CN-550000-BDV22-W0020000.pdf

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TASK WORK ORDER FOR

MASTER UN:VERSiTγ AGREEMENT

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Master Agreement#:

BDV22

Cost Center#‐ Task Work()rder#:

977 - 01

University:

Embry_Riddie Aeronau‖cal Universly

Task Work Order Description:

Bridge Girder Alternatives for Extremely Aggressive Environments

The start dale of this task work order is:

Upon execution of the Task Work Order by the Departmenl.

lssuance of a Notice to Proceed.

As specified in Exhibit A (Scope of Service).

ln accordance with lhe above referenced contract, you are authorized to perform the tasks detailed in attached Exhibit A (Scope of Services). All services required under this Task Work Order will be compleled by:

113112017 or the end date of the Master Agreement, whichever occurs firsl.

For the required services, compensation shall be $ 104.604.00 as described in the attached Exhibit B (Method of Compensation).

Fund Typel

□ Sttb Funds EO Federal Funds

App‖cable Appendices:(!f cheCked,Appendix must be attached to the TWO)

Appendix 1 Terms for Federal Aid Contracts Appendix 2 Terms for lnformation Technology Resources Appendix 3 Terms for Federal Transit Administrataon Other:

Note: Master University Agreement cannot be used for grant disbursement to subr€cipients

Depa ment Contact:

Name: Phone: 850-414-4616

Office: Email: oatti.brannon@dot.state.fl.us

Departmenta;Approval:

」 Darrv‖ Dockstader Manaqer.Research center (Name) (Ti‖e)

Legal Review:

ル血

Project Title: Bridge Girder Alternatives for Extremely Aggressive Environments

Principal Investigator: Dr. Jeffery Brown Associate Professor, Civil Engineering

College of Engineering

Phone: 386-225-7458

Email: brownj I 1 2@erau.edu

Contractual Contact: Nancy McCaffrey Contract Administrator

Office of Sponsored Research Administration Phone: 836-226-7996

Email: mccaffrn@erau.edu

Project Manager: Will Potter

Assistance State Structures Design Engineer

Structures Office 605 Suwannee Street, MS 80

Tallahassee, FL 32399-0450

Phone: 850-921-7111

Email: william.potter@dot.state.fl .us

Exhibit A - Scope of Service

Bridge Girder Alternatives for Extremely Aggressive Environments

Statement of Need and Backoround

The vast length of coastline around Florida, where most Floridians and tourists live and play, is an extremely aggressive environment for bridges. However, this is where many bridges are needed and are located to serve the communities. Current methods utilized by FDOT to protect the bridges from the aggressive environment include but are not limited to, raising the superstructure, increasing concrete cover, and improving the concrete mix design. Raising the superstructure is a practice that is not always an option given the geographic location or other reasons. lncreasing the concrete cover results in excess materials that increases weight and underutilizes the effectiveness of the reinforcement. lmproving the concrete mix design can be costly and to some degree limited. ln any case, the aggressive environment leaves our structures vulnerable to durability issues related to corrosion.

The enhancements that have occurred with FRP (Fiber Reinforced Polymer) composites over the years, both manufacturing and material, have shown promise for use in the transportation infraslructure. FRP composites have been utilized as stand-alone syslems in bridge structures;

however, most systems are proprietary. The focus of this research is to develop a non-proprietary FRP or hybrid-FRP bridge girder that can utilize a standard design methodology and be utilized on short to medium span bridges in an aggressive environment.

Obiectives and Supportino Tasks

The objective of this research is to identify or develop non-proprietary bridge girder design alternatives that utilize FRP or FRP components, rank the designs for viability, and further develop selected alternatives. The alternatives shall be designed for extremely aggressive environments. The alternatives should have the ability to be utilized on 30 ft. to 75 ft. bridge spans and should have a design methodology that can be utilized by any designer. The methodology shall encompass all design aspects which include global and local design, connection design between girder and deck, and bearing design. The girder, including connections, shall withstand all applicable MSHTO LRFD loading criteria. Each individual component of the girder shall have the ability to be manufactured by multiple vendors/contractors and possibly multiple methodologies. The proposed girder must be adaptable to current bridge elements such as a concrete deck and elastomeric bearings.

Emphasis on constructability/field installation shall be given a high priority. Lastly, consideration shall be given for maintenance accessibility, service life (75 years), and cost effectiveness.

Anticipated Tasks

Kickoff Meeting - The University will schedule a kickoff teleconference that shall be held within the first 30 days of execution. The project manager, principal investigator, and research performance coordinator will attend. The purpose of the meeting is to review the tasks and deliverables.

Task 1 - Perform an extensive literature search on FRP and hybrid-FRP structural systems.

Review existing bridge systems/projects that have utilized FRP and hybrid-FRP girders, FRP components, and/or FRP reinforced concrete components in new construction. Review components or systems that could be utilized in the proposed bridge girder. Assess the state of development and/or condition state, if used in a bridge system, of the existing systems and/or components through reports and owner contact. lnvestigate the design and construction methodologies.

Task 1 Deliverable - Upon completion of Task 1, the university will submit to the research online poftal at https: / / f dotlrp1 . dot . state. f1. us / ResearchcontractAd,nini s trat ion / a report that includes the findings of the literature search along with a survey and status of existing projects or bridges.

