C. J. Naito Main

Executive Summary
This report summarizes the methodology and findings of testing perforated waffle slab subassemblies for the purpose of seismic assessment of existing industrial facilities where such systems are commonly used. Two types of subassemblies were considered. The first ("A") accounts for waffle slab/circular column interaction when subjected to bi-directional reversed cyclic loading. The second ("B") represents a waffle slab/partially infilled frame configuration when subjected to unidirectional cyclic loading in the plane of the infill wall.

Findings in the form of global and local load-deformation relationships, crack patterns, modes of failure, and stress-strain relations are presented. The observed damage initiation and propagation reflected the flexibility of the tested waffle slab/circular column subassembly and the brittle nature of failure of the tested waffle slab/infilled frame subassembly. The provided idealized relations for the different aspects of the performance of these subassemblies are readily usable for finite element modeling of structural systems where these subassemblies may represent parts of the whole system.

Development of Subassemblies
A 60% scale was chosen for the subassemblies. This is the largest scale manageable by the laboratory facility. This scale allowed the use of common concrete mixes and reinforcement sizes. It is expected that this reduced scale will not affect the accuracy of the results and accordingly conclusions can be drawn from the test results on the performance of similar full-scale subassemblies. The gross cross-sectional dimensions were scaled linearly (by a factor of 0.6) in all cases. The use of standard reinforcement sizes, however, prevented direct application of the scale factor to the bars used in the existing structure. Instead, the quantities and distributions of reinforcement were chosen to reproduce the desired reduced-scale capacity. To accomplish this, the bars were first scaled to the closest available diameter. The spacing was then modified to produce the correct reduced-scale capacity. For flexural reinforcement this entailed a decrease or increase in the flexural moment arm by slightly changing the effective depth of the cross section. For transverse reinforcement this corresponded to a variation in the spacing of adjacent hoops, stirrups or ties. It is expected that the reduced scale and the necessary geometrical adjustment will not affect the accuracy of the results and accordingly conclusions can be drawn from the test results on the performance of the full-scale geometrically similar subassemblies.

Research Team
Clay Naito, Lead Researcher
Assistant Professor Khalid Mosalam, Principal Investigator

Publications
K. M. Mosalam, C. J. Naito, "Seismic evaluation of gravity-load-designed column-grid system," Journal of Structural Engineering, Vol. 128, No. 2, Feb. 2002, pages 160-168.
C. J. Naito and K. M. Mosalam, "Seismic Evaluation of Perforated Reinforced Concrete Waffle Slab Systems for Industrial Facilities," Report to Sponsor, University of California Berkeley, May 2000.

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