• Structural Engineering and Mechanics
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• 제32권2호
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• pp.251-267
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• 2009

Reinforced concrete (RC) structures consist of two different materials: concrete and steel bar. The stress transfer behaviour between the two materials through bond plays an important role in the load-carrying capacity of RC structures, especially when they subject to lateral load such as blast and seismic load. Therefore, bond and slip between concrete and reinforcement bar will affect the response of RC structures under such loads. However, in most numerical analyses of blast-induced structural responses, the perfect bond between concrete and steel bar is often assumed. The main reason is that it is very difficult to model bond slip in the commercial finite element software, especially in hydrodynamic codes. In the present study, a one-dimensional slide line contact model in LS-DYNA for modeling sliding of rebar along a string of concrete nodes is creatively used to model the bond slip between concrete and steel bars in RC structures. In order to model the bond slip accurately, a new approach to define the parameters of the one-dimensional slide line model from common pullout test data is proposed. Reliability and accuracy of the proposed approach and the one-dimensional slide line in modelling the bond slip between concrete and steel bar are demonstrated through comparison of numerical results and experimental data. A case study is then carried out to investigate the bond slip effect on numerical analysis of blast-induced responses of a RC column. Parametric studies are also conducted to investigate the effect of bond shear modulus, maximum elastic slip strain, and damage curve exponential coefficient on blast-induced response of RC columns. Finally, recommendations are given for modelling the bond slip in numerical analysis of blast-induced responses of RC columns.

• Structural Monitoring and Maintenance
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• 제2권3호
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• pp.269-282
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• 2015

Civil structures should be designed with the lowest cost and longest lifetime possible and without service failure. The efficient and sustainable use of materials in building design and construction has always been at the forefront for civil engineers and environmentalists. Timber is one of the best contenders for these purposes particularly in terms of aesthetics; fire protection; strength-to-weight ratio; acoustic properties and seismic resistance. In recent years, timber has been used in commercial and taller buildings due to these significant advantages. It should be noted that, since the launch of the modern building standards and codes, a number of different structural systems have been developed to stabilise steel or concrete multistorey buildings, however, structural analysis of high-rise and multi-storey timber frame buildings subjected to lateral loads has not yet been fully understood. Additionally, timber degradation can occur as a result of biological decay of the elements and overloading that can result in structural damage. In such structures, the deficient members and joints require strengthening in order to satisfy new code requirements; determine acceptable level of safety; and avoid brittle failure following earthquake actions. This paper investigates performance assessment and damage assessment of older multi-storey timber buildings. One approach is to retrofit the beams in order to increase the ductility of the frame. Experimental studies indicate that Sprayed Fibre Reinforced Polymer (SFRP) repairing/retrofitting not only updates the integrity of the joint, but also increases its strength; stiffness; and ductility in such a way that the joint remains elastic. Non-linear finite element analysis ('pushover') is carried out to study the behaviour of the structure subjected to simulated gravity and lateral loads. A new global index is re-assessed for damage assessment of the plain and SFRP-retrofitted frames using capacity curves obtained from pushover analysis. This study shows that the proposed method is suitable for structural damage assessment of aged timber buildings. Also SFRP retrofitting can potentially improve the performance and load carrying capacity of the structure.

• Steel and Composite Structures
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• 제42권4호
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• pp.539-552
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• 2022

Concentrically braced frames (CBFs) possess high stiffness and strength against lateral loads; however, they suffer from low energy absorption capacity against seismic loads due to the susceptibility of CBF diagonal elements to bucking under compression loading. To address this problem, in this study, an innovative damper was proposed and investigated experimentally and numerically. The proposed damper comprises main plates and includes a flange plate angled at θ and a trapezius-shaped web plate surrounded by the plate at the top and bottom sections. To investigate the damper behaviour, dampers with θ = 0°, 30°, 45°, 60°, and 90° were evaluated with different flange plate thicknesses of 10, 15, 20, 25 and 30 mm. Dampers with θ = 0° and 90° create rectangular-shaped and I-shaped shear links, respectively. The results indicate that the damper with θ = 30° exhibits better performance in terms of ultimate strength, stiffness, overstrength, and distribution stress over the damper as compared to dampers with other angles. The hysteresis curves of the dampers confirm that the proposed damper acts as a ductile fuse. Furthermore, the web and flange plates contribute to the shear resistance, with the flange carrying approximately 80% and 10% of the shear force for dampers with θ = 30° and 90°, respectively. Moreover, dampers that have a larger flange-plate shear strength than the shear strength of the web exhibit behaviours in linear and nonlinear zones. In addition, the over-strength obtained for the damper was greater than 1.5 (proposed by AISC for shear links). Relevant relationships are determined to predict and design the damper and the elements outside it.

