Reflections on the Beginnings of Prestressed Concrete in America
ineteen seventy-nine will be the 25-year Silver Jubilee of the founding of the Prestressed Concrete Institute. o Q Q To commemorate this important anniversary, the PCI o JOURNAL is presenting a series of papers on the early history (based on personal experiences and recollections) of Q prestressed and precast concrete in North America. These 0 Qo papers will be narrated by the persons who participated in the o early development of the industry.
Q Part 1 (in the last issue) traced the events that led to the O O construction of the Walnut Lane Bridge and particularly the o significant role that Professor Gustave Magnel played in O Q introducing prestressed concrete to America. O o Q ci Part 2 (appearing in this issue) recounts the major o Q accomplishments American engineers made in launching the Q precast prestressed concrete industry. Q
We believe that these series of articles will not only be o QO fascinating to read but will serve as a historical record of one O L of the most exciting periods in the annals of construction. O oci p O p 0000000000000000000000000000000000 O Part 2 O O O 0 Dynamic American 0 0 engineers sustain 0 0 Magnet s momentum 0 0 0 0 Charles C. Zoliman O Director of Engineering ci Urban Engineers of Maryland, Inc. ci ci Q Q O ci ci ci 0 Q In a free and competitive society such Q as ours, stagnation spells doom. ci (Evelyn H. Harris)
he momentum generated by Pro- • What were the lessons we learned Tfessor Gustave Magnel (culminat- from the Walnut Lane Bridge? ing in the construction of the Walnut • How did Professor Magnel s insis- Lane Bridge) carried across North tence on high quality materials and America. Reluctantly at first, then workmanship ultimately lead to the enthusiastically, American engineers acceptance of steel forms and exter- and contractors learned the neces- nal vibration, the horizontal mixer and high strength concrete? sary skills so as to be able to use prestressed concrete for their struc- • Who was responsible for the de- tures. Then in typical American fash- velopment and subsequent use of stress-relieved wire and seven-wire ion, to maximize the potential of strand, essentially an American inno- prestressed concrete, they con- vation which revolutionized the indus- ceived new construction methods, try? innovated new devices and im- • How did the first pretensioning plant proved existing prestressing tech- come into being in North America and niques. what were the early types of precast How did all this come about? concrete products?
30 • How did the prestressed block beam those early days, the influence of Pro- come about which is also a totally in- fessor Magnel continued to be felt. Re- dependent American development? garding one particular aspect of pre- • What were the events leading to the stressed concrete, the Professor was construction of the Tampa Bay uncompromising, namely, his insistence Bridge, an important structure which on workmanship and the quality of the sustained the momentum created by component materials of prestressed the Walnut Lane Bridge? concrete. • Why was the influence of William This particular point came to light Dean, an open-minded talented pub- dramatically in the spring of 1949 when lic servant with no real preferences, a group made up of those responsible so decisive to the growth of the for constructing the Walnut Lane Bridge young precast prestressed industry? visited Europe to inspect prestressed • How did standardization of bridge concrete construction (see the "After- beams get initiated? math" at the end of Part 1 of this series of papers). The above are some of the ques- Anthony Horst, general contractor for tions for which I will attempt to pro- the Walnut Lane Bridge, asked Profes- vide answers. But more importantly, sor Magnel during a dinner meeting, if it this narrative is an intensely human were possible to attain "zero slump." story reflecting courage, failure, in- With a smile, Magnel answered that ventiveness, coincidences, tragedy he would have liked to specify "minus and triumph. slump" for the concrete of the Walnut Lane Bridge. He continued, "Tomorrow, at my laboratory in Ghent, in your pre- Quality of Materials sence, I will batch no-slump concrete and Workmanship and you will see water coming to the sur- face." And that s exactly what hap- Despite the gradual "Americanization" pened! of prestressed concrete construction in Tony Horst, who was used to "pour-
PCI JOURNAUJuly-August 1978 31 Fig. 1. Wood forms for Walnut Bridge.
ing" 3000-psi (20.7 kPa) concrete with materials must meet relatively high a high slump of approximately 5 to 6 in. strength and durability standards.t] (127 to 152 mm) was duly impressed. [It On the other hand, Horst knew that a must be appreciated, of course, that 30 batching plant at the site of his three- years ago the requirement for a 5000-psi span structure, which could produce (34.5 kPa) concrete on a job site was no-slump concrete, was impractical due extremely rare.] to lack of storage space for raw mate- Horst was obviously in a predicament. rials and working space. To install a How was he going to comply with Mag- batching plant would also be too costly nel s requirement of no-slump concrete? since only a relatively small amount of On the one hand, he was aware that the high strength concrete was needed. professor was uncompromising where An additional consideration was that workmanship and quality were con- Horst realized that if prestressed con- cerned. [Professor Magnel knew from crete, particularly post-tensioning at the rigorous laboratory experiments and site, was ever to get off the ground in the long years of field experience that the United States, he needed the coopera- component materials of prestressed tion of the ready-mixed concrete indus- concrete, i.e., steel and concrete, "work try, which he would obviously receive by harder" (as compared to conventional using ready-mixed concrete for this first reinforced concrete) under high structure. stresses. Therefore, the quality of both Because of all the above consid- erations, Horst had no other choice but to use transit ready-mixed concrete for How appropriate a term for what is usually done at the job the Walnut Lane Bridge even though the site. However, one "pours" soup, not concrete. Quality haul from the concrete plant to the cast- concrete should be "placed." ing site was nearly an hour s drive. Horst tThe concrete should have at least an ultimate strength of realized fully well that he would not get 5000 psi (34.5 kPa), consistently, and the cold drawn wires at least 220,000 psi (1517 kPa). , "no-slump" concrete out of the mixer.
32 rig. Z. Placing reinforcement in wood forms for Walnut Lane Bridge.
To make matters worse, Sam Baxter nal vibrating in addition to internal vibrat- (at the afore-mentioned dinner) re- ing, was imperative. minded Horst that in accordance with This dual consolidation of the concrete the contract, Professor Magnel had the is essential if honeycombs and/or cold last word. No approval from Professor joints are to be avoided. Such vibrating, Magnel meant no approval from the City with high frequency and relatively low of Philadelphiatt and the Professor de- amplitude vibrators could only be effec- manded "no-slump" concrete! tively done through the use of properly Fortunately, Professor Magnel was braced and stiffened heavy gauge steel also an eminently practical man. He un- forms to which vibrators could be at- derstood the problem and eventually tached, permanently or temporarily. agreed to a maximum of 2-in. (51 mm) Preload Corp. had based their cost es- slump on condition "you are going to timates on the use of two sets of wood use steel forms so that, to insure com- forms (see Figs. 1 and 2) for the main paction, you can vibrate the concrete span girders and another two sets for energetically by means of external vibra- the approach span girders. They in- tion ... of course, you will do this in tended to place and internally vibrate the combination with internal vibration." concrete through side windows which This modified provision was not well were to be located slightly above the received by the Preload Corp. (fab- bottom flange of the girder in each panel ricators of the concrete girders). But Pro- between 14 ft 6 in. (about 5 m) on center fessor Magnel was drawing on his long diaphragms. experience in prestressed concrete work. He had learned that with low slump, but high strength concrete for ttQuoting from Baxter s letter to A. W. Horst, June 17, 1949: "Since Professor Magnel was designated in the docu- -beams having relatively thin webs ift re- ments which accompanied the proposal, as the engineer lation to their depth (which makes plac- who would be responsible for this work, I must insist that the procedures and methods adopted will have his ap- ing of concrete difficult) energetic exter- proval."
PCI JOURNAUJuly-August 1978 33 Preload Corp. objected to the use of steel forms because their high costs could not be depreciated with only seven uses for each of the four forms. Very reluctantly and against his better judg- ment, Professor Magnel resolved the impasse, by yielding to Preload s pres- sure. In doing so, however, he predicted there would be trouble and indeed there was! Preload attempted to provide what- ever external vibrating the wood forms could withstand without damage or dis- placement, hoping the less intense vi- brating "would do the job nevertheless." As Professor Magnel had anticipated, the abundance of concrete placing prob- lems throughout the entire concreting job was caused primarily by insufficient external vibrating. Energetic vibrating would have caused misalignment of the forms and would have torn them apart after only two or three uses, requiring the purchase of additional forms. This method would have been most un-
Seven uses for wood forms is very good, but is not suffi- ciently economical for steel forms.
Fig. 3. Placing of concrete in Walnut Lane test girder.
