Seismic upgrading of building structures using posttensionin

Using high strength post-tensioned steel cables as bracing, the proposed technique seeks to improve the dynamic behavior of a seismically deficient building structure based on the following principles: (1) By increasing the stiffness of an existing building structure, and consequently modifying its dynamic characteristics, this technique can "detune" the structure and make it less responsive to earthquake excitations that have predominant periods of vibrations equal or somewhat higher than that of the original soil-foundation-superstructure system; (2) The introduction of prestress helps overcome problems associated with brace buckling and the subsequent deterioration of post-buckling stiffness and strength under cyclic loadings encountered by conventional concentric bracings; (3) The seismic upgrade can be designed to ensure that the required inelastic deformations under the maximum credible earthquake, in case it's not feasible to keep the structural response within the elastic range, do not exceed those supplied by the available ductility in the existing structure.;The main objectives of this study are (i) to investigate the effectiveness of this seismic upgrading technique based on the use of post-tensioned steel cables or rods, (ii) to study the associated special design and construction requirements, and (iii) to evaluate the relative merits of this technique with respect to other alternatives.;In order to achieve these goals, the dynamic behavior of a six-story steel moment resisting frame (MRF) structure was diagnosed through analytical studies and laboratory earthquake simulation tests. Based on the data obtained, a seismic upgrade using post-tensioning was designed and constructed. The upgraded post-tensioned frame (PTF) structure was then tested on the earthquake simulator. Results from these analytical and experimental works was scrutinized and evaluated, and the effectiveness of this seismic upgrading technique was clearly demonstrated.;As a design application of this seismic upgrading technique in an actual scenario, a four story RC MRF building located in Mexico City which had been damaged by the 1985 earthquake was chosen as a case study. Analytical studies were conducted to identify its structural characteristics and the cause for the observed damage. Seismic upgrade using the post-tensioning technique was then designed, detailed and analytically evaluated.;Conclusions drawn from the studies reported in this dissertation have clearly shown that this seismic upgrading technique based on the use of post-tensioned steel cables or rods is indeed very effective in improving the dynamic behavior of certain types of building structure under earthquakes. The study also shows that this technique could be used advantageously for designing and constructing new structures as well.