- مبلغ: ۸۶,۰۰۰ تومان
- مبلغ: ۹۱,۰۰۰ تومان
This paper investigates the performance of polyurethane foam-infill bridge deck panels (PU sandwich panels) after being exposed to various environmental conditions. These panels were constructed with woven E-glass fiber/polyurethane facesheets that were separated by a trapezoidal-shaped, low-density polyurethane foam. Corrugated web layers were introduced into the core to enhance the panel's structural characteristics. The PU panels were manufactured through a one-step vacuum assisted resin transfer molding (VARTM) process. An experimental program was designed to simulate their in situ environments. The environmental conditions used included different conditioning regimens to examine the behavior of both GFRP laminates and PU sandwich panels. The GFRP laminates, which were made from the same materials as the PU sandwich panels, were exposed to ultraviolet radiation, a deicing solution at both room temperature and elevated temperature, and thermal cycling. The PU sandwich panels were exposed to thermal cycling (a series of freeze–thaw, mid–high temperatures, and mid– high relative humidity cycles). The thermal cycling exposure was conducted in a computer-controlled environmental chamber to duplicate seasonal effects in Midwestern states. Following the exposure regimens, tensile strength tests and four-point loading tests were performed on the GFRP laminates and the PU sandwich panels, respectively. The evaluation was based on visual inspection, strength, stiffness, and failure modes, as compared to those that were not conditioned (the control). The results of this study revealed that degradation did exist due to the effects of thermal cycling and the deicing solution. The ultraviolet radiation, however, did not cause any degradation. These results were within the recommended environmental durability design factors of the FHWA guidelines.
GFRP laminates and PU sandwich panels were successfully manufactured using a VARTM process in which a new polyurethane resin was used as a matrix. These specimens were conditioned under different conditioning regimens. Tensile strength tests and four-point loading tests were then performed on the GFRP laminates and the PU sandwich panels, respectively. The degradation was determined in terms of ultimate strength and stiffness. The following conclusions were drawn from this study: i. The PU sandwich panels displayed linear-elastic behavior throughout the majority of their response during the static flexural testing with only a slight decrease in stiffness near failure.ii. Neither the tensile strength nor the tensile modulus was adversely affected when the facesheet and web core coupons were exposed to ultraviolet radiation. Instead, each increased as a result of the post-curing of the resin system. iii. The deicing solution, under both room temperature and elevated temperature, reduced the ultimate tensile strength and the tensile modulus of elasticity in both the facesheet and the web core coupons. iv. Thermal cycling conditioning reduced the ultimate tensile strength and increased the tensile modulus of elasticity for the facesheet coupon specimens by approximately 6% and 0.5%, respectively. v. The flexural behavior of the PU sandwich panels exposed to thermal cycling in an environmental chamber resulted in a 24% degradation in the ultimate strength but a slight increase in stiffness. Failure of the conditioned panels under the subsequent static loading occurred in the same manner as the control panels. vi. Manufacturing these specimens utilizing polyurethane resin within the VARTM process resulted in a strength reduction that is consistent with FHWA guidelines. The FHWA recommends an environmental durability factor of 0.65 to account for properties degrading over time and represents a 35% decrease in strength.