K Fig. 4a. Appearance of Walnut Lane test girder.
economical. Even less intense vibration When the forms were stripped, the sight damaged the forms and maintenance was appalling: honeycombs throughout became greater than anticipated with a the girder, cold joints, displacement of corresponding increase in cost. If this wire units, and reinforcing steel wire additional expense had been considered were only too evident (see Fig. 4b). initially, Preload could easily have af- Unfortunately, attention had not been forded the use of steel forms. It should be mentioned that the plac- ing of 80 cu yds (61 m3) of concrete in the test girder (see Fig. 3) took a full day under the guidance and supervision of a Belgian technician experienced in pre- stressed concrete work. When the forms were stripped, the appearance of the fin- ished test girder was perfect, as can be seen in Fig. 4a. However, after the tech- nician departed for Belgium, the general contractors workers, particularly their superintendent, had taken over placing the 80 cu yds (61 m3) of concrete in the first girder which was to become a part of the bridge. The workers were very proud indeed when they had completed the job, includ- ing the vibrating, in about half the time it took to complete the test girder. But their Fig. 4b. Appearance of first bridge pride and satisfaction did not last long. girder cast (fascia girder).
PCI JOURNAL/July-August 1978 35 paid to the instruction and advice given sibly opening up new opportunities for by the Belgian technician. Eventually, other designers and builders, everyone the general contractors learned how to connected with the job would want to be fabricate a perfect girder, but at great credited and recognized on successful expense and emotional grief. All this an- completion of the project. On the other guish could have been avoided if the hand, if there were any errors or mis- contractors had only followed the good judgments Baxter knew fully well that he advice which they had paid for in the first alone would have to shoulder the blame. place. Eventually, the bridge was completed As is almost always the case when to the satisfaction of all concerned, par- European construction methods have to ticularly the Philadelphia officials. The be reconciled with American construc- high standards of workmanship which tion practices, many problems surfaced Professor Magnel demanded were met, during the actual construction of the though completion of the Bridge went bridge. Fortunately, Samuel Baxter, beyond the scheduled date. The con- Chief Engineer and Surveyor for the city crete did not attain the required strength of Philadelphia stayed on top of the job for prestressing transfer as early as was at all times. With the help of Max hoped for since the slump was gradually Barofsky, his assistant in charge of all increased far beyond the agreed upon 2 field construction, differences were in. (51 mm) to compensate for placing amicably resolved, one by one, at times problems (Fig. 5).t by compromise, at other times with Sam Baxter later analyzed these prob- strong letters. The following is an extract lems. Addressing the First United States from a letter Baxter wrote to the general Conference on Prestressed Concrete contractor: held at the Massachusetts Institute of "The bridge is being built for the Technology, in August of 1951 (attended City, and is being paid for by the City. by over 600 representatives from all The contract requires that methods of segments of the construction industry), procedures, schedules of work, and he recalled: similar items are subject to the ap- "Specifications called for a 2-in. proval of the Engineer (Magnel). We slump concrete (very dry compared have found that several such matters with usual mixes in this country) and of have been started without discussion a 5400-lb strength in 28 days. Placing or approval by us ... I am sure that a dry mix in an I-beam cross section is you and Preload will understand the tough enough, but in this case, it had necessity of following the thoughts ex- to be pushed through a 7-in, web filled pressed in this letter and will act ac- in part with cable ducts for the pre- cordingly." stressing wires. Large voids appeared Baxter felt, and rightly so, that be- in two of the early girders. cause the Walnut Lane Bridge was an "As a result of requests from the imaginative and significant design, pos- field, slump was gradually increased to 21/2, 3 and 31/2 in. This made it easy to place the concrete but led to other dif- `Letter from Baxter to Henry W. Horst, general contractor, ficulties. The 5400-lb strengths origi- October 15, 1949. nally attained in 15 days now took the tMagnel used to tell the story of his visit to the site toward full 28 days. Girder production took the end of construction. There he saw the last girder on its soffit waiting to be stressed. He asked the girder: "Tell me, twice as long, since prestressing could my little friend, why are you not stressed?" And the girder not be started until the concrete had would say, "Well, my dear professor, they put too much attained the required strengths. water in my concrete. I am still too weak and not strong "Next time we will keep a 2-in. enough to be stressed." And Magnet would shrug his slump and find ways of placing it or shoulders. . . and smile. This latter method is what William E. Dean would advocate else, widen the web intentionally in the as discussed later on in this paper. design."t
36 Fig. 5. Copy of original 28-day report of compression tests of concrete specimen. Note date (beginning of project) and the 3-in. slump!
Baxter s keen observation did not, Because there I saw Anderson consis- however, end the controversy of "low tently making zero-slump concrete for slump" concrete. In 1954, Professor his prestressed beams! Magnel addressed a luncheon meeting "So, don t tell me anymore that you of the Concrete Industry Board of New cannot make zero slump concrete, be- York City. He said: cause I have seen it with my own eyes. Of course, you must use what .. I returned yesterday from the we call in Belgium an Eirich mixer, in Northwest where I visited with my other words, a horizontal mixer. That is good friend, Arthur Anderson. And— the only way that you will be able to ladies and gentlemen—Tacoma will make high strength concrete for pre- become famous for a second time! stressed work."
PCI JOURNAL/July-August 1978 37 What caused this outburst (for Profes- duced. Further research showed that he sor Magnel was angry) was that he had could overstress the design working been taken to task by American contrac- stress by about 10 percent, keep it at tors for a statement he had made re- that level for about 2 minutes, and slowly garding the inability or unwillingness of reduce the jacking pressure until the de- Americans to make high strength con- sign stresses were reached. This, in crete. The controversy had gone far fact, is what American engineers would enough to be published in the influential later call "stress relieving." Engineering News Record with the Unfortunately, Professor Magnel s headline: " Americans make soup, not original method of stress relieving was concrete, says Belgian Professor."` cumbersome, time consuming and not Today, manufacturers of concrete always reliable because labor had to be mixers to be used in prestressing plants relied upon with constant supervision, all produce only one type of mixer, namely, of which was very costly. the horizontal mixer! Charles Sunderland, then chief en- In retrospect then, a major lesson gineer for John A. Roebling Sons, Co., Walnut Lane Bridge taught us was that believed very strongly he could improve steel forms and external vibration are upon Magnel s method. In his opinion, prerequisites if sound and economical the desired results claimed by Magnel prestressed concrete products are to be were not achieved. Sunderland was produced. This has been recognized by convinced that only 2 minutes of over- the pretensioning industry which today stressing were not enough and that uses almost exclusively, steel forms and stress relieving belonged in the mill, external vibration. rather than at the job site. Spurred by this challenge, he developed a unique manufacturing technique for stress re- Stress- Relieved Wire lieving wire. Eventually he was able to furnish the site, and later the pretension- Still another major benefit directly at- ing plants, with a stress-relieved wire far tributable to the Walnut Lane Bridge is superior in characteristics than any other the American improvement in the man- prestressing wire produced in the world. ufacture of cold drawn steel wire and the subsequent manufacture of strands Roebling Sons were the first to pro- using such wires. This development duce a wire for the prestressing industry played a decisive role in the future which had a higher ultimate strength, growth of the prestressed concrete in- less creep and other improved prop- dustry not only in North America but erties, allowing for higher working around the world. stresses. During World War II, when Professor Stress-relieved wire was a significant Magnel conducted laboratory tests on contribution to prestressing. In a short the phenomenon of creep, he discov- time, it became the only type of wire ered that the stress losses in the wires, used world-wide for prestressed con- due to creep, were too high at high work- crete. Until that time, the European wire ing stresses. These losses had to be re- manufacturers were selling cold drawn wires "as drawn" not realizing (or perhaps unwilling to admit) the neces- Engineering News-Record, February 25, 1954, p. 23. sity of reducing steel creep in pre- WUnfortunately, John A Roebling Sons Co., was unable to stressed concrete and the importance of capitalize or generate sufficient compensation for its tre- mendous research and development efforts, much less fi- stress relieving at the mill. nancial gain. Other wire producers who did not have these One of the major reasons the test costs to depreciate, entered the market shortly after this de- velopment, and contributed to the firm s demise. girders for the Walnut Lane Bridge per-
38 PCI JOURNAUJuly-August 1978 39 24n nnn
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Fig. 7. Stress-strain diagram of Roebling s stress-relieved wire as used for Walnut Lane Bridge. (Note: Tensile test on 0.276-in. diameter high elastic limit wire; coil No. 28; 80D stock; Heat 2: 5068; from 10,000 lb production lot for Preload Corp.; June 16, 1949.)
formed so well was the use of Ameri- originally were designed for the can-made wire with improved charac- European-made wire having less desir- teristics (see Fig. 7). These girders able creep characteristics.
