• Smart Structures and Systems
• /
• 제4권4호
• /
• pp.493-515
• /
• 2008

Semi-active control systems have attracted a great deal of attention in recent years because these systems can operate on battery power alone, proving advantageous during seismic events when the main power source of the structure may likely fail. The behavior of semi-active devices is often highly non-linear and requires suitable and efficient control algorithm. This paper presents the comparative study and performance of variable semi-active friction dampers by using recently proposed predictive control law with direct output feedback. In this control law, the variable slip force of semi-active variable friction damper is kept slightly lower than the critical friction force, which allows the damper to remain in the slip state during an earthquake, resulting in improved energy dissipation capability. This control algorithm is able to produce a continuous and smooth slip forces for a variable friction damper. The numerical examples include a structure controlled with multiple variable semi-active friction dampers and with multiple passive friction dampers. A parameter, gain multiplier defined as the ratio of damper force to critical damper control force, is investigated under four different real earthquake ground motions, which plays an important role in the present control algorithm of the damper. The numerically evaluated optimum parametric value is considered for the analysis of the structure with dampers. The numerical results of the variable friction dampers show better performance over the passive dampers in reducing the seismic response of structures.

• Structural Engineering and Mechanics
• /
• 제65권4호
• /
• pp.401-408
• /
• 2018

Concentric braced frames are commonly used in steel structures to withstand lateral forces. One of the drawbacks of these systems is the possibility that the braces are buckled under compressive loads, which leads to sudden reduction of the bearing capacity of the structure. To overcome this deficiency, the idea of the Buckling Restrained Brace (BRB) has been proposed in recent years. The length of a BRB steel core can have a significant effect on its overall behavior, since it directly influences the energy dissipation capability of the member. In this study, numerical methods have been utilized for investigation of the optimum length of BRB steel cores. For this purpose, BRBs with different lengths placed into several two-dimensional framing systems with various heights were considered. Then, the Response History Analysis (RHA) was performed, and finally, the optimum steel core length of BRBs and its effect on the responses of the overall system were investigated. The results show that the shortest length where failure does not occur is the best length that can be proposed as the optimum steel core length of BRBs. This length can be obtained through a formula which has been derived and verified in this study by both analytical and numerical methods.

• Geomechanics and Engineering
• /
• 제21권1호
• /
• pp.73-84
• /
• 2020

In the seismic design of bridges, formation of plastic hinges plays an important role in the dissipation of seismic energy. In the case of conventional fixed-base bridges, the plastic hinges are allowed to form in the superstructure alone. During seismic event, such bridges may be safe from collapse but the superstructure undergoes significant plastic deformations. As an alternative design approach, the plastic hinges are guided to form in the soil thereby utilizing the inevitable yielding of the soil. Rocking foundations work on this concept. The formation of plastic hinges in the soil reduces the load and displacement demands on the superstructure. This study aims at evaluating the seismic response of bridge pier supported on rocking shallow foundation. For this purpose, a BNWF model is implemented in OpenSees platform. The capability of the BNWF model to capture the SSI effects, nonlinear behavior and dynamic loading response are validated using the centrifuge and shake table test results. A comparative study is performed between the seismic response of the bridge pier supported on the rocking shallow foundation and conventional fixed-base foundation. Results of the study have established the beneficial effects of using the rocking shallow foundation for the seismic response analysis of the bridge piers.

• 항공우주시스템공학회지
• /
• 제9권4호
• /
• pp.55-61
• /
• 2015

In this study, we peformed optimal design of a composite skid landing gear, one of the solid spring shock absorbers, for light vertical takeoff and landing aircraft. Although a solid spring type has poor energy dissipation capability, it is commonly used for light aircraft where sink speeds are low and shock absorption is non-critical in terms of simplicity, low cost and weight reduction. In this paper, design parameters of solid spring such as sink speed, gear leg length, deflection and landing load factor were reviewed. In order to meet structural requirements such as deflection and strength, finally, we conducted optimal design of the composite skid landing gear for VTOL UAV using genetic algorithm and pattern search algorithm.

