MBTC 1057
PRE-DESIGNED TIMBER BRIDGES OF THREE TYPES FOR ARKANSAS COUNTY ROADS

PREPARED BY:
Dr. Larry G. Pleimann, Civil Engineering, University of Arkansas
Gregory R. Riley, Civil Engineering, University of Arkansas

FUNDED BY:
Mack-Blackwell Rural Transportation Center, University of Arkansas
Arkansas Highway and Transportation Department
Federal Highway Administration

June 2000

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TABLE OF CONTENTS

Acknowledgments
Abstract
1.0 Introduction
2.0 Purpose and Scope
3.0 Literature Review
4.0 Background on Types of Timber Bridges
5.0 Bridge Design Computer Program
6.0 Timber Bridge Designs of Three Types
7.0 Conclusions and Recommendations
List of References

LIST OF FIGURES
Figure 1: National Interstate and State Bridge Data
Figure 2: National City/County/Township Bridge Data
Figure 3: Arkansas Interstate and State Bridge Data
Figure 4: Arkansas City/County Bridge Data
Figure 5: Isometric Section of Solid Sawn Stringer Bridge
Figure 6: Isometric Section of Solid Sawn Stringers with Dowel Laminated Deck
Figure 7: Isometric Section with Glulam Stringers and Transverse Deck
Figure 8: Isometric Section with Glulam Stringers and Doweled Transverse Deck
Figure 9: Isometric Section of Longitudinal Glulam or Dowel Laminated Deck
Figure 10: Isometric Section of Longitudinal Stress-laminated Deck
Figure 11: Isometric Section of Stress-laminated Deck Using Glulam Stringers
Figure 12: Cross-sections Used for Stress-laminated Box Girder Bridges
Figure 13: Cross-section of T-Beams with FRP Tension Reinforcement

LIST OF TABLES
Table 1: Published Bridge Data for the Fifty States and the District of Columbia
Table 2: Published Bridge Data for the State of Arkansas
Table 3: Responses to Questionnaire
Table 4: Type 1 Designs with 6 x 12 Stringers
Table 5: Type 1 Designs with 8 x 12 Stringers
Table 6: Type 1 Designs with 10 x 12 Stringers
Table 7: Type 1 Designs with 6 x 14 Stringers
Table 8: Type 1 Designs with 8 x 14 Stringers
Table 9: Type 1 Designs with 10 x 14 Stringers
Table 10: Type 2 Designs with 5 inch wide Glulam Stringers
Table 11: Type 2 Designs with 6.75 inch wide Glulam Stringers
Table 12: Type 2 Designs with 8.5 inch wide Glulam Stringers
Table 13: Type 2 Designs with 10.5 inch wide Glulam Stringers
Table 14: Type 3 Designs with 5 inch wide Glulam Stringers
Table 15: Type 3 Designs with 6.75 inch wide Glulam Stringers
Table 16: Type 3 Designs with 8.5 inch wide Glulam Stringers
Table 17: Type 3 Designs with 10.5 inch wide Glulam Stringers

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ACKNOWLEDGMENTS

The author takes this opportunity to thank many people who have been of great help in accomplishing the work of this project and in producing this final report. These include three former graduate students, Mr. S. Grant Jordan who wrote the original version of PCBRIDGE, Mr. Lee R. Shaw who made some important improvements in the program, and Mr. Gregory R. Riley who used PCBRIDGE to do the designs listed herein and who drew all the pages of drawings and specifications [hard copies available upon request from MBTC].

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ABSTRACT

The National Bridge Inventory every year lists the percentage of bridges in the United States under various jurisdictions that are "structurally deficient" or "functionally obsolete." That percentage is largest for "city/county/township" bridges. In recent years the two major causes for the rapid deterioration of those bridges with typical steel or concrete superstructures have been the use of deicer chemicals and the lack of adequate maintenance monies.

An alternative that could be of competitive cost and that could contribute to the economy of the state of Arkansas by further developing its timber industry would be the use of economical well-designed, well-constructed "modern" timber bridges for the replacement of sub-standard bridges on county and city roads.

A computer program written in 1991 was used to design a range of adequate simple span timber bridges of three different types with accompanying plans and guide specifications for them for ready use by Arkansas county road and bridge departments. The three types include 1) solid sawn stringers with transverse solid sawn deck planks, 2) glulam stringers with transverse glulam decks, and 3) stress-laminated full-span glulam stringers, all constructed of Southern Pine (SP).