40
Fig. 8. Typical machine made concrete blocks as used by Ross Bryan for block beams. Block A: terminal end block at live end of beam; Block B: Standard unit; Block C: Positioning block; Block D: Special grooved end block at dead end of beam.
stranded galvanized cables and fittings Prestressing Machine- as shown in Figs. 9a and 9b.2 Prefabri- Made Concrete Blocks cation would keep site Work to a minimum and hence, lower costs. Totally independent of the events sur- Block A in Fig. 8 is the typical live end rounding the Walnut Lane Bridge, Ross terminal unit. Block B is a standard unit; Bryan, consulting engineer in Nashville, Block C, the positioning unit, and Block Tennessee, conceived the idea of D, the special end block unit having prestressing machine-made concrete grooves in the two side faces and in the blocks (see Fig. 8). 1 This was accom- end face. The construction procedure plished with the aid of factory-made was then to anchor the tensioning cable stressing units such as Roebling s with standard fittings in the terminal end
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PCI JOURNAUJuly-August 1978 41 Fig. 10a. Erection of block-beams hauled 176 miles from fabricating plant to erection site, Obion County, Tennessee (about 1950). unit; to place the cable in therecess was cast between them which embed- outside the line-up standard units; and to ded and bonded the stressing units. wrap the cable around the special end A cast-in-place concrete wearing sur- unit, thereby eliminating two end fittings face would complete the structure at one end of the beam thus formed. erected with a minimum of skilled field Tennessee s Highway Department labor. erected beams made this way for spans C. L. Johnson, partner in the consult- up to 50 ft (15 m) for secondary road ing engineering firm of Johnson and An- bridges (Figs. 10a and 10b). After plac- derson, Pontiac, Michigan, approached ing the beams side by side, concrete the same problem in a slightly different
Fig. 10b. Completed three-span block-beam bridge in Tennessee.
42 OD ti M N
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Fig. 11. Typical machine made blocks as used in Michigan area. Only three kinds of blocks are required to make up a Michigan block-beam.
manner. Typical I-shaped blocks as Of particular interest are the joints shown in Fig. 11, were stamped out on a (see Figs. 11 and 12) which are poured Besser machine in a block plant. At the instead of butted, with a rich grout in its left of Fig. 12, the position block is small lip or bead cast around the edge of shown; at the center is the typical block one race of the block. Better control of and at the right, the end block. the total length of the girder was insured.
Fig. 12. Typical Michigan area blocks as produced by Besser machine.
PCI JOURNAL/July-August 1978 43 TUBES TO BE PLACED NOTE : BEADS MAY BE REVERSED AROUND G.B.S. TO
o wn ^ I MPUJMrcuILLU uirw .r CUNGRETt IS NUUKtu Fig. 13. Michigan block-beam as made up before stressing.
FINISHED GIRDER Fig. 14. Michigan block-beam as made up after stressing.
Fig. 15. Testing of Michigan block-beam with 1.5 live load.
44 Fig. 16a (top). Erection of typical block-beam in Michigan.
Fig. 16b (bottom). Close-up of block- beam during erection showing post-tensioning wire unit.
It was also speedier and more economi- 15 illustrates a load test and Figs. 16a cal than a troweled mortar joint, per- and 16b show the erection of such a formed by unskilled labor. Fig. 13 is a block-beam. line drawing of a girder assembled while However, with the advent of the pre- Fig. 14 shows a completed girder. Fig. tensioning plant and the stranded ten-
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Fig. 17. Typical precast concrete channel slab as used around 1950 in Pennsylvania. dons (as will be explained further in this m), primarily because deflections be- article), the prestressing of factory-made came excessive beyond that span length concrete blocks fell into disuse and was for highway truck loadings and also be- eventually replaced with the more cause of lack of transverse rigidity of economical Florida-developed double channel slabs. Petersen and Baskin tees and California-developed single tee realized that if they were to survive in a panels which have a greater load competitive market, they had to extend capacity with greater span possibilities the spans to 50 ft (15 m) at least, and if and more versatility. possible, beyond that. The concrete block development is They found their answer in Great Bri- mentioned here for its historical interest, tain while visiting a pretensioning plant for the skill, ingenuity and talent shown near London. Here they observed the by Ross Bryan and C. L. Johnson who precasting of small products (such as had a pioneering spirit of their own. building joists, planks) using 2 mm It should be recognized that while (0.076 in.) diameter piano wires—"toys" Bryan s bridge was the first prestressed as Professor Magnel would say. Magnet bridge completed in the United States, it always thought in terms of large struc- was a block bridge for secondary roads, tural members having to carry heavy while the Walnut Lane Bridge was the loads. first large girder type bridge on a main After this visit to the British plant, city parkway. Thus, both bridges could Petersen and Baskin were convinced be considered as firsts in their own right. that plant-produced pretensioned beams In passing, it should also be men- (as opposed to the post-tensioned tioned that Ross Bryan played a major beams Freyssinet and Magnel were ad- role in getting some of the early preten- vocating) were the answer to their spe- sioning plants started. cific problem. This was the "answer" provided, of course, they could practi- cally and economically resolve three Plant Produced major foreseeable problems, namely: Pretensioned Members 1. Rigidity of the member 2. A suitable anchorage system Among the members of the group who 3. An efficient prestressing wire travelled to Europe with Sam Baxter in May, 1949, were Robert Petersen and 1. Theoretically, the first problem Ben Baskin, president and chief en- could easily be resolved by adding a gineer, respectively, of the Concrete bottom slab to the legs of the channel Products Co. of America, Pottstown, (Figs. 18a and 18b) so as to shape a Pennsylvania (about 35 miles northwest monolithic cross section (Fig. 18c). A of Philadelphia). Officially, they went box-like beam having the required stiff- along for the "ride," but in reality, they ness and transverse stability was ob- had a serious problem on their minds tained and, thus, the problem of rigidity and hoped to find the answer in Europe. could be solved. As astute businessmen, they kept the But how would they form the inside problem to themselves. But first, a little faces of the box? At that stage of de- background. In 1947, Concrete Products velopment, they could not find the an- began producing, under controlled con- swer. They decided, therefore, to use ditions and rigid state inspections, pre- cardboard sonotubes and the cross sec- cast concrete channel slabs (Fig. 17) for tions shown in Figs. 19a and 19b re- secondary bridges for Pennsylvania s sulted. State Highway Department. The spans, The former section (Fig. 19a) was ca- however, were limited to about 36 ft (11 pable of carrying H20-S16 truck loads
PCI JOURNAUJuly-August 1978 47 _H.
z W N
6 24 I6"4 36°
(a) Channel Slab + (b) Bottom Slab = (c) Box Girder
Fig. 18. Logical development from channel slab into box girder.
Note: This section is used for members having clear spans from 18 to 36 ft; for spans from 18 to 28 ft the depth is 17 in. and the diameter of the holes is 10.5 I I in. For clear spans from 30 to 36 ft the depth of the { members is 21 in. and the holes, which extend to i...... ...... ^:.a. within 2 ft of the ends, are 12.5 in. The width of all members is 3 ft. The number of steel cables, 0.25 in. in diameter, ranges from 27 to 76 for clear spans from 18 to 36 ft.
Fig. 19a. First design of box girders for short spans using sonovoids (1950).
