Structures built next to each other in congested cities are likely to pound on each other during strong ground shaking caused by earthquakes. The main objective of this study is to examine the problem of mutual structural pounding to identify its effect on structures and then propose solutions to mitigate its effects. Mutual pounding of structural systems with varying mass, stiffness, and seismic joint gaps, subjected to several different input motions are examined. To evaluate the effects of pounding, the numerical results with and without pounding have been considered. The resilience between two impacting masses is represented by linear springs and also nonlinear Hertz model contact stiffness. Pounding causes a large increase in the shear force in the stories higher than the top pounding story, a large increase in the accelerations of the pounding floors and also large overturning effects on both structures. The parametric study of pounding of structures in series showed that in most cases the corner structures are penalized more than the interior structures. The study of the effect of foundation flexibility on the structural pounding response showed that a proper consideration of this parameter must be included in the analysis. To alleviate the pounding effects to avoid damage to structural elements and supported secondary equipment, it was found necessary to join the structures by rigid links and brace all the stories of at least the taller structure. Joining of the floors is required to reduce the excessive floor accelerations caused by impact, whereas the story bracings are required to reduce the excessive story shears or bending moments in the higher stories caused by pounding of the lower floors. It is observed that except for very soft soils, the proposed pounding mitigation scheme will increase the shear force transmitted to the foundation, thus requiring a strengthening of the foundation as well. Since the forces in the rigid links connecting the two structures were observed to be reasonable, the joining of the two structures does not pose any special problem; it can be easily accomplished by using large-size steel rods hooked properly with both structures. In the case of column pounding where the floors of one structure pound on the columns of the other structure, the pounding mitigation strategy is to provide K-bracings on all pounding columns and diagonal bracing in the other stories to reduce high bending moment in the column, and to rigidly join them to avoid high pounding acceleration. / Ph. D.

published_or_final_version / Civil Engineering / Master / Master of Philosophy

The Linked Column Frame (LCF) is a new brace-free lateral structural steel system intended for rapid return to occupancy performance level. LCF is more resilient under a design level earthquake than the conventional approaches. The structural system consists of moment frames for gravity that combines with closely spaced dual columns (LC) interconnected with bolted links for the lateral system. The LC links are sacrificial and intended to be replaced following a design level earthquake. The centerpiece of this work was a unique full-scale experiment using hybrid simulation testing; a combination of physical test of a critical sub-system tied to a numerical model of the building frame. Hybrid simulation testing allows for full scale study at the system level accounting for the uncertainties via experimental component and having the ability to model more conventional behavior through numerical simulation. The experimental subsystem consisted of a two story LCF frame with a single bay while the remainder of the building was numerically modeled. Two actuators per story were connected to the specimen. The LC links have been designed to be short and plastically shear dominated and the LCF met the design intent of 2.5% inter-story drift limits. For evaluating the LCF response, hybrid testing was performed for ground motion at three different intensities; 50%, 10% and 2% probability of exceedence in 50 years for Seattle, Washington ground motions. The system overall had exhibited three distinct performance levels; linearly elastic, rapid return to occupancy where only the replaceable links would yield, and collapse prevention where the gravity beam components also became damaged. Results demonstrated a viable lateral system under cyclic and seismic loading, offering a ductile structural system with the ability to rapidly return to occupancy.

