Robert B. Fleischman

Dynamic behavior of rocking and hybrid cantilever walls in a precast concrete building

This paper discusses the dynamic response of precast, post- tensioned, rocking, and hybrid cantilever walls that provided lateral force resistance to a three-story precast concrete building built at half-scale. The building was subjected to extensive shake- table testing on the NEES large high-performance outdoor shake table. The tests provided a landmark opportunity to observe the dynamic response of this type of lateral force-resisting system. Excellent performance was observed overall. Comparison between the assumptions made during the design of the wall and the exper- imental results allowed the validation of the presented design procedure and of the reinforcement detailing in the critical region at the base of the walls.

Seismic performance of perimeter lateral-system structures with highly flexible diaphragms

Building structures are typically designed using the assumption that the floor systems serve as a rigid diaphragm between the vertical elements of the lateral force-resisting system (lateral system). However, perimeter lateral-system structures with long floor spans possess diaphragms that behave quite flexibly. Difficulty can exist in predicting diaphragm force demand in these structures. Thus, current design may provide insufficient strength to maintain elastic diaphragm response. Inelastic diaphragm response exacerbates the effects of diaphragm flexibility. Such response may lead to poor seismic performance, including nonductile diaphragm failure or structural instability due to high drift demands in the gravity system. An analytical study was performed to determine the effect of diaphragm flexibility and strength on the seismic performance of perimeter lateral-system structures with highly flexible diaphragms. Nonlinear transient analyses were performed using ground motions suites corresponding to multiple levels of hazard for high seismic zones. Design recommendations for flexible diaphragms are presented.

Damage Evaluations of Precast Concrete Structures in the 2010–2011 Canterbury Earthquake Sequence

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.

Experimental evaluation of pretopped precast diaphragm critical flexure joint under seismic demands

Precast concrete diaphragm seismic response is examined in experimental research integrating model-based simulation with physical testing. The experimental substructure is the diaphragm critical flexural region of a prototype precast parking structure. This region is expected to undergo significant inelastic flexural deformation, while potentially nonductile regions remain elastic on the basis of capacity design rules from an emerging design methodology. The physical test is conducted at half-scale. The test specimen is detailed using diaphragm reinforcement intended to meet deformability requirements. Predetermined displacement histories are applied to the test specimen on the basis of nonlinear transient dynamic analyses of the prototype structure. The loading history is applied by a test fixture capable of simultaneously providing shear, axial, and moment to the joint. Moment strength, stiffness, rotational deformation capacity, and progressive damage are examined under a sequence of increasing intensity earthquakes. Design recommendations are provided.