Investigation of Two Bridge Alternatives for Low Volume Roads - Phase II Volume 1 of 2 Concept 1: Steel Beam Precast Units, TR-410, 2000

This project continues the research which addresses the numerous bridge problems on the Iowa secondary road system. It is a continuation (Phase 2) of Project HR-382, in which two replacement alternatives (Concept 1: Steel Beam Precast Units and Concept 2: Modification of the Benton County Beam-in-Slab Bridge) were investigated. In previous research for concept 1, a precast unit bridge was developed through laboratory testing. The steel-beam precast unit bridge requires the fabrication of precast double-tee (PCDT) units, each consisting of two steel beams connected by a reinforced concrete deck. The weight of each PCDT unit is minimized by limiting the deck thickness to 4 in., which permits the units to be constructed off-site and then transported to the bridge site. The number of units required is a function of the width of bridge desired. Once the PCDT units are connected, a cast-in-place reinforced concrete deck is cast over the PCDT units and the bridge railing attached. Since the steel beam PCDT unit bridge design is intended primarily for use on low-volume roads, used steel beams can be utilized for a significant cost savings. In previous research for concept 2, an alternate shear connector (ASC) was developed and subjected to static loading. In this investigation, the ASC was subjected to cyclic loading in both pushout specimens and composite beam tests. Based on these tests, the fatigue strength of the ASC was determined to be significantly greater than that required in typical low volume road single span bridges. Based upon the construction and service load testing, the steel-beam precast unit bridge was successfully shown to be a viable low volume road bridge alternative. The construction process utilized standard methods resulting in a simple system that can be completed with a limited staff. Results from the service load tests indicated adequate strength for all legal loads. An inspection of the bridge one year after its construction revealed no change in the bridge's performance. Each of the systems previously described are relatively easy to construct. Use of the ASC rather than the welded studs significantly simplified the work, equipment, and materials required to develop composite action between the steel beams and the concrete deck.

Investigation of Two Bridge Alternatives for Low Volume Roads - Phase II Volume 2 of 2, Concept 2: Beam in Slab Bridge, TR-410, 2000

This project continues the research which addresses the numerous bridge problems on the Iowa secondary road system. It is a continuation (Phase 2) of Project HR-382, in which two replacement alternatives (Concept 1: Steel Beam Precast Units and Concept 2: Modification of the Benton County Beam-in-Slab Bridge) were investigated. In previous research for concept 1, a precast unit bridge was developed through laboratory testing. The steel-beam precast unit bridge requires the fabrication of precast double-tee (PCDT) units, each consisting of two steel beams connected by a reinforced concrete deck. The weight of each PCDT unit is minimized by limiting the deck thickness to 4 in., which permits the units to be constructed off-site and then transported to the bridge site. The number of units required is a function of the width of bridge desired. Once the PCDT units are connected, a cast-in-place reinforced concrete deck is cast over the PCDT units and the bridge railing attached. Since the steel beam PCDT unit bridge design is intended primarily for use on low-volume roads, used steel beams can be utilized for a significant cost savings. In previous research for concept 2, an alternate shear connector (ASC) was developed and subjected to static loading. In this investigation, the ASC was subjected to cyclic loading in both pushout specimens and composite beam tests. Based on these tests, the fatigue strength of the ASC was determined to be significantly greater than that required in typical low volume road single span bridges. Based upon the construction and service load testing, the steel-beam precast unit bridge was successfully shown to be a viable low volume road bridge alternative. The construction process utilized standard methods resulting in a simple system that can be completed with a limited staff. Results from the service load tests indicated adequate strength for all legal loads. An inspection of the bridge one year after its construction revealed no change in the bridge's performance. Each of the systems previously described are relatively easy to construct. Use of the ASC rather than the welded studs significantly simplified the work, equipment, and materials required to develop composite action between the steel beams and the concrete deck.

Effect of Delay in Testing Asphalt Concrete Specimens for Marshall Stability, MLR-86-08, Draft, 1986

The Central Laboratory has been delaying the mix design testing of 2 1/2" X 4" Marshall specimens for stability, until the next day after molding. For example, if the mixes are made and samples molded on Friday a man would have to come in and work on Saturday to test these specimens. The reason for this is that the ASTM-01559 "Resistance to Plastic Flow of Bituminous Mixes Using Marshall Apparatus," states that "the specimens after being molded shall be carefully transferred to a smooth, flat surface and allowed to stand overnight at room temperature, before being weighed, measured and tested." The AASHTO procedure, AASHTO Designation T-245-82 "Resistance to Plastic Flow of Bituminous Mixtures using Marshall Apparatus," does not say when the specimens shall be tested for stability. The IDOT Lab. Specifications, Test Method No. Iowa 502-8 and test method No. Iowa 506-C "compacting asphaltic concrete by the Marshall Method" and "Resistance to Plastic Flow of Bituminous Mixtures Using the Marshall Apparatus," respectively, only state that the specimens shall be cooled before testing. Due to the above conflict in specifications, a number of mix samples were tested, in the Central Lab, for stability on different days. This should furnish enough information to allow us to change the procedure and to test for stability the same day molded, or be able to delay the testing for 3 days or more.