This report contains tables of designs for the first type using six different SP stringer sections, for the second type using four different standard widths of SP glulam stringers, and for the third type using the same four separate widths of SP glulam stringers. The designs were done concentrating on flexural adequacy. The reader is guided through simple procedures so that the span length and/or the depth of the primary bending sections may be changed so that the designs may harmonize with any desired allowable deflection limitation, or desired smaller "load duration factor."

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1.0 INTRODUCTION

1.1 Deterioration of the American Infrastructure
It is a commonplace currently to speak of the deterioration of the American transportation infrastructure. The national media periodically have reports on the crumbling of pavements that should have lasted much longer, or of bridge failures caused by the combination of such deterioration and the lack of adequate funding for maintenance within the separate jurisdictions responsible for particular road and bridge systems. Some of these failures have led to loss of life which demonstrated just how serious the problem is.

There are many sources for the deterioration of the U.S. public transportation systems. These include lack of maintenance because of a lack of adequate funding, heavier traffic volumes, and heavier loads particularly as truck traffic strives for increased efficiency by using larger axle loads and longer strings of trailers. In addition, certain environmental factors have effected a faster deterioration. Especially within the context of bridge and pavement maintenance, the increased use of deicing chemicals that began in the sixties has led to more rapid deterioration of reinforced concrete bridge decks and pavements.

The infiltration of chloride ions into the concrete causes the pH surrounding the reinforcing steel to become acidic. This change in pH allows the steel to oxidize. The resulting iron oxide crystals expand as much as 16 times the volume of the source steel [Crumpton, 1985]. The internal expansion produces high tensile stresses in the concrete. This leads to cracking near the top surface and spalling of the concrete follows. The direct exposure of the underlying reinforcement to the environment and traffic loads hastens the deterioration of the slab. Unless the damaged area is repaired, a significant loss of strength and/or service life of a pavement or deck will occur.

Most efforts to control the corrosion of deck and pavement reinforcement have been directed toward protection of the steel bars. Additional concrete cover, surface sealants for the concrete, corrosion inhibitors mixed with the concrete, reduced concrete permeability, cathodic protection, epoxy coating, and galvanizing are examples. The use of fusion epoxy coated bars has become standard in the effort to protect concrete reinforcing steel from corrosion, certainly in the state of Arkansas. However, epoxy coating may not be the final answer since small cracks in the coating may hasten local corrosion [Clear, 1992]. Epoxy coating is also being used with pavement dowel bars. Few other alternatives have been proposed for the protection of steel reinforcement apart from the suggestion of using more expensive stainless steel [Black, et al, 1988], or to search for another more effective coating.

An alternate effort has attempted the development of other forms of reinforcement that are not susceptible to corrosion. Fiber reinforced polymer (FRP) bars provide one such option. This "composite" material consists of thin high-strength synthetic fibers embedded within a hardened polymer matrix. FRP bars have already been used for slabs on grade, as prestressing tendons [Preis and Bell, 1987; Nanni, 1991], in marine environment structures, and in structures wherein non-magnetic properties are important such as magnetic resonance imaging installations [Roll, 1991], and large transformer foundation pads. The bars are not susceptible to corrosion and have high tensile strength.

The attention of the nation was brought vividly to focus on the problem of bridge deterioration in 1967. The Silver Bridge over the Ohio River between Kanauga, Ohio and Pt. Pleasant, West Virginia failed under afternoon rush hour traffic. The bridge was a 40 year old steel suspension bridge of a total length of 1750 feet. It had been inspected as recently as April of 1965. But on that day it was ready to fail and let 75 cars and trucks fall into the river, killing some 46 people. Later investigation showed that the combination of a lack of adequate maintenance and the use of deicer chemicals had led to the rapid deterioration of the main suspension "cables." However, they weren't cables per se, but eyebar links that are often susceptible to deterioration and fatigue fracture.

The Silver Bridge failure led directly to the establishment of the Federal Bridge Inspection program. Working through the state departments of transportation, the program instituted an inspection survey that intended initially to increase the frequency of inspections so that every federal, state, and smaller local jurisdiction bridges would be inspected at least once every two years. The results of this inspection were to be included in a national data base, or bridge inventory system. In Arkansas, the Arkansas Highway and Transportation Department (AHTD) has worked to increase the inspection frequency, especially for those bridges whose condition is problematic. Some bridges are inspected every year if not more often.