• Steel and Composite Structures
• /
• 제44권2호
• /
• pp.283-294
• /
• 2022

In this study, a new seismic retrofit scheme of building structures is developed by combining a steel moment frame and steel slit plates to be installed inside of an existing reinforced concrete frame. This device has the energy dissipation capability of slit dampers with slight loss of stiffness compared to the conventional steel frame reinforcement method. In order to investigate the seismic performance of the retrofit system, it was installed inside of a reinforced concrete frame and tested under cyclic loading. Finite element analysis was carried out for validation of the test results, and it was observed that the analysis and the test results match well. An analytical model was developed to apply the retrofit system to a commercial software to be used for seismic retrofit design of an example structure. The effectiveness of the retrofit scheme was investigated through nonlinear time-history response analysis (NLTHA). The cyclic loading test showed that the steel frame with slit dampers provides significant increase in strength and ductility to the bare structure. According to the analysis results of a case study building, the proposed system turned out to be effective in decreasing the seismic response of the model structure below the given target limit state.

• Structural Engineering and Mechanics
• /
• 제87권5호
• /
• pp.487-498
• /
• 2023

Unreinforced masonry (URM) buildings are extensively adopted in many of the growing nations, particularly in India. Window or door openings are required for architectural or functional reasons, which pose a threat to the building's safety. The past earthquakes have shown that the seismic capability of these structures was very weak. Strengthening these unreinforced masonry walls using welded wire mesh (WWM) is one of the most commonly and economical methods. The present experimental study investigates the impact of openings on the shear behaviour of URM walls and the effectiveness of WWM in enhancing the shear performance of masonry wall. In the experimental program 16 specimens were cast, 8 unstrengthen and 8 strengthened specimens, under 8 unstrengthen and strengthened specimens, every 2 specimens had 0%, 5%, 10%, and 15% openings and all these walls were tested under diagonal compression. The results show that the shear carrying capacity reduces as the opening percentage increases. However, strengthening the URM specimens using WWM significantly improves the peak load, shear strength, ductility, stiffness, and energy dissipation. Furthermore, the strengthening of the URM walls using WWM compensated the loss of wall capacity caused by the presence of the openings.

• Steel and Composite Structures
• /
• 제37권1호
• /
• pp.91-98
• /
• 2020

Steel plate shear walls are recently used as efficient seismic lateral resisting systems. These lateral resistant structures are implemented to provide more strength, stiffness and ductility in limited space areas. In this study, the seismic behavior of the multi-story steel frames with steel plate shear walls are investigated for buildings with 4, 8, 12 and 16 stories using verified computational modeling platforms. Different number of steel moment bays with distinctive lengths are investigated to effectively determine the deflection amplification factor for low-rise and high-rise structures. Results showed that the dissipated energy in moment frames with steel plates are significantly related to the inside panel. It is shown that more than 50% of the dissipated energy under various ground motions is dissipated by the panel itself, and increasing the steel plate length leads to higher energy dissipation capability. The deflection amplification factor is studied in details for various verified parametric cases, and it is concluded that for a typical multi-story moment frame with steel plate shear walls, the amplification factor is 4.93 which is less than the recommended conservative values in the design codes. It is shown that the deflection amplification factor decreases if the height of the building increases, for which the frames with more than six stories would have less recommended deflection amplification factor. In addition, increasing the number of bays or decreasing the steel plate shear wall length leads to a reduction of the deflection amplification factor.

