t*| , GIFT OF * " The Bridge THE CONCRETE BRIDGE A book on why the Concrete Bridge is replacing other forms of Bridge Construction By JNO. B. LEONARD and W. P. DAY If. Am. Sor. C. E. AlMC. M. Am. .Sor. C. E. SAN FRANCISCO COPYRIGHT 1913 BY LEONARD & DAY CONSULTING ENGINEERS RIALTO BUILDING, SAN FRANCISCO PRICE, $1.00 Gift of PREFACE The purpose of this publication is to supply information as to the vast strides made in California during the past few years in the use of reinforced concrete for permanent bridge construction. It is believed that there exists in the minds of the public a limited understanding of what has been accomplished in this direction. I strong conviction is growing to-day, however, in favor of the desirability of structures of this character, due to the satisfaction given by those in existence. The publishers realize that they have only touched briejly upon the subject. Through their connection with all of the work shown herein, they are in possession of tletailed knowledge of both the design and construction of each. They invite and will cheerfully answer any inquiries addressed to them for further information. JNO. B. LEONARD. W. P. DAY. l-'i-l>ruary 20. 1913. 528-530 Riallo Building. San Francisco, California. 264233 / '' ( 'Conformity with environment, economic use of material, pleasing outline and appropriate use of ornament make toward beautiful bridges, which are a sure indication of a progressive community." C rzi Why it is the bridge |HE USE OF REINFORCED CONCRETE for the construction of bridges, in the State of California, has increased during the last few years in a very marked degree. With the advance in scientific infor- mation as to the action of steel and concrete in supporting loads, designers and builders have advanced, step by step, until today long spans and important structures are entirely feasible in the hands of competent engineers and constructors. As a result, many highway bridges throughout the State are built of reinforced concrete, this type taking the place of the old combination structures of steel and timber. Nor is the use of the material in this State confined to highway bridges. There are a few carrying heavy interurban cars, and the largest and heaviest locomotives. In general, there are two types of reinforced concrete bridges the flat span and the arched span. Each type lends itself to variation, in accordance with the ideas of the designer. The flat span is sometimes built without girders, more often with girders run- ning the long way of the span. The arched span is sometimes built as a continuous arch Page Seven EASE OF CONSTRUCTION u u u u u u u 0000000000000000 u u eg with side walls and earth roadway. Occasionally the side walls are omitted, and the roadway is carried on columns resting on the arch. The arch is not always the full width of the bridge, the width being made up of two or more individual arches with a light floor between. It is interesting to know that reinforced concrete construction tends toward the use of our home products. Timber for temporary supports and moulding forms is easily obtained on our own coast; cement and reinforcing steel are manufactured in our own State; sand and gravel are obtained usually on the site of the bridge, or at least not very far away; our rock quarries produce an abundance of crushed rock, where it is desirable to use this material. Annoying delays that often occur in the building of steel bridges are avoided by reason of the fact that cement and reinforcing steel are manufactured in California. Methods of construction vary, of course, with the design and the location. Forms and temporary supports for flat span bridges offer no particular difficulty. Temporary supports generally called falsework for arches must be carefully designed and executed. Usually there is water under the arch, and piles are driven to carry the posts of the false- work. The proper time to begin construction is the low water period. This gives the contractor ample time during the spring season to place his plant on the site, and make general preparation for the work. Extreme care should be used in the proportioning of the concrete mixture, as well as in the method of casting. The ideal arch is that in which the work is carried on so continuously, that no joints occur as a result of the previous work 1'age Eight DURABILITY 1 I) U u U u 0000000000000000 u u u u ED drying out before the next can take hold, and yet not so fast but that the regular shrinkage in setting has been allowed for. Contractors usually