Freeze-Thaw Durability and Long-Term Performance Evaluation of Shotcrete in Cold Regions

This study’s aim was to evaluate the freeze-thaw durability of shotcrete in cold regions and predict its long-term performance. One benchmark mix design from the WSDOT was chosen to prepare samples for performance evaluation. Shotcrete specimens were conditioned in accordance with ASTM C666. The long-term freeze-thaw performance after certain cycles was evaluated using the dynamic modulus of elasticity test (ASTM C215), fracture energy test (RILEM 50-FMC), and X-ray CT microstructure imaging analysis. Probabilistic damage analysis was conducted to establish the relation between the durability life and the damage parameter for different probabilities of reliability using the three-parameter Weibull distribution model. The fracture energy test was found to be a more sensitive test method than the dynamic modulus of elasticity for screening material deterioration over time and for capturing accumulative material damage caused by rapid freeze-thaw action, because of smaller durability factors (degradation ratios) obtained from the fracture energy test. X-ray CT imaging analysis is capable of detecting microcracks that form and pore evolution in the aggregate and interface transition zone of conditioned samples. Moreover, the continuum damage mechanic-based model shows potential in predicting long-term material degradation and the service life of shotcrete

Durability and Smart Condition Assessment of Ultra-High Performance Concrete in Cold Climates

The goals of this study were to develop ecological ultra-high performance concrete (UHPC) with local materials and supplementary cementitious materials and to evaluate the long-term performance of UHPC in cold climates using effective mechanical test methods, such as “smart aggregate” technology and microstructure imaging analysis. The optimal UHPC mixture approximately exhibited compressive strength of 15 ksi, elastic modulus of 5,000 ksi, direct tensile strength of 1.27 ksi, and shrinkage of 630 at 28 days, which are characteristics comparable to those of commercial products and other studies. The tensile strength and modulus of elasticity in tension, dynamic modulus, and wave modulus show slight increases from the original values after 300 freeze-thaw (F-T) cycles, indicating that UHPC has excellent frost resistance in cold climates. Although porosity deterioration was observed in the F-T cyclic conditioning process, no internal damage (cracks or fractures) was found during imaging analysis up to 300 cycles. Since structures for which UHPC would be used are expected to have a longer service life, more F-T cycles are recommended to condition UHPC and investigate its mechanical performance over time. Moreover, continuum damage mechanic-based models have the potential to evaluate damage accumulation in UHPC and its failure mechanism under frost attack and to predict long-term material deterioration and service life

Smart FRP Composite Sandwich Bridge Decks in Cold Regions

INE/AUTC 12.0

Test Methods and Bond Performance Characterization of Shotcrete-Concrete Interface

ORSO 135461Shotcrete is becoming popular for vertical and overhead applications where conventional formwork and repairs are difficult and costly. However, the substrate and the shotcrete overlay interface can be vulnerable, and the bond properties in this region are not well understood. Furthermore, the interface bond could be adversely affected by long-term freeze-thaw weathering in northern states leading to debonding from the existing substrate and corrosion of rebars. Hence, characterization of the shotcrete-substrate interface bonds is critical for the performance evaluation of shotcrete construction. To this goal, this study evaluated the shotcrete-concrete interface bond using four representative substrate surface preparation methods: chipped, pressure-washed, sandblasted, and as-cast, under three different loading conditions: tensile, shear, and Mode-II fracture. The study also investigated the long-term freeze-thaw durability of these bonds and introduced a probabilistic damage model to predict their service lives

On the Compliance and Energy Release Rate of Generically-unified Beam-type Fracture Specimens

A unified approach is proposed to evaluate the compliance and energy release rate (ERR) of generic beam-type interface fracture specimens. Based on a sub-layer Timoshenko beam theory, the classic composite (rigid joint), shear deformable (semi-rigid joint), and interface deformable (flexible joint) bi-layer beam models are revisited, from which the compliance and ERR of the generic beam-type fracture specimens are determined. According to specific combinations of loading conditions and material properties of each sub-layer, the generic fracture specimens are reduced to the conventional fracture specimens for actual applications. The effects of the crack tip deformation on the ERR of the interface crack are compared among the three different joint models, from which the evolving accuracy of the joint models to the ERR predictions of beam-type fracture specimens is manifested. The derived explicit formulas and improved solution for the compliance and ERR of the common beam-type fracture specimens can be effectively used to reduce data in interface fracture experiments and increase accuracy of fracture toughness evaluation of dissimilar material interfaces

Analysis and design optimization of fiber-reinforced plastic (FRP) structural beams.

