Shaking Table Test for Evaluating the Seismic Performance of Steel Frame Retrofitted by Buckling-Restrained Braces

To investigate the seismic performance of buckling-restrained braces under the earthquake action, the shaking table test with a two-story 1/4 scale model is carried out for the ordinary pure steel frame and the buckling-restrained bracing steel frame with low-yield-point steel as the core plate. The failure modes, dynamic characteristics, acceleration response, interstory drift ratio, strain, shear force, and other mechanical properties of those two comparative structures subjected to different levels of seismic waves are mainly evaluated by the experiment. The test results show that under the action of seismic waves with different intensities, the apparent observations of damage occur in the pure frame structure, while no obvious or serious damage in the steel members of BRB structure is observed. With the increase in loading peak acceleration for the earthquake waves, the natural frequency of both structures gradually decreases and the damping ratio gradually increases. At the end of the test, the stiffness degradation rate of the pure frame structure is 11.2%, while that of the buckling-restrained bracing steel frame structure is only 5.4%. The acceleration response of the buckling-restrained bracing steel frame is smaller than that of the pure steel frame, and the acceleration amplification factor at the second story is larger than that at the first story for both structures. The average interstory drift ratios are, respectively, 1/847 and 1/238 for the pure steel frame under the frequent earthquake and rare earthquake and are 1/3000 and 1/314 for the buckling-restrained bracing steel frame, which reveals that the reduction rate of lateral displacement reaches a maximum of 71.71% after the installation of buckling-restrained brace in the pure steel frame. The strain values at each measuring point of the structural beam and column gradually increase with the increase of the peak seismic acceleration, but the strain values of the pure steel frame are significantly larger than those of the buckling-restrained bracing steel frame, which indicates that the buckling-restrained brace as the first seismic line of defense in the structure can dramatically protect the significant structural members. The maximum shear force at each floor of the structure decreases with the increase in height, and the shear response of the pure frame is apparently higher than that of the buckling-restrained bracing structure.

Characterization of Six-Degree-of-Freedom Sensors for Building Health Monitoring

Six-degree-of-freedom (6DoF) sensors measure translation along three axes and rotation around three axes. These collocated measurements make it possible to fully describe building motion without the need for an external reference point. This is an advantage for building health monitoring, which uses interstory drift and building eigenfrequencies to monitor stability. In this paper, IMU50 6DoF sensors are characterized to determine their suitability for building health monitoring. The sensors are calibrated using step table methods and by comparison with earth’s rotation and gravity. These methods are found to be comparable. The sensor’s self-noise is examined through the power spectral density and the Allan deviation of data recorded in a quiet environment. The effect of temperature variation is tested between 14 and 50 °C. It appears that the self-noise of the rotation components increases while the self-noise of the acceleration components decreases with temperature. The comparison of the sensor self-noise with ambient building signal and higher amplitude shaking shows that these sensors are in general not sensitive enough for ambient signal building health monitoring in the frequency domain, but could be useful for monitoring interstory drift and building motion during, for example, strong earthquake shaking in buildings similar to those examined here.

Optimal Seismic Design of Stiffness and Gap of Hysteretic-Viscous Hybrid Damper System in Nonlinear Building Frames for Simultaneous Reduction of Interstory Drift and Acceleration

The viscous-hysteretic hybrid (HVH) damper system recently introduced by one of the authors has a clear property that, when the hysteretic dampers with gap mechanism become active (stiffness element starts working), the acceleration of building frames with this damper system as a stopper attains large values in spite of the advantageous feature to prevent excessive deformation. It is therefore desired that both the maximum interstory drift and the maximum acceleration exhibit an acceptable value with appropriate compromise. The double impulse as a simplified version of one-cycle sine wave as a representative of the main part of near-fault ground motions can simulate the maximum interstory drifts properly. However, it cannot simulate the maximum accelerations due to its impulsive nature. In this case, the sine wave corresponding to the double impulse can play an important role in the reliable simulation of the maximum accelerations. Even in such circumstance, the analysis using the double impulse is important because it enables to obtain the critical timing of the input, i.e. the nonlinear resonant frequency of the sine wave without repetition. The investigations on the criticality of the sine wave corresponding to the critical double impulse show that the critical timing of the double impulse leads to the nonlinear resonant frequency of the sine wave in view of the maximum interstory drift, the maximum top acceleration and the maximum relative acceleration for the constant input acceleration and the constant input velocity except for some cases. It is demonstrated finally that the index in terms of the maximum interstory drift and the maximum acceleration can be introduced as an appropriate parameter for deriving the optimally compromised gap quantity of hysteretic dampers with gap mechanism for various input velocity levels and various hysteretic damper stiffness ratios.

