different geometrical and material variations of the Quake-Shield masonry reinforcing method. The configuration analysis gives more insight in the behaviour of reinforced masonry. For the configuration analysis two independent seismic reinforcing measures, NSM FRP strips and EB FRP layer, are applied separately to the FEM model. This is done to investigate its individual effect on the behaviour of reinforced masonry. Strip spacing has a significant effect on the load bearing capacity. If an epoxy is used as adhesive, which is much stronger and stiffer than the adhesive used by Quake-Shield, an increase in load bearing capacity is achieved but also sudden failure after the peak load is observed. This is an undesirable failure mode and reduces the total energy that the reinforced masonry can absorb. Results of the different configurations used for the EB layer show that the polymer (PU) base layer has the most significant contribution of the used EB FRP layer materials when considering overall ductility and energy absorption of the reinforced masonry.