• Title, Summary, Keyword: Base shear force

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Shear behavior of exposed column base connections

  • Cui, Yao
    • Steel and Composite Structures
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    • v.21 no.2
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    • pp.357-371
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    • 2016
  • Column base connections are critical components in steel structures because they transfer axial forces, shear forces and moments to the foundation. Exposed column bases are quite commonly used in low- to medium-rise buildings. To investigate shear transfer in exposed column base plates, four large scale specimens were subjected to a combination of axial load (compression or tension) and lateral shear deformations. The main parameters examined experimentally include the number of anchor rod, arrangement of anchor rod, type of lateral loading, and axial force ratio. It is observed that the shear resisting mechanism of exposed column base changed as the axial force changed. When the axial force is in compression, the resisting mechanism is rotation type, and the shear force will be resisted by friction force between base plate and mortar layer. The specimens could sustain inelastic deformation with minimal strength deterioration up to column rotation angle of 3%. The moment resistance and energy dissipation will be increased as the number of anchor rods increased. Moreover, moment resistance could be further increased if the anchor rods were arranged in details. When the axial force is in tension, the resisting mechanism is slip type, and the shear force will be resisted by the anchor rods. And the shear resistance was reduced significantly when the axial force was changed from compression to tension. The test results indicated that the current design approach could estimate the moment resistance within reasonable acceptance, but overestimate the shear resistance of exposed column base.

Effects of Higher Modes on the Response Spectra of High-rise Buildings considering the Kinematic Interaction of a Foundation System (기초체계의 운동학적 상호작용을 고려한 고층건물의 응답스펙트럼에 미치는 고차모드의 영향)

  • Kim, Yong-Seok
    • Journal of the Earthquake Engineering Society of Korea
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    • v.19 no.3
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    • pp.85-92
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    • 2015
  • Response spectra of a building are made with a SDOF system taking into account a first mode shape, even though higher modes may affect on the dynamic responses of a high-rise building. A soft soil layer under a building also affects on the responses of a building. In this study, seismic responses of a MDOF system were investigated to examine the effects of higher modes on the response of a tall building by comparing them with those of a SDOF system including the kinematic interaction effect. Study was performed using a pseudo 3D finite element program with seven bedrock earthquake records downloaded from the PEER database. Effects of higher modes on the seismic responses of a tall building were investigated for base shear force and base moment of a MDOF system including story shear forces and story moments. Study results show that higher modes of a MDOF system contribute to a reduction of base shear force up to 1/4-1/5 of KBC and base moment. The effect of higher modes is more significant on the base shear force than on the base moment. Maximum story shear force and moment occurred at the top part of a building rather than at a base in the cases of tall buildings differently from short buildings, and higher modes of a tall building affected on the base forces making them almost constant at the base. A soft soil layer also affects some on the base shear force of a high-rise building independently on the soft soil type, but a soft soil effect is prominent on the base moment.

Design Shear Force Reduction Factor of Upper Structure in Seismic Base-isolated System Considering Response Acceleration Decrement Effect (면진구조의 응답가속도 감소효과를 고려한 상부구조의 설계전단력 저감계수)

  • Chen, Hao;Oh, Sang-Hoon
    • Journal of the Architectural Institute of Korea Structure & Construction
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    • v.35 no.7
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    • pp.165-170
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    • 2019
  • The structural damage caused by earthquake to the upper structure of seismic base-isolated system can be suppressed effectively because it is designed to concentrate the input energy on the seismic isolation floor. Further, the response acceleration of seismic base-isolated system can be greatly reduced compared to the seismic structure because of the long period, which means that the design shear force of the seismic base-isolated system can be reduced appropriately. However, when the design shear force is determined to be reduced, the design stiffness will decrease, and the response acceleration will increase oppositely. Therefore, for finding the extent to which the design shear force of the upper structure can be reduced, this paper considered the seismic base-isolated structure as the analytical model and proposed the design shear force reduction factor of the base-isolated structure through the dynamic response analysis, while considering the decrement effect of response acceleration. The research result shows that the response acceleration of the isolated the upper structure can be reduced by 50%~70% of the seismic structure under the same design conditions, and the design shear force can be reduced by up to 40%. By increasing the design stiffness over to 1.8 times of the original design value, the design shear force can be reduced to the same extent as the response acceleration can be reduced compared to the seismic structure.

