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Electrical high voltage bushings have exhibited vulnerability during past earthquakes. The good performance of bushings mounted on rigid base observed during shake table testing does not correlate well with their performance in the field. It is suspected that the seismic performance of high voltage bushings is improved when mounted on a rigid base as opposed to when mounted on more flexible cover plates of transformers. In this study, the seismic response of bushings was investigated numerically and experimentally for various mounting conditions. The addition of flexural stiffeners on the transformer cover plates was explored as a mean to stiffen the base of the bushings and mitigate their seismic vulnerability. Linear dynamic analyses conducted on four transformer-bushing system models of various voltages, sizes and geometries showed that the simple approach of stiffening the cover plates of transformers is beneficial to the seismic response of high voltage bushings. Shake table testing was conducted on a 230kV porcelain bushing mounted on a support structure incorporating a cover plate and two stiffener configurations. Test results confirmed that stiffening the cover plates is beneficial to the seismic response of high voltage bushings.

Evidence indicates that the dynamic behavior of rigid wall – flexible diaphragm (RWFD) structures is dominated by the diaphragm’s response instead of the walls’ response, and this is a significant departure from the underlying assumptions of the widely used equivalent lateral force method in current building codes. RWFD buildings are common in North America and other parts of the world, and incorporate rigid in-plane concrete or masonry walls and flexible in-plane wood, steel or “hybrid” roof diaphragms. With the use of a numerical computer modeling sequence developed specifically for this type of building, this study investigates a variety of building archetypes for response to earthquakes with the intent to develop a simpler, more rational approach to the engineering design of RWFD buildings. A representative list of building archetypes is developed from a variety of common parameters found in North America involving the building size, shape, diaphragm material, and diaphragm connections. Archetypes are developed under ASCE 7-10 and this study’s proposed design methodologies and then evaluated for building performance under FEMA P-695 methodology. In addition to evaluating the impact of the different parameters, two separate seismic force levels were utilized during the assessment to represent both moderate and high seismic exposures.

The present study focuses on the development of a two-dimensional (2D) simplified numerical framework of rigid wall – flexible diaphragm (RWFD) structures that can be used to validate design approaches. This type of low-rise industrial buildings, which is widely used in North America, incorporates rigid in-plane concrete or masonry walls and flexible in-plane wood, steel or “hybrid” roof diaphragms. The approach is detailed enough to capture the nonlinear response of RWFD buildings, as well as simplified enough to efficiently conduct a large number of nonlinear time-history analyses. The 2D numerical modeling framework is based on a three step sub-structuring approach including: (1) hysteretic response database for diaphragm connectors, (2) 2D inelastic diaphragm model incorporating hysteretic connector response and (3) 2D building model incorporating hysteretic diaphragm model response. The diaphragm connector database (step 1) is developed for both wood deck connectors (common nails, cut and rolled thread screws) and steel deck connectors (pins, screws, button punch and welds) using cyclic test data available in the literature. Two well-known hysteretic models (Wayne –Stewart and CUREE-SAWS) are used for estimating/fitting hysteretic parameters of each connector type. The analytical model of the inelastic roof diaphragm (step 2) is generated to account for the elastic shear deformation of deck panels, elastic flexural deformations of chord members as well as inelastic deformations of deck-to-frame connectors (from the connector database – step 1). This model is developed to have monotonic and cyclic analysis capabilities. The last step of the proposed analytical framework is a two dimensional model of a RWFD building developed in RUAUMOKO2D to account for the inelastic response of roof diaphragms (based on the analytical roof diaphragm model – step 2) and the out-of-plane walls as well as P-Δ effects. This simplified building model is also capable of representing a typical three dimensional RWFD structure without any torsional eccentricity. Both the proposed analytical model of the roof diaphragm and the proposed simplified building model are validated with experimental and analytical studies available in the literature. Furthermore, a parametric study is conducted to examine the influence of: (i) different base fixity of the out-of-plane walls, (ii) P-Δ effects, (iii) inherent viscous damping and (iv) direction of shaking on the collapse assessment of RWFD structures. The seismic collapse capacity of a current code compliant RWFD building incorporating concrete tilt-up walls with a “hybrid” (wood sheathing panels and steel joists) deck diaphragm is evaluated using the proposed analytical model with the FEMA P-695 methodology.

