Study on the Earthquake Behavior of Concrete Structures
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of the inter-story post-yield stiffness to the variance of seismic response,
Engineering Mechanics, 2008, 25(7): 133-141.
Abstract:
The remarkable discreteness of seismic response of structures under
strong earthquakes significantly restricts the implementation of performance
based seismic design. Response variation may be caused by the variant
ground motions and the seismic capabilities of structures. Based on
numerical simulations, the influence of structural stiffness after yielding
on the inelastic seismic response for multi-degree of freedom (MDOF)
structural systems is discussed. By avoiding degradation of structural
stiffness after yielding, damage concentration in structures may be
prevented which would also reduce the discreteness of inelastic seismic
responses. Moreover, it is studied that structures with higher stiffness
after yielding are more effective to control the seismic performance
of structures, that will achieve the aims of performance based seismic
design.
Key words: earthquake response; inelastic MDOF system; stiffness
after yielding; discreteness; performance based design
Seismic
nonlinear analytical models, methods and examples for concrete structures
Engineering Mechanics, 2006, 23(sup. II). 131-140.
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.
Keywords: reinforced concrete, seismic, nonlinear, fiber model,
shear wall, multi-layer shell
Elasto-plastic
Analysis for A Steel Frame-Core Wall Structure
Sichuan Building Science, 2008, 34(3): 5-10.
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.
Keywords: nonlinear analysis, structure, seismic, fiber model,
shear wall, multi-layer shell
Introduction
of Robustness for Seismic Structures
Building Structures, 2008, 38(6): 11-15.
Abstract:The concept of robustness
of structures is firstly introduced in this paper. And importance with
enough robustness for seismic structures in preventing collapse of the
structures under strong intensity earthquake attack is discussed. Then
the approaches to increase the robustness of seismic structures, including
structural systems, strength and ductility of structure, failure modes
and redundancy, are suggested.
Keywords: seismic structure; robustness; structural systems;
integrity; failure mode; strength; ductility; redundancy elements.
Study
on lateral load patterns of pushover analysis using incremental dynamical
analysis for RC frame structures
Journal of Building
Structures, 2008, 29(2): 132-140.
Abstract: In this research, the nonlinear
static p rocedures with different lateral load patterns were compared
by using incremental dynamical analysismethod based on a six2storey
and a ten2storey RC frame fibermodel. For each story of different frames,
the inter2story shear force vs. drift curves computed by pushover analysis
by using different lateral load patterns and time history analysis with
a series of earthquake records on the design site have been compared
to give a rational lateral load pattern of pushover analysis. Finally,
for a whole frame structure, the lateral load pattern choice was suggested,
that is,
uniform load pattern was better for the stories near foundation; load
pattern with the story heights taken into consideration was suitable
for the mid stories and the SRSS pattern or Chinese Code pattern was
suitable for upper stories. It is also shown that the nonlinear static
p rocedure gives a safe estimation of the inelastic seismic response
statistically for regular RC frames with good numerical stability.
Keywords: RC frame; fiber model; pushover analysis; incremental dynamic
analysis; inter-storey shear force and drift relation
Abstract: Precise prediction for
the hysteretic behaviors of reinforced concrete (RC) column under seismic
load is important to assess the safety of RC structures under earthquake.
Due to the overturning moment in the earthquakes, besides being subjected
to seismic lateral forces, RC columns also experience variable axial
loads. Therefore the influence of variable axial forces must be taken
into account when to study the hysteretic behaviors of RC columns under
cyclic loads. In this paper, a numerical analysis model based on a fiber
model program have been validated firstly through the rational hysteretic
simulations of two RC columns under various patterns of axial loads,
Then a frame column has been simulated under various patterns of variable
axial loads by numerical method. The analytical results indicate that
the variety of axial loads has considerable effect on the hysteretic
behaviors of RC columns. Because of the randomness of axial loads and
to facilitate carrying on experimental researches and analyzing earthquake-resistant
behaviors for RC structures, a equivalent fixed axial load method is
put forward to determine the seismic behaviors of RC column in structures
under earthquake.