for spans from 18 to 36 ft (5.5 to 11 m), the latter (Fig. 19b) for spans ranging from 38 to 50 ft (11.6 to 15.2 m). The standard width for both was 3 ft (0.91 m). The depths were 17, 21, or 33 in. (432, 533, or 838 mm) depending on the span. The cost of forming was reduced to a minimum, being limited to exterior side forms. r:ji.I. Concrete Products eventually found an elegant solution to their "inside forming" riddle. The procedure Ben Baskin devised was simple and ingeni- Note: This cross section is for pretensioned pre- ous, 3 as we all know today. However, for stressed concrete bridge members, for clear spans several years, it remained a closely from 38 to 50 ft. The number of steel cables, each 0.25 in. in diameter, ranges from 48 to 80—de- guarded secret. At that time, Concrete pending on the span. The width of all the members Products competitors could not fathom is 3 ft and the depth is 33 in. The diameter of the hole, which extends to within 2 ft of the ends of each how it was done. Of course, the "secret" member, is 24.75 in. eventually leaked out and the box girder became, and still is today, a very popu- Fig. 19b. First design of box girders for lar, useful and practical pretensioned long spans using sonovoids (1950). product employed throughout North
48
America and elsewhere. Further refine- Dr. Arthur R. Anderson who later built ments allowed spans to be increased to his own plant in Tacoma, Washington. 100 ft (30.5 m) and even beyond, with The successful load testing of this transportation and erection remaining as beam was a tremendous, innovative the only problems to be solved. achievement. This development set an 2. The next problem was to find an example which put into motion the economical, temporary anchorage to forthcoming pretensioning industry. hold the stressed wire to the stressing It was not long after the casting of the bed. Ben Baskin was able to produce an first pretensioned box beam sponsored inexpensive sleeve-type device which by Pennsylvania s Dept. of Highways, could be swaged readily onto the wire that • an elaborate testing program on holding the stress induced in the wire. full-sized box beams was initiated at This device was to be the forerunner to Fritz Engineering Laboratory, Lehigh the strandvise now used universally University, Bethlehem, Pennsylvania. throughout the industry. Under the direction of Dr. Carl Ekberg, Professor at the Civil Engineering 3. The last problem was the most dif- School and Professor William J. Eney, ficult one to solve. It was not practically director of the Fritz Engineering Labo- feasible to use a great number of piano ratory, and head of the Department of wires to take care of the large prestress- Civil Engineering and Mechanics, the ing forces required by the superim- program was to last for several years. posed loads produced by the heavy From this test program numerous test AASHO (today s AASHTO) truck load- reports and papers were published ings. Unfortunately, the use of larger di- which provided an extremely valuable ameter single wires was not a viable source of reference material.5 solution because bond requirements As a direct result of these tests and could not be satisfied with such wires. In their publication, in 1955 the Pennsyl- desperation, Ben Baskin turned to Wal- vania Department of Highways approved ter O. Everling, Chief of Research for the use of prestressed box girders for six United States Steel. Prodded by Baskin, bridges over the Vine Street Expressway Everling came up with the stranded in downtown Philadelphia. This project seven wire unit! was the first large-scale application of Bond tests were subsequently con- box girders in the United States. A total ducted on the t/a-in. (6.35 mm) diameter of 570 girders were required. Of these strand (made up of seven smaller wires) 553 were 48 ft long (14.63 m) (Fig. 20a), and these were, indeed, successful. 26 were 60 ft long (18.3 m). Some of Baskin then built the first pretensioned them (Fig. 20b) required up to 94 - 3/s-in. bed in North America, between 1949 (2400 mm) diameter strands producing and 1950. The bed length was 120 ft an initial prestressing force of 1128 kips (36.57 m). During the spring of 1950, he (5020 kN). This was a tremendously produced the first American preten- large pretensioning force to cope with in sioned bridge beam having a span 1955. length of 30 ft (9.14 m), a width of 3 ft In summary, then, to Concrete Prod- (0.914 m) and a depth of 17 in. (432 ucts of America goes the credit for mm), on his new stressing bed. having built the first pretensioned bed, The beam was successfully tested to destruction at the plant in Pottstown, in addition to his many other accomplishments, Dr. Arthur Pennsylvania, on May 20, 1950, in the R. Anderson was responsible for the instrumentation on the Walnut Lane Bridge test girder. presence of many State and City Public Works officials. The testing was done "In the early 1960s, about the time both Petersen and Bas- kin retired, the plant was sold to the American Marietta under the direction and supervision of Corporation.
PCI JOURNAL/July-August 1978 49
"2" 12" 6 3 3 6° 3° 3" 6
8 STRANDS 1.H
N
•I I ^ I• cr cV fV 2 STRANDS 1 2 ° 3" 14 S PA. AT 12 = 6 STRANDS „ 21 STRANDS 3 -0 ^ 11/,2
Fig. 20a. One of box girders for Vine Street Expressway in Philadelphia with fifty-eight ^-in, diameter strands with force of 698 kips (1955).
9" 6 SPA. AT 3"-- I -6° 9" 7STRANDS
STAND. 4 /2 I FIBRE DUCTS N H TYPE I - w ORANGEBURG B1. -o ST D. OR EQUAL =
III 2 QI- A-- TYP. H O1 1 ^. N N1/ OD . a .k_,. N >- ^ d N O N I5 STRANDS 24 SPA. AT 1^^2 =3 O" 19 STRANDS 3 -0" 23 STRANDS
Fig. 20b. One of box girders for Vine Street., xpressway in Philadelphia with ninety-four ^-in. diameter strands with force of 1128 kips! (1955).
50 ,i7 ))1PETERSBURE119 ST. t PORT TAMPA
•• •
PRESTRESSED CONCRETE TRESTLE SECTIONS ^J TOTAL LENGTH: 17,424
rJ GULF OF MEXICO
LOWER TAMPA BAY BRIDG PRESTRESSED CONCRETE TRESTLE SECTIONS TERRA CEIA IS EMBANKMENTS T^ J • • • • PINEY POINT FERRY ^J
o I 2 PALMETTO 541 APR SCALE-MILES Fig. 21. Location map of Lower Tampa Bay Bridge.
for having produced the first box girder known as the Sunshine Skyway. This as a logical extension of their precast crossing connects the city of Brandenton channel slab and for having been the to St. Petersburg, Florida (Fig. 21). driving force behind the development of This project had laid dormant for sev- the stranded wire. This important inno- eral years since bids taken around 1946 vation was to become the basic element exceeded the allocated budget. The which made the pretensioning industry proposal was to construct a 17,500 ft possible, practical and economical in (5334 m) trestle bridge calling for pre- North America. cast reinforced concrete units (Fig. 22) having spans of 36 ft (11 m) and a total width, out-to-out, of 37 ft 5 in. (11.4 m), William Dean s including curbs (see next page).. Influence Preload surmised that in using pre- stressed concrete, the 36 ft (11 m) span During the early construction stages of could, perhaps, be increased to 48 ft the Walnut Lane Bridge, the Preload (14.63 m) without appreciable increases Corp. learned of the revived plans by in concrete quantities for the super- Florida s State Highway Department in structure. At first sight it appeared Tallahassee, to construct the proposed (and the actual construction later con- Lower Tampa Bay crossing later to be firmed that assumption) that substantial
PCI JOURNAL/July-August 1978 51 37511 out to out 41821 — 281 roadway— 4 81"2 319 1 11" Symmetrical about t— White cement concrete curb /}f _ In lolr 7Z slab min. Slope 1. per ft—.,
N TNN m
Flacks centered on end diaphrams for setting deck on, .. pile cap .-- ^.. 1 427 lit 2 9g" 1l9d I 8 0411 1191 -5111- g lO" 3911. 3 911_4.._ 21 4,__-_ 5110 2l Half section at half point Half section at pile bent Fig. 22. The original precast reinforced concrete trestle for the Lower Tampa Bay Bridge consists of a precast deck divided along center line into two identical sections. The deck is erected on four-pile precast concrete bents spaced 36 ft on centers. For contrast see Fig. 25.
savings could be achieved in the sub- repetitious and identical spans?] Ed structure of the entire structure. If a pre- Thwaits and I left on a Sunday night in stressed concrete design were used, April 1950 for Tallahassee to keep the only three pier bents would be required Monday morning appointment. to span the 144 ft (44 m) distance be- The reception we received, while very tween tower bents whereas four pier polite, was cold indeed. Bill Dean s bents would be needed for the precast comment, "I have gone sour on pre- design. This scheme would save one stressed concrete," put us into a state of pier every 144 ft (44 m) in approximately shock. Fortunately, Ed Thwaits kept very 17,500 ft (5334 m) of trestle. calm. Always the suave and smooth dip- Ed Thwaits, Preload s Vice-President lomat, he replied: "We are very sorry and sales manager, and I arranged to that you feel that way and, I guess, there meet with William Dean, Chief Bridge is not much that we can do about it. Engineer for Florida s Highway Depart- However, since we are here, perhaps ment, to explore the possibilities of a you would like to look at some photo- prestressed concrete design substitu- graphs we have on the construction of tion. Preload would cover all design the Walnut Lane Bridge." costs but then could hopefully collect Being the congenial Southerner, Dean subsequent earnings produced from an- could not very well turn us down. In- chorage royalties. deed, we had come all the way from We were all exuberant with high New York. We proceeded to show him, hopes and expectations [after all, how and to elaborate on, the photographs. often do you have 17,500 ft (5334 m) of Dean, through his questions, appeared to warm up to the subject as we pro- gressed with the photographs. At what •William Ennes Dean was born on November 15, 1909, and died December 30, 1965. He retired from the Florida State we thought was the opportune moment, Road Department in 1962 after 30 years of distinguished Thwaits mentioned to Dean that we had service. brought a short film on the construction tThe Sclayn Bridge has two 205-ft (62.5 m) spans with a maximum depth at each midspan of not more than 6 ft 8 in. of the Sclayn Bridge in Belgium,t the first (2 m). continuous prestressed concrete bridge
52 to be built in addition to being the longest. Would he and his staff be in- terested in seeing it? Dean s face brightened. "It so hap- pens that tonight the local ASCE chapter holds its monthly meeting at the Naval Base, and we do not have a speaker. N 545 5 Perhaps, Mr. Zollman would care to be o N the speaker, talk about the Walnut Lane Bridge and show the film." We not only jumped at the chance but also offered to take care of the refresh- ments for the "happy hour" which usu- ally followed such meetings.
