This paper describes the seismic performance evaluation of reinforced concrete bridge columns under constant and varying axial forces. For this purpose, nine identical circular reinforced concrete columns were designed seismically by KIBSE (2021) and KCI (2021). A comparison of lateral forces with theoretical strength shows that the safety factor for columns under varying axial forces is less marginal than those under constant axial forces. In addition, columns under varying axial forces exhibit significant fluctuations in the hysteretic response due to continuously varying axial forces. This is particularly prominent when many varying axial force cycles within a specific lateral loading cycle increase. Moreover, the displacement ductility of columns under varying axial forces does not meet the code-specified required ductility in the range of varying axial forces. All varying axial forces affect columns' strength, stiffness, and displacement ductility. Therefore, axial force variation needs to be considered in the lateral strength evaluation of reinforced concrete bridge columns.

As earthquakes have increased in Korea recently, people are paying attention to the seismic performance of buildings built in the past. Many school buildings in Korea were built based on standard drawings before the seismic design was applied. However, since school buildings are often designated as emergency evacuation facilities in case of disasters such as earthquakes, seismic evaluation and retrofit must be done quickly. This study investigated the failure modes among structural components (beams, columns, and joints), focusing on 1980s standard drawings for school buildings. The effects of column axial force, partial masonry infills, and different material strengths for concrete and rebar were considered for detailed evaluation. As a result, most of the joints were found to be the weakest among structural components. Column axial forces tended to make the joints more vulnerable, and partial masonry infills increased the possibility of joint failure and shear failure in columns.

The clamping of torque shear high strength bolt is induced when the pin-tail is broken. However the tension forces induced shank of the bolt do not be known by now. This study focused to develop a quantitative method to identify the induced tension by analyzing the electric energy of which electric torque wrench (rpm 20) was applied to high strength bolt at the break of pin tail. Based on this co-relation between tension and accumulated current, the regressive analysis was derived. The error rate between tension and accumulated current was 5.06%.

The clamping of torque shear high strength bolt is induced when the pin-tail is broken. However the tension forces induced shank of the bolt do not be known by now. This study focused to develop a quantitative method to identify the induced tension by analyzing the electric energy of which electric torque wrench was applied to high strength bolt at the break of pin tail. Based on this co-relation between tension and accumulated current, the regressive analysis was derived. The error rate between tension and accumulated current was 2.24%.

Grouted connections have been widely used for offshore structures such as connection method of jacket and mono-pile structures. It is recommended high strength concrete for grouting between pile and sleeve because it is so rapidly hardening that helpful to fatigue strength. This study investigates axial strength of pile to sleeve grouted connections made by 130MPa of high strength concrete. Push-out test were performed to evaluate the axial strength of the grouted connections with different shear-key spacing.

Torque control method and turn of nut method are specified as clamping method of high strength bolts in the steel construction specifications. Quality control of torque coefficient is essential activity because torque control method, which is presently adopted as clamping method in domestic construction sites, is affected by variation of torque coefficient. The clamping of torque shear bolt is based on KS B 2819. It was misunderstood that the tension force of the TS bolt was induced generally at the break of pin-tail specified. However, the clamping forces on slip critical connections do not often meet the intended tension, as it considerably varies due to torque coefficient dependent on the environmental factors and temperature variables despite the break of the pin tail.This study was focused to evaluate the effect of environmental factors and errors of installing bolts during tightening high strength bolts. The environmental parameters were composed of 'wet' condition, 'rust' condition, 'only exposure to air' condition. And the manufacture of trial product was planned to identify the induced force into the bolts. The algorithm for a trial product was composed of the relation between electricity energy taken from torque shear wrench and tension force from hydraulic tension meter.

Single layer free-form structures are being highlighted in the field of architecture due to its attractive shape. In these structures, node connecting system is very important because the node must resist bending and axial stress simultaneously. So the local and global stabilities of entire structure can be determined by the stiffness of node system. In this study, therefore, various types of bending test with axial force were performed. As a result, bending capacity with axial force of a new spherical node for free-form structure could be performed and structural capacities were checked to use in real structure.