Keywords: fiber model; variable axial load; concrete column;
earthquake-resistant behavior; hysteretic analysis
Numerical
Simulation for the Hysteresis Behavior of RC Columns under Cyclic Loads
Engineering Mechanics, 2007, 24(12): 76-81
Abstract£ºPrecise prediction
for the hysteresis behaviors of reinforced concrete (RC) columns under
seismic loads is important to assess the safety of RC frames and bridges
during sever earthquake. Due to the complicated material behavior and
complex external force during the earthquake, an accurate simulation
of the behaviors under seismic loads currently mainly depends on numerical
method, and more precisions are demanded for the hysteresis constitutive
laws of concrete and steel reinforcement. In this paper, a fiber model
program is developed with more precise hysteresis constitutive laws
of concrete and steel reinforcement. Two columns, which are under cyclic
compressive-bending loads, with different axial load ratios and reinforcement
ratios are analyzed and the simulation results are found agreed well
with test results.
Key words: fiber model; cyclic load; concrete column; hysteretic
relation; numerical analysis
High
Performance Simulation for Building Structures under Disaster
Proc. 1st Symp. on High Performance Computing (HPC) Technology
in Engineering Design, 2007. Dec. 11-12, Shanghai: 93-101.
Abstract: Buildings and building
clusters could be destroyed by disaster load, such as earthquake and
blast. Accurate prediction for the behavior of building structures in
various disasters provided by high-performance numerical computing is
important to structural design. The Department of Civil Engineering
in Tsinghua University developed a series of advanced numerical models
including material laws and element models. Therefore, base on parallel
computing and nonlinear methods, analyses about some extreme problems
of building structures such as collapse, overturning and the loss of
earthquake damage of urban building clusters are successfully processed.
Hence, the analyses provide important advice for disaster prevention
and mitigation.
Keywords: building structure, high-performance simulating analysis,
finite element model, progressive collapse, blast wave, urban building
clusters
Study
on the Accuracy and Applicability of the Pushover Analysis
Earthquake Resistant Engineering and Retrofitting, 30(1),
2008, 55-59.
Abstract:
The nonlinear static pushover analysis procedure is now widely used
as a simple method to estimate the inelastic seismic response for building
structures. However, the accuracy of the method still needs to be validated
because of the inherent limitation in the theory of the method. Besides,
there are some confines on the application of this method. In this paper,
a 6-storey RC frame and an 18-storey RC frame-wall structure are analyzed
with both pushover method and the incremental dynamical analysis method
respectively. The comparison between the results of the two methods
shows that the pushover method can be used only for low structures which
are controlled by the first modal shape. It is also shown that for the
structures which are influenced by the higher modal shape evidently,
pushover analysis always gives the much lower capacity result.
Keywords: pushover analysis, RC frame, frame-wall structure,
IDA
Spatial
finite element analysis for the whole-process of RC core tubes based
on the layered shell element
Proc. 11th Conf. on earthquake resistance technology
of high-rise buildings, Nov. 2007. Kunming, China, 184-189.
Abstract£ºAs the most
widely used lateral resistant structures, RC core tubes consist of various
members and perform spatial mechanical behaviors. Therefore, how to
accurately simulate the RC tubes for the whole process of nonlinear
behaviors is a significant subject in seismic analysis of structures.
Based on the layered shell element the whole process simulation of a
pseudo-dynamic testing on RC core tubes is presented in the paper. By
correct modeling of the key structural elements (such as walls, coupling
beams, reinforcements), the model is able to reflect the spatial behavior
of the tube as well as the complicated nonlinear behaviors of the yielding
and shear failure of coupling beams, cracking of the tube and so on.
Furthermore, results from the simulation match well with those from
the tests, which show the finite element model is of some help on elasto-plastic
calculation of high-rise RC tubes in severe earthquakes.
Keywords£ºCore tube, Finite
element, Layered shell, Elasto-plastic calculation, Seismic Analysis
Elasto-plastic
time-history computational model for steel frame-core wall structures
Architecture Technology, 2007, 38(sup.), 242-244.
Parametric
study of structural stiffness after yielding on inelastic seismic response
for multi-degree of freedom structural systems
Journal of Disaster Prevention and Mitigation Engineering,
27(sup.), 2007, 158-162.
