<p>Better understanding of the structural behaviour of concrete and masonry structures is facilitated through experimental testing. Although some experimental testing of reinforced masonry (RM) rectangular walls is reported in literature, little experimental data is available on RM walls with flanges or with boundary element. Unlike those pertaining to rectangular walls, seismic design provisions of flanged and end-confined masonry walls are not available in North American masonry design codes.</p> <p>In the current study, the response of seven half scale fully grouted RM shear walls, all with the same length but different end configurations and aspect ratios is investigated. The goal of the study was to evaluate and document the enhanced ductile behaviour of rectangular RM shear walls when flanges and boundary elements are structurally connected at the wall ends. Another goal was to extract specific seismic performance parameters of reinforced concrete-block rectangular, flanged and end-confined shear walls based on quasi-static experimental results. Finally, nonlinear dynamic analysis was conducted on the test walls to quantify seismic force modification factors used in seismic design.</p> <p>High levels of ductility accompanied by relatively small strength degradation were observed in all walls in general with a significant increase in ductility and displacement capabilities for the flanged and end-confined walls compared to the rectangular ones. The drift levels attained at 20% strength degradation by the rectangular, the flanged, and the end-confined walls were 1.0%, 1.5%, and 2.2%, respectively. The ductility values of the flanged and end-confined walls were, respectively, 1.5 and 2.0 times that of their rectangular wall counterparts. In addition to the enhanced ductility, a saving of more than 40% in the amount of vertical reinforcement was achieved using the proposed alternative strategies while maintain the lateral resistance. The relationship between the energy dissipation and the ratio of the post-yield to the yield displacement was found to be almost linear for the test walls. Wall stiffnesses degraded rapidly to about 60% of their gross stiffness at very low drift levels (0.1 % drift). Measured compressive strain at the wall toes were almost double those specified in both North American codes. Extent of plasticity over the wall height was about 75% of the wall length. Equivalent plastic hinge lengths, needed in wall displacement predictions, using theoretical curvatures and experimental displacement ductilities varied between 17% and 40% of the wall length at ultimate load for all the tested walls. The test results indicated that higher seismic force modification factors should be assigned to the flanged and endconfined RM shear walls compared to values currently assigned to rectangular walls.</p> <p>The data presented in this study is expected to facilitate better understanding of RM wall behaviour under in-plane load to researchers, practicing engineers, and code developers. This study aimed at presenting the flanged and end-confined categories as cost-effective alternatives to enhance the seismic performance of midrise RM construction in North America.</p> / Thesis / Doctor of Philosophy (PhD)

Reinforced concrete moment-resisting frames are structural systems that work to resist earthquake ground motions through ductile behavior. Their performance is essential to prevent building collapse and loss of life during a seismic event. Seismic building code provisions outline requirements for three categories of reinforced concrete moment-resisting frames: ordinary moment frames, intermediate moment frames, and special moment frames. Extensive research has been conducted on the performance of special moment-resisting frames for areas of high seismic activity such as California. More research is needed on the performance of intermediate moment frames for areas of moderate seismicity because the current code provisions are based on past observation and experience. Adapting dynamic analysis software and applications developed by the Pacific Earthquake Engineering Research (PEER) Group, a representative concrete intermediate moment frame was designed per code provisions and analyzed for specified ground motions in order to calculate the probability of collapse. A parametric study is used to explore the impact of changes in design characteristics and building code requirements on the seismic response and probability of collapse, namely the effect of additional height and the addition of a strong column-weak beam ratio requirement. The results show that the IMF seismic design provisions in ACI 318-08 provide acceptable seismic performance based on current assessment methodology as gravity design appeared to govern the system. Additional height did not negatively impact seismic performance, while the addition of a strong-column weak-beam ratio did not significantly improve results. It is the goal of this project to add insight into the design provisions for intermediate moment frames and to contribute to the technical base for future criteria.

