Hybrid braced frame with buckling-restrained and strong braces to mitigate soft story

2021 ◽  
Vol 181 ◽  
pp. 106610
Author(s):  
Niloufar Mashhadiali ◽  
Siamak Saadati ◽  
Seyed Amir Mohammad Mohajerani ◽  
Parviz Ebadi
Keyword(s):  
Braced Frame ◽  
Soft Story

Design Development of a Four-Story Strongback Braced Frame

2018 ◽  
Vol 763 ◽  
pp. 1050-1057 ◽  
Author(s):  
Barbara Simpson ◽  
Stephen Mahin
Keyword(s):  
Design Space ◽  
Ground Motions ◽  
Design Development ◽  
Braced Frames ◽  
Braced Frame ◽  
Soft Story ◽  
Numerical Studies ◽  
Steel Truss ◽  
Uniform Drift ◽  
Large Earthquakes

Conventional braced frames tend to concentrate damage in one or a few stories during large earthquakes, indicative of “weak” or “soft” story behavior. To mitigate this behavior, several studies have proposed a modified braced frame, or “strongback”, that utilizes an essentially elastic vertical steel truss to impose a uniform drift distribution. While a subassemblage experimental test and past numerical studies have shown that the strongback system can successfully delay or prevent weak or soft story behavior, the dynamic behavior of this system has not been systematically assessed or evaluated. This study defines the design space for a four-story strongback system. The ability of the strongback to mitigate weak story behavior under a far-field suite of ground motions was assessed using the performance-based methodology in FEMA P695.

Drift Concentration of a Three-Story Special Concentrically Braced Frame with Strongback under Earthquake Loading

2017 ◽  
Vol 863 ◽  
pp. 287-292 ◽  
Author(s):  
Chui Hsin Chen ◽  
I Jung Tsai ◽  
Yao Tang
Keyword(s):  
Case Studies ◽  
Permanent Deformation ◽  
Local Deformation ◽  
Braced Frame ◽  
Soft Story ◽  
Concentrically Braced Frame ◽  
Drift Ratio ◽  
Concentrically Braced ◽  
Structural Demand ◽  
Strength And Stiffness

In conventional special concentrically braced frame (SCBF) structures, the buckling of the braces leads to severe reduction in system strength and stiffness. Therefore soft story mechanisms followed by large permanent deformation are commonly observed in SCBF structures. The strongback system using additional structural components along the height of the building to resist local deformation is able to improve the distribution of the drift. This research conducted case studies to investigate the effects of strength and stiffness of the strongback system on the behavior of typical three-story SCBF system. The primary variables to be investigated are stiffness factor α (strongback stiffness/SCBF stiffness) and strength factor β (strongback strength/SCBF strength). We conducted nonlinear dynamic analyses to evaluate the effectiveness of α and β on structural demand parameters including maximum drift ratio and drift concentration factor (DCF). Analyses results show that although strongback system with excessively high α and β will reduce maximum drift ratio and DCF of SCBF systems, it is noneconomic. On the other hand, strongback systems with low α and β (α<0.0048 and β<0.054) have only little effects on improving structural behavior. The case studies suggested that 0.0096≤α≤0.0168 and 0.081≤β≤0.134 accounting for both efficiency and economics can be used in the design of the selected SCBF systems.

Seismic evaluation of single-storey steel buildings

1999 ◽  
Vol 26 (4) ◽  
pp. 379-394 ◽  
Author(s):  
M S Medhekar ◽  
DJL Kennedy
Keyword(s):  
Seismic Performance ◽  
Response Spectrum ◽  
Time History ◽  
Analytical Models ◽  
Steel Buildings ◽  
Concentrically Braced Frames ◽  
Braced Frame ◽  
Seismic Zones ◽  
Concentrically Braced Frame ◽  
Concentrically Braced

The seismic performance of single-storey steel buildings, with concentrically braced frames and a roof diaphragm that acts structurally, is evaluated. The buildings are designed in accordance with the National Building Code of Canada 1995 and CSA Standard S16.1-94 for five seismic zones in western Canada with seismicities ranging from low to high. Only frames designed with a force modification factor of 1.5 are considered. Analytical models of the building are developed, which consider the nonlinear seismic behaviour of the concentrically braced frame, the strength and stiffness contributions of the cladding, and the flexibility, strength, and distributed mass of the roof diaphragm. The seismic response of the models is assessed by means of a linear static analysis, a response spectrum analysis, a nonlinear static or "pushover" analysis, and nonlinear dynamic time history analyses. The results indicate that current design procedures provide a reasonable estimate of the drift and brace ductility demand, but do not ensure that yielding is restricted to the braces. Moreover, in moderate and high seismic zones, the roof diaphragm responds inelastically and brace connections are overloaded. Recommendations are made to improve the seismic performance of such buildings.Key words: analyses, concentrically braced frame, dynamic, earthquake, flexible diaphragm, low-rise, nonlinear, seismic design, steel.

scholarly journals Seismic Response of RC Frames with a Soft First Story Retrofitted with Hysteretic Dampers under Near-Fault Earthquakes

2021 ◽  
Vol 11 (3) ◽  
pp. 1290
Author(s):  
Santiago Mota-Páez ◽  
David Escolano-Margarit ◽  
Amadeo Benavent-Climent
Keyword(s):  
Cost Effective ◽  
Far Field ◽  
Soft Story ◽  
Near Fault ◽  
Rc Frames ◽  
Story Drift ◽  
Number Of Cycles ◽  
Rc Frame Structures ◽  
Near Fault Earthquakes ◽  
Hysteretic Dampers

Reinforced concrete (RC) frame structures with open first stories and masonry infill walls at the upper stories are very common in seismic areas. Under strong earthquakes, most of the energy dissipation demand imposed by the earthquake concentrates in the first story, and this eventually leads the building to collapse. A very efficient and cost-effective solution for the seismic upgrading of this type of structure consists of installing hysteretic dampers in the first story. This paper investigates the response of RC soft-story frames retrofitted with hysteretic dampers subjected to near-fault ground motions in terms of maximum displacements and lateral seismic forces and compares them with those obtained by far-field earthquakes. It is found that for similar levels of total seismic input energy, the maximum displacements in the first story caused by near-fault earthquakes are about 1.3 times larger than those under far-field earthquakes, while the maximum inter-story drift in the upper stories and the distribution and values of the lateral forces are scarcely affected. It is concluded that the maximum displacements can be easily predicted from the energy balance of the structure by using appropriate values for the parameter that reflects the influence of the impulsivity of the ground motion: the so-called equivalent number of cycles.

Multi-axis testing of concrete-filled steel tube columns forming ductile soft-story in multi-story buildings

2021 ◽  
Vol 183 ◽  
pp. 106736
Author(s):  
Hamidreza A. Yazdi ◽  
M. Javad Hashemi ◽  
Riadh Al-Mahaidi ◽  
Emad Gad
Keyword(s):  
Steel Tube ◽  
Concrete Filled Steel Tube ◽  
Soft Story
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