Deflection Response of Glass Fiber-Reinforced Pultruded Components in Hot Weather Climates

Presented in this paper are the experimental results pertaining to the deflection response of E-glass/polyester pultruded structural elements when subjected to bending and temperature profiles comparable to those encountered in hot weather conditions. Experiments were conducted on tubular components subjected to an applied force resulting in a maximum stress corresponding to 4% of the composite material strength. In one case, five component tests were carried out in an environmental condition in which the air temperature was first gradually increased from 20°±2°C?to?72°±2°C, then decreased to 60°±2°C in 1?h. In another case, one component was tested under an air temperature that was first gradually increased from 20?to?60°C, then kept at 60°±2°C for 215?h. Test results are compared with those obtained in another study at laboratory conditions (22°±2°C). It is concluded that the increase in the deflection of glass-reinforced pultruded components in hot climates is substantial and must always be accounted for in the design of pultruded structures.     

Long-Term Compression Performance of a Pultruded GFRP Element Exposed to Concrete Pore Water Solution

A durability study was performed on a pultruded glass fiber reinforced polymer (GFRP) compression element of a hybrid GFRP/steel joint for concrete structures. GFRP elements were immersed in alkaline pore water solutions of different temperatures during 18?months. Moisture uptake occurred very quickly, within a few days, mainly through a wicking effect along the fiber/matrix interfaces and matrix cracks. The loss of matrix stiffness due to swelling led to a first rapid and significant drop in element compression strength, because of the loss of matrix resistance against buckling of the compressed fibers. In the second phase, strength reduction due to chemical glass and matrix degradation occurred at a much slower rate. It was found that the Arrhenius rate law could predict the element strength decrease. Due to the less harsh environment in practice, the strength and stiffness decrease was found to be acceptable, thereby making it possible to assure structural safety and serviceability of the hybrid GFRP/steel joint after 70?years of service.     

Durability of Fiberglass Composite Sheet Piles in Water

The durability of fiberglass composite sheet piles in water was studied through the specimens cut from flanges and webs of pultruded sheet pile sections. The experiments were performed to evaluate the water absorption at ambient temperature in complete immersion, and its effect on the tensile properties and the freeze-thaw resistance of the saturated composites. The high temperature at 70°C was used to accelerate the tests, and 100°C (boiling water) to verify the state of saturation. The non-Fickian absorption behavior of the pultruded composites was modeled based on the Berens and Hopfenberg two-phase absorption theory to predict the long-term performance and the change in mechanical properties of saturated composites. The results indicated that the water absorption process of the pultruded sheet pile composites followed a combination of Fickian diffusion and polymeric relaxation. The percent absorption at saturation was about 1.72% for the flange and 3.11% for the web. The water absorption model predicted that saturation would be reached after 5.8 years for the flange and after 14.5 years for the web immersed in tap water at ambient temperature. The tensile strength was found to decrease initially with the increase in the percent water absorption, and finally stabilize at the state of saturation. On the other hand, there was no noticeable change in the tensile modulus of elasticity during the entire water-aging period. The saturated composites showed excellent resistance to freeze-thaw cycling from 4.4 to ?17.8°C.     

Theoretical and Experimental Analysis of GFRP Bridge Deck under Temperature Gradient

The temperature difference between the top and bottom of a glass fiber reinforced polymer (GFRP) composite deck, ～ 65°C ( ～ 122°F), is nearly three times that of conventional concrete decks ～ 23°C ( ～ 41°F). Such a large temperature difference is attributed to the relatively lower thermal conductivity of GFRP material. In this study, laboratory tests were conducted on two GFRP bridge deck modules (10.2 and 20.3?cm deep decks) by heating and cooling the top surface of the GFRP deck, while maintaining ambient (room) temperature at the deck bottom. Deflections and strains were recorded on the deck under thermal loads. Theoretical results (using macro approach, Navier-Levy, and FEM) were compared with the laboratory test data. The test data indicated that the GFRP deck exhibited hogging under a positive temperature difference (i.e., Ttop>Tbottom, heating test; Ttop and Tbottom are temperatures at top and bottom of the deck, respectively) and sagging under a negative temperature difference (i.e., Ttop相似文献   