This federal inspection program led to the common usage of phrases such as "structurally deficient" and/or "functionally obsolete." The results of the annual inspections are kept in a national bridge inventory and are published periodically. The author first noticed a typical summary of results in an annual November issue of Better Roads magazine which began to publish such data in 1978. In the 1989 issue, for example, of the some 588 thousand bridges in the fifty states and the District of Columbia, a little over 38 percent, 225 thousand, were still "structurally deficient" and/or "functionally obsolete." Of that number, almost exactly two-thirds, 151 thousand, were on rural highways or city streets, off the federally funded system.

Tables 1 and 2 below summarize the results of the Better Roads data for the entire nation and for the state of Arkansas from the year when essentially all the states reported complete results for their jurisdiction until the present. The following Figures 1 through 4 present the same data in a graphical format.

TABLE 1: Data published in "Better Roads" magazine
from the National Bridge Inventory
for the fifty United States and the District of Columbia

Reporting Year	Total Interstate & State Bridges	Total Substandard	Total Percent Substandard	Total City/County/ Township Bridges	Total Substandard	Total Percent Substandard	Total All Bridges	Total Substandard	Total Percent Substandard
1981	264,894	53,464	20.2	309,637	123,141	39.8	574,531	176,605	30.7
1982	263,303	58,379	22.2	307,292	154,171	50.2	570,595	212,568	37.3
1983	264,078	62,830	23.8	302,775	165,928	54.8	566,853	228,758	40.4
1984	266,686	71,607	26.9	316,189	176,487	55.8	582,875	248,094	42.6
1985	269,129	71,584	26.6	317,112	177,618	56.0	586,241	249,202	42.5
1986	269,125	76,160	28.3	315,752	169,657	53.7	584,877	245,817	42.0
1987	271,125	77,179	28.5	315,555	166,201	52.7	586,680	243,380	41.5
1988	272,337	77,787	28.6	314,606	161,915	51.5	586,943	239,702	40.8
1989	274,678	74,910	27.3	313,039	150,552	48.1	587,717	225,462	38.4
1990	275,202	75,367	27.4	310,134	145,654	47.0	585,336	221,021	37.8
1991	280,817	75,069	26.7	312,399	132,995	42.6	593,216	208,064	35.1
1992	281,670	74,424	26.4	319,080	132,480	41.5	600,750	206,904	34.4
1993	279,073	69,473	24.9	309,077	121,951	39.5	588,150	191,424	32.5
1994	280,575	68,910	24.6	308,610	117,928	38.2	589,185	186,838	31.7
1995	281,840	70,784	25.1	309,365	116,720	37.7	591,205	187,504	31.7
1996	281,398	70,126	24.9	307,845	112,281	36.5	589,243	182,407	31.0
1997	280,898	68,810	24.5	309,142	110,645	35.8	590,040	179,455	30.4
1998	279,543	68,466	24.5	309,792	109,626	35.4	589,335	178,092	30.2

TABLE 2: Data published in "Better Roads" magazine
from the National Bridge Inventory
for the State of Arkansas

Reporting Year	Total Interstate & State Bridges	Total Substandard	Total Percent Substandard	Total City/County/ Township Bridges	Total Substandard	Total Percent Substandard	Total All Bridges	Total Substandard	Total Percent Substandard
1981	6,539	1,100	16.8	7,671	5,930	77.3	14,210	7,030	49.5
1982	6,539	1,100	16.8	7,671	5,930	77.3	14,210	7,030	49.5
1983	6,691	1,777	26.6	8,017	6,522	81.4	14,708	8,299	56.4
1984	6,628	2,005	30.3	7,707	6,691	86.8	14,335	8,696	60.7
1985	6,639	2,011	30.3	7,656	6,456	84.3	14,295	8,467	59.2
1986	6,649	2,008	30.2	6,330	4,296	67.9	12,979	6,304	48.6
1987	6,644	1,786	26.9	6,307	4,175	66.2	12,951	5,961	46.0
1988	6,667	1,511	22.7	6,325	4,147	65.6	12,992	5,658	43.5
1989	6,687	1,425	21.3	6,196	3,927	63.4	12,883	5,352	41.5
1990	6,719	1,647	24.5	6,146	3,588	58.4	12,865	5,235	40.7
1991	6,750	1,617	24.0	5,990	3,159	52.7	12,740	4,776	37.5
1992	6,768	1,554	23.0	5,925	2,821	47.6	12,693	4,375	34.5
1993	6,782	1,151	17.0	5,822	2,642	45.4	12,604	3,793	30.1
1994	6,797	1,142	16.8	5,730	2,576	45.0	12,527	3,718	29.7
1995	6,838	1,152	16.8	5,672	2,487	43.8	12,510	3,639	29.1
1996	6,850	1,136	16.6	5,586	2,354	42.1	12,436	3,490	28.1
1997	6,882	1,134	16.5	5,470	2,158	39.5	12,352	3,292	26.7
1998	6,941	1,109	16.0	5,405	2,048	37.9	12,346	3,157	25.6

