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Ad T Vermeltfoort - One of the best experts on this subject based on the ideXlab platform.

  • The contribution of CASIEL infill walls to the shear resistance of steel frames The contribution of CASIEL infill walls to the shear resistance of steel frames
    2006
    Co-Authors: Bright M Ng&apos, Dirk R W Martens, Ad T Vermeltfoort
    Abstract:

    In Europe, calcium silicate element (CASIEL) walls are increasingly employed as partitions and external claddings in buildings. The CASIEL infills and the frames mutually interact through frame-wall interfaces. This interaction has a significant influence on the load transmission paths of building structures. In order to safeguard the walls and the frames, as well as the finishes from damages, this behaviour needs to be understood and translated into design guidelines. This paper presents results of experiments conducted on 10 large-scale CASIEL-infilled steel frames monotonically loaded by in-plane shear. Parameters investigated included frame size, rigidity of frame connections, frame-wall interface gaps, and bearing wedges at the frame top-corners. In general, there was an initial stiff load deflection response followed by a much less stiff response during which frame-wall separation occurred and another stiff response leading to, in the majority of cases, Diagonal tension cracking in the infill walls. Shear sliding along the top most bed joint was observed in some specimens. The cracking phase was followed by a less stiff phase, but with an increasing load resistance leading to ultimate failure through crushing of the wall. Increasing the size of the bounding frames increased the stiffness of the infilled frames and moderately increased the cracking loads. Initial gaps between the roof beams and CASIEL wall panels resulted in reduced infilled frame stiffnesses during the transition phase, although they did not significantly reduce the cracking loads. By using bearing wedges in the top corners, the influence of the top gaps was practically eliminated. This technique may be significant in developing a construction technique for industrial application of infilled frames. The rigidity of the frame connections did not significantly influence the stiffnesses and cracking loads of the infill panels. Thirdly, experimental results are presented before, finally, giving some conclusions. 1.1 Defining 'infilled frames' and 'CASIELs' Infilled frames can simply be defined as beams and columns confining walls, as shown, for instance, in Figure 1: Infilled frames -beams and columns confining walls When the walls are not deliberately isolated from the frame, they interact with the frame producing a structural behaviour that is different from a simple addition of the two components. In a mutually beneficial relationship, the infill wall provides lateral rigidity while the bounding frame provides some ductility. If this interaction is ignored in the design assumptions, the actual stress path in the building may be significantly deviant from the assumptions, and potentially risky. If the composite action is assessed it can lead not only to a safer design but also to lighter frames and connections, which in turn are cheaper. 195 In the last two to three decades, a new way of building walls, namely with calcium silicate elements (CASIELs) in thin-layer mortar, has evolved (Berkers 1995). Calcium silicate elements are large building 'stones', produced by mixing sand, lime and water, moulding and curing under conditions of pressurized steam, as illustrated in Finishing costs are also significantly reduced, due to the smoothness of the surface of calcium silicate elements. Other factors cited in favour of calcium silicate elements include excellent structural performance of the material, environmental friendliness (the material can be crushed and used as earth fill or reused to produce other calcium silicate products after the structure's life span), better quality products due to production of elements in factory controlled conditions and possibilities of construction during cold/rainy weather conditions. CASIEL-infilled frames Although a lot of research has been done on infilled frames in the past, there has not yet been any research involving infill walls constructed from CASIELs. Most full -scale experiments have been on frames infilled with clay or concrete brick masonry (e.g. While similarities may be expected between the behaviour of CASIEL walls and traditional brick masonry infills, significant differences might also occur. The major difference in the two types of walls is that the former has much fewer and much thinner joints than the latter. Depending upon the scale at which the wall is regarded, either of the wall types may be seen as more homogenous than the other. From a global point of view, a masonry wall, with small bricks, may be seen as a 'homogenous' composite while a CASIEL wall is an articulation of large blocks with discontinuities at the thin-layer joints. On the other hand, at a local level, CASIELs may be taken as homogeneous (and isotropic) while brick walls appear as a heterogeneous articulation of bricks and mortar through discrete interfaces. A second peculiarity of CASIEL walls has to do with the construction process. By virtue of the size of the elements and the handling equipment, some working space, as illustrated in Theoretically, steel frames contribute ductility and infill walls contribute stiffness to infilled frames. The infill wall acts as a Diagonal Brace to the frame. The effectiveness of the Diagonal Brace depends upon the frame-to-wall stiffness ratio, the contact, bond and shear characteristics at the frame-wall interface and the strength of the infill under biaxial loading (reference). In this study the influence of the following factors was investigated: (a) a structural configuration factor: the frame-to-wall stiffness ratio, (b) an interface detail factor: a gap below the roof beam, and (c) a construction technique: the use of a corner bearing wedge. Tests apparatus A testing apparatus was required for the purpose of providing a platform for the specimen and applying in-plane loading. The basic requirements of such an apparatus have to do with the way the apparatus interacts with its own support, normally the structural floor, and the way it interacts with the specimen at the specimen supports and point of load introduction

Tomaso Trombetti - One of the best experts on this subject based on the ideXlab platform.

