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Continuous fiber reinforced thermoplastics (CFRTPs) are valued for their high strength-to-weight ratios, corrosion resistance, and recyclability over traditional structural materials. However, CFRTPs are difficult to fabricate compared to thermoset composites, a significant barrier to their adoption in construction and infrastructure. The University of Maine's Advanced Structures and Composites Center has developed several innovative manufacturing and post-processing techniques to address fabrication challenges. The Continuous Forming Machine (CFM) is a processing device for non-reactive thermoplastic pultrusion, efficiently producing structural profiles like rods, plates, and channels. The CFM platform can be expanded with co-processes to create parts such as field-bendable concrete reinforcing bar. Further, effective post-forming processes will be crucial for adapting CFRTP components to on-site infrastructure applications. Localized thermoforming targets specific bending regions within a CFRTP component, offering a field-friendly approach over stamp thermoforming. Using localized heating methods, such as embedded heating elements, CFRTP panels can be locally thermoformed into three-dimensional components. Additional work has been performed to mitigate wrinkle formation in the bending of thick-gauge CFRTP laminates by implementing modifications to component architecture. This research presents significant advancements towards the widespread adoption of CFRTPs for infrastructure, demonstrating the technology's adaptability for onsite manufacturing and its future impact on sustainable construction practices. [ABSTRACT FROM AUTHOR]

Recently, 3D printing of large, structural polymer parts has received increasing interest, especially for the creation of recyclable structural parts and tooling. However, the complexity of large-scale 3D polymeric printing often dictates resource-intensive trial and error processes to achieve acceptable parts. Existing computational models used to assess the impact of fabrication conditions typically treat the 3D-printed part as a continuum, incorporate oversimplified boundary conditions and take hours to days to run, making design space exploration infeasible. The purpose of this study is to create a structural model that is computationally efficient compared with traditional continuum models yet retains sufficient accuracy to enable exploration of the design space and prediction of part residual stresses and deformations. To this end, a beam-based finite element methodology was created where beads are represented as beams, vertical springs represent inter-bead transverse force transfer and multi-point, linear constraints enforce strain compatibility between adjacent beads. To test this framework, the fabrication of a large Polyethylene terephthalate glycol (PETG) wall was simulated. The PETG was modeled as linearly elastic with an experimentally derived temperature-dependent coefficient of thermal expansion and elastic modulus using temperature history imported from an ABAQUS thermal model. The results of the simulation were compared to those from a continuum model with an identical material definition, showing reasonable agreement of stresses and displacements. Further, the beam-based model required an order of magnitude less run time. Subsequently, the beam-based model was extended to allow separation of the part from the printing bed and the inclusion of part self-weight during fabrication to assess the significance of these effects that pose challenges for existing continuum models. [ABSTRACT FROM AUTHOR]

In the design of conventional steel and concrete highway girder bridges, the amount of live load carried by a single girder is quantified through distribution factors (DFs). However, moment DFs for the recently developed fiber-reinforced polymer (FRP) composite tub (CT) girders are not defined in current design codes, leaving questions as to these bridges' live load distribution. To address this, two diagnostic live load tests were performed on an in-service CT girder bridge under heavy truck loads. The measured strains from each test were analyzed and compared with predictions from a calibrated, high-fidelity finite-element (FE) model, which was shown to accurately predict the live load distribution. Then, a simplified FE model was developed that was also shown to accurately predict the live load distribution at a significant computational discount. The simplified model was subsequently used in a parametric study to assess current CT girder design practices, which were found to be consistently conservative. One conclusion was that unintended end restraint of the girder significantly impacted the maximum measured flexural strains, and the high-fidelity FE model required modification and calibration to capture this effect. However, simplified FE models that were not calibrated to the field data were shown to reasonably accurately predict the live load distribution to the most heavily loaded, interior girders. Ultimately, the results of this study show that live load moment DFs should be developed that are specific to the CT girder to ensure efficient future designs with this new technology. [ABSTRACT FROM AUTHOR]

