JOURNAL OF AGRICDLTffiALlSEARCH 



DEPARTMENT OF AGRICULTURE 



Vol. VI Washington, D. C, May 8, 1916 No. 6 



TESTS OF THRKE LARGE -SIZED REINFORCED -CON- 

 CRETE SLABS UNDER CONCENTRATED LOADING 



By A. T. GoLDBECK, Engineer of Tests, and E. B. Smith, Associate Mechanical Engi- 

 neer, Office of Public Roads and Rural Efigineeri^ig 



INTRODUCTION 



Numerous instances occur in reinforced-concrete design in which the 

 use of slabs supported at two ends only is required, and in many such 

 cases the critical loading is concentrated at one or more points. Such 

 a condition may exist on slab-bridge floors, box culverts, on floors of 

 buildings where heavy machinery is housed, and in other constructions 

 where loads are concentrated. 



If a slab, supported at two ends and carrying a single concentrated load, 

 is imagined to be divided into narrow strips extending from support to 

 support, it would seem reasonable to assume that the strip immediately 

 under the load carries a ver}^ large part of it and that the adjacent 

 strips receive a smaller amount, depending upon their distances from 

 the load. The most remote strips, those at the edges of the slab, would 

 then probably receive very little load. The question which concerns 

 the designer of such a slab is that of the relative magnitude of the stresses 

 at different distances from the load. 



Up to a few years ago the technical literature on this subject was prac- 

 tically nonexistent, and the result was that engineers relied largely on 

 their judgment when called upon to design slabs subjected to concen- 

 trated loads. Very naturally, large variations in load-distribution 

 assumptions were made, and as a consequence there were great differ- 

 ences in the design even when the span and load to be carried were 

 practically identical. 



The necessity for definite knowledge on this subject was very forcibly 

 brought to the attention of the engineers of the Office of Public Roads 

 and Rural Engineering a few years ago, and a set of tests was made by 

 one of the authors on slabs of 3-foot and 6-foot span length.^ These 

 tests gave some useful and rather surprising results that have since been 



' Goldbeck, A. T. Tests of reinforced-concrete slabs under concentrated loading. In Amer. See. Testing 

 Materials, Proc. i6th Ann. Meeting 1913, v. 13, p. SsS-.'iyj, 10 fig. 1913. Discussion, p. 874-883, 4 fig. 



Journal of Agricultural Research, Vol. VI, No. 6 



Dept. of Agriculture, Washington, D. C. May 8, 1916 



dj D— 8 



(205) 