• Computers and Concrete
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• 제33권6호
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• pp.689-706
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• 2024

This study is aimed at identifying structural element stiffness influence on vertical earthquake response of mid-rise R/C frame buildings. To this aim, a mid-rise RC building structure is designed as per the new Turkish Seismic Code for Buildings-2018, and 3D FE model of the building is established. Based on the established FE model, a total number of six buildings are considered depending on certain percentage increase in beam, slab, and column. The time-history response analyses (THA) are performed separately for only horizontal (H) and horizontal +vertical (H+V) earthquake motions to make a comparison between the load cases. The analysis results are presented comparatively in terms of the monitoring parameters of the base overturning moment (M_o), the top-story lateral displacement (d_L) and the top-story vertical displacement (d_V). The obtained results reveal that the base overturning moment and the top-story vertical displacement are affected by vertical earthquake motion regardless of the increase in the dimension of beam, slab, and column. However, vertical earthquake motion is not effective on the top-story lateral displacement due to no change between H and H+V load. The dimensional increase in either slab or beam leads to a considerable increase in the base overturning moment and the top-story vertical displacement while causing decrease in the top-story lateral displacement. In addition, the dimensional increase in column has a positive effect on the decrease in the monitoring parameters of the base overturning moment (M_o), the top-story lateral displacement (d_L) and the top-story vertical displacement (d_V).

• 지구물리와물리탐사
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• 제9권1호
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• pp.60-66
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• 2006

세 개의 서로 다른 사암 샘플들 -두 개의 합성 샘플과 한 개의 현장 샘플- 에 대해 현장 저류층의 대표적인 구속압력과 공극압력하에서 초음파 시험이 수행되었다. 세가지 사암 샘플들은 (a) 캘사이트 시멘트(calcite intergranula. cement (CIPS))로 만든 합성사암, (b) 실리카 시멘트(silica intergranular cement)로 만든 합성 사암 (c) Otway Basin 의 Boggy Creek 1 시추공에서 시도되는 $CO_2$ 파일럿 프로젝트의 대상 암석층 중 Waarre 층으로부터 추출한 코아 샘플로 구성되어 있다. 공극률은 각각 32%, 33%, 26%이다. 초기시험은 실내건조(room-dried) 상태에 있는 코아들에 대해 구속응력을 5 MPa 씩 단계별로 65 MPa 까지 증가시키며 이루어졌다. 그리고 나서 모든 코아들에 처음에는 온도 $22^{\circ}C$에서 6 MPa 공극압력으로 기체상의 $CO_2$를, 그 다음에는 온도 $22^{\circ}C$ 에서 7 MPa 부터 17 MPa 까지 5 MPa 씩 증가시키면서 액체상의 $CO_2$를 주입하였다. 구속응력은 10MPa부터 65 MPa까지 달리 하였다. P와 S 초음파 파형들이 유효응력이 증가할 때마다 기록되었다. 속도-유효응력 반응들이 P 파와 S 파에 대해 실험 자료들로부터 계산되었으며, 감쇠(1/Qp)들은 스펙트럼 비 방법을 이용하여 파형들로부터 계산되었다. 각각의 사암들에 대한 이론적인 속도-유효응력 계산은 $CO_2$ 압력-밀도 와 $CO_2$ 체적계수-압력 상 다이어그램(phasediagram), Gassmann 유효 매질 이론(effective medium theory)을 이용하여 구하였다. 기체상의 $CO_2$ 주입은 속도-유효응력에서 건조상태(공기로 포화된 상태)에 비해 거의 무시할만한 변화를 가져왔다. 다양한 공극압력에서 액체상의 $CO_2$ 주입은 공기로 포화된 상태에 비해 속도-유효응력 반응을 평균 약 8% 정도 낮게 한다. 실험자료들은 높은 유효응력에서 Gassmann 계산들과 일치한다. 이러한 이론과 일치하는 "임계" 유효응력은 사암의 종류에 따라 달라진다. 이 차이는 각각의 사암 종류의 미세구조에서 미세 균열 수의 차이에 기인한 것이라 생각된다. 높은 유효응력에서의 이론과 의미있게 일치하였으며, $CO_2$ 주입 시 현장에서의 탄성파 거동을 예상하는데 있어서 어느 정도 확신을 준다.