In this paper, the mechanics of inflatable drop-stitch panels are investigated, including the impact of large shear deformations, nonlinearity due to wrinkling of the panel skin that occurs under net compressive strain, work done by the confined internal air, and the effect of the drop-stitch yarns on the panel skin stresses. A large deflection finite element (FE) analysis framework is presented that allows for a panel's stability and post-buckling response to be quantified. The FE code is verified through comparison with available analytical solutions, and the impact of critical response drivers is examined. The FE models are then used to explore the capacity of panel walls when used as part of a shelter subject to realistic wind and snow loads and to assess the dependence of the capacity on the important design parameters of inflation pressure and panel depth. The analyses indicate that while the drop-stitch panel capacity is sensitive to the panel depth and inflation pressure, panels with reasonable cross-sectional dimensions are viable for use in structural applications where they must support significant compression and bending. Future work should focus on increasing the structural efficiency and capacity by increasing the panel shear stiffness and operational inflation pressure. [ABSTRACT FROM AUTHOR]

This work focuses on simulating the thermal history of a vertical wall consisting of a thermoplastic composite material, poly(ethylene terephthalate) glycol (PETG) with short carbon fiber reinforcement, manufactured using a Big Area Additive Manufacturing (BAAM) system. The incremental deposition process used in additive manufacturing, which corresponds to the repeated deposition of hot material onto cooler material, contributes to the presence of residual stresses and part warping. The prediction of these mechanisms is dependent on thermal history of the part, and the major motivation of this work was to improve the accuracy of finite element (FE) models used to quantify the thermal history of large-format additively manufactured parts. Thermocouples were placed throughout the part at varying heights to measure temperature as a function of time. The FE model developed found a thermal contact conductance between the printed part and the bed of 10 W/m2K and convection coefficient values that linearly varied from 3 to 15 W/m2K through the wall height when making a temperature comparison with the output from the thermocouples. It is also demonstrated that the FE model with a constant convection coefficient under-predicts model temperature at the beginning of the manufacturing process when compared against the model with a variable convection coefficient. The impact of this difference was seen in the stress values, which were larger for the model with a constant convection coefficient. Finally, a correlation equation was derived which allows the findings to be generalized to other vertical structures manufactured on the BAAM. In summary, this work offers valuable insights on material characterization, real-time thermocouple placement, and FE modeling of large-format additively manufactured parts. [ABSTRACT FROM AUTHOR]

A method is proposed to locally heat areas of thick (>25.4 mm) continuous glass fiber reinforced thermoplastic (C-FRTP) composites with embedded wire mesh resistive heating elements. Four test specimens including 10.6 cm wide nichrome mesh heating elements embedded in C-FRTP laminates were fabricated and used for heating trials, showing that the composite can be locally heated to near the thermoplastic forming temperature over its entire thickness in less than 1 hour. The heating trials were simulated using a purpose-built finite difference model to investigate detailed temperature distributions. The simulations show that the internal resistive heating elements are capable of locally increasing the temperature of the composite with negligible effect on the adjacent material. Heating efficiency is between 73% and 77%, with temperature differences in the z -direction at peak temperatures less than 35°C. Temperature uniformity can be improved by longer heating times and more heating elements. The local heating method does not cause deconsolidation of the part. The heating method was also experimentally assessed on a more complex cross-section laminate with varying thickness and a foam core using stainless steel mesh heating elements. Results from the first heating tests were applied to the experimental assessment of the more complex laminate to reduce z -direction temperature differences. Numerical simulation of the heating of the foam core laminate showed a z -direction temperature range of 15.5°C. The results of this study show that embedded resistive heating is a cost-effective and simple method for heating a local portion of a thick fiber reinforced thermoplastic composite. [ABSTRACT FROM AUTHOR]

