NATIONAL COOPERATIVE HIGHWAY RESEARCH PROGRAM (NCHRP) REPORT 609

NATIONAL COOPERATIVE HIGHWAY RESEARCH PROGRAM (NCHRP) REPORT 609: RECOMMENDED CONSTRUCTION SPECIFICATIONS AND PROCESS CONTROL MANUAL FOR REPAIR AND RETROFIT OF CONCRETE STRUCTURES USING BONDED FRP COMPOSITES

This report, co-authored by the founder of SDR, Dr. Mohsen Shahawy in 1992, was innovative work that would go on to standardize the use of Fiber Reinforced Polymer (FRP) by highway agencies for the repair and retrofit of concrete structures. The work introduced FRP as an economically viable alternative to traditional repair that is light weight, durable, easy to install, and has a high strength-to-weight- and stiffness-to-weight ratio. The report acknowledged the lack of universally accepted construction specifications and procedures regarding the application of FRP repair systems. The NCHRP report, through extensive research of 109 specimens, addressed the shortcomings of the time and proves to be a valuable resource, still applicable to this day. It addresses issues related to the construction of FRP repair systems, including FRP defects, irregularities of the concrete surface, groove size tolerance for Near-Surface Mounted (NSM) reinforcement, and environmental conditions during installation. The report also includes the following supplementary attachments: Recommended Process Control Manual that incorporates steps on implementing Quality Insurance Policy and Program Overview, QA Guidelines for Construction Activities, and methodology for Implementing and Monitoring the QA Program. The findings, and the Process Control Manual introduced in this report, generated enormous strides in the standardization of FRP for repair and retrofit and became a valuable resource for engineers.

PCI BRIDGE DESIGN MANUAL (EXAMPLES DEVELOPMENT)

The scope of this work by SDR involved developing 10 bridge design examples to be included in the widely distributed PCI Bridge Design manual. The bridge types included prestressed concrete bulb-T, box beam, U-beam, double-T, and precast concrete stay-in-place deck panel system. The design was based on the latest AASHTO LRFD Specifications, which included refined calculation methods for several elements, such as prestressed loss and shear analysis. The work included using bridge analysis software, performing hand calculations and cross checking the results to confirm accuracy, and reviewing the latest AASHTO code.

INTERMEDIATE DIAPHRAGM STUDY

Included in the ongoing development of the LA DOTD Bridge Design and Evaluation Manual, SDR performed extensive research on the controversial topic of intermediate diaphragms in bridge design. There is speculation as to whether intermediate diaphragms (IDs) distribute live loads along the main girders and whether IDs help resist lateral impact from vehicular collision or cause wider-spread damage to multiple girders, rather than just the exterior girder. Research has shown that the flexural rigidity of the connection between the intermediate diaphragm and the precast girders determines, to a great extent, the effectiveness of the IDs. SDR conducted research to determine the true performance of IDs by performing a literature review, followed by a sensitivity study to optimize the finite element models, then performed a parametric study taking into account all the of the parameters known to influence the IDs, ultimately developing standard design recommendations to be implemented in the BDEM. Based on the findings of the research, it was decided that removal of intermediate diaphragms has insignificant effect on the live load moment at mid-span under normal loading conditions for BT-78, LG-25 girders, and quad-beam bridges; therefore, it was recommended to remove intermediate diaphragms from straight, skewed, and curved bridges for the aforementioned bridge types.

LADV-11 DESIGN VEHICLE RESEARCH

LADV-11 was developed to alleviate the need for designers to check all eight of the Louisiana Special Design Vehicles (LSDV) for Strength II conditions with a specific load factor. This complicated process required large design efforts and often resulted in new bridges not meeting the minimum load rating design criteria. Research from the extensive parametric study conducted by SDR resulted in the development of variable magnification factors for moment, shear, and support reactions that could then be multiplied by the HL-93 design load in place of analyzing the 8 LSDV vehicles. These magnification factors were developed using an “Upper Boundary Approach Method” and resulted in substantial time and cost savings by allowing engineers to design for only one vehicle while ensuring that minimum load rating requirements are met.

LOUISIANA BRIDGE DESIGN AND EVALUATION MANUAL (BDEM)

LOUISIANA BRIDGE DESIGN AND EVALUATION
MANUAL (BDEM)

On behalf of the LA DOTD, SDR created the Bridge Design and Evaluation Manual (BDEM). The BDEM consists of four major parts: Policies and Procedures, Design Specifications, Design and Detail Aids, and Background Information. The document was created with the objective of obtaining uniformity and establishing standard policies and procedures in the preparation of engineering and construction plans for bridge and highway structures. All LA DOTD-related projects are required to follow this manual as a reference.

Temperature Range Study

The temperature range study was conducted to investigate the actual typical Louisiana temperature range for the calculation of temperature induced stress and movements in bridge design. AASHTO specifications regarding temperature range are not indicative of Louisiana’s climate; therefore, modifications were determined and summarized in the LA DOTD BDEM.

LU GIRDER DEVELOPMENT

On behalf of the LA DOTD and as part of the continuing effort in the development of the Bridge Design and Evaluation Manual, SDR designed an optimized U girder as well as formulated live load moment and shear distribution factors for the proposed U girder with depths exceeding 65 inches, providing 33 sheets of standardized LU girder plans. The study identified the FDOT U girder to be an ideal candidate for further development based on ease of fabrication, cross sectional efficiency, and transportation purposes. A parametric study involving finite element models was conducted for the proposed LU-72, 78, and 84 girder sections. The study considered several parameters known to affect live load distribution, including span length, girder spacing, girder stiffness, and overhang width. This parametric study incorporated 96 primary FE models and 18 additional models to expand the study to include additional overhang widths. The results of the study yielded live load distribution factors exceeding limitations of AASHTO specifications to use in lieu of the AASHTO equations for the new proposed girder sections.