A large inventory of low rise masonry buildings in Canada and elsewhere in the world were built using unreinforced or partially reinforced load bearing wall. The majority of existing masonry structures is deficient in resisting seismic force demands specified in current building codes. Therefore, they pose significant risk to life safety and economic wellbeing of any major metropolitan centre. Because it is not economically feasible to replace the existing substandard buildings with new and improved structures, seismic retrofitting remains to be an economically viable option. The effectiveness of surface bonded carbon fiber-reinforced polymer (CFRP) sheets in retrofitting low-rise load bearing masonry walls was investigated in the current research project. The retrofit technique included the enhancements in wall capacity in shear and flexure, as well as anchoring the walls to the supporting elements through appropriate anchorage systems. Both FRP fan type anchors and steel sheet anchors were investigated for elastic and inelastic wall response. One partially reinforced masonry (PRM) wall and one unreinforced masonry (URM) wall were built, instrumented and tested under simulated seismic loading to develop the retrofit technique. The walls were retrofitted with CFRP sheets applied only on one side to represent a frequently encountered constraint in practice. FRP fan anchors and stainless steel sheet anchors were used to connect the vertical FRP sheets to the wall foundation. The walls were tested under constant gravity load and incrementally increasing in-plane deformation reversals. The lateral load capacities of both walls were enhanced significantly. The steel sheet anchors also resulted in some ductility. In addition, some small-scale tests were performed to select appropriate anchor materials. It was concluded that ductile stainless steel sheet anchors would be the best option for brittle URM walls. Analytical research was conducted to assess the applicability of truss analogy to retrofitted walls. An analytical model was developed and load displacement relationships were generated for the two walls that were retrofitted. The analytical results were compared with those obtained experimentally, indicating good agreement in force resistance for use as a design tool.

Squat reinforced concrete shear walls are stiff structural elements incorporated in buildings and other structures and are capable of resisting large seismic demands. However, when not properly designed, they are prone to shear-related brittle failure. To improve the seismic behaviour of these structural elements, a retrofitting bracing system incorporating superelastic Shape Memory Alloys (SMAs) was developed. Superelastic Shape Memory Alloys (SMAs) are smart materials with the ability to sustain and recover large pseudo-plastic deformations while dissipating energy. The SMA bracing system consists of tension-only SMA links coupled with rigid steel elements. The SMA links were designed to sustain and recover the elongation experienced by the bracing system, while the steel elements were designed to sustain negligible elastic elongations. The SMA bracing system was installed on third-scale, 2000 mm × 2000 mm, shear walls, which were tested to failure under incremental reverse cyclic loading. The experimental results demonstrated that the tension-only SMA braces improve the seismic response of squat reinforced concrete walls. The retrofitted walls experienced higher strength, greater energy dissipation, and less permanent deformation. The re-centering properties of the SMA contributed to the reduction of pinching in the hysteretic response due mainly to the clamping action of the SMA bracings while recovering their original length. The walls were numerically simulated with the nonlinear finite element program VecTor2. The numerical simulations accurately captured the hysteretic response of both the original and the retrofitted walls. A parametric study was conducted to assess the effect of axial loading and size of the SMA braces.

The application of retrofit options to existing heritage buildings has become one of the most interesting topics in construction. In Victoria, BC, Canada, only 4% of commercial or institutional heritage buildings have been upgraded to current building codes in the last 10 years. Remaining 96% buildings exist with poor energy performance characteristics and a risk to occupant safety in the event of a damaging earthquake. This study investigates the importance and benefits of simultaneous energy and seismic retrofitting of existing heritage buildings. It presents a case study for a building with identifiable heritage value, located in Victoria, BC, Canada, and analyzes five feasible options in terms of energy retrofitting and presents a solution for both seismic and energy upgrading. To this aim, the energy retrofit options are compared based on the amount of saved energy, annual heating demand and estimated costs. The seismic solution is designed based on the weakness and needs of the building, and cost-effectiveness. Finally, the best solution is selected for a building that dates back to the beginning of the 20th century. This study shows that the integration of energy and seismic retrofitting of heritage buildings provides economic benefits to owners while improving energy savings and building safety. / Graduate / 2021-08-31

