Strengthening of Existing Single Span Steel Beam and Concrete Deck Bridges, HR-238, Part 1, 1983

The Phase I research, Iowa Department of Transportation (IDOT) Project HR-214, "Feasibility Study of Strengthening Existing Single Span Steel Beam Concrete Deck Bridges," verified that post-tensioning can be used to provide strengthening of the composite bridges under investigation. Phase II research, reported here, involved the strengthening of two full-scale prototype bridges - one a prototype of the model bridge tested during Phase I and the other larger and skewed. In addition to the field work, Phase II also involved a considerable amount of laboratory work. A literature search revealed that only minimal data existed on the angle-plus-bar shear connectors. Thus, several specimens utilizing angle-plus-bar, as well as channels, studs and high strength bolts as shear connectors were fabricated and tested. To obtain additional shear connector information, the bridge model of Phase I was sawed into four composite concrete slab and steel beam specimens. Two of the resulting specimens were tested with the original shear connection, while the other two specimens had additional shear connectors added before testing. Although orthotropic plate theory was shown in Phase I to predict vertical load distribution in bridge decks and to predict approximate distribution of post-tensioning for right-angle bridges, it was questioned whether the theory could also be used on skewed bridges. Thus, a small plexiglas model was constructed and used in vertical load distribution tests and post-tensioning force distribution tests for verification of the theory. Conclusions of this research are as follows: (1) The capacity of existing shear connectors must be checked as part of a bridge strengthening program. Determination of the concrete deck strength in advance of bridge strengthening is also recommended. (2) The ultimate capacity of angle-plus-bar shear connectors can be computed on the basis of a modified AASHTO channel connector formula and an angle-to-beam weld capacity check. (3) Existing shear connector capacity can be augmented by means of double-nut high strength bolt connectors. (4) Post-tensioning did not significantly affect truck load distribution for right angle or skewed bridges. (5) Approximate post-tensioning and truck load distribution for actual bridges can be predicted by orthotropic plate theory for vertical load; however, the agreement between actual distribution and theoretical distribution is not as close as that measured for the laboratory model in Phase I. (6) The right angle bridge exhibited considerable end restraint at what would be assumed to be simple support. The construction details at bridge abutments seem to be the reason for the restraint. (7) The skewed bridge exhibited more end restraint than the right angle bridge. Both skew effects and construction details at the abutments accounted for the restraint. (8) End restraint in the right angle and skewed bridges reduced tension strains in the steel bridge beams due to truck loading, but also reduced the compression strains caused by post-tensioning.

Strengthening of Existing Single Span Steel Beam and Concrete Deck Bridges, HR-238, Part II, 1985

The unifying objective of Phases I and II of this study was to determine the feasibility of the post-tensioning strengthening method and to implement the technique on two composite bridges in Iowa. Following completion of these two phases, Phase III was undertaken and is documented in this report. The basic objectives of Phase III were further monitoring bridge behavior (both during and after post-tensioning) and developing a practical design methodology for designing the strengthening system under investigation. Specific objectives were: to develop strain and force transducers to facilitate the collection of field data; to investigate further the existence and effects of the end restraint on the post-tensioning process; to determine the amount of post-tensioning force loss that occurred during the time between the initial testing and the retesting of the existing bridges; to determine the significance of any temporary temperature-induced post-tensioning force change; and to develop a simplified design methodology that would incorporate various variables such as span length, angle-of-skew, beam spacing, and concrete strength. Experimental field results obtained during Phases II and III were compared to the theoretical results and to each other. Conclusions from this research are as follows: (1) Strengthening single-span composite bridges by post-tensioning is a viable, economical strengthening technique. (2) Behavior of both bridges was similar to the behavior observed from the bridges during field tests conducted under Phase II. (3) The strain transducers were very accurate at measuring mid-span strain. (4) The force transducers gave excellent results under laboratory conditions, but were found to be less effective when used in actual bridge tests. (5) Loss of post-tensioning force due to temperature effects in any particular steel beam post-tensioning tendon system were found to be small. (6) Loss of post-tensioning force over a two-year period was minimal. (7) Significant end restraint was measured in both bridges, caused primarily by reinforcing steel being continuous from the deck into the abutments. This end restraint reduced the effectiveness of the post-tensioning but also reduced midspan strains due to truck loadings. (8) The SAP IV finite element model is capable of accurately modeling the behavior of a post-tensioned bridge, if guardrails and end restraints are included in the model. (9) Post-tensioning distribution should be separated into distributions for the axial force and moment components of an eccentric post-tensioning force. (10) Skews of 45 deg or less have a minor influence on post-tensioning distribution. (11) For typical Iowa three-beam and four-beam composite bridges, simple regression-derived formulas for force and moment fractions can be used to estimate post-tensioning distribution at midspan. At other locations, a simple linear interpolation gives approximately correct results. (12) A simple analytical model can accurately estimate the flexural strength of an isolated post-tensioned composite beam.

