• 한국지진공학회논문집
• /
• 제13권3호
• /
• pp.51-65
• /
• 2009

콘크리트 교량의 합리적인 내진설계는 지진이 발생할 때 연성파괴메커니즘이 유도될 수 있도록 적절하게 교각 연성도를 확보하는 것이다. 현행 기준에서는 이를 위해 휨모멘트의 설계지진력을 산정할 때 응답수정계수를 도입하고 있으며, 연성도 확보를 위한 횡방향철근량을 규정하고 있다. 그러나, 이러한 내진규정은 일반적으로 단면이 크게 설계되는 우리나라에서는 횡방향철근이 과다하게 산정되는 비합리적이었다. 이를 개선하기 위해 소요연성도에 기반한 새로운 내진설계법이 제안되었으나 거동특성과 횡방향철근의 유효구속력이 다른 중공단면에 적용하기 위해서는 향후 많은 검증과 보완이 필요하다. 이에 본 연구에서는 축방향철근의 겹침이음과 횡방향철근량을 변수로 한 중공단면기둥을 제작하여 준정적 재하실험을 수행하였으며 다양하게 내진거동특성을 분석하고 내진성능을 확인하였다. 본 연구 결과는 향후 중공단면교각의 연성도(성능)기반 내진설계를 위한 기초자료로 제공될 수 있다.

• Earthquakes and Structures
• /
• 제9권1호
• /
• pp.49-71
• /
• 2015

The present paper aims at evaluating damage and collapse behavior of low-rise buildings with unidirectional mass irregularities in plan (torsional buildings). In previous earthquake events, such buildings have been exposed to extensive damages and even total collapse in some cases. To investigate the performance and collapse behavior of such buildings from probabilistic points of view, three-dimensional three and six-story reinforced concrete models with unidirectional mass eccentricities ranging from 0% to 30% and designed with modern seismic design code provisions specific to intermediate ductility class were subjected to nonlinear static as well as extensive nonlinear incremental dynamic analysis (IDA) under a set of far-field real ground motions containing 21 two-component records. Performance of each model was then examined by means of calculating conventional seismic design parameters including the response reduction (R), structural overstrength (${\Omega}$) and structural ductility (${\mu}$) factors, calculation of probability distribution of maximum inter-story drift responses in two orthogonal directions and calculation collapse margin ratio (CMR) as an indicator of performance. Results demonstrate that substantial differences exist between the behavior of regular and irregular buildings in terms of lateral load capacity and collapse margin ratio. Also, results indicate that current seismic design parameters could be non-conservative for buildings with high levels of plan eccentricity and such structures do not meet the target "life safety" performance level based on safety margin against collapse. The adverse effects of plan irregularity on collapse safety of structures are more pronounced as the number of stories increases.

• Steel and Composite Structures
• /
• 제19권6호
• /
• pp.1449-1466
• /
• 2015

Mixed structures consist of two parts: a lower part and an upper part. The lower part is usually made of concrete while the upper part is made of steel. Analyzing these structures is complicated and code-based design of them has many associated problems. In this research, the seismic behavior of mixed structures which have reinforced concrete frames and shear walls in their lower storeys and steel frames with bracing in their upper storeys were studied. For this purpose, seventeen structures in three groups of 5, 9 and 15 storey structures with different numbers of concrete and steel storeys were designed. Static pushover analysis, linear dynamic analysis and incremental dynamic analysis (IDA) using 15 earthquake records were performed by OpenSees software. Seismic parameters such as period, response modification factor and ductility factor were then obtained for the mixed (hybrid) structures using more than 4600 nonlinear dynamic analysis and used in the regression analysis for achieving proper formula. Finally, some formulas, effective in designing such structures, are presented for the mentioned parameters. According to the results obtained from this research, the response modification factor values of mixed structures are lower compared to those of steel or concrete ones with the same heights. This fact might be due to the irregularities of stiffness, mass, etc., at different heights of the structure. It should be mentioned that for the first time, the performance and seismic response of such structures were studied against real earthquake accelerations using nonlinear dynamic analysis, andresponse modification factor was obtained by IDA.