The evening was a memorable one 4" and in retrospect I believe it proved to be decisive in swinging Bill Dean over to Fig. 23. Cross section of Tampa Bay the proposed prestressed bridge. beam as designed by the author while During the evening, beginning with a staying in a Tallahassee hotel. The sociable dinner attended by Dean, his beams were later cast in a yard near the principal assistant, Tom Jennings, Ed bridge site. Thwaits and myself, an atmosphere of mutual trust, respect and confidence de- veloped. These mutual feelings, despite time, cordial, smiling and in excellent the diverse background of the partici- spirits. The subject of the bridge was pants, were to last until Bill Dean s un- discussed and Thwaits suggested that timely death at the relatively young age could develop (while in Tallahassee) a of 57. preliminary design and analysis for a It was during this dinner that Dean, typical span of his bridge—and roughly who had the highest regard for Hardy estimate the cost for such a structure. Cross (the greatest American engineer For the balance of that day and evening in Dean s opinion) discovered that I had I worked in my Tallahassee hotel room been a student of Cross s." Well, that did with a pocket-sized slide rule,t to de- it! My "stock" went up sky-high with termine an economical span and an ac- Dean and with it, the prospects for the ceptable I-beam cross section. prestressed design. The next day, we submitted our sug- I believe that the technical presenta- gested I-beam design (Fig. 23) to tion I made at the local ASCE meeting Dean together with our supporting com- was well received (Fig. 24) as were the putations. Dean seemed to be satisfied. refreshments. Dean was the hero of the He did not find anything wrong on a evening. Not only had he saved the day quick check but asked whether he could by finding a speaker on such short keep the computations. I gave him the notice but he found one that provided originals (there were no Xerox machines refreshments for a meeting expected to be dull. Instead, the evening was most This incident is mentioned here only because one never congenial and successful (no mean feat knows how an incidental remark can greatly influence a serious decision-making process! in a dry county!) tMagnel s philosophy was that in view of the many assump- tions an engineer has to make, the accuracy obtained in Tampa Bay Crossing using a pocket-sized slide rule was more than enough—if an engineer thought he needed a full-sized slide rule, he The day following the meeting, was not much of an engineer. Naturally, Magnel always Thwaits and I faced another Dean, this used a pocket-sized slide rule.
PCI JOURNAUJuly-August 1978 53 MEM6ZR8: C AL A. MAThA 0-tsADav tL,e., rLA k SNAIFk J_ OLOV CR TAYLO IA£K14NVi 1., —, kA.f9.^.... _ •^ syv A' A MARION Gi- NON PAAAM.A A tY, V A. I4 "o MERRILL R. DAR08R Y6^ -a eKe-w, xth. J Tt STATE ROAD DEPARTMENT OF FLORIDA TRUSTER , RA ¢. SR. 4CAMA, FCA. TALLAHASSEE April 12, 1950 V
Mr. E. B. Thvaits Vice President The Preloed Corporation 211 Fast 37th Street New York, l6, N. Y.
Dear Mr. Thv its: s The Navy Reserve personnel and all of,Engineer guests enjoyed and appreclat- ed the program which you end Mr. Zollman presented on your last trip to Talle- bassee. All persons who were privileiged to see and hear it have expressed a desire to be present at another program along the same lines and on the same subject.
Captain Jams D. Wilson, District Civil Engineer for the Sixth Ravel District has stated that he will make every effort to be present at any future programs we arrange and sponsor which are as essential to the progress of construction and engineering as the one which you presented to us. I am convinced that the Itavy Civil Engineer Corp will welcome the opportunity to sponsor your program wherever they have a Regular or Reserve Organization.
Mr. Dean has advised me that you and Mr. Zollssn will probably be in Tallahass sometime during the month of May, 1950. if yuu wish to put on another program at that time we will be glad to sponsor it and make the necessary arrangements for advertising and for a place to accommodate the turnout we could have. It is expected that we could have approximately sixty engineers and construction men present, if given time to do the necessary advertising.
With two weeks notice we can schedule the program on a date to suit your convenieece ,
Yours truly,
?. E. Arnow cc: Captain James D. Wilson Dist. Civil Engneer
31 511 out to out 4 8Zr —14+ 141 4181 ¢ gu 3+-^ Crown of roadway I In { 311 Condwt Whlte cement concrete curb 6q+ slab, I e 1011 --- Drip
I Cement/i ! + ntwmediatw 1 0►. A •- t I mortar joint transverse T Top of1 r 6^^ ^j 611 ! l luo hole for 1 11 stiffener
pile cap 7n ju 6n 21, Expansion plates 4 Macalloy bar ^ ai tMrd po+nts I 6 - 6 --- (, 61--►1+--- 6r Halt secuon at expansion end Half section at third point
Crown of roadway v to Vanes 1" open joint
i1
- 1 I ti^Q 1 1 •$II ^F 7 V 411x21^x141+ I I 1! key
Note: The prestressed concrete trestle consists of six 48-ft I-shaped stringers supported on concrete pile bents and carrying cast-in-place deck. Pre- stressing is in stringers and is provided by three 1- in.-diameter British-made Macalloy bars.
Fig. 25. Typical cross sections of prestressed concrete superstructure and elevation of prestressed beam for Tampa Bay Bridge (for contrast see Fig. 22). Note that this was the first use of the Lee-McCall system of prestressing in the United States.
in those days!) and returned to New self that prestressing was a sound con- York puzzled and wondering what the cept after all and had kept the door open next step would be. Two days later, the for further discussions. Many meetings mail brought us not only the computa- followed between Dean and the con- tions I had made but additional compu- sultants to the State of Florida, namely, tations for deflections, camber, cracking Parsons, Brinckerhoff, Hall Mac- load, ultimate load (the whole bit) in Donald. These meetings resulted in the Dean s handwriting on standard yellow bridge cross sections shown in Fig. 25. paper. Apparently, Dean had convinced him- `Now known as Parsons, Brinckerhoff, Quads and Douglas.
PCI JOURNAL/July-August 1978 55 developed and completed for a pre- stressed design much like the one I had developed that day in the hotel in Tal- lahassee. The difference was that the Lee-McCall bar and anchorage stressing units were used instead of the Blaton- Magnel system. (Preload had acquired patent rights for both systems.) Bids were taken in 1951 for the Tampa Bay Crossing and included a rather elaborate program for the testing of full-sized members. The construction of that bridge cross- ing sustained the momentum initiated by the Walnut Lane Bridge and is de- scribed in detail by Maurice N. Quade of Parsons, Brinckerhoff, Hall Mac- Donald in his paper "15 Mile Toll Bridge Under Construction Across Lower Tampa Bay," appearing in ASCE s Civil Engineering. s "Tests Establish Construction Proce- Fig. 26. Typical Tampa Bay beam dures for Prestressed Beams in Tampa in storage yard. Bay Bridge," written by Dean appeared in a following issue of Civil Engineering.8 (Fig. 26 shows a beam in the storage For Bill Dean it was a momentous de- yard not too far from the site, later used cision, the effect of which was to be felt for this bridge.) for many years throughout the entire That first meeting in Dean s office construction industry. And why did he marked the beginning and was a make that decision? After all, as a civil catalyst for the dynamic growth of pre- servant of the State of Florida there was stressed concrete in Florida. Dean s no immediate nor long-range monetary account of the meeting is of value and return to be expected. All he could ex- can be found in the fourth and fifth para- pect was criticism from entrenched ves- graphs in the closing paper he gave at ted interests in other construction mate- the First National Prestressed Concrete rials and construction problems galore Short Course held at St. Petersburg, since, except for the Walnut Lane Florida, October 10-12, 1955. Bridge, there was no other structure of The course was cosponsored by the the magnitude of the proposed trestle. newly-formed Prestressed Concrete In- He was not disappointed in either. But it stitute and the University of Florida, De- did not faze him as he was, if not some- partment of Civil Engineering (see Fig. what conceited, certainly a competent 27). and above all a fearless engineer who At this course six memorable papers had the courage to base his decision were presented. 9 Of particular interest is solely on the merits of the material. Bill Dean s closing paper on the "Out- There could not have been any other look to the Future of Prestressed Con- justification. crete." Even 23 years later, Dean s Eventually, contract documents were presentation is thought provoking. (Note: Dean s paper is reprinted in the Forerunner of the Stressteel bars. Appendix.)
56 NATIONAL TRESSED CONCRETE. SHORT COURS
OCTOBER 10, 11, and 12, 195
Co-sponsored by
The DEPARTMENT OF CIVIL ENGINEERING (as a public service function of the Engineering and Industrial Experiment Station) and The PRESTRESSED CONCRETE INSTITUTE
PytY a The First National Prestressed Concrete Short Comae will offer an exceltentopportunityfor the 2^ ^ y practicing and student engineer to become familiar with the theory and design of prestressed, concrete structures. You will have a chance to meet and hear outstanding engineers. The r course will give you an outlook on the tremendous future of prestressed concrete. E N
• PROGRAM. The first two days of the Short Course will be devoted to lectures encompassing a review of beam theory, basic theory of prestressing, prestressing methods, materials used in prestressed concrete, post-tensioning and pre-tensioning, design of simply supported beams, design of beams having variable cross sections, etc. There will be design sessions where registrants will have an opportunity to design both simple and complicated structures. Each class will be limited to 50 registrants in order to permit personal supervision.
a The third day will be devoted to papers, movies and slides presented by outstanding engineers in the field of prestressed concrete. Various topics involving materials, design, manufacture, present use and future possibilities of prestressed concrete structures will be discussed.
