Gaochuang Cai

Deterioration of Basic Properties of the Materials in FRP-Strengthening RC Structures under Ultraviolet Exposure

This paper presents an experimental study of the basic properties of the main materials found in reinforced concrete (RC) structures strengthened by fibre reinforced polymer (FRP) sheets with scope to investigate the effect of ultraviolet (UV) exposure on the degradation of FRP, resin adhesive materials and concrete. The comparison studies focused on the physical change and mechanical properties of FRP sheet, and resin adhesive materials and concrete before and after UV exposure. However, the degradation mechanisms of the materials under UV exposure were not analyzed. The results show that the ultimate tensile strength and modulus of FRP sheets decrease with UV exposure time and the main degradation of FRP-strengthened RC structures is dependent on the degradation of resin adhesive materials. The increase in the number of FRP layers cannot help to reduce the effect of UV exposure on the performance of these materials. However, it was verified that carbon FRP materials have a relatively stable strength and elastic modulus, and the improvement of the compression strength of concrete was also observed after UV exposure.

Application of Variance Analyses Comparison in Seismic Damage Assessment of Masonry Buildings Using Three Simplified Indexes

The reasonable assessment of potential damage type of masonry structures in seismic-prone zone is very significant to strengthen existing masonry structures and guide the construction of the new building. The primary objective of the study is to propose and determine a reasonable assessment index to predict the damage type of masonry structures in different seismic intensity zones using the survey results of the 2008 Wenchuan earthquake and variance analyses comparison methods. Three potential theory assessment indexes are considered in the evaluation of damage of masonry structures, including wall density index , strength index , and combined index . In order to compare the feasibility of the three indexes, One-way analysis of variance and Scheffe’s method were used for in-depth discussion. Based on the proposed assessment indexes, further analyses and recommendations were provided. Results show the combined index has a high potential to predict the damage levels of masonry structures. Based on the study, several recommendations were provided for the masonry structures in seismic-prone zones.

In Situ Strain and Damage Monitoring of GFRP Laminates Incorporating Carbon Nanofibers under Tension

In this study, conductive carbon nanofibers (CNFs) were dispersed into epoxy resin and then infused into glass fiber fabric to fabricate CNF/glass fiber-reinforced polymer (GFRP) laminates. The electrical resistance and strain of CNF/GFRP laminates were measured simultaneously during tensile loadings to investigate the in situ strain and damage monitoring capability of CNF/GFRP laminates. The damage evolution and conduction mechanisms of the laminates were also presented. The results indicated that the percolation threshold of CNFs content for CNF/GFRP laminates was 0.86 wt % based on a typical power law. The resistance response during monotonic tensile loading could be classified into three stages corresponding to different damage mechanisms, which demonstrated a good ability of in situ damage monitoring of the CNF/GFRP laminates. In addition, the capacity of in situ strain monitoring of the laminates during small strain stages was also confirmed according to the synchronous and reversible resistance responses to strain under constant cyclic tensile loading. Moreover, the analysis of the resistance responses during incremental amplitude cyclic tensile loading with the maximum strain of 1.5% suggested that in situ strain and damage monitoring of the CNF/GFRP laminates were feasible and stable.

Simplified Density Indexes of Walls and Tie-Columns for Confined Masonry Buildings in Seismic Zones

ABSTRACT This paper discusses and quantifies the minimum requirements of walls and tie-columns in confined masonry (CM) buildings located in earthquake-prone regions. A research database including 238 damaged CM buildings obtained from the 2008 Wenchuan earthquake survey is established and comprehensively examined. The requirements of masonry walls in CM buildings are discussed, and a simplified tie-column density index is proposed for evaluating the potential damage of the structures. Besides, the minimum requirements of reinforced concrete tie-columns and their maximum allowable spacing in CM buildings at different seismic intensity zones are discussed.

Effect of Infills on Seismic Performance of Reinforced Concrete Frame structures—A Full-Scale Experimental Study

ABSTRACT The wall collapse-initiated disaster in infilled reinforced concrete (RC) frame structures has been increasingly concerned by research community recently. This paper studies the seismic performances of a bare RC frame and three RC frames infilled by different lightweight materials in full scale under cyclic loads, including hollow bricks, gypsum blocks, and autoclaved lightweight concrete panels. The main studied performances include lateral resistance capacity, stiffness, wall damage, ductility, and energy dissipation capacity of the frames. Based on the experimental results and literature research, this paper discusses ideal infill materials for RC frame structures and skeleton curve of the frames.