In past earthquake events, the seismic vulnerability of underground pipelines caused significant life and economic losses. Seismic retrofit of critical underground pipelines has become an urgent need of our society to improve the performance and serviceability of these critical lifeline systems as well as enhance public safety. The cured in place pipe (CIPP) liner technology consists of installing flexible polymeric liners with thermosetting resin inside existing pipelines. Compared with traditional expensive and disruptive excavation and replacement of aging and structurally unsound pipelines, CIPP provides an economic and environmentally friendly alternative for pipeline rehabilitation. However, the lack of verification and quantification of the seismic performance of CIPP liner under transient ground deformation remains a critical deficiency in current practice. This paper is one of two companion papers that reports on the results of large-scale testing at the Cornell University and University at Buffalo equipment sites of the George E. Brown, Jr. Network for Earthquake Engineering Simulation (NEES) to characterize the seismic performance of CIPP linings. Full-scale quasi-static and dynamic tests were performed on four water-pressurized ductile iron (DI) pipelines (6.0 in. nominal diameter and 30 ft. nominal length) reinforced with the Starline® 2000 liner, one type of CIPP liner manufactured by Progressive Pipeline Management, LLC, West Deptford, NJ. This paper briefly describes the behavior of the liner-strengthened DI pipelines under static loading and focuses on their response under transient ground deformations (TGD). Moreover, based on the joint response under quasi-static loading, this paper proposes a new constitutive numerical model for the longitudinal behavior of liner-reinforced joints and cracked sections of pipe that considers strength degradation and energy dissipation. Both the test results and numerical analyses indicate that CIPP liner provides substantial longitudinal strength to the joints of DI pipelines and improve significantly their seismic behavior under high intensity TGD.

In this study, modeling strategies and modeling challenges for hybrid sliding-rocking (HSR) segmental bridges are investigated. The HSR bridges lie into the framework of Accelerated Bridge Construction (ABC) for seismic regions. The substructure of HSR bridges consists of segmental columns (termed HSR-SD columns) that incorporate internal unbonded post-tensioning and joints designed to exhibit controlled sliding (termed slip-dominant joints). The superstructure of HSR bridges consists of girders (termed HSR-RD girders) that incorporate internal unbonded post-tensioning (PT) and joints designed to exhibit rocking (termed rocking-dominant joints). Slip-dominant joints provide energy dissipation with small damage, while rocking-dominant joints offer high self-centering. Major modeling challenges for the HSR bridges include: (i) accurate representation of the joint response modes, namely sliding and rocking, (ii) reliable modeling of the contact/impact interactions between the PT tendons and the concrete segments in the vicinity of the joints, and (iii) sufficient modeling of the concrete crushing in the highly confined regions in the vicinity of rocking-dominant joints. Two modeling strategies will be presented. In the first strategy, an HSR-SD pier column is modeled using the ABAQUS finite element (FE) software. This column was part of the substructure of a bridge specimen and was subjected to quasi-static lateral cyclic loading in the Structural Engineering and Earthquake Simulation Laboratory (SEESL) at the University at Buffalo. The concrete segments were modeled using 3D solid elements, the mild reinforcement was modeled by beam elements embedded into the segments, while the PT tendons were modeled using truss elements. The contact/impact and friction amongst the concrete segments and between concrete segments and PT tendons was enforced using the penalty method. Explicit dynamics and mass scaling were employed to run analyses. The numerical solution was in good agreement with the experimental data. However, it required vast computational resources and time. Analyses halted due to numerical instabilities resulting from strain localization at the concrete solid elements. The second strategy involved modeling of HSR bridges using common structural analysis software. A model of the large-scale bridge specimen subjected to shake table testing in SEESL was developed using SAP2000. The concrete segments were modeled with beam elements. At the joints, contact elements exhibiting axial compression-only hysteretic response and lateral frictional/sliding response were employed. The bearing contact of the internal tendons on the concrete segments was modeled by stiffening shear springs. The model provided better results when the response was dominated by joint rocking. However, numerical instabilities and analysis failures were observed when the joint sliding was intense.

