104 STEEL OFFICE BUILDINGS. CHAP. II. 



be self-supporting without walls, partitions or floors. In no case shall the overturning moment 

 due to wind pressure exceed 75 per cent of the resisting moment of the structure. In the calcu- 

 lations for wind bracing the working stresses for dead and live loads may be increased 25 per 

 cent providing the sections are not less than required for dead and live loads. Chimneys shall 

 be designed to resist a wind pressure of 20 Ib. ( of 30 Ib.) per square foot acting on the vertical 

 projection of the chimney. Curtain walls carried on the framework of steel or reinforced concrete 

 buildings shall be designed to resist a horizontal pressure of 30 Ib. per square foot acting hori- 

 zontally on the outside of the entire surface of the wall. 



8. Minimum Loads on Roofs. Roofs shall be designed for the minimum loads specified by 

 Schneider and given in Table VI. 



9. Live Loads on Columns. For columns carrying more than five floors, the live load may 

 be reduced as follows: 



For columns supporting the roof and top floor no reduction. 



For columns supporting each successive floor a reduction of 5 per cent of the total live load 

 may be made until 50 per cent is reached, which reduction of the load shall be used for the columns 

 supporting all remaining floors. No column shall, however, be designed for a live load of less 

 than 20,000 Ib. The above reduction is not to apply to the live load on columns of warehouses, 

 and similar buildings which are liable to be fully loaded on all floors at the same time. 



10. Loads on Foundations. The loads on foundations shall not exceed the following in 

 tons per square foot: 



Ordinary clay and dry sand mixed with clay 2 



Dry sand and dry clay 3 



Hard clay and firm, coarse sand 4 



Coarse sand and gravel 5 



Shale rock 8 



Hard rock 20 



For all soils inferior to the above, such as loam, etc. never more than I ton per square foot. 



The loads on foundations shall be assumed to be the same as for the footings of columns. 

 The area of the bases of the foundation shall be proportioned for the dead load only as follows. 

 That foundation which has the largest ratio of live load to dead load shall be selected and pro- 

 portioned for the combined dead and live loads. The dead load on this foundation shall be 

 divided by the area thus found, and this reduced pressure per square foot shall be the permissible 

 pressure to be used for the dead loads of all foundations. 



11. Pressure on Masonry and Wall Plates. The maximum pressure on masonry and wall 

 plates shall not be greater than the values given in Table VIII. 



12. Bases. Structural steel columns shall rest on either cast iron, cast steel or built steel 

 bases proportioned so as to distribute entire load of the column on the concrete or masonry founda- 

 tion. Columns carrying wind stresses shall be firmly anchored with at least two anchor bolts 

 to a mass of concrete whose weight is at least i| times the up-lift in the column. All columns 

 shall be properly secured to the bases. 



13. Shape of Foundations. Foundations under columns shall be symmetrical except under 

 wall columns, where the center line of the column must lie within the middle third of the founda- 

 tion. In this case the average intensity of the pressure on the soil shall not exceed one-half the 

 safe load allowed for a symmetrical section. In cases where the wall column load exceeds the 

 above safe loads the column must rest upon a steel or reinforced concrete girder or cantilever 

 having a column or columns at the inner end. The foundation shall then be designed for the 

 combined loads. 



14. Rolled Beams. The depth of rolled beams in floors shall be not less than one-twentieth 

 of the span, and if used as roof purlins not less than one-thirtieth of the span. In case of floors 

 subject to shocks and vibrations the depth of beams and girders shall be limited to one-fifteenth 

 of the span. If shallower beams are used the sectional area shall be increased until the maximum 

 deflection is not greater than that of a beam having a depth of one-fifteenth of the span, but the 

 depth of such beams shall in no case be less than one-twentieth of the span. 



15. Expansion. Provision shall be made for expansion and contraction corresponding to a 

 variation of temperature of 150 degrees Fahr. where necessary. Expansion rollers shall not be 

 less than 4 inches in diameter. 



16. Cast Iron. The allowable stresses in cast iron shall be as follows: 



Compression = 12 ooo Ib. per sq. in. 

 Tension = 2 500 Ib. per sq. in. 



Shear = i 500 Ib. per sq. in. 



17. Steel Columns. Columns shall be of rolled or built sections. No wall column or column 

 with eccentric loads shall be used which does not have at least one solid plate or web of metal in or 



