10 



MICHIGAN ROADS AND FORESTS 



MICHIGAN BRIDGES AND CULVERTS. 

 By L. C. Smith, Bridge Engineer. 



The object of this discussion is to inspire 

 the construction of better and more substan- 

 tial highway bridges throughout this state. 

 Mi. re substantial bridges are required by the 

 traffic of today. Economy of maintenance 

 demands it. Good bridges are necessary to 

 future road improvement. 



With the increased interest in road build- 

 ing, there should also be a similar stimula- 

 tion in bridge building. 



The Michigan state law provides that: "All 

 bridges shall have a clear roadway of at least 

 sixteen feet and shall be capable of carrying 

 a ten-ton moving load." In another place it 

 provides: "There shall be no bridge, culvert 

 or artificial roadway of any kind constructed 

 in any public highways of this state over any 

 water course thereof having a roadway of less 

 than sixteen feet in width, and the same shall 

 be built of sufficient strength to safely carry 

 a ten-ton load." 



These two sections provide particularly the 

 same thing, except that in the last section the 

 word "moving" is omitted, which is, of course, 

 fatal to the design of a bridge greater than 

 ten-foot span. 



The law, as seen above, provides for a ten- 

 ton moving load, and the traction engines 

 which are sold in this state and used here vary 

 in weight from nine to eighteen tons, the 

 larger per cent being heavier than ten tons, 

 when allowance is made for coal, water and 

 engineer. It can be readily seen that for 

 township, county and village officers to prop- 

 erly protect themselves against damage suit 

 they must build bridges which will safely 

 carry a ten-ton traction engine, at least, and 

 it does not take much forethought to see that 

 with the heavier engines, which are being 

 made, the required carrying capacity of 

 bridges will be increased to fifteen tons. The 

 Illinois State Bridge Engineer designs all 

 bridges to carry an eighteen-ton traction en- 

 gine. 



The State Highway Department called for 

 reports from the township highway commis- 

 sioners and county drain commissioners, to 

 give the amounts expended on bridges for the 

 year of 1909. Ninety-seven per cent of the 

 highway commissioners reported an expendi- 

 ture of $613,191.94; twenty-nine of the sixty- 

 three county drain commissioners reported an 

 expenditure of $52,206.78, making a total 

 amount reported of $665,398.72, and estimat- 

 ing those who failed or refused to report in 

 the same proportion, we have a total expendi- 

 ture of three-fourths of a million dollars for 

 bridges and culverts. Nearly a quarter of a 

 million of this was spent for wood and metal 

 culverts and short span steel bridges with 

 wood floors, which will have to be repaired 

 within five years at the outside and more than 

 likely will have to be totally replaced in fif- 

 teen years. 



One of the greatest problems concerning 

 bridges today is reflooring. The average oak 

 floor lasts not more than five years without 

 repair, and we all know that keeping up wood 

 floors is a large and continual drain on the 

 treasury. Don't buy a bridge with a wooden 

 floor, no matter how low the first cost is or 

 what span the bridge is to be. A great many 

 of our old steel bridges are strong enough to 

 carry thin reinforced concrete floors. The 

 expense of such a floor is not as great as 

 might be supposed at first thought. 



A bridge of 150 ft. span and 16 ft. roadway 

 in Montr-e Township, Genesee County, was 

 relic "'red ia-t Mimmer with a "S'/i" reinforced 

 concrete floor, 2400 square feet in all for a 

 cost of $1035. This cost included 8" steel 

 stringers, which cost $595, leaving the cost of 

 the thin concrete floor and reinforcing $440 

 for 2400 square feet, or 18J/2 cents per square 

 foot. Xew oak floor would cost $50 per 

 thousand, including laying, or for a wood floor 

 3" thick the cost would have been 15 cents per 

 si|iiare foot, or $360. To this must be added 

 the steel stringers needed in cither floor, 



BRING THE TWO TOGETHER 



WHAT? The stone that can be found in almost any Township and the 

 FORT WAYNE ROCK CRUSHER. With this machine you can crush field 



stone, quarry stone or any kind of stone, 

 and the result is Good Roads at a reason- 

 able cost. 



A complete Fort Wayne Crushing 

 Plant will pay big divi- 

 dends to any Town- 

 ship or Contractor. 



The Fort Wayne 

 is serviceable, con- 

 venient, durable and 

 always on the job. 



The Fort Wayne Mounted Crusher, with Elevator, Screen and Portable Bin 



We make Crushers, Steam Rollers, Road Graders, Dump Wagons, Scrapers 

 and Plows, Hauling Engines and Culvert Pipe. 



You should have our catalogue. Send us your name and address and 

 it is yours. 