• An optional field trip to one of the casting yards in the area is also being planned to acquaint the registrants with the manufacturing methods being employed in the production of prestressed concrete products.
• LOCATION: Due to the large number of engineers expected to attend this Short Course, the classroom facilities of the University of Florida and accommodations available in Gainesville would not be sufficient on the dates indi- cated. It is therefore planned to hold the Short Course at the Maritime Base, St. Petersburg, Florida, where facilities to accommodate the expected registration are available. Moreover, the city of St. Petersburg has ample hotel and restaurant facilities at summer rates during the time the course is to be held.
\\ \ I t //// FEES. The registration fee will be $25. 00 for the three-day period. This will include box lunches for the three days and possibly an evening picnic.
HOTEL RATES are from $2.50 to $4.00 for single rooms, and $5.00 to $10.00 for double rooms. It is also possible for uni- versity students to stay in dormitories located at the Base for $1.00 per day.
.. ^ ='-_ The limited size of the lecture sessions will, to turn, limit total attendance. It will therefore be necessaryy to register in advice. Details of the program and final registration cards will be sent to allpatwm Indicating their interest by returning the enclosed self-addressed card as soon as possible.
Fig. 27. Flyer advertising PCI s first national prestressed concrete short course.
PCI JOURNAUJuIy-August 1978 57 Fig. 28. Bill Dean and the author together at the 1955 PCI Course in St. Petersburg, Florida. During Dean s last years his eyesight was failing.
Fig. 28 shows a picture of Bill Dean Standardization of and me taken at the 1955 PCI Course in Bridge Beams St. Petersburg. The design and construction of the By 1955 much had happened in Tampa Bay bridge had a tremendous Florida (and throughout the United effect on Dean. He learned, the hard States) since the day Dean first became way, that the thin minimum cross section interested in prestressed concrete. In a of the beam used for the trestle, which letter to me he wrote: was patterned after European practice, .. In the past 5 years our pre- was not suited to American construction stressed practice has expanded to practice. proportions far beyond our anticipa- These thin beams (Fig. 29a) were in- tions. We now have a dozen simul- viting underflange cracking which was taneous projects underway with pre- hard to control. The logical corrective stressed spans. Prestressed piles and measure was to "fatten" up the other small parts are regular construc- member. 10 In this fashion, the beam tion items ..." shown in Fig. 29b came about and was That was an understatement. Indeed, subsequently used on other Florida tres- shortly after our first trip to Tallahassee, tles. The increase in concrete material Bill Dean met Harry Edwards, a con- was negligible but the benefits substan- sulting engineer who had moved from tial. the north to Lakeland, Florida, and be- The philosophy of "stubby" beams tween the two of them—well, Harry Ed- rather than "skinny" beams (theoretically wards will tell the story as it happened, equally structurally sound) was best ex- in his own words, in the next article in pressed at the time when bridge beams this series. were being standardized for highways. About the time Dean became Chair- 1 was Chairman of PCI s Technical Activities Committee man of the newly formed Joint (TAC) in 1957 and had asked Dean to serve as Chairman of the Bridge Committee. AASHO-PCI Committee, the Federal
58 ^N Under Flange CracLing T:4
^ NI N
T
14 I ,-I
Fig. 29a. Typical underflange cracking Fig. 29b. Revised Tampa Bay girder as which at times occurred in originally used in subsequent structures. designed girder.
Bureau of Public Works (BPW) was girders for the Arroyo Seco Pedestrian ready to publish "Standards, Pre- Overpass at 110th Street in Los stressed Concrete Beams for Bridge Angeles, California. Spans 30 to 100 Feet." They had de- This overpass became the first pre- veloped detailed "skinny" beams mod- stressed concrete structure on the West eled after the European concept of Coast. The resident engineer on that beams. Dean courageously convinced project was Ted Guttl who had pro- the BPW of the unsoundness of their duced the detailed engineering drawings "Standards." They never were pub- for the Walnut Lane Bridge. lished, thus averting what would have The adventures of Gutt in the Midwest been a disaster for the young precast and on the West Coast in connection prestressed industry. with prestressed concrete should make for exciting reading rounding out the story of prestressed concrete s de- Prestressed Concrete velopment in the East, South, Midwest Spreads Across U.S. and California leaving it to Arthur Ander- son to tell of the developments in the Meanwhile, with prestressed concrete Northwest. applications thriving in Florida and In other developments, Tulsa, Ok- through the South, the Midwest was also lahoma, contractor Percy F. Blair and his developing applications. The newly father modified the button anchorage formed Prestressed Concrete Corpora- tion,l- headquartered in Kansas City, Now called the Federal Highway Administration Missouri (mid-1950), had developed a tAt the time, I was Chief Engineer for the Prestressed Con- new post-tensioned stressing system crete Corporation. using the "button-head" as the basis for Ted Gutt is presently chairman of PCI s Plant Certification anchorage. This system was used for Committee and an Assistant Vice-President of the Pre- stressed and Architectural Concrete Division of the Tanner the first time for two 110-ft (33.5 m) span Companies in Phoenix, Arizona.
PCI JOURNAL/July-August 1978 59 Bridges; the casting of 26,000 channel slab panels [shaped 5 by 19 ft (1.52 by 5.79 m)] in 140 concrete molds in 190 days in Albany, Georgia, for the United States Marine Corps warehouses; the advent of the headed wire; and many other facets of concrete work. Travelling through the United States, made slide presentations on prestressed concrete at meetings of many local ASCE Chapters and other professional Fig. 30. Testing of soffit beam made up societies. I had the pleasure of par- by masonry blocks (Tulsa, Oklahoma). ticipating as guest speaker in a variety of symposia held at several universities, colleges and conventions. And finally was able to contribute to the work of system using nuts instead of plates and various technical committees. cast and erected the first precast pre- Above all, it was my good fortune to stressed concrete buildings in the Mid- have known and worked with such west in Tulsa, Oklahoma, on designs dynamic men and outstanding engineers had made. (Fig. 30 shows the testing of as Professor Gustave Magnel and the anchorage on a soffit beam made up William E. Dean. Even with diverse by masonry blocks.) backgrounds, they had much in com- mon. Closing Thoughts On the one hand, the international, cosmopolitan, amiable and good natured The late 1940s and all of the 1950s Professor Magnet could travel anywhere were exciting, fascinating and gratifying in the world and would be received by a years for those involved in concrete delegation of former students. He was construction and wanting to meet the an outstanding engineer whose main challenges. They were years of pre- interest was education although he felt casting, prestressing, high strength con- testing, actual field practice and experi- crete, admixtures, vacuum concrete, ence were essential to verify his steam curing—one greater challenge theories. He was at home with royalty after another. (tutoring Prince Baudouin of Belgium I was in the midst of it all: the prospect who later became King ) but equally at of the Walnut Lane and the Tampa Bay ease with the penniless student who was looking for help (and which the Professor gave liberally). When prodded, Magnet would tell us with a chuckle of the times the Palace limousine would call on Saturday mornings On the other hand, Bill Dean was the to deliver him to the palace for tutoring. He would wear, ac- public servant, the impetuous South- cording to protocol, a cutaway suit with high. hat. It sounds incongruous in this day and age, but that was the way it was erner deeply in love with the South and done. Magnet had a very close rapport with King Baudouin ready to fight the Civil War all over and he intended to dedicate his prestressed concrete televi- sion and observation tower that he was designing to the again.t He was a cautiously coura- King. Unfortunately, death overcame him before construc- geous man with daring and vision whose tion began and the prospective tower died with him, as he only ambition was to design and build was the driving force. better engineered structures. tThose who attended the San Francisco World Conference in 1957 will still remember, no doubt the loud rebel yell He was, also, a modest professional booming through the banquet hall when the band started to engineer who refused nomination by the play "Dixie." The Soviet delegation sat at his table. They could not understand it—of course they could not! Florida ASCE Chapter for the Ernest E.