This paper details the development and experimental assessment of a friction-type connector, designed to transfer shear flow between the top flange of a fiber-reinforced polymer (FRP) tub girder and a composite concrete deck for bridge applications. In contrast with previously used bearing-type connectors, this system relies on a deformed FRP surface to transfer shear via direct interlock with the concrete deck. The connector is materially efficient, simple to fabricate, can be used with lower-grade structural or stainless-steel fasteners, and provides a high degree of interface stiffness. Six compression-shear specimens were tested to assess the connector fatigue resistance and ultimate connection strength. Additionally, two short beam specimens were tested in three-point bending, one of which was subjected to fatigue loading. Based on the compression-shear tests and short beam tests, the connection exhibited strength exceeding that predicted by AASHTO for frictional concrete-concrete connections. The connection strengths were significantly greater than the factored demand required by AASHTO for a typical model FRP bridge girder. The cyclic loading of the connection in both compression-shear and beam bending showed that connection stiffness and strength do not significantly degrade, due to the application of 1 × 106 to 6 × 106 cycles of traffic-induced factored fatigue load. [ABSTRACT FROM AUTHOR]

This research addresses the evaluation of five, non-composite, simple-span steel girder bridges using field load testing and finite element (FE) analysis. During field loading, maximum moments of between 74% and 87% of the moment caused by AASHTO HL-93 loading with impact were applied to the structures. Strain readings indicated partial to full unintended composite action and significant restraint at the girder ends for all structures. HL-93 operating load ratings were modified using the strain measurements recorded during diagnostic load tests, leading to an average increase in moment rating factor of 52%. A novel approach of calibrating 3D FE models was developed that captures the observed full and partial composite action observed during testing, as well as restraint of the girder ends, giving good agreement between model-predicted and measured strains. The FE models were used to directly predict bridge capacities and rating factors while explicitly capturing girder yielding and load redistribution. The effects of unintended composite action, end restraint and concrete deck stiffness on capacity were examined using these models. The most conservative FE-estimated rating factors that ignored unintended composite action and end restraint – which are likely unreliable at large loads – were 54% higher than the conventional, code-based rating factors. [ABSTRACT FROM AUTHOR]

Braided, inflatable structural members with axial reinforcing cords have the ability to accommodate loading with a low mass and small storage volume. These members are particularly attractive for space-based applications. There is currently a need to develop computationally efficient structural design methodologies for these unique, compliant, inflatable structural members so that engineers can more-effectively perform structural analyses and conduct structural-optimization studies. In this paper, an analysis methodology is developed for the three-dimensional, large-displacement, materially nonlinear behavior of these inflatable, slender members that includes the effect of the internal inflation pressure. A three-dimensional, corotational, flexibility-based fiber-beam element is employed to handle geometric and material nonlinearities. Comparisons are made with the in-plane and out-of-plane response of component-level testing of inflatable straight tubes, as well as to higher-fidelity shell-based finite-element models. The model results show good agreement with both shell-based finite element (FE) models (with a significantly decreased number of degrees of freedom), and results of component-level tests well past the point where test specimens lose internal prestress due to bending and exhibit a nonlinear response. [ABSTRACT FROM AUTHOR]

In this study, soil-structure interaction in a buried arch bridge system is numerically investigated with two models. Model predictions of arch bending moments and ultimate capacities are compared with the load test performance results of two buried structures from a companion paper. A novel finite-element model was developed using an arch discretized with beam elements and soil discretized with spring elements initialized during progressive backfill simulation. Nonlinear soil-spring force is determined from vertical overburden pressure and earth pressure coefficient dependent on arch deflection. A nonlinear soil-continuum finite-element model was developed using software with Mohr-Coulomb soil plasticity. Experimental moments are compared with model results for backfilling, a series of service-level line loads, and ultimate capacity with an apex line load. The soil-spring model does reasonably well at predicting arch moments and ultimate capacity, and the incorporation of deflection-dependent earth pressure is important when predicting ultimate capacity. The soil-continuum model agrees well with the soil-spring model for service positive moments. [ABSTRACT FROM AUTHOR]

