The Birmingham age-herald., 1915-05-07
LETTERS TO EDITOR
Mathematical AnaIysis of Wall

TO the Editor of The Age-Herald
 A statement in your issue of May { lslo' of one of the examining committee appointed to examine the Blacksmith walls by the commissioners at the gen. erai probe as to the cause of the disaster. states that he found wall in good condi- tion."
 Just what good condition" means in his judgment. the writer Twill leave for the Judgment of others. It Is very trua that men were tearing down part of the walls by means of picks, steel bars. etc. wfen We, the examining committed were making our examination. but did not everyone passing the ruins note that the .ront ana rear of the building were be- Ing torn away at that time only, which portion of building the firemen saved from high degree of heat by water. which was thrown through the windows at the ends of building? There were no openings in the side of building where the walls broke and where the writer made his examination. So, you will see from MT. Fidler's examination that the walls were in good condition. at the front and rear, where the walls did not fall
 For the reason that engineers have very little data relative to the physical properties of mortar and brick that has undergone intense heat and continuous Freezing and thawing as has the Steele Smith walls, I suggested that a thorough examination be made of said walls so that the public and engineers may have a record thereof
 The writer wishes to call attention 10 some of the characteristics of the east wall. The east wall, which was 14O feet long, gave way at the center, falling to the east. leaving the two ends of the building as they were, with part of the side walls racking off from the top of the ends of the building tas those passing noted) The 14O feet of the east wall lowered unsupported. approximately 4o feet above adjacent buildings. The top ~ feet of building was a 13-inch wall Ten feet of wall underneath 13-inch wall 17la-lnch wall extending from third floor to fourth floor offsetting 4la inches at the third floor.
 The writer sets forth a mathematical analysis based on the straight line formula which Is used by more than ab per cent of expert concrete engineers who recognize the fact that if the formula errs 1t errs on the side of safety.
 The east side of east wall was plane. and in this analysis l treat 1t as being absolutely 8 vertical plane. l also as- sume that the wall was perfectly rigid at the third floor line. and that one cubic foot of wall weights 13O pounds. l do
 
 where aggregate is the best, and strength is known to be, and certainly do not consider tensile strength of mortar which has undergone intense heat and continu- ous freezing and thawing as kad this wall.
 The city allows 160 pounds pressure on line and cement mortar, which is con servatIve. supposing that the wind pres sure is six pounds per square foot. as 10 supposed to be, then the extreme fiber of the mortar would have been stressed to 1g pounds per square inch. supposing that during the meantime the wall re- mained in a vertical plane. which could not have been true. due to the law of deflection with the low modulus of elasticity of mortar. and, therefore, the tendency of the center of gravity of the towering portion of wall was to travel east and stress the extreme fiber of the mortar the more.
 A 4.2-pound wind would have stressed the extreme fiber of the mortar to 160 pounds per square inch, in view to analysis of design.
 The thickness that any practical engi- neer would have required for an unsup- ported wall towering as wall mentioned would have been 46 inches at the third floor, figuring the pressure of the wind at 30 pounds per square foot and the maximum mortar stress at 160 pounds per square inch at the extreme fiber of mortar.
 I do not say that l6O pounds Is all that good mortar could or should be stressed under bending moment. neither do I say that the Steele-Smith wall could have stood such a stress at the 4la-inch offset at the third floor. where water saturated the mortar which, during cold weather. | was continuously freezing and thawing When the interior portion of wall was frozen for only short distance, exert ! ing a pressure from 20.0O0 to 30,000 pounds | per square inch. the bond of the interior brick and mortar was weakened, and as | observed from my examination. was substantially destroyed.
 l If any engineer wishes to criticize these | figures let him be sure as to how tho | wall was loaded, and then he may crit- | cize as best suits him. Let such an engf- neer be sure to give the thickness of . wall, burned and unburned. that he him self would work under during 3o-pound | windstorm.
 The writer believes that a test should l be made of these walls. as to tensile and compressive strength of mortar and brick He thinks that this would be noth. | ing but fair to science, and to our neigh- boring cities, who may be governed to . ldegree as to how good a burned wall that ! has stood a severe winter may bA Respectfully submitted.
 J. c. oAUNrr.
 Architect and Engineer. t Birmingham. May {. 1915 ~ rnnp4~ns> H>vnnsf b11l1AfnR