The fatigue life of steel bridges can be extended by externally bonding carbon fiber–reinforced polymer (CFRP) patches to the damaged elements to arrest the crack propagation. In this paper, the influence of the patch pretension level, stiffness, and fiber orientation on the stress intensity factor levels are investigated. A three-dimensional finite-element model of the double-sided CFRP patch-strengthened specimen is used to study the fracture behavior of an inclined edge crack under different combinations of loading Modes I and II. The introduction of a compressive stress by pretensioning of the CFRP patch prior to bonding produced a significant reduction of up to 70% in stress intensity factors (SIFs) for different crack lengths, which led to increasing the remaining fatigue life of the steel member. The increase in the CFRP patch-to-steel axial stiffness ratio reduced the SIFs by up to 30%. The optimum benefit of using the CFRP patch to reduce mode I SIF was accomplished when the patch axial s...

Slender recycled plastic pins (RPPs) can be used to stabilize earthen slopes by driving the RPPs into the face of the slope to intercept the sliding surface and “pin” the slope. The RPPs will be subjected to lateral (bending) forces, and their ability to resist deformation will strongly influence the success of the RPPs for stabilizing slopes. Arrhenius modeling was used to predict the time for the RPPs to reach creep failure. Engineering properties and strain rate effect of four different types of RPPs were evaluated and are reported in this paper. Arrhenius modeling showed creep failure ranged from 50 to 3,900 years at field temperature and stress levels. Compressive strengths ranged from 11 to 20 MPa and compressive moduli from 580 to 1,280 MPa at 1% strain, while flexural strengths ranged from 9 to 25 MPa and flexural moduli from 620 to 1675 MPa at 1% strain.

Strengthening of bridge superstructures composite beams with external post-tensioned tendons is a good technique for strengthening the existing structures. In this study, a numerical model is illustrated to study the nonlinear simulation of composite beams stiffened with externally post-tensioned tendons. The accuracy of the developed numerical model is validated using comparisons between the numerical and existing test data. The influence of various strengthening parameters is investigated, which include draped versus straight tendons, tendon length, the effect of post-tensioning on reinstating the flexural behavior of an overloaded beam, tendon eccentricity, and the degree of shear connection. A good agreement between the proposed model and the test data is obtained. The results demonstrate that at the same tendon eccentricity, the trapezoidal profile shows better behavior for the strengthened beams. However, more ductility is obtained when using the straight tendon profile. Applying post-tensioning through the beam of full length helps to reduce the creation of fatigue cracks, which always start at stress raisers, and subsequently increases the fatigue life of the composite beam. Also, the external post-tensioning effectively maintains the flexural behavior of the overloaded strengthened beam after unloading in comparison to the un-strengthened beam. It is observed that 80% degree of shear connection or higher is recommended to obtain the desired performance of the external post-tensioning force for strengthening composite beams.

Bonding a composite patch to a cracked steel section is an efficient technique to reinforce cracked members or to delay fatigue crack growth in the structural elements. In this paper, a numerical study was performed to highlight the effect of bonded prestressed composite patches on the fracture parameters, such as crack tip opening displacement and the plastic zone. A three-dimensional finite element model of the double sided strengthened specimen is used to study the fracture behavior of an inclined edge crack under different combinations of modes I and II loading conditions. The influence of the pretension level, patch stiffness ratio, and fiber orientation on the crack tip opening displacement and plastic zone are also investigated. The introduction of a compressive stress by pretensioning of the composite patch prior to bonding produces a significant reduction in the crack tip opening displacement and plastic zone. This pretensioning reduces the crack tip driving force and subsequently reduces...

The fiber-reinforced polymeric (FRP) composite can be joined by adhesive bonding or mechanically fastening the composite element. Carbon fiber-reinforced polymers (CFRP) and glass fiber-reinforced polymers (GFRP) are the most common types of polymers. Mechanically fastened or bolted joints do not need treatments, and the surface temperature and other environmental effects such as humidity do not affect its strength. In this research, the previous research that describes the behavior of the composite bolted joint (CBJ) is presented and summarized including the modes of failure of the CBJ, and the experimental works that explain the bearing failure (BF) of the CBJ. In addition, the effects of bolt clamping force (BCF) and techniques that are used to simulate the progressive failure and damage in composite materials and finite element simulation works are surveyed.

Due to the complexity of composite material, numerical methods are generally utilized in their analysis and design. Commercial finite element (FE) codes, such as ANSYS and ABAQUS, allow the implementation of user subroutines in the program, which provides the advantage of using high meshing and solving technologies besides the improvement of materials and/or elements models. Nonlinearities arise for many engineering problems, for example, the progressive damage of a composite element that contains sources of stress concentration or damage localization such as holes, bolts, and/or flaws causes nonlinear material behavior. In order to simulate this nonlinear behavior, especially in 3D, an accurate material constitutive model is required. Therefore, the objective of this paper was to simulate the 3D progressive damage model of composite materials by using simple numerical models. In this paper, ANSYS user subroutine (USERMAT) was used to simulate the progressive damage behavior of a composite plate containing holes using simple models. Three different material models were used: ply discount model (PDM), simple progressive damage model (SPDM) by adding an empirical progressive damage criteria to the PDM, and continuum damage mechanics model (CDMM). Good agreements were observed between SPDM, CDMM, and published experimental results. Furthermore, CDMM showed the least dependence on mesh size. Three different damage evolution laws, linear, quadratic, and degradation laws, were adjusted and tested. It was found that there was no significant difference in the predicted failure load between these selected laws.