Free Vibrations of Pultruded FRP Elements: Mechanical Characterization, Analysis, and Applications

The research shows the results of experimental tests to establish the dynamic parameters of fiber-reinforced polymer (FRP) structural elements in the free vibration field. The tests and the analysis consider the simply supported configuration of pultruded elements characterized by glass fiber reinforcement, glass fiber-reinforced polymer (GFRP) and the thermosetting vinylester matrix subjected to flexural, transversal, and torsional vibrations. Comparison between the experimental results and numerical analysis and the finite element method is also presented. The dynamic response of GFRP structural elements is compared with the behavior of steel and aluminum elements. The results show a good performance, especially in the case of open cross-sectional profiles, considering the advantages deriving from the ratio between the dead load and total load of fiber reinforced composite material. Finally, the use of pultruded GFRP elements for new-built decks is investigated to detect possible resonance phenomena due to human-induced periodic vibrations.     

Fabrication and Testing of Cuff Connections for GFRP Box Sections

A new type of connection between beams and columns has been designed and fabricated specifically for use with glass fiber reinforced plastic (GFRP) pultruded box members. The work is built on previous efforts in the area of GFRP connections, which demonstrated that innovative connections between box sections are superior to connections based on concepts from steel construction for connecting I-beams. The new connection element is designed as a monolithic connection for frame members and is fabricated using a vacuum assisted resin transfer molding process. Individual connection specimens have been fabricated and tested to verify their performance under cyclic static loads in a test frame designed to simulate conditions in a moment resisting frame. The connection configuration was found to fare better from the standpoint of both strength and stiffness in comparison with previous attempts at developing GFRP beam-to-column connections.     

Static and Fatigue Behavior of Thick Pultruded GFRP Plates with Surface Damage

Glass fiber-reinforced polymer (GFRP) bridge decks suffering frequent cyclic loading of heavy wheels require relatively thick pultruded composites. To examine the behavior of 12 mm thick pultruded GFRP plates containing surface layers and to study the influence of surface damage, which may be present on such decks, static and fatigue tensile tests were carried out. Severe indentation yielded not only visible damage, but also an invisible damage in the unidirectional layer. Loss of cross section area due to both damages affected the static ultimate loads. Fatigue cracks were found around higher stress concentrations on the surface layer as early as approximately 10% of the total fatigue life. These initial cracks, however, barely affected the fatigue life because delamination of the surface layers prevented the cracks from propagating. The invisible shear crack due to indentation barely affected the fatigue life since earlier splitting between initially damaged and undamaged fibers mitigated the crack propagation.     

Investigating a Structural Form System for Concrete Girders Using Commercially Available GFRP Sheet-Pile Sections

This paper presents a new girder consisting of a trapezoidal pultruded glass fiber-reinforced polymer (GFRP) hat-shaped section commercially available as a sheet pile, but used in this study as a structural form for concrete. It can also offer continuity in the transverse direction through a pin-and-eye connection. Five 610?mm×325?mm and 3,300-mm-long girders were tested in flexure to examine different bond systems, voided and solid concrete cores, and the performance in positive and negative bending. Bond systems were wet adhesive bond to freshly cast concrete, adhesively bonded coarse aggregates, and mechanical shear studs. No slip was observed between concrete and the GFRP section until delamination failure occurred within a thin layer of cement mortar that remained attached to GFRP. The studs failed by pull out from the concrete flange. In general, 47–75% of the full strengths of concrete and GFRP were reached at ultimate bond failure. Wet adhesive bonding was the simplest and quickest to apply, while resulting in a comparable strength to other systems. A “moment-curvature” analytical model, incorporating a robust bond failure criterion, was developed, validated, and used in a parametric study. It showed that varying the concrete compressive strength or thickness of the GFRP section has insignificant effect on the bond failure load. Also, there are critical values for shear span-to-depth ratio, shear strength of cement mortar, concrete strength, and width of the top GFRP flange, beyond which, the desired flexural failure mode would precede bond failure.     

