260 



STRENGTH OF MATERIALS 



The strain diagram of concrete in compression, shown in Fig. 157, 

 illustrates the fact that there is no well-defined elastic limit, and that 

 the modulus of elasticity changes as the load increases. 



The table on page 259 also illustrates the variation in the modulus 

 of elasticity of concrete in compression.* In the first ten tests tin- 

 cement used in making the test specimens was Alpha Portland, in 

 the next sixteen it was Germania Portland, and in the remaining 

 ones Alsen Portland. 



Problem 175. From the strain diagram of concrete in compression shown in 

 Fi.i:. l-'.T, compute the modulus of elasticity at 1800 lb./in. 2 and at 2400 lb./in. 2 . 

 The height of the block tested was ]o in. 



Problem 176. A concrete beam in. x 6 in. in cross section, and with a 

 span, is supported at both ends and loaded in the middle. The load at failure is 

 1008 Ib. Find the maximum liber stress. 



COMPH1>M\ I STRENGTH AND Mm LIS OF II.ASIK rrv <>F 

 < IM.I.I; CON< IJI-.TI: Cl : 



211. Cinder concrete. The preceding table summarizes the results 

 of a series of tests made on cinder concrete cubes at the Watertown 



* Watertown Arsenal Report, 1899. 