Design Manual for Strengthening Single-Span Composite Bridges by Post-Tensioning Part 3, HR-238, 1985

The authors have post-tensioned and monitored two Iowa bridges and have field tested the post-tensioning of a composite bridge in Florida. In order to provide the practical post-tensioning distribution factors given in this manual, the authors developed a finite element model of a composite bridge and checked the model against a one-half scale laboratory bridge and two actual composite bridges, one of which had a 45 deg skew. Following a brief discussion of this background research, this manual explains the use of elastic, composite beam and bridge section properties, the distribution fractions for symmetrically post-tensioned exterior beams, and a method for computing the strength of a post-tensioned beam. Also included is a design example for a typical, 51.25-ft (15.62-m) span, four-beam composite bridge. Moments for Iowa Department of Transportation rating trucks, H 20 and HS 20 trucks, have been tabulated for design convenience and are included in the appendix.

Load Ratings for Standard Bridges, HR-239 Phase III, 1998

In this report, 25 secondary bridge standards for three types of bridges are rated for the AASHTO HS20-44 vehicle configuration and five typical Iowa legal vehicles. The ratings apply only to those bridges which: (1) are built according to the applicable bridge standard plans, (2) have no structural deterioration or damage, and (3) have no added wearing surface in excess of 0.5-in. (1.27-cm) integral wearing surface. Appendix A contains the results of the original October 1982 report on load ratings for standard bridges.

Design Manual for Strengthening of Continuous-Span Composite Bridges, HR-333, 1993

The need for upgrading a large number of understrength bridges in the United States has been well documented in the literature. This manual presents two methods for strengthening continuous-span composite bridges: post-tensioning of the positive moment regions of the bridge stringers and the addition of superimposed trusses at the piers. The use of these two systems is an efficient method of reducing flexural overstresses in undercapacity bridges. Before strengthening a given bridge however, other deficiencies (inadequate shear connection, fatigue problems, extensive corrosion) should be addressed. Since continuous-span composite bridges are indeterminant structures, there is longitudinal and transverse distribution of the strengthening axial forces and moments. This manual basically provides the engineer with a procedure for determining the distribution of strengthening forces and moments throughout the bridge. As a result of the longitudinal and transverse force distribution, the design methodology presented in this manual for continuous-span composite bridges is extremely complex. To simplify the procedure, a spreadsheet has been developed for use by practicing engineers. This design aid greatly simplifies the design of a strengthening system for a given bridge in that it eliminates numerous tedious hand calculations, computes the required force and moment fractions, and performs the necessary iterations for determining the required strengthening forces. The force and moment distribution fraction formulas developed in this manual are primarily for the Iowa DOT V12 and V14 three-span four-stringer bridges. These formulas may be used on other bridges if they are within the limits stated in this manual. Use of the distribution fraction formulas for bridges not within the stated limits is not recommended.