Task 2 - Conceptually and analytically develop ideas and concepts of viable non-proprietary bridge girder alternatives for use in extremely aggressive environments. Perform a ranking analysis of the alternatives to rate viability. The ranking should be based on, but not limited to, the design process, constructability, material, maintenance, service life, cost and FDOT project manager coordination. Develop further and structurally analyze selected bridge girders of the three most viable alternatives.

Task 2 Deliverable - Upon completion of Task 2, the university will submit to the research online portal at https://fdotwpl .dot-state.f1.us/ResearchcontractAdministration/ a report that discusses in detail the developed ideas and concepts considered. The report shall include both drawings and details of each viable alternative and include pros and cons for each concept. The pros and cons shall incorporate all aspects considered in the ranking including design, construction, material, maintenance, service life, and cost. The report shall include discussion and results of the structural analysis of the top three alternatives.

Task 3 - Draft and Final Reports

Ninety (90) days prior to the end date of the task work order, the university will submit to the research online portal at https : / / f dotwpl . dot . state. f 1 . us /ResearchconLractAdministration/ a draft final report. The Draft Final Report shall be prepared in accordance with the Guidelines for University Presentation and Publication available at htto://www.dot.state.fl.us/research-center/Proiect Mqt Resources.shtm

Task 3 Deliverable - Upon Department approval of the draft final report, the university will submit the Final Report on two (2) CDs. Both CDs shall contain the report in PDF and Word formats. CDs should be labeled in a professional manner and include contract number, task work order number, project title and date.

Closeout Meeting - The University will schedule a closeout teleconference that shall be held during the final 30 days of the task work order. The project manager, principal investigator, and research performance coordinator will attend. The purpose of the meeting is to review the proiect performance and next steps.

Embry-Riddle Aeronautical University Technical Plan

RFRP-14/15-003

1. Introduction Current FDOT guidelinesl allow for the use of FRP materials in a limited number of bridge superstructure applications:

. GFRP and cFRP reinforcinB bars in bridge decks and cast-in-place flat slabs

. Strengthening of existing structural elements with externally bonded CFRP

. Pultruded shapes for structural elements and bridge decks in pedestrian bridges

The proposed research seeks to integrate state-of-the-art FRP composites technologies from a range of industries, including the aerospace, wind energy, and offshore marine sectors, in an effort to develop a non-proprietary FRP bridge girder for civil engineering applications. The advantages associated with FRP composites related to strength-to-weight ratio, durability, corrosion resistance, and their ability to conform to complex geometries are well understood. There is a rich body of literature devoted to the use of these materials in civll Infrastructure that dates back to the late 1970s. Nonetheless, several factors have limited their widespread use in bridge superstructure applications:

. Limited data surrounding long-term performance

. Lack of ductility due to inherent brittleness in FRP materials

. Difficulty assessing damage during inspections under field conditions o Manufacturing challenges related to economies of scale and variability in shape requirements

. lnherent tensions between intellectual property rights and the need for standardization

The primary component of this research plan is a comprehensive conceptual design study that willv include existing non-proprietary FRP bridge girder concepts as well as novel concepts and ideas to address the challenges described above. ln addition to standard considerations related to strength and serviceability, emphasis will also be placed on manufacturing processes, material costs, and integration v with accelerated bridge construction (ABC) practices. The study will also consider how each proposed concept can be adapted to exlsting FDOT bridge inspection protocols and long-term maintenance v requirements.

Embry-Riddle Aeronautical University has assembled a team of faculty with broad expertise in the field

\, of composites in response to this RFRP. The Pl, Dr. Jeff Brown, has been connected to academic research on FRP composites in civil infrastructure since beginning his PhD at the University of Florida in

2002. This work has included several projects with the Structures Research Center in Tallahassee in collaboration with his PhD advisor, Dr. Trey Hamilton. Dr. Daewon Kim (co-Pl) brings expertise in the area of advanced composites manufacturing within the aviation/aerospace sector. Dr. Kim is also actively Involved in research related to structural health monitoring of aerospace composites. The third member of the faculty research team, Dr. Ali Tamijani (co-Pl), has extensive experience in the design and

\, optimization of composite systems for aerospace structures. This m ulti-disciplina ry research team is v uniquely poised to advance the state-of-the-art for FRP bridge girders in extremely aggressive environments.

Embry-Riddle Aeronautical University Technical Plan

RFRP-14/1s-003

2. Literature Review (Task 1) There is a large body of literature surrounding the use of FRP composites in civil infrastructure. We have identified four primary categories for this previous work that we will investigate and summarize:

. Existing standards, specifications, and guidelines

. Material systems and manufacturing methods

. Current applications of FRP bridge girders o Advanced composites systems

The overall strategy for completing the literature survey is to develop a clear understanding of work that has been completed while simultaneously identifying current knowledge gaps related to FRP bridge girders. The ultimate goal will be to provide FDOT researchers and engineers with a conceptual framework that connects traditional bridge design methods that have evolved around reinforced concrete and steel elements with methods and standards that are appropriate for FRP composites.

