• Structural Engineering and Mechanics
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• v.17 no.3_4
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• pp.539-556
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• 2004

In this paper, the design, fabrication and characterization of a piezoelectric friction damper are presented. It was sized with the proposed practical procedure to minimize the story drift and floor acceleration of an existing 1/4-scale, three-story frame structure under both near-fault and far-field earthquakes. The design operation friction force in kip was numerically determined to range from 2.2 to 3.3 times the value of the peak ground acceleration in g (gravitational acceleration). Experimental results indicated that the load-displacement loop of the damper is nearly rectangular in shape and independent of the excitation frequency. The coefficient of friction of the damper is approximately 0.85 when the clamping force on the damper is above 400 lbs. It was found that the friction force variation of the damper generated by piezoelectric actuators with 1000 Volts is approximately 90% of the expected value. The properties of the damper are insensitive to its ambient temperature and remain almost the same after being tested for more than 12,000 cycles.

• Structural Engineering and Mechanics
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• v.38 no.1
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• pp.27-37
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• 2011

This paper presents the results of a study on the capability of nonlinear quasi-static finite element modelling in simulating the hysteretic behaviour of CFRP and GFRP-retrofitted RC exterior beam-column joints under cyclic loads. Four specimens including two plain and two CFRP/GFRP-strengthened beam-column joints tested by Mahini and Ronagh (2004) and other researchers are modelled using ANSYS. Concrete in compression is defined by the modified Hognestad model and anisotropic multi-linear model is employed for modelling the stress-strain relations in reinforcing bars while anisotropic plasticity is considered for the FRP composite. Both concrete and FRP are modelled using solid elements whereas space link elements are used for steel bars considering a perfect bond between materials. A step by step load increment procedure to simulate the cyclic loading regime employed in the testing. An automatically reforming stiffness matrix strategy is used in order to simulate the actual seismic performance of the RC concrete after cracking, steel yielding and concrete crushing during the push and pull loading cycles. The results show that the hysteretic simulation for all specimens is satisfactory and therefore suggest that the numerical model can be used as an inexpensive tool to design of FRP-strengthened RC beam-column joints under cyclic loads.

• Steel and Composite Structures
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• v.13 no.5
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• pp.473-487
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• 2012

An experimental study was performed to investigate the seismic performance of steel reinforced concrete (SRC) special-shaped columns. For this purpose, 17 steel reinforced concrete special-shaped column specimens under low-cyclic reversed load were tested, load process and failure patterns of the specimens with different steel reinforcement were observed. The test results showed that the failure patterns of these columns include shear-diagonal compression failure, shear-bond failure, shear-flexure failure and flexural failure. The failure mechanisms and characteristics of SRC special-shaped columns were also analyzed. For different SRC special-shaped columns, based on the failure characteristics and mechanism observed from the test, formulas for calculating ultimate shear capacity in shear-diagonal compression failure and shear-bond failure under horizontal axis and oblique load were derived. The calculated results were compared with the test results. Both the theoretical analysis and the experimental results showed that, the shear capacity of T, L shaped columns under oblique load are larger than that under horizontal axis load, whereas the shear capacity of +-shaped columns under oblique load are less than that under horizontal axis load.

• Earthquakes and Structures
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• v.5 no.5
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• pp.527-552
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• 2013

Development of flexural yielding and large rotation ductilities in the plastic hinge zones of frame members is synonymous with the spread of bar reinforcement yielding into the supporting anchorage. Yield penetration where it occurs, destroys interfacial bond between bar and concrete and reduces the strain development capacity of the reinforcement. This affects the plastic rotation capacity of the member by increasing the contribution of bar pullout. A side effect is increased strains in the compression zone within the plastic hinge region, which may be critical in displacement-based detailing procedures that are linked to concrete strains (e.g. in structural walls). To quantify the effects of yield penetration from first principles, closed form solutions of the field equations of bond over the anchorage are derived, considering bond plastification, cover debonding after bar yielding and spread of inelasticity in the anchorage. Strain development capacity is shown to be a totally different entity from stress development capacity and, in the framework of performance based design, bar slip and the length of debonding are calculated as functions of the bar strain at the loaded-end, to be used in calculations of pullout rotation at monolithic member connections. Analytical results are explored parametrically to lead to design charts for practical use of the paper's findings but also to identify the implications of the phenomena studied on the detailing requirements in the plastic hinge regions of flexural members including post-earthquake retrofits.

