Numerical evaluation of the retrofit effectiveness for GFRP retrofitted concrete slab subjected to blast pressure

For retrofitting structures against blast loads, sufficient ductility and strength should be provided by using high-performance materials such as fiber reinforced polymer (FRP) composites. The effectiveness of retrofit materials needs to be precisely evaluated for the retrofitting design based on the dynamic material responses under blast loads. In this study, refined FEM analysis with high-strain rate dependent material model and debonding failure model is conducted for evaluating the FRP retrofitting effectiveness. The structural behavior of reinforced concrete (RC) slab retrofitted with glass fiber reinforced polymer (GFRP) under blast pressure is simulated and the analysis results are verified with the previous experimental results.     

Interaction between CFRP-repair and initial damage of wide-flange steel beams subjected to three-point bending

This paper presents the interaction between carbon fiber reinforced polymer (CFRP) composites and the level of damage in steel beams. An experimental program is conducted with three different sizes of notches at midspan of the beams to simulate initial damage prior to repair. A three-dimensional finite element analysis (FEA) is conducted to predict experimental behavior. Unlike existing predictive models that assume perfect bond between CFRP and steel substrate, the proposed modeling approach explicitly accounts for the bond–slip behavior of CFRP–steel interface. CFRP-repair improves the load-carrying capacity of damaged beams that have failed by crack propagation across the steel section with wide opening of the notch. For repaired beams; stress concentrations at a damage location result in local debonding of the CFRP sheet, followed by complete debonding failure of the sheet. These failure modes are found to be independent of the level of initial damage (notch depth). CFRP-repair delays crack-formation of the repaired beams; however, such an effect is not significant once a crack propagates towards the upper flange. The level of initial damage influences debonding propagation rates of the CFRP. Two distinct bond–slip responses of the CFRP–steel interface are experimentally observed.     

Behaviour of hybrid FRP–UHPC beams in flexure under fatigue loading

The fatigue behaviour of innovative hybrid FRP–UHPC beams under flexural loading is investigated in this paper. The beams were made up of a pultruded GFRP hollow box section beam with a cast-in-place UHPC layer on top and either a CFRP or SFRP sheet bonded along the bottom. Four hybrid beams were tested under variable amplitude loading, to determine the effect of cyclic loading on flexural strength and stiffness. Analysis also included the development of a modified S–N curve and evaluation of fatigue damage using the Palmgren–Miner rule. It was found that insignificant loss in strength and stiffness occurred for all beams, where the fatigue damage estimated using the Palmgren–Miner rule overestimated the fatigue life. It was postulated, by comparison, that the hybrid beams reinforced with CFRP sheets may perform better under fatigue loading than the beams reinforced with SFRP sheets.     

多丝碳纤维拉索研制及静载试验研究

为了解决拉索锈蚀和疲劳问题,提高其耐久性,采用轻质、高强、耐腐蚀和耐疲劳的碳纤维(CFRP)筋制作拉索.以环氧树脂砂浆为粘结剂,研制CFRP筋粘结式锚具及成套拉索,并进行了静载试验.分析了影响CFRP拉索锚固性能的各种因素,并进行了相关试验.研究结果表明,筋表面粗糙程度、锚具内锥度、粘结胶的性能和灌浆压力等直接影响锚具的锚固性能.所研制的多丝CFRP拉索的性能稳定,锚固效率系数达95%以上,可直接应用于实际工程.     

Modeling the residual strength of carbon fiber reinforced composites subjected to cyclic loading

Fatigue and residual strength data available in literature were modeled with a modified two-parameter wear-out model based on strength degradation. The model explicitly accounts for the maximum applied stress and the stress ratio and requires a limited number of experimental data to predict with accuracy the fatigue life of a series of polymer-based composites. In this paper a substantial modification of the model is proposed in order to enhance its capability in predicting the residual strength kinetics with emphasis to the “sudden drop” of strength before catastrophic failure. It is argued that the strength degradation kinetics under given loading conditions can be obtained from the statistical distribution of cycles to failure under the same loading conditions. From the new approach no new parameters are introduced, limiting to a minimum the experimental data needed to predict the residual strength. The strength degradation law reliability is verified on three different materials data sets appeared in literature. The results indicate that both the fatigue life and the residual strength are related to the statistical distribution of the static strength.     

Experimental and numerical investigation of composite bolted π-joint subjected to bending load

This present work investigated the failure mechanism of a novel composite bolted π-joint subjected to bending load by experimental and finite element simulation. A test sample manufactured by resin transfer moulding process (RTM) was tested. A 3D progressive damage model developed in ABAQUS/Standard was used to simulate the failure of the π-joint. Based on good correlation of failure load and damage distribution between experimental results and FE prediction, further investigation was extended to the effect of two primary assembly clearances on mechanical behavior of the π-joint. The study results reveal that delamination of the fillet region in L-preform is the π-joint's failure mode. Moreover, the assembly clearances have little effect on the failure load of the joint.     

Fracture mechanisms and failure analysis of carbon fibre/toughened epoxy composites subjected to compressive loading

This study investigates the failure mechanisms of unidirectional (UD) HTS40/977-2 toughened resin composites subjected to longitudinal compressive loading. A possible sequence of failure initiation and propagation was proposed based on SEM and optical microscopy observations of failed specimens. The micrographs revealed that the misaligned fibres failed in two points upon reaching maximum micro-bending deformation and two planes of fracture were created to form a kink band. Therefore, fibre microbuckling and fibre kinking models were implemented to predict the compressive strength of UD HTS40/977-2 composite laminate. The analysis identified several parameters that were responsible for the microbuckling and kinking failure mechanisms. The effects of these parameters on the compressive strength of the UD HTS40/977-2 composite systems were discussed. The predicted compressive strength using a newly developed combined modes model showed a very good agreement to the measured value.