JANUARY 26, 1934. SOUTHWEST BUILDER. AND 'CONTRACTOR

This picture shows giant pantograph being used t i mah» cross section of 16-lt. Colorado RiverAqueduct tunnel, A" accurate reductio" 1 to 24 of contour of tunnel excauation. is tracedon sheet of paper, 12x 12 inches, Cross sect ion. shows if tunnel is being driven ;" conjormit yto engineer's design.

Pantograph IsUsed in Making Cross.Secrions of Aqueduct Tunnels

To determine as the work progresseswhether the bores are being driven true tothe engineer's design and the fixed gradesis one of the important duties of the engi-neers in charge of the construction of the 91miles of tunnels on the Colorado River Aque-duct of the Metropolitan Water District ofSouthern California. This requires the mak-ing of accurate cross sections of the tunnelsas the excavation advances, generally at in-tervals of about five feet.Because of the .size of the tunnels which

will have an inside diameter of approximately16 ft., use of' methods formerly in voguewould have been cumbersome and expensive.However, by resort to' giant pantographs thiswork, has been greatly simplified and. expe-dited. This instrument was- .originally de-signed for the .enlargrnent Dr reduction' of:pictures but it has been, adapted to practical

engineering work with remarkable successand it is possible with the pantograph tomake an accurate cross section of rock ex-cavation in the tunnels in about ten minutes,whereas by some old methods it would haverequired hours of laborious and patient effort.For the making of tunnel cross sections the

District purchased at the outset a number ofProebsteel pantographs capable of making areduction of about 1 to 24 to accurate scaleof the tunnel excavation. The pantograph.is mounted on a tripod made of steel pipe.An aluminum plate 16x16 inches with a hubin the center, to which the pantograph is at-tached, is bolted to an adjustable uprightstandard clamped in the top of the tripod.This plate is set at the proper level on themain axis of the tunnel and adjusted with aspirit level. A sheet of cross section paper,12x12 inches, on which the' cross section of

--:;21-

the excavation is traced, is fastened on thealuminum plate. The frame of the panto-graph is made of spruce and has a workablerange of from 5 ft ...3-in. to 12 ff. 4-in. Arubber roller is fitted on the end of theextension arm which is drawn over the sur-face of the rock with a long rod by. the manoperating the pantograph.Conformity of the excavation to the engi-

neer's design is' determined by placing atemplate made to exact scale over the crosssection tracing made by the pantograph. Thistemplate is. cut to the line of excavationrequired.' Any projection over this requiredline-Is-at once indicated and instructions aregiven for the amount of additional excavationnecessary at that point. The amount of over-break is also indicated by the template. Areaof the cross section as recorded by the pan-tograph is determined by a planomiter.

---0--Plasterer Loses Appeal to Save

State LicenseNelson S. McCartney, Burlingame plaster-

ing contractor; lost his appeal to obtainrein-statement of his state contractor's license,which was r~voked several months ago." ')P~tition for reinstatement was denied byGlen V. Slater, assistant registrar of con-tractors, in confirming recommendationsmade by Orman Lutz, referee, as a result ofa formal hearing and investigations conductedduring the last three months.Revocation of the original license followed

a hearing on charges that McCartney hadsubstituted a cheaper and inferior grade of'plaster in construction of a Burlingame homethan the quality which his customer hadauthorized. .In applying for reinstatement, McCartney

.was given an opportunity to introduce experttestimony to disprove the report of Abbot's. Hanks, Inc., San Francisco, engineers andchemists, which resulted in cancellation of'his license.While several contractors and associates of

McCartney testified in his behalf at a recenthearing conducted by Referee Lutz at Bur-lingame, McCartney failed to produce tech-nical or expert testimony to refute the Hanksreport, according to Mr. Slater.