A thesis submitted to the Faculty of Science, University of the Witwatersrand, Johannesburg, in fulfilment of the requirements for the degree of Doctor of Philosophy. Johannesburg, 2015. / In this thesis the crustal structure beneath two areas of Africa is investigated. In Sudan, the new constraints on the crustal structure beneath the northern part of the Khartoum basin have been obtained. In East Africa, the size of the Tanzania Craton, and the differences between the Eastern and Western branches of the East African Rift System (EARS) have been determined. In southern Tanzania, the debate on the secular variation between Proterozoic and Archean crust has been investigated. The approach used in this thesis involves different data sets and methods. In first part of the thesis, the crustal structure of the northern part of the Mesozoic Khartoum basin is investigated by using two modelling methods: H-k stacking of receiver functions, and a joint inversion of receiver functions and Rayleigh wave group velocities. H-k stacking indicated that the crust is 33-37 km thick with an average of 35 km, and the crustal Vp/Vs ratio is 1.74-1.81 with an average of 1.78. Similar results were obtained from the joint inversion for Moho depth, as well as an average shear wave velocity of 3.7 km/s for the crust. These results provide the first seismic estimates of Moho depth for a basin in Sudan. When compared to average crustal thickness for unrifted Proterozoic crust in eastern Africa, our results indicate that only a few kilometers of crustal thinning may have occurred beneath the Khartoum basin. This finding is consistent with estimates of effective elastic plate thickness, which indicate little modification of the Proterozoic lithosphere beneath the basin, and suggests that there may be insufficient topography on the lithosphere-asthenosphere boundary beneath the Sudanese basins to channel plume material westward from Ethiopia. In the second part of the thesis, the uppermost mantle structure beneath East Africa is investigated by using a standard singular value decomposition algorithm model. Results reveal fast Pn velocities beneath the Mozambique Belt to the east of the craton, the Kibaran Belt west of the craton, and beneath the northern half of the Ubendian Belt to the southwest of the craton. These results indicate that the cold, thick lithosphere of the Tanzania Craton extends beneath the Proterozoic mobile belts and the areal extent of the cratonic lithosphere is much larger than is indicated iv by the mapped boundaries of the craton. The results also show that the Pn velocities beneath the volcanic provinces along the Western Branch are not anomalously slow, which indicates little, if any, perturbation of the uppermost mantle beneath them. This is in contrast to the upper mantle structure at depths ≥ 70 km beneath the volcanic regions, which is clearly perturbed. The fast Pn velocities beneath the Western Branch contrast with the slow Pn velocities (7.5-7.8 km/s) beneath the Eastern Branch in Kenya, indicating that the upper mantle beneath the Eastern Branch has been altered more than beneath the Western Branch. In the third part, the crustal structure beneath two Proterozoic mobile belts, the Usagaran and the Ubendian belts, is investigated by using the Non-Dominated Genetic Algorithm method. In the Usagaran belt, results show an average Moho depth of 35 km for station MAFI and 41 and 42 km for stations MOGR and MIKU, respectively. In the Ubendian Belt, results showed an average Moho depth of 43 km beneath the Ufipa sub-terrane compared to 39 km for Wakole sub-terrane. These results indicate localized thickening in the Ufipa sub-terrane, but not beneath the entire Ubendian Belt. These results indicate that is no clear evidence that Paleoproterozoic crust in East Africa is substantially thicker than Archaean crust.

This study is directed to the application of bamboo as alternative material in civil construction. The study also extends to discuss the new applications of bamboo Angustifolia Kunth in construction, such as shear walls and bamboo boards. The investigation involved the following tasks: (a) Evaluation of physical and mechanical properties of bamboo Angustifolia Kunth; (b) Proposing a new type of joint (connection) using culms and natural coupling assembly which can be used in bamboo frame structures. Bamboo dowels are used to create a monolithic joint to support gravitational and lateral forces efficiently; (c) Evaluating the behavior of bamboo Angustifolia Kunth through extensive laboratory work in order to determine the stresses that structural elements such as columns and beams can support under the action of gravitational and lateral external load, and then comparing with the permissible stresses given by the design and construction codes in each region; and (d) Conducting theoretical dynamic analysis of bamboo frame structures using Newmark Beta method and experimental validation to determine maximum values of acceleration, velocity and displacement. The information needed for this analysis are taken from the earthquake El Centro in California on 1940. From the results of this study, it can be concluded that the use of Angustifolia Kunth bamboo for civil structures composed only of bamboo elements offer safety, are economical and offers rapid construction method. This is very suitable for tropical and semitropical places preferably at an average of 2500 meter above the sea level, and advisable if they are located around the fire belt susceptible to seismic forces and earthquakes. It may be an ideal solution for low income populations in need of an immediate housing solution. / Includes bibliography. / Dissertation (Ph.D.)--Florida Atlantic University, 2018. / FAU Electronic Theses and Dissertations Collection

