The specific initial task was in conjunction with the 
structural group's research on ''Yield Criteria of Reinforced 
Concrete under Biaxial Moments and Loads,'' (Lenschow and Sozen, 
1966) and involved the precision determination of the z defroma- 
tions and the x- and y-in-plane displacements of a reinforced 
concrete slab 84 x 42 x 4 inches being loaded in increments 
until failure under two schemes of loading: one for bending 
(Fig. 14) and the other for torsion (Fig. 15). The accuracy 
requirements specified maximum standard deviations of + 0.1 
mm in x, y, and z coordinates of points throughout the slab. 
Because of the attractiveness of the stereometric 
camera approach, and in spite of our awareness that recent 
results obtained by Konecny (1965), Wasil & Merchant (1964), and 
others seemed to indicate that such an approach might not 
fully satisfy the accuracy requirements in our case, it was 
decided to start with a stereometric camera and modify it, if 
needed, to fulfill the accuracy requirements. A ZEISS SMK-40 
stereometric camera was used in this phase of the project. 
This joint effort was financially supported by the 
University Research Board. 
Test Apparatus 
A sketch of the slab-testing apparatus is given in Fig 16. 
The stereometric camera was positioned atop the structure in a 
mounting yolk approximately 2.5 m above the slab which was 
to be tested. The optical axes of the camera were held in 
a vertical direction, with the Z axis (Fig. 12) pointing down- 
wards. Metallographic (IV-0) glass plates of 1.25 mm thickness, 
ASA = 50, were used. Photographs were taken at the zero load 
and after increment of loading in this static test, to record 
the conditions of the specimen. The photographs were observed