70 OAMBBIA STEEL. 



TABLES OF SAFE LOADS TERRA COTTA FLOOR 

 ARCHES. 



The Table of Safe Loads for Flat Arches, page 71, is applicable 

 to all shapes of blocks. The areas given are obtained by passing 

 a plane through the blocks at right angles to all the webs and 

 are the areas for 1-foot width of arch. Generally speaking, end 

 construction blocks of various shapes, but of the same depth 

 and cross sectional area, have equal strength. The weight of 

 the arch has not been deducted in Table of Safe Loads for Flat 

 Arches. Therefore, this and other dead loads must be deducted 

 to obtain the net safe live load for any arch and span. 



EXAMPLE. What load will an 8-inch arch carry (using a 

 Factor of Safety of 5), for a span of 5 feet 6 inches, the blocks 

 having a sectional area parallel to the beams, of 44.25 square 

 inches? 



Area of 8-inch block in Table = 37 sq. ins. 



44.25 -4- 37 = 1.19, Ratio of Actual Area to Tabular Area. 



Safe Load in Table = 228, X 1.19 = 271 pounds = Safe 



Load for Actual Area. 

 Weight of Arch = 44.25 X 12 = 531 cu. in. X .06 = 32 



Ibs. per sq. ft. 

 271 - 32 = 239 Ibs. = Safe Load in Ibs. per sq. ft. for 



S. F. of 7. 

 271 X 7 ^ 5 = 379, - 32 = 347 Ibs., Safe Load for S. F. of 5. 



Tables of Safe Loads for Segmental Arches in spans up to 10 

 feet are given on pages 72 and 73. The areas of the blocks for 

 which the safe loads are given are the areas per foot of arch 

 parallel with beams. The weight of the arch blocks has been 

 deducted in the Table, so that only the dead load of concrete 

 fill, plastering, etc., must be deducted to obtain net live load. 



Segmental arch construction is cheaper than flat arch con- 

 struction, and is the stronger of the two. Where for any reason 

 a flat arch is not deemed necessary, this is an admirable floor 

 construction to use. 



Even with this type of construction, the flat ceiling may be 

 secured by suspending a metal lath ceiling below the arch from 

 the bottom of the beams. To do this, however, adds so much 

 to the cost that it is generally cheaper to use the Flat Arch. 



Segmental Arches can also be built with a raised skew. This 

 flattens the arch and reduces the amount and consequently the 

 expense of the cinder concrete fill, but it also reduces the strength 

 of the arch. 



In Segmental Arches, the thrust on the beams (particularly 

 at the bottom of beams) is very great, and where there is any 

 doubt of the beams' sustaining the thrust, it is desirable to use 

 steel tie rods. These tie rods may be fireproofed or left unpro- 

 tected, the best practice being to protect them. 



