Key Engineering Materials Vols. 400-402

Abstract: The value of sensitive factors in structural reliability analysis greatly affects reliability calculation results. These factors must be accurately determined and studied to improve the accuracy of calculated results. Based on the analysis of existing sensitivity calculation methods, a new practical sensitive factor analysis method was put forward to analyzing sensitive factors in structural strength reliability calculations. The dimensionless sensitive indexes of structural reliability were defined in the new method to compare the influence degree of random parameters to reliability. And the method was applied to analyze sensitivity under the two conditions of the structural resistance decreasing and not changing with time. Random variables, defined by their probability distribution and corresponding distribution parameters, were used to describe uncertainties in the reliability calculation. Different forced state RC columns were taken as examples to analyze the structural sensitivity, and sensitive factors affecting the columns’ structural reliability were obtained. The results show that the reliability of time-varying structure has descended to some extent compared with that without time-varying structure, and the effect from the random parameters to reliability index. The example and theory demonstrate the feasibility and rationality of the new method. This article has certain reference value to the structural design, construction and detection.

Abstract: Based on the improved equation of concrete heat-generation rate and an improved calculation method of temperature stress, the temperature effect of concrete hydration heat is simulated successfully in ANSYS. Comparison between the numerical simulation results and test results of a scaled model of blast furnace foundation indicates that the calculated temperature field based on the improved equation and method is much closer to that of test than which obtained by the old equation and method. By using the stress superposition principle, the temperature-stress field can be calculated with considering the change of material behavior with temperature and time.

Abstract: This paper studies the seismic performance of FRP-strengthened RC interior non-seismically detailed beam-wide column and beam-wall joints after limited seismic damage. Four eccentric and concentric beam-wide column joints and two beam-wall joints, initially damaged in a previous study, were repaired and tested under constant axial loads (0.1 and 0.35 ) and lateral cyclic loading. The rapid repair technique developed, aimed to restore the original strength and to provide minimum drift capacity. The repair schemes were characterized by the use of : 1) epoxy injection and polymer modified cementitious mortar to seal the cracks and replace spalled concrete and 2) glass (GFRP) and carbon (CFRP) sheets to enhance the joint performance. The FRP sheets were effectively prevented against possible debonding through the use of fiber anchors. Comparison between responses of specimens before and after repair clearly indicated reasonable restoration in strength, drift capacity, stiffness and cumulative energy dissipation capacity. All specimens failed with delamination of FRP sheets at beam-column joint interfaces. The rapid repair technique developed in this study is recommended for mass upgrading or repair of earthquake damaged beam-column joints.

Abstract: In coastal areas, corrosion has been found in bridge piers made of Portland cement concrete. In an trail to protect the piers from further damages, Ba bearing sulphoaluminate cement concrete was tested as the repairing layers. It is showed that the Ba bearing sulphoaluminate cement concrete has a lower porosity and a more compact structure than Portland cement concrete under the same conditions, and consequently, better performances, such as high strength and corrosive resistance both in lab and real corrosive environments. Stimulating experiments indicate that Ba bearing sulphoaluminate cement is more suitable for repairing bridges in coastal area.

Abstract: Based on experimental study and stress-strain curve of the concrete confined by circular CFRP-steel tube subjected to axial load, the fiber element approach was used to analyse load-deformation curves of the concentrically compressed concrete filled circular CFRP-steel tubular stub columns, and it shows that the results predicted check well with those of the tests and are on the safe side. Influences of confinement factor of the steel tube and the that of the CFRP tube on curves were analysed. The typical load-deformation curves were proposed and it could be defined as following four stages, e.g., elasticity stage, nonlinear stage, strengthening stage and softening stage. The method presented here is suitable for load-deformation curves analysis of the concentrically compressed concrete filled steel tubular (CFST) stub columns with circular cross-section also.

Abstract: The improvement of the load carrying capacity of concrete columns under a triaxial compressive stress results from the strain restriction. Under a triaxial stress state, the capacity of the deformation of concrete is greatly decreased with the increase of the side compression. Therefore, confining the deformation in the lateral orientation is an effective way to improve the strength and ductility of concrete columns. This paper carried out an experimental investigation on axially loaded normal strength concrete columns confined by 10 different types of materials, including steel tube, glass fiber confined steel tube (GFRP), PVC tube, carbon fiber confined PVC tube (CFRP), glass fiber confined PVC tube (GFRP), CFRP, GFRP, polyethylene (PE), PE hybrid CFRP and PE hybrid GFRP. The deformation, macroscopical deformation characters, failure mechanism and failure modes are studied in this paper. The ultimate bearing capacity of these 10 types of confined concrete columns and the influences of the confining materials on the ultimate bearing capacity are obtained. The advantages and disadvantages of these 10 types of confining methods are compared.

Abstract: The principle of electrochemistry is adopted in this test. The current is switched on 7 RC beams strengthened with CFRP of different measures (include: not strengthened L-0, strengthened with one layer of CFRP on the bottom L-1, coated only with epoxy resin L-2, strengthened with one layer of CFRP on the bottom and coated with epoxy resin on the lateral L-3, strengthened with two layers of CFRP on the bottom L-4, strengthened with one layer of CFRP on the bottom and alternately on the lateral L-5, strengthened with CFRP entirely L-6) when the beams are working in corrosive environment. So the corrosion speed of the beams becomes fast. Comprehensive comparison of mechanical property and transformation rule among them has been made. The different effects of the enhancement in durability are analyzed and its reason is researched. The test results indicate that the durability of the beams strengthened with CFRP can be enhanced significantly especially in the beam strengthened with CFRP entirely L-6.

Abstract: The resistance factor in the draft version of Chinese Technical code for the application of fiber reinforced polymers in civil engineering for the shear-resistant design of reinforced concrete beams with U-wrap FRP strengthening is assessed from the probabilistic standpoint. The assessment using a resistance-factor-related computational uncertainty factor indicates that the average reliability indexes, for either unstrengthening or strengthening, increases at a slowing rate as load effect ratio increases from 0.10 to 2.5, and that the average reliability indexes for strengthened beams would dramatically decrease up to 19.2%~28.5% with the resistance factor specified in the code for U-wrap strengthening. A so-called reliability strengthening ratio is introduced to evaluate the change in average reliability index before and after strengthening with different resistance factors. A parametric study on this factor shows that if the reliability level in strengthened reinforced concrete beams is kept to be consistency with their corresponding unstrengthened beams, a value of 0.67 could be applied. The proposed relationship between reliability strengthening ratio and the resistance factor could be also used in personalized designs.

Abstract: Precast concrete construction with prestressed precast hollow core slab as floor and roofing is being extensively used in the Gulf region. These one way slabs are sometimes subjected to unforeseen loads with a partition wall in shear zone or as a cantilever. A detailed experimental program involving full-scale load testing of hollow core slabs has been conducted involving testing of virgin and CFRP strengthened slabs in flexure and shear. This paper presents the results of the experimental and numerical evaluation of flexural and shear behavior of the hollow core slabs. The hollow-core slabs were modeled using the nonlinear finite element software DIANA and the load deflection behavior and ultimate capacity were evaluated numerically. For the FE model, concrete was modeled using Drucker-Prager with tension cut-off failure criterion, and Von-Mises plasticity with multilinear isotropic hardening was used to model the prestressing strands. Comparison between the experimental and the numerical results indicated that the finite element model predicted experimentally determined results successfully.

Abstract: The new way of using mechanical joint element (MJE) to cross the interface of new and old concrete to reinforce the combination is put forward. The splitting strength tests of young and old concrete were carried out to investigate the effects on splitting strength of MJE and different materials used to embed the MJE. The working mechanism of the MJE in split test is discussed emphatically. The shear tests of young and old concrete were carried out too. The effects on shear strength of MJE and interface agent are discussed. The mechanism of MJE in shear test is analyzed synchronously.