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Woman With Clever TalkImposes on .Architects

Recently several architects have' receiveda call from a prospective client-s-a womanseemingly well educated and refined whotalks quite deliberately and at considerablelength about a residence she- proposed tobuild upon a large lot, a hillside site, in Hol-lywood. She is much interested in music forwhich provisions must be made. She discus-ses the style of architecture, the cost, her fi-nances, the family relations and draws afloor plan. She then 'suggests an appoint-ment, will leave her card,but upon openingher hand bag suddenly discovers she has lostor misplaced her 'purse. Then follows a pan-tomime of' distress, a story of a trip with afriend who has gone on to. a beach town andshe has no way of reaching her destination.It .concludes in: the architect advancing justa"car fare to reach a suburban town.

SOUTHWEST BUILDER' AND CONTRACTOR

Economical and' Safe Reconstruction,Is Proposed f~r Public Schools,Engineer Offers Plan to Eliminate HazardsConclusive Answers to Many Problems Involved

By Martin Pohl(Copyrighted 1933by Martin Pohl), (Continued from last 'w€ek) "

Xm""::GENERALDETAILS OF CONS,TRUC-TION FOR CLASS ROOM BUILDINGS

Means of Tying Existing Buildings to,' theNew Strengthening Devices. To derive the'full benefit from the various reinforcementdevices proposed in Section VII, it is of ut-most importance that all parts of the build-ring, be -securely tied and interlocked withthe new strengthening, device. This purposeis achieved by the various pilasters and brac-ing details shown in' Figs. 37 and 39. Thesedetails,' however," will require 'modificationsto' suit the needs' and' special- conditions ofthe individual projects.Pilasters. The 'installation of .pilasters will

be necessary at each vertical bent, panel, orother strengthening device... In Class "A" frame structures pilasters are'required at the exterior face of all outside'walls and at corridor side of interior longi-tudinal walls., In ·buildings of the brick bearing wall type.with, steel lintels supported by, brick piers,the concrete encasing the steel columnmust extend .;ir the form of van inside pil-aster, as::-shown by' dotted lines in Fig. 37.This measure is necessary in order to prevent.lateraL _displacement of lintels or "pushingthrough': at their bearings.An acceptable alternative is the design of

a steel bracket extended from the column to,lintel, or any other detail worked in con-junction with the strut member along the.inside face oJ the exterior wall. The strutmember' is .a part of the horizontal bracingsystem indicated in Fig. 37. ', If solid reinforced concrete walls are usedas a vertical stiffening device, the inside pil-asters at exterior walls are to be cast as anintegral part with the wall, as shown in Fig.34 (see issue of Jan. 19). This method ofconstruction will add greatly to the strengthof the vertical panel due to the increase ofits moment of inertia. ,Even if the ends 'of the exterior brick walls

are rigid enough not to require strengthen-ing by, a special transverse frame, it is nev-ertheless imperative to install pilasters atcorners, since the corners of the building re-ceive most strain by impact of earthquakeaction. Also, torsional moments generallyreach their maximum in both the horizontaland vertical plane at the corners of a build-ing.. The pilasters at the interniediate reinforce-ment devices serve merely as an importantdetail for tying the existing structure to thenew strengthening device, but the corner pil-asters Tulfill a primary structural function,as explained in Section XI, and are to bedesigned with this particular purpose in viewas discussed in the issue of 'January 19 underthe heading "Strengthening by System ofOutside Buttresses."KeysIn brick' piers are to be provided for

anchors, as shown in Fig. 37. The latter

Sixth installment of report entitled"Survey of Earthquake Damage and Gen-eral Recommendations for Redesign andReconstruction of Public School' Build-ings," by Martin Pohl, consulting engineer,architectural department, Los AngelesBoard of Education. First installment waspublished in issue of December 15. "

must be provided at all floor levels and atwindow heads to secure direct lateral sup-port of lintels, girders and floor joists; andat intervals between such points as bendingand shear resistance of pilaster will necessi-tate. The reinforcing, steel in the pilaster(Figures 37, 39 and 40), is to be determinedby assuming beam E!,action over a spanequal to-the spacmg' of anchors; addi-tional ,reinforcing is to be provided ,tomake up a reinforcing detail consistent withsound 'construction principles. The anchorsare to be designed for one-tenth of all loadstributary by the weight of the pier and thepilaster, lintel and joist reactions, etc. Ifdetail shown in Fig. 40 is used, the net area'of the anchors at threads must be introduced'for tension value, and the total number ofthreads must be sufficient for shear re-sistance.Preparing Surfaces of Contact for Guniting

Pilasters. The brick pier must be "toothed"out at the ends of the pilasters, and hori-zontal reinforcement encased 'in concretemust extend into such places, .so as to com-pletely 'interlock the present brick pier andthe concrete pilaster.Before guniting the pilaster the old brick

work must .be well cleaned and saturated.Complete saturation of all surfaces of contactcannot be achieved by merely wetting thebrickwork previous to guniting. It must bekept wet for several days before concrete isapplied.

