• Korean Journal of Materials Research
• /
• v.22 no.9
• /
• pp.454-458
• /
• 2012

Various adhesive materials are used in flip chip packaging for electrical interconnection and structural reinforcement. In cases of COF(chip on film) packages, low temperature bonding adhesive is currently needed for the utilization of low thermal resistance substrate films, such as PEN(polyethylene naphthalate) and PET(polyethylene terephthalate). In this study, the effects of anhydride and dihydrazide hardeners on the low-temperature snap cure behavior of epoxy based non-conductive pastes(NCPs) were investigated to reduce flip chip bonding temperature. Dynamic DSC(differential scanning calorimetry) and isothermal DEA(dielectric analysis) results showed that the curing rate of MHHPA(hexahydro-4-methylphthalic anhydride) at $160^{\circ}C$ was faster than that of ADH(adipic dihydrazide) when considering the onset and peak curing temperatures. In a die shear test performed after flip chip bonding, however, ADH-containing formulations indicated faster trends in reaching saturated bond strength values due to the post curing effect. More enhanced HAST(highly accelerated stress test) reliability could be achieved in an assembly having a higher initial bond strength and, thus, MHHPA is considered to be a more effective hardener than ADH for low temperature snap cure NCPs.

• Journal of the Korean Society for Aeronautical & Space Sciences
• /
• v.36 no.1
• /
• pp.72-78
• /
• 2008

In this study, advanced (fluid-structure interaction (FSI)) analysis system has been developed in order to predict turbine cascade performance with blade deformation effect due to aerodynamic loads. Intereference effects due to the relative movement of the rotor cascade with respect to the stator cascade are also considered. Reynolds-averaged Navier-Stokes equations with one equation Spalart-Allmaras and two-equation k-ω SST turbulence models are solved to accurately predict fluid dynamic loads considering flow separation effects. A fully implicit time marching scheme based on the (coupled Newmark time-integration method) with high artificial damping is efficiently used to compute the complex fluid-structure interaction problem. Predicted aerodynamic performance considering structural deformation effect of the blade shows somewhat different results compared to the case of rigid blade model. Cascade performance evaluations for different elastic axis positions are importantly presented and its aeroelastic effects are investigated.

• Earthquakes and Structures
• /
• v.10 no.4
• /
• pp.939-963
• /
• 2016

According to the new directives about the rational and efficient use of energy, thermal bridges in buildings have to be avoided, and the thermal insulation (TI) layer should run without interruptions all around the building - even under its foundations. The paper deals with the seismic response of multi-storeyed reinforced concrete (RC) frame building structures founded on an extruded polystyrene (XPS) layer placed beneath the foundation slab. The purpose of the paper is to elucidate the problem of buildings founded on a TI layer from the seismic resistance point of view, to assess the seismic behaviour of such buildings, and to search for the critical parameters which can affect the structural and XPS layer response. Nonlinear dynamic and static analyses were performed, and the seismic response of fixed-base (FB) and thermally insulated (TI) variants of nonlinear RC building models were compared. Soil-structure interaction was also taken into account for different types of soil. The results showed that the use of a TI layer beneath the foundation slab of a superstructure generally induces a higher peak response compared to that of a corresponding system without TI beneath the foundation slab. In the case of stiff structures located on firm soil, amplification of the response might be substantial and could result in exceedance of the superstructure's moment-rotation plastic hinge capacities or allowable lateral roof and interstorey drift displacements. In the case of heavier, slenderer, and higher buildings subjected to stronger seismic excitations, the overall response is governed by the rocking mode of oscillation, and as a consequence the compressive strength of the XPS could be insufficient. On the other hand, in the case of low-rise and light-weight buildings, the friction capacity between the layers of the applied TI foundation set might be exceeded so that sliding could occur.