  • EXPERIMENTS ON CRESCENT SHAPED Brace, A NEW SIMPLE HYSTERETIC BRACING DEVICE
    place:Santiago Chile, 2017
    Co-Authors: Antoine Dib, Michele Palermo, Stefano Silvestri, Tomaso Trombetti
    Abstract:

    Over the last fifty years, extensive researches have been conducted in the field of seismic isolation systems, innovative earthquake resisting systems and supplemental damping, showing a potential step towards the boosting of the seismic performance of buildings. The Crescent Shaped Braces (CSB) is a new simple steel hysteretic device, recently proposed by some of the authors to be used as an enhanced Diagonal Brace in framed structures, within the Performance Based Design framework. By making use of CSBs as lateral resisting system, thanks to the peculiar shape of such devices, the seismic design may be optimized due to the uncoupling of its lateral stiffness from its yield strength. In the present study, the main results of experimental tests conducted on scaled CSB specimens (designed according to simplified design formulas developed by the authors) realized with different cross-sections are presented. Both monotonic pseudo-static tests and cyclic tests have been performed in order to further assess the seismic behavior of such devices. The overall experimental response in terms of stiffness, strength, ductility and global instability is compared with the design formulations, while the detailed hysteretic response is compared with the results of numerical simulations developed with commercial software. It is shown that the overall experimental behavior of CSBs is well captured by the design formulas and that commercial software are suitable to simulate the hysteretic response of such device

Dib, Antoine <1988> - One of the best experts on this subject based on the ideXlab platform.

  • The Development of a New Hysteretic Device: The Crescent Shaped Brace
    Alma Mater Studiorum - Università di Bologna, 2017
    Co-Authors: Dib, Antoine <1988>
    Abstract:

    The Crescent Shaped Braces (CSB) is a new simple steel hysteretic device proposed to be used as an enhanced Diagonal Brace in framed structures. The CSB allows the practical designer to choose the lateral stiffness independently from the yield strength of the device, due to its peculiar ad-hoc shape. In the present thesis, a complete study referring to the CSB has been presented. Analytical formulas have been developed to describe the behavior of such devices under tensile and compressive loads, in elastic and post-yielding phases. The same device has been studied through extensive numerical simulations to assess the seismic capacity and its response under cyclic loads. As well, the main results of experimental tests conducted on thirteen scaled CSB specimens realized with different cross-sections are presented. The overall experimental response in terms of stiffness, strength, ductility and global instability is compared with the design formulations and with the results of numerical simulations developed with commercial software. It is shown that the overall experimental behavior of CSB is well captured by the design formulas and that commercial software are suitable to simulate the hysteretic response of such device. After the validation of the hysteretic capacities of the Crescent Shaped Braces, a new seismic concept has been proposed within the PBSD and the concept of the enhanced first story. It relies on the total separation between the Vertical Resisting System (VRS) and the Horizontal Resisting System (HRS) in order to attain a certain objective curve of the structure. An applicative example has been studied following this concept and exploiting the advantages of the CSBs as seismic dissipative devices, to be used for the HRS. Some indicative uses of the CSB have been presented, like horizontal link, angle reinforcement for beam-column joints and façade dissipative elements

Bright M Ng&apos - One of the best experts on this subject based on the ideXlab platform.

  • The contribution of CASIEL infill walls to the shear resistance of steel frames The contribution of CASIEL infill walls to the shear resistance of steel frames
    2006
    Co-Authors: Bright M Ng&apos, Dirk R W Martens, Ad T Vermeltfoort
    Abstract:

    In Europe, calcium silicate element (CASIEL) walls are increasingly employed as partitions and external claddings in buildings. The CASIEL infills and the frames mutually interact through frame-wall interfaces. This interaction has a significant influence on the load transmission paths of building structures. In order to safeguard the walls and the frames, as well as the finishes from damages, this behaviour needs to be understood and translated into design guidelines. This paper presents results of experiments conducted on 10 large-scale CASIEL-infilled steel frames monotonically loaded by in-plane shear. Parameters investigated included frame size, rigidity of frame connections, frame-wall interface gaps, and bearing wedges at the frame top-corners. In general, there was an initial stiff load deflection response followed by a much less stiff response during which frame-wall separation occurred and another stiff response leading to, in the majority of cases, Diagonal tension cracking in the infill walls. Shear sliding along the top most bed joint was observed in some specimens. The cracking phase was followed by a less stiff phase, but with an increasing load resistance leading to ultimate failure through crushing of the wall. Increasing the size of the bounding frames increased the stiffness of the infilled frames and moderately increased the cracking loads. Initial gaps between the roof beams and CASIEL wall panels resulted in reduced infilled frame stiffnesses during the transition phase, although they did not significantly reduce the cracking loads. By using bearing wedges in the top corners, the influence of the top gaps was practically eliminated. This technique may be significant in developing a construction technique for industrial application of infilled frames. The rigidity of the frame connections did not significantly influence the stiffnesses and cracking loads of the infill panels. Thirdly, experimental results are presented before, finally, giving some conclusions. 1.1 Defining 'infilled frames' and 'CASIELs' Infilled frames can simply be defined as beams and columns confining walls, as shown, for instance, in Figure 1: Infilled frames -beams and columns confining walls When the walls are not deliberately isolated from the frame, they interact with the frame producing a structural behaviour that is different from a simple addition of the two components. In a mutually beneficial relationship, the infill wall provides lateral rigidity while the bounding frame provides some ductility. If this interaction is ignored in the design assumptions, the actual stress path in the building may be significantly deviant from the assumptions, and potentially risky. If the composite action is assessed it can lead not only to a safer design but also to lighter frames and connections, which in turn are cheaper. 195 In the last two to three decades, a new way of building walls, namely with calcium silicate elements (CASIELs) in thin-layer mortar, has evolved (Berkers 1995). Calcium silicate elements are large building 'stones', produced by mixing sand, lime and water, moulding and curing under conditions of pressurized steam, as illustrated in Finishing costs are also significantly reduced, due to the smoothness of the surface of calcium silicate elements. Other factors cited in favour of calcium silicate elements include excellent structural performance of the material, environmental friendliness (the material can be crushed and used as earth fill or reused to produce other calcium silicate products after the structure's life span), better quality products due to production of elements in factory controlled conditions and possibilities of construction during cold/rainy weather conditions. CASIEL-infilled frames Although a lot of research has been done on infilled frames in the past, there has not yet been any research involving infill walls constructed from CASIELs. Most full -scale experiments have been on frames infilled with clay or concrete brick masonry (e.g. While similarities may be expected between the behaviour of CASIEL walls and traditional brick masonry infills, significant differences might also occur. The major difference in the two types of walls is that the former has much fewer and much thinner joints than the latter. Depending upon the scale at which the wall is regarded, either of the wall types may be seen as more homogenous than the other. From a global point of view, a masonry wall, with small bricks, may be seen as a 'homogenous' composite while a CASIEL wall is an articulation of large blocks with discontinuities at the thin-layer joints. On the other hand, at a local level, CASIELs may be taken as homogeneous (and isotropic) while brick walls appear as a heterogeneous articulation of bricks and mortar through discrete interfaces. A second peculiarity of CASIEL walls has to do with the construction process. By virtue of the size of the elements and the handling equipment, some working space, as illustrated in Theoretically, steel frames contribute ductility and infill walls contribute stiffness to infilled frames. The infill wall acts as a Diagonal Brace to the frame. The effectiveness of the Diagonal Brace depends upon the frame-to-wall stiffness ratio, the contact, bond and shear characteristics at the frame-wall interface and the strength of the infill under biaxial loading (reference). In this study the influence of the following factors was investigated: (a) a structural configuration factor: the frame-to-wall stiffness ratio, (b) an interface detail factor: a gap below the roof beam, and (c) a construction technique: the use of a corner bearing wedge. Tests apparatus A testing apparatus was required for the purpose of providing a platform for the specimen and applying in-plane loading. The basic requirements of such an apparatus have to do with the way the apparatus interacts with its own support, normally the structural floor, and the way it interacts with the specimen at the specimen supports and point of load introduction

J. S. Hwang - One of the best experts on this subject based on the ideXlab platform.

  • Equivalent Damping Ratios of Structures with Supplemental Viscous Dampers
    2015
    Co-Authors: J. S. Hwang
    Abstract:

    The current design formulas such as those provided by FEMA273/274 for building structures with supplemental viscous dampers were derived based on the shear building assumption. However, for medium-rise to high-rise buildings that deform in a combined form of shear and bending when subjected to seismic loading, the design using existing formulas may result into an actual damping ratio much lower than what is expected by the design. Therefore, the actual seismic performance of the structure may be worse than what is expected by the design. In this study, modified design formulas are derived considering both shear and flexural deformations of the building structures subjected to ground excitations. The modified formulas are derived for two often used installation schemes of viscous dampers including Diagonal-Brace-damper system and K-Brace-damper system. Numerical verifications have indicated that the modified design formulas predict a more accurate viscous damping ratio contributed by linear viscous dampers and ensure a more conservative design for the structure with nonlinear viscous dampers