Experimental Evaluation on the Base Shear Force of a Bas Isolation System (면진구조물의 기초전단력에 대한 실험적 평가)

  • 김영중
    • Proceedings of the Earthquake Engineering Society of Korea Conference
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    • pp.169-177
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    • 1999
  • The base shear force and the overturning moment are important factors for the earthquake design of a structure. These should be predicted exactly especially when the nonlinear seismic isolation bearings are used against earthquake motions. Generally these are derived by the acceleration responses of a structure with the he assumed masses. However these can be contaminated by the noise in the measured responses and the uncertainty of assumed masses. This paper presents the results of the derived base shear force and overturning moment compared with the measured results by multi-axis load cells. Also discussions are made on the cross-coupling effects of the multi-axis load cell.

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Comparison of bracket bond strength in various directions of force (교정용 브라켓에 가해지는 힘의 방향에 따른 결합강도의 비교)

  • Lee, Hyun-Jung;Lee, Hyung-Soon;Jeon, Young-Mi;Kim, Jong-Ghee
    • The korean journal of orthodontics
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    • v.33 no.5
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    • pp.359-370
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    • 2003
  • The purpose of this study was to evaluate the bond strength of orthodontic brackets bonded to metal bar with chemically cured adhesive (Ortho-one, Bisco Co, USA) in various types and directions of force application. Three types of metal bracket with different bracket base configurations; Micro-Loc base(Tomy Co, Japan), Chessboard base(Daesung Co, Korea), Non-etched Foil-Mesh base(Dentaurum, Germany); were used in this study. Peel, shear, tensile bond strengths were measured by universal testing machine and compared each other. The peel force directions applied were $0^{\circ},\;15^{\circ},\;30^{\circ},\;45^{\circ},\;60^{\circ},\;75^{\circ},\;90^{\circ}$ And then, in consideration of the different surface area of the bracket bases, the bond strength Per unit area were calculated and compared. The results obtained were summarized as follows: 1. The bond strengths according to the types and the directions of the forces were greatest at the shear forces in all three bracket base configuration groups(p<0.01). 2. As the peel force direction grew higher in degree, peel bond strength decreased. The Patterns of peel bond strength change according to force direction was similar in all three bracket base configurations. The minimum bond strength was 60 degree-peel bond strengths in all three bracket base configurations. 3. In Micro-Loc base group, minimum peel bond strength$(_{60}PBS)$ was in $29\%$ level of shear bond strength and $52\%$ level of tensile bond strength. In Chessboard base group, $_{60}PBS$ was in $34\%$ level of shear bond strength and $61\%$ level of tensile bond strength. In Non-etched Foil-Mesh base group, $_{60}PBS$ was in $34\%$ level of shear bond strength and $55\%$ level of tensile bond strength. 4. The bond strengths per unit area were lowest in Non-etched Foil-Mesh base group and highest in Chessboard base group(p<0.05). However, there were no differences in shear bond strength, tensile bond strength, $75^{\circ}\;and\;90^{\circ}$ per unit area between Micro-Loc and Chessboard base groups.

Shear Strength Incorporated with Internal Force State Factor in RC Slender Beams (내력상태계수 도입을 통한 RC보의 전단강도분석)

  • 정제평;김희정;김우
    • Proceedings of the Korea Concrete Institute Conference
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    • pp.912-917
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    • 2003
  • In this paper a new truss modeling technique for describing the beam shear resistance mechanism is proposed based on the reinterpretation of the well-known relationship between shear and the rate of change of bending moment in a reinforced concrete beam subjected to combined shear and moment loads. The core of the model is that a new perspective on the shear resistance can be gained by viewing the internal stress filed in terms of the superposition of two base components of shear resistance; arch action and beam action. The arch action can be described as a simple tied-arch which is consisted of a curved compression chord and a tension tie of the longitudinal steel, while the beam action between the two chords can be modeled as a membrane shearing element with forming a smeared truss action. The compatibility of deformation associated to the two action is taken into account by employing an experimental factor or internal state force factor a. Then the base equation of V=dM/dx is numerically duplicated. The new model was examined by the 362 experimental results. The shear strength predicted by the internal force state factor a show better correlation with the tested values than the present shear design.

