5.2 Concrete Structures II
Feasibility of High-Rise Buildings with PRESSS-technology
M. Palmieri & S. Pampanin
ABSTRACT: This paper presents a first investigation on the feasibility of high-rise buildings using PRESSS-Technology and its seismic performance capabilities. This solution, in fact, can develop a very stable inelastic behaviour without leading to structural damage in the plastic hinge regions and while guaranteeing residual displacements within the operational limits due to its self-centring behaviour. On the base of an existing reference building, composed by the interaction of different resisting systems strategies, two different systems, namely wall systems and frame systems will be afterwards analysed in details. While looking at the responses of these two different resisting systems, the seismic response when implementing a monolithic type of connection is then compared to that of a PRESSS-technology alternative for both wall and frame systems. The Hybrid solution, proposed and analyzed on four different heights of Tall Buildings, from 15 to 45 stories, appear to be a valid alternative to the monolithic connection, having comparable response in terms of interstory drifts and shear-moment demand, but considerably advantages when looking at the overall performance in terms of low-damage, negligible residual-permanent displacements as well as when including possible benefits in the constructability of the whole system. On the contrary the displacement design approach, although it has shown great potentials and flexibility, in its actual formulation is still lacking of a reliable accuracy on the peculiar response of taller structures.
Tests and Analysis on Flexural Deformability of Reinforced Concrete Columns with Wing Walls
Toshimi Kabeyasawa, Yousok Kim, Mitsuharu Sato, Hwang Hyunseong & Yoji Hosokawa
ABSTRACT: A series of tests on reinforced columns with wing walls have been conducted from 2007 to 2010. Following the shear tests in the first three years, flexural tests were conducted for six specimens in 2010, to investigate the effects of the moment-to-shear ratios of loading, the reinforcement details and the width and length of the wing walls on the flexural deformability. The specimens with thin wing walls showed strength decay after the ultimate strength in flexure, due to the compression failure of concrete and buckling of the re-bars at the wall ends under the larger deformation amplitudes. As for the specimens with thick wing walls, the strength decay was much less generally, and was very slight in case of the well-confined detail at the wall edges. Although the strength decay was different, all specimens showed ductile and stable behaviour in flexural failure mode up to the maximum loading drift level, owing to the inelastic energy dissipation by the wing walls, by which the damage to the column is relatively relieved. The observed ultimate strengths and deformations are compared with calculation in proposed design form for practice, by which fair correlations are obtained for both.
Drift Capacity of Lightly Reinforced Soft Storey Structures
A. Wibowo, J.L. Wilson, E.F. Gad & N.T.K. Lam
ABSTRACT: Lightly reinforced concrete columns and soft storey configurations are prevalent in many old buildings in regions of lower seismicity. This type of structure is believed to have a very low lateral load and drift capacity from a conventional design perspective. Furthermore, the application of design standards in low and moderate seismic regions such as Australia, results in most of the lightly reinforced structures being deemed unsafe in an earthquake. Therefore, an earthquake damage reconnaissance, experimental field test, and laboratory study of non ductile columns has been undertaken to examine the drift capacity and failure mechanism of such columns.
Firstly, a field reconnaissance was conducted in China after the Wenchuan Earthquake in 2008, particularly in regions with similar design intensity MMI VI to VIII experienced in Australia. A comparison between the Wenchuan Earthquake and the characteristics of design earthquakes in Australia was made to provide insight for the development of future design standards and for the assessment of existing buildings in Australia.
A unique experimental field testing of a precast soft storey building in Carlton Melbourne was then undertaken. Four tests were conducted to measure the drift capacity and load-deflection behaviour of such buildings. The experimental results together with a comparison with theoretical predictions showed that the precast columns with weak connection had significant displacement capacity controlled by the column rocking irrespective of strength degradation.
Lastly, a laboratory research project has been undertaken to investigate the collapse behaviour of insitu lightly reinforced concrete columns. The effect of variation of axial load ratio and longitudinal reinforcement ratio on flexural, yield penetration, and shear displacement as components of the drift capacity were observed. Interesting outcomes showed that lightly reinforced concrete columns were able to sustain lateral drift considerably greater than the code recommendations, whilst the present shear capacity predictions tended to overestimate the nominal shear strength of the column.
Seismic Retrofit of Masonry Buildings with Polymer Grid
A. Dusi, E. Manzoni, M. Mezzi & G. Stevens
ABSTRACT: The performance of masonry walls reinforced using innovative polymer grids embedded into thin plaster layers as a tools for the seismic enhancement of brick masonry buildings have been investigated by experimental tests. A number of diagonal compression, shear compression and out-of-plane tests were executed on sample panels; experimental activities included pseudo-dynamic and shaking table tests on infills and reduced scaled buildings mock-ups, respectively. The results of the experimental activities are presented and discussed. Experimental campaigns have been supported by theoretical and numerical investigations; based on the experimental data and on the results of detailed numerical simulations, simplified models to be used as tools for the design of the retrofitting intervention are hereinafter proposed. The models, calibrated on the experimental evidence, properly consider the collapse mechanisms as well as the grid effect in the evolution of the above mentioned mechanisms.
Shake Table Test of a Three-Span Bridge Model
H. Sun, B. Li, K. Bi, N. Chouw, J.W. Butterworth & H. Hao
ABSTRACT: Damage due to pounding and unseating between bridge girders is a common occurrence in almost all major earthquakes. It results from opening or closing relative displacements in excess of the seating length or gaps provided at the expansion joints. In the design of bridge girders, the only measure usually suggested in current design manuals to avoid out-of-phase movement is to ensure that neighbouring girders have similar fundamental frequencies, ignoring effects such as those due to non-uniform ground motions at adjacent supports. To understand bridge girder response including pounding effect, this paper reports the shake table testing results of a scaled bridge model with three identical spans constructed using polyvinylchloride (PVC). Ground motions considering non-uniformity, time delay, coherency loss and different stiffness of site soil were executed by three separately controllable shake tables. Results showed that in the presence of non-uniform ground motions relative displacement between girders and thus pounding force increases. Column bending moment generally decreases with pounding. Opening and closing relative displacement increase as soil stiffness decreases.