The 7th German-Japanese Bridge Symposium, July 30-August 1, 2007 Osaka, JAPAN (GJBS07), full paper + extended abstract (p.84-85)

The main objective of this study is to develop a methodology to assess seismic vulnerability of concrete structures and to estimate direct losses related to structural damage due to future seismic events. This dissertation contains several important components including development of more detailed demand models to enhance accuracy of fragility relationships and development of a damage assessment framework to account for uncertainties. This study focuses on concrete structures in the Mid-America region where a substantial seismic risk exists with potential high intensity earthquakes in this geographic region. The most common types of concrete structures in this area are identified based on the building inventory data and reinforced concrete (RC) frame buildings and tilt-up concrete buildings are selected as case study buildings for further analysis. Using synthetic ground motion records, the structural behavior of the representative case study buildings is analyzed through nonlinear time history analyses. The seismic performance of the case study buildings is evaluated to describe the structural behavior under ground motions. Using more detailed demand models and the corresponding capacity limits, analytical fragility curves are developed based on appropriate failure mechanisms for different structural parameters including different RC frame building heights and different aspect ratios for tilt-up concrete structures. A probabilistic methodology is used to estimate the seismic vulnerability of the case study buildings reflecting the uncertainties in the structural demand and capacity, analytical modeling, and the information used for structural loss estimation. To estimate structural losses, a set of damage states and the corresponding probabilistic framework to map the fragility and the damage state are proposed. Finally, scenario-based assessments are conducted to demonstrate the proposed methodology. Results show that the proposed methodology is successful to evaluate seismic vulnerability of concrete structures and effective in quantifying the uncertainties in the loss estimation process.

Due to the lack of capacity design principles as well as of appropriate structural details, most of the reinforced concrete building designed primarily for gravity loads as typical of pre- 1970s code provisions, are expected and has been demonstrate to suffer sever damage or total collapse under the earthquake excitation. Due to the use of plain round bar and inadequate reinforcing details, critical shear failure in the joint connection region could occur, leading to sever damage when not total collapse of the building. In this research project, a comprehensive experimental programme was carried to investigate the seismic performance of existing beam column joints prior and after retrofit intervention with a recently proposed low-invasive retrofit technique based on a metallic haunch system. The joint performance was evaluated in terms of the principal tensile stresses that caused the joint shear cracks in the joint panel zone. Quasi-static cyclic tests under uni-directional or bidirection loading regime were carried out to record the response of a series of under-designed beam column joints (with either a wide-beam or a deep-beam solution, deformed or plain round bars with end hooks). The experimental results were used to investigate the effect of structural detailing and loading regime on the seismic performance. To retrofit the potential deficiencies in the existing beam-column joints, the feasibility and efficiency of a low invasive retrofit solution based on a diagonal metallic haunch was investigated. The proposed haunch retrofit solution aims to provides an economic, ease of implementation alternative to protect the joint from the brittle shear failure by relocating the beam plastic hinge away form the joint panel zone. To achieve the desired capacity design (hierarchy of strength) and sequence of event, a simplified analytical formulation has been adopted to account for the joint shear strength in terms of principle tensile/compression stresses prior and after the retrofit intervention. A useful visualization tool based on a M-N (moment-axial load) performance domain can be adopted to evaluate the actual performance point and events, by comparing demand vs. capacity. Designed charts are proposed based on displacement compatibility conditions to evaluate the efficiency of the haunch solution. In addition, a complete step-by step design procedure to implement the retrofit strategy and intervention to achieve the desired hierarchy of strength, by using the proposed diagonal metallic haunch solution, is derived and presented. The effectiveness of the proposed haunch solution and reliability of the derived analytical design/assessment procedure, were validated through experimental tests of 2-D and 3-D subassemblies, shown in the first experimental part to have the most vulnerable behaviour in the joint panel zone. Conceptual issues related to the design of the retrofit intervention, when moving from a 2-D to a 3-D behaviour are discussed. The experimental results showed an excellent performance of the proposed intervention, able to protect the panel zone region (by limiting the principle tensile stress demand), while enforcing the formation of a plastic hinge in the beam, far away from the joint interface. As a result, a much more stable inelastic response could be developed, confirming the high potential of such a low-invasive, low-cost retrofit intervention on under-designed frame systems. In conclusion, a simple numerical model, based on a lumped plasticity approach, was developed and validated on the experimental results to capture the full response of the subassembly prior and after the retrofit intervention.