While the research described in this proposal will focus on the design of FRP bridge girders as individual structural elements, the literature review will also include an emphasis on how FRP bridge girders will ultimately perform in a completed bridge system.

Existing Standards, Specilications, and Guidelines

At the national level, there are currently no adopted specifications for incorporating FRP composite bridge girders into the superstructure of a vehicle bridge. AASHTO specifications do existforthe design of FRP pedestrian bridges2 as well as concrete-filled FRP tubes (CFFT)3. The cFFT specification addresses the desiBn of flexural members to serve as beam elements, but current FDOT guidelines limit their use to arches for bridge culvertsl.

ln 2010, an AScE project team finalized a document for the American composites Manufacturing

Association (ACMA) entitled Pre-Stondord for Lood ond Resistonce Factor Design (LRFD) of Pultruded

Fiber Reinforced Polymer Structures4. This pre-standard describes its intended use as supporting "the design of new buildings and other structures," but the document is clearly not intended to encompass the design of bridge superstructure elements (i.e. FRP bridge girders). The commentary section on loads and load combinations (C1.5) limits the applicability of the pre-standard to building construction and excludes vehicle loads on bridges. This pre-standard document is currently being balloted within the

ASCE Fiber Composites and Polymers Standards Committee, and the final standard is expected to be released sometime in 20155.

Numerous additional standards exist that support the use of FRP materials in civil infrastructure applications. The American Concrete lnstitute (ACl) and AASHTO have developed standards pertaining to FRP reinforcing bars6'7 and external strengthening/repair of concrete structuress'e. Our general approach assumes that these standards are outside the scope of the current study, with the exception of potential hybrid FRP-concrete bridge girder systems that might include internal FRP reinforcement.

Nonetheless, we intend to utilize these references as a critical jumping-off point for evaluating proposed

RFRP-14/15_003

FRP bridge girder concepts. The information contained in these documents related to the strength and durability of FRP materials is directly applicable to FRP bridge girder configurations.

Material Systems and Manufacturing Methods

A primary advantage often attributed to composite materials is the flexibility that designers have to tailor the strength characteristics of FRP laminates in different directions based on structural demands.

Different fiber types (typically carbon or glass) are strategically integrated with different matrix materials (thermosets or thermoplastics) to obtain targeted strength and weight properties. Cost is a major consideration for these systems, and the civil engineering sector has tended to focus on glass fibers with thermoset resins for structural element fabrication. The major exception to this rule is external strengthening of existing structures, which tends to rely heavily on carbon fiber fabrics.

Different manufacturing methods for composites have also evolved over time, and different industries have developed the manufacturing infrastructure necessary to support their needs. Manufacturing is typically the area where more traditional materials like steel and concrete have a competitlve advantage. There are four primary methods for fabricating composite parts:

1. Pultruded shapes

2. Open-mold hand lay-up

3. Vacuum lnfusion Process (Vacuum Assisted Resin Transfer Molding - VARTM)

4. Autoclave curing of pre-impregnated laminates

The proposed literature review will first investigate the extent to which these different manufacturing methods have been deployed in civil infrastructure applications. Other industries, including wind energy and aerospace, will also be investigated. A prelimlnary literature review has revealed very little regarding the relative costs associated with these different manufacturing methods. We plan to reach out to industry experts through the American Composites Manufacturing Association (ACMA) to begin developing a framework for assessing manufacturing costs for FRP bridge girders. lncorporating these manufacturing costs into the decision matrix for evaluating different FRP bridge girder alternatives in

Task 2 will be critical to ensuring viability in the marketplace.

Pultruded shapes and Vacuum lnfusion Process (VlP) structural shapes appear to be the most promising with regards to balancing cost, flexibility in shape profiles, and required part quality. Hand lay-up methods are susceptible to manufacturing defects, and the large scale of FRP parts required for bridge girder applications will limit the applicability of hand-layup methods. Autoclave methods, while frequently used in the aviation and aerospace sector, will likely prove to be cost-prohibitive. There are also limitations related to part size (length and thickness) that may be difficult to overcome when attempting to apply autoclave methods to FRP bridge girder manufacturing. As a result, the current plan is to focus heavily on pultruded and VIP structural shapes.

Considerations for pultruded and vIP structural shapes in FDOT proiects The current FDOT Stondord Specificotions t'or Rood ond Bridge Constructionlo provides detailed requirements for FRP material properties that will be used in FDOT projects. Requirements for

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Embry-Riddle Aeronautical University TechnicalPlan RFRP-14/1s-003 pultruded shapes reference the ASCE Pre-Stondord for Load ond Resistance Foctor Design (LRFD) of Puttruded Fiber Reinforced Polymer Structuresa. Specific properties for vacuum infusion processed (VlP) structural elements are listed directly in the FDOT Standard Specifications document. The requirements for VIP structural shapes are identical to the ASCE Pre-Standard, but slightly lower values are specified forVlPFRPplates. AsampleoftherequirementsforpultrudedandVlPshapesisprovidedinTablel.

Table 1. Minimum physical property requirements for pultruded and VIP structural shapes.