Load Ratings for Standard Bridges, HR-239, 1982

The load ratings for these Standard bridges were calculated in compliance with the 1978 AASHTO Manual for Maintenance Inspection of Bridges, using the appropriate allowable stresses for the materials specified by the Standard plans. Distribution of loads is in compliance with the Manual unless otherwise noted. Except for truss spans, all bridges with roadway widths of 18 ft. or less were rated for one lane of traffic. All 18 ft. roadway truss bridges were rated for both one and two lanes of traffic. All bridges with roadway widths exceeding 18 ft. were rated for two lanes of traffic. If the posting rating for two lane bridges was less than legal, then the bridges were rated for traffic restricted to one lane, or to one lane centered in the roadway, as noted on the summary sheet. The ratings are applicable to bridges built in accordance with the standard plans and which exhibit no significant deterioration or damage to the structural members, and which have no added wearing surface material in excess of that noted on the summary sheets and used in the calculations. The inventory and operating ratings were based upon the standard AASHTO HS20-44 loading. The legal load ratings were based upon the three typical Iowa legal vehicles shown on page 5. The legal load ratings were based upon the maximum allowable Operating Rating stresses specified in the Manual. Refer to notations on the summary sheets for additional qualifications on the load ratings for specific standard bridge series. Load ratings for standard bridges with wood floors must be based upon existing conditions of attachment of the wood flooring to the top flanges of longitudinal steel stringers. The ratings must be reevaluated if the existing lateral support conditions are not in accordance with conditions used for the rating and noted on the summary sheets. Details of most of the standard bridges are included in the three books of "Iowa State Highway Commission, Bridge Standards," issued in June, 1972. Copies of plans for those standard bridges that were rated, and that are not included in the original books of standard plans, are being furnished under separate cover with these rating summaries.

Feasibility Study of Dynamic Overload and Ultimate Load Tests of Full-Scale Highway Bridges, HR-160, 1973

As a result of the construction of the Saylorville Dam and Reservoir on the Des Moines River, six highway bridges are scheduled for removal. Five of these are old high-truss single-lane bridges, each bridge having several simple spans. The other bridge is a fairly modern (1955) double 4-span continuous beam-and-slab composite highway bridge. The availability of these bridges affords an unusual opportunity for study of the behavior of full-scale bridges. Because of the magnitude of the potential testing program, a feasibility study was initiated and the results are presented in this two-part final report. Part I summarizes the findings and Part II presents the supporting detailed information.

Standard Specifications for Highway and Bridge Construction, 2012

When referenced, the 2012 edition of the Iowa Department of Transportation’s (Iowa DOT) Standard Specifications for Highway and Bridge Construction shall be used for contract work awarded by the Iowa DOT. They may also be incorporated by reference in other contract work on secondary, urban, local systems, or other contract work in which the Iowa DOT has an interest. As modified by the General Supplemental Specifications, these Standard Specifications represent the minimum requirements and may be modified by Supplemental Specifications, Developmental Specifications, and Special Provisions on specific contracts. These Standard Specifications have been written so the Contractor’s responsibilities are indicated by plain language using the Imperative Mood and Active Voice form. Sentences are of the form: Construct isolation joints at all points where driveways meet other walks, curbs, or fixtures in the surface. Ensure finished members are true to detailed dimensions and free from twists, bends, open joints, or other defects resulting from faulty fabrication or defective work. Personnel preparing the JMF shall be Iowa DOT certified in bituminous mix design. The Contracting Authority’s responsibilities are (with some exceptions) indicated by the use of the modal verb “will”. Sentences are of the form: The Engineer will obtain and test density samples for each lot according to Materials I.M. 204. Payment will be the contract unit price for Fabric Reinforcement per square yard (square meter). These standard specifications contain dual units of measure: the United States Standard measure (English units) and the International System of Units (SI or “metric” units). The English units are expressed first then followed by the metric units in parentheses. The measurements expressed in the two systems are not necessarily equal. In some cases the measurements in metric units is a “hard” conversion of the English measurement; i.e. the metric unit has been approximated with a rounded, rationalized metric measurement that is easy to work with and remember. The proposal form will identify whether the work was designed and shall be constructed in English or metric units.