XIV-RECONSTRUCTION SCHEMES PRO-POSED FOR AUDITORIUMS ANDBUILDINGS OF SIMILAR TYPE

This classification includes auditoriums,gymnasiums, large study halls, libraries andshops. Buildings belonging to this class ofstructure are characterized by their generallayout which extends over a large area with-out intermediate cross walls or other meansof stiffening.Rigidity for this type of construction may

be supplied in two ways:A. By sufficiently rigid exterior walls.B. By individual piers or bents.Which of the two methods is to be adopted

depends upon the physical character of thebuilding, its general layout, and proportionsof wall openings, etc. If solid or practicallysolid end walls are available, type "A" maybe the most economical as well as the mosteffective solution.

XV-REDESIGN AND STRENGTllENINGOF AUDITORIUMS UTILIZING THERIGIDITY OF PRESENT WALLS

General Method of Design. This method

of strengthening requires the installation ofa framework in either the top or the bottomchord plane of the roof trusses, whicheveris most adaptable to the reconstruction lay-out. :The structural function of this frame isto transfer all lateral forces due to earth-quake motion and wind to the end or trans-verse walls or to some other rigid parts,which in turn must be investigated for theloading imposed by the frame and the in-crements of lateral force due to their ownweight. In Figure 38 is given a diagramaticlayout of a structure-belonging to the groupof buildings under consideration which wlilillustrate all necessary design,operations.Determination and Application of Seismic

Loading-The panel loads ','P" represent allincrements of lateral earthquake forces. Ifthe bracing system is located in an inclinedtop chord plane, the horizontal panel loads"P" are to be resolved into their components,as shown. The vertical component is to beresisted by the pier. The panel load "P" dueto all loads "w" (see explanatory note underFigure 38), is transmitted to. the bracing sys-tem by: direct application." "R'" representsthe reaction of the pier when ,the pieris cons'idered laterally supported at itsfooting and at height", of bracing truss.All seismic forces due to lintel and girderreactions in the wall are transmitted to the. bracing system by th~:agency of the piers.

Stability ,of Present Masonry Piers andSuggestions for Additional Security. Underthe lateral earthquake loading tributary tothe weight of the masonry and the spandrelreactions, the pier 'acts as a beam supportedat its footing and, at height of the' bracingtruss and is to be investigated for bending,shear, and direct compression load. Even ifa statical 'calculation shows the maximumcompressive stress and shear to be withintheir' permissible limits, it is suggested thatthe. piers be strengthened individually, asshown in Figures 39 and 40. The purpose ofthis new strengthening device is to preventsingle bricks and small units of masonry fromsliding out or "pushing through" at lintelseats or at other heavy concentrations. In-visible cracks in the masonry, doubtful bond-ing, the customary type of workmanship, andthe impossibility of determining the qualityand strength of the mortar in each and everycase throughout the entire job, would neces-sitate the strengthening device as a precau-tionary measure, even though not r'1quiredfor purely statical purposes.Recommendations for Reconstruction. 'I'he

reconstruction work recommended for thisclass of buildings is chiefly confined to par-apets, bond beams, strengthening of masonrywalls and piers, and the installation of lateralbracing in the roof truss system.A. Remodeling Scheme Pertaining to All

Buildings of this Group. As shown in Fig.39, parapets, bond beams forming the archi-trave, and strengthening devices of piers arecast as an integral .part, and the reinforcedconcrete pilasters bind all brickwork, lintelseats, and other concentrations in: the piersinto one homogeneous structural unit, Underthe design proposed, parapet walls and cor-nices could not be shaken down by even aviolent quake. By the-use of this design andby careful attention to all details of con-struction, a hazard of serious consequence tohuman life would be-eliminated.B. Buildings with Steel Trusses. Buildings

with steel trusses are in most cases equippedwith sway bracing. These bracings, however,are merely a matter of conventional design.