60 0 AREA= 814 IN2.^ 0C- GALIPEAULT 3^6 AASHO BEAM STANDARDS BRIDGE BEAM l`i 11%x," 1%t 7" 1SL 11)4." z Sca.1e: 3/411 1-O" Iz C U CD D ? CD 0 AREA=7891rrjz 0C AREA=5601tv2 CD CDC m a 1 C.9 AREA= 369 IN
m ^ 0) AREA = 276 4•N ^ AASHO CD t2,. ->r- ^` TYPE tV kQ 0 , i ______^O y 6., E 3r M^t ^ gyn. Q. L ^i I3 6 5 M, ^^Nj E^
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^ T Q1 3tarX 4 3/¢ 3/4X3/+Lrr 3/4k ." 22" chamfer -46 chamfer 18 chamfer chamfer k 2 rO " yt ti 24" 2 0 TYPE TYPE II TYPE III TYPE IV and rn AS NOTED (SPAN 30 -45 FT.) SPAN 40-60 FT.) SPAN 55-80 FT. (SPAN 70-100 FT. Howard Award because he felt others made by both men—innovative, daring equally deserved the honor. However, for their time, but cautious—were even- when I had convinced the Nominating tually recognized by their peers. Sadly Committee (with Bill Dean s knowledge), enough, the two men never met. that he had earned the right to be nomi- On October 18, 1950, at an imposing nated, he eventually accepted it. ceremony I attended, the world re- Both men understood the potential of nowned and respected Franklin Institute prestressed concrete, what it would in Philadelphia presented Professor mean to the construction industry and Magnel with the Frank P. Brown Medal mankind when the first step towards its for his outstanding contribution to the use had been made. In their own special development of engineering techniques way, both men courageously made that for prestressed concrete. In 1957, the first, giant step! American Society of Civil Engineers Prudent and cautious, Professor Mag- honored William E. Dean with the Ernest nel would progress step-by-step through E. Howard Award for his contribution to tests which he planned, guided and the advancement of prestressed con- supervised in his own elaborate labora- crete. tory where he was the master. He Both awards were well deserved and checked his theories and the computa- know for a fact that both men, particu- tion results he intended to present to the larly Professor Magnel (for he was a profession at large and only then would foreigner) cherished these awards. he apply these in the field. Safety, The Prestressed Concrete Institute through well thought out practical en- honored Dean with a Special Award in gineering concepts and excellent work- 1964 for the 1548 ft (472 m) long, pre- manship were his overriding criteria. stressed Sebastian Inlet Bridge in In his own way, Bill Dean was the Florida. Dean s imaginative design same. He proved this when he re- eliminated construction falsework, quested exhaustive field tests on full- through the use of precast pretensioned sized beams with and without deck components for its 380 ft (116 m) three- slabs, for the Tampa Bay trestle before span continuous main section. 11 This allowing fabrication of the beams. Dean project is quite an accomplishment for a understood the potential, and limitations, man who had started off with, "I have of American labor as related to the gone sour on prestressed concrete." American economy. In 1965, Bill Dean was invited to re- This understanding was the basis for present the PCI the following year at the the I-beam standards as they were de- quadrennial FIP Congress (Inter- veloped under his chairmanship. He nationale Federation de Ia Precon- personally made the computations, for trainte) in Paris and to present a paper he remained a prudent and meticulous on prestressed concrete bridges de- designer even when swamped in "ad- signed and built in the early 1960s. Un- ministrative" work. Perhaps the fortunately, Dean died that winter and it superimposing of the European type was left to me to pick up the pieces beam on the AASHO-Type IV beam as Dean had already prepared, to complete shown on Fig. 31 will make that abun- the paper and to present the material in dantly clear (see previous page). Paris, which I did. No wonder then that the contributions At the conclusion of the presentation, gave homage to Dean and projected a candid photograph showing Dean lec- 1 applied this concept with great success for two bridges, part of a 14,000 ft (4246 m) trestle on Maryland s Eastern turing at some previous convention. Shore, What a twist of fate!
62 Editor s Note: It must be appreciated Institute at the quadrennial meeting of that during all the years that Charles the prestigious FIP Congress in Paris. Zollman knew Bill Dean, Dean never once offered him a consulting job. But Charles Zollman to this day admits that unwittingly, through his death, Bill Dean this meant more to him than any mone- left him the legacy of the greatest gift tary reward that he could ever have re- one could receive, that is, the honor of ceived. As he said, "I homme propose officially representing the United States et Dieu dispose" (Man proposes and on behalf of the Prestressed Concrete God disposes).
REFERENCES 1. Zollman, Charles C., "Trends in Linear 8. Dean, W. E., "Tests Establish Construc- American Prestressed Concrete Con- tion Procedures by Prestressed Beams struction," Precontrainte-Prestressing, in Tampa Bay Bridge," Civil Engineering, Brussels, Belgium, Nos. 1 and 2, 1952. January 1953. 2. Coff, L., "Prestressed Concrete—A New 9. Papers presented at the Prestressed Frontier," Engineering News Record, Concrete Short Course, St. Petersburg, September 1, 1949. Florida, October 10-12, 1955: 3. Ziverts, George J., "A Study of (a) Bryan, Ross, "Applications of Pre- Cardboard Voids for Prestressed Con- stressed Concrete Principles." crete Box Slabs," PCI JOURNAL, V. 9, (b) Zollman, C. C., "Structures of Un- No. 3, June, 1964, pp. 66-93 and No. 4, usual Design." August 1964, pp. 33-60. (c) Everling, W. 0., "Steel Wire for Pre- 4. Bender, Brice F., and Kriesel, William G., stressed Concrete." "Precast, Prestressed Box Beams; A (d) Wenzel,, Harold B., "High Strength State-of-the-Art Report," PCI JOURNAL, Concrete." V. 14, No. 1, February 1969, pp. 72-95. (e) Smith, Eugene, "Major Prestressed 5. Ekberg, C. E., Jr., "The Characteristics of Concrete Projects." Prestressed Concrete Under Repetitive (f) Dean, William, "Outlook to the Future Loading," PCI JOURNAL, V. 1, No. 3, of Prestressed Concrete." December 1956, pp. 7-16. 6. Quade, Maurice N., "15 Mile Toll Bridge 10. Dean, W. E., "Peculiarities and Under Construction Across Lower Tampa Shortcomings of Prestressed Concrete in Bay," Civil Engineering, April, 1952. Florida Bridge Practice," PCI JOURNAL, 7. Closner, J. J., and Vick, A. D., "Pre- V. 2, No. 1, June, 1957, pp. 32-37. stressed Concrete Trestles Over Tampa 11. Dean, W. E., "Sebastian Inlet Bridge," Bay," Construction in the South, Sep- PCI JOURNAL, V. 10, No. 6, December tember 1953. 1965, pp. 35-42.
NOTE: A reprint of William Deans paper on the "Outlook to the Future of Prestressed Concrete" is given in the Appendix on the following pages.
PCI JOURNAL/July-August 1978 63 OUTLOOK TO THE FUTURE OF PRESTRESSED CONCRETE
By William Dean t
he title of this paper would indicate a increasing faster than any past experience Tclairvoyant ability on my part for which would indicate. make no claim. In some twenty-five years of Having watched the development of pre- engineering practice I have had little experi- stressed concrete for the past several years, ence with the use of crystal balls, tea leaves wonder if a condition somewhat analogous to or Zodiacal science. this traffic problem does not exist in the field In recent years the prediction of future of prestressed practice. Certainly we can say trends in developments has become a highly that five years ago there existed much inter- specialized field in business management est in prestressed work, and there were that has important branches in engineering. strong indications of considerable develop- While I have little detailed knowledge of the ment in the field. However, I wonder how methods employed by scientific prognos- many of us foresaw the rapidity with which ticators, the general procedure seems to be a the development would come about. process of collecting data on trends as they It is just a little over five years since Charlie have developed in the past, drawing curves Zoliman made his first visit to my office in from past through present and then by ex- Tallahassee to discuss a possible design for trapolation projecting these curves into the fu- use on the trestle portion of the Sunshine ture and attempting to draw conclusions Skyway. Up until that time Charlie was the therefrom. only engineer with any reliable information This general procedure is a very important and experience in prestressed concrete that I part of traffic engineering. In the planning of had met; although, I had met quite a number modern highway facilities recognition of prob- of them that were quite inexperienced and able future traffic problems, five, ten, twenty grossly misinformed. or more years in the future, is a necessary As a result of some of those other meet- part of the design if further obsolescence is to ings, I must confess, as Charlie told you all be avoided. Traffic engineers have been quite this morning, that I had considerable preju- successful in predicting general trends; how- dice, but I will not admit that Charlie sold me ever, in the matter of actual volume at some anything. He showed me by fact and by rea- future date ail these predictions very often son, and as an outgrowth of that first visit to underestimate by a considerable amount. my office, in April of 1950, the design was Highway traffic is developing at an acceler- developed for the trestle portion of the Sun- ated rate, and quite often the slope of the shine Skyway which did have a very impor- curve representing future traffic is consid- tant part, I think, in furthering prestressed erably steeper than predicted. Prediction of practice in this country. I can say that Charlie future requirements for ten years are often introduced me to prestressing. It is something reached in less than five. Demand is often for which I will always have a warm spot in my heart and much gratitude. This paper is reprinted from PCI s First National Prestressed We are now concluding a three-day con- Concrete Short Course, presented at St. Petersburg, ference designed to further prestressed prac- Florida, October 10-12, 1955. tice. It has been my pleasure to attend and tChief Bridge Engineer, Florida Highway Department, Tal- participate in several such conferences, and lahassee, Florida. as an indication of trend we might look back