The Point Sur Lighthouse is an unreinforced stone masonry building completed in 1889 on the central coast of California. The lighthouse is listed on the National Register of Historic Places and is still an active aid to navigation. The original first-order Fresnel lens was removed from the lantern room and placed in safekeeping due to its high risk of damage in the event of a strong earthquake. The lens has been approved to return to its original setting but the seismic performance of the building must first be assessed in order to ensure the safety of the lens and lighthouse, specifically the out-of-plane behavior of the unreinforced masonry walls, the implementation of possible seismic retrofit schemes, and the effects of the lens’s added weight. This research focuses on the dynamic behavior of the lighthouse in its current state and the changes in the dynamic behavior each of the proposed seismic retrofit schemes might cause. For the purposes of this research, dynamic behavior is considered as natural frequencies, mode shapes, and related structural properties. The dynamic behavior of the lighthouse was assessed using two main methods: forced vibration testing and finite element computer modeling. Forced vibration testing is a nondestructive testing method that can be used to directly characterize dynamic behavior of a structure, and finite element computer modeling is useful for the design and simulation of dynamic behavior of both new and existing structures. The combination of these two methods on the Point Sur Lighthouse will work to develop and prove state-of-the-art seismic retrofitting techniques.

This research introduces and develops a counter-intuitive seismic retrofit strategy, referred to as “Selective Weakening” (SW), for pre-1970s reinforced concrete (RC) frames with a particular emphasis on the upgrading of exterior beam-column joints. By focusing on increasing the displacement and ductility capacities of the beam-column joints, simple retrofit interventions such as selective weakening of the beam and external post-tensioning of the joint can change the local inelastic mechanism and result in improved global lateral and energy dissipation capacities. The thesis first presents an extensive review of the seismic vulnerability and assessment of pre-1970s RC frames. Following a review of the concepts of performance-based seismic retrofit and existing seismic retrofit solutions, a thorough conceptual development of the SW retrofit strategy and techniques is presented. A “local-to-global” design procedure for the design of SW retrofit is proposed. Based on the evaluation of the hierarchy of strength at a subassembly level, a capacity-design retrofit outcome can be achieved using various combinations of levels of beam-weakening and joint post-tensioning. Analytical tools for the assessment and design of the SW-retrofitted beam-column joints are developed and compared with the test results. Nine 2/3-scaled exterior joint subassemblies were tested under quasi-static cyclic loading to demonstrate the feasibility and effectiveness of SW retrofit for non-ductile unreinforced beam-column connections. Parameters considered in the tests included the presence of column lap-splice, slab and transverse beams, levels of post-tensioning forces and location of beam weakening. Extensive instrumentation and a rigorous testing regime allowed for a detailed experimental insight into the seismic behaviour of these as-built and retrofitted joints. Experimental-analytical comparisons highlighted some limitations of existing seismic assessment procedures and helped in developing and validating the SW retrofit design expressions. Interesting insights into the bond behaviour of the plain-round bars, joint shear cracking and post-tensioned joints were made based on the experimental results. To complement the experimental investigation, refined fracture-mechanic finite-element (FE) modelling of the beam-column joint subassemblies and non-linear dynamic time-history analyses of RC frames were carried out. Both the experimental and numerical results have shown the potential of SW retrofit to be a simple and structurally efficient structural rehabilitation strategy for non-ductile RC frames.

This thesis examines the seismic internal retrofitting of existing deficient reinforced concrete (RC) structures by using structural steel members. Both experimental and numerical studies were performed. The strengthening methods utilized with the scope of this work are chevron braces, internal steel frames (ISFs), X-braces and column with shear plate. For this purpose, thirteen strengthened and two as built reference one bay one story portal frame specimens having 1/3 scales were tested under constant gravity load and increasing cyclic lateral displacement excursions. In addition, two &frac12 / scaled three bay-two story frame specimens strengthened with chevron brace and ISF were tested by employing continuous pseudo dynamic testing methods. The test results indicated that the cyclic performance of the Xbrace and column with shear plate assemblage technique were unsatisfactory. On the other hand, both chevron brace and ISF had acceptable cyclic performance and these two techniques were found to be candidate solutions for seismic retrofitting of deficient RC structures. The numerical simulations by conducting nonlinear static and dynamic analysis were used to estimate performance limits of the RC frame and steel members. Suggested strengthening approaches, chevron brace and ISF, were also employed to an existing five story case study RC building to demonstrate the performance efficiency. Finally, design approaches by using existing strengthening guidelines in Turkish Earthquake Code and ASCE/SEI 41 (2007) documents were suggested.