Evaluation of Post-Tension Strengthened Steel Girder Bridge Using FRP Bars, 2003

Many state, county, and local agencies are faced with deteriorating bridge infrastructure composed of a large percentage of relatively short to medium span bridges. In many cases, these older structures are rolled or welded longitudinal steel stringers acting compositely with a reinforced concrete deck. Most of these bridges, although still in service, need some level of strengthening due to increases in legal live loads or loss of capacity due to deterioration. Although these bridges are overstressed in most instances, they do not warrant replacement; thus, structurally efficient but cost-effective means of strengthening needs to be employed. In the past, the use of bolted steel cover plates or angles was a common retrofit option for strengthening such bridges. However, the time and labor involved to attach such a strengthening system can sometimes be prohibitive. This project was funded through the Federal Highway Administration’s Innovative Bridge Research and Construction program. The goal is to retrofit an existing structurally deficient, three-span continuous steel stringer bridge using an innovative technique that involves the application of post-tensioning forces; the post-tensioning forces were applied using fiber reinforced polymer post-tensioning bars. When compared to other strengthening methods, the use of carbon fiber reinforced polymer composite materials is very appealing in that they are highly resistant to corrosion, have a low weight, and have a high tensile strength. Before the post-tensioning system was installed, a diagnostic load test was conducted on the subject bridge to establish a baseline behavior of the unstrengthened bridge. During the process of installing the post-tensioning hardware and stressing the system, both the bridge and the post-tensioning system were monitored. The installation of the hardware was followed by a follow-up diagnostic load test to assess the effectiveness of the post-tensioning strengthening system. Additional load tests were performed over a period of two years to identify any changes in the strengthening system with time. Laboratory testing of several typical carbon fiber reinforced polymer bar specimens was also conducted to more thoroughly understand their behavior. This report documents the design, installation, and field testing of the strengthening system and bridge.

A Continuous Span Aluminum Girder Concrete Deck Bridge - Part 2 of 2: Fatigue Tests of Aluminum Girders, Final Report, 1997

In 1957, the Iowa State Highway Commission, with financial assistance from the aluminum industry, constructed a 220-ft (67-m) long, four-span continuous, aluminum girder bridge to carry traffic on Clive Road (86th Street) over Interstate 80 near Des Moines, Iowa. The bridge had four, welded I-shape girders that were fabricated in pairs with welded diaphragms between an exterior and an interior girder. The interior diaphragms between the girder pairs were bolted to girder brackets. A composite, reinforced concrete deck served as the roadway surface. The bridge, which had performed successfully for about 35 years of service, was removed in the fall of 1993 to make way for an interchange at the same location. Prior to the bridge demolition, load tests were conducted to monitor girder and diaphragm bending strains and deflections in the northern end span. Fatigue testing of the aluminum girders that were removed from the end spans were conducted by applying constant-amplitude, cyclic loads. These tests established the fatigue strength of an existing, welded, flange-splice detail and added, welded, flange-cover plates and horizontal web plate attachment details. This part, Part 2, of the final report focuses on the fatigue tests of the aluminum girder sections that were removed from the bridge and on the analysis of the experimental data to establish the fatigue strength of full-size specimens. Seventeen fatigue fractures that were classified as Category E weld details developed in the seven girder test specimens. Linear regression analyses of the fatigue test results established both nominal and experimental stress-range versus load cycle relationships (SN curves) for the fatigue strength of fillet-welded connections. The nominal strength SN curve obtained by this research essentially matched the SN curve for Category E aluminum weldments given in the AASHTO LRFD specifications. All of the Category E fatigue fractures that developed in the girder test specimens satisfied the allowable SN relationship specified by the fatigue provisions of the Aluminum Association. The lower-bound strength line that was set at two standard deviations below the least squares regression line through the fatigue fracture data points related well with the Aluminum Association SN curve. The results from the experimental tests of this research have provided additional information regarding behavioral characteristics of full-size, aluminum members and have confirmed that aluminum has the strength properties needed for highway bridge girders.

Precast Concrete Panel Thickness for Epoxy-Coated Prestressing Strands, HR-353, Interim Report, 1994

A recommended minimum thickness for prestressed concrete (P/C) bridge deck panels containing 3/8-in. diameter, 270-ksi, low-relaxation, grit-impregnated, epoxy-coated prestressing strands is being evaluated by testing prototype panel specimens. As of January 1994, specimens from ten castings have been tested. The specimens in the first five castings were constructed to establish a preliminary minimum thickness for P/C panels. The specimens in the last five castings were constructed to 1) confirm the minimum panel thickness requirement, 2) measure the development length of epoxy-coated strands in specimens containing multiple strands, 3) measure the development length of uncoated strands in specimens containing multiple and single strands, 4) observe if concrete cracks form in thin panel specimens that have a raked top surface and are reinforced with welded wire fabric and either epoxy-coated or uncoated strands, 5) measure the transfer length for specimens containing a single uncoated strand, and 6) observe the seating characteristics of the grips used for uncoated strand and epoxy-coated strands. These tests have produced several initial findings. The preliminary recommended thickness for P/C panels containing grit-impregnated, epoxy-coated strands is 3 in. and the tentative development length for uncoated and coated multiple strands is approximately 45 in. and 24 in., respectively. Further tests will address confirmation of the recommended P/C panel thickness and establish the transfer and development lengths of single and multiple, uncoated and grit-impregnated epoxy-coated strands.

Residual Stresses and Fatigue Behavior of Welded Structural Members, HR-94, 1967

A research project entitled "Residual Stresses and Fatigue Behavior of Welded Structural Members" was conducted at the Structural Research Laboratory of the Engineering Research Institute at Iowa State University under the sponsorship of the Iowa State Highway Commission. The objective of the project was to study experimentally the fatigue behavior of flange plates in welded beam sections as influenced by different residual stress distributions which are caused by different sizes of welds.