In this investigation, the elasto-plastic behavior and the seismic performance of concrete reinforced frame structures reinforced are evaluated by applying the Pushover method. This evaluation is done on several cases: with high ductility steel (Grade 40), conventional steel (Grade 60) and high strength steel (Grade 75). For the previous, the capacity curve graph obtained from the displacement coefficient method was used to measure the capacity of the structure. In addition, the performance of the structure for different levels of seismic design are evaluated with the resulting values of ductility and rigidity of each case. The results showed that reinforcing a structure with a Grade 40 reinforcing steel increases the energy dissipation capacity, and if reinforced with a Grade 75 reinforcing steel increases the strength capacity in the structure. Finally, the comparative result of the various cases are presented to demonstrate the influence of reinforcing steel on the plastic behavior of concrete reinforced frame structures.

<p>Composite plate shear walls – concrete-filled (C-PSW/CF) are a new innovative lateral force resisting system intended for high-rise buildings. The walls consist of parallel steel faceplates connected with tie bars and filled with concrete. This dissertation introduces the C-PSW/CF </p> <p>system and coupled C-PSW/CFs consisting of C-PSW/CF walls and composite coupling beams. Three studies are presented herein covering seismic design parameters for C-PSW/CFs, non-linear modeling techniques for composite coupling beams, and the design philosophy for coupled C-PSW/CFs.</p> <p> </p> <p>The first study summarizes the results of a recent FEMA P695 study completed to verify seismic design parameters for uncoupled C-PSW/CFs with rectangular flange plate boundary elements. Seven archetype structures were: (i) designed, (ii) modeled using a benchmarked fiber-based finite element analysis approach, (iii) subjected to nonlinear pushover analysis, (iv) subjected to incremental nonlinear dynamic analysis to failure for 22-sets of scaled ground motions, and (v) the results were statistically analyzed to assess performance. These structures ranged from three (3) to twenty-two (22) stories and included both planar and C-shaped wall configurations. As part of this design process, recommendations for stiffness approximations for linear analysis of C-PSW/CFs</p> <p>were developed. Additionally, these nonlinear incremental dynamic analysis results were post-processed to determine the rotation and strain demands at the base of these structures at the design basis, maximum considered, and failure level earthquakes. These results showed that the rotation and strain demand at failure level earthquakes were comparable regardless of the ground motion. Ultimately, this FEMA P695 approach verified the R factor of 6.5, C_d factor of 5.5, and Ω₀ of 2.5 for C-PSW/CFs with boundary elements. </p> <p><br></p> <p>The second study proposes modeling approaches for composite coupling beams used in combination with C-PSW/CFs. Capturing the behavior of these components is critical to understanding the system behavior of coupled C-PSW/CFs, as the coupling beam components undergo yielding, plastification, and fracture prior to collapse of coupled C-PSW/CF walls. Although steel-concrete composite walls have been a known structural system for decades, only recently have coupled C-PSW/CF systems been investigated and implemented as a seismic force resisting system. As the interest in coupled C-PSW/CF systems increases, the necessity of reliable nonlinear modeling techniques for pushover, cyclic, and seismic analysis has become apparent. This paper presents fiber-based options for modeling composite coupling beam components of coupled C-PSW/CF walls for use in nonlinear and seismic response analyses. Recommendations include effective steel and concrete stress-strain curves, modeling parameters for fiber-based </p> <p>materials, and concentrated plasticity options for additional computational efficiency. These recommendations are then implemented for a full-scale coupling beam section. </p> <p><br></p> <p>In the final study, a capacity design principle is used to establish a basis for the seismic design of coupled composite plate shear walls – concrete filled (CC-PSW/CF) systems. This design philosophy implements a strong wall-weak coupling beam approach, where flexural yielding in coupling beams occurs before flexural yielding at the base of walls. The coupling beams are sized </p> <p>to resist the calculated seismic lateral force level. The walls are sized to resist an amplified seismic lateral force corresponding to the overall plastic mechanism for the structure, while accounting for the capacity-limited forces from the coupling beams and the coupling action between the walls. Based on this philosophy, recommendations and requirements for appropriate sizing of coupling beams and C-PSW/CFs are presented. These recommendations are used to design four example (8-22 story) structures and evaluate their seismic behavior. The structures were modeled using 2D finite element models and fiber-based models subjected to monotonic and time history analysis. </p> <p>The nonlinear inelastic behavior and seismic responses of the example structures were in accordance with the capacity limited design philosophy (strong wall-weak beam), thus confirming the philosophy’s  efficacy. </p>