<div>Ensuring the resilience of a state’s transportation network is necessary to guarantee an acceptable quality of life for the people the network serves. A lack of resilience in the wake of a seismic event directly impacts the states’ overall safety and economic vitality. With the recent identification of the Wabash Valley Seismic Zone (WBSV), Department of Transportations (DOTs) like Indiana’s have increased awareness for the vulnerability of their bridge network. The Indiana Department of Transportation (INDOT) has been steadily working to reduce the seismic vulnerability of bridges in the state in particular in the southwest Vincennes District. In the corridor formed by I-69 built in the early 2000s the bridge design is required to consider seismic actions. However, with less recent bridges and those outside the Vincennes District being built without consideration for seismic effects, the potential for vulnerability exists. As such, the objective of this thesis is to develop a robust seismic vulnerability assessment methodology which can assess the overall vulnerability of Indiana’s critical bridge network. </div><div><br></div><div>A representative sample of structures in Indiana’s bridge inventory, which prioritized the higher seismic risk areas, covered the entire state geographically, and ensured robust superstructure details, was chosen. The sample was used to carry a deterministic seismic vulnerability assessment, applicable to all superstructure-substructure combinations. Analysis considerations, such as the calculation of critical capacity measures like moment-curvature and a pushover analysis, are leveraged to accurately account for non-linear effects like force redistribution. This effect is a result of non-simultaneous structural softening in multi-span bridges that maintain piers of varying heights and stiffnesses. These analysis components are incorporated into a dynamic analysis to allow for the more precise identification of vulnerable details in Indiana’s bridge inventory.</div><div><br></div><div>The results of this deterministic seismic assessment procedure are also leveraged to identify trends in the structural response of the sample set. These trends are used to identify limit state thresholds for the development of fragility functions. This conditional probabilistic representation of bridge damage is coupled with the probability of earthquake occurrence to predict the performance of the structure for a given return period. This probabilistic approach alongside a Monte Carlo simulation is applied to assess the vulnerability of linked bridges along key-access corridors throughout the state. With this robust seismic vulnerability methodology, DOTs will have the capability of identifying vulnerable corridors throughout the state allowing for the proactive prioritization of retrofits resulting in the improved seismic performance and resiliency of their transportation network.</div>

This study focuses on non-ductile reinforced concrete (RC) frames built outside current practices. These structures are quite vulnerable to collapse during earthquakes. One option to retrofit buildings with poorly detailed RC columns is to construct full-height masonry infill walls to provide additional means to resist loads caused by gravity and increase lateral stiffness resulting in a reduction in drift demand. On the other hand, infill can cause reductions in drift capacity that offset the benefits of reductions in drift demand. Given these two opposing effects, this investigation addresses the following question: are poorly detailed RC frames with masonry infill walls any safer than similar RC frames without infill walls?

京都大学 / 新制・課程博士 / 博士(工学) / 甲第24900号 / 工博第5180号 / 新制||工||1989(附属図書館) / 京都大学大学院工学研究科建築学専攻 / (主査)教授 西山 峰広, 教授 池田 芳樹, 教授 山本 貴士 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DFAM

PC panel strengthening technique was developed in M.E.T.U. Structural Mechanics Laboratory in order to respond the need of practical and efficient pre-quake seismic strengthening procedures applicable to RC framed structures. The idea behind the method is simply to convert the non-structural infills into load bearing structural elements by gluing PC panels over the existing infill wall surface. The remarkable advantages of the procedure is not only the considerable amount of seismic performance improvement but also the simplicity of application, very low levels of disturbance to the occupants and most importantly, the applicability during service. A number of PC panel application parameters were experimentally investigated by previous researchers. The success of PC panel method on seismic performance improvement of RC frames with different aspect ratios was experimentally investigated in the present study. Total of fifteen, 1:3 scaled, one-bay, two-storey RC frames were tested in three various aspect ratio series. Constant axial load was applied to the columns and reversed cyclic load was applied in the lateral direction. Hollow brick v infilled frame and cast-in-place RC infilled frame were the lower and upper bound reference specimens, respectively. Seismic performance indicators such as response envelope curves, lateral load carrying capacities, cumulative energy dissipations, initial stiffness indicators and ductility values clearly showed the effectiveness of PC panel application over different geometry of RC frames of concern. Moreover, PC panel application either with rectangular or with strip shaped PC panels provided seismic performance improvement to be almost equal to that of cast-in-place RC infill application for all series. Equivalent diagonal strut concept was followed in analytical studies to simulate the infills of RC frame openings. The required strut material properties were estimated from total of eighteen individual wall panel tests. The bond-slip effect, due to utilization low strength of concrete and plain rebars, was also investigated and introduced to the analytical frame models. Non-linear push over analysis was performed for all specimens in OpenSees computer software. The analytical results were compared with that of experimental response envelopes.