E-Glass/Vinylester Composites in Aqueous Environments: Effects on Short-Beam Shear Strength

The paper present the results of extended (225 weeks) aqueous immersion of E-glass/vinylester composites, fabricated by the resin infusion process. Two different architectures (unidirectional and bidirectional) are tested to assess effects of temperature levels between 5 and 60°C on the short-beam shear strength. Tests show the competing effects of plasticization and postcuring balanced by hydrolytic degradation. The maximum reduction in performance is seen through immersion in deionized water at 60°C wherein pronounced interface and fiber level degradation is noted. Cycling between the two extremes of 5 and 60°C is also seen to cause acceleration of some interface and bulk resin related degradation phenomena. Experimental results obtained from hygrothermal aging at 23°C are compared with predictions based on an Arrhenius type model, and it is shown that good correlation can be obtained in sets where degradation mechanisms remain the same. Shortcomings of this type of model for life predictions are discussed to emphasize viability of use in design.     

Durability of Glass Fiber-Reinforced Polymer Reinforcing Bars in Concrete Environment

Accelerated aging tests are being conducted on more than 20 types of glass fiber-reinforced polymer (GFRP) reinforcing bars, which are produced from different combinations of constituent materials, manufacturing parameters, sizes and shapes, and surface coatings. The specimens are being subjected to various sustained tensile loading (22 to 68% of ultimate strength) in three types of alkaline environments: NaOH, simulated pore-water solution, and embedded in concrete. Time to rupture or residual strength, as applicable, have been determined. Additionally, stress corrosion mechanisms were evaluated by various microstructural analyses. The results showed clearly that alkaline ions and moisture could penetrate or diffuse through the resin (or through cracks and voids) to the interphases and the fibers. For GFRP bars embedded in moist concrete under various sustained stress levels, three types of stress corrosion mechanisms have been identified: stress dominated, crack propagation dominated, and diffusion dominated.     

Durability Prediction for GFRP Reinforcing Bars Using Short-Term Data of Accelerated Aging Tests

This paper presents a procedure based on the Arrhenius relation to predict the long-term behavior of glass fiber-reinforced polymer (GFRP) bars in concrete structures, based on short-term data from accelerated aging tests. GFRP reinforcing bars were exposed to simulated concrete pore solutions at 20, 40, and 60°C. The tensile strengths of the bars determined before and after exposure were considered a measure of the durability performance of the specimens. Based on the short-term data, a detailed procedure is developed and verified to predict the long-term durability performance of GFRP bars. A modified Arrhenius analysis is included in the procedure to evaluate the validity of accelerated aging tests before the prediction is made. The accelerated test and prediction procedure used in this study can be a reliable method to evaluate the durability performance of FRP composites exposed to solutions or in contact with concrete.     

Effect of Aging Environment on Degradation of Glass-Reinforced Epoxy

The effects of immersing coupons of glass-reinforced epoxy in four different liquid media at two separate temperatures were investigated in this study which is aimed at examining the durability of fiber-reinforced plastics currently being used in the construction industry. A commercially available epoxy resin was reinforced with 47% by weight of an epoxy-compatible, E-glass woven fabric. Composite samples were soaked for up to 5 months in distilled water, a saturated salt solution (30g/100 cc NaCl), a 5-molar NaOH solution, and a 1-molar hydrochloric acid solution. Aging was conducted at room temperature and at 60°C. Samples were harvested periodically and their tensile and fracture properties determined. The fracture surfaces were also examined using scanning electron microscopy. Results show that commercial epoxy resins used in glass fiber-reinforced polymers are fairly durable. It was found that all the solutions marginally degraded the mechanical properties of the neat resin, especially at the higher temperature; this was mainly the result of polymer hydrolysis. The strength of the composites, however, was reduced by more than 70% by the acid at room temperature and by the alkali at the elevated temperature. Water immersion was less damaging than either acid or alkali soaking, and immersion in brine had the least effect on mechanical properties. As evidenced by SEM micrographs, the worst cases of damage involved attack on the glass fibers in acid at 60°C compared to room temperature. Therefore, reinforcing glass fibers have to be protected from attack by liquid media to improve the durability of composites.     

