Clay J. Naito, Ph.D., P.E.
Professor of Structural Engineering
Dept. of Civil and Environmental Engineering

Contact Information

Current Research:

NSF: Development of a Blast and Ballistic Resistant Precast Concrete Armored Wall System

NEES-CR: Impact Forces from Tsunami-Driven Debris

Inspection Methods & Techniques to Determine Non Visible Corrosion of Prestressing Strands in Concrete Bridge Components

Daniel P. Jenny PCI Fellowship: Analytical Assessment of the Resistance of Precast Strucutres to Blast Effects

Development of a Seismic Design Methodology for Precast Diaphragms

Development of a Welding Procedure Specification for Field Welding of Precast Concrete Connections

Use of Polyurea for Blast Hardening of Concrete Construction

Estimation of Concrete Respone Under Varying Confinement

Evaluation of Bond Mechanics in Prestressed Concrete Applications

Horizontal Shear Capacity of Composite Beams Without Ties

Lateral Resistance of Plywood and Oriented Strand Board Sheathing After Accelerated Weathering

Past Research Projects

Performance of Bulb Tees with Self Consolidating Concrete

FRP Bridge Decks with RC Parapets

Blast Resistance of a Load Bearing Shear Wall Building

Lehigh@NEES Equipment Site

Reserarch Experinece for Undergraduates

Seismic Evaluation of a Three Story WoodFrame Apartment Building with Tuck-Under Parking

Design of RC Bridge Beam-Column Connections

Response of Waffle Slab Building Systems to Seismic Loads

Seismic Evaluation of Asymmetric Multi-Story Wood-Frame Buildings

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

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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