• Structural Engineering and Mechanics
• /
• 제82권1호
• /
• pp.107-120
• /
• 2022

The bracing members capable of active control against seismic loads to reduce earthquake damage have been widely utilized in construction projects. Effectively reducing the structural damage caused by earthquake events, bracing systems equipped with retrofitting damper devices, which take advantage of the energy dissipation and impact absorption, have been widely used in practical construction sites. Shape Memory Alloys (SMAs) are a new generation of smart materials with the capability of recovering their predefined shape after experiencing a large strain. This is mainly due to the shape memory effects and the superelasticity of SMA. These properties make SMA an excellent alternative to be used in passive, semi-active, and active control systems in civil engineering applications. In this research, a new system in diagonal braces with slit damper combined with SMA is investigated. The diagonal element under the effect of tensile and compressive force turns to shear force in the slit damper and creates tension in the SMA. Therefore, by creating shear forces in the damper, it leads to yield and increases the energy absorption capacity of the system. The purpose of using SMA, in addition to increasing the stiffness and strength of the system, is to create reversibility for the system. According to the results, the highest capacity is related to the case where the ratio of the width of the middle section to the width of the end section (b₁/b) is 1.0 and the ratio of the height of the middle part to the total height of the damper (h₁/h) is 0.1. This is mainly because in this case, the damper section has the highest cross-section. In contrast, the lowest capacity is related to the case where b₁/b=0.1 and the ratio h₁/h=0.8.

• Steel and Composite Structures
• /
• 제43권2호
• /
• pp.165-183
• /
• 2022

Most transportation departments have recognized and developed procedures to address the ever-increasing weights of trucks traveling on bridges in a service today. Transportation agencies also recognize the issues with overheight vehicles' collisions with bridges, but few stakeholders have definitive countermeasures. Bridges are becoming more vulnerable to collisions from overheight vehicles. The exact response under lateral impact force is difficult to predict. In this paper, nonlinear impact analysis shows that the degree of deformation recorded through the modeling of the unprotected vehicle-girder model provides realistic results compared to the observation from the US-61 bridge overheight vehicle impact. The predicted displacements are 0.229 m, 0.161 m, and 0.271 m in the girder bottom flange (lateral), bottom flange (vertical), and web (lateral) deformations, respectively, due to a truck traveling at 112.65 km/h. With such large deformations, the integrity of an impacted bridge becomes jeopardized, which in most cases requires closing the bridge for safety reasons and a need for rehabilitation. We proposed different sacrificial cushion systems to dissipate the energy of an overheight vehicle impact. The goal was to design and tune a suitable energy absorbing system that can protect the bridge and possibly reduce stresses in the overheight vehicle, minimizing the consequences of an impact. A material representing a Sorbothane high impact rubber was chosen and modeled in ANSYS. Out of three sacrificial schemes, a sandwich system is the best in protecting both the bridge and the overheight vehicle. The mitigation system reduced the lateral deflection in the bottom flange by 89%. The system decreased the stresses in the bridge girder and the top portion of the vehicle by 82% and 25%, respectively. The results reveal the capability of the proposed sacrificial system as an effective mitigation system.

• 한국재난정보학회 논문집
• /
• 제15권3호
• /
• pp.418-426
• /
• 2019

연구목적: 내진성능이 부족한 중 저층의 RC 격자 구조물의 내진능력을 해석한 후, 보와 기둥의 내진성능 개선을 위해 강재 슬래브 이력형 댐퍼(SSHD)를 설치하고, 지진이 발생할 때 구조물의 손상 및 인적피해를 최소화 하는 방안을 제시하는 데 그 목적이 있다. 연구방법: 내진설계가 되지 않은 격자 형태의 전철 역사를 대상으로 내진성능을 파악하고, 내진성능이 부족할 경우 공기를 최소화 할 수 있는 방법인 SSHD 시스템을 설치하는 것으로 가정하여 구조물의 내진성능 평가 및 보강을 검토한다. 연구결과: SSHD를 적용하여 구조물을 보강한 후, 고유치 해석을 수행한 결과 장변방향으로는 0.548s의 고유주기를 나타내었으며, 단변방향으로는 0.593s의 고유주기를 가지고 있는 것으로 나타났다. 결론: SSHD에 대하여 반복하중 실험을 수행 한 결과, 댐퍼의 전단강성은 103%, 에너지소산량은 111% 및 109%로 나타나고, 모든 기둥과 보 부재의 소성회전각은 $I_o$수준을 만족하는 것으로 나타나 보강효과가 충분할 것으로 판단된다.