yes man has always been a builder but his structures have endured only when the materials we used were able to resist the forces that make you most of those forces we have found it easy to comprehend that we and the sun the rain and the snow understanding them we have build our shelters against them simply absurd then as we acquire new skills and imagination with increasing comfort grace and beauty and with  fans we might say to ourselves this is good this is beautiful for sometimes in unexpected places and without a moment's warning our seemingly solid or will he even twist and strain wrenching our homes in its violent spasm filling our minds with he out of the iron we make our steel and out of the steel we create the strength to support our building even against the shock of or quake for while eager to shock can play havoc with those buildings which are poorly designed or built of insubstantial material there have been many examples that structures built of steel or reem forged with steel have been able to withstand the shock of  in the pacific north where a convincing example was that which with its steel construction withstood the earthquake of one hundred forty nine in long beach california the beautiful villa reviere constructed  steel was a notable survivor of the earthquake of one nine hundred thirty three and then i've been california the ivan high school with its modern steel reinforced construction suffered only minimum damage in the severe to does not like to think of children trapped in a collapsing school house from such convincing evidence we have the proof that steel is an important factor in the construction of earthquake resistant buildings but in order to understand why we must know something about the nature of earthquakes themselves to begin with movements of some kind are going on in the earth's crust some where all the time movements way in their own way are as restless as the changing tides of the sea many of these movements are so minor that we ourselves do not feel them but we know they're going on because they're sensitive recording instruments constantly tell and so on the other hand there are movements so strong and violent that we do feel them and very sharply many of these movements have taken place along the pacific coast region which to many people has become known as the earthquake belt of north america let it not be assumed however that earthquakes are confined to this so called earthquake  actually earthquakes have occurred in every state the strongest shocks of record in the united states occurred in eighteen eleven eighteen twelve in missouri another quake originating in south carolina and hundred six which found one thousand miles away earthquakes are no respecters of locality they occur because of some slipping or rupturing within the earth and this produces a fault sometimes these faults or even visible on the earth's surface such as the famous san andreas fault in california it was the slipping along this fault which caused the san francisco earthquake of ninety six and several later and the core the outer crust upon which we live has an average depth of twenty to thirty miles beneath this craft is the mantle extending to a depth of about seventeen hundred miles and beyond the the core extending about two thousand one hundred fifty miles to the center of the earth now as already mentioned we know that movements are taking place constantly in the earth's crust and mantle as the seismic waves by studying these waves we learn much about the origin and intensity of the earthquake shock such studies are made that seismological laboratory located at strategic points throughout the world where seismic waves whenever they occur are scientifically recorded on sensitive instruments known as s but one of many delicate instruments which tell of movements in the earth structure one unique instrument for instance has been installed in a tunnel under the san gabriel mountains of southern california a device so designed as to measure the long term as the strains accumulate the resulting movement to slight to be seen with the naked eye can be measured and recorded and it is hoped that such findings may make it possible someday actually to forecast when and where earthquakes will occur also a special type of seismographs so sensitive a breath can set in motion is used to measure the actual movement at the earth's surface during an earthquake and its aftershock data gathered in this and other ways scientists are able to recreate the movement and behavior of earthquakes long past for example a mechanical device which simulates the ground motion of the long beach break of nineteen thirty three terrorist creating shocks of varying degrees of intensity helps to determine how structures will react to possible future this study is all the more significant because the test structure is an actual scale model of an actual building located in that bush in montgomery street in san francisco the alexander building a slender sixteen story structure built on a framework of steel like it's a laboratory model the building itself is furthering your quick research for sensitive instruments to measure acceleration due to shock have been installed in the building at several different levels with the aid of these instruments it is possible to study the building's reaction to the forces created by your quick movement whenever they occur leads of course are only a few examples of many types of research going forward all the time and we have learned from such research that different types of buildings react in different ways to work great shape these differences can be overstated by comparing the reactions of a low structure tall slender structure and an l shaped structure in the case of the low structure when the earth's movement causes the base to move the roof because of its inertia tends to lag behind and does not immediately fall on the ground its weight therefore creates considerable stress in the members connecting the floor to the roof the resulting strain known as shearing strain may cause the structure to collapse unless the members are properly braced and tied together with the top slender structure experiencing the same ground movement the building oscillate causing various b an consequently the frame must have sufficient flexibility to permit the structure to assume the distorted shape without sex recently and the structure will suffer excessive damage in the i was shaped structure if the ground movement is parallel to one wing this wing because of its l have considerable resistance to the shock but the other weighing is broadside to the movement and consequently will deflect more the unequal deflection between the two wings would cause