L. P. Ye

Experimental study on seismic strengthening of RC columns with wrapped CFRP sheets

Eight specimens, including two strengthened after being loaded to yield level to imitate strengthening with some damage and one strengthened under a sustained axial load to imitate strengthening under service condition, were tested under constant axial load and lateral cyclic load to investigate seismic performance of RC columns strengthened with carbon fiber reinforced polymer sheets (CFRP sheets). The ductility enhancement with the confinement of CFRP sheets was studied by the strain development and distribution in the CFRP sheets. Based on the experimental results, a confinement factor of CFRP and an equivalent transversal reinforcement index were suggested. Thus, the seismic design method of the current Chinese seismic design code for RC columns can be directly used in determining the amount of CFRP required for seismic strengthening. 2003 Elsevier Ltd. All rights reserved.

BOND-SLIP MODELS FOR FRP SHEET/PLATE-TO-CONCRETE INTERFACES

A meso-scale finite element model is first presented for simulating the debonding behavior of FRP-to-concrete bonded joints in simple shear tests. In this model, both the FRP plate/sheet and the concrete are modeled using elements of mesoscopic sizes so that the shapes and paths of cracks during the entire debonding process can be appropriately captured. Results obtained from this model are next presented to provide insight into the debonding failure process. Finally, based on a finite element parametric study and existing test results, three bond-slip models of different levels of sophistication are presented. These proposed models are far more accurate than all existing bond-slip models.

Nonlinear FE Model for RC Shear Walls Based on Multi-Layer Shell Element and Micro-Plane Constitutive Model

Nonlinear simulations for structures under disasters have been widely focused in recent years. However, precise modeling for the nonlinear behavior of reinforced concrete (RC) shear walls, which are the major lateral-force-resistant structural member in high-rise buildings, still has not been successfully solved. In this paper, based on the principles of composite material mechanics, a multi-layer shell element model is proposed to simulate the coupled in-plane/out-plane bending or the coupled bending/shear nonlinear behaviors of RC shear wall. The multi-layer shell element is made up of many layers with different thickness. And different material models (concrete or steel) are assigned to various layers so that the structural performance of the shear wall can be directly connected with the material constitutive law. And besides the traditional elasto-plastic-fracture constitutive model for concrete, which is efficient but does not give satisfying performance for concrete under complicated stress condition, a novel concrete constitutive model, referred as micro-plane model, which is originally proposed by Bazant et al., is developed to provide a better simulation for concrete in shear wall under complicated stress conditions and stress histories. Three 10-story buildings under static push-over load and dynamic seismic load, with various shear wall arrangements, were analyzed with the shear wall model proposed in this study. The simulation results show that the multi-layer shell elements can correctly simulate the coupled in-plane/out-plane bending failure for tall walls and the coupled in-plane bending-shear failure for short walls. And with micro-plane concrete constitutive law, the cycle behavior and the damage accumulation of shear wall can be precisely modeled, which is very important for the performance-based design of structures under disaster loads.

Simulation for the Collapse of RC Frame Tall Buildings under Earthquake Disaster

China is a country that suffers a lot from the earthquake disaster. The major reason for the human death and property losses in earthquake is the collapse of the tall buildings. Hence, correct simulation for the failure modes and accurate prediction for the collapse of the tall buildings under earthquake disaster is very useful for studying the safety of buildings and evaluating losses during earthquakes[1]. However, a lot of simplifications must be carried out in the existing simulations to overcome the numerical problems because the grave nonlinearity exists when collapse happens. This may lead to the results away from a real phenomenon. In this study, a fiber model for reinforced concrete (RC) structures (referred as THUFIBER) is developed, which is based on the general-purpose finite element package of MSC.MARC that carries significant capacity of solving nonlinear problems. In this model, the concrete and the reinforcement inside the structural elements are modeled respectively with different fibers as shown in figure 1 so that the cyclic behavior of material can be properly simulated. Pushover and dynamic time-history analysis for a RC frame tall building are carried out to illustrate the capacity of the proposed model. And dynamic time-history analysis is emphasized in this paper to discuss the collapse modes of the structure. The results show that THUFIBER can simulate the collapse and failure process of the structure under the dynamic loads such as complicated seismic loads, including the softening and fracture behaviors of structural elements, and further the program shows good convergence in the non-linear cases. So THUFIBER has a strong and promising ability for nonlinear analysis including collapse numerical simulation. nOpen image in new window n nFigure 1 nSection dicretization of the fiber model n n nOpen image in new window n nFigure 2 nSimulation for the Collapse of the frame