The Performance Analysis of the Difference Types of Steel Bracing for the Reinforced Concrete Building

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The Performance Analysis of the Difference Types of Steel Bracing for the Reinforced Concrete Building

Ayaanle Alia aInstitute of Civil Engineering, Structural Engineering Program,

stanbul Kültür Üniversitesi

Erdal Coskunb,

b Professor, Department of Civil Engineering, stanbul Kültür Üniversitesi

Abstract: – The recent earthquakes that happen in this world caused disastrously and impacts on the existing constructions. The rein- forced concrete structures were designed primarily for gravity loads. They were considering lateral forces that may be much smaller than that prescribed by the current codes. Therefore, enough knowledge is necessary for those structures that need rehabilitation after the earthquake. This study is concerned with the uses of steel bracing systems in an existing building in from of retrofitting and the rehabilitation of structural elements damage during seismic activities. Steel bracing, it's easy to connect the frame structure after the earthquake damages the structural-elements of the building. This study has deeply studied the comparison of the different types of concentric bracing systems. The importance of this research is to compare the different kinds of concentric bracing-systems. Also, to know the most resistible steel-bracing and the most useful during the earthquake.

Keywords: Earthquake, pushover analysis, steel bracing, seismic, retrofitting.

INTRODUCTION

The steel bracing is supporting the model frame, so it's one of the methods of retrofitting for the seismic tremor harms of the current structures. Steel bracing is utilizing to prevent the horizontal forces acting on the building. The lateral-loads are the powers coming when wind and seismic-loads subject to the building. Steel bracing is making of steel, and it helps the structures for the protection of the horizontal loads. It takes part in the vitality energy dissipation through strain and pressure during the quake. The structural components such as beams and the column support the structure for the loads coming in the vertical direction, and the purpose of using steel bracing is to protect the horizontal loads coming from the earthquake or winds. Inserting steel bracing to the structure can be internally or externally it depends on the situation of the structure after the earthquake. There are two types of steel bracing concentric or eccentric steel bracing so, in this investigation, we will consider concentric bracing so concentric bracing. CSB is separating into two like SCBF and CBF. The distinction between these two concentric bracings is, SCBF can resist more loads and pressure than the CBF. SCBF is used to diminish the distortion for the delicate story and gives the Story steadiness for the seismic actuates a reaction.

Objectives and Scope of this Study

The importance of this investigation is to assess the performance of the concentric bracing system during seismic activities. The performance of the steel-bracing in the RC buildings has analyzed by SAP2000.

The following are the objectives of the study.

The enhancing the Safety of the existing structures that harm during the seismic tremor.

  • Checking the performance of the various types of concentric steel bracing system through the existing Rc structure.

Evaluation of the impacts of the horizontal loads acting on the building.

Increasing Safety against the horizontal loads that are working on the building during the seismic activity.

The Pushover Analysis Method

This method is the applying pattern of direct lateral-loads on the frame, starting from zero to a value of cross ponding to an exact displacement-level and determining the possible weak members and the failure members of the structure. The performance of the building is evaluating by using hinges position at the target-displacement or the performance-point corresponding to an exact earthquake-level. The acceptable performance is if the demand is less than the capacity of all the hinges positions as the loading and assessment procedures are only virtually correct concerning the real-earthquake hazards.[1]

History of Pushover Analysis:

A list of researchers studies the pushover method, and they are as follow: –

  • (Fajfar and Fischinger-1987) these researchers propose the N2 method as a non-linear procedure appropriate to the design of regular building oscillating mainly in a single mode.

  • (CSM) capacity spectrum method approved ATC-40 (ATC 1996), was the first introduced in the 1970s through freeman as a quick assessment procedure for the evaluation of vulnerability structures during the earthquake (Freeman 1975; Freeman 1978). The analysis procedure is compers to the capacity of the building in a curve called pushover-curve and the demand of the ground-motions under construction in the way of elastic response spectrum. [2]

  • (Mahaney-1993) this researcher proposed the acceleration-displacement-response-spectrum (ADRs) that the spectral-accel- eration versus spectral-displacement is plotting in a curve, with a period (T) stands for the radial lines. The crossing of the capacity-spectrum and the demand-spectrum make available of the displacement-demand and the inelastic-accelerationthe capacity spectrum method was-updated (FEMA-440 2006).[3]

  • The federal-emergency-management-agency first introduced Coefficient-Method (CM) in the USA (FEMA-273 1997) and then developed a pre-standard for the rehabilitation of the structures in seismic hazards FEMA-365 (2000). Later this method is updated into FEMA-440 (2006).

