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Arbetet har genomförts i samarbete med Malmö Gatukontor med målet att samla in information om fiberförstärkta plastkompositer (fiber-reinforced polymer; FRP). FRP-kompositer kan vara ett intressant alternativ till konventionella byggnadsmaterial på grund av sina goda materialegenskaper. FRP har inte använts i gångbroar i Sverige tidigare och materialet är därför relativt okänt för byggbranschen. Studiens syfte var att undersöka och dokumentera beständigheten för FRP-gångbroar som påverkas av den omgivande miljön. Arbetet har genomförts som en litteraturstudie. Huvuddelen av studien fokuserade på att utvärdera olika nedbrytningsprocesser för att kunna bedöma potentiella svagheter hos FRP kompositer i gångbroar. Kopplingspunkter mellan olika delar i FRP broar har också studerats och dess inverkan på den totala beständigheten av konstruktionen har evaluerats. Studien ger en överblick av hur beständighetsparametrar för FRP-kompositer påverkas av olika typer av nedbrytning. Från denna överblick värderades nedbrytning genom fuktabsorption, höga och/eller cykliska temperaturer och UV-strålning som de faktorer som mest påverkar materialegenskaperna för FRP-kompositer. Studien konstaterar även att effekten av samverkan mellan olika nedbrytningsprocesser måste beaktas då materialet utsätts för flera olika angrepp i naturliga miljöer. Denna synergi gör att det är svårt att värdera effekten av varje enskilt angrepp. På grund av brist på information kunde inte kopplingspunkterna mellan komponenter i överbyggnadskonstruktionen i gångbroar fullständigt utvärderas, med avseende på dess påverkan på den totala beständigheten. Studien kunde dock konstatera att kopplingspunkter bör undvikas om det är möjligt, då vibrationer, utmattning och termisk expansion kan orsaka högre spänningsnivåer i kopplingspunkterna. Resultaten från studien syftar till att ge vägledande information vid projektering av gångbroar med FRP-kompositer. / This bachelor thesis was written in cooperation with Malmö Streets and Parks Department to collect information on fiber-reinforced polymer (FRP) composites. In today’s building industry, FRP composites provide an interesting alternative to conventional building materials because of their superior material properties. FRPs are suggested to be a sustainable solution meeting the future requirements in infrastructure and especially bridge design. The use of FRP composites in pedestrian bridge applications have not previously been utilized in Sweden and thus the material is relatively unknown to the building industry. The aim of this study was primarily to examine the performance in terms of durability of FRP pedestrian bridges subjected to the effects of the surrounding environment by conducting a literature review. The main part of this study was to evaluate different types of degradation to assess the potential weaknesses of FRP composites during in-service use in pedestrian bridges. The connections between the different members and components in FRP bridges were also studied and their impact on the overall durability of the construction was evaluated. The results from this study provided an overview of the durability characteristics of FRP composites subjected to different types of degradation. From this overview it was concluded that degradation by moisture absorption, high and/or cyclic temperature, and UV-radiation had the most significant impact on the material properties in FRP composites. This study also concludes that the effects of synergism between the different types of degradation need to be considered since FRP composites are subjected to many types of degradations in natural environments. Because of the effects of synergism, the individual effects of the different types of degradations can be difficult to evaluate. Due to lack of information, the impact on overall durability in pedestrian bridges from the connections between components in the superstructure could not be fully evaluated. However, it was found that connections should be avoided if possible due to vibrations, fatigue, and thermal expansions that may cause higher stress levels in the connection points. The results of this study aims to provide guidance when designing FRP composite pedestrian bridges.