Time-Dependent Deformation of Pultruded Fiber Reinforced Polymer Composite Columns

This paper describes an experimental investigation into the time-dependent deformation of pultruded glass fiber reinforced polymer (GFRP) composite columns under an axial-compressive loading at the environmental controlling room with a constant temperature and relative humidity. Tests were conducted on two types of cross-sectional columns: closed-cross section such as square tube (box) and opened-cross section such as wide flange. Both types of columns were 1,200 mm in length, and had cross-sectional dimensions of 102 mm×102 mm and with a 6.4 mm thickness. A total of eight GFRP composite columns were tested at four different stress levels; 20, 30, 40, and 50% of the average ultimate compressive strength from the short-term column tests. The experiments were conducted for approximately 2,500 h with an individual hydraulic loading jack system. The test results indicate that Findley’s power law model can be successfully used to predict time-dependent deformation of GFRP composite columns, and the time-dependent compressive elastic modulus would be decreased as much as 30% of initial value over a 50-year period.     

Bond to Concrete of FRP Rebars after Cyclic Loading

The bond mechanism of fiber-reinforced polymer (FRP) rebars to concrete was studied to evaluate the effect of cyclic loading. Five different types of 12.0- and 12.7-mm rebars were tested. The FRP rods were embedded in concrete blocks and were subjected to up to 450,000 cycles at service stress level. The loading was accompanied by immersion in water at 60 and 20°C to accelerate deterioration effects. Pullout behavior of the rods was determined at the end of the loading period. The results indicated a reduction in the bond strength after loading. Three mechanisms of failure were identified: (1) Abrasion of the surface of the rod, which, in the case of uniform resin throughout the rod, may lead to a reduction of 20–30% in the bond strength; (2) delamination of the outer layer of the resin at the surface of the rod, which may lead to a reduction of up to 60% in the bond strength; and (3) abrasion of cement particles entrapped between the rod and the concrete, which serves as the main source of “bond” for smooth rods leading to approximately 70% of reduction in the bond strength. There was no significant change in the effect of curing temperature on the loss of bond.     

Multifunctional Hybrid GFRP/Steel Joint for Concrete Slab Structures

A multifunctional hybrid glass fiber-reinforced polymer (GFRP)/steel joint has been developed for the transfer of compression and shear forces in thermal insulation sections of concrete slab structures used in building construction. The new pultruded cellular GFRP element improves considerably the energy savings of buildings due to its low thermal conductivity. The quasi-static behavior of the GFRP element in insulating and load-transferring joints at the fixed support of cantilever beams was investigated. Two loading modes were investigated: a moment dominant mode and a shear dominant mode. Results show that the GFRP element is not critical at the ultimate limit state. Ductile failure occurs either in the concrete during yielding of the steel bars, or only in the steel bars that penetrate the hybrid GFRP/steel joint. In moment mode, the GFRP element only transfers the compressive forces from the bending moments. In shear mode, in addition to the moment transfer, about 43–63% of the shear forces are transferred in the element webs at ultimate limit state due to tilting of the element. The application proves that multifunctionality can lead to competitive solutions for GFRP composites used in load-carrying components and can compensate for the relatively high material cost.     

Characterization of a Low-Profile Fiber-Reinforced Polymer Deck System for Moveable Bridges

Moveable bridges in Florida typically use open steel grid decks due to weight limitations. However, these decks present rideability, environmental, and maintenance problems, as they are typically less skid resistant than a solid riding surface, create loud noises, and allow debris to fall through the grids. Replacing open steel grid decks with a lightweight fiber-reinforced polymer (FRP) deck can improve rideability and reduce maintenance costs, simultaneously satisfying the strict weight requirement for such bridges. In this investigation, a new low-profile, pultruded FRP deck system successfully passed the preliminary strength and fatigue tests per AASHTO requirements. Two two-span deck specimens were tested, one with the strong direction of the deck placed perpendicular to the supporting girders, whereas the other had a deck placed with 30° skew. This paper also describes a simplified finite-element approach that simulates the load–deformation behavior of the deck system. The results from the finite-element model showed a good correlation with the deflection and strain values measured from the tests.     