• Steel and Composite Structures
• /
• 제39권3호
• /
• pp.337-352
• /
• 2021

The study presented experimental and numerical investigation on the seismic performance of steel reinforced concrete (SRC) L-shaped column- reinforced concrete (RC) beam joints. Various parameters described as steel configuration form, axial compressive ratio, loading angle, and the existence of slab were examined through 4 planar joints and 7 spatial joints. The characteristics of the load-displacement response included the bearing capacity, ductility, story drift ratio, energy-dissipating capacity, and stiffness degradation were analyzed. The results showed that shear failure and flexural failure in the beam tip were observed for planar joints and spatial joint, respectively. And RC joint with slab failed with the plastic hinge in the slab and bottom of the beam. The results indicated that hysteretic curves of spatial joints with solid-web steel were plumper than those with hollow-web specimens. The capacity of planar joints was higher than that of space joints, while the opposite was true for energy-dissipation capacity and ductility. The high compression ratio contributed to the increase in capacity and initial stiffness of the joint. The elastic and elastic-plastic story deformation capacity of L-shaped column frame joints satisfied the code requirement. A design formula of joint shear resistance based on the superposition theory and equilibrium plasticity truss model was proposed for engineering application.

• Earthquakes and Structures
• /
• 제19권6호
• /
• pp.485-498
• /
• 2020

Non-ductile detailing of Reinforced Concrete (RC) frames may lead to structural failure when the structure is subjected to earthquake response. These designs are generally encountered in older RC frames constructed prior to the introduction of the ductility aspect. The failure observed in the beam-column joints (BCJs) and accompanied by excessive column damage. This work examines the seismic performance and failure mode of non-ductile designed RC columns and exterior BCJs. The design was based on the actual building in Tainan City, Taiwan, that collapsed due to the 2016 Meinong earthquake. Hence, an experimental investigation using cyclic testing was performed on two columns and two BCJ specimens scaled down to 50%. The experiment resulted in a poor response in both specimens. Excessive cracks and their propagation due to the incursion of the lateral loads could be observed close to the top and bottom of the specimens. Joint shear failure appeared in the joints. The ductility of the member was below the desired value of 4. This is the minimum number required to survive an earthquake with a similar magnitude to that of El Centro. The evidence provides an understanding of the seismic failure of poorly detailed RC frame structures.

• Steel and Composite Structures
• /
• 제11권4호
• /
• pp.273-290
• /
• 2011

In current ductility-based earthquake-resistant design, the estimation of design forces continues to be carried out with the application of response modification factors on elastic design spectra. It is well-known that the response modification factor (R) takes into account the force reduction, strength, redundancy, and damping of structural systems. The key components of the response modification factor (R) are force reduction ($R_{\mu}$) and strength ($R_S$) factors. However, the response modification and strength factors for structural systems presented in design codes were based on professional judgment and experiences. A numerical study has been accomplished to evaluate force reduction, strength, and response modification factors for special steel moment resisting frames. A total of 72 prototype steel frames were designed based on the recommendations given in the AISC Seismic Provisions and UBC Codes. Number of stories, soil profiles, seismic zone factors, framing systems, and failure mechanisms were considered as the design parameters that influence the response. The effects of the design parameters on force reduction ($R_{\mu}$), strength ($R_S$), and response modification (R) factors were studied. Based on the analysis results, these factors for special steel moment resisting frames are evaluated.

• Earthquakes and Structures
• /
• 제6권5호
• /
• pp.561-580
• /
• 2014

After strong earthquakes conventional frames used worldwide in multi - story steel buildings (e.g. moment resisting frames) are not well positioned according to reparability. Two innovative systems for seismic resistant steel frames incorporated with dissipative fuses were developed within the European Research Program "FUSEIS" (Vayas et al. 2013). The first, FUSEIS1, resembles a vertical Vierendeel beam and is composed of two closely spaced strong columns rigidly connected to multiple beams. In the second system, FUSEIS2, a discontinuity is introduced in the composite beams of a moment resisting frame and the dissipative devices are steel plates connecting the two parts. The FUSEIS system is able to dissipate energy by means of inelastic deformations in the fuses and combines ductility and architectural transparency with stiffness. In case of strong earthquakes damage concentrates only in the fuses which behave as self-centering systems able to return the structure to its initial undeformed shape. Repair work after such an event is limited only to replacing the fuses. Experimental and numerical investigations were performed to study the response of the fuses system. Code relevant design rules for the seismic design of frames with dissipative FUSEIS and practical recommendations on the selection of the appropriate fuses as a function of the most important parameters and member verifications have been formulated and are included in a Design Guide. This article presents the design and performance of building frames with FUSEIS 1-1 based on models calibrated on the experimental results.