KINERJA STRUKTUR GEDUNG BETON BERTULANG DENGAN BENTANG KANTILEVER 4 M MENGGUNAKAN METODE ANALISIS PUSHOVER

The advance of technology and design in construction field are developing. Therefore, variety of structural design becomes unique. The shape of building with cantilever seems increasingly atrractive because it is rated to have high architecture. Cantilever form with a longer span of more than 1/3 L is increasingly desirable because it provides a unique exterior appearance,as well as a double function other than as a room can also functioned as a canopy.The building is designed to be a 7-storey building with cantilever beam on the 6th – 7th floor for 4 m. This study used the reference of SNI 03-2847-2013 in designing the main structural elements of reinforced concrete, SNI 03-1726-2012 for the designing the earthquake load, SNI 03-1727-2013 and PPIUG1983 for gravity load planning. From the results of analysis, the interstory drift that occurs both the X-direction and the direction of Y is 50.544 mm and 39.956 mm, each of which qualifies the interstory drift limit according to SNI 03-1726-2012. Structural performance levels are being catagories in immediate occupancy level which means there is no structural damage and the building can be used immediately according to its function AbstrakKemajuan teknologi dan desain di bidang konstruksi semakin berkembang. Hal tersebut, membuat beragamnya variasi desain struktur yang semakin hari semakin unik. Bentuk-bentuk gedung dengan kantilever tampaknya semakin diminati karena dinilai mempunyai arsitektur yang tinggi. Bentuk kantilever yang mempunyai bentang lebih panjang, yaitu lebih dari 1/3 L makin diminati karena memberikan tampilan eksterior yang unik, serta dapat berfungsi ganda selain sebagai ruangan juga dapat difungsikan sebagai kanopi. Gedung yang didesain merupakan gedung 7 lantai dengan balok kantilever pada lantai 6 dan 7 sepanjang 4 m. Penelitian ini menggunakan acuan SNI 03-2847-2013 dalam mendesain elemen struktur utama beton bertulang, SNI 03-1726-2012 untuk perencanaan beban gempa, SNI 03-1727-2013 dan PPIUG 1983 untuk perencanaan beban gravitasi. Dari hasil analisis didapatkan besar simpangan yang terjadi baik arah x maupun arah Y adalah sebesar 50,544 mm dan 39,956 mm, dimana masing-masing memenuhi syarat batas simpangan antar lantai sesuai SNI 03-1726-2012. Level kinerja struktur termasuk level immediate occupancy yang berarti tidak terjadi kerusakan structural dan gedung dapat segera dipakai sesuai dengan fungsinya.

Vibration control in buildings under seismic excitation using optimized tuned mass dampers

Earthquakes can cause vibration problems in many types of structures, generating large displacements. The interstory drift is a design criterion very used in seismic analysis and the structural control is an alternative to reduce these displacements and improve the performance of these structures adapting them to the imposed criteria. TMD is a device widely used due to the simple principle of operation and many successful applications in real life practice. This paper investigates the use of optimized TMD for reduction of maximum horizontal displacement at the top floor and interstory drift of a steel building under seismic excitation considering three scenarios: single TMD at the top floor; MTMD horizontally arranged at the top floor; and MTMD vertically arranged on the structure. By a metaheuristic optimization algorithm, the parameters and positions of the devices are obtained. Three real and one artificial earthquakes are employed in the simulations. The results showed that all proposed scenarios are efficient in reducing top floor response and interstory drift to values below of the interstory drift limits allowed by the standard code consulted. However, Scenario 2 presented the best reduction for the top displacement and interstory drift to the critical floor for the worst earthquake considered.