Displacement Based Seismic Design of Concentric Braced Frames and Development of Large Strain POF Sensors for Structural Health Monitoring

This research has two major parts: (a) Direct Displacement Based Seismic Design (DDBD) of Concentric Braced Frames (CBF) through numerical study and experimental testing using advance instrumentation and (b) development of single mode Polymer Optical Fiber (smPOF) sensors for large strain applications in structural health monitoring and structural testing.;Displacement Based Design of Concentric Braced Frames. DDBD is an approach that enables us to assess the nonlinear response of MDOF structures by analyzing the equivalent linear SDOF models. The DDBD parameters for CBFs were evaluated by numerical modeling and experimental testing. Due to expected small lateral displacements, advanced instrumentation (LED sensors) was used to record the structural response.;Steel concentrically braced frames could provide more strength and stiffness than moment frames with the same amount of steel. Their energy dissipation mechanism is mainly dominated by buckling of braces. Therefore they have lower ductility when compared with the moment frames. Because of the expected type of failure, the behavior of these structures is different from other types of steel frames. This behavior of CBFs attracted our attention for DDBD development.;To model the buckling of the braces, a new buckling model was developed and calibrated. This model provides accurate prediction for buckling of braces.;The proposed model was validated though 14 experimental tests on various braces. In the presented research, a 1/5 scaled four story CBF with two type of braces was tested and analyzed. A total of 6 earthquake records with a variety of scale factors were used in the shaking table tests of CBFs. The maximum displacement profiles along with the effective yield displacement were determined for the CBF. In DDBD, the effective yield displacement is the yield displacement of the equivalent SDOF system. Yield displacement and equivalent damping were determined through the nonlinear monotonic and cyclic reversed pushover analysis of 2, 4, 8, 12, and 16 stories CBFs. The target displacement profile was also determined by conducting a series of nonlinear time history analysis. The shift period versus displacement ductility of the equivalent system was also determined. Finally, the developed approach and parameters were successfully evaluated through a series of nonlinear time history analysis on a CBF.;Development of Large Strain smPOF Sensors for Structural Health Monitoring. In this part of the research single mode Polymer Optical Fiber (smPOF) sensors were successfully developed and tested for large strain measurements up to 10%. POFs are flexible in bending and durable in harsh environmental conditions. Conventional electrical strain gages typically fail at 3% strain in steel and 1% strain in concrete structures. The sensors were tested on the surface of aluminum coupons and embedded inside of the concrete structural members.;To develop the sensors, the POFs were axially tested to determine their mechanical propertied for the calibration. Then, three construction materials were tested to prepare an appropriate embedment for embedding of POFs inside of concrete structural members. The special cement paste mixture was chosen because of its bond with the POF (base on the pull out tests). The embedded fibers demonstrated very good performance inside of real concrete structural members under cyclic loading.;Due to attenuation of POFs, they should be coupled with glass fibers outside of the gauge length. For this purpose, the surface of POFs should be carefully cleaved. New cleaving methods were proposed in this research based on the tests on various novel methods. In addition an effective coupling method was also developed and employed. The data acquisition system along with Mach-Zender interferometric system were employed to measure the large strain values. The developed sensors were mounted on aluminum coupons. They measured up to 10% tensile strain and 1% compressive strain. The POF sensors presented very good repeatability which resulted in reliable calibration curves. Additionally, based on the conducted calibration tests, the probable calibration errors were estimated. Finally, the ability of these sensors for large strain measurement was successfully validated with a new test on an aluminum coupon. Summarizing, the developed POF sensors demonstrated impressive ability in large strain measurement with low error rates.