Physical Property Minimum Value Test Method (Puttruded4/VlP

Long. tensile strength Tra nsverse tensile strength Long. tensile modulus

Transverse tensile modulus

Interlaminar shear strength Glass transition temperature Coefficient of thermal expansion

ASTM D638/D3039

ASttM D2344

ASttM D4065

ASttM D696

Note: Property requirements for pultruded shapes and VIP shapes are identical unless noted.

Two major issues associated with these minimum physical property requirements will be addressed in the literature review. First, they appear to have been developed for building applications. This does not preclude their use in FRP bridge girder applications, but some additional consideration may be warranted. The anisotropic nature of FRP composites has implications for local buckling and overall member stability. lnterlaminar fracture may also develop as a limit state for strength. Second, and more importantly, many practicing civil/structural engineers would be hard-pressed to design and specify a laminate stacking configuration, matrix type, and fiber-volume fraction for an FRP composite that meets these minimum requirements. A major goal of this research will be to develop a framework that begins to close the gap between civil/bridge engineering and composites design/manufacturing.

This knowledge gap was a primary motivation for including two experts in composites design and manufacturing from the aerospace field as co-Pls on this proposal.

Durability A significant body of literature also exists surrounding the durability of FRP composites in civil infrastructu refi'12'13't4. The ASCE Pre-standard for pultruded shapes identifies durability performance criteria. FRP composite systems must retain t5% of their material properties after exposure to specified environmental conditions related to moisture, ultraviolet radiation, alkali, and freeze-thaw. We plan to investigate the basis for these criteria and assess their applicability to FRP bridge girders.

Creep and stress rupture are also important considerations when glass fibers are used. The fundamental LRFD design equation in the ASCE Pre-standard is given as:

RulTQRn where R, R* and rp correspond to the factored structural demand placed on an element, the element's nominal strength, and the strength reduction factor, respectively. The additional term, 1", is a time effect factor that accounts for the duration over which loads act throughout a structure's service life. For the case of dead load with a load factor of 1.4 acting on a structure with a service life of 50 years, the time

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Embry-Riddle Aeronautical University Technical Plan

RFRP-14/1s-003 effectfactorisspecifiedas0.4. Forthestandarddeadandliveloadcombination(1,.2D+1.61),thetime effectfactorvariesdependingonthesourceoftheliveload.0.6isusedwhentheliveloadsourceis "storage", 0.8 when the source is "occupancy", and 1.0 when the source is "impact". Accounting for creep and stress rupture effects on a vehicle bridge with a 75year service life may require additional consideration. Before beginning the conceptual design phase for FRP bridge girders, we plan to survey existing literature related to creep and stress rupture in glass FRP composites to ensure that these effects are properly accounted for.

Current Applications of FRP Bridge Girders

Preliminary research for this proposal has revealed several demonstration projects and research studies related to FRP bridge girders:

Hillman Composite Beams (proprietary system)

Steel-free multi-girder hybrid bridge deck system

European FRP bridge girder demonstration projects

Hillman Composite Beams The Hillman Composite Beam is a patentedlt, hybrid composite beam (HCB) system. Research has been published on the performance of this system based on installed bridges in the State of Missourilu. The company's website provides nine case studies for highway bridges, two railway bridges, one military bridge, and one pier. The novelty of this hybrid system is that each bridge girder contains a tied arch. A foam material is used to form the arch within the FRP composite shell, and steel tendons tie the arch ends together. These tendons are bonded to directly to the FRP composite, which provides environmental protection for the entire system (Figure 2).

Though the intent of this research is to develop a non-proprietary FRP bridge girder system, the HCB bridges that are currently in-service represent an excellent opportunity to gain insight from other State

DOTs and their experience with this system. ln addition to surveying all of the published literature associated with these bridges, Task 1 will also include conversations with DOT personnel from Missouri, Maine, Virginia, New Jersey, and West Virginia who are responsible for maintaining these bridges. Many

Figure 1. Missouri DOT Bridge 80439, Douglas County, Missouri. lmages obtained from HCB websitelT

Em bry-Ridd le Aeronautical University of these bridges have been in-service for over five years, and at least one in Maine is located in a harsh marine environment.

Rebar shear connectors for clP deck

Technical Plan

RFRP-14/15-003

FRP She‖

Concrete

Foam

Steel tendons

Figure 2. conceptual design for Hillman composite Beam (derived from images in Us Patent s7562499 82)

Steel-free multi-girder hybrid bridge deck system A research Broup from the University of Calgary, Canada, has completed extensive research related to the development of a hybrid FRP-concrete bridge girder. A PhD dissertation published in January 20L5 by Dr. Donna Chen18 contains detailed analytlcal and experimental data for the concept illustrated in

Figure 3. This research effort reveals a number of challenges related to incorporating FRP structural elements in brid8e systems. Achieving proper bond for shear transfer between concrete and FRP components in a hybrid system is not trivial, and this group's design included an "epoxy bonded coarse silica sand aggregate laye/'between the Ultra-High Performance Concrete (UHPC) cast-in-place deck and the pultruded GFRP box beam. Post-tensioned GFRP threaded rods were also used to aid in shear transfer. This work also included testing of a quarter-scale bridge model. Significant effort in the form oftransverse post-tensioning and horizontal straps using GFRP threaded rod was required to ensure adequate moment distribution in the multi-girder bridge system. These elements are visible in the experimental setup photo provided in Figure 3.