Abstract: The remarkable discreteness
of seismic response of structures under strong earthquakes significantly
restricts the implementation of performance based seismic design. Response
variation may be caused by the variant ground motions and the seismic
capabilities of structures. Based on numerical simulations, the influence
of structural stiffness after yielding on the inelastic seismic response
for multi-degree of freedom structural systems is discussed. By avoiding
degradation of structural stiffness after yielding, damage concentration
in structures may be prevented which would also reduce the discreteness
of inelastic seismic responses. Moreover, it is studied that structures
with higher stiffness after yielding are more effective in controlling
the seismic performance of structures, that will achieve the aims of
performance based seismic design.
Keywords: earthquake response; inelastic
MDOF system; stiffness after yielding; discreteness; performance based
design, cumulative hysteretic energy dissipation
Numerical
Simulation for the Hysteresis Behavior of Prestressed Conrete Structures
under Cyclic Loads
Earthquake
Resistant Engineering, 28(6), 2006, 25-29.
Abstract: Due to progressively using
in practical construction of prestressed concrete structures, the researches
for seismatic performance of prestressed concrete (PC) structures has
remarkable significance in engineering practice. Because of the complicated
behavior of material and loads, the precise simulation of PC structures
or members under cyclic loads has to depend on numerical model. In this
paper, a numerical analysis model for the simulation of PC member structures
has been developed on the basis of a fiber model program. A PC frame,
an unbonded PC frame and an unbonded PC column under cyclic loads are
simulated with the developed program. The comparison of the results
between simulations and tests indicates that, for the reason of using
rational hysteretic material model and exactly considering the influence
of prestressing, the numerical analysis model based on fiber models
developed in this study can accurately predict the hysteretic properties
of PC structures and can be used in the parametric analysis and mechanism
study.
Keywords: fiber model; cyclic load; prestressed
concrete; analysis method
High
strength/performance structural materials and the developments of modern
engineering structures and the design theory
Proc. 1st International Forum on Advances in Structural
Engineering, Beijing: China Building Industry Press, Beijing, 2006,
208-250.
Abstract: This paper firstly presents
the latest development of high strength/performance structural materials
in recent years. The rational applications and examples of high strength/
performance structural materials in the structural systems to obtain
high performance are discussed and presented. The positive functions
of high strength reinforcement used in reinforced concrete frame structures,
that can enhance the structural performance against earthquake and reduce
the structural seismic damage, are investigated in detail with nonlinear
pushover analysis and dynamic analysis. The results show that the high
seismic performance of the reinforced concrete frames, including a delayed
appearance of plastic hinges at the bottom story columns feet, to form
a rational failure mechanism under strong earthquake, and a small residual
displacement after earthquake that cause an easy retrofitting after
earthquake, can be obtained by replacing normal strength reinforcement
with high strength reinforcement in the columns. Finally, the development
of the safety and design theory for the structures using high strength/performance
materials are discussed.
Keywords: High strength/performance concrete;
High strength/performance steel; Engineering Structures; Structure safety;
Design theory; Accidental event; Earthquake resistance.
Nonlinear
FE model for RC shear walls based on multi-layer shell element and microplane
constitutive model
Proc.
Computational Methods in Engineering And Science (EPMESC X),
Tsinghua University Press & Springer-Verlag, Aug. 2006, Sanya, Hainan,China,
2006, CDROM.
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
Shear
force distribution in RC frame-shearwall structures under static and
dynamic loads
Proc. 1st National Symposium on the Research Progress
for the Safety of Cities and Engineering, Tangshan, 2006, 306-312
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
Dynamic
analysis of unbonded prestressed concrete frame
Proc. 1st National Symposium on the Research Progress
for the Safety of Cities and Engineering, Tangshan, 2006, 689-694.
Abstract£ºAt
present, unbonded prestressing technology has been obtained extensive
use, and the research to aseismatic performance of unbonded prestressed
concrete(UPC) structures or members has remarkable significance in engineering
practice. Because of the complicated behavior of material and loading,
the exact simulation of UPC structures or members under dynamic loads
has to utilize numerical model. In this paper, 3 UPC frames have been
simulated under dynamic loads with the use of a fiber model program.
The numerical results indicate that UPC frames have an excellent recentering
property and a small energy-dissipated capacity. And during an earthquake,
in spite of taking strengthed measures£¬there is still a possibility
of the occurrence to plastic-hinge in the bottom of UPC frame column
(first storey).
Keywords£ºfiber model; dynamic
load; unbonded; prestressed; concrete frame