Global ETD Search

21	Cyclic testing and assessment of shape memory alloy recentering systems Speicher, Matthew S. 15 December 2009 (has links) In an effort to mitigate damage caused by earthquakes to the built environment, civil engineers have been commissioned to research, design, and build increasingly robust and resilient structural systems. Innovative means to accomplish this task have emerged, such as integrating Shape Memory Alloys (SMAs) into structural systems. SMAs are a unique class of materials that have the ability to spontaneously recover strain of up to 8%. With proper placement in a structural system, SMAs can act as superelastic "structural fuses", absorbing large deformations, dissipating energy, and recentering the structure after a loading event. Though few applications have made it into practice, the potential for widespread use has never been better due to improvements in material behavior and reductions in cost. In this research, three different SMA-based structural applications are developed and tested. The first is a tension/compression damper that utilizes nickel-titanium (NiTi) Belleville washers. The second is a partially restrained beam-column connection utilizing NiTi bars. The third is an articulated quadrilateral bracing system utilizing NiTi wire bundles in parallel with c-shape dampers. Each system was uniquely designed to allow a structure to undergo large drift demands and dissipate energy while retaining strength and recentering ability. This exploratory work highlights the potential for SMA-based structural applications to enhance seismic structural performance and community resilience. Shape memory alloy SMA NiTi Recentering Seismic retrofit Smart materials Shape memory alloys Earthquake resistant design Structural design Earthquake engineering Nickel-titanium alloys
22	Seismic Retrofit of Concrete Columns by Transverse Prestressing Sabri, Amirreza 09 September 2013 (has links) Performance of buildings and bridges during past earthquakes has indicated that many of these structures are vulnerable to seismic damage and structural collapse. The deficiencies in pre-1970s design codes have resulted in poor performance of reinforced concrete structures during seismic excitations. The Richter Magnitude 6.6 - 1971 San Fernando Earthquake raised awareness for seismic retrofit needs of existing buildings for the first time. The majority of deficiencies of vulnerable concrete columns can be overcome through seismic retrofits that involve additional transverse reinforcement. This can be done either by providing reinforced concrete, steel, or fibre-reinforced polymer (FRP) jackets around existing columns; or by applying transverse prestressing to columns (RetroBelt System). The research project presented in this thesis involves a seismic retrofit methodology for seismically deficient building and bridge columns, utilizing the use of high-strength packaging straps as external reinforcement for transverse prestressing. The emphasis in the project is placed on experimental research. Three seismically deficient full-size reinforced concrete columns, with a circular, a square and a rectangular cross- section, either critical in shear or flexure, were designed, built and tested under simulated seismic loading. The results indicate that external prestressing of columns in transverse direction with high-strength steel straps improves ductility and energy dissipation capacity of seismically deficient columns. They further indicate that current analytical techniques can be used to predict the force-displacement relationships of columns. A design approach is presented for the retrofit methodology investigated. Seismic Retrofit Concrete Column Transverse Prestressing building bridge earthquake reinforced concrete seismic retrofit high-strength packaging straps transverse reinforcement RetroBelt transverse prestressing simulated seismic loading
23	Seismic Retrofit of Concrete Columns by Transverse Prestressing Sabri, Amirreza January 2013 (has links) Performance of buildings and bridges during past earthquakes has indicated that many of these structures are vulnerable to seismic damage and structural collapse. The deficiencies in pre-1970s design codes have resulted in poor performance of reinforced concrete structures during seismic excitations. The Richter Magnitude 6.6 - 1971 San Fernando Earthquake raised awareness for seismic retrofit needs of existing buildings for the first time. The majority of deficiencies of vulnerable concrete columns can be overcome through seismic retrofits that involve additional transverse reinforcement. This can be done either by providing reinforced concrete, steel, or fibre-reinforced polymer (FRP) jackets around existing columns; or by applying transverse prestressing to columns (RetroBelt System). The research project presented in this thesis involves a seismic retrofit methodology for seismically deficient