ppt presentation

1. “Techniques for Mitigation of Soft Storey on Tall
Building under lateral Loads”
DEPARTMENT OF CIVIL ENGINEERING
RABINDRANATH TAGORE UNIVERSITY
BHOPAL (M.P.)
Guided by: Submitted by:
Prof Rachana Bajaj Mukesh Dhurvey
Asst.Professor M.Tech. 4th Sem
UIT, RNTU, Bhopal Enrollment No. - AU191180
UIT, RNTU, Bhopal

2. Abstract
• The soft-story plays a significant role in its seismic success in high-rise
construction. At the level of the soft story, the uniformity of the framework
is discontinuous because of no infill walls or differences in floor height. It
is this consistency that causes the structural collapse of multi-stored
buildings under the burdens of the earthquake.
• The study is carried out by taking into consideration earthquake with a
soft-story effect and mitigation techniques like BRB-brace, crescent brace
and combination to prevent soft story.
• Moreover, the displacement, story drift, time period is compared after
examining the above structure. There is also a study of different design
parameters, and significant results have been obtained.

3. CONTENT
 Introduction
 Literature Review
 Problem Definition
 Proposed Work
 Result and Analysis
 Conclusion
 Future work
 References

4. INTRODUCTION
• A soft-story is described as a story in a building that has considerably less
rigidity or insufficient ductility (energy absorption capacity) to withstand
the building stresses caused by the earthquake. If a building has a floor
that is 70 per cent less rigid than the level above it, it is called a building
on a soft story.
• This soft storey provides a significant weakness in an earthquake. Since
soft stories are usually associated with commercial spaces and garages,
they are often on a building's lower floor, which means that when they
fall, they will take the entire building down with them, causing significant
structural damage that can make the structure completely unusable.

5. CRESCENT AND BUCKLING RESISTANCE BRACE
• The Crescent Shaped Braces (CSB) is a new simple steel hysteretic device,
recently proposed by our group of research at the University of Bologna to be
used as an enhanced diagonal brace in framed structures, within the
Performance Based Seismic Design framework.
• In Japan, at the end of the 1980s, the concept of BRBs was developed. It
appears in the United States following the 1994 Northridge earthquake and is
now accepted as a lateral load resistant solution as regulated by current
standards.
• In an earthquake, a building distributes a significant quantity of cinematically
power into the Structure, and the degree of damage to the building depends
on its dissipation. Earthquake resistant systems are designed to efficiently
dissipate energy from the Structure through ductile and controlled production.

6. Fig. of Braces
Crescent Brace

7. LITERATURE REVIEW
• Niloufar Mashhadiali (Journal of Constructional Steel Research
Volume 181, June 2021) :
• Aim – This paper proposes a hybrid CBF bracing system to reduce soft-
story mechanisms and improve the structural behaviour of the CBF system.
• Proposed work – The proposed system is composed of a buckling
restrained brace (BRB) or an energy dissipation device and a strong brace
(SB) in one span. The strong braces are designed to have an elastic
performance during an earthquake. The direction of BRB and SB are
changed, inversely, story by story in a zigzag form. This improves both the
soft story mechanisms and the buckling capacity of CBFs. In this study, a
set of 6-story structural models with different bracing patterns including
inverted-V, multi-X, zipper, hexa (hexagonal bracing configuration),
and strong back braced frames were evaluated through nonlinear static
(pushover) and dynamic analyses (IDA).

8. • Hanqin Wang, 1 Yulong Feng (Hindawi Advances in Civil
Engineering Volume 2019):
• Aim- A series of nonlinear pushover analyses and response
history analyses are conducted to investigate the key factors
affecting the DCE of BRBFs.
• Proposed work – Then, parametric analyses are performed to
investigate the influence of two stiffness distribution parameter
(in the horizontal and vertical directions) on the DCE of a 6-
story BRBF dual system designed according to the Chinese
seismic code. The results show that increasing the MF stiffness
and avoiding abrupt changes in the BRB stiffness between
stories can effectively mitigate the DCE of BRBFs. Finally, the
correlations between various damage performance indices are
analysed.