64 Written 23 years ago, many of the concepts Dean talked about are still relevant today.
and examine some of the principal develop- livered in an attitude involving approximately ments associated with these gatherings. equal parts of interest and cautious skepti- The engineering profession and construc- cism. tion industry had a significant introduction to Despite its amateurish nature some basic prestressed practice at the First United States problems, as they appeared at the time to Conference on Prestressed Concrete held at one average practicing engineer, were listed. Massachusetts Institute of Technology in the Some of these were lack of: simple practical summer of 1951. The sponsors of this con- method of linear prestressing, freer patents, ference had hoped for a registration of 200 to authentic design criteria, authentic test of 300. Actual registration was more than twice large scale members on which the design the anticipated number. Attendance included criteria might be based and only a limited teachers and students of structural engineer- number of reliable construction firms with ex- ing, practicing engineers, prospective man- perience in prestressing. The past four years ufacturers of materials for prestressing, pro- has seen presently acceptable solutions to ponents and patent holders of certain pre- every one of these problems. stressing methods and a representation from The next conference that might be remem- the construction industry. bered was a part of the Centennial of En- At that time the first major prestressed gineering in Chicago in the Fall of 1952. Pre- bridge in the United States, the Walnut Lane stressing was given a very important part on Bridge at Philadelphia, was about complete, the program. Interest was such that the ses- and a few smaller bridges and structures had sion on prestressing had to be moved from been built or were under process of construc- the original scheduled meeting place to the tion in other parts of the country. Papers largest ballroom of the Conrad Hilton Hotel given at this conference described construc- and even there late comers had to be satis- tion in the United States up to that time; how- fied with standing room only. In the year m- ever, many of the constructions described mediately past the contract had been let for were of European structures. Valuable data the structures on the Sunshine Skyway total- on the properties of material for prestressing ing 363 trestle spans with precast, pre- were given by manufacturers who were nat- stressed concrete girders. At the time this urally looking for markets, and considerable was the largest contract for prestressed factual data on design concepts and methods members ever let in any part of the world. were presented. Since that time the Skyway construction The general air of most attendants was one has been very considerably exceeded in of intense interest with a generous portion of other big contracts. You just saw an example skepticism. The experience of one of the con- of that presented by our last speaker. Now, tributors, with whom I am well acquainted, this same brash contributor whose efforts at might be cited. With considerable brashness, the MIT conference has been described was and against all rules of discussion, he ac- again in attendance. This time, with an in- cepted an assignment to discuss certain crease in enthusiasm and a considerable re- theoretical and practical design concepts. A duction in skepticism, he described test to paper was conceived in ignorance, written out destruction of full size members being used of a vast background of inexperience and de- on the Skyway. These tests had shown
PCI JOURNAL/July-August 1978 65 member performance which fully justified de- of any one of these groups would be as un- sign computations and indicated an accept- likely as a tripod standing on two legs. I might able margin of safety for the intended sur- say, parenthetically, that although many men face. may have similar educational backgrounds, it It is believed that these tests, which were appears that there are certain factors of given wide publicity in the technical press, temperament and disposition and thinking and the use of prestressing on the Skyway that will usually place a man particularly in had much to do with the acceptance of pre- one of these groups. stressing by both engineers and the construc- I have often noticed some of my associates tion industry. Certainly the contributor re- who have become established in one of these ferred to was hard-put in answering letters groups try to get into another, and too often from many engineers, and for months the they are not successful at it. I notice on our contractor s yard literally swarmed with pro- program listed under the officers of the Pre- spective competitors. stressed Concrete Institute two engineers It might be worth noting that the MIT con- who are business men and one practicing ference was sponsored and largely guided by consulting engineer; under the directors I see an academic group, the faculty of a major three business men and one who is a very technical college; the Centennial of Engineer- noted teacher and author. To me that is a ing was sponsored by four professional significant grouping of men. It is a significant societies and was largely a gathering of prac- combination of talents, and I think that the ticing engineers. Since these conferences, success that we have enjoyed in prestress- there have been many others of much impor- ing, the success that has been realized, tance throughout the country, and hundreds cannot be attributed to any one of those of prestressed structures of many types have groups, but all have had their importance and been designed and constructed. necessary part in it. The most significant development in the This particular conference, while directed prestressing field in the last two or three by the academic group and participated in by years has been the growth of a large and all the above mentioned groups, has a very healthy construction industry with numerous strong backing of the business firms making firms equipped and ready to manufacture up the principal membership of the Pre- many building parts of prestressed concrete. stressed Concrete Institute. This has been a Without this group there would be little pros- happy and progressive partnership. The reg- pect of rapid advancement in the field. The istrants have come from all groups, and method of construction may be the subject of work here has been, at least to this speaker, advanced thinking in research, it may be put distinctive. We have not only heard informa- in the form of workable plans, but under our tive general papers but have spent two days American system of operation, which pray in consideration of detailed design standards; God may never change, it is of little value its basic significance, to me, my friends, oc- until sound business men consider it suffi- curs here. ciently practical to warrant capital investment These past three days we have not only from which a profit can be reasonably ex- been preaching the gospel, we have been re- pected. The large growth of prestressing ceiving members into the congregation. As at plants, representing the substantial capital in- all other prestressed conferences attended by vestments by many business firms, indicates the speaker, the interest here has been keen; the practical acceptance of the method by however, to me it has been particularly signif- this important group. icant due to the general registrant participa- It might be worth pointing out that in the tion. We might ask how it is possible to get a development and advance in structural prac- large group to attend a conference like this tice, the work of the academic group, of the and to do the detailed work of this one. Prob- practicing engineers and the business men ably the answer is that most of us realize that from the construction and materials industries if we are to keep abreast of structural prac- form inseparable and interrelated parts. Major tices, we have no choice in the matter. Pre- advancement without the proper contribution stressing as an accepted construction
66 method is here with us. Accepting this as a and touched on a very few high spots in the fact, it behooves all of us to learn how to live advancement of prestressed concrete from a with it, to learn its applications together with logical and interesting theory of a few years its limitations. past to the practical and generally recognized At several points in this paper reference construction method of today. Perhaps the has been made to significant advances and trend that has been shown has been suffi- developments. Certainly any mention of these ciently evident to warrant a little prognostica- would be lacking if the Criteria for Pre- tion. It does not seem that we would need stressed Concrete Bridges, published by the any crystal ball, tea leaves or other im- United States Bureau of Public Roads, was pedimenta and paraphernalia of the occult art omitted. While these criteria were developed to say that prestressed concrete has earned principally to govern highway bridges, they a permanent place in American construction are laws that are applicable to prestressing in practice. It is not going to supplant the older general. Most engineers very properly look and universally accepted construction askance at any radically new technical de- methods in reinforced concrete, steel or tim- velopment until it has been subjected to bers, but it does add another type from which exhaustive test, tried in the light of experience a choice can be made. While prestressed and suitable rules for its use are developed. concrete will not supplant conventional con- Some two years past, a joint committee of struction types, there are many applications two of the major technical societies of the where it can be expected to do a better job, country was set up to develop a code for pre- and in these applications it will certainly take stressing. The establishment of this proposed over. To try and list these applications would code by this committee has been delayed for be pointless. It would seem sufficient to say various reasons, and in the meantime pre- that as hundreds have been found in the stressing is so logical and practical and has past, thousands will probably be found in the aroused such wide interest that construction future. would not wait for the development of the Getting back to that MIT conference and code. In order to achieve uniform practice in that amateurish paper by the rash contributor, highway bridges, the Bureau sought out and about the only statement with any degree of sorted a composite of the most informed opin- sagacity, and that only a simple truism, was ions and presented their criteria to the en- the following concluding statement: "When gineering and construction industry. we learn to build as good a structure as we There is hardly any way to measure the are now building at a reduction in cost or a importance of this booklet to the development superior structure for the same cost, pre- of prestressing practice. Many engineers who stressed construction is sure to gain a wide are hesitant, or in doubt as to the proper ap- acceptance in American structural practice." plications, unit stresses, design concepts and The conditions set forth in this four year old so forth, have been reassured by knowing statement have been fully met, and the pre- that an organization having the well deserved dicted acceptance has been realized. prestige of the Bureau, with its background of In concluding it might be appropriate to ob- careful, conservative practice, has officially serve that all of us who expect to make a approved prestressed construction. The living in structural work, whether we belong to Criteria, where possible, will be revised and the academic group, practicing engineers or improved from time to time; however, as the construction industry, will do well to learn presently published, they can be used with as much as possible about prestressing, its the assurance that structures designed in ac- design, its applications, construction methods cordance with their specification will produce and limitations, for if we are to keep abreast serviceable, practical structures with ade- of modern practice, we will be dealing with quate margins of safety. the subject of prestressed concrete for the So far, we have been looking backward rest of our careers.
PCI JOURNAUJuly-August 1978 67