A buried composite arch bridge system using concrete-filled fiber-reinforced polymer tube arches was recently developed for short span bridges. The research reported in this and a subsequent paper seeks to advance understanding of soil-structure interaction in these bridges through laboratory testing and numerical modeling simulations of subscale arch systems. This paper focuses on the experimental testing of stiffness-matched, half-scale three-arch bridge systems with 5:1 and 8:3 span-to-rise ratios tested in a controlled laboratory environment. Arches were cast in concrete foundations, placed in a self-reacting, timber soil box, and covered with decking. Deflection, strain, and soil pressure were recorded at eighth points along the span of the center arch and only at the apex and foundations of the outer arches. The bridges were backfilled with lifts of compacted granular soil until soil grade elevation was 610 mm above the decking apex. The bridges were loaded with a sequence of line loads at seven different positions along the span and were then loaded to failure with an apex line load. Experimental results reported here include the effects of backfilling, service live-load testing, and ultimate loading. [ABSTRACT FROM AUTHOR]

A significant portion of the nation's aging bridge inventory consists of flat slab concrete bridges. Many of these bridges were constructed in the middle third of the 20th century, and although they are in generally good condition, they were not designed to carry modern highway loads. This research builds on prior studies that indicate that the equivalent strip width method-prescribed by AASHTO and widely used for the analysis of flat slab bridges-may be overly conservative and lead to underprediction of bridge structural capacity. The development of finite-element (FE) analysis software designed specifically for the load rating of flat slab bridges is presented. The FE software formulation and convergence were verified by comparison with predictions from commercial FE software under realistic loading scenarios. Results of live load tests of an instrumented, in-service flat slab bridge are reported. The FE model-predicted slab moments were shown to be conservative relative to the moments inferred from the load test data for a range of truck positions. Fourteen in-service flat slab bridges were load rated with both FE analysis and the equivalent strip method to assess the degree of conservatism inherent in the AASHTO approximate analysis. The results show an average increase in rating factor of approximately 26% when using FE analysis and that 58% of the bridges predicted to be under capacity using AASTHO approximate methods are sufficient based on FE analysis. [ABSTRACT FROM AUTHOR]

This paper describes the structural performance of an innovative wood plastic composite (WPC) sheet piling. Tensile coupon tests were performed to determine tensile strength and modulus over a range of strain rates for both WPC and specimens cut from commercially available vinyl sheet piles. Full scale four-point bending tests were conducted up to failure on 20 sets of joined pairs of WPC Z-piles with four different span lengths. For comparison, bending and coupon-level tension tests were also conducted on commercially available vinyl Z-piles and coupons cut from them. The coupon-level tests indicated that WPC had on average a 14% greater modulus than the vinyl specimens in the initial linear range, defined as between 10 and 40% of the respective material's ultimate tensile strength. However, if the modulus is computed over the same stress range of 10-40% of the WPC ultimate tensile strength, both materials have a similar modulus. The vinyl had a tensile strength 3.6 times that of the WPC. During the bending tests, the hollow cross section WPC Z-piles failed primarily in bending-induced tension, while the solid vinyl Z-piles exhibited buckling of the compression flange. Creep rupture testing was conducted for pair of WPC Z-piles in a four-point bending setup to determine long-term load-carrying capacity. No loss of load-carrying capacity was observed during the 90-day test and creep rates generally decreased during the test. However, creep deflections were larger than what would normally be exhibited by wood structural members. While additional studies are needed to address the effects of water absorption on WPC properties, the findings show promise for wood plastic composite light duty sheet piling retaining wall structures. [ABSTRACT FROM AUTHOR]

A statistical lattice model was developed to investigate the energy associated with damage and failure of wood. The model incorporates several important morphological aspects of wood such as grain direction, early wood percentage and grain geometry. The model was developed to investigate progressive damage under enforced boundary displacements and has been adapted to predict fracture energy related phenomena. In this particular study, notched specimens were loaded in uniaxial tension while monitored by a passive acoustic emission (AE) measurement system. The energy associated with the mechanical damage was measured by the AE instruments and compared with the energy released by ruptured elements in the lattice model. Cumulative energy release was tracked as a function of specimen load and deformation in both model and experiment. A ratio was established between the cumulative AE energy released at the first drop in load and the cumulative fracture energy released when the model load-deformation relationship becomes significantly non-linear. An additional ratio was established between the total fracture energy measured prior to 50% of peak strain and the total fracture energy measured prior to peak strain. The magnitudes of these energy release ratios vary owing to a change in failure modes between the short model and the larger specimens; however, the shape of the AE energy release curve up to failure coincides well with that predicted by the model simulations. [ABSTRACT FROM AUTHOR]