THE GOOD ROADS MACHINERY COMPANY, Fort Wayne, Ind. 



which makes $360 plus $595, or $955. The 

 difference in cost of the two floors would only 

 be $80, without any consideration of the most 

 .mportant item, namely: How long will it 

 last? The concrete floor will continue to 

 grow stronger with age and on the other hand 

 the wooden floor would need repairs in five 

 years. The concrete would tend to stiffen the 

 whole bridge and distribute the concentrated 

 loads over a larger area, and the wood floor 

 is at best a springy, shakey,"roughriding and 

 expensive proposition. An ordinary plank 

 bridge floor weighs about 30 pounds per square 

 foot, while the concrete floor weighs 60 pounds 

 per square foot, both weights including steel. 



When in need of a new bridge floor for an 

 old steel or wrought iron bridge, don't go at 

 it blindly, but have a competent bridge engi- 

 neer inspect the trusses and abutments and 

 determine whether or not the bridge is suf- 

 ficiently strong to carry a concrete floor. If 

 the bridge is worth it and can be reinforced 

 to make it sufficient to carry a reinforced 

 concrete floor, by all means invest. 



Another subject of vital importance, re- 

 garding old steel and iron bridges, is the pres- 

 ervation of what we already have. We know 

 of no better way than to paint them, but how 

 many of the ordinary steel highway bridges 

 are properly painted? The deterioration of 

 steel acted upon by the elements has caused 

 more bridge iailures than any other one thing, 

 unless it be insufficient foundation. 



There are several types of bridges in use in 

 Michigan at the present time, which we will 

 consider as to their suitability and value for 

 improving the road. 



(1) Wooden bridges and culverts. 



(2) Steel bridges on wooden piles and steel 

 legs. 



(3) Steel bridges on concrete abutments 

 with concrete floors. 



(4) Reinforced concrete bridges. 



The above mentioned types of bridges and 

 culverts have been used in Michigan with vary- 

 ing degrees of benefit. It is safe to say that 

 hardly a bridge on any highway that is reg- 

 ularly inspected to insure the safety of the 

 traveling public. Not until a plank in the 

 floor is broken or a washout carries away the 

 approach of a bridge, or the whole thing col- 

 lapes, is a bridge given more than a passing 

 thought. Therefore, it is necessary to builcl 

 bridges and culverts that do not need con- 

 tinual repair and maintenance. 



The use of wood in the construction of 



bridges and culverts, or bridge floors is per- 

 missible only in the very newest of localities 

 and in any case can be termed nothing but 

 the most temporary of structures. 



Bridges with steel superstructure on ste 

 legs or wood piling with wooden floors ar 

 not much better than the wooden bridges an 

 are of no more use in making our highwa; 

 permanent than an all wood structure. 



Steel bridges with concrete or mason 

 abutments and with wood floors are not in t 

 permanent class, as the floors rapidly wear ou 

 The life of a plank floor on a bridge wit! 

 ordinary travel is not more than five years, 

 with an average of one-third of the plan' 

 being replaced in that interval. 



For spans of greater length than fifty t" 

 steel bridges with concrete foundations and 

 floors are the most economical and best struc- 

 tures to build unless the location adapts itself 

 to arch construction. Reinforced concrete 

 arches can be successfully used for highw 

 purposes up to one hundred foot span. 



Having considered briefly about all kinds o: 

 bridges and culverts in use at the present 

 time, let us turn our attention to the adapta- 

 bility cf concrete for making permanent 

 bridges for all time to come. It is brittle as 

 stone and can be used to support enormous 

 loads, as in foundations, bridges, and the like, 

 provided it is so placed as to receive no ten- 

 sion or pull. With the addition of steel in the 

 concrete to- withstand any pull, we have a 

 combination of material excellently adapted 

 for many purposes where stone could not be 

 used. 



In the ordinary beam of any material the 

 upper surface is in compression and the lower 

 surface is in tension, or the particles of the 

 lower side of the beam tend to separate when 

 load is applied. The natural arrangement, 

 therefore, in a concrete beam is to design so 

 that the upper portion is composed of con- 

 crete, which takes care of compression, and 

 with steel imbedded near the bottom to re- 

 sist the pull or tension. The concrete, b; 

 surrounding the steel, makes a surer bind be 

 tween the two materials and also protec' 

 the steel from any action of the weather 

 any other cause of destruction to it. Concrete 

 and steel expand and contract almost th 

 same, so it is safe to use the combinatio 

 without danger of separation due to temper- 

 ature. To make a safe combination of con- 

 crete and steel, it is necessary to know just 

 how much of a load each can stand, and just 



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