Dr. Chen's dissertation provides a list of peer-reviewed conference proceedingsts'2o'2''22 and peer-reviewed journal articles23 (three of which are still underreview). An earlier published study from

2012'z4 highlights the performance of individual hybrid beams that relied only on shear studs between the deck and GFRP pultruded section. The literature review included in Task 1 of the current proposal will summarize these findings in an effort to assess the viability of this concept for use in extremely aggressive environments in Florida.

It should also be noted that this research study did not necessarily approach the problem from a design perspective (i.e. the researchers did not begin with target strength and serviceability limit states and then attempt to design an FRP girder that that satisfied these criteria). During the proposed conceptual design study (Task 2 of the current proposal), this concept will be evaluated in the context of several simple bridge design scenarios. This process will provide general requirements for cross-section geometry that can then be related to cost.

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Embry-Riddle Aeronautical University Technica!P!an

RFRP-14/15-003

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Figure 3. Conceptual design and experimental testing of multi-girder Hybrid FRP-concrete bridge from University of Calgary study. lmage from PhD dissertation by Dr. Donna Chen18.

European FRP bridge girder demonstration proiects A 2OO8 paper in the ASCE Journal of Bridge Engineering2s describes experimental testing for a full-scale carbon FRP bridge girder. A demonstration project (the Pumacon Bridge) using the same configuration had been completed in Spain in 2004. A large foam core was wrapped with pre-impregnated carbon fiber fabrics, which was then subjected to vacuum assisted low-temperature curing cycle at 80 "C.

Pultruded GFRP shapes were bonded to the top of the girder to serve as shear connectors between the girder and the slab.

Figure 4. Full scale Carbon FRP bridge girder test (European demonstration project). Photo from ASCE Journal of Bridge Engineering paper by Gutierrez et al2s.

A2012 conference paper by Carlo Paulotto et a1.26 describes the evolution of full-scale FRP bridge girder demonstration projects across Europe. ln addition to the Pumacon bridge that was completed in 2004, Paulotto discusses two identical FRP girder bridges that were erected in 2OO7 in Madrid, Spain. These bridges each consisted of 3 simple spans (33 ft,46ft, and 33 ft). The girders were fabricated using both carbon and glass pre-impregnated fabrics that were placed in an open, reusable, steel mold (no foam core was utilized). The total weight of the 46 ft girder was -4.7 kips. As an interesting point of reference, a 46 ft long Florida l-beam that is 36 in deep (FlB 36) is estimated to weigh over 38 kips

(based on data found in Florida l-Beam Training Webinar2T).

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Embry-Riddle Aeronautical University Technical Plan

RFRP-14/1s-003

Figure 5. Carbon/Glass FRP bridge girder erected in2OO7 in Madrid, Spain. Photos from2Ol2 CICE conference paper by

Paulotto et a126.

A third project discussed by Paulotto was a 78 ft simple span pedestrian bridge girder that was constructed from glass FRP using a vacuum infusion process (VlP)-also commonly referred to as vacuum assisted resin transfer molding (VARTM). ln this method, dry glass fabric is placed in an open steel mold to achieve the desired thickness and a vacuum bagging material is used to seal off the surface. Once sealed, a vacuum is pulled between the bag and the mold and resin is allowed to infuse the part. This process eliminates the need for large volumes of pre-impregnated fabrics and allows the entire part to be saturated simultaneously.

Figure 6. Glass FRP pedestrian bridge girder manufactured in 2010 using the VIP/VARTM method. Photos from 2012 CICE conference paper by Paulotto et a126.

The preliminary literature review for this proposal did not reveal any subsequent reports related to the long-term durability and performance of these in-service FRP bridge girders. We plan to investigate this issue further and make direct contact with the researchers who were involved in these projects. We were also unable to locate any information about the design process and/or methodologies used to determine the dimensions and FRP system details for these specific bridges.

Advanced Composites SYstems

The previous discussion on existing literature has focused exclusively on the use of FRP composites in traditional civil engineering applications. ln order to ensure that the proposed conceptual design study is up-to-date and takes advantage of the many recent advances made in the composites manufacturing industry, we also plan to survey the use of FRP composites as primary structural elements in the aviation/aerospace sector. Many of the challenges facing broader use and acceptance of composites in

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Em bry-Ridd le Aeronautical University Technical Plan RFRP-14/1s-003 civil infrastructure are also of concern to the aviation/aerospace industry. Although lighter, the economic utility of FRP composite primary structures is often limited by their higher fabrication costs.

These higher costs are commonly attributed to:

The need for large autoclaves

Out-time limitations for pre-impregnated materials (i.e. once a pre-preg is removed from the freezer for processing, there is a limited amount of time it can stay at room temperature before it must be cured at an elevated temperature in an autoclave).