JANUARY 26, 1934. SOUTHWEST BUILDER ,AND; CONTRACTOR

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-24-

Although they add to the rigidity in the trusssystem, they have usually been found to beeither incomplete in their layout as a lateralbracing truss, or inadequate in the membersand their connections to resist the 'stressestransmitted to them by seismic loading.It is suggested that the present systems of

bracing be completed by rearranging or add-ing members and strengthening their connec-tions for their actual design loads. Wherethis is not feasible, a new bracing truss mustbe installed. Figure 38 presents a methodof bracing which will adapt itself most favor-ably to similar conditions. Horizontal brac-ing trusses must be designed for the panel.Ioads. "P" as illustrated In the p~oblemshown in Figure 38.Various other types of bracing trusses will

be shown in the next issue when details ofdesign and construction will be given andthe adaptability of these types to variousreconstruction schemes will be discussed.C. Buildings' with Timber Trusses. During

investigations it was often found that largetimber trusses over auditoriums, etc., werebadly deformed" their tension rods sl~ckeneddue to shrinkage in timber, and their seatsin the masonry attacked by dry rot, to suchan extent, in some cases, as to render ques-tionable the value of anchors at support andthe shear resistance of the timber. Excessivedeformation of the main trusses often causedcomplete reversal of stresses in the smallertrusses carried by the main trusses, thus put-ting compression into tension members andcausing the latter to buckle, and as a resultthe weight of the roof was actually br?~ghtdown to the ceiling joists. These conditIonsare not the result of earthquake damage, buton the theory that the effect of a quake wavespreads progressively throughout the build-ing until it finds a weakness in the structure,such weak parts are apt to become the causeof failure of some other part of the building.The wooden sway bracing has always been

inadequate, and in its present state it failsentirely to answer its purpose.The attempt to save the wooden trusses by

extensive repair work would be an expensiveprocedure; moreover, any such system ofwooden bracing cannot be depended upon forlateral support, since many factors such asshrinkage, etc., which are beyond the controlof the engineer, enter into consideration. Itis proposed, therefore, to remove the entireroof and ceiling and to replace the timbertrusses by new steel trusses, except in shopbuildings and similar small layouts. Thenew steel trusses are to receive a bracingsystem especially designed to resist lateral'loading and to bind the roof structure to thewalls of the building, giving it an effect ofunit mass against earthquake motion.

Details of DesignA. Bond Beams. Continuous bond beams

of reinforced concrete, functioning as a partof the strengthening device proposed in Fig.39, may at the same time be utilized for cor-nice construction. The additional width willgreatly increase its lateral 'resistance. Thebond beam is to be designed for bending in ahorizontal direction assuming for its span the;ft&tance between the center line of piers.",..,"·'B.'Parapet Walls. Parapet walls are to bedesigned as vertical cantilevers and re,in-forced for their fixed end-moments at thebond beam.C. Pilasters. The pier is to be investigated

as a simple beam supported at its footing andat height of horizontal bracing truss, The

SOUTHWEST BUILDER AND' CONTRACTOR'

loading consists of the increments of lateralearthquake force due'to its one weight actingas uniform load, and the spandrel and lintelreactions acting as concentrated loads at thepoint of their support. Pilasters, if requiredfor statical reasons, should be designed forthe effect of the entire bending and shear,permitting the brick pier merely to functionunder direct 'compression load, Under thisassumption, and by neglecting the direct

compression stress due to the weight of thepilaster, the, proposed strengthening devicesfor the' brick piers shown in Figs. 39 and 40may be analyzed as shown with Figure 41.Special care is to be taken in the design of,the necessary number of keys. .Each key isto be reinforced with stirrups' sufficient toresist the shear stress "T", as illustrated inFigure 41.

