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Volume 9, Number 4, March 2012
 

Abstract
The damping effect of a Concrete-filled Rectangular Steel Tube (CRST) frame structure is studied in this paper. Viscous dampers are employed to insure the function of the building especially subjected to earthquakes, for some of the main vertical elements of the building are not continuous. The shaking table test of a 1:15 scale model was conducted under different earthquake excitations to recognize the seismic behavior of this building. And the vibration damping effect was also investigated by the shaking table test and the simulation analysis. The nonlinear time-history analysis of the shaking table test model was carried out by the finite element analysis program CANNY. The simulation model was constructed in accordance with the tested one and was analyzed under the same loading condition and the simulation effect was then validated by the tested results. Further more, the simulation analysis of the prototype structure was carried out by the same procedure. Both the simulated and tested results indicate that there are no obvious weak stories on the damping equipped structure, and the dampers can provide the probability of an irregular CRST frame structure to meet the requirements of the design code on energy dissipation and deformation limitation.

Key Words
concrete-filled rectangular steel tube; high-rise building; viscous damper; shaking table test; nonlinear time-history analysis.

Address
Xilin Lu and Hongmei Zhang: State Key Laboratory of Disaster Reduction in Civil Engineering, Tongji University, Shanghai, 200092, China
Chunguang Meng: Architecture Design & Research Institute of Tongji University, Shanghai 200092, China

Abstract
Based on the heterogeneous characterization of concrete at mesoscopic level, Realistic Failure Process Analysis (RFPA3D) code is used to simulate the failure process of concrete-filled tubular (CFT) stub columns. The results obtained from the numerical simulations are firstly verified against the existing experimental results. An extensive parametric study is conducted to investigate the effects of different concrete strength on the behaviour and load-bearing capacity of the CFT stub columns. The strength of concrete considered in this study ranges from 30 to 110 MPa. Both the load-bearing capacity and loaddisplacement curves of CFT columns are evaluated. In particular, the crack propagation during the deformation and failure processes of the columns is predicted and the associated mechanisms related to the increased load-bearing capacity of the columns are clarified. The numerical results indicate that there are two mechanisms controlling the failure of the CFT columns. For the CFT columns with the lower concrete strength, they damage when the steel tube yields at first. By contrast, for the columns with high concrete strength it is the damage of concrete that controls the overall loading capacity of the CFT columns. The simulation results also demonstrate that RFPA3D is not only a useful and effective tool to simulate the concrete-filled steel tubular columns, but also a valuable reference for the practice of engineering design.

Key Words
concrete-filled tubular (CFT) stub column; load-bearing capacity; failure process; heterogeneity; numerical simulation.

Address
W.C. Zhu, L. Ling, Y.M. Kang and L.M. Xie: School of Resource and Civil Engineering, Northeastern University, Shenyang 110004, China
C.A. Tang: School of Civil and Hydraulic Engineering, Dalian University of Technology, Dalian, 116024, China

Abstract
The service loads are often decisive in the design of concrete structures. The evaluation of the cracking moment, Mcr, is an important issue to predict the performance of the structure, such as, the deflections of the reinforced concrete beams and slabs. To neglect the steel bars of the section is a simplification that is normally used in the computation of the cracking moment. Such simplification leads to small errors in the value of this moment (typically less than 20%). However, these small errors can conduce to significant errors when the values of deflections need to be computed from Mcr. The article shows that an error of 10% on the evaluation of Mcr can lead to errors over 100% in the deformation values. When the deformation of the structure is the decisive design parameter, the exact computing of the cracking moment is obviously very important. Such rigorous computing might lead to important savings in the cost of the structure. With this article the authors wish to draw the attention of the technical community to this fact. A simple equation to evaluate the cracking moment, Mcr, is proposed for a rectangular crosssection. This equation leads to cracking moments higher than those obtained by neglecting the reinforcement bars and is a simple rule that can be included in Eurocode 2. To verify the accuracy of the developed model, the results of the proposed equation was compared with a rigorous computational procedure. The proposed equation corresponds to a good agreement when compared with the previous approach and, therefore, this model can be used as a practical aid for calculating an accurate value of the cracking moment.

Key Words
reinforced concrete; concrete beams; cracking; deformations; serviceability.

Address
A.V. Lopes and S.M.R. Lopes: Department of Civil Engineering, University of Coimbra, CEMUC, Portugal

Abstract
This paper discusses a new constitutive model called the high-rate brittle microplane (HRBM) model and also presents the details of a new software package called the Virtual Materials Laboratory (VML). The VML software package was developed to address the challenges of fitting complex material models such as the HRBM model to material property test data and to study the behavior of those models under a wide variety of stress- and strain-paths. VML employs Continuous Evolutionary Algorithms (CEA) in conjunction with gradient search methods to create automatic fitting algorithms to determine constitutive model parameters. The VML code is used to fit the new HRBM model to a well-characterized conventional strength concrete called WES5000. Finally, the ability of the new HRBM model to provide high-fidelity simulations of material property experiments is demonstrated by comparing HRBM simulations to laboratory material property data.

Key Words
constitutive modeling; optimization algorithms; microplane models.

Address
Mark D. Adley, Andreas O. Frank and Kent T. Danielson: U.S. Army Engineer Research and Development Center Impact and Explosive Effects Branch, ATTN: CEERD-GM-I 3909 Halls Ferry Road Vicksburg, MS 39180-6199 USA

Abstract
In this paper, we examine the behavior of the High-Rate Brittle Microplane (HRBM) concrete model based on a series of penetration experiments. These experiments were conducted with three different slab thicknesses (127, 216 and 254 mm) that provided a significant challenge for the numerical simulations. The 127 mm slab provided little resistance, the 216 mm slab provided nominal resistance and the 254 mm slab approached the perforation limit thickness of the projectile. These experiments provide a good baseline for evaluating material models since they have been shown to be extremely challenging; in fact, we have not encountered many material models that can provide quantitatively predictive results in terms of both projectile exit velocity and material damage. In a companion paper, we described the HRBM material model and its fit to various quasi-static material property data for WES-5000 concrete. In this paper, we show that, when adequately fit to these quasi-static data, the HRBM model does not have significant predictive capabilities, even though the quasi-static material fit may be exceptional. This was attributed to the rate-dependent response of the material. After various rate effects were introduced into the HRBM model, the quantitative predictive nature of the calculations dramatically increased. Unfortunately, not much rate-dependent material property data are in the literature; hence, accurate incorporation of rate effects into material models is difficult. Nonetheless, it seems that rate effects may be critical in obtaining an accurate response for concrete during projectile perforation events.

Key Words
numerical modeling; strain-rate dependence; microplane models.

Address
Andreas O. Frank, Mark D. Adley, Kent T. Danielson and Henry S. McDevitt, Jr.: U.S. Army Engineer Research and Development Center Impact and Explosive Effects Branch, ATTN: CEERD-GM-I 3909 Halls Ferry Road Vicksburg, MS 39180-6199 USA


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