High number of required fasteners and detail parts

Additionally, there are several performance issues with composite structures:

. Poor damage tolerance

. Catastrophic failure due to damage (no ductility) o Non-visible damage

. Weak out-of-plane bond properties

New composite architectures for next-generation aircraft are highly scrutinized for fabrication costs as well as performance. To address these challenges, researchers at NASA's Advanced Composite

Technology Wing Program have investigated the feasibility of unitized stitched-com posite concepts for use in aircraft airframe applications2s. Conventional manufacturing is achleved through the assembly of numerous small parts. Although fabrication of each part is simple, the assembly process requires a significant touch labor and tooling. The extensive use offastenersalso leadsto structural d isco ntin u ities, corrosion, and fatigue-related concerns. Stitched-composites manufacturing techniques result in a high degree of structural unitization by providing z-direction reinforcement for the composite panel. This additional reinforcement improves the damage tolerance properties of composite structures. Another added benefit is the ability to arrest crack growth and delamination2s.

A concept that is currently under development by NASA and Boeing involves integrating pultruded CFRP rods into stitched composite panels. The Pultruded Rod Stitched Efficient Unitized Structure (PRSEUS) system30'31 (Figure 7) combines several structuralelements running in orthogonaldirections (i.e. the skin stack, frame cap stack, frame stack, stringer tear straps, and stringer stack). Dry fiber fabrics are first stitched together using a 3-D stitching machine and foam core elements are used to offset the pultruded stringer rods from the panel surface. Once the dry fiber stack is fully formed, the fiber layers are infused with resin using VIP/VARTM and allowed to cure into an integral part.

The PRSEUS system was designed to resist both the in-plane and out-of-plane loading that is typically encountered in aircraft structures. FRP bridge Birders represent a fundamentally different type of structural element, and the stringer and frame stacks illustrated in Figure 7 may not prove to be useful.

Nonetheless, the potential to incorporate 3-D stitching technology and panel reinforcement with pre-cured threaded rods may provide significant advantages over traditional FRP laminates and stand-alone pultruded shapes. The literature review for Task 1 will include these advanced composites manufacturing technologies with an emphasis on their applicability to FRP bridge girders.

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RFRP-14/1s-003

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Summary of Planned Literature Review ln general, there seems to be a gap in the literature. On one hand, there are numerous general accounts that demonstrate FRP composites being used successfully in bridge girder applications. On the other hand, there is very little (none?) in the way of literature that describes how fundamental principles structural mechanics and FRP composites might be applied to meet a specified design objective related to vehicle bridge girders. For example, the ASCE Pre-Standard document describes a methodology for determining the capacity of a pultruded member in flexure and shear considering strength, stability, and serviceability limit states. No consideration is given, however, to the potential for developing composite action with a cast-in-place reinforced concrete deck. The work of Chen and El-

Hacha from the University of Calgary suggests that this is not a trivial matter. Composite action with cast-in-place bridge decks has clearly been achieved (as illustrated by the European demonstration projects), but we appear to be lacking a standard methodology that practicing structural designers can use to obtain predictable results.

The author of the most comprehensive textbook on the subject of FRP composites in civil infrastructure", Lawrence C. Bank, made an insightful comment in an article from 1993 entitled

"Questioning Com posites"33:

Here lies the most critical issue reloting to the widespreod use of composite moteriols in the construction industry: A fromework is needed thot will ollow orchitects ond structural engineers to specify composite moteriols for civil engineering structures in o similor foshion to how they now specify conventionol materiols. Within such o framework, composites con be considered competitively ogainst steel ond concrete, ond their use will not be restricted to specialized products, monufocturer-fobricotors ond coptive clients.

Our preliminary literature review indicates that the building blocks for such a framework are present.

What is missing, however, is a comprehensive conceptual design study that takes into account more than the traditional factors frequently cited to promote composites (e.g. high strength-to-weight ratio and corrosion resistance). The proposed research seeks to lay a foundation for the development of non-proprietary standard designs for FRP composite bridge girders. By incorporating factors such as manufacturing costs, constructability, inspection, maintenance, and service-life, we hope to provide a

3. Conceptual Design Study (Task 2)

Embry-Riddle Aerona utica I University Technical Plan

RFRP-14/15-003

useful framework that FDOT officials, structural bridge engineers, and the FRP composites manufacturing industry can use to incorporate composites more broadly within the State's bridge inventory.

The proposed conceptual design study for FRP composite bridge girders will consist ofthe following major components:

. Design req uirements o concept development o Preliminary analysis and design o Evaluation criteria o Detailed analysis for top three concepts

. Practical design methodologies for top three concepts

Design Requirements

The major design requirements outlined in the RFRP include the following:

. Strength and Serviceability per AASHTO LRFD and FDOT Structures Design Guidelines (5DG)

. 75 year service-life in an "Extremely Aggressive Environment" per FDOT SDG

. 30 ft. to 75 ft simply supported span lengths o Practical design methodology including:

o Global and local strength requirements o Connectlons between deck and girder for composite action o End bearing with standard elastomeric pads o Girders can be manufactured by multlple vendors using standard methods

. Design is compatible with Accelerated Bridge Construction techniques

. Girder can be inspected and maintained

. Girder is cost-competitive over its service-life with traditional materials (Reinforced/Prestressed concrete)

One design requirement we plan to emphasize involves ductility and the ability of the FRP bridge girder to retain load carrying capacity after visible damage occurs. The Pl, Jeff Brown, was involved with a previous FDOT research project investigating non-destructive evaluation methods for FRP bridge decks

(SDK7S-177-17341. The stiffened panel system shown in Figure 8 failed in shear and inter-laminar fracture during laboratory testing. Unfortunately, the basic geometry of the system would prevent an inspector from identifying this type of damage in field applications because the top and bottom surfaces of the FRp deck remain intact. While there are nondestructive evaluation techniquesthat are capable of identifying non-visible damage beneath the surface of FRP composites (e.g. thermal imaging, ultrasound, and acoustic emissions), deployment on full-scale, in-service systems has not been proven. As a result, the concepts developed through the proposed research will be highly scrutinized for their ability to

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Embry-Riddle Aeronautical University present visible damage yet retain a significant percentage of reserve strength capacity.

discussed in further detail in the section on Concept Development.