• Steel and Composite Structures
• /
• 제45권3호
• /
• pp.455-466
• /
• 2022

Despite the considerable lateral stiffness and strength of the Concentrically Braced Frame (CBF), it suffers from low ductility and low seismic dissipating energy capacity. The buckling of the diagonal members of the CBF systems under cyclic loading ended up to the shortcoming against seismic loading. Comprehensive researches have been performing to achieve helpful approaches to prevent the buckling of the diagonal member. Among the recommended ideas, metallic damper revealed a better success than other ideas to enhance the behavior of CBFs. While metallic dampers improve the behavior of the CBF system, they increase constructional costs. Therefore, in this paper, a new steel damper with flexural mechanism is proposed, which is investigated experimentally and numerically. Also, a parametrical revision was carried out to evaluate the effect of thickness, slenderness ratio, angle of the main plate, and height of the main plates on the proposed damper. For the parametrical study, 45 finite element models were analyzed and considered. Experimental results, as well as the numerical results, indicated that the proposed damper enjoys a stable hysteresis loop without any degradation up to a high rotation equal to around 31% that is significantly considerable. Moreover, it showed a suitable performance in case of ductility and energy dissipating. Besides, the necessary formulas to design the damper, the required relations were proposed to design the elements outside the damper to ensure the damper acts as a ductile fuse.

• 한국구조물진단유지관리공학회 논문집
• /
• 제25권4호
• /
• pp.12-19
• /
• 2021

최근 전 세계적으로 지진이 빈번하게 발생하면서 지진으로부터 철근콘크리트 시설물의 내진설계 및 내진보강에 대한 연구가 활발히 진행되고 있다. 특히 철근콘크리트 구조물의 압축부재인 기둥은 지진에 의한 횡력에 취약하여, 적절한 내진보강공법이 필요하다. 따라서 본 연구에서는 시공이 빠르고 간편한 벨크로 내진보강재를 개발하고자 하였다. 벨크로 내진보강재 개발을 위해 기존 공업용 벨크로의 부착성능과 인장력을 증가시켰으며, 공업용 벨크로와 개발된 벨크로 내진보강재의 인장성능을 비교하기 위해 직접인장실험을 수행하였다. 또한 공업용 벨크로와 벨크로 보강재로 보강된 RC 기둥의 내진성능을 예측하기 위한 해석연구를 수행하였다. 해석결과를 바탕으로 비내진 RC 기둥의 벨크로 보강재의 보강에 따른 강도와 연성능력에 대하여 검토하였다. 해석결과 공업용 벨크로와 벨크로 보강재로 보강된 비내진 RC기둥의 강도와 연성능력이 모두 증가함을 확인하였으며, 개발된 벨크로 내진보강재의 내진 성능이 공업용 벨크로 보다 크게 나타남을 확인하였다.

• Earthquakes and Structures
• /
• 제12권4호
• /
• pp.397-407
• /
• 2017

To estimate the structural seismic demand, some methods are based on an equivalent linear system such as the Capacity Spectrum Method, the N2 method and the Equivalent Linearization method. Another category, widely investigated, is based on displacement correction such as the Displacement Coefficient Method and the Coefficient Method. Its basic concept consists in converting the elastic linear displacement of an equivalent Single Degree of Freedom system (SDOF) into a corresponding inelastic displacement. It relies on adequate modifying or reduction coefficient such as the inelastic deformation ratio which is usually developed for systems with known ductility factors ($C_{\mu}$) and ($C_R$) for known yield-strength reduction factor. The present paper proposes a rational approach which estimates this inelastic deformation ratio for SDOF bilinear systems by rigorous nonlinear analysis. It proposes a new inelastic deformation ratio which unifies and combines both $C_{\mu}$ and $C_R$ effects. It is defined by the ratio between the inelastic and elastic maximum lateral displacement demands. Three options are investigated in order to express the inelastic response spectra in terms of: ductility demand, yield strength reduction factor, and inelastic deformation ratio which depends on the period, the post-to-preyield stiffness ratio, the yield strength and the peak ground acceleration. This new inelastic deformation ratio ($C_{\eta}$) is describes the response spectra and is related to the capacity curve (pushover curve): normalized yield strength coefficient (${\eta}$), post-to-preyield stiffness ratio (${\alpha}$), natural period (T), peak ductility factor (${\mu}$), and the yield strength reduction factor ($R_y$). For illustrative purposes, instantaneous ductility demand and yield strength reduction factor for a SDOF system subject to various recorded motions (El-Centro 1940 (N/S), Boumerdes: Algeria 2003). The method accuracy is investigated and compared to classical formulations, for various hysteretic models and values of the normalized yield strength coefficient (${\eta}$), post-to-preyield stiffness ratio (${\alpha}$), and natural period (T). Though the ductility demand and yield strength reduction factor differ greatly for some given T and ${\eta}$ ranges, they remain take close when ${\eta}>1$, whereas they are equal to 1 for periods $T{\geq}1s$.