A fiber reinforced polymer (FRP) composite cellular deck system was used to rehabilitate a historical cast iron thru-truss structure (Hawthorne St. Bridge in Covington, Virginia). This research seeks to address following technical needs and questions to advance FRP deck application. The critical panel-to-panel connections were developed and evolved through a four-stage study and finally realized using full width, adhesively bonded tongue and groove splices with scarfed edges. Extensive experimental study under service, strength and fatigue loads in a full-scale two-bay mock-up test and a field test was performed. Test results showed that no crack initiated in the joints under service load and no significant change in stiffness or strength of the joint occurred after 3,000,000 cycles of fatigue loading. Various issues related to constructability of FRP deck systems were investigated and construction guidelines and installation procedures for the deck system were established. The structural performance of the FRP-on-steel-superstructure system was examined in the laboratory and field under service load. Tests results confirmed the following findings: (1) the clip-type of panel-to-stringer connection provides little composite action as expected, which fulfilled the design intention; (2) local effects play an important role in the performance of FRP deck; (3) the FRP deck design is stiffness driven rather than strength driven like traditional concrete deck. Finally, an FEM parametric study was conducted to examine two important design issues concerning the FRP decks, namely deck relative deflection and LDF of supporting steel girders. Results from both FEM and experiments show that the strip method specified in AASHTO LRFD specification (AASHTO 2004) as an approximate method of analysis can also be applied to unconventional FRP decks as a practical method. However, different strip width equations have to be determined by either FEM or experimental methods for different types of FRP decks. In this study, one such an equation has been derived for the Strongwell deck. In addition, the AASHTO LDF equations for glued laminated timber decks on steel stringers provide good estimations of LDFs for FRP-deck-on-steel-girder bridges. The lever rule can be used as an appropriately conservative design method to predict the LDFs of FRP-deck-on-steel-girder bridges. / Ph. D.

The primary objective of this research was to investigate the shear strength of concrete bridge decks with GFRP top-mat reinforcement. Several models currently exist to predict the shear strength during the design process; however, previous research at Virginia Tech indicates that the existing equations are overly conservative. For this research, a series of concrete decks with varying lengths were tested in a laboratory environment in a two-span continuous configuration, during which data was collected on deflections, rebar strain, crack widths, and ultimate load. It was concluded that the existing equations, particularly the guidelines of ACI 440, are grossly over-conservative for GFRP-reinforced concrete bridge decks continuous over multiple supports. It was suggested that this is due to multiple factors, including additional support provided by the typically-neglected steel reinforcement in the bottom mat and a higher shear strength of the uncracked portion of concrete due to higher compressive stresses in the section as a result of the continuous deck configuration. The second objective of this research was to investigate the effects of environmental exposure on the composite deck and the individual GFRP rebar. Three deck specimens were subjected to differing environmental conditions, including one that was placed into service at an interstate weigh station. All three decks were tested in the same manner as those in the shear investigation. Additionally, live load tests were conducted on the weigh station deck during the time it was in place and tensile tests were conducted on rebar that were extracted from the concrete decks. In the live load testing, the GFRP strains increased by more than 200% over the period of service, which was likely due to a combination of a reduction in GFRP stiffness and a greater amount of cracking. During the laboratory tests on the decks, no clear correlation between conditioning and deflections or cracking was found. The ultimate strength actually increased with conditioning, with the weigh station specimen exhibiting the highest shear strength. Finally, the results of the rebar tensile tests suggested a decrease in both modulus of elasticity and ultimate tensile strength of the GFRP with environmental exposure when compared to unconditioned bars. / Master of Science

The purpose of this research was to investigate the effectiveness and durability of GFRP bars as reinforcement for concrete decks. Today's rapid bridge deck deterioration is calling for a replacement for steel reinforcement. The advantages of GFRP such as its high tensile strength, light weight, and resistance to corrosion make it an attractive alternative to steel. The first objective of this research was to perform live load testing on a bridge deck reinforced with GFRP in one span and steel in the other. The results were compared to the findings from the initial testing performed one year earlier. The strains and deflections of the bridge deck were recorded and the two spans compared. Transverse stresses in the GFRP bars, girder distribution factors, and dynamic load allowances were calculated for both spans. From the live load tests, it was concluded that the GFRP-reinforced span results were within design parameters. The only concern was the increased impact factor values. The second objective was to perform live load tests on a slab reinforced with GFRP installed at a weigh station. Two live load tests were performed approximately five months apart. Peak strains in the GFRP and steel bars were recorded and compared. The peak stresses had increased over time but were within design allowable stress limits. The third objective of this research was to investigate the long term behavior and durability of the GFRP reinforcing bars cast in a concrete deck. The strain gauges, vibrating wire gauges, and thermocouples in the bridge deck were monitored for approximately one year using a permanent data acquisition system. Daily, monthly, and long term fluctuations in temperature and stresses were examined. It was concluded that the vibrating wire gauges were more reliable than the electrical resistance strain gauges. It was further observed that the main influence over strain changes was temperature fluctuations. / Master of Science