building and bridge columns, utilizing the use of high-strength packaging straps as external reinforcement for transverse prestressing. The emphasis in the project is placed on experimental research. Three seismically deficient full-size reinforced concrete columns, with a circular, a square and a rectangular cross- section, either critical in shear or flexure, were designed, built and tested under simulated seismic loading. The results indicate that external prestressing of columns in transverse direction with high-strength steel straps improves ductility and energy dissipation capacity of seismically deficient columns. They further indicate that current analytical techniques can be used to predict the force-displacement relationships of columns. A design approach is presented for the retrofit methodology investigated. Seismic Retrofit Concrete Column Transverse Prestressing building bridge earthquake reinforced concrete seismic retrofit high-strength packaging straps transverse reinforcement RetroBelt transverse prestressing simulated seismic loading
24	AN EXPERIMENTAL STUDY OF THE RESPONSE OF REINFORCED CONCRETE FRAMES WITH WOOD PANEL INFILLS TO SIMULATED EARTHQUAKES Charles Skehan Kerby (12446373) 22 April 2022 (has links) <p>Masonry infills historically have increased in-plane stiffness and reduced drift demands of reinforced concrete frames. An inherent risk remains during intense ground motions that unreinforced masonry infills can develop shear cracks, fail out-of-plane, or lead to the formation of captive-column conditions. This study explored the use of full-bay, plywood panel infills in non-ductile reinforced concrete frames as a novel seismic retrofit. Wood infills were constructed from layers of APA 3/4” Rated Sheathing plywood panels. Infills were tested using two single-bay, single-story concrete frames at 1/3 scale, with initial periods between 0.1 and 0.3 seconds once infilled. External post-tensioning was provided to the columns during all series to prevent column shear failure and doubled as dowel connections between the concrete frame and wood panel infill. Test series were performed on a uniaxial earthquake simulator with the frame bay parallel to the direction of ground motion. Wood infills were approximately 0.36∗𝑏, 0.18∗𝑏, and 0.09∗𝑏 thick, where b is the column width. Multi-layer infills were screw-laminated via a 6” square grid. Infills were tested in previously damaged and nominally pristine frames.</p> <p>During similar ground motions, masonry infills reduced the effective period of the pristine bare frame by approximately 50%. In nominally pristine frames, one-panel plywood infills reduced the bare frame period by a maximum of 50%, and two-panel infills by 60%. One and two-panel wood infills reduced drift demands in comparison to the pristine bare frame by a factor of 1√2∗𝑛 in previously damaged frames and by 12∗𝑛 in nominally pristine frame, where n is the number of panels of plywood across the infill thickness. There was no extra reduction in drift demands resulting from increasing the wood infill thickness beyond two panels. One-panel wood infills failed via out-of-plane buckling causing splitting at a drift demand of approximately 1.5%.</p> <p>The results of this study confirm that wood panel infill retrofits are structurally viable alternatives to stiffen non-ductile reinforced concrete frames. Plywood panel infills reduced drift demands more efficiently per unit thickness and unit weight than masonry infills; the resilience and ease of construction of wood infills suggest expanded use should be explored. Experimental study of full-scale wood infills is needed before this retrofit method could become field deployable.</p> Earthquake Engineering Structural Engineering Reinforced Concrete (RC) Seismic Retrofit Drift Demands Timber Infill Earthquake Simulation Infilled Frames
25	Seismic Retrofit of Reinforced Concrete Frame Buildings with Tension Only Braces Khosravi, Sadegh 13 October 2021 (has links) Reinforced concrete buildings built prior to the enactment of modern seismic codes are often seismically deficient. These buildings may have inadequate strength and ductility to withstand strong earthquakes. Conventional retrofit techniques for such frame buildings involve adding reinforced concrete shear walls or structural bracing systems to the existing bays. These techniques can be intrusive and result in lengthy down times and expensive structural interventions. An alternative to conventional techniques is the use of high-strength prestressing strands or cables, diagonally placed as tension elements. This technique was researched and used in a limited manner after the 1985 Mexico City Earthquake. It has since been further investigated at the University of Ottawa through experimental and analytical research (Shalouf and Saatcioglu (2006), Carrière (2008), Molaei (2014)). While the use of steel strands as tension bracing