Each figure plots a total number of bridges from 1981 through to the present, the total number substandard in that category, and the percent substandard for that category. A cursory examination of Figures 1 and 3 for Interstate and State Bridges for the nation and for Arkansas leads one to the same conclusions. The total number of bridges in this category seems relatively stable, but with some decided increase as the general network of roads is enlarged and upgraded. The percent of those national bridges that are substandard is relatively low in both cases, but far higher than they should be. Fortunately, the percent substandard of Interstate and State Bridges is lower in Arkansas than the national average, and the last decade has shown a consistent decrease in that percentage both at the national and Arkansas levels. In Arkansas during that time period the rate of decrease has been even more pronounced. When attention is focused on a problem, and the seriousness and importance of the problem is understood, the American people respond. Arkansans are a particularly self-reliant and practical people, and it is not surprising that they have responded in a more intense fashion.

Consideration of the corresponding Figures 2 and 4 for "City/County/Township" Bridges at the national level and for Arkansas is even more dramatic, and, in places, puzzling. First, in both cases, the absolute numbers of substandard bridges and the corresponding percentages are much higher than for the Interstate and State bridges. This is understandable for a variety of reasons. The bridges of the Interstate system and many of the bridges on U.S. highways within the separate states are part of a newer system. Also, the federal government has typically more power to tax for maintenance monies than the individual states, especially if the state is predominantly rural and less affluent. The obverse of such a situation is that the "state-aid" bridges, as they are called in Arkansas, are less well funded. In times of financial distress the first item to be neglected is maintenance and so the bridges suffer. Also, the audience for a substandard bridge on the Interstate and state system is larger since the daily traffic count on these bridges is typically larger. The larger audience can bring much more political pressure for repairs than say the small population of a poor county concerned with a local bridge. Despite these factors, the changes in the "City/County/Township" category have been dramatic both at the national and Arkansas levels. At the national level, after a peak in 1984, there has been a steady reduction in the absolute number and percentage of substandard bridges. The same trend is evident in the Arkansas "City/County" bridge data but the reduction is even more dramatic. The peak value is again in 1984, but the percent substandard is 86.8. By 1998 percent substandard has been brought to a much lower value, 37.9, but that is still higher than the national average for this category, 35.4 percent. Arkansas has made major improvement in its state-aid bridges, but still has a way to go to catch up with the nation in this category.

Some of the data is curious for the state of Arkansas. The total number of bridges in the City/County system has also been dropping. One major reason for this may be the increased popularity in substituting systems of multiple culverts for bridges. It could be interesting in the future to do a more detailed study of the history of the changes in Arkansas's off-federal-jurisdiction bridges. Despite the dramatic reduction in the absolute number of Arkansas' substandard state-aid bridges, the reduction of its percentage substandard for the same category is not as pronounced.

1.2 Timber as an Alternative
Part of the motivation for this study is the conviction that timber, as a bridge structural material, can make a significant contribution to bridge replacement needs in the United States, particularly for shorter span bridges in the "City/County/Township" jurisdictions. The other part of the motivation is the recognition that this conviction is not widely shared by many people both in and out of the bridge engineering community.

The first ways for humans to cross streams were either to ford them at shallow points, or to make use of convenient exposed stones in the stream bed. Perhaps the use of a naturally fallen tree inspired our ancestors to intentionally fell trees for similar use. Later masonry arches were also used. It has been the author's experience in teaching structural design of both masonry and timber, that the two materials, although the oldest and most natural of structural materials, are also the least understood and the most maligned. Actually, because they are both natural materials they are, therefore, more random in their behavior, more difficult to model mathematically, and more complicated than either steel and/or reinforced concrete. This complexity has delayed the development of their adequate and complete "engineering." Their lesser strength, when not adequately "engineered," has led to a poor reputation for both materials.