Integral abutment bridges (IABs) with short steel H-pile (HP) supported foundations (<=4 m of pile depth) are economical for many environmentally sensitive sites with shallow bedrock. However, such short piles may not develop an assumed, fixed-end support condition at some depth below the pile cap, which is inconsistent with traditional pile design assumptions involving an equivalent length for bending behavior of the pile. In this study, the response of an IAB with short HP-supported foundations and no special pile tip details such as drilling and socketing is investigated. Instrumentation of a single-span IAB with 4-m-long piles at one abutment and 6.2- to 8.7-m-long piles at the second abutment is described. Instrumentation includes pile strain gauging, pile inclinometers, extensometers to measure abutment movement, earth pressure cells, and thermistors. Pile and bridge response during construction, under controlled live load testing, and due to seasonal movements are presented and discussed. Abutment and pile head rotations due to self-weight, live load, and seasonal movements were all found to be significant. Measured abutment movements were likely affected by both temperature changes and deck creep and shrinkage. Based on the field study results presented here, moderately short HPs driven to bedrock without special tip details appear to perform well in IABs and do not experience stresses larger than those seen by longer piles. [ABSTRACT FROM AUTHOR]

This study focuses on the in-plane load-deflection and buckling response of pressurized fabric arches of constant circular cross section. These lightweight portable structural members support tents used for temporary medical facilities, disaster-relief shelters, and military applications. A quadratic Timoshenko beam element is developed for materially and geometrically nonlinear analysis based on a virtual work principle that includes work done by internal pressure due to deformation-induced volume changes. The inability of the arch fabric to carry compressive stress is addressed with a nonlinear moment-curvature relationship that captures the effect of fabric tensile stiffness, internal pressure, and axial load. A corotational formulation and cylindrical arc-length solver are used to permit large displacement analysis and the tracking of postbuckling softening response. A convergence study demonstrates the good performance of the element and the solver. Results of laboratory load tests on a 9.5 m-span semicircular inflated fabric arch are presented, and shown to agree well with the model predictions. Parametric studies are conducted to examine the significance of inflation pressure and lateral restraint on arch deflections and buckling under the action of code-specified snow loads. The numerical studies show that the work done by the confined air significantly increases arch load capacity, and that shear deformations of woven fabrics can significantly reduce arch capacity. [ABSTRACT FROM AUTHOR]

While composite-reinforced glulam beams have been used in several bridge demonstration projects, knowledge of their fatigue behavior is quite limited. In this study, the response of full- and partial-length fiberglass composite-reinforced glulam beams under fatigue cycling followed by quasi-static bending to failure is examined. To mimic anticipated in-service conditions, a hygrothermal cycling regime was developed that replicates the effective stress history of a 50-year service life with a 55-day period in a moisture-controlled kiln. In addition, some of the beams had initial delaminations introduced between the reinforcing and the wood similar to those observed in field investigations of reinforced glulam bridge girders. For the partial-length reinforced beams, reinforcing with both confined and unconfined ends was considered. The results of the postfatigue tests to failure were compared with the expected strength. In addition, the stiffness of the beams was monitored during the fatigue cycling. It was found that, with the exception of the unconfined, partial-length reinforced beams, all specimens had a residual strength that compared favorably with the expected strength. Further, neither the preconditioning nor the fatigue cycling had an appreciable impact on the stiffness of the reinforced beams. The unconfined, partial-length reinforced beams did not perform well under fatigue loading and do not seem to be a viable alternative for use as reinforced glulam bridge girders. [ABSTRACT FROM AUTHOR]