Electrical substations perform a key role in electrical transmission and distribution; the ability for a substation to remain functional during and after a seismic event contributes significantly to the resilience of the clients supplied. Many legacy components currently installed in the main grid substations were designed with minimal consideration of lateral loads and are not qualified per IEEE693. One of the more critical high-voltage substation components that are vulnerable to earthquake damage is the 500kV freestanding current transformer (CT). The CT is particularly vulnerable due to the slenderness and mass distribution of the component. Current transformers are typically constructed from a combination of aluminum and brittle porcelain. Two novel retrofit measures were investigated utilizing base rocking and supplemental damping to reduce the seismic amplification in the CT while also potentially providing post-earthquake self-centering capability. The retrofit measures utilize both shift in system frequency and energy dissipation through supplemental damping to reduce seismic demands on the CT. The purpose of the research was to conceptually develop, detail design, analyze and experimentally validate the retrofit measures. A desired feature of the retrofit measures was for minimal or no residual displacement following the seismic event, which was implemented in the retrofit through a preloaded centering mechanism. Based on the analyses and experiments, the proposed retrofit measures exhibited significantly decreased demands on the CT and true self-centering.

The primary component in eccentrically braced frames (EBF) is the link as its plastic strength controls the design of the frame as well as the entire building within which it is installed. EBFs are the first part of building design and every other component is sized based on the forces developed in the link. Oversized link elements lead to the use of unnecessary materials and can increase construction costs. Additionally, the advantages of using a continuous member of the same depth for both the link and the controller beam (in terms of the cost and the time) motivates researchers to find a way to control the link strength in conventional EBFs. Previous studies on the link-to-column connections in EBF have shown that the links are likely to fail before reaching the required rotation due to fractures at low drift level. Moreover, improving the strength of the links in EBF depends primarily on their ability to achieve target inelastic deformation and to provide high ductility during earthquakes. Therefore, in this study, the concept of tuned link strength properties in EBF, T-EBF, is experimentally introduced as a solution to improve the performance of the link in conventional EBF by cutting out an opening in the link web. Furthermore, a new brace-to-link connection is proposed to bolt the brace member with the link in contrast to the conventional method of welding them. This new idea in continuous beam design was investigated to verify the stability of the tuned eccentrically braced frame, either welded or bolted, with a bracing member. A total of four full-scale cyclic tests were conducted to study the ability of T-EBF to achieve inelastic deformation. The specimens have two different cross sections: W18x76 and W16x67, two different sections where the brace was welded to the link, and two other specimens at different sections where the brace was bolted to the link were examined. The experimental results indicate that the link in T-EBF can achieve high rotation, exceeding 0.15 rad, and an overstrength factor equal to 1.5. Failure involved included web buckling at very high rotation. The T-EBF displayed a very good, non-replaceable ductile link. The experiments were followed by an isotropic kinematic-combined hardening model in the finite element analyses (FEA). The FEA analysis is developed to predict the effect of web opening configuration on the local section stresses and strains and global characteristics of the frame. FEA exhibits good agreement with the experimental results and can capture the inelastic buckling behavior of the sections. The link configuration parameters of the T-EBF were studied extensively on a W18x76 shear link subjected to the 2016 AISC seismic design provisions loading protocol (ANSI/AISC 341-16, 2016). The parametric study also included the performance of a range of wide flange sections. The analysis shows that the reduced web section has effect on the plastic strain in which low plastic strain observed near ends and connections and high at the center of the web. Results also demonstrate that if the shear link is appropriately sized with web opening and intermediate web stiffeners provided, an excellent shear link with high ductility under cyclic loads can be obtained. Changing the configuration of the opening cutout also had a significant effect on reducing the transition zone cracks.