Nevertheless, the early history of bridges in the world and in the United States is a history of the use of timber as a structural material. The effort to recall these long lasting and previous successes has become a project for the timber industry. The reader is directed to the first two chapters of Mike Ritter's Timber Bridges: Design, Construction, Inspection, and Maintenance [Ritter, 1990]. Another good example is a recent article in the magazine Public Roads [Duwadi and Ritter, 1997] that traces the history of timber bridges from the beginnings of the United States to the present, and describes the development of the technologies of lamination and pressure treatment that are the basis of "modern" timber bridges, and the source of the current competitiveness of timber with other bridge structural materials.

Despite the major technological developments in the latter half of the twentieth century with respect to timber bridges, there is still a basic current mind-set in the bridge design community against the use of timber as a bridge structural material. Ritter [1990, p. 1-19] offers his own explanation to that hesitancy. "Perhaps the biggest obstacle to the acceptance and the use of timber has been a persistent lack of understanding related to design and performance of the material." Ritter, in turn, quotes Johnson [1986] as to the causes of this "lack of understanding."

The timber industry is one of those industries that has not made a substantial unified effort to generate and distribute technical information. This has been interpreted by some engineers as a reflection on the suitability of the material itself, and not as an indictment of the industry for failing to provide the information. The reason the timber industry has not met the challenge is quite obvious once one looks at the respective industries.

Johnson goes on to say that whereas the steel and cement industries have both separately and, on occasion, together actively promoted structural steel and reinforced concrete as structural bridge materials, the multiple parts of the timber industry have not.

That is a dated statement, because in 1989, under the auspices of the Department of Agriculture's U.S. Forest Service, the National Timber Bridge Initiative Program was established, domiciled at their Northeastern Area office in Morgantown, West Virginia. The project is now called the National Wood in Transportation Program. Part of the program is a competitive cost sharing arrangement for encouraging the design and construction of innovative demonstration timber bridge projects, with an annual national budget that varies each year, but is in the order of 1.0 to 1.5 millions dollars.

Each state of the Union has received benefits from the program. The author has been shown several such bridge projects in Arkansas. He also witnessed and filmed the installation of an innovative bridge project in Washington County. That bridge was a "stress laminated box girder" structure that incorporated all of the current lamination developments in timber structural materials. The timber bridge initiative program was been the source of a number of significant solutions to local bridge replacement needs across the United States, but it has not caused a major revision of attitude toward timber bridges.

Another part of the Forest Service's information strategy was a series of timber bridge design conferences. The author has attended several of these conferences. He remembers vividly the opening address at one such conference held in Birmingham, Alabama. The speaker was the then Secretary of State for Alabama, a man who was also a licensed professional civil engineer. His primary point was that the potential economic advantage of the use of timber bridges for his state was two-fold. On the one hand they promised a relatively cheap solution to the problem of replacing substandard spans on Alabama rural roads. On the other hand they gave promise to promoting the growth of the important timber industry of his state. The increased use of timber bridges has an identical two-fold potential for the state of Arkansas. The sections for the Washington County stress-laminated box girder timber bridge mentioned earlier had been manufactured of mixed oak from Southern Illinois. They could just as well have been manufactured by and contributed to the economy of northwest Arkansas.

It would be a mistake, however, to think that this mutually contributive economic solution is without problems. At this writing the onset of global warming is being taken with increased seriousness. The world weather is being threatened by the most significant El Nino of several decades. A five hundred year flood in North Dakota and southern Canada was been preceeded by numerous summers of hundred year floods throughout the world. The contribution of forests in exchanging oxygen for carbon dioxide becomes exceedingly important. The conflict between human use that can be made of forest products as fuel, paper, structural material, and raw material for the chemical industry has to be balanced with values provided by forests remaining intact, i.e., flood protection, erosion control, wildlife habitat, oxygen manufacture, soil humus, and human recreation. Even intense reforestation is not necessarily an answer if the method of it defies the need for biodiversity in the forest. Obviously, this is an area needing the wisest of human decisions, and the ability to compromise on goals that include values that are not just short-sighted immediate human values. Trade-offs are inevitable, but the author is still of the belief that the use of well-engineered and constructed timber bridges will have some significant part to play in the real solution of Arkansas' rural bridge replacement needs.

1.3 Timber Bridges in Arkansas
The common American mind-set that views the design of timber bridges as a waste of money is widespread in Arkansas as well. It is the author's experience and opinion that this is true not only among the general public but also at all echelons of the bridge design-construction- maintenance community as well.