prefer to cast side walls before remov- ing the falsework, but this is apt to produce cracking in the walls, which, while not dangerous, is unsightly. The proper method is to allow the arch to take its natural form before casting the walls. All arches drop at the crown when the falsework is removed, owing to the compression of the arch under its own weight. The probable drop at the crown may be very closely calculated and allowed for in the forms, in addition to the allowance for the compression of the falsework timbers. The element of cost is naturally of first importance to the prospective builder, and is worthy of careful consideration. In^the first place, it is generally understood that a concrete bridge is more costly than a steel bridge. This statement, needs explanation in order to convey the truth. It so happens that a concrete bridge may be cheaper than a steel one, depending entirely upon the live or moving load. For example, it is cheaper to build a reinforced concrete bridge, to carry locomotive and train loads, than it is to build a steel bridge for the same loads. On the other hand, a light highway bridge of steel with timber floor is cheaper than a concrete one. Concrete bridges are so heavy in themselves that the addition of a heavy live load does not materially alter their design. With the steel bridge, the live load is the all important factor, a heavy live load necessitating a very much heavier structure, as well as more costly. Concrete bridges designed to carry loco- motive loads are at least 15 per cent cheaper than steel bridges designed for the same loading. The only type of steel highway bridge that is cheaper than a concrete bridge is Page Nine PERMANENCY 0000000000000000000000000 that with a timber floor. Timber floors wear rapidly and must be teplaced about once in three years, depending, of course, on the traffic. Under the usual conditions, if a steel bridge be built with a solid concrete floor to avoid the replacing of the timber, the cost of the structure will equal that of a concrete bridge. It is a well-known fact that all steel bridges must be painted periodically in order to preserve them. It is equally well known that after forty or fifty years at the most, the steel has deteriorated to such an extent as to make replacement of the structure a necessity. It must be borne in mind, also, that county bridges will not last as long as railroad bridges, because the former are not given the same care as the latter. It may be seen, therefore, that steel bridges require main- tenance, and that further, they have a limited existence. Concrete bridges require abso- lutely no maintenance, and the effect of age is to strengthen rather than weaken. From the foregoing, it is manifestly impossible to set a definite ratio of cost between a concrete and steel bridge. Cost is always a question of locality, of availability of materials, and of the foundations, all of which vary in each case. Steel bridges are sometimes, in fact often, built on cylinder piers, which cannot compare as supports with the solid piers used for concrete bridges. Assuming, however, that a concrete highway structure for a given locality can be built for $100,000, we may safely say that, ordinarily, a steel bridge, with timber floor, can be built for $85,000, and that its life, with proper maintenance, is fifty years. On this basis the annual charge for the steel bridge would be about as follows: Page Ten OW UP-KERP cn I) 00000000000000000 ED Average annual charge for repainting, assuming the bridge is painted once in 5 years at a cost of $3,000 $ 600.00 Average annual charge for renewing floor 400.00 Annual interest charge at 4 per cent on the investment 3,400.00 Annual sinking fund for renewal at end of 50 years at 4 per cent compounded 556.75 Total annual charge $4,956-75 The only charge against the^concrete bridge is the annual interest on the investment, which, at 4 per cent, amounts to $4,000, or a net saving of $956.75 per year in favor of the concrete bridge. In addition to the advantage shown in the preceding, in favor of the concrete bridge, there is the artistic difference between the two, for which no monetary value may be assigned. The artistic side of bridge building has been given less attention than its impor- tance warrants. Concrete lends itself beautifully to this phase of design. The Oakland Avenue Bridge, shown on pages 12-13, was designed with a view to pleasing appearance, and exemplifies the ability of concrete to meet this condition. Page Eleteti THE CONCRETE BKIDQE Showing