9. • Niloufar Mashhadiali, Ali Kheyroddin (2018 Published by Elsevier
Ltd):
• Aim – This paper aims to propose an innovative braced frame named
hexa-braced frame for the improvement of the seismic response of
conventional steel-braced frames.
• Proposed work - In the proposed system, vertical structural elements
connect the V and inverted-V bracings over three stories to form the
hexagonal bracing configuration, in which two stories. A set of 4,10 and 20
story building models were used to evaluate the seismic response of the
proposed bracing system through nonlinear static (monotonic and cyclic)
and dynamic analysis. The results were compared with the responses of
similar X-braced frame models as the benchmark.

10. Problem definition
• The evaluation of structures, such as building structures with soft stories,
becomes more critical as they have been severely damaged or collapsed in
the earthquakes due to their unique collapse mechanisms.
• In this condition, the role of the structural engineer becomes more critical if
the building located in a seismically active zone.
• To provide the solution which meets the structural performance of the
building as specified by the governing Code and simultaneously providing
satisfactory output to clients, a structural engineer should have a sound
understanding of the response of different types, parts, and configuration of
a building during a seismic event.
• So, structure engineer needs a design procedure that can calculate seismic
demands of the irregular building.

11. Fig.1-Flow diagram of proposed work
Design of building
Load application
Seismic force calculation Change of stiffness
Building analyzed and Output
parameters noted

12. PROPOSED WORK
• To study the effect of soft story on G+26 RCC structure under response
spectrum method
• To study the effect of the mitigation techniques using BRB and crescent
brace, combination of BRB and crescent brace.
• To study the effects of these mitigation techniques on soft-story
characteristics of the building model and seismic performance of the
building
• To compare the results of different models in terms of displacement, drift,
time period and story stiffness.

13. Continues….
• Model 1: G+26 with soft story
• Model 2: G+26 with soft story with BRB Braces
• Model 3: G+26 with soft story with Crescent braces
• Model 4: G+26 with soft story with crescent and BRB brace
In the first model, a reinforced concrete frame building situated in the IV zone
is taken for study. The plan area of the building is 25 x 15 m, with 3m as the
height of each typical story. It consists of 5 bays in X-direction and three bays
in Y-direction.

14. Isometric Views of Model with Soft Story
Model Plan View of Building with Soft Story

15. Isometric Views of Model Soft Story with BRB
Elevation view of Model Soft Story with BRB

16. Isometric Views of Model with Soft Story
with CRESCENT brace
Elevation view of Model with Soft Story with
CRESCENT braces

17. RESULTS AND DISCUSSIONS
• The results obtained are of different parameters such as story displacement,
Storey drifts, Base shear, Modal Periods, etc. The results obtained by
carrying out by linear static Analysis for G+26, Storey Buildings as listed.
• Subsequent Discussions made about the Results Obtained based on the
story drifts, time period, displacement and story stiffness, etc. for
Symmetric buildings individually and also considering the Storey effect of
Symmetric buildings by comparing the responses of the structure for 26
story Buildings.

18. STORY DISPLACEMENT WITH RESPONSE SPECTRUM METHOD
10.6
10.8
11
11.2
11.4
11.6
11.8
displacement
Top stories
DISPLACEMENT IN X DIR
NORMAL WITH SOFT STORY
SOFT STORY WITH BRB
SOFT STORY WITH CRESCENT BRACE
SOFT STORY WITH BRB & CRESCENT
BRACE
15.4
15.6
15.8
16
16.2
16.4
16.6
16.8
17
17.2
17.4
17.6
displacement
Top stories
DISPLACEMENT IN Y DIR
NORMAL WITH SOFT STORY
SOFT STORY WITH BRB
SOFT STORY WITH CRESCENT BRACE
SOFT STORY WITH BRB & CRESCENT BRACE