This negative mind-set does not have as significant a discouraging effect on creativity and flexibility in the "Interstate and State" system, because the public is accustomed to seeing steel stringers under concrete decks for most major bridges and overpasses on the Interstate, federal, and state highways of Arkansas. Timber superstructures could be a viable option for many of these bridge structures. But the bridge design section of the AHTD has honed the design of concrete-deck-over-steel-stringers bridges to the point that it is very easy and therefore very economical for the AHTD to continue their use for both short and long spans. Nevertheless, there is some flexibility emerging in the bridge department of the AHTD that is probably caused as much as anything by the need to modify designs in terms of life-cycle costs instead of initial construction costs. The issue of bridge superstructure and deck deterioration plays a large role in these changes.

Several years ago the author attended a one-day short course sponsored jointly by the AHTD, and the "Arkansas Area Prestressed Concrete Council." The latter was at that time a new organization unknown to the author. The membership of the organization consists of precast prestressed concrete element producers who are interested in the potential Arkansas market. The vast majority of the Council's members are domiciled in states bordering Arkansas because there are very few such producers inside the borders of Arkansas. The primary selling point of the conference was the superior durability performance of precast stringers as described in a presentation given by a staff member of the Portland Cement Association (PCA) [Rabbat, 1993]. The address was a comparative study of the durability of certain types of bridge superstructures using data taken from the National Bridge Inventory. The primary point of the article was that bridges with prestressed concrete stringers were longer lasting. The structural material with the poorest record in the study was timber. The author's own reaction to this was that the development of the technology that underlies "modern" timber bridges is so relatively new and seldom used that one could believe that the study was not a fair comparison with respect to timber.

The author in previous years kept lists provided by the AHTD of the distribution of various structural materials for the superstructures of state-aid bridges in Arkansas. His recollection is that approximately half of the superstructures of those bridges in an era about a decade ago were made of timber.

Negative reaction to the decay of traditional timber bridges has led many county judges and their road and bridge departments to make a commitment to find inexpensive alternatives to timber bridges. Used railroad flatbeds have been used. These were cheap at first, but their price has risen with their popularity. They are difficult to "load rate" because their strength reduction due to previous fatigue loading is not easy to evaluate. Moreover, sometimes they are "modified" in an unsafe manner in order to be fitted to a particular bridge site. Also, corrosion of these all-steel superstructures is not easy to prevent.

Another popular program for some counties has been the use of side-by-side precast concrete channel sections for use in various span lengths for county bridge replacements. The author is not certain when these plans were developed. The copies he has for both the bridge sections and the plans for the forms list the University of Arkansas Division of Agriculture Cooperative Extention Service in the title block. He believes, however, that the design of the sections was developed initially by AHTD for the sake of state-aid bridges in the mid-60's. Several counties in the state made early use of these plans and have produced the sections for their own bridge replacement program for quite some time. Washington County is an example of such early use. Craighead County, with Jonesboro as County Seat, and Jefferson County, with Pine Bluff as County Seat, have newer and more advanced production facilities for year round production of the channel sections.

The plans allow varying standard lengths of 19, 25, and 31 feet, depending on whether the main girder reinforcement consists of #9, #10, or #11 rebars respectively. Most counties with which the author is familiar use a 30 foot span length and #11 rebars. Seven of the 3'-7.5" wide channel sections side by side provide sufficient width for two standard lanes and space for precast curb units at the two outside edges.

Counties that use this system have found it very economical. Some other counties purchase similar units from a few precast manufacturers in the state. All in all, this has been a very useful and successful program for short span bridge replacement on counties in the state.

The scope for this project will be described in more detail later. The initially intended scope included surveying some 21 counties in the southern third of the state for help in identifying bridge sites where economic comparison could be made of alternate bridge replacement schemes including as many as three types of timber superstructure bridges. The response to a questionnaire sent by the author to the county judges in those 21 counties was so discouraging in terms of the positive response to the use of timber bridge superstructures yet so interesting as to the variety of types of bridges systems used, that the author decided finally to send the questionnaire to all 75 of the counties in the state. Table 3 following gives the results of the questionnaire in tabular form. The questionnaire was modified twice as the early responses indicated difficulties the counties experienced in understanding the intent of some of the questions. The three separate versions of the one-page questionnaire sent to the county judges appear in the Appendix. If blanks occur in Table 3 it is because the person responding from the individual county did not include a response to that question. Three lines in the table are completely blank because the county judge and/or road and bridge department director chose not to respond not only to the initial mailing but to as many as three follow-up mailings. All this is indicative of busy schedules, but the responses (or lack thereof) also indicate a general disinterest in timber as a bridge superstructure material. Nevertheless, that 72 counties out of 75 eventually responded makes the answers useful.