a twisting action and if the building is not properly braced and tied together this twisting or torsion may cars failure at that junction of the two wing obviously of buildings are to withstand these destructive forces they must be constructed of suitable material materials which will not fail it is for this reason that steel and steel reinforced materials have become the key to our great resistance construction teleni is the ability of a material to undergo distortion that is to absorb energy without breaking steel has this ability strength which is measured by its ability to withstand tension compression and shear stresses and it has the ability to impart strength to other materials concrete is a good example here a transparent four makes it possible to see how steel reinforcing bars are placed to best impart their strength to a co for this reinforcement the beam will gain both here strength and tension strength this can be shown by making a comparative test of two concrete beams of exactly the same dimension the first beam reinforced  steel the second and reinforce the pressure is applied equally on both b and a load of five thousand pounds the unre steel reinforced beam has sustained only minor cracks  as the load increases the damage becomes visible but the beam will not give way even at thirty thousand pounds it will not give way simply because of the strength of its reinforcing steel perhaps no one knows this better than a wrecking crew and gauged in the modern single building if there was a not reinforced whether they be a brick stone concrete or any other material they can be brought down without much difficulty if those walls be reinforced with steel the wreckers have a bigger job on their hands it will take a tremendous amount of battering to even tip the walls away and even then the steel still hold the only way it can be removed finally is with a chisel or cutting  designed to resist or flee as another example a brand new high school in helena montana on the one month old collapsed in the earthquake of one nine hundred thirty five it was a partially steel reinforced building but again not designed to resist earthquakes otherwise it might be standing today many aspects of good design but in so far as earthquake resistance is concerned fact is of prime importance the various components of any building must be tied together in such a way as to provide structural continuity to a continuity would be entirely lacking for instance in a platform resting on four upright but not fastened to them such a structure might support a sizeable load but only so long as the force of the load continued to be pretty cool if the structure were subjected to  horizontal forward in as much as its parts are not tied together it would simply topple suppose however that platform and uprights are fastened together and partially b now the structure offers some resistance devor is our movement but not enough resistance to withstand twisting or torsion so that again the structure will fail it is only when all members are properly tied together on all sides that the structure achieves through continuity and the strength to resist movement from any and all direction perhaps a more homely illustration is the simple cardboard carton with its lid open the carton offers little resistance to outside pressures but if the lid is closed in securely fastened the condom has strength to resist forces from any direction the lid forms what is known in structural design as a diaphragm which when properly tidy and give strength t in order to provide a maximum of structural continuity here again is one of the advantages of steel for in addition to its strength and dexterity steel is workable that can be fashioned and fitted in countless ways which not only facilitate construction but make it possible to achieve complete structural continuity much of this is done before the steel even reaches the construction site at the fabricating works where steel is fabricated into such modern techniques intricate assemblies of every size and description can be fabricated and transported to the construction site where erection time and save because of the work already done at the sho base plates are fastened to their anchor both and as the building grows each member is tied into other members so that finally all units are integrated into one endless continuity it is from this continuity and from the strength of its steel that the building example with steel reinforcement the beauty and utility of brick can be used in new and safer ways glass becomes stronger and sa even buildings with many openings and large areas of glass can withstand shock if they are properly designed and construct  or eat material has a purpose and for all building materials there is one common denominator steel nor have we seen the limits of what we can do public spirited man everywhere i working constantly to advance our knowledge of or quake every quake resistant the dine and construction geologists scientists structural engineers research engineers architects earthquake man and building man the knowledge they contribute is bible to our welfare but that knowledge alone is not enough it must be followed by public understanding and public action so it is the public officials all over the country are re examining their building codes and causing code to be redesigned codes which will protect the people of their communities not only against fire flood and storm but against the unpredictable stradivari right to sensible compliance with these codes many communities of cause schools and other buildings to b because of unfaith design or construction many communities realizing the danger and overhanging parapets and other gingerbread construction haven't acted legislation requiring them to be remedied or removed and with good wisdom or even if the building stands it's unsupported pepperton ornamentation are more than likely to be shaken down when the earthquake strikes and b where to those below in the city of los angeles the building code requires that some types of purpose be removed and replaced with steel reinforced bond being which when tied into the main structure reduce hazard and often give additional strength to the building removal is not always required however i was certain types of cap but it is possible to tie them into the structure with steel bracing thus reducing the accident ha so we know what we must do we must make our homes and our buildings safe we must build them soundly to give them lasting strength and those interested with public responsibility must see the we can arm ourselves against it we can use our weapon steel and when we use it wisely even the earthquake will lose its terror our people will be safe