98 AN ANALYSIS OF TESTS OF WATER-TIGHT BULKHEADS. 



/ 



pi ih + -)l's 



M= — = = inch-tons, 



24 70 



and the required section modulus — 



S = - = 



I M ^''+h^'' 



y f 700 



taking the permissible stress, /, equal to ten tons per square inch as explained 

 above. 



If the top of the bulkhead is h feet above the water-line of deepest 

 immersion, the maximum bending moment may still be reckoned equal to 



— , but now — 

 24 



P==±a~hy ions, 

 70 



and hence — ■ . . 



^_ {l-hyis 

 1400 



The section moduli so determined are given in Table I for a series of values 

 of /, h and .y ranging between the extremes of present practise. 



In Table II are given the section moduli of several series of different 

 types of stiffeners, both with and without face plates or reversed bars. 

 Since the value of /, which enters in the calculation of 5 in Table I, has 

 been chosen under the assumption that the bulkhead plating contributes 

 to the strength of the stiffener, the same assumption has been made in the 

 calculation of 5 as given in Table II. In general a strip of bulkhead plat- 

 ing of about same sectional area as that of the flange which is attached 

 to the bulkhead has been assumed to work with the stiffener. Wliere a 

 face plate is added to the free flange of the stiffener, it has likewise been 

 given about the same sectional area as the flange so as to balance approxi- 

 mately the hypothetical strip of bulkhead plating. Thus the neutral axis 

 of a stiffener with face plate will come to lie theoretically at the middle 

 of the web of the bar. 



