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Oakland, CA, United States

Burkett L.,RutherfordChekene Consulting Engineers | Maffei J.,Maffei Structural Engineering
NCEE 2014 - 10th U.S. National Conference on Earthquake Engineering: Frontiers of Earthquake Engineering | Year: 2014

San Francisco International Airport's new air traffic control tower is a 67 m (220 ft) tall structure within 4 km (2.5 miles) of the San Andreas Fault, founded on an extremely soft soil profile. The site consists mostly of Bay Mud in the 36 m (120 ft) depth above Franciscan bedrock. The building is designed to meet the demanding functional constraints of a continuously occupied control tower, and to remain operational following a major earthquake. The structural system consists of a cylindrical reinforced concrete core wall over a pile foundation with a single main pile cap. The tower is surrounded by a three-story base building housing FAA and Airport functions. The core wall is designed to have nonlinear behavior occur in a plastic hinge region located just above the roof of the base building. Unbonded vertical post tensioning is placed over the height of the core wall to minimize residual earthquake deformation and to close flexural cracks that form in the plastic hinge region. Buckling-restrained braces, oriented horizontally, brace the tower into the roof diaphragm of the base building, providing backstay support without overloading the base structure. The design is analyzed using nonlinear response-history analyses and site-specific earthquake ground motions. Ground motions are selected probabilistically to produce a suite with appropriate dispersion around a conditional-mean spectrum. The authors carried out a nonlinear soil-structure interaction study to assess the ductility demands for deep foundation elements extending to bedrock. The analyses demonstrate that while the soft soil profile attenuates much of the bedrock motion before it reaches the ground surface, large displacements occur deep in the soil, which impose nonlinear deformation demands on the foundation piles. Source

Zhang D.,Nazarbayev University | Fleischman R.,University of Arizona | Restrepo J.,University of California at San Diego | Sause R.,Lehigh University | And 3 more authors.
NCEE 2014 - 10th U.S. National Conference on Earthquake Engineering: Frontiers of Earthquake Engineering | Year: 2014

An innovative floor anchorage system is being developed through a multi-university NSF/NEES research project. The system, involving a ductile anchorage connector between the lateral force resisting system (LFRS) and the floor diaphragm, reduces inertial forces during major earthquakes. The system permits relative motion of the floor between the primary (vertical) elements of the LFRS and the gravity load resisting system at a predefined diaphragm force cut-off level. The system has the potential to reduce floor accelerations and inertial forces, thereby reducing the seismic demand on the LFRS. This paper presents the initial analytical studies and experimental work toward developing prototype configurations for the floor anchorage isolation system. The analytical studies identified the relationship between reduction in seismic demands and the amount of relative displacement between the LFRS and the floor diaphragm. This relative displacement is limited within practical limits to prevent too large of an increase in gravity column inter-story drifts. The product of these studies is a feasible design space and configuration for the anchorage system that optimizes the competing requirements of reducing structure seismic response while limiting relative displacement between the LFRS and the floor diaphragm. These optimized designs and configurations are being validated using physical experiments including large scale component tests at NEES@Lehigh and shake table testing at NEES@UCSD. Source

Maffei J.,Maffei Structural Engineering | Burkett L.,Rutherford Chekene | Bazzurro P.,University of Pavia
NCEE 2014 - 10th U.S. National Conference on Earthquake Engineering: Frontiers of Earthquake Engineering | Year: 2014

The Health Sciences Instruction and Research facility is a 430,000 ft2 (40,000 m2) complex of two laboratory buildings and three adjoining tower structures that house stairs, elevators, and mechanical ducts. Built in 1963, the laboratory buildings are steel moment-frame structures made of large built-up sections. The authors evaluated the facility using seismic performance levels defined specifically for the project according to the client objective of minimizing research disruption following an earthquake. Nonlinear response-history analysis, at seven levels of hazard, is used to incrementally evaluate the structure. The evaluation uses a state-of-the-art probabilistic analysis with Monte Carlo simulation to define the seismic performance benefit of various retrofit schemes. Fragility curves specific to the building and its systems are developed, considering 16 engineering demand parameters including relative movement of separation joints and elongation of column splices after tension yielding (peak and residual). The demand parameters are chosen to represent both the peak severity and the extent (e.g., over several floors) of potential damage. The approach goes beyond current performance-based tools by incorporating issues such as intersecting rather than sequential performance states. The study provides the owner with a menu of retrofit measures that allows them to optimize the seismic performance of the facility under various given scenarios of construction funding and functional constraints. Source

Fleischman R.B.,University of Arizona | Restrepo J.I.,University of California at San Diego | Pampanin S.,University of Canterbury | Maffei J.R.,Maffei Structural Engineering | And 2 more authors.
Earthquake Spectra | Year: 2014

The 2010-2011 Canterbury earthquake sequence provides a rare opportunity to study the performance of modern structures designed under well-enforced, evolving seismic code provisions and subjected to severe ground shaking. In particular, New Zealand makes widespread use of precast concrete seismic systems, including those that are designed to respond identically to cast-in-place concrete structures (emulative systems) and, in more recent years, those that take advantage of the unique jointed properties of precast construction. New Zealand building construction also makes extensive use of precast elements for gravity systems, floor systems, stairs, and cladding. Although not always classified as part of the primary seismic force-resisting system, these "secondary" elements must undergo the compatible displacements imposed in the earthquake. Damage evaluations for several of these structures subjected to strong shaking provide the ability to examine the differences in seismic performance for systems of distinct design intent and standards, including the performance of secondary elements. © 2014, Earthquake Engineering Research Institute. Source

Maffei J.,Maffei Structural Engineering | Telleen K.,Maffei Structural Engineering | Ward R.,SunLink Corporation | Kopp G.A.,University of Western Ontario
Journal of Structural Engineering (United States) | Year: 2014

Currently, ASCE standards do not provide specific guidance on wind loads for solar arrays of photovoltaic panels, in terms of either prescriptive design or requirements for wind tunnel testing. Guidance is needed, particularly for arrays of low-profile tilted panels on flat or low-slope roofs, because they are markedly different aerodynamically from structures currently addressed in the building code. This paper presents recommendations for the structural design of these solar arrays for wind-loading. Recommendations include (1) categorizing solar array support-systems according to their height above the building roof and how they distribute forces to the roof, (2) developing pressure coefficients that are applicable to structurally interconnected roof-bearing support systems, (3) considering load cases that include uniform wind pressure on the array and nonuniform (gust) patterns, (4) determining appropriate stiffness and boundary conditions for structural analysis, and (5) use of testing to verify behavior and calibrate analytical models. © 2013 American Society of Civil Engineers. Source

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