Abstract£ºAs one of the
most widely used lateral resistant structures, reinforced concrete (RC)
core tube consists of diverse members and appears spatial mechanical
behaviors. Therefore, how to accurately simulate the RC tubes for the
whole process of nonlinear behaviors is an important problem in seismic
analysis of structures. Based on the multi-layer shell element, the
whole process simulation of a pseudo-static testing on RC core tubes
is presented in the paper. By correct modeling of the key parts (such
as walls, coupling beams, reinforcement), the numerical model is able
to simulate the spatial behavior of the tube as well as the complicated
nonlinear behaviors such as the yielding and shear failure of coupling
beams, cracking of the tube and so on. Results from the simulation match
well with those from the tests. Using the proposed core-tube model,
an elastoplastic analysis for a practical framed core-tube structure
is conducted, to illustrate the implementation of proposed model in
real structures. The tube model based on multi-layer shell is helpful
in the elasto-plastic analysis of high-rise building under severe earthquakes.
Abstract: Structures will enter
nonlinear stage during strong earthquakes. Hence accurate prediction
for the structural nonlinear behaviors is important to the safety and
loss assessment during earthquakes. This paper reviews the existed nonlinear
analytic models for structures and presents some novel models for structural
nonlinear analysis that recently developed by the Tsinghua University.
With these models, the material stress-strain relationship can be connected
directly with the force-displacement behavior of the structural elements.
So that the complicated coupled axial force-bending moment-shear force
behaviors can be properly simulated, as well as the corresponding cycle
behaviors. With the secondary development user subroutines, convenient
pre and post process functions and extinct nonlinear capacity of general
purpose FE software of MSC.MARC, the spatial seismic responds of structures
can be precisely simulated. A steel frame-core wall structure with an
eccentric tube is analyzed with static pushover and dynamic time-history
analysis to demonstrate the applications of the new models.
Abstract: Structures will enter
nonlinear stage in strong earthquake, precisely prediction for the nonlinear
behavior of reinforced concrete (RC) structures in earthquake is important
to assess the aseismic safety of the structures. This paper presents
the programs recently developed by the Civil Engineering Department
of Tsinghua University, which include the fiber model based the program
THUFIBER for RC frames, the program NAT-PPC for prestressed concrete
(PC) frames, and multi-layer shell element based shear wall program.
These programs can connect the nonlinear nodal force/nodal displacement
relationship of elements directly with the nonlinear stress/strain relationship
of materials. So complicated cycle behaviors and coupled axial force-biaixal
bending-shear behaviors of the RC structures can be correctly simulated.
And furthermore, with the convenient pre/post process and nonlinear
capacity of common finite element software, these programs not only
can precisely simulate the spatial structural nonlinear seismic response,
but also can simulate some extreme nonlinear problems such as blast
or collapse. The precision and the capacity of the programs are illustrated
in this paper with a series of researches and applications.
Abstract: High strength steel reinforcement in the shear walls of frame-shear wall structures can efficiently increase the safety margin and change the seismic force distribution because the shear wall will yield after the frame. With the fiber model program THUFIBER and the multi-layer-shell program, which are developed by Tsinghua University and are based on the general purpose finite element software of MSC.MARC, two 8-story reinforced concrete frame-shear wall structures, whose shear wall are reinforced with normal and high strength steel respectively, are studied with static pushover and dynamic analysis. The effect of high strength steel in the shear wall to the control of seismic performance of the structures is emphasized. The results show that with high strength steel in the shear wall, the softening behaviors of frame and shear wall are changed. The yield strength of the shear wall is increased while it still has the same the deformation capacity. And the safety margin of the whole structure is efficiently increased which benefits the seismic capacity of the structure.
Keywords: frame-shear wall; high-strength reinforcement; pushover; dynamic; nonlinear
FE model for RC shear walls based on multi-layer shell element and microplane
Abstract: Nonlinear simulations for structures under disasters have been widely focused on 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 and the coupled in-plane 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 rebar) 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 microplane 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 walls under static push-over load and cyclic load were analyzed with the proposed shear wall model for demonstration. 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 microplane 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.
Keywords: shear wall, nonlinear analysis, microplane, finite element, multi-layer shell element
force distribution in RC frame-shearwall structures under static and
Abstract: The distribution of internal force in frame-wall structure during the nolinear phases concerns the safety of structure. A fiber model and a multi-layer-shell model for reinforced concrete(RC) structures based on the general-purpose finite element package of MSC.Marc is used to simulate the frame structure and the shear-wall structure respectively. In the pushover and dynamic time-history analysis of a frame-wall structure, the distribution of shear force between the frame and shear wall during different phases is studied.
Key words: frame-wall structure; pushover; dynamic; nolinear; distribution of shear force