Rock Island Centennial Bridge, Final Report on Construction of the Mississippi River Bridge Between Rock Island, Illinois and Davenport, Iowa, 1945

The Rock Island Centennial Bridge spanning the Mississippi River between Rock Island, Illinois and Davenport, Iowa was opened to traffic on July 12, 1940. It is a thoroughly modern, four-lane highway bridge, adequate in every respect for present day high speed passenger and transport traffic. The structure is ideally situated to provide rapid transit between the business districts of Rock Island and Davenport and serves not only the local or shuttle traffic in the Tri-City Area, but also heavy through motor travel on U.S. Highways 67 and 150. The Centennial Bridge is notable in several respects. The main spans are box girder rib tied arches, a type rather unusual in America and permitting simplicity in design with pleasing appearance. The Centennial Bridge is the only bridge across the Mississippi providing for four lanes of traffic with separation of traffic in each direction. It is a toll bridge operating alongside a free bridge and has the lowest rates of toll of any toll bridge on the Mississippi River. It was financed entirely by the City of Rock Island with no obligation on the taxpayers; there was no federal or state participation in the financing. But perhaps the most outstanding feature of the new bridge is its great need. A few remarks on the communities served by the new structure, the services rendered, and some statistics on cross-river traffic in the Tri-City Area will emphasize the reasons for constructing the Centennial Bridge.

Development of Preliminary Load and Resistance Factor Design of Drilled Shafts in Iowa, RB03-012, 2014

The Federal Highway Administration (FHWA) mandated utilizing the Load and Resistance Factor Design (LRFD) approach for all new bridges initiated in the United States after October 1, 2007. To achieve part of this goal, a database for Drilled Shaft Foundation Testing (DSHAFT) was developed and reported on by Garder, Ng, Sritharan, and Roling in 2012. DSHAFT is aimed at assimilating high-quality drilled shaft test data from Iowa and the surrounding regions. DSHAFT is currently housed on a project website (http://srg.cce.iastate.edu/dshaft) and contains data for 41 drilled shaft tests. The objective of this research was to utilize the DSHAFT database and develop a regional LRFD procedure for drilled shafts in Iowa with preliminary resistance factors using a probability-based reliability theory. This was done by examining current design and construction practices used by the Iowa Department of Transportation (DOT) as well as recommendations given in the American Association of State Highway and Transportation Officials (AASHTO) LRFD Bridge Design Specifications and the FHWA drilled shaft guidelines. Various analytical methods were used to estimate side resistance and end bearing of drilled shafts in clay, sand, intermediate geomaterial (IGM), and rock. Since most of the load test results obtained from O-cell do not pass the 1-in. top displacement criterion used by the Iowa DOT and the 5% of shaft diameter for top displacement criterion recommended by AASHTO, three improved procedures are proposed to generate and extend equivalent top load-displacement curves that enable the quantification of measured resistances corresponding to the displacement criteria. Using the estimated and measured resistances, regional resistance factors were calibrated following the AASHTO LRFD framework and adjusted to resolve any anomalies observed among the factors. To illustrate the potential and successful use of drilled shafts in Iowa, the design procedures of drilled shaft foundations were demonstrated and the advantages of drilled shafts over driven piles were addressed in two case studies.

Design of Piles for Integral Abutment Bridges, HR-252, 1984

More and more, integral abutment bridges are being used in place of the more traditional bridge designs with expansion releases. In this study, states which use integral abutment bridges were surveyed to determine their current practice in the design of these structures. To study piles in integral abutment bridges, a finite element program for the soil-pile system was developed (1) with materially and geometrically nonlinear, two and three dimensional beam elements and (2) with a nonlinear, Winkler soil model with vertical, horizontal, and pile tip springs. The model was verified by comparison to several analytical and experimental examples. A simplified design model for analyzing piles in integral abutment bridges is also presented. This model grew from previous analytical models and observations of pile behavior. The design model correctly describes the essential behavioral characteristics of the pile and conservatively predicts the vertical load-carrying capacity. Analytical examples are presented to illustrate the effects of lateral displacements on the ultimate load capacity of a pile. These examples include friction and end-bearing piles; steel, concrete, and timber piles; and bending about the weak, strong, and 45° axes for H piles. The effects of cyclic loading are shown for skewed and nonskewed bridges. The results show that the capacity of friction piles is not significantly affected by lateral displacements, but the capacity of end-bearing piles is reduced. Further results show that the longitudinal expansion of the bridge can introduce a vertical preload on the pile.