Considering current and future applications of composite materials in civil engineering structures, a need exists for developing a design analysis and optimization approach for FRP shapes to improve their performance efficiency and competitiveness in relation to conventional materials. An analytical approach for design of pultruded FRP shapes under bending is proposed, and based on this approach, a computer program is developed to carry out the analysis of FRP sections. This analytical approach combines micro/macromechanics analyses with the Mechanics of thin-walled Laminated composite Beam model (MLB) to evaluate the response of existing pultruded FRP beams. Based on buckling analyses of individual composite plates under axial and shear loading, the critical local buckling strength of FRP sections is predicted and appropriate design equations are proposed; the effect of the stiffness of the flange-web connection on the buckling response of component plates is considered, and an approximate coefficient of restraint for the plate analysis is proposed for use in design. An energy method combined with nonlinear elastic theory is developed for analyzing the flexural-torsional buckling behavior of FRP I-beams. Allowing for distortion of the web and using a 5th order polynomial shape function for the buckled web shape, an analysis approach for lateral-distortional buckling of I-beams is also proposed. The proposed analytical models correlate closely with experimental data and ANSYS finite element results. A global approximation method to optimize material architecture and structural shape of FRP beams is developed. For existing FRP shapes, a multiobjective design optimization formulation is proposed to optimize fiber architecture, which can greatly enhance the load carrying capacity of a section. The global approximation method is extended to concurrently optimize material architecture and cross-sectional area for new FRP beams. The proposed method can concurrently optimize the dimensions and material architecture of a given shape, and as an illustration, a new winged-box (WB) shape is optimized. It is significant that through this study, new optimal material architecture and structural shapes for FRP beams are obtained for structural applications, and the proposed method can be used to develop various innovative shapes for specific applications

Impact Mechanics and High-Energy Absorbing Materials: Review

In this paper a review of impact mechanics and high-energy absorbing materials is presented. We review different theoretical models (rigid-body dynamics, elastic, shock, and plastic wave propagation, and nonclassical or nonlocal models. and computational methods (finite-element, finite-difference, and mesh-free methods. used in impact mechanics. Some recent developments in numerical simulation of impact (e.g., peridynamics) and new design concepts proposed as high energy absorbing materials (lattice and truss structures, hybrid sandwich composites, metal foams, magnetorheological fluids, porous shape memory alloys. are discussed. Recent studies on experimental evaluation and constitutive modeling of strain rate-dependent polymer matrix composites are also presented. Impact damage on composite materials in aerospace engineering is discussed along with future research needs. A particular example for the design of a sandwich material as an impact mitigator is given in more detail. This brief review is intended to help the readers in identifying starting points for research in modeling and simulation of impact problems and in designing energy absorbing materials and structures

Buckling of delaminated bi-layer beam-columns

► Delamination tip deformation in improved buckling analysis. ► Application of flexible joint model to buckling. ► Capture of buckling mode transition. An improved analytical model is presented to analyze the delamination buckling of a bi-layer beam-column with a through-the-width delamination. Both the transverse shear deformation and local delamination tip deformations are taken into consideration, and two delaminated sub-layers as well as two substrates in the intact (un-delaminated) regions are modeled as individual Timoshenko beams. A deformable interface is introduced to establish the continuity condition between the two substrates in the intact regions. Consequently, a flexible joint is formed at the delamination tip, and it is different from the conventional rigid joint given in most of studies in the literature, in which the local delamination tip deformations are completely ignored. In contrast to the local delamination buckling in our previous study ( Qiao et al., 2010), the present model accounts for the global deformations of the intact region in the delaminated composite beam-column, thus capable of capturing the buckling mode shape transitions from the global, to global–local coexistent, and to local buckling for asymmetric delamination as the interface delamination increases. Good agreement of the present analytical solutions with the full 2-D elastic finite element analysis demonstrates the local deformation effects around the delamination tip and verifies the accuracy of the present model. Parametric studies are conducted to investigate the effects of loading eccentricity, delaminated sub-layer thickness ratio, and interface compliance on the critical buckling load for the delaminated composite beam-column. Transitions of buckling modes from the global to local delamination buckling are also disclosed as the thickness of one sub-layer reduces from the thick sub-layer to a thin film. The developed delamination buckling solution facilitates the design analysis and optimization of laminated composite structures, and it can be used with confidence in buckling analysis of delaminated composite structures