The quality of continuous fiber reinforced polymer matrix composite parts and structures depends strongly on the friction during the composite forming process. The two major types of friction that cause deformations during this process are ply-ply friction and tool-ply friction. One of the challenges in the composite forming process is the occurrence of wrinkling and shape distortion of the fabric caused by the surface differences between the forming tool and surface of the laminate. Frictional measurements of composites can vary widely depending on processing parameters, measurement technique, and instruments used. In this study, a commercial rheometer was used to evaluate tool-ply friction of unidirectional carbon fiber epoxy prepreg at various contact pressures, temperatures and sliding velocities. Viscoelastic properties such as the complex viscosity (η*), storage modulus (G'), loss modulus (G"), and loss factor (tan δ) were used to determine the critical transition events (such as gelation) during cure. An understanding of changes in viscoelastic properties as a function of time, temperature, and cure provides insight for establishing a suitable processing range for compression forming of prepreg systems. Surface imaging results were coupled with rheological results to qualitatively examine the effects of processing parameters on prepreg distortions. Changes in gap height over the measurement interval qualitatively describe the changes in contact area and contact mechanisms between the tool-ply surfaces. The results indicate that friction behavior of the prepreg system is a contribution of adhesive and frictional forces, where increase in viscosity, reduction in gap height, and cure of the sample correlate to higher friction values. / Master of Science / The quality of composite parts and structures depends strongly on the friction present during the composite forming process. One of the major challenges in the forming process is the occurrence of wrinkling and shape distortions of the fabric caused by the surface differences between the forming tool and material. The presence of these defects can compromise the final material property and lead to failure when in use. Frictional measurements of composites can vary widely depending on processing parameters, measurement technique, and instruments used. The extent of interaction between the tool and surface of the material depends on the tooling height, and by extension, contact area, which cannot easily be monitored with traditional test designs. A commercial rheometer was used in this study to evaluate tool-ply friction of unidirectional carbon fiber epoxy prepreg at various contact pressures, temperatures, and sliding velocities. Gap height and torque were monitored to provide information on the frictional dependence of processing parameters. In addition, surface-imaging results were coupled with rheological results to examine the relationship between friction and fiber distortions. The understanding of changes in material property with respect to the tooling process is the key to optimizing the composite forming process.

A thermo-structural model was developed to predict the failure of compressively loaded fiber-reinforced polymer (FRP) laminates during fire. The thermal model was developed as a one-dimensional heat and mass transfer model to predict the thermal response of a decomposing material. The thermal properties were defined as functions of temperature and material decomposition state. The thermal response was used to calculate mechanical properties. The structural model was developed with thermally induced bending caused by one-sided heating. The structural model predicts out-of-plane deflections and compressive failure of laminates in fire conditions. Laminate failure was determined using a local failure criterion comparing the maximum combined compressive stress with the compressive strength. Intermediate-scale one-sided heating tests were performed on compressively loaded FRP laminates. The tests were designed to investigate the effect of varying the applied stress, applied heat, and laminate dimensions on the structural response. Three failure modes were observed in testing: kinking, localized kinking, and forced-response deflection, and were dependent on the applied stress level and independent of applied heating. The times-to-failure of the laminates followed an inverse relationship with the applied stress and heating levels. The test results were used to develop a relationship which relates a non-dimensionalized applied stress with a non-dimensionalized slenderness ratio. This relationship relates the applied stress, slenderness ratio, and temperature of the laminate at failure and can be used to determine failure in design of FRP laminate structures. The intermediate-scale tests were also used to validate the thermo-structural model with good agreement. / Master of Science