Heavy Agricultural Loads on Pavements and Bridges, HR-1073, 1999

During the harvest season in Iowa, it is common to have single axle loads on secondary roads and bridges that are excessive (typical examples are grain carts) and well beyond normal load limits. Even though these excessive loads occur only during a short time of the year, they may do significant damage to pavements and bridges. In addition, the safety of some bridges may be compromised because of the excessive loads, and sometimes there may be little indication to the users that damage may be imminent. At this time there are no Iowa laws regulating axle loads allowed for agricultural equipment. This study looks at the potential problems this may cause on secondary roads and timber stringer bridges. Both highway pavement and timber bridges are evaluated in this report. A section (panel) of Iowa PCC paved county road was chosen to study the effects of heavy agricultural loads on pavements. Instrumentation was applied to the panel and a heavily loaded grain cart was rolled across. The collected data were analyzed for any indication of excessive stresses of the concrete. The second study, concerning excessive loads on timber stringer bridges, was conducted in the laboratory. Four bridge sections were constructed and tested. Two of the sections contained five stringers and two sections had three stringers. Timber for the bridges came from a dismantled bridge, and deck panels were cut from new stock. All timber was treated with creosote. A hydraulic load was applied at the deck mid-span using a foot print representing a tire from a typical grain cart. Force was applied until failure of the system resulted. The collected data were evaluated to provide indications of load distribution and for comparison with expected wheel loads for a typical heavily loaded single axle grain cart. Results of the pavement tests showed that the potential of over-stressing the pavement is a possibility. Even though most of the tension stress levels recorded were below the rupture strength of the concrete, there were a few instances where the indicated tension stress level exceeded the concrete rupture strength. Results of the bridge tests showed that when the static ultimate load capacity of the timber stringer bridge sections was reached, there was sudden loss of capacity. Prior to reaching this ultimate capacity, the load sharing between the stringers was very uniform. The failure was characterized by loss of flexural capacity of the stringers. In all tests, the ultimate test load exceeded the wheel load that would be applied by an 875 bushel single axle grain cart.

Identification of Practices, Design, Construction, and Repair Using Trenchless Technology, TR-570, 2010

Trenchless technologies are methods used for the construction and rehabilitation of underground utility pipes. These methods are growing increasingly popular due to their versatility and their potential to lower project costs. However, the use of trenchless technologies in Iowa and their effects on surrounding soil and nearby structures has not been adequately documented. Surveys of and interviews with professionals working in trenchless-related industries in Iowa were conducted, and the results were analyzed and compared to survey results from the United States as a whole. The surveys focused on method familiarity, pavement distress observed, reliability of trenchless methods, and future improvements. Results indicate that the frequency of pavement distress or other trenchless-related issues are an ongoing problem in the industry. Inadequate soil information and quality control/quality assurance (QC/QA) are partially to blame. Fieldwork involving the observation of trenchless construction projects was undertaken with the purpose of documenting current practices and applications of trenchless technology in the United States and Iowa. Field tests were performed in which push-in pressure cells were used to measure the soil stresses induced by trenchless construction methods. A program of laboratory soil testing was carried out in conjunction with the field testing. Soil testing showed that the installations were made in sandy clay or well-graded sand with silt and gravel. Pipes were installed primarily using horizontal directional drilling with pipe diameters from 3 to 12 inches. Pressure cell monitoring was conducted during the following construction phases: pilot bore, pre-reaming, and combined pipe pulling and reaming. The greatest increase in lateral earth pressure was 5.6 psi and was detected 2.1 feet from the centerline of the bore during a pilot hole operation in sandy lean clay. Measurements from 1.0 to 2.5 psi were common. Comparisons were made between field measurements and analytical and finite element calculation methods.