The recently constructed buildings are ensuring seismic safety with enhanced design criteria. But, the buildings unapplied enhanced design criteria are very weak. In this study, steel grid shear wall is proposed as a solution of seismic retrofit to ensure safety of the existing buildings for the earthquake. And the structural performance experiments were carried out under axial force and cyclic lateral loads. The two specimens were made of a reference RC frame and steel grid shear wall in-filled RC frame. The test setup configured with two dynamic actuators, for the axial force with a 500kN capacity actuator and for the cyclic lateral load applied with the 2,000kN actuator. Compared with control specimen, the strength, stiffness, ductility, energy dissipation capacity of the seismic retrofit structures is evaluated.

고력볼트의 초기 체결력은 미끄럼표면조건에 따라, 일정시간이 경과될 때까지, 축력저하가 발생한다. 이 연구는 미 끄럼접합부 표면에 도장이 되어있는 경우, 도장의 크리프현상에 따른 축력저하에 관한 예측 모델을 찾는 것이다. 이 실험연구 범위는 무기질 아연 프라이머로 도포된 볼트접합부의 장기축력저하에 한정한다. 실험에 적용된 볼트종 류는 다크로 도포된 토크쉬어 볼트이다. 대상 표면의 도막 두께는 각각 96, 168, 226㎛ 이었다. 도막두께가 증가될 수록, 초기 체결이후 축력이완율은 도막의 크리프 때문에 10%에서 18%로 증가되었다. 장기축력예측을 위한 정량적 인 모델은 도막두께에 따른 크리프 스트레인과 경과된 시간사이에 회귀분석 결과로 얻어진다. 이 실험연구를 통해 미끄럼표면 도막의 크리프 거동특성을 알 수 있다면, 일정시간 경과후 고력볼트 체결력은 초기 체결력으로부터 구 할 수 있다. 본 실험결과를 근거로 각 도막두께에 대한 장기축력이완이후의 고력볼트 체결력에 관한 정량적인 수식 을 제안하였다.

The initial clamping forces of the high strength bolts depending on the different faying surface conditions drop within 1,000 hours regardless of loading any other external force or loosening of the nut. This study focused on the mathematical model for relaxation confined to creep on coated faying surface after initial clamping. The quantitative equation for estimating long term relaxation was derived from nonlinear regression analysis for relation between the creep strain of coated surface and the elapsed time.

スクーターCVT(無段變速機)はゴムVベルトで繋がれた駆動プーリーと従動プーリーとで構成されている。また、それぞれのプーリーは固定フランジと稼動フランジで構成されている。 駆動プーリーの稼動フランジはフランジの中の遠心ローラーとランププレートがあり、駆動プーリーの速度が増加することによって遠心ローラーの動きで稼動フランジは固定フランジ方向に動いて変速が成り立つ。 アジア全域に広がっているゴムVベルトCVTは簡単な構造で成り立っていて維持補修が易しくて低価という長所を持っている。 この研究ではスクーターCVTの駆動プーリーと従動プーリーの 軸力解釈を理論的に遂行し、現場で使用可能になるように修飾化した。

Dry CVT(Continuously variable transmission) consists of a driving pulley and a driven pulley joined by rubber V-belt. Each pulley consists of a fixed flange and a movable flange. The movable flange of the driving pulley has the centrifugal roller and a ramp plate in the flange. In this study, the formula with respect to relationship between a driving pulley and a driven pulley was derived, based on theoretical investigation about Dry CVT of a common and practical auto-bicycle(125cc). Also, the axial forces on the driving pulley and the driven pulley were analyzed.