(To be continued)

Structural Engineer Author of SeismicReport Pupil of Breslau

The report on "Survey of EarthquakeDamage and 'General Recommendations forRedesign and Reconstruction of PublicSchool Buildings" by Martin Pohl, which isbeing published in Southwest Builder andContractor, has attracted wide attentionamong engineers, technical men and thoseinterested and con-cerned, in construc-tion, and naturallyan interest has beenaroused in the au-thor, concerningwhose experienceand qualificationslittle has been said,the report beingpublished entirelyon its own merits.It is only fair, how-ever, that those in-terested s h 0 u 1dk now somethingabout him.Martin Pohl was

born in Germany,December 6, 1896, c:

and s~cured his professional schooling andfirst experience there, but since Februa~y,1923 has been continually employed WIthpro~inent engineering firms in New y'orkand California and is a citizen of the UnitedStates. Following' the earthquake of March10, 1933, he was employed by the Los AngelesBoard of Education as consulting structuralengineer to study the damaged buildings andpropose methods for redesign and recon-struction. He had previously been employedby the board in 1927 and 1928 as structuralengineer for the design and preparation ofdetailed drawings for auditoriums and otherbuildings.Mr. Pohl is a graduate of Staatsbauschule.

Zittau Technical University, Berlin, where hestudied under Mueller Breslau, foremost au-thority on the "theory of elasticity," underwhose guidance he became thoroughly famil-iar with the fundamentals in design methodsof statically indeterminate structures, such asthe theory of elastic energy, principle of leastwork, theory of elastic curve, area moments,theory of elastic weights, conjugate beams,kinetic theory of structures and slope deflec-tion method. During his entire practice hehas kept pace with the present day knowl-edge and practice in design and constructionof the principal types of structures.His professional experience began as struc-

tural engineer with Beton & Monierbau, Ber-lin, April, 1920, to February, 1923, engaged indesign and supervision of construction of'reinforced concrete arch, slab and girder

-'Martin Pohi

bridges and the Berlin subway extensionthrough Friedrich Strasse. Coming to Los An-geles he was first employed as structural engi-neer by Architect Otto Neher from April,1923, to March, 1926. Then followed a yearwith Noerenberg & Johnson and a periodwith the Los Angeles Board of Education.In May, 1928, Mr. Pohl went to New York

as structural engineer for the Dwight P. Rob-inson Company, making design studies aswell as detail and construction drawings forthe North Boston station building, powerj lants in Rio de Janerio and Honolulu, andseveral tall building frames. The followingyear he was with Lockwood Greer: Engineersin New York city designing structural fea-tures of new airport and office building forAmerican Aeronautical Corporation on LongIsland. In 1930 he was structural engineer ,with Charles M. Rudow, Chicago, =nd in 1931returned to New York to design and detailfor Dwight P. Robinson Company steel struc-American Potash & Chemical Corporationat Trona, Calif.Mr. Pohl states it is his intention to sup-

plent his report on public school buildingslater with practical design problems illustrat-ing the practicability of the theories advancedand the benefit resulting therefrom with re-gard to economy and safety and the method'.:>1 determining the relative degree of rigidity'of various types of framed structures as wellas selid panels.

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Construction on Up-swing AsYear 193 3 Closes

The consecutive monthly gains in construc-tion contracts recorded since July, 1933, werecontinued into December quite ignoring theseasonal tendencies customary during the pe-riod. The contract total reported in Decem-ber by F. W. Dodge Corporation covering the37 Eastern States amounted to $207209500'this was an increase of approximatel; 28' pe;cent over the November total which itselfregistered a gain of almost 12 per cent overOctober. In fact the total for the final monthof 1933 was larger than that recorded for anyother month since October, 1931, and wasmore than 272 times as large as the contractvolume recorded for December, 1932.Of the December contract total $155,862,-

800 was for publicly-financed constructionwhile the remaining total of $51,346,700 wasfor privately-financed undertakings. Public-ly-financed construction contracts during De-cember were almost nine times as large asthe total for this class of work shown duringApril when such construction contracts wereat their lowest point. Privately-financedcontracts let during December w.,.rp higher