Field and Laboratory Evaluation of Precast Concrete Bridges, TR-440, 2001

Recent data compiled by the National Bridge Inventory revealed 29% of Iowa's approximate 24,600 bridges were either structurally deficient or functionally obsolete. This large number of deficient bridges and the high cost of needed repairs create unique problems for Iowa and many other states. The research objective of this project was to determine the load capacity of a particular type of deteriorating bridge – the precast concrete deck bridge – which is commonly found on Iowa's secondary roads. The number of these precast concrete structures requiring load postings and/or replacement can be significantly reduced if the deteriorated structures are found to have adequate load capacity or can be reliably evaluated. Approximately 600 precast concrete deck bridges (PCDBs) exist in Iowa. A typical PCDB span is 19 to 36 ft long and consists of eight to ten simply supported precast panels. Bolts and either a pipe shear key or a grouted shear key are used to join adjacent panels. The panels resemble a steel channel in cross-section; the web is orientated horizontally and forms the roadway deck and the legs act as shallow beams. The primary longitudinal reinforcing steel bundled in each of the legs frequently corrodes and causes longitudinal cracks in the concrete and spalling. The research team performed service load tests on four deteriorated PCDBs; two with shear keys in place and two without. Conventional strain gages were used to measure strains in both the steel and concrete, and transducers were used to measure vertical deflections. Based on the field results, it was determined that these bridges have sufficient lateral load distribution and adequate strength when shear keys are properly installed between adjacent panels. The measured lateral load distribution factors are larger than AASHTO values when shear keys were not installed. Since some of the reinforcement had hooks, deterioration of the reinforcement has a minimal affect on the service level performance of the bridges when there is minimal loss of cross-sectional area. Laboratory tests were performed on the PCDB panels obtained from three bridge replacement projects. Twelve deteriorated panels were loaded to failure in a four point bending arrangement. Although the panels had significant deflections prior to failure, the experimental capacity of eleven panels exceeded the theoretical capacity. Experimental capacity of the twelfth panel, an extremely distressed panel, was only slightly below the theoretical capacity. Service tests and an ultimate strength test were performed on a laboratory bridge model consisting of four joined panels to determine the effect of various shear connection configurations. These data were used to validate a PCDB finite element model that can provide more accurate live load distribution factors for use in rating calculations. Finally, a strengthening system was developed and tested for use in situations where one or more panels of an existing PCDB need strengthening.

The Effects of Headcut and Knickpoint Propagation on Bridges in Iowa, TR-541, 2008

The overarching goal of the proposed research was to provide a predictive tool for knickpoint propagation within the HCA (Hungry Canyon Alliance) territory. Knickpoints threaten the stability of bridge structures in Western Iowa. The study involved detailed field investigations over two years in order to monitor the upstream migration of a knickpoint on Mud Creek in Mills County, IA and identify the key mechanisms triggering knickpoint propagation. A state-of-the-art laser level system mounted on a movable truss provided continuous measurements of the knickpoint front for different flow conditions. A pressure transducer found in proximity of the truss provided simultaneous measurements of the flow depth. The laser and pressure transducer measurements led to the identification of the conditions at which the knickpoint migration commences. It was suggested that negative pressures developed by the reverse roller flow near the toe of the knickpoint face triggered undercutting of the knickpoint at this location. The pressure differential between the negative pressure and the atmospheric pressure also draws the impinging jet closer to the knickpoint face producing scour. In addition, the pressure differential may induce suction of sediment from the face. Other contributing factors include slump failure, seepage effects, and local fluvial erosion due to the exerted fluid shear. The prevailing flow conditions and soil information along with the channel cross-sectional geometry and gradient were used as inputs to a transcritical, one dimensional, hydraulic/geomorphic numerical model, which was used to map the flow characteristics and shear stress conditions near the knickpoint. Such detailed flow calculations do not exist in the published literature. The coupling of field and modeling work resulted in the development of a blueprint methodology, which can be adopted in different parts of the country for evaluating knickpoint evolution. This information will assist local government agencies in better understanding the principal factors that cause knickpoint propagation and help estimate the needed response time to control the propagation of a knickpoint after one has been identified.