[Show abstract][Hide abstract] ABSTRACT: In this paper, a method for estimating modal masses is presented by extending the procedure proposed by a previous study for estimating the first modal mass to a procedure which allows the estimation of modal masses of higher order modes. System matrices are first obtained by using a general system identification technique, and then the natural frequency and damping ratio of each mode are extracted from the obtained system matrices. Controllability and observability matrices are constructed by using both the identified system matrices and the modal space system matrices in which the modal masses are considered as unknown variables. The modal masses can be obtained based on the fact that the multiplication of the controllability and observability matrices does not change with the type of the system matrices, including the modal space ones. The advantage of the proposed method is that an accurate estimation of the modal mass of a higher mode is possible without the information on the modal vector which is difficult to experimentally identify. The proposed method was applied to a real-world 39 story building structure with an active mass damper and higher order modal masses of the building were identified. The dynamic responses analytically obtained by using the identified modal masses were found very close to the measured responses.
No preview · Article · Sep 2015 · Engineering Structures
[Show abstract][Hide abstract] ABSTRACT: Recently in Korea, extensive research on developing a new style of Korean traditional wooden house, Hanok, has been conducted for duplicating architectural plan composition and appearance of the Hanok and for improving construction and economic efficiencies. The beam–column joint of the new Hanok is composed of general timber and steel plates for ensuring workability on site and enhancing the structural performance while a traditional Hanok simply adopts general mortise and tenon joints. In this study, the lateral stiffness of a 2-story new Hanok was evaluated by conducting the static lateral loading tests using a 1/4 scale specimen. The ‘I’ shaped plan part of the specimen was first tested and the effective rotational stiffness of the joints with steel plates was estimated by comparing roof displacements of the test specimen and a numerical model. The effective stiffness of the specimen increased with increasing vertical loads and decreased with increasing roof displacements. An equation for estimating the joint rotational stiffness was proposed with regard to the steel plate type based on the test result from the ‘I’ shaped plan specimen. The effectiveness of the equation was verified by showing that roof displacement of the test specimen with ‘L’ shaped plan could be approximately estimated by using an analytical model having joint rotational stiffness determined by using the proposed equation.
No preview · Article · Jul 2015 · Engineering Structures
[Show abstract][Hide abstract] ABSTRACT: An abnormal vibration accident caused by human rhythmic excitations occurred in the upper floors of a 39 story steel building in Seoul, Korea. In this paper, the effects of human rhythmic excitations on the global vertical vibration of a high-rise steel building were evaluated. Experimental tests were conducted to measure the natural frequencies and the floor acceleration responses of the building. Also, using three-dimensional finite element model, the vertical natural frequency of the building was estimated by conducting modal analysis, and time history analyses were performed by applying the various human rhythmic excitations to the floor slab of a fitness center in the 12th floor of the building. The modal analysis results verified that the building has the global vertical vibration mode of 2.7 Hz natural frequency which was identified by experimental tests. The vertical accelerations of the floors resulting from the time history analyses also agreed very well with the experimental results. Finally, it was concluded that the resonance phenomenon between building structure and human rhythmic excitations with the step frequency of 2.7 Hz caused the abnormal vertical vibration accident of the building.
No preview · Article · Jan 2014 · Journal of Constructional Steel Research
[Show abstract][Hide abstract] ABSTRACT: The purpose of this paper is to identify through experiments the finite element (FE) model of a building structure using a magnetorheological (MR) fluid damper. The FE model based system identification (FEBSI) technique evaluates the control performance of an MR damper that has nonlinear characteristics as equivalent linear properties such as mass, stiffness, and damping. The Bingham and Bouc-Wen models were used for modeling the MR damper and the equivalent damping increased by the MR damper was predicted by applying an equivalent linearization technique. Experimental results indicate that the predicted equivalent damping matches well with the experimentally obtained damping.
No preview · Article · Dec 2013 · SMART STRUCTURES AND SYSTEMS
[Show abstract][Hide abstract] ABSTRACT: In this paper, the field vibration measurement tests have been conducted for investigating the exact causes of the abnormal vibration accident which occurred on last July 5, 2011 in TechnoMart, a 39 story steel building structure. The vertical accelerations of the building floors were measured under the 40 movie-theater operation and human rhythmic movements in a fitness center which were estimated as ones of the vibration sources. From field tests, it could be identified that the building has global vertical vibration mode of 2.7 Hz natural frequency and human group rhythmic movements having frequency component mainly close to 2.7 Hz in a fitness center caused the resonance of the vertical mode. Especially, the fact that the identified damping ratio of the vertical mode by observing the free vibration response after the human group excitation was just 0.3%, implies that response amplification could be so significant that only 23 people could excite the 39 story building having the total mass of 30 thousands of metric ton move globally up and down. Tuned mass damper (TMD) is being considered as a measure for keep this resonance by adding damping to the building. The TMD design results shows that the acceleration level resulting from the same human excitation can be reduced to one fourth of that of the building without TMD.