Lightweight, portable air-pressurized beams and arches serve as primary load-carrying members for a number of civilian and military structures. These members are made from synthetic fibers that are woven or braided into a circular cross section. The pressurized air provides structural capacity by pretensioning the fabric and through its behavior as a confined gas. In this paper, a beam finite element is developed for the analysis of pressurized fabric beams based on virtual work principles. Work done by internal pressure due to deformation-induced volume changes is included in the formulation. A nonlinear moment-curvature relationship accounts for fabric wrinkling, and shear deformations are incorporated. A mixed-interpolation Timoshenko beam element is used to discretize the virtual work expression. A numerical method for determining the moment-curvature relationship of an inflated beam made from a fabric obeying a nonlinear stress–strain relationship is developed. Results of experiments on pressurized fabric beams loaded in three- and four-point bending are presented, and the finite-element model is shown to accurately predict experimentally observed load-deflection response for a range of pressures. Simulations demonstrate that in addition to prestressing the fabric, the pressurized air significantly increases beam capacity as the beam volume decreases due to deformation. [ABSTRACT FROM AUTHOR]

This study addresses the development and structural testing of a hybrid sheathing panel designed to improve the lateral resistance of light wood-frame shear walls. The panel consists of thin outer sheets of oriented-strand board (OSB) bonded to strips of fiber-reinforced polymer (FRP) that are sandwiched between the OSB panels at the edges. The FRP-reinforced panel material selection and fabrication are summarized. Monotonic and cyclic tests were conducted to assess the performance of single-connector sheathing-to-framing connections using both OSB and FRP-reinforced OSB. Twenty-four full-scale shear walls were tested under monotonic and cyclic racking loads to determine the benefits of FRP-reinforced OSB to wall lateral load resistance. For a 102 mm perimeter nail spacing, FRP-reinforced OSB-sheathed walls exhibited increases in peak capacity and energy dissipation under cyclic loading of 27 and 73%, respectively, compared to walls sheathed with conventional OSB. Based on these experimental results, FRP-reinforced OSB panels appear to have significant potential for increasing the energy dissipation capacity and lateral load resistance of wood-frame structures subjected to extreme lateral loads. However, their full utilization will require higher strengths for critical shear wall components such as tension ties and framing interconnections, as well as improvements in sheathing-to-framing fastener performance. [ABSTRACT FROM AUTHOR]

A dowel-type shear connector for achieving composite action in glulam bridge girders supporting a concrete deck is described. Direct shear tests of the connector show that its ultimate capacity is unaffected by fatigue, but that gaps do develop between the dowel and glulam after load cycling. Two 10.7-m-long glulam girders reinforced on the tension face with a fiber-reinforced polymer (FRP) and having composite concrete decks were loaded to failure after being subjected to fatigue cycling. The test results indicate stiffness increases of over 200% and strength gains of over 60% relative to the expected response of a noncomposite girder. Measured flexural strains showed a strain discontinuity at the glulam-concrete interface, as expected. A numerical model for rigorously analyzing FRP-glulam-concrete girders is overviewed, and its predictions are shown to compare favorably with the results of the girder tests. Finally, the design of a 21.3-m-span FRP-glulam-concrete bridge that is slated for completion in Fairfield, Maine, during the summer of 2003 is discussed to demonstrate the practical application of the results presented in this manuscript. [ABSTRACT FROM AUTHOR]

Focuses on the development and implementation of a layered analysis method for predicting the response of fiber-reinforced polymers-reinforced glulam beams with partially composite concrete beams. Development of layered moment-curvature analysis technique; Discussion on the model verification; Conclusions.

Presents a study which examined the effect of dowel looseness on the structural response of jointed concrete pavements. Analysis of the practical case of a Winker foundation; Modeling techniques and solution strategies; Significance of nonlinear joint load transfer.

Presents the development and implementation of a general, three-dimensional embedded bending member suitable for modeling dowel action. Desire to model rigid concrete pavement slabs with doweled joints; Unit vectors and element definition; Usage of solid brick elements.

Focuses on the development of robust multigrid-preconditioned conjugate-gradient methods suitable for the solution of large-scale three-dimensional finite element problems in structural mechanics. Formulation of intergrid transfer of information; Modeling nodal contact constraints; Dicussion on rigid pavement model problem.