• Structural Engineering and Mechanics
• /
• v.58 no.2
• /
• pp.199-216
• /
• 2016

A large number of bridges were built several decades ago, and most of which have gradually suffered serious deteriorations or damage due to the increasing traffic loads, environmental effects, and inadequate maintenance. However, very few studies were conducted to investigate the vibration behaviors of a damaged bridge under moving vehicles. In this paper, the vibration behaviors of such vehicle-bridge system are investigated in details, in which the effects of the concrete cracks and bridge surface roughness are particularly considered. Specifically, two vehicle models are introduced, i.e., a simplified four degree-of-freedoms (DOFs) vehicle model and a more complex seven DOFs vehicle model, respectively. The bridges are modeled in two types, including a single-span uniform beam and a full scale reinforced concrete high-pier bridge, respectively. The crack zone in the reinforced concrete bridge is considered by a damage function. The bridge and vehicle coupled equations are established by combining the equations of motion of both the bridge and vehicles using the displacement relationship and interaction force relationship at the contact points between the tires and bridge. The numerical simulations and verifications show that the proposed modeling method can rationally simulate the vibration behaviors of the damaged bridge under moving vehicles; the effect of cracks on the impact factors is very small and can be neglected for the bridge with none roughness, however, the effect of cracks on the impact factors is very significant and cannot be neglected for the bridge with roughness.

• Earthquakes and Structures
• /
• v.12 no.1
• /
• pp.13-21
• /
• 2017

Recent seismic events occurred in Italy (Emilia-Romagna 2012, Abruzzo 2009) and worldwide (New Zealand 2010 and 2011) highlighted some of the weaknesses of precast concrete industrial buildings, especially those related to the connecting systems traditionally employed to fasten the cladding panels to the internal framing. In fact, one of the most commons fails it is possible to observe in such structural typologies is related to the out-of-plane collapse of the external walls due to the unsatisfactory behaviour of the connectors used to join the panels to the perimeter beams. In this work, the strengthening of a traditional industrial building, assumed as a case study, made by precast reinforced concrete is proposed by the adoption of a dual system allowing the reinforcement of the structure by acting both internally; by pendular columns and, externally, on the walls. In particular, traditional connections at the top of the walls are substituted by devices able to work as a slider with vertical axis while, the bottom of the walls is equipped with two or more hysteretic dampers working on the uplift of the cladding panels occurring under seismic actions. By means of this approach, the structure is stiffened; obtaining a reduction of the lateral drifts under serviceability limit states. In addition, its seismic behaviour is improved due to the additional source of energy dissipation represented by the dampers located at the base of the walls. The effectiveness of the suggested retrofitting approach has been checked by comparing the performance of the retrofitted structure with those of the structure unreinforced by means of both pushover and Incremental Dynamic Analyses (IDA) in terms of behaviour factor, assumed as a measure of the ductility capacity of the structure.

• Journal of the Korea Institute of Information and Communication Engineering
• /
• v.13 no.11
• /
• pp.2373-2377
• /
• 2009

In this paper, the threshold voltage characteristics have been analyzed using three dimensional Poisson's equation for FinFET. The FinFET is extensively been studing since it can reduce the short channel effects as the nano device. We have presented the short channel effects such as subthreshold swing and threshold voltage for PinFET, using the analytical three dimensional Poisson's equation. We have analyzed for channel length, thickness and width to consider the structural characteristics for FinFET. Using this model, the subthreshold swing and threshold voltage have been analyzed for FinFET since the potential and transport model of this analytical three dimensional Poisson's equation is verified as comparing with those of the numerical three dimensional Poisson's equation.

• Journal of the Earthquake Engineering Society of Korea
• /
• v.3 no.3
• /
• pp.21-32
• /
• 1999

A ground motion resulting from the destructive earthquakes can subject reinforced concrete members to very large forces. The reinforced concrete shear walls are designed as earthquake-resistant members of building structure in order to prevent severe damage due to the ground motions. The current research activities on seismic behavior of reinforced concrete member under ground motions have been limited to the shaking table test or equivalent static cyclic test and the obtained results have been summarized and proposed for the seismic design retrofit of structural columns or shear walls. The present study predicted the seismic response and failure behavior of reinforced concrete shear wall subjected to base acceleration using the finite element method. A decrease in strength and stiffness, yielding of reinforcing bar, and repetition of crack closing and opening due to seismic load with cyclic nature are accompanied by the crack which is necessarily expected to take place in concrete member. In this study the nonlinear material models for concrete and reinforcing bar based on biaxial stress field and algorithm of dynamic analysis were combined to construct the analytical program using the finite element method. The analytical seismic response and failure behaviors of reinforced concrete shear wall subjected to several base accelerations were compared with reliable experimental result.