• Steel and Composite Structures
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• v.28 no.4
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• pp.427-438
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• 2018

Static stability is a decisive factor in the design of domes. Stability-related external factors, such as load and supports, are incorporated into structural vulnerability theory by the definition of a relative rate of joint well-formedness ($r_r$). Hence, the instability mechanism of domes can be revealed. To improve stability, an optimization model against instability, which takes the maximization of the lowest $r_r$ ($r_{r,min}$) as the objective and the discrete member sections as the variables, is established with constraints on the design requirements and steel consumption. Optimizations are performed on two real-life Kiewitt-6 model domes with a span of 23.4 m and rise of 11.7 m, which are initially constructed for shaking table collapse test. Well-formedness analyses and stability calculation (via arc-length method) of the models throughout the optimization history demonstrate that this proposed method can effectively enhance $r_{r,min}$ and optimize the static stability of shell-like structures. Additionally, seismic performance of the optimum models subjected to the same earthquake as in the shaking table test is checked. The supplemental simulations prove that the optimum models are superior to the original models under earthquake load as well.

• Earthquakes and Structures
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• v.15 no.3
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• pp.243-251
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• 2018

The dynamic responses of a rocking wall-moment frame (RWMF) with a post-tensioned cable are investigated. The nonlinear equations of motions are developed, which can be categorized as a single-degree-of-freedom (SDOF) model. The model is validated through comparison of the rocking response of the rigid rocking wall (RRW) and displacement of the moment frame (MF) against that obtained from Finite Element analysis when subjected ground motion excitation. A comprehensive parametric analysis is carried out to determine the seismic performance factors of the RWMF systems under near-fault trigonometric pulse excitation. The horizontal displacement of the RWMF system is compared with that of MF structures without RRW, revealing the damping effect of the RRW. Frame displacement spectra excited by trigonometric pulses and recorded earthquake ground motions are constructed. The effects of pulse type, mass ratio, frame stiffness, and wall slenderness variations on the displacement spectra are presented. The paper shows that the coupling with a RRW has mixed results on suppressing the maximum displacement response of the frame.

• Journal of the Korean Society for Advanced Composite Structures
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• v.6 no.2
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• pp.85-90
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• 2015

The finite element stress analysis of large sized rectangular water tank structures made of stainless steel materials is carried out for various combined load cases. The combined load cases for a large size of 5,000ton are further determined using the specification(KS B6283) established from the Korean Standards Association. The changed water capacity due to the size of reservoirs could be heavily dependent for evaluating seismic effects, especially for large reservoirs. For the better numerical efficiency, the rectangular panels are modelled using the ANSYS ADPL module. The numerical results obtained for different load cases mainly show the effect of the interactions between the different load combination and other various parameters, for example, the water capacity, and different stainless steel materials. The structural performance for various load combinations is also evaluated.

• Journal of Korean Society of Steel Construction
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• v.15 no.4 s.65
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• pp.447-456
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• 2003

In this study, the proper shape of dampers was determined when the outside frame formed a rectangle. The proper shape of dampers is rectangular, having the same ratio as the outside frame. The design was based on the impact energy dissipated by the seismic performance of the mainly rectangular dampers. This study sought to compare both strength and energy dissipation between nonlinear analysis data and experimental data through load-displacement curves. The use of the ANSYS FEM software was suggested to analyze the nonlinear behavior of rectangular dampers subjected to cyclic loading. The target of this study was to determine what shape was efficient for rectangular tensile brace dampers. The safety of the developed rectangular dampers was also checked for better fabrication.

• Proceedings of the Earthquake Engineering Society of Korea Conference
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• 2001.04a
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• pp.387-393
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• 2001

Installing vibration control devices in the structure rises as a solution instead of increasing structural strength considering construction cost. Especially, viscoelastic dampers show excellent vibration control performance at low cost and are easy to install in existing structures compared with other control devices. Therefore, cost-effectiveness of structure with viscoelastic dampers needs to be evaluated. Previous cost-effectiveness evaluation method for the seismically isolated structure(Koh et al., 1999;2000)is applied on the building structure with viscoelastic dampers, which combines optimal design and cost-effectiveness evaluation for seismically isolated structures based on minimum life-cycle cost concept. Input ground motion is modeled in the form of spectral density function to take into account acceleration and site coefficients. Damping of the viscoelastic damper is considered by modal strain energy method. Stiffness of shear building and shear area of viscoelastic damper are adopted as design variables for optimization. For the estimation of failure probability, transfer function of the structure with viscoelastic damper for spectral analysis is derived from the equation of motion. Results reveal that cost-effectiveness of the structure with viscoelastic dampers is relatively high in how seismic region and stiff soil condition.

• Journal of the Earthquake Engineering Society of Korea
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• v.9 no.3 s.43
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• pp.69-75
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• 2005

In this paper, the comparative performance of repaired RC columns using steel and CFRP is presented. Also, the effect of transverse reinforcement ratio on the behavior of the steel and the CFRP repairing is investigated. Monotonic and cyclic load tests are conducted on nine RC column specimens with different repairing strategies and transverse reinforcement ratios to compare the load-displacement curves and the hysteretic behaviors. From the tests, it is observed that both steel and CFRP jacket repairings can significantly increase the displacement ductility and the ultimate load capacity of damaged columns.