No preview · Article · Dec 2013 · Engineering Structures
[Show abstract][Hide abstract] ABSTRACT: A waffle-shaped precast concrete panel named WAS has been newly developed as a floor system. Compared to the conventional double tee (DT), the WAS has a more spacious connection area between the panels while having a shallower depth, which possibly results in an enhanced performance of the connection. Experimental studies were performed to examine the flexural behavior of the WAS according to several primary parameters: the panel types, prestress levels applied to the panels, panel sizes, and the existence of steel ties. Connection tests were also performed on the short and long edges of each panel against out-of-plane shear. The test results showed that the WAS panels yields satisfactory flexural capacity similar to the DT up to ultimate state, and they satisfy the deflection limit for serviceability while their stiffnesses were less than those of DT panels. It was also found that the ultimate flexural strength of the WAS panel increases as the applied prestress increases, and that the connections can undertake the applied bending moment and properly transfer the developed shear force between WAS panels. The enhanced performance of the WAS connection makes it possible to efficiently design the panels addressing the moment distribution, and to enhance the serviceability (less deflection and cracking) and structural continuity/integrity of the WAS system while still being able to reduce its depth.
No preview · Article · Jan 2012 · Advances in Structural Engineering
[Show abstract][Hide abstract] ABSTRACT: In this study, a decentralized algorithm for operating a semiactive MR damper was presented. The frictional force of the MR damper was determined based on the assumed shape functions using the displacement and velocity of the damper piston itself. The seismic response control performance of the MR damper was numerically and experimentally evaluated and compared to that of the passively or semiactively operated MR damper. The results from numerical analysis of SDOF system indicated that passively operated MR damper to have an optimal frictional force less than about 30% of the base shear force provided the smallest displacement response spectrum over all the periods. The proposed MR damper showed the better performance in reducing the absolute acceleration with the larger frictional force than the passive one. Also, the results from a three-storey benchmark building indicated that the proposed decentralized MR damper provided control performance equivalent to or better than the performance shown by the semiactive MR damper using a centralized LQR algorithm. Finally, the effectiveness of the proposed MR damper was verified through experimental tests of a full-scale five-storey steel structure with the MR dampers.
No preview · Article · Dec 2011 · Journal of Intelligent Material Systems and Structures
[Show abstract][Hide abstract] ABSTRACT: In this study, the performances of a passive tuned mass damper (TMD) and a semi-active TMD (STMD) were evaluated in terms of seismic response control of elastic and inelastic structures under seismic loads. First, elastic displacement spectra were obtained for damped structures with a passive TMD and with a STMD proposed in this study. The displacement spectra confirmed that the STMD provided much better control performance than passive TMD and the STMD had less stroke requirement. Also, the robustness of the TMD was evaluated by off-tuning the frequency of the TMD to that of the structure. Finally, numerical analyses were conducted for an inelastic structure of hysteresis described by the Bouc-Wen model. The results indicated that the performance of the passive TMD whose design parameters were optimized for an elastic structure considerably deteriorated when the hysteretic portion of the structural responses increased, and that the STMD showed about 15-40% more response reduction than the TMD.
No preview · Article · Sep 2011 · SMART STRUCTURES AND SYSTEMS
[Show abstract][Hide abstract] ABSTRACT: The real-time hybrid testing method (RT-HYTEM) is a structural testing technique in which the numerical integration of the equation of motion for a numerical substructure and the physical testing for an experimental substructure are performed simultaneously in real-time. This article presents the quantitative evaluation of the seismic performance of a building structure installed with a magnetorheological (MR) damper using RT-HYTEM. A building model is identified from the force-vibration testing results of a full-scale five-story building and is used as the numerical substructure, and an MR damper corresponding to an experimental substructure is physically tested using a universal testing machine (UTM). First, the force required to drive the displacement of the story, at which the MR damper is located, is measured from the load cell attached to the UTM. The measured force is then returned to a control computer to calculate the response of the numerical substructure. Finally, the experimental substructure is excited by the UTM with the calculated response of the numerical substructure. The RT-HYTEM implemented in this study is validated because the real-time hybrid testing results obtained by application of sinusoidal and earthquake excitations and the corresponding analytical results obtained using the Bouc-Wen model as the control force of the MR damper with respect to input currents are in good agreement. Also, the results from RT-HYTEM for the passive -on and -off control show that the structural responses did not decrease further by the excessive control force, but decreased due to the increase of the current applied to the MR damper. Also, two semi-active control algorithms (modulated homogeneous friction and the clipped-optimal control algorithms) are applied to the MR damper in order to optimally control the structural responses. To compare the RT-HYTEM and numerical results, Bouc-Wen model parameters are identified for each input current. The results of the comparison of experimental and numerical responses show that it is more practical to use RT-HYTEM in semi-active devices such as MR dampers. The test results show that a control algorithm can be experimentally applied to the MR damper using RT-HYTEM. This article provides a discussion on each algorithm with respect to the seismic performances.