the possibility for artistic treatment and suggestive of the adaptability of reinforced concrete for city, suburban or park bridges Portals Oakland Avenue Bridge Piedmont, California Page Twelve THE CONCRETE BRIDGE Practical and picturesque, thin hridffc i.s an excellent example of ornnmental 'concrete cousiruciinn und its power to enhance the natural surroundings Oakland Avenue Bridge Piedmont, California CLEAR SPAN OF 130 FEET LENGTH OVER ALL 363 FEET ROADWAY 22 FEET WITH Two 6 FOOT OVERHANGING SIDEWALKS BUILT 1911 Page Thirteen THE CONCRETE BRIDGE A happy and niix/cni i>nin<'<-riii i THE CONCRETE BRIDGE Of simple design and economical construction, it is readily seen that it Inld^e i>/' be made an ornament in similar locations Ross Bridge No. 3 type can MAIN SPAN 22 PEET END SPANS 10 FEET LENGTH OVER ALL 43 FEET ROADWAY 20 FEET IN THE CLEAR BUILT 1909 Page Seventeen THE CONCRETE BRIDGE . ^romantic countryside. The concrete, blending with offers no harsh contrast even when new Page Eighteen Ross Bridge No. 2 CLEAR SPAN 48 FEET LENCTH OVER ALL 81 FKKT ROADWAY 20 FKKT IN THE CLEAR BUILT I'.NK.I HE CONCRETE BRIDGE of Marin County's artistic bridgi-s: of the romrr/r .^i /(/!< Bridge at San Anselmo Marin County, California CLEAR SPAN 46 FEET ROADWAY 40 FEET LENGTH OVER ALL 80 FEET BUILT 1910 in design Page N ineteen One of the longest concrete bridges on the Pacific Coast. Each pier rests on 250 piles and is of extremely masxi Eel River Bridge Near Eureka Humboldt County, California Page Twenty THE CONCRETE BRIDGE tion, to withstand the heavy drift. Eel River has a rapid current and is often filled with drifting saw logs SEVEN 200 FOOT SPANS LKNI;TH OVER ALL 1451 FEET ROADWAY 22J FEET CLEAR BUILT 1911 Page Twenty-one Greeted jointly l>\ l-'resnn its ireifflil. milling In /In' stability of the ireir Operated as easily as a timber structure. Not subject to deterioration, but increasing in strength with its age Inijfir nnil. through rage Twenty-five THE CONCRETE B R D Q E Thix coinliinatiim hrirli. nifl *li>n<>li irhirh controls the water from Buena Vista Lake Old Headquarters Weir Miller & Lux, Inc. Kern County, California LENGTH OVER ALL 16.3 FEET ROADWAY 13 FEET IN THE CLEAR HKIGHT FROM FLOOR OF WEIR TO lionoM (IK HKIIM;E SLAB 19 FEET BUILT 1911 Page Twenty-six THE CONCRETE BRIDGE Another view of the Old Headquarters Weir, showing the ro r<'f Inulfre. llic the tl meeting each cud on a l(> degree curve. Built on solid rock and locornotirrs hiinlinf! t-urs ln-nvily laden with limestone American River Bridge Near Auburn Placer County, California THREE 140 FOOT CLEAR SPANS LENGTH OVER ALL 652 FEET BUILT 1011 Page Thirty THE CONCRETE BRIDGE This bridge stands 75 feet above the river, anil the sJn-ir or ii seen. Note the heavy Mallei compound engine, intliciiti East approach of American River Bridge Near Auburn, Placer County, California With birdseye view of river ? crosses the river is here plainly nd upon the structure Page Thirty-one THE CONCRETE BRIDGE The cnri-c of this e for flood water, while conforming Essex Street Bridge San Luis Obispo CLEAR SPAN 60 FEET LENGTH OVER ALL 120 FEET BUILT 19011 Page Thirly-lwo THE CONCRETE RR1DQE An example of the concrete girt low Marsh Street Bridge City of San Luis Obispo San Luis Obispo County, California CLEAR SPAN OF 40 FEET LENGTH OVER ALL 80 FEET BUILT 1909 Page Thirty-three THE CONCRETE BRIDOE llnili to replace an old type combination structure of steel and wood. Notable for extremely low cost of construction Lindo Channel Bridge Chico Butte County, California Two SPANS, EACH 87 FEET CLEAR ROADWAY 28S FEET CLEAR LENGTH OVER ALL 204 FEET BUILT 1912 Pngt Thirty-four THE CONCRETE BRIDGE Situated far up in the mountains, this structure is interesting lin~i7irSr~j, ;7n>wr depth excarnted to reach bedrock, the bottom of the mid-river filer bcin/s nearly^SO fri't beloir the tenter Bridge over Stanislaus River Between Stanislaus and Tuolumne Counties, California Two 100 FOOT SPANS AND ONE 50 FOOT SPAN LENGTH OVER ALL 350 FEET BUILT 1909 Pate '1'hirly-five This - Riri'r iit'iir Modesto, connecting San Joaquin islftux Counties Ripon Bridge Two 110 FOOT SPANS LKNUTH OVER AM. 280 FEET BUILT 1908 I'age Thirty-six THE CONCRETE BRIDGE This is an original design rrv tht Peninsular Railway ('.OHI/HIIIY to carry lln'ir hi'iirv inlcritrban cars Alum Rock Bridge San Jose, California decided that CLEAR SPAN 130 FEET APPROACH SPANS 40 FEET LENGTH OVER ALL 250 FEET BUILT 1913 Thirty-seven CONCRETE This bridge has and ifht'ii completed will be 1100 feet long. Designed