高品质自卸车厢体用NM450耐磨钢板的开发

采用Nb、Ti、Cr、B微合金化成分,设计和开发了高品质自卸车厢体用0.20%～0.25%C耐磨钢NM450。该钢14 mm板900℃淬火200℃回火的组织为回火板条马氏体,并有少量弥散分布的第二相粒子,具有良好的综合性能。NM450钢抗拉强度1459 MPa,延伸率19%,冲击功104 J,表面硬度值450HBW。在弯曲角度为180°,弯头直径为168 mm条件下,弯曲试样合格。采用CHW-70C焊丝,焊接性能良好,焊接接头抗拉强度839MPa,焊缝冲击功113 J,焊缝硬度值282HV,在弯曲角度为90°,弯头直径为168 mm条件下,弯曲试样合格。     

Measurement of Epoxy Resin Tension, Compression, and Shear Stress–Strain Curves over a Wide Range of Strain Rates Using Small Test Specimens

The next generation aircraft engines are designed to be lighter and stronger than engines currently in use by using carbon fiber composites. In order to certify these engines, ballistic impact tests and computational analyses must be completed, which will simulate a “blade out” event in a catastrophic engine failure In order to computationally simulate the engine failure, properties of the carbon fiber and resin matrix must be known. When conducting computer simulations using a micromechanics approach, experimental tensile, compressive, and shear data are needed for constitutive modeling of the resin matrix material. The material properties of an Epon E862 epoxy resin will be investigated because it is a commercial 176°C (350°F) cure resin currently being used in these aircraft engines. These properties will be measured using optical measurement techniques. The epoxy specimens will be tested in tension, compression and torsional loadings under various strain rates ranging from 10?5?to?10?1?s?1 and temperatures ranging from room temperature to 80°C. To test the specimens at high temperatures, a specialized clear temperature chamber was used. The results show that the test procedure developed can accurately and quickly categorize the material response characteristics of an epoxy resin. In addition, the results display clear strain rate and temperature dependencies in the material response.     

60 mm厚低屈强比高强钢板Q500qE组织与性能研究

通过JMatpro软件、扫描电镜、力学性能测试,对Q500qE 60 mm厚度500 MPa级低屈强比高强钢板进行了连续冷却转变(CCT)曲线、钢板显微组织与力学性能、焊接接头力学性能分析。结果表明,通过控轧控冷工艺：终轧温度800～840℃,入水温度660～680℃和终冷温度400～450℃,该钢组织为铁素体+贝氏体+马氏体/奥氏体岛,两相交界处和贝氏体内部存在大量大角度晶界。钢板1/4和1/2厚度位置屈服强度≥500 MPa,抗拉强度≥640 MPa,屈强比≤0.80,-40℃低温冲击功≥200 J,焊接热影响区-40℃低温冲击功≥100 J。     

Bond strength of multi-step and simplified-step systems

PURPOSE: To measure and compare the in vitro shear bond strength (SBS) of the following three pairs of multi- and simplified-step dentin bonding systems: OptiBond vs. OptiBond FL, All-Bond 2 vs. One-Step, and Tenure vs. Tenure Quik. MATERIALS AND METHODS: 60 extracted human mandibular molars were sectioned perpendicular to the long axis 1 mm above the CEJ to expose the dentin bonding surface. After being wet-ground to 600 grit with SiC abrasive papers, rinsed and dried, the teeth were individually mounted in phenolic rings with epoxy resin, and randomly assigned into six equal groups of 10 each. The dentin surfaces were treated with the above mentioned dentin bonding systems, and a gelatin cylinder filled with resin composite (Pertac-Hybrid) was directly bonded to each pretreated surface. After 7-day storage in 37 degrees C water followed by thermocycling, the specimens were shear tested to failure on an Instron machine. Data were analyzed by independent t-tests, one-way ANOVA, and Duncan's Multiple Comparison tests at alpha = 0.05. RESULTS: Except for the pair Tenure/Tenure Quik, the differences between the pairs All-Bond 2/One-Step and OptiBond/OptiBond FL were statistically significant with All-Bond 2 and OptiBond FL yielding higher shear bond strength (P < 0.05). Findings of this study indicated that OptiBond FL was the only simplified-step system showing improved bond strength.