F Wayne Klaiber

Precast modified beam-in-slab bridge system : An alternative replacement for low-volume roads

As a means of extending available resources, the Black Hawk County Engineers Office, Black Hawk County, Iowa, has developed a precast bridge system specifically for low-volume roads with spans up to approximately 40 ft (12.19 m). The design, referred to as the precast modified beam-in-slab bridge (PMBISB), consists of four precast panels, which are fabricated at the countys casting facility, transported to the bridge site, and joined with a cast-in-place concrete joint. The PMBISB design is similar to the modified beam-in-slab bridge (MBISB) system previously developed by the Iowa State University Bridge Engineering Center (ISU BEC). Two defining features of the MBISB, the transverse arched deck and the alternative shear connector (ASC), are both incorporated in the PMBISB. Allowable stress design methods were applied, and the PMBISB is designed to resist an alternative truck loading [five 20-kip (89-kN) axles spaced on 4 ft 3 in.– (1,295-mm) centers], which is representative of local vehicles. An individual panel consists of three longitudinal W-sections that are embedded in a transversely arched concrete deck. Reinforcement within the deck is limited to that required in the ASC and that needed for crack control. All construction is preformed by county forces with existing equipment. The PMBISB system saves Black Hawk County approximately

Field and Laboratory Testing of Precast Concrete Channel Bridges

16,000, or 17% per bridge, compared with conventional designs. ISU BEC load-tested the first PMBISB to determine service-level performance and the behavior of the joined panels. The design has been further refined and five additional PMBISBs have been constructed on the basis of the results and field experience.

Evaluation of Steel Girder Bridge Strengthened with Carbon Fiber–Reinforced Polymer Posttension Bars

The precast channel bridge (PCB) was commonly constructed on Iowas secondary roads approximately 40 years ago. Each PCB span consists of eight to 10 simply supported precast panels ranging in length from 19 to 36 ft. The panels resemble a steel channel in cross section; the web is orientated horizontally to form the roadway deck, and the vertical legs act as shallow beams. Bundled bars in each leg are used for flexural reinforcement. Many of the approximately 600 PCBs in Iowa show signs of significant deterioration. Typical deterioration consists of spalled concrete cover and corrosion of the bundled primary reinforcement. The objective of this research was to assess the structural sufficiency of the deteriorated PCBs through field and laboratory testing. Four deteriorated PCBs were instrumented with strain gauges to measure strains in both the concrete and the reinforcing steel and with transducers to measure vertical deflections. Responses from loaded trucks were recorded and analyzed. Test results rev...

Cost-Effective Structures for Off-System Bridges

This project investigated the effectiveness of carbon fiber–reinforced polymer (CFRP) composite materials to strengthen an existing, structurally deficient steel girder bridge. The bridge selected for strengthening with the CFRP posttensioning system is a three-span continuous steel stringer bridge on IA-141 approximately 1.6 mi west of Bayard, Iowa. The research program consisted of several tasks, and the main emphasis was the installation of the strengthening system and associated field testing. The bridge was instrumented to measure strain at selected critical locations and tested before installation of the posttensioning system, shortly following posttensioning, and after approximately 1 and 2 years of service to assess changes in behavior resulting from the addition of the posttensioning system and time. During the application of the posttensioning strengthening system, strain was measured to investigate the response of the bridge to the applied posttensioning forces. After the last follow-up test was completed, the posttensioning force was removed (and reapplied) to investigate any loss of posttensioning force that may have occurred during the 2-year period. In general, the installation of the posttensioning system required no special equipment or training other than access equipment, an acetylene torch to remove a portion of several diaphragms, and a hydraulic jack. A three-person crew was able to install the system in just over 1 day. On the basis of an analysis performed by using an HS-20 truck, it was found that the posttensioning strengthening system reduced the dead and live load induced moments by approximately 3% to 5%, allowing the bridge to carry additional live load.

METHODS OF STRENGTHENING EXISTING HIGHWAY BRIDGES

Nearly half of the 587,000 bridges in excess of 6.1 m (20 ft) long on public roads in the United States are located off the Federal Aid System, are on local rural and urban roads or rural minor collectors, and are classified as off-system bridges. Approximately one-third of the off-system bridges are structurally deficient or functionally obsolete. The majority of states with large bridge populations are rural states with large percentages of structures owned by counties and other local agencies. Many of these bridges are on low-volume roads. Given the size of the deficient bridge population and the concentration of these bridges largely on locally owned networks, a recent NCHRP synthesis (NCHRP 32-08, Cost Effective Structures for Off-System Bridges) has explored the current practices regarding the maintenance, rehabilitation, and replacement of off-system bridges. The administrative aspects of off-system bridge ownership and management were explored, including sources and problems of funding, bridge asset management, design policies for off-system bridges, exploration of the environmental process, and discussions of interagency partnering and coordination problems. A significant body of work exists on effective bridge maintenance and rehabilitation. A significant discussion of bridge strengthening, including specific techniques used on low-volume-road bridges, was also examined. Concerning bridge replacements, the literature and owner survey were used to provide information on successful concepts currently being used. In addition to successful bridge replacement options, discussion of the use of standard plans, design aids, and software is promoted as leading to standard and efficient low-volume-road bridge replacements.