When taking steps away from tried and true designs, there is always a degree of uncertainty that arises. With the introduction of fiber-reinforced polymers (FRP) in double-web I-beams (DWIB) to replace steel beams in bridge applications, there are many benefits along with the disadvantages. A bridge has been built with this new type of beam after only short-term proof testing for validation. Nondestructive evaluation (NDE) is a way to implement health monitoring of the bridge beams and needs to be assessed. The principal underlying infrared thermal imaging (IR) nondestructive evaluation (NDE) is to induce a thermal gradient in the beam through heating and monitor how it changes. Delaminations determined by others to be the critical form of deterioration, would be expected to affect the heat conduction in these beams. This project used a halogen lamp to heat the surface of the beam followed by an observation with an IR camera. Calculations of an ANSYS finite element analysis (FEA) model were compared with a series of laboratory tests. The experimental results allowed for validation of the model and development of an IR inspection procedure. This work suggests that for high quality beams of the type considered that an IR procedure could be developed to detect delaminations as small as one inch in length; however, the size would be underestimated. / Master of Science

A group of researchers, engineers, and government transportation officials have teamed up to design two bridges with simply-supported FRP composite structural beams. The Toms Creek Bridge, located in Blacksburg, Virginia, has been in service for six years. Meanwhile, the Route 601 Bridge, located in Sugar Grove, Virginia, has been in service for two years. Researchers have conducted load tests at both bridges to determine if their performance has changed during their respective service lives. The key design parameters under consideration are: deflection, wheel load distribution, and dynamic load allowance. The results from the latest tests in 2003 yield little, yet statistically significant, changes in these key factors for both bridges. Most differences appear to be largely temperature related, although the reason behind this effect is unclear. For the Toms Creek Bridge, the largest average values from the 2003 tests are 440 me for service strain, 0.43 in. (L/484) for service deflection, 0.08 (S/11.1) for wheel load distribution, and 0.64 for dynamic load allowance. The values for the Route 601 Bridge are 220 me, 0.38 in. (L/1230), 0.34 (S/10.2), and 0.14 for the same corresponding paramters. The recommended design values for the dynamic load allowance in both bridges have been revised upwards to 1.35 and 0.50 for the Toms Creek Bridge and Route 601 Bridge, respectively, to account for variability in the data. With these increased factors, the largest strain in the toms Creek Bridge and Route 601 Bridge would be less than 13% and 12%, respectively, of ultimate strain. Therefore, the two bridges continue to provide a large factor of safety against failure. / Master of Science

As fiber reinforced polymer (FRP) structures find application in highway bridge structures, methodologies for describing their long-term performance under service loading will be a necessity for designers. The designer of FRP bridge structures is faced with out-of-plane damage and delamination at ply interfaces. The damage most often occurs between hybrid plys and dominates the life time response of a thick section FRP structure. The focus of this work is on the performance of the 20.3 cm (8 in) pultruded, hybrid double web I-beam structural shape. Experimental four-point bend fatigue results indicate that overall stiffness reduction of the structure is controlled by the degradation of the tensile flange. The loss of stiffness in the tensile flange results in the redistribution of the stresses and strains, until the initiation of failure by delamination in the compression flange. These observations become the basis of the assumptions used to develop an analytical life prediction model. In the model, the tensile flange stiffness is reduced based on coupon test data, and is used to determine the overall strength reduction of the beam in accordance the residual strength life prediction methodology. Delamination initiation is based on the out-of-plane stress sz at the free edge. The stresses are calculated using two different approximations, the Primitive Delamination Model and the Minimization of Complementary Energy. The model successfully describes the onset of delamination prior to fiber failure and suggests that out-of-plane failure controls the life of the structure. / Master of Science