elements proves to be an effective technique, the resulting stiffening effects on the frames lead to increased seismic force demands and higher based shear, as well as increased axial forces on the attached columns, potentially generating net tension, foundation uplift and excessive compression. Relatively low elongation characteristics of high-strength cables and slack caused by yielding strands and associated pinching of hysteresis curves reduce potential energy dissipation capacity. The current research aims to improve the previously observed deficiencies of the system. One of the improvements involve the use of shape memory alloys (SMA) in the middle of the cables, which reduce/eliminate residual deformations upon yielding and associated pinching of the hysteresis curves. SMA allows energy dissipation in the system while forcing the structure to recover from its inelastic deformations because of the flag-shape hysteretic characteristics of the material. The feasibility of the cable-SMA assembly as tension brace elements is illustrated through dynamic analyses of selected prototype buildings. The other improvement is the development of progressively engaging, initially loose multiple strands as tension cables. These cables are placed loosely to engage in seismic resistance at pre-determined drift levels, thereby eliminating premature increase in seismic force demands until their participation is required as the frame capacity is reached. Tests of a large-scale reinforced concrete frame, designed following the requirements of the 1965 National Building Code of Canada NRC (1965) as representative of existing older frame buildings in Canada, are conducted under simulated seismic loading to assess the effectiveness of the proposed system. The verification of the concept is extended analytically to prototype buildings and the effectiveness of the system is demonstrated for mid-rise and low-rise frame buildings. concrete frames bracing cables ductility drift control earthquake engineering shape memory alloys (SMA) seismic retrofit seismic design braces PEC progressively engaging braces
26	Seismic Retrofit of Load Bearing URM Walls with Internally Placed Reinforcement and Surface-Bonded FRP Sheets Sabri, Amirreza 22 June 2020 (has links) Concrete block masonry is a common building material used worldwide, including Canada. Reinforced masonry buildings, designed according to the requirements of recent building codes, may result in seismically safe structures. However, unreinforced masonry (URM) buildings designed and constructed prior to the development of modern seismic design codes are extremely vulnerable to seismic induced damage. Replacement of older seismically deficient buildings with new and seismically designed structures is economically not feasible in most cases. Therefore, seismic retrofitting of deficient buildings remains to be a viable seismic risk mitigation strategy. Masonry load bearing walls are the most important elements of such buildings, potentially serving as lateral force resisting systems. A seismic retrofit research program is currently underway at the University of Ottawa, consisting of experimental and analytical components for developing new seismic retrofit systems for unreinforced masonry walls. The research project presented in this thesis forms part of the same overall research program. The experimental component includes design, construction, retrofit and testing of large-scale load bearing masonry walls. Two approaches were developed as retrofit methodologies, both involving reinforcing the walls for strength and deformability. The first approach involves the use of ordinary deformed steel reinforcement as internally added reinforcement to attain reinforced masonry behaviour. The second approach involves the use of internally placed post-tensioning tendons to attain prestressed masonry behaviour. The analytical component of research consists of constructing a Finite Element computer model for nonlinear analysis of walls and conducting a parametric study to assess the significance of retrofit design parameters. The results have led to the development of a conceptual retrofit design framework for the new techniques developed, while utilizing the seismic provisions of the National Building Code of Canada and the relevant CSA material standards. Masonry Seismic Retrofit Urm Wall Earthquake Frp Reinforcement Internally Placed Load Bearing Experimental Analytical Sap2000 Finite element Fem Prestressing Amir Amir sabri Saatcioglu Sika Seismic retrofit Post-tensioning Nonlinear Design Retrofit design Masonry design Frp design Polyurea Epoxy Injection Surface Treatment Seismic retrofitting Wall Test Mortar Shear Instrumentation Drift Strain Gauge Shell Shell Elements Stress Contour Concrete Steel Block Concrete block Sap Flextur Surface Bond Post tensioning Sheet Unreinforced masonry

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