The consideration of nonstructural damage in seismic engineering has increased over recent decades as a direct result of two observations: the first being that modern seismic design provisions have made great strides in preserving life safety as a primary objective, and the second being that the resulting loss and consequences from nonstructural damage can be tremendous, even in well-designed structures. This problem has been addressed in design guidelines by applying some form of serviceability considerations to limit displacements and has been one of the main concerns within numerous advancements of performance-based earthquake engineering. However, the treatment of the equivalent structural damping provided by nonstructural elements has, for the most part, been kept at widely accepted rule of thumb approximations (e.g. 5% damping) even though there is little evidence to suggest that this is appropriate in all cases, particularly at intensity levels relevant to serviceability limit states. The consideration of the specific nonstructural components of a building is merited as these are the elements that the limit state is meant to protect; this point is furthered when considering a comprehensive performance assessment where the entire building’s contents are inventoried and accounted for in terms of damage. This study looks at the development of a procedure to quantify the equivalent structural damping offered by drift sensitive nonstructural components in order to quantify how a building’s nonstructural inventory may affect its seismic response. The scope of the work focuses on cold-formed steel framed gypsum partition walls and external façade systems which are analyzed using mechanical models based on recent test results. The study considers both the detailing and inventory of partitions as well the type of external façade system. To illustrate the procedure, an eight-story moment frame designed according to Eurocode 8 and incorporating various partition wall and façade details is considered. The effects of the supplemental structural damping provided by the nonstructural components on the seismic performance of the building under serviceability limit ground motions are illustrated and are shown to be quite variable, in contrast to the assumptions typically made in practice.

Pressurized fire suppression sprinkler piping is a critical nonstructural system that must remain operational after an earthquake, particularly in critical facilities. However, recent earthquake events have demonstrated the vulnerability and sometimes poor performance of fire extinguishing sprinkler piping subsystems. In order to better understand the seismic behavior of fire suppression systems and their interaction with other structural members and nonstructural subsystems, two series of experimental studies were conducted in the Structural Engineering and Earthquake Simulation Laboratory (SEESL) at the State University of New York in Buffalo. In the first series, a total of 48 tee joint components for sprinkler piping systems with nominal diameters from ¾” to 6’’ and made of various materials and joint types (black iron with threaded joints, chlorinated polyvinyl chloride (CPVC) with cement joints, and steel with grooved-fit connections) were tested under reverse cyclic loading to determine their rotational capacities at which leakage and/or fracture occurred. The failure mechanisms observed in the piping joints were identified and the ATC-58 framework was applied to develop a seismic fragility database for pressurized fire suppression sprinkler joints. Subsequently, two-story, full-scale (11 ft. × 29 ft.) fire extinguishing sprinkler piping subsystems were tested on the University at Buffalo Nonstructural Component Simulator (UB-NCS). A total of three specimens with different materials and joint arrangements were tested with various level of bracing systems under dynamic loading. All three fully braced specimens performed well under a Maximum Considered Earthquake (MCE) level of loading, validating current code-based requirements for bracing system design. Unbraced systems, however, which are typically installed in low to moderate seismic regions or could exist in older construction, did not perform as well as the fully braced systems. Damage to sprinkler heads, failures of vertical hangers, as well as a branch line fracture, were observed during the tests.

The seismic vulnerability and inadequate behaviour of existing school buildings observed during past earthquakes in Italy have raised awareness of the need to upgrade their performance. This paper examines different retrofit strategies for three case study school buildings, representing the main typologies found within the Italian school building stock. The three building typologies investigated in this study are representative of reinforced concrete (RC), precast concrete (PC) and unreinforced masonry (URM) school buildings. A seismic performance assessment was carried out using detailed numerical models that consider the main structural deficiencies documented for older buildings in Italy, generally designed and built before the 1970s. The retrofit interventions were specifically aimed at mitigating these main structural deficiencies in order to meet current building code limit state requirements. These requirements are set to limit the damage to non-structural elements and prevent non-ductile failure mechanisms in the structural system, following a typical building code and practitioner-oriented process. The retrofit alternatives were then evaluated through increasing ground shaking intensities to quantify risk-based decision variables, such as the expected annual loss and mean annual frequency of collapse. The results highlight the level of adequacy of each retrofit option in reducing both the economic losses and collapse vulnerability. To predict the economic feasibility of these interventions, a cost-benefit analysis was also conducted using estimated implementation costs of each retrofit alternative. Lastly, the results were also compared with the outcome of the seismic risk classification guidelines, recently proposed in Italy.