19. 0.0001475
0.000148
0.0001485
0.000149
0.0001495
0.00015
0.0001505
0.000151
0.0001515
0.000152
0.0001525
DRIFT
(mm)
TOP STORY
STORY DRIFT IN X DIR
NORMAL WITH SOFT STORY
SOFT STORY WITH BRB
SOFT STORY WITH CRESCENT
BRACE
SOFT STORY WITH BRB &
CRESCENT BRACE
0.00022
0.000221
0.000222
0.000223
0.000224
0.000225
0.000226
0.000227
0.000228
0.000229
0.00023
DRIFT
(mm)
TOP STORY
STORY DRIFT IN Y DIR
NORMAL WITH SOFT STORY
SOFT STORY WITH BRB
SOFT STORY WITH CRESCENT
BRACE
SOFT STORY WITH BRB &
CRESCENT BRACE
STORY DRIFT WITH RESPONSE SPECTRUM METHOD

20. Conclusion
 The story displacement increased as the soft story occurs in the building.
The stiffness of the structure reduced due to the soft story, which implies
increasing the max story displacement.
 The added BRBs are affective at dissipating energy and controlling inter-
story drift, thus improving the seismic performance of the original MRF.
 The added BRBs can provide the initial stiffness and energy dissipation for
the MRF, thus reducing the structural displacement response under
earthquakes. The BRB stiffness ratio between stories affects the damage
mechanism of the frame

21. The lateral strength of a building is sum of all the stiffness from column; bracing is
added at each storey. So, the low strength in the lowest floor causing the failure occurs
especially during earthquake. For a building that is not provided any lateral load
resistance component such as bracing, the strength is consider very weak and easy fail
during earthquake.
 Displacement, story drift has been increased by structural irregularities, as the soft
story reduced the inertia force the displacement increased on particular floors.
 The values of story drift are within the permissible limit as per is 1893, which is
0.004 times the story height.

22. Future work
 In the present thesis, analysis of a multi-story building under the effect of
discontinuity in stiffness, which is the soft story, is studied.
 The present work can extend for an exhaustive study of various types of
irregulars and a generalized conclusion for design, or such irregular
buildings can be made, which can help in understanding the behaviour of
such irregular buildings.

23. References
 Hybrid braced frame with buckling-restrained and strong braces to mitigate soft
story Author links open overlay panel, Niloufar Mashhadiali, Research,
Volume, June 2021, 106610.
 Composite behaviour in RC buildings retrofitted using buckling-restrained
braces with elastic steel frames, Panumas Saingam, All Science Journal
Classification (ASJC) codes.
 Damage Concentration Effect of Multi-storey Buckling-Restrained Braced
Frames Hanqin Wang, Advances in Civil Engineering / 2019
 Ashwini S Gudur1 Prof. H S Vidyadhar2: Dynamic Wind Analysis of Tall
Building Provided with Steel Bracing as Per Proposed Draft for Indian Wind
Code and Effect of Soft Storey (Part 2)

24. References
 Inel M., Özmen H.B., Bilgin H., Re-Evaluation of Building
Damage During Recent Earthquakes in Turkey, Engineering
Structures, Vol.30, No.2, (412-427), 2008
 Inel M. And Ozmen H., Effects of Plastic Hinge Properties in
Nonlinear Analysis of Reinforced Concrete Buildings,
Engineering Structures Vol.28(1494-1502), 2006
 Athanassiadou C.J., Seismic Performance of RCC Plane Frames
Irregular in Elevation Engineering Structures, Doi:
10.1016/J.Engstruct.2007.07.015, 2007

25.  Ruiz E. And Diederich R., The Mexico Earthquake of September
19,1985 –The Seismic Performance of Buildings with Weak First
Story, Earthquake Spectra Vol.5 No:1 1989
 Esteva L., Nonlinear Seismic Response of Soft First Story Buildings
Subjected to Narrow Band Accelograms, 10th World Conference of
Earthquake Engineering, Rotterdam, 1992.
 Chang S. And Kim. S. Structural Behaviour of Soft Story Buildings,
National Earthquake Engineering Congress, (449-459), 1994.89
References

26. THANK YOU