Yongchang Guo

Concrete Cover Separation in FRP-Plated RC Beams: Mitigation Using FRP U-Jackets

AbstractConcrete cover separation is a common failure mode of RC beams strengthened with a fiber-reinforced polymer (FRP) plate externally bonded to the tension face (FRP-plated RC beams). This failure mode initiates at the critical plate end and then propagates at the level of steel tension reinforcement in the direction of increasing moment. Plate-end anchorage by FRP U-jackets has been specified in some design guidelines as a mitigation measure to delay or suppress concrete cover separation, although its effectiveness is far from clear. This mitigation method is more attractive than other options because the same strengthening material is used and the installation procedure is simple. This paper presents the first systematic experimental study on the use of FRP U-jackets for mitigating plate-end concrete cover separation failure, with particular attention to the effect of inclination angle between the U-jacket and the beam axis. A total of 10 full-scale FRP-plated RC beams were tested. The test results...

Behavior and Three-Dimensional Finite Element Modeling of Circular Concrete Columns Partially Wrapped with FRP Strips

Fiber-reinforced polymer (FRP) jacketing/wrapping has become an attractive strengthening technique for concrete columns. Wrapping an existing concrete column with continuous FRP jackets with the fiber in the jacket being oriented in the hoop direction is referred to as FRP full wrapping strengthening technique. In practice, however, strengthening concrete columns with vertically discontinuous FRP strips is also favored and this technique is referred to as FRP partial wrapping strengthening technique. Existing research has demonstrated that FRP partial wrapping strengthening technique is a promising and economical alternative to the FRP full wrapping strengthening technique. Although extensive experimental investigations have hitherto been conducted on partially FRP-confined concrete columns, the confinement mechanics of confined concrete in partially FRP-confined circular columns remains unclear. In this paper, an experimental program consisting of fifteen column specimens was conducted and the test results were presented. A reliable three-dimensional (3D) finite element (FE) approach for modeling of partially FRP-confined circular columns was established. In the proposed FE approach, an accurate plastic-damage model for concrete under multiaxial compression is employed. The accuracy of the proposed FE approach was verified by comparisons between the numerical results and the test results. Numerical results from the verified FE approach were then presented to gain an improved understanding of the behavior of confined concrete in partially FRP-confined concrete columns.

Stress-Strain Behavior of Circular Concrete Columns Partially Wrapped with FRP Strips

Fiber-reinforced polymer (FRP) jacketing or wrapping has become an attractive strengthening technique for concrete columns. Within this strengthening technique, FRP composites are wrapped around the concrete column with the fibers in the jacket being oriented in the hoop direction. In practice, the FRP jackets can be either continuous or discontinuous along the column height and thus the resulting column is referred to as fully or partially wrapped FRP-confined concrete columns. Existing research has demonstrated that the partially strengthening technique by discrete FRP strips is a promising and economic alternative to the fully FRP strengthening technique. Although a number of experimental investigations have been conducted on partially wrapped FRP-confined concrete columns, the stress-strain behavior of FRP-confined concrete in partially wrapped concrete columns is not yet understood. This paper presents an experimental program to investigate the axially compressive behavior of circular concrete columns partially wrapped with FRP strips. The test results are presented and compared with the predictions from a typical analysis-oriented stress-strain model to examine its reliability and accuracy. It has been demonstrated that the model provides reasonably accurate predictions of the ultimate axial stress of partially FRP-confined concrete while it usually underestimates the ultimate axial strain.

Antiseismic analysis of double-layer grid shell structures

Publisher Summary The chapter discusses the geometrical optimum design and the anti-seismic analysis of double-layer grid shell structures. The characteristic of free vibration of grid shell structures with respect to geometric parameter is studied in the chapter. The variations of eigenfrequency of shell structures with the ratio of height-to-span, span, grid division frequency, and thickness of a shell are discussed in the chapter. The Newmark method is used to calculate the stresses and displacements of grid shell structures under earthquake action. The analysis results show that at the specified span, the eigenfrequency of the structure will increase with the increase of the height-to-span ratio at beginning and then decrease afterwards. At the specified span and height-to-span ratio, the eigenfrequency of the structure increases little with the increase of the thickness and the grid division frequency of the grid shell structures.