Laboratory tests of steel simple torsionally unbalanced models

Abstract

The objective of this work is to obtain estimations of the amplification factors and used for torsion design of buildings, from experiments. For this study, simple one-storey torsionally unbalanced (TU) steel models were considered. Models consisted of a deck supported on four columns with a selected arrangement of hinges at column ends. Two theoretical structural eccentricities (e = 0.05 and 0.15) were considered. Models were excited with a simple long-period pendulum consisting of a hanging platform with a forced-vibration generator on it. Eight models were tested at several excitation levels (frequencies and force magnitudes) in both ranges of behaviour: elastic and inelastic. Experiments were conducted at three frequency ratios of excitation. Registered accelerations of the pendulum platform indicate that the experimental set-up leads to excitations that resemble narrow-band seismic ground motions. Frame shear force estimations, based on accelerations recorded at both deck sides, indicate that torsion design factors ( and ) depend on eccentricity. Estimations of frame shears based on measurements indicate that for normalized eccentricities e 0.025, the amplification can be between 2 and 3; while factor resulted between 0.0 and 1.6. systems can provide a good global understanding of the structural behaviour of buildings, more recent analytical studies turned to linear and nonlinear multi-storey systems, most of them modelled as shear beams.In addition to these analytical studies, understanding of the torsion structural behaviour has also been gathered from experiments and from instrumented buildings when they are either subjected to earthquakes or excited with forced-vibration generators. For instance Maheri et al.[1] tested a series of structural models. Their experimental work was limited to the study of frequencies and mode shapes within the linear response.As for measurements in buildings, Foutch [2] used two forced-vibration generators to study the vibration characteristics of a 12-storey steel frame building. These generators were placed at the building top. Frequencies and mode shapes obtained from experiments were compared with those computed with finite-element models. His results confirmed that displacement amplifications can arise in some structural frames when the building is susceptible to twist. Important observations on building torsion were also obtained by Lu and Hall [3] who monitored two instrumented buildings during the 1987 Whittier Narrows Earthquake. They concluded that symmetric buildings are particularly sensitive to accidental torsion.The previous findings obtained from measurements of either models or buildings are also important because they support some of the results obtained from analytical studies. However, it seems that additional work is needed to support other results, which can be incorporated in building codes. For instance, some one-storey model studies [4,5] observed that the amplification factor related with the estimation of design eccentricity benefits more large-eccen...

Péndulo De Prueba Para El Estudio Dinámico De Modelos Estructurales

“…En la segunda parte, se presenta una descripción global de la respuesta de los modelos con el propósito de ilustrar sus características. En este trabajo no se presentan con detalle los resultados de torsión de los modelos estructurales probados; para mayor información al respecto se puede consultar el trabajo de De la Colina et al (2007).…”

“…También se presenta la descripción general de la respuesta de los modelos, pero sólo para entender el tipo de movimiento generado por el aparato. Mayores detalles de la respuesta estructural de los modelos se pueden consultar en De-la-Colina et al (2007).…”

“…Por lo tanto, el modelo se pudo estudiar con dos grados de libertad. Una descripción de la respuesta torsional se presenta en De-la-Colina et al (2007). En este caso, X 1 se define como el desplazamiento lateral de la masa m 1 asociada a la plataforma y al generador y X 2 es el desplazamiento lateral total del centro de masas de la cubierta o techo del modelo (m 2 ).…”

An Alternative Recommendation for Design Eccentricity by Consideration of Uncoupled Frequency Ratio

“…Using unidirectional excitations may not be sufficient for accurately estimating the torsional response, as the parameters that control the torsional response, such as stiffness, radius of gyration, and location of the center of stiffness, can be significantly altered under bi-directional excitations [13][14][15][16][17][18] . While many experimental studies are still required to examine and verify the effects of torsional coupling, there are a few studies available that have already been conducted 19,20 .…”

Tasarım Eksantrikliği İçin Alternatif Bir Öneri

“…Çünkü çift yönlü deprem yüklemesi sebebiyle kattaki dönme artacağından bu da rijitlikte, dönme yarıçapında değişime, rijitlik merkezinin değişimine sebebiyet vereceğinden çift yönlü deprem yüklemesi daha kritik bir yükleme durumudur [12][13][14][15][16][17]. Tüm bu özetlenen çalışmalara rağmen literatürde, YK-D etkileri konusunda hala büyük miktarda özellikle deneysel çalışmaya ihtiyaç duyulmaktadır, ancak bazı deneysel çalışmalar şöyle verilebilir [18], [19].…”