    Assessment of the pushover method procedure

    The pushover procedure performed to the analysis of the lateral base-shear and the roof-displacement relationship of the building. The pushover-curve for the structure, including the initial linear, in which the frame members are deforming in their elastic behavior to the inelastic region, where the beam and the column members start developing plastic-hinges. If the lateral defor- mation continues, the other plastic deformation happens to the structure.

    Modal Pushover Analysis (MPA):

    this method has been establishing to account for the more significant mode effects. This analysis method is highly exact if the building is very deforming into the zone of stiffness and failure in strength. This method is making on the supposition of the standard model-analysis that extended into an inelastic system. The seismic response is determined in the modeling development of the seismic effects by pushover analysis using force distribution in each mode. The calculation of the complete reaction of the structure is obtaining by combining these model responses through the SRSS model combination method.

    Methodology:

    This part is the modeling and base-shear analysis of the structures. The most significant part of this is about designing the RC models and checking their strength by SAP2000 programming. SAP2000 programming is utilizing for all models during this study, and it's using for checking the quality and limit of the structural components before reaching the highest expecting dis- placement of the models. There are two methods used during this study, such as the pushover method and THA.

    Displacement During Pushover Analysis

    The force-displacement method shows the displacement modification curve below has higher precision and can be used for tensile frames through a computer because the computer software can't do displacement-based for the pushover method. So, the dis- placement force method must be making, even if i has lower precision. The computer analysis will adjust the incremental dy- namic, which represents 2% of the displacement process, to decrease the variation of the pushover curve in the building response using the pushover method. Also, to get the non-linearity behavior of the building, the pushover curve must be defined. [4] [5] [5] Figure 1: Displacement modification curve [4]

    Plastic Hinges

    The occurrence of the plastic hinges is the building by using the pushover method will vary according to the no of story, also the type of bracing system and the type of plan shape of the structure. The plastic hinges will reach different limits according to the deformation of the steel bracing system because of the failure moment underground motion. In this study, plastic-hinges will be under three properties. (IO) immediate occupancy, (LS) life safety, Cp collapse prevention, A, B, C, D, E according to the con- dition of the hinges. This part, the comparison between the same no of stories and the plan shape, will be analyzed by the pushover curve on the X and Y-axis. [4]

    FiguTorep4:baprslan of the models

    FiguTorep4:baprslan of the models

    Modeling

    The SAP2000 v20 software is utilizing to develop a 3D model and carry-out static non-linear pushover method. Five-story frames are modeling to consider the performance of the different types of steel-bracing system on structural behavior (sap2000-v20). This model is a residential RC building with the same plan geometric located in Okmeydani Istanbul, Turkey at coordinate 41.059243 °, and 28.952586 with a 10% probability of being exceeded in 50 years or 475-year return period and design spectrum and site parameters in table 1.

    Table 1: [7]

    Site Class

    SS

    S1

    SDS

    SD1

    PGA

    PGV

    D

    S S =0.827

    S 1 = 0.234

    PGA = 0.341

    PGV = 21.4

    S S = 0.827

    S 1 = 0.234

    The Properties for the Geometrical Plan:

    The properties for the geometrical plan dimension:

    • The floor plan dimension is 31m2.

    • The base width and length of each room are 36M2.

    • The height of each story is 3.5M.

    • The building type is a residential structure.