• Journal of the Korea Concrete Institute
• /
• v.28 no.2
• /
• pp.187-196
• /
• 2016

The current seismic design code prescribes that coupling beam should be reinforced using diagonally bundled bars. However, the use of a diagonally bundled bars has a negative effect on constructability and economic efficiency. In the present study, the seismic performance of 4 coupling beams with the different details of reinforcement was evaluated through a cyclic reversal loading test. The specimens were constructed to measure the results of the experimental variable regarding the details of shear reinforcement. Next, the seismic performance of the coupled shear wall system evaluated by methods proposed in the FEMA P695. The cyclic reversal loading test results of this study showed that the performance of coupling beams with relaxed reinforcement detail was almost similar to that of a coupling beam with the ACI detail and meet the level which requested from standard. The result of the seismic evaluation showed that all coupling beams are satisfied with the design code and seismic performance.

• International Journal of Concrete Structures and Materials
• /
• v.9 no.3
• /
• pp.345-367
• /
• 2015

Past earthquakes have signaled the increased collapse vulnerability of mainshock-damaged bridge piers and urgent need of repair interventions prior to subsequent cascading hazard events, such as aftershocks, triggered by the mainshock (MS). The overarching goal of this study is to quantify the collapse vulnerability of mainshock-damaged substandard RC bridge piers rehabilitated with different repair jackets (FRP, conventional thick steel and hybrid jacket) under aftershock (AS) attacks of various intensities. The efficacy of repair jackets on post-MS resilience of repaired bridges is quantified for a prototype two-span single-column bridge bent with lap-splice deficiency at column-footing interface. Extensive number of incremental dynamic time history analyses on numerical finite element bridge models with deteriorating properties under back-to-back MS-AS sequences were utilized to evaluate the efficacy of different repair jackets on the post-repair behavior of RC bridges subjected to AS attacks. Results indicate the dramatic impact of repair jacket application on post-MS resilience of damaged bridge piers-up to 45.5 % increase of structural collapse capacity-subjected to aftershocks of multiple intensities. Besides, the efficacy of repair jackets is found to be proportionate to the intensity of AS attacks. Moreover, the steel jacket exhibited to be the most vulnerable repair intervention compared to CFRP, irrespective of the seismic sequence (severe MS-severe or moderate AS) or earthquake type (near-fault or far-fault).

• Journal of the Earthquake Engineering Society of Korea
• /
• v.17 no.1
• /
• pp.1-10
• /
• 2013

In order to predict inelastic displacement response without nonlinear dynamic analysis, the equal displacement rule can be used for the structures with longer natural periods than the characteristic period, $T_g$, of earthquake record. In the period range longer than $T_g$, peak displacement responses of elastic systems are equal or larger than those of inelastic systems. In the period range shorter than $T_g$, opposite trend occurs. In the equal displacement rule, it is assumed that peak displacement of inelastic system with longer natural period than $T_g$ equals to that of elastic system with same natural period. The equal displacement rule is very useful for seismic design purpose of structures with longer natural period than $T_g$. In the period range shorter than $T_g$, the peak displacement of inelastic system can be simply evaluated from the peak displacement of elastic system by using the inelastic displacement ratio, which is defined as the ratio of the peak inelastic displacement to the peak elastic displacement. Smooth hysteretic behavior is more similar to actual response of real structural system than a piece-wise linear hysteretic behavior such as bilinear or stiffness degrading behaviors. In this paper, the inelastic displacement ratios of the smooth hysteretic behavior system are evaluated for far-fault and near-fault earthquakes. The simple formula of inelastic displacement ratio considering the effect of $T_g$ is proposed.