Steel frame construction with unreinforced masonry infill walls is a common system found in high-rise structures built in the late nineteenth and early twentieth centuries. Recorded performance of this dual system during seismic events shows that the structures are able to resist a high level of lateral loads without collapse, primarily because a majority of damage is confined to the infill walls instead of the gravity carrying frame. To better understand expected performance of this structural system in different seismic risk regions, a prototypical building was analyzed using modal and nonlinear static procedures based on currently accepted evaluation guidelines. Nonlinear results from the computer model were compared with calculated target displacements for seventeen cities likely to have steel frame construction with unreinforced masonry infill in order to determine expected damage levels at varying levels of seismic risk. It was concluded that the structural system studied could experience damage in all seismic risk regions, including post-yield damage of the structure, although in low risk regions that damage is confined entirely to the infill walls. Practicing structural engineers should be aware that in all seismic risk zones existing steel frame buildings with unreinforced masonry infill, while able to resist a high magnitude of displacement without complete structural failure, will require additional lateral support under currently accepted rehabilitation guidelines.

Reinforcement of soil enables a soil slope or wall to be retained at angles steeper than the soil material’s angle of repose. Geosynthetic Reinforced Soil (GRS) systems enable shortened construction time, lower cost, increased seismic performance and potentially improve aesthetic benefits over their conventional retaining wall counterparts such as gravity and cantilever type retaining walls. Experience in previous earthquakes such as Northridge (1994), Kobe (1995), and Ji-Ji (1999) indicate good performance of reinforced soil retaining walls under high seismic loads. However, this good performance is not necessarily due to advanced understanding of their behaviour, rather this highlights the inherent stability of reinforced soil against high seismic loads and conservatism in static design practices. This is an experimental study on a series of seven reduced-scale GRS model walls with FHR facing under seismic excitation conducted using a shake-table. The models were 900 mm high, reinforced by five layers of stiff Microgrid reinforcement, and were founded on a rigid foundation. The soil deposit backfill was constructed of dry dense Albany sand, compacted by vibration (average Dr = 90%). The influence of the L/H ratio and wall inclination on seismic performance was investigated by varying these important design parameters throughout the testing programme. The L/H ratio ranged from 0.6 – 0.9, and the walls were primarily vertical except for one test inclined at 70o to the horizontal. During testing, facing displacements and accelerations within the backfill were recorded at varying levels of shaking intensity. Mechanisms of deformation, in particular, were of interest in this study. Global and local deformations within the backfill were investigated using two methods. The first utilised coloured horizontal and vertical sand markers placed within the backfill. The second utilised high-speed camera imaging for subsequent analysis using Geotechnical Particle Image Velocimetry (GeoPIV) software. GeoPIV enabled shear strains to be identified within the soil at far smaller strain levels than that rendered visible by eye using the coloured sand markers. The complementary methods allowed the complete spatial and temporal development of deformation within the backfill to be visualised. Failure was predominantly by overturning, with some small sliding component. All models displayed a characteristic bi-linear displacement-acceleration curve, with the existence of a critical acceleration, below which deformations were minor, and above which ultimate failure occurs. During failure, the rate of sliding increased significantly. An increase in the L/H ratio from 0.6 to 0.9 caused the displacement-acceleration curve to be shallower, and hence the wall to deform less at low levels of acceleration. Accelerations at failure also increased, from 0.5g to 0.7g, respectively. A similar trend of increased seismic performance was observed for the wall inclined at 70o to the horizontal, when compared to the other vertical walls. Overturning was accompanied by the progressive development of multiple inclined shear surfaces from the wall crest to the back of the reinforced soil block. Failure of the models occurred when an inclined failure surface developed from the lowest layer of reinforcement to the wall crest. Deformations largely confirmed the two-wedge failure mechanism proposed by Horii et al. (2004). For all tests, the reinforced soil block was observed to demonstrate non-rigid behaviour, with simple shearing along horizontal planes as well as strain localisations at the reinforcement or within the back of the reinforced soil block. This observation is contrary to design, which assumes the reinforced soil block to behave rigidly.

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