AN ANALYSIS OF TESTS OF WATFR-TIGHT BULKHEADS. 89 



The total number of analyzed tests here recorded is fourteen, of which 

 six were with double stiff eners, eight with single stiffeners; but several of 

 these tests were made at two or more heads of water. The main results 

 are given on Plates 28-31, and each test is given a number for reference. 



In cases where deflections were measured at several different heads of 

 water on the same bulkhead, the test generally commenced with a small 

 or moderate head, increasing in stages up to the maximum. After the 

 deflections at maximum head had been taken, the pressure was removed 

 by letting the water run oft' completely, whereafter the permanent set was 

 measured. The permanent set so found corresponds therefore only to the 

 maximum head, and is not applicable to the deflections measured at the 

 smaller heads, which existed prior to the maximum. For the purpose of 

 analysis it would therefore be preferable to proceed in the reverse order, 

 first subjecting the bulkhead to the maximum head and then to the smaller 

 heads, since in that case the permanent set, measured after tlie test, would 

 be applicable to all the readings. 



Only in case of test No. 7 was this order of procedure followed. 



b. METHOD OF ANALYSIS. 



The deflections used in this analysis, represented on the diagrams by 

 heavy lines, are always the elastic deflections, i. e., the observed deflections 

 minus the permanent set. They are marked: "Obs. Blast. Defl.," and are 

 drawn through the observed points irrespective of fairness of the curve, 

 generally representing the mean deflections for two or more stifl'eners. 

 The curves of permanent set are given in dotted lines. 



In cases where deflections have been measured at smaller heads pre- 

 vious to the maximum, the permanent set to be deduced has been estimated 

 as a fraction of that found after the stiffeners had been exposed to the 

 maximum head. In all cases where such estimate has been made it is 

 clearly stated on the diagrams. 



The curves of observed deflections refer in all cases to the middle stif- 

 fener or stiffeners in order as far as possible to eliminate the influence of 

 the bulkhead plating in supporting the stiffeners by its tension. 



The first question which occurs in the analysis is whether the tension, T, 

 of the stiffeners shall be taken into account. As stated above it was found, 

 in most of the cases here analyzed, that the tension might be neglected 

 or that it might be found approximately and then simply added to the 

 stress corresponding to pure bending. Only in one case, that of test No. 

 12, did the tensional stress exceed one ton per square inch, but, as evi- 