Figure 3: Building geometry

Table 2: Dead and live load details of beams

Story no

Beam Lo- cation

Uniformly dis- tributed

Load (kN /m)

Concentrated Loads (kN) at 2/3 L locations

Dead Load (DL)

Live Load (LL)

DL

LL

Stories 1

to 5

Exterior

24

5

Interior

3

0

46.2

35.4

Roof

Exterior

10

2

Interior

7

0

56.3

16.8

Story no

Beam Lo- cation

Uniformly dis- tributed

Load (kN /m)

Concentrated Loads (kN) at 2/3 L locations

Dead Load (DL)

Live Load (LL)

DL

LL

Stories 1

to 5

Exterior

24

5

Interior

3

0

46.2

35.4

Roof

Exterior

10

2

Interior

7

0

56.3

16.8

B1 (300 × 600 mm2)

At left and right supports

Top bars

As = 3800 mm2

Bottom bars

As = 2200 mm2

B2 (300 × 600 mm2)

At left and right supports

Top bars

As = 3423 mm2

Bottom bars

As = 1722 mm2

B3 (300 × 600 mm2)

At left and right supports

As = 1670 mm2

Bottom bars

As = 1540 mm2

Published by : http://www.ijert.org

International Journal of Engineering Research & Technology (IJERT)

ISSN: 2278-0181

Vol. 9 Issue 07, July-2020

Figure 5: Five story model [2]

IJERTV9IS070293

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(This work is licensed under a Creative Commons Attribution 4.0 International License.)

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Steel Bracing System

The function of the steel bracing is to protect from the earthquake. Also, increasing the strength of the RC building. After more research and application, this idea has become more relevant for seismic protection because of the simplicity of the implementa- tion, and its more relatively cheaper than the shear wall. For example, Sugano and Fujimura performed a series of tests on a frame model of one story, which had been strengthened by a steel bracing system. They compared with a masonry infilled wall. They aimed to understand the effect of each of these systems; then, they found that the steel bracing system has more strength than the masonry filled wall during the seismic activity. [8]

Concentrically and Eccentrically braced frames: –

The steel bracing system is designed primarily to resist the earthquake and wind loads. The members of the steel Bracing are intending to work in compression and tension like the truss. Steel bracing members assist in a decrease in the sheer force demand and reducing the bending moment on the columns and the beams in the structure, also they decrease the lateral displacement of the building. The earthquake loads are shifting as an axial load in the steel bracing members. It's possible to use different kinds of an eccentrically bracing frame like K shaped in the global bracing along with the building height. Sometimes it's possible to use concentrically steel bracing systems like X, V, Z, diagonal bracing inside the vertical members of the structure.

Figure 6: Concentrically and eccentrically braced frames [8]

RESULT

SAP2000 is utilizing to compute and check the performance response for the various types of steel bracing. The type of structure selected during this study is an Rc frame. The pushover method is applying to the models; then, the result is plotting into a curve. The purpose behind choosing this strategy is checking the performance of the steel bracing and its strength. The pushover proce- dure is designing for all structures that are establishing is presented in the curve-below. During this investigation, SAP2000 is utilizing to examine the response performance of the different kinds of steel-bracing when it's been using to the strengthened RC structure, then estimate the-performance for the different types of the steel-bracing. During this study, each steel bracing has made different displacement, and their strength was different from each other. Also, the un-braced building joints are stiff, so pushing causes a joint failure. This curve clearly defines that inserting the structure for the steel bracing is dramatic increases the strength of the building and allows the building can stand with high acceleration and greater magnitude of the earthquake.

[9]

Inter-Story Drift

The inter-story drift ratio is the maximum percentage drift between two floors divided by their story height. The measuring parameter both structural and non-structural damages on the building. The steel-bracing structure results show a decrease in peak inter-story drift. Story drift for both braced and fixed structures is shown in Figure 9 to decrease at upper stories in a fairly linear manner. Top floors have lesser story drifts compared to lower story drifts because of their low displacement values, but in the case of steel-bracing, the inter-story-drift of the first story is less than the second story inter-story drift which should not have been the case.

Displacement of the Different Types of Steel Bracing System

the comparison of the dynamic load-displacement in the x-direction for the different types of steel bracing is compering during this research investigation. This investigation proves that the top story floors have greater-displacement than the lower stories; also, this study demonstrates that the uses of steel bracing in the building frame it dramatically decