Papers by Author: Li Juan Li

Abstract: This paper presented the on-site test results on two-way RC slabs with and without FRP-strengthening. Two slabs strengthened with BFRP, one slab strengthened with CFRP and one slab without strengthening were tested on a practical engineering structure being repaired. The effects of different load cases on mid-span deflection, distribution of stresses around the steel bars at the top and bottom of slabs were analyzed.

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: Based on high strength concrete (HSC), the improved HSC concrete was produced by adding different contents of fine grain rubber particles and polypropylene fibers. The grain size of the rubber particle is 420 m and the rubber content is 1%, 2%, and 3% of the mass of cementitious material respectively. The volume fraction of polypropylene fiber is 0.1%.The performance of HSC, rubber particle improved high strength concrete (RHSC), polypropylene fiber improved high strength concrete (PHSC) and polypropylene fiber hybrid rubber particle improved high strength concrete (PRHSC) before and after high temperature are studied. The investigation methods used are the external surface inspection, weight loss and residual strength testing. The experimental results show that rubber particles can improve the workability of HSC and PHSC under normal temperature. Polypropylene fiber can significantly improve the spalling failure resistance property of HSC and RHSC.

Abstract: For a quantitative analysis and better understanding of the stress-strain response and their effects on interface debonding and crack initiation and propagation of alternative hard and soft multi-layers under circumscription loading, to explore methodologies of optimum design of surface multi-layers, large strain elasto-plastic finite element method is used to evaluate the mechanical behaviors of TiN/Ti multi-layer films on rigid substrate under hard asperity indentation. The results show that with the same total thickness of the film, the alternate hard and soft multi-layers with larger ratio could endure larger circumscription loading, and the different total thickness of multi-layers could affect the circumscription loading greatly. So there must be a circumscription loading in this multi-layer film structures. Generally speaking, the circumscription loading has something to do with the material modulus, the radius of the press-head, the thickness ratio of soft and hard layers, and the total thickness of alternate hard and soft multi-layers. For a quantitative analysis of this problem, finite element method is utilized to analyze the phenomena of the plastic indentation. According to analysis of the film deformation, the maximum bending stress, and the surface bending stress, and those parameters that have influence on different alternative films are studied. The study of this paper is expected to provide some theoretical basis for the optimum design of multi-layer film structures.