TechnicalPlan RFRP-14/1s-003

This will be v v V

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Figure 8. Shear and inter-laminar fracture in stiffened panel FRP bridge decks. lmages from FDOT Report BDK75 -g77-L7l?Al .

Concept Development

The preliminary literature review for this proposal has resulted in six preliminary concepts for FRP bridge girders that we plan to explore. Additional concepts may develop as the literature review of Task 1 is completed and/or after we engage in conversations with FRP composites manufacturers. At a minimum, we plan to perform a comprehensive conceptual design study that includes the following FRP com posite girder types:

o Stand-alone pultruded sections (l-beams and rectangular box beams) o Built-up pultruded sections (stiffened plate girders and composite box-girders) o Three categories of Vacuum lnfusion Processed (VlP)/VARTM open box-girders o Traditional fabric layuP o 3-D stitched laminates o lntegrated pultruded rods

. Hybrid concrete-FRP sections

Stand-alone pultruded sections The ASCE Pre-Stondord for Lood and Resistonce Foctor Design (LRFD) of Pultruded FRP Structures provides an established framework for the design of pultruded FRP members. The first step will be to combine the AASHTO LRFD Bridge Design Specifications with the ASCE Pre-Standard to determine general section geometry requirements for pultruded GFRP shapes. We will perform this task for 30 ft., 50 ft., and 75 ft. simple span bridges to determine the range of section geometries that might be expected. Special attention will be needed for the design of shear stud connectors between the pultruded girders and the concrete deck as the ASCE Pre-standard does not address composite action.

The general concept for a pultruded GFRP l-beam bridge is illustrated in Figure 9. lssues related to cross-bracing and framing for moment distribution will also be considered.

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Embry-Riddle Aeronautical University Technical Plan RFRP-14/1s-003

Figure 9. Pultruded GFRP girder bridge.

Built-up pultruded sections One potential limitation with the stand-alone pultruded sections is that designers will be limited to the specific shapes for which manufacturers have developed the requisite pultrusion tooling. The cost associated with developing precision ground tooling dies is considerable. One potential work-around would be to develop a standard design and manufacturing process for built-up pultruded sections.

Under this scenario, pultruded FRP sheets are connected using pultruded plate connector elements.

Mechanical and/or adhesive fastening methods can be used to transfer load between the plates. The advantage of this method is that a la rge volume of standardized connector elements could be produced economically while the plates themselves could be cut to size according to the specific structural demands.

Designing the connections will not be trivial, but there is considerable literature cited in the AscE Pre-

Standard that deals with bolted connections ofpultruded FRP shapes. lfthese connections could be made using only adhesives along the bond-lines, considerable savings would be realized in manufacturing costs. The issue of shear connectors for the deck will also need to be addressed, but the findings from the stand-alone pultruded sections should also apply to this concept. The built-up box-girder approach also introduces concerns related to non-visible damage. lt should be possible, however, to slightly overdesign interior components such that any damage wlll always manifest on the outside of the section first. Finally, considerations for interior diaphragms and/or framing will also be provided in the detailed analysis section if this concept is identified as one of the top-three.

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Embry-Riddle Aeronautical University Technical Plan

RFRP-14/15-003

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Figure 10. Conceptual design for pultruded GFRP plate built-up box-girder bridge. Section geometry for 30 ft., 50 ft. and

75 ft. simple span bridge applications to be determined through proposed research.

ln general, a major shortcoming of pultruded sections is that the primary fiber direction is typically limited to the axis of themember. This results in structural elements that are susceptible to shear failure. tt is possible to achieve m ulti-directional fiber orientations in pultruded shapes (in fact, the ASCE

Pre-Standard requires that FRP structural members have fibers oriented in a minimum of two directions separated by a minimum of 30 degrees), but this adds to the complexity of creating fiber pre-forms for the pultrusion process.

The unidirectional nature of pultruded elements also complicates the design of connections for built-up box-girders. Because the strength properties of connecting elements are highly anisotropic, multiple failure modes related to block-shear must also be considered. A final complicating issue related to the built-up box-girder alternative is tied to the non-ductile nature of FRP composites. Minor imperfections in connections for steel structures are typically not a concern because localized stress concentrations pultruded plate fastener

Embry-Riddle Aerona utical U niversity Technical Plan RFRP-14/1s-003 result in ylelding that redistributes load to nearby material. when the ultimate strength of FRP composites is exceeded, a brittle failure occurs that results in permanent damage for the part. lf mechanical fasteners are used to join composite parts together, dimensional tolerances for holes must be extremely tight in order to ensure that all fasteners participate in load transfer.