Full-text · Article · Dec 2010 · Journal of Intelligent Material Systems and Structures
[Show abstract][Hide abstract] ABSTRACT: A new type of hollow slab making use of plastic air balls has been developed, which can effectively reduce the amount of concrete and self weight of concrete structures. In this study, flexural and free vibration tests were carried out to investigate flexural behaviour, including the flexural stiffness, cracking, strength, and ductility. Six test specimens were examined: two conventional RC slabs; two hollow slabs; and two partially precast concrete slabs. The test parameters also included two different types of plastic balls. The test results showed that the hollow slabs yield a satisfactory flexural behaviour (i.e., crack pattern, and flexural strength) which is similar to that of conventional concrete solid slabs up to the ultimate state. It was also found that the current design provisions for concrete solid slabs are applicable to hollow slabs, without significant modification, for the evaluation of flexural strength and initial stiffness essential to the serviceability check.
No preview · Article · Aug 2010 · Advances in Structural Engineering
[Show abstract][Hide abstract] ABSTRACT: Since the school buildings are generally used as public shelters when the natural disasters such as flood and earthquake occur, it must be designed to show enough structural performance when subject to earthquake. Major failure mode of the school buildings observed in past earthquakes were shear failure of column of which length is shortened by infilled masonry blocks. In this study, the seismic risk of the reinforced concrete school building structure was evaluated by using the seismic performance evaluation methods of low-story RC structures developed in Japan and the required seismic performance index which is obtained according to the KBC2008 seismic hazard map and soil types. In this paper, the seismic performance of the school building is evaluated by considering this short-column effects, building shape and deterioration.
[Show abstract][Hide abstract] ABSTRACT: This paper deals with the numerical model of a bracing-friction damper system and its deployment using the optimal slip load distribution for the seismic retrofitting of a damaged building. The Slotted Bolted Connection (SBC) type friction damper system was tested to investigate its energy dissipation characteristic. Test results coincided with the numerical ones using the conventional model of a bracing-friction damper system. The placement of this device was numerically explored to apply it to the assumed damaged-building and to evaluate its efficiency. It was found by distributing the slip load that minimizes the given performance indicies based on structural response. Numerical results for the damaged building retrofitted with this slip load distribution showed that the seismic design of the bracing-friction damper system under consideration is effective for the structural response reduction.
Full-text · Article · Sep 2008 · SMART STRUCTURES AND SYSTEMS
[Show abstract][Hide abstract] ABSTRACT: In this study, a seismic design methodology of the friction dampers based on the storey shear force distribution of an elastic building structure is proposed. First, using two normalization methods for the slip-load of a friction damper, numerical analysis of various single degree-of-freedom (SDOF) systems is performed. From this analysis, the effect of the slip-load and brace stiffness is investigated and optimal stiffness ratios of the brace versus primary structure are found. Second, from the numerical analysis for five multistorey building structures of different natural periods and numbers of story, reasonable decision method for the total number of installation floors, location of installation and distribution of slip-loads are drawn. In addition, an empirical equation on the optimal number of installation floor is proposed. Finally, the superiority of the proposed method compared to the existing design method is verified from numerical analysis.
No preview · Article · Apr 2008 · Engineering Structures
[Show abstract][Hide abstract] ABSTRACT: In this paper, excitation systems using a linear mass shaker (LMS) and an active tuned mass damper (ATMD) are presented to simulate the wind induced responses of a building structure. The actuator force for the excitation systems is calculated by using the inverse transfer function of a target structural response to the actuator. Filter and envelop functions are used to prevent the actuator from exciting unexpected modal responses and an initial transient response and thus, to minimize the error between the wind and actuator induced responses. The analyses results from a 76-story benchmark building problem for which the wind load obtained by a wind tunnel test is given, indicate that the excitation system installed at a specific floor can approximately reproduce the structural responses induced by the wind load applied to each floor of the structure. The excitation system designed by the proposed method can be effectively used for evaluating the wind response characteristics of a practical building structure and for obtaining an accurate analytical model of the building under wind load.
No preview · Article · Jan 2008 · SMART STRUCTURES AND SYSTEMS
[Show abstract][Hide abstract] ABSTRACT: This paper presents a design of a tuned liquid mass damper(TLMD) for controlling bi-directional response of high-rise building structure subjected to windload. The proposed damper behaves as a tuned mass damper(TMD) of which mass is regarded as the mass of a tuned liquid column damper(TLCD) and the case wall of the TLCD itself in one direction and the TLCD in the other direction. Because the proposed device has coupled design parameter along two orthogonal directions, it is very important to select designing components by optimal fine tuning. In the designing TLMD, for easy maintenance, the rubber-bearing with small springs was applied in TMD direction. In this study, the Songdo New City Tower 1A in Korea, which has been designed and constructed two TLCDs in order to control bi-directional response, was chosen as the model building structure. The results of rotation test proved the effectiveness of bi-directional behavior of TLMD.