During the past several decades, earthquakes have caused extensive damage to buildings, including wood-frame, single-family dwellings, in the United States. In order to mitigate future losses, existing buildings in earthquake prone areas should be evaluated for their seismic safety. This is also an important issue for buildings in Oregon due to the Cascadia subduction zone along its west coast. One seismically vulnerable element observed in wood-frame, single-family dwellings is the shear walls. In general, assessment of shear wall seismic performance can be accomplished by a building-specific engineering calculation. Extra effort is required if the effects of plan irregularity are a concern. This project aims to facilitate seismic evaluation of wood-frame dwellings by proposing a new engineering-based rapid visual screening method to examine the expected performance level of the structure's exterior shear walls to resist lateral forces from ground motions, including torsional forces induced from plan irregularity. In order to achieve the objective, SAPWood software was used to perform a series of nonlinear time-history analyses for 480 representative models, covering different combinations of shape parameters and shear wall opening-related parameters. The evolutionary parameter hysteresis model was used to represent the load-displacement relationship of structural panel-sheathed shear walls and a ten parameter CUREE hysteresis model for gypsum wallboard sheathed walls. The calculated maximum lateral drifts were used as basic information for the development of the new method. Through the development process, the significance of both plan configuration and shear wall openings were emphasized as they affect the overall seismic performance of a building through building mass, lateral stiffnesses, and eccentricities. Within the study range, single-family dwellings with two stories, a larger percentage of openings, and having a garage door were shown to be more vulnerable to seismic events. Plan configuration and shear wall openings were important features especially in houses located in high 1 (0.5g ≤ S[subscript a] < 1.0g) and high 2 (1.0g ≤ S[subscript a] < 1.5g) seismicity regions, as they could potentially lead to severe damage. For low and moderate seismicity, the performance ranges from satisfying the collapse prevention limit to the immediate occupancy limit. The developed piRVS (plan irregularity Rapid Visual Screening) takes into consideration the shape of the floor plan, number of stories, base rectangular area, percent cutoff, and openings from doors/windows and garage doors, and supports evaluation at the immediate occupancy (IO), life safety (LS), and collapse prevention (CP) performance levels. The piRVS provides relatively more conservative assessment results than FEMA 154 and ASCE 31 Tier 1. Its prediction for the two applicable Northridge earthquake damage samples is reasonable. This method will help architects, engineers, building officials, and trained inspectors in examining the expected seismic performance of shear walls, considering the effects of plan irregularity in wood-frame, single-family dwellings / Graduation date: 2012

Performance-based design has gained interest in recent years among structural designers and researchers. Performance-based design includes selection of appropriate building sites, structural systems and configurations, as well as analytical procedures used in the design process, to confirm that the structure has adequate strength, stiffness and energy dissipation capacity to respond to the design loads without exceeding permissible damage states. Although performance-based seismic design has advanced for some materials and structural types, such as steel and reinforced concrete buildings and bridges, its application to light-frame structures remains largely unexplored. The objective of this research was to explore the potential for the application of performance-based engineering concepts to the design and assessment of woodframe structures subject to earthquakes. Nonlinear dynamic time-history analysis was used to predict the performance of shearwalls considering a suite of scaled characteristic ordinary ground motions to represent the seismic hazard. Sensitivity studies were performed to investigate the relative effects of damping, sheathing properties, fastener type and spacing, panel layout, and other properties on the performance of wood shearwalls. In addition, the effects of uncertainty in ground motions and variability in sheathing-to-framing connection hysteretic parameters were investigated. Issues such as the contribution of nonstructural finish materials, different seismic hazard regions, and construction quality also were investigated and modification factors to adjust peak displacement distributions were developed. The peak displacement distributions were then used to construct performance curves and design charts as a function of seismic weights for two baseline walls. Finally, fragility curves were developed for the baseline walls considering different nailing schedules, corresponding allowable seismic weights, and various overstrength (R) factors. / Graduation date: 2004

Thesis (Ph. D.)--University of Washington, 2006. / Vita. Includes bibliographical references (leaves 266-272).