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Determination of critical excitation in seismic analysis of structures

  • Kamgar, Reza;Rahgozar, Reza
    • Earthquakes and Structures
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    • v.9 no.4
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    • pp.875-891
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    • 2015
  • Earthquake can occur anywhere in the world and it is essential to design important members in special structures based on maximum possible forces that can be produced in them under severe earthquake. In addition, since the earthquake is an accidental phenomena and there are no similar earthquakes, therefore the possibility of strong earthquakes should be taken into account in earthquake-resistant design of important structures. Based on this viewpoint, finding the critical acceleration which maximizes internal forces is an essential factor in structural design. This paper proposes critical excitation method to compute the critical acceleration in design of important members in special structures. These critical accelerations are computed so that the columns' internal shear force at the base of the structure at each time step is maximized under constraints on ground motion. Among computed critical accelerations (of each time step), the one which produces maximum internal shear force is selected. A numerical example presents to show the efficiency of critical excitation method in determining the maximum internal shear force and base moment under variety of constraints. The results show that these method can be used to compute the resonant earthquake which have large enough effective duration of earthquake strong motion (between 12.86 sec to 13.38 sec) and produce the internal shear force and base moment for specific column greater than the same value for selected earthquakes in constructing the critical excitation (for different cases about 2.78 to 1.29 times the San Fernando earthquake). Therefore, a group of them can be utilized in developing the response spectrum for design of special structures.

Seismic force evaluation of RC shear wall buildings as per international codes

  • Jayalekshmi, B.R.;Chinmayi, H.K.
    • Earthquakes and Structures
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    • v.10 no.1
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    • pp.191-209
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    • 2016
  • Seismic codes are the best available guidance on how structures should be designed and constructed to ensure adequate resistance to seismic forces during earthquakes. Seismic provisions of Indian standard code, International building code and European code are applied for buildings with ordinary moment resisting frames and reinforced shear walls at various locations considering the effect of site soil conditions. The study investigates the differences in spectral acceleration coefficient ($S_a/g$), base shear and storey shear obtained following the seismic provisions in different codes in the analysis of these buildings. Study shows that the provision of shear walls at core in low rise buildings and at all the four corners in high rise buildings gives the least value of base shear.

Dynamic Analysis for Base Isolated Structure with Shear Keys (쉬어키를 가진 면진건축물의 동적해석)

  • Han, Duck-Jeon;Kim, Tae-Ho
    • Journal of Korean Association for Spatial Structures
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    • v.7 no.1
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    • pp.45-53
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    • 2007
  • Recently, high-rise base isolated building structures with shear keys are often constructed in Japan which frequently occurs earthquakes. High-rise buildings are less damaged because those buildings have longer natural period than md or low rise buildings. The shear key is device that prevents the base isolators operating by the wind loads not by the earthquake loads. In case of big base shear force acts on the shear keys by earthquake, this device is broken and base isolator is operated. Therefore, seismic intensities play a role in acting on the shear keys. If wind loads are hither than the earthquake loads, the shear keys designed by wind loads are not operated in earthquakes. So, the requirements of shear keys in high-rise base isolated building structures must be examined in Korea with moderate seismic legions. In this study shear keys are applied with 5 and 15 stories base isolated building structures and investigated their dynamic responses to original and 1/2 scale downed El Centre NS(1940) ground motions. The results show that the yield shear forces of the shear keys affect significantly the dynamic behavior of base isolated building structures

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Role of membrane forces in seismic design of reinforced concrete liquid storage structures

  • Schnobrich, W.C.
    • Structural Engineering and Mechanics
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    • v.10 no.6
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    • pp.533-543
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    • 2000
  • To prevent major cracking and failure during earthquakes, it is important to design reinforced concrete liquid storage structures, such as water and fuel storage tanks, properly for the hydrodynamic pressure loads caused by seismic excitations. There is a discussion in recent Codes that most of the base shear applied to liquid containment structures is resisted by inplane membrane shear rather than by transverse flexural shear. The purpose of this paper is to underline the importance of the membrane force system in carrying the base shear produced by hydrodynamic pressures in both rectangular and cylindrical tank structures. Only rigid tanks constrained at the base are considered. Analysis is performed for both tall and broad tanks to compare their behavior under seismic excitation. Efforts are made to quantify the percentage of base shear carried by membrane action and the consequent procedures that must be followed for safe design of liquid containing storage structures.