Michael Pollino

Braced Ductile Shear Panel: New Seismic-Resistant Framing System

AbstractThe conceptual design of an innovative seismic-resistant steel framing system capable of providing stiffness and ductility to new or existing structures is presented. The bracing system consists of concentric X-braces connected in series with rectangular sacrificial shear panels. The braces are designed to remain elastic during seismic events while the shear panels are sized and configured to dissipate ample energy through plastic deformation-induced stable hysteretic behavior. Detailed three-dimensional nonlinear finite-element analyses using ABAQUS are performed to characterize and quantify the effects of the design parameters on the local response of the bracing system and to adjust the design so that potential buckling of the elements is mitigated. The finite element predicted force-displacement curves of bracing systems that achieve the desired local behavior when subjected to a specified interstory drift are in turn translated into a SAP2000 nonlinear link element. Embedment of the link elem...

Development of a Seismic Isolation System for Commercial Storage Racks

This paper provides an overview of an analysis performed on a new base isolation system developed for seismic isolation of steel pallet storage racks. Pallet storage racks are often found in warehousing for material storage and are designed to store materials on pallets in horizontal rows with multiple levels which are accessed by forklift trucks. The new isolation system provides seismic isolation in the cross-aisle direction by incorporating heavily damped elastomeric bearings (referred to here as seismic mounts) and low-friction bearing plates. The objective of the base isolation system is to reduce horizontal accelerations of the rack to eliminate product shedding and structural damage during a major earthquake without interfering with normal, day-to-day material handling operations. The paper presents a summary of numerical results (transient structural, finite element analysis simulation) comparing storage rack response against actual tests performed on a triaxial shake table in the Structural Engineering and Earthquake Simulation Laboratory (SEESL) at the University at Buffalo (see Filiatrault[1] et al. 2008 for comprehensive test details). The simulation model was then used to determine a set of optimal seismic isolation parameters that satisfy the practical range of rack shelf loads and configurations that can be expected in typical warehouse and store installations.Copyright

Rehabilitation of steel concentrically braced frames with rocking cores for improved performance under near-fault ground motions

This article focuses on evaluating the adequacy of a seismic rehabilitation technology which adds rocking cores to deficient steel concentrically braced frames in near-fault regions. Two demonstration buildings were rehabilitated with the technology. Seismic performance of the rehabilitated buildings was evaluated through numerical simulations. Analysis results suggest that the code-compliant concentrically braced frames may be vulnerable to collapse under the fault-normal components of the near-fault ground motions, approximately having a probability of exceedance of 10% in 50 years. It is found that the Rocking Core technology is effective in reducing the inter-story drift responses of the demonstration buildings under near-fault earthquakes. The rehabilitated systems can further benefit from the use of hysteretic energy dissipating links between the rocking cores and existing concentrically braced frames. This article also addresses the influence of the rocking cores on modal properties of the rehabilitated buildings. It is found that the rocking core with moderate stiffness does not significantly alter the modal properties of a rehabilitated concentrically braced frame.

Bidirectional Seismic Behavior of Controlled Rocking Four-Legged Bridge Steel Truss Piers

The behavior and design of four-legged controlled rocking bridge steel truss piers to three components of seismic excitation are presented in this paper. The controlled rocking approach for seismic protection allows a pier to uplift from its base, limiting the force demands placed on the bridge pier and deck, and can allow the structure to remain elastic during an earthquake, preventing damage toward the goal of keeping the bridge operational immediately following the earthquake. Passive energy dissipation devices [steel yielding devices (SYDs) or fluid viscous dampers (VDs)] are used at the uplifting location to control pier response. The bidirectional kinematic and hysteretic cyclic behavior of controlled rocking piers with SYDs is presented and verified with nonlinear static pushover analysis. This fundamental behavior is used to develop design equations to predict peak pier displacements, uplifting displacements, and forces (frame shear and leg axial force). Dynamic response history analyses are performed, compared with the design equations, and shown to provide reasonably accurate results for design. The use of fluid VDs in the controlled rocking system is then discussed.

Improved Blast Protection of Buildings through Implementation of Ductile Building Envelope Connectors

The rise of intentional or unintentional explosions on both defense critical and conventional buildings is of domestic and international concern and requires the development of enhanced, cost effective solutions for the blast protective design and rehabilitation of structures. This study explores the feasibility of a simple, costeffective building envelope connector that provides an energy absorbing mechanism for mitigating the effects of air-blast pressures onto a building from a ground explosion. The blast resistant ductile connectors (BRDC) are intended to be sacrificial and easier and cheaper to replace compared to building envelope panels and/or the primary lateral force resisting system (LFRS). The primary objective of the BRDCs are to provide improved blast protection over a wide range of blast scenarios offering an additional mitigation strategy for design professionals and advancing building performance for facility owners. The feasibility of the BRDCs was assessed through closed-form theoretical calculations applying principals of conservation of energy, conservation of momentum, and a generalized single degree of freedom dynamicmechanical model to estimate the response of a concrete building envelope panel. Transient nonlinear finite element analyses are used to verify the theoretical results. This study found that for a reasonably wide range of blast scenarios the BRDC was able to fully dissipate the energy from a blast event, leaving the LFRS and building envelope panel undamaged. The results of the finite element model correlated well with the results of the theoretical evaluation within an appropriate design range. Designs of a potential BRDC using standard structural sections with minimal fabrication were evaluated through nonlinear finite element analyses and experimental testing. The BRDC system could be especially beneficial for the rehabilitation of existing buildings since the envelope connectors are more practical to replace than enhancement of envelope panels or LFRS.