Advanced Materials Research Vols. 163-167

Abstract: Overall 12 specimens were experimentally investigated in this paper to study the hysteretic behaviors of the concrete-filled square CFRP-steel tubular (S-CFRP-CFST) beam-columns. The test results indicated that CFRP can provide transverse confinement effect and longitudinal strengthening effect for the concrete filled square steel tubular (S-CFST) beam-columns effectively and the local buckling of the steel tube is deferred. The hysteretic load-deflection curves and the hysteretic moment-curvature curves at the mid-span of all the specimens are generally plump, and it shows these specimens have good hysteretic performance. In the later loading period, the load bearing capacity drops.

Abstract: Based on the established limit state equation and connected with a large amount of statistic analysis of testing data, central point law in first order second moment method (FOSM) is adopted to the reliability analysis of bonded rebars with inorganic material. The adhesive anchorage design suggestion of bonded rebars with inorganic material is proposed. By means of comparing the calculation results to experimental results, it can be concluded that the calculation methods of anchorage length can be used to the calculation of designing concrete bonded rebars.

Abstract: Strengthening by CFRP sticking to steel plates can exploit advantages of the two materials. The viscoelastic nature of FRP composites make it imperative that the creep behavior of the composite material should be taken into account for the analysis and design of any strengthening structure. In this paper, a creep experiment of a CFRP-steel composite under different stress levels has been introduced. The failure types, average yield load, ultimate loads, and initial longitudinal elastic modulus of the composite specimens were investigated through the short-term tests. Material coupons were subject to axial tensile load at various stress levels for time duration up to 500 hours in the long-term tests, and the results indicate that the strain increase with time and the ultimate creep strain increase with the increase of the initial strain. For the evaluation of the viscoelastic behavior of the composite material, the model developed by Findley was adopted. The agreement of the model results with the experimental data indicates this medel could be used to estimate the creep effectively at engineering analyses.

Abstract: The effective stress range (ESR) and the number of stress cycles (NSC) are two key parameters in fatigue damage evaluation. The inaccuracies in predicting remaining fatigue life can be attributed to either one of these two parameters. A sensitivity analysis is described to address the effects of four cycle-counting methods on ESR and NSC for various fatigue details, which including rain-flow counting (RF), mean-crossing-peak counting (MCP), level-crossing counting (LC) and simple-range counting (SR). Using field monitoring data under normal traffic of Wei River Bridge, the comparative results of four methods showed that RF was more conservative than MCP and SR. The relationships between RF and other three counting methods were determined in the form of a correlation coefficient and a linear regression line. Therefore, values obtained for ESR and NSC by MCP, LC and SR can be converted to values for RF, which is used for comparison and transformation of fatigue life evaluation results using different cycle-counting methods.

Abstract: Self-locked anchor is a new type of underreamed anchor, and which is more and more frequently used in both new construction and structural retrofitting or strengthening projects. Nevertheless, current design codes do not contain suitable design recommendations for these anchors. This study investigates the anchorage mechanisms of self-locked anchor under combined tension and shear loadings. The experimental parameters mainly include anchor diameters (Φ16 and Φ20) and loading angles (0°, 30°, 45°, and 60°). The present results indicate the characters of axial and transverse deformations, the ultimate bearing capacity, the fracture pattern of anchor, and the breakout model of concrete.

Abstract: Numerical simulations were conducted to investigate the bearing behaviour of steel foot pipe. Main mechanical affections occur at the lateral zone, and the maximal stress occurs at the lateral end of the pipe. With the increase of cross direction load, the maximal stress increases and exceeds the strength of material, and the pipe is pulled out. The influencing factors of bearing capacity of the steel foot pipe were studied. Some important results different from engineering experiences are as following: 1) to steel foot pipe that can not penetrate the soft base, its reasonable dip angle is very small for its low longitudinal bearing capacity; 2) steel pipe with diameter of 42mm is unsuitable for foot steel pipe because its low cross bearing capacity; 3) to a given geological condition and pipe parameter, the reasonable length of steel pipe is certain, extra longer pipes can’t obtain larger capacity; 4) surrounding rock near the support structure should be especially reinforced by drilling grouting holes along the whole steel pipe.

Abstract: The objective of this study is to investigate the flexural behaviors and ductility of reinforced concrete beam with near-surface mounted (NSM) GFRP bars. A total of 5, simply supported rectangular cross-section beams strengthened with NSM GFRP bars and two control beams are tested in this paper. The mode of failure, load-deflection relationship, strain distributions along the height of the beam on mid-span cross-section, and ductility of the beams are analyzed. The studies indicate that the yield and ultimate load have a significant increase compared with the control specimen. Especially, the ultimate load has a more measurable improvement than the yield load. The strain distribution along the height of specimen shows a clear nonlinear characteristic as a result of the crack propagating and steel yield. Also, the studies show that GFRP bars has played an important role in the flexural capacity of the strengthened beam during the stage from the yield to the failure of the beam. Besides, the strengthened beam is considered to be ductile using the displacement ductility index.

Abstract: The authors propose a structural strengthening method combining the concepts of preplaced aggregate concrete (PAC) and steel wire mesh reinforce mortar strengthening. The steel bar/wire mesh reinforce preplaced aggreate concrete (SWPAC) composite structural strengthening is targeted at cases where large increase of structural resistance are required, sectional enlargement is restraint and hash fire protection and durability requirements. The preliminary experimental study shows that the proposed structural strengthening method is practically feasible. The strengthened structure is ductile enough to work as structural members. For thin layer strengthening, lateral confinement of the strengthening concrete would be a key topic for later investigations.

Abstract: External bonding of fiber reinforced polymer (FRP) plates or sheets composites has become a popular technique for strengthening concrete structures all over the world. The bond strength between FRP and concrete is a key factor controlling debonding failure of various forms in FRP-strengthened concrete structures. Based on the test data, the bond strength model of FRP-concrete was proposed using multiple linear regression and dimensional analysis, in which the effect of multiple factors on dependent was considered. Finally, the proposed model was verified through the test data, and then compared with 12 bond strength models have been found in the existing literature. The result shows that the proposed model has a better accuracy. It can be used to predict the bond strength of FRP-concrete.

Abstract: A new type of complex reinforcement method for steel structure seldom used in pratical engineering mainly due to lack of theoretic and experimental support. The experiment with this method for H-section steel beams and the results of that are introduced in this paper. The mechanical properties of the steel and CFRP material are given. The carrying capacity and the load-displacemengt curves of each specimen beams are obtained as well as the stress and strain of every feature points on the middle cross section of the beams. The results may provided reference for practical engineering.