VIP/VARTM open box-girders

Trd ditio nal Ia bric I ay u p Additional shear strength in composites is achleved by providing fibers in more than one direction.

Open-mold lay-up methods (see Figure 5) allow for uni-directional continuous fabrics to be stacked at different angles in order to achieve a desired fiber-direction profile. Woven fabrics can also be incorporated into the laminate stack to achieve 0/90' and +/- 45"fiber orientations. Once the desired fiber configuration has been achieved, a vacuum infusion process (VlP) is employed to saturate the fibers with resin. The vacuum ensures a relatively high-quality part with a low degree of voids.

Open-top box-girder section geometry is well-suited to the VIP/VARTM method. The depth and width of the cross-section can be adjusted using reconfigurable male molds, and the thickness of the cross-section can vary depending on the specific fiber stacking sequence. This ability to change section geometry provides designers some degree of flexibility to meet specific structural demands (e.g strength and serviceability requirements).

3-D stitched laminates The ablllty to orient fibers in more than one in-plane direction provides significant advantages over pultruded shapes. Parts formed by the traditional VIP/VARTM method are, however, still susceptible to interlaminar shear failulre and delamination. Advances in 3-D stitching technology have helped to mitigate some of these concerns. 3-D stitching involves the use of specialized equipment to sew layers offabric together and provide reinforcement for the composite in the out-of-plane direction. Weplan to investigate whether or not non-visible/interlaminar damage in FRP bridge girders can be arrested before the ultimate strength of the element is compromlsed. lt may also be possible to design these stitches such that non-visible/interlaminar damage manifests on the surface as visible damage.

Integrated pultruded rods A final area that we plan to investigate related to VIP/VARTM open box-girders is integrating pre-cured pultruded carbon FRP rods directly into the laminate stack. The overall goal of these supplementary reinforcements is to provide additional stiffness for the FRP bridge girder as well as provide reserve capacityforthe structure. Co-Pl Tamijani hasextensive experience with the design and optimization of composite structures for the aerospace sector. Specifically, Dr. Tamijani's experience working with

Boeing to evaluate the structural integrity of damaged PRSEUS panels3s provides a unique skill-set to determine how PRSEUS concepts can be effectively deployed in FRP composlte bridge girder applications.

Embry-Ridd le Aerona utica I U niversity TechnicalPlan RFRP-14/1s-003

Figure 11. 3-D stitching machine used to fabricate aerospace composites. lmage obtained from May 2012 issue of Compositesworld magazine35.

opporfuntties for 3-D stitching

(stitched into tercbn face)

Figure 12. VIP/VARTM open box-girder concept. Section geometry for 30 ft., 50 ft. and 75 ft. simple span bridge applications to be determined through proposed research.

Hybrid concrete-FRP section The proposed conceptual design study will also include several hybrid concrete-FRP section alternatives.

Previous research by Chen and El-Hacha indicates that developing composite action between pultruded

FRP shapes and concrete is difficult. To address this challenge, we plan to develop concepts with pultruded GFRP sections that incorporate both vertical and horizontal shear studs. The geometry shown in Figure 1-3 is representative of the type of geometries we intend to explore. Multiple concepts will be considered.

ARTM

Figure 13. Proposed concept for hybrid concrete-FRP bridge girder.

RFRP_14l15_003

Preliminary Analysis and Design

Each concept described in the previous section will be evaluated in the context of a simple two-lane r7 bridBe with shoulders ("50 feet wide), cast-in-place reinforced concrete deck, wearing surface, and v railing. Variable girder spacing will also be investigated for each concept. This preliminary analysis will rely on standard AASHTO LRFD design guidelines for loading and serviceability requirements. HL-93 liveY load and the self-weight ofthe bridge girder, concrete deck and railing will be included. Fatigue v properties for the proposed material systems will also be considered.

This preliminary analysis will result in general section geometry requirements. For pultruded sections, designs will be based established methods outlines in the ASCE Pre-Standard. The VIP/VARTM box-v girder designs will be based on composite laminate theory as well as fundamental solid mechanics principles. A finite element analysis will be performed for each proposed section that includes orthotropic material properties based on the fiber orientation ofthe laminate. A buckling analysis will v also be performed to ensure that the specified cross-section d;mensions remain stable up to the v controlling limit state.

v Evaluation Criteria

An evaluation framework will be developed in order to rank each of the proposed concepts. Specific criteria include:

1. Material qua ntities

\, 2. Material costs

3. Manufacturing costs

a. Tooling Y b. Fabrication v 4. constructability r, a. Transportation considerations

\7 b. On-site maneuverabilitY

c. Effect on construction timeline

5. Durability\' 6. Maintenance and inspection \' 7. Ma nufacturing adaptability

8. Design methodology

\-. 9. Comparison to traditional RC/PC construction

\7 Considerable work is anticipated to determine the manufacturing costs associated with each concept.

We plan to attend the upcoming American Composites Manufacturing Association (ACMA) conference in Dallas, Texas, in an effort to establish relationships with existing composites manufacturers. We also

\? anticipate a high level of collaboration with FDOT project engineers in order to assess the

\7 constructability of the proposed…