본 연구에서는 화재시 매입형 합성기둥의 높은 축력비에 따른 내화성능을 알아보기 위해 유한요소해석 프로그램(ANSYS)을 통한 해석을 실시하였다. 온도에 따른 응력-변형률 곡선을 적용하여 ASTM E 119 가열곡선과 축력비 0.7, 0.6, 0.5에 따른 과도상태 열전달해석 및 정적구조해석을 실시하였으며, 해석조건과 동일한 조건에서의 재하가열실험을 실시하였다. 또한, 기준식(Eurocode 4)에 따라 가열시간에 따 른 합성기둥의 공칭압축강도를 산정하고, 축력비로 나타내어 해석값 및 실험값과 비교하였다. 해석 및 실험과 기준(Eurocode 4)을 통해 가열시 간에 따른 단면별 온도분포를 확인하고, 이에 따른 내화성능을 측정해 비교분석하였다. 유한요소해석 결과 축력비 0.5에서는 내화시간 180분 으로 실험값과 유사한 값이 도출된 반면, 축력비 0.6, 0.7에서 내화시간 150분과 60분이 도출되어 실험결과에 비해 다소 높은 결과가 도출된 것을 알 수 있었다. 그리고 기준식(Eurocode 4)에 따라 산정한 축력비에 따른 내화시간이 실제 실험값에 비해 다소 낮게 평가하고 있다는 것을 확인하였다. 그러나 축력비 0.7에서는 기준(Eurocode 4)이 실험값에 비해 다소 높게 평가하는 것을 확인하였다. 이에 따라 고축력에서의 매입형 합성기둥의 내화특성(시간-축력비 관계)을 확인하고, 도출된 매입형 합성기둥의 실험 및 해석데이터를 Eurocode기준의 검증의 자료로 활용할 수 있을 것으로 보인다.

본 연구에서는 축력을 받고 있는 철근콘크리트 보에 대한 4점 굽힘 시험을 실시하였다. 조작변인으로 변위제어를 통한 단조하중과 반복하중이 있다. 통제변인으로는 축력 강도와 4점 굽힘 시험 등 조작변인 이외의 모든 변수를 동일하게 실시하였다. 조작변인에 따른 변위-하중 그래프를 관찰하였다. 관찰결과 변-하중 그래프의 초기 기울기와 최대하중의 변위는 거의 일치하였다. 하중 변화 양상도 동일하였다. 다만 최대하중의 크기가 다르게 나타났다. 파괴 형상 또한 다르게 나타났다.

Many of recent field observations and researches have been shown that axial force variation due to vertical ground motion can affect the shear capacityRC column . However, the majority of shear strength models of RC columns in current design codes and predictive approaches have been developed based on experiments with constant axial loads. Thus, this paper evaluates the experimental seismic performance of RC columns subjected to varying axial loads. The axial loading patterns included constant and variable loading considering the characteristic of overturning moment and vertical ground motion. The observations of experimental results, including the effect on shear strength, and ductility are discussed compared with the case of constant axial load.

현수교 주 케이블은 케이블 밴드의 볼트 축력에 대한 정기적인 유지 관리가 매우 중요하다. 현수교 케이블 밴드의 볼트 축력은 시간이 경과함에 따라 케이블 소선의 크리프 현상, 볼트의 릴렉세이션, 하중 변동, 케이블 소선의 재배열 등으로 인해 축력 감소 현상이 발생하게 된다. 본 연구에서는 국내 현수 교량(SR대교)의 케이블 밴드가 시간이 경과하면서 발생하는 축력 감소 현상에 대해 그 원인 및 감소량 등에 대한 현장 측정 및 이론적 검토, 안전율 검토, 장기적인 이력 관리 등을 수행하였다. 그 결과, 케이블 밴드 볼트 축력 감소는 주 케이블 소선에 사용된 아연 도금층의 소성 변형에 크게 영향받는 것을 확인하였으며, 이에 대한 이론적 체계 및 장기 이력 관리에 대한 적용성을 확립하였다.