Assessment and strengthening of an old reinforced concrete building in Tripoli

Abstract

According to a study conducted by the GIS center at the University of Balamand in 2006, approximately 343 buildings in Tripoli need to be strengthened against earthquake. Cracks occur when the stress resulting from external loads and internal phenomena such as moisture, thermal movement and chemical reaction, etc. exceed the strength of the member. Moreover some of the building and foundation are not well confined, not properly reinforced, or not poured with a good concrete quality, which decrease their capability in operating properly. The purpose of this investigation is to repair an existing historical building against a nearby earthquake, by limiting its deflection, strengthening its members and foundation and fixing its cracks. The methodology procedure for repairing cracks consists of two parts: 1- Visual inspection and data collection 2-Cracks analysis and the selection of an appropriate strategy method. The building was modeled on Zeus NL software after the data collection with a nearby earthquakes time history to determine its period, displacement, and pushover analyses, then the values were compared to FEMAs allowed displacement. Based on the types, structural function and the renovation purpose, the cracks repair strategy is selected. Epoxy injection and stitching and doweling were mainly used for dormant cracks to restore their integrity. More advanced techniques were used for active cracks to regain their original strength. Dry packing, polyurethane and epoxy injection, stitching and doweling were mainly used for active crack in order to seal the cracks whereas polyurethane injection and routing and sealing were used for dormant cracks. Regarding the strengthening procedure, the buildings period was found to be 1.9 seconds; it enters the plastic region after 1.54 seconds and at a displacement of 0.110878 m, and then fails simultaneously. According to FEMA, the maximum allowable displacement was calculated to be 7.8 cm to reach immediate occupancy behavior. The best suggested solutions are either adding steel bracings or adding dampers in the ground floor to reduce the displacement. Concrete jacketing the columns is a must to add the required stirrups and steel bars reinforcement to allow the columns to resist the earthquake loads, and the beams should be wrapped twice with carbon fiber polymers to confine them and increase their ductility. As for foundations, the use root piles or angle piles is the best solution to be used since it has the least disturbance of the building and the neighborhood and at the same time stability is achieved, and since the addition of extra structural elements and digging can disturb the neighborhood foundations. It is concluded that cracks present in reinforced concrete structure need to be repaired because they accelerate the deterioration of the structure and reduce its durability. The building also needs to be system based strengthened against earthquake to decrease its deflection to a certain limit and member based strengthened so that its columns and beams resist the new earthquake stresses. Moreover, root piles to avoid several types of failures should repair the strip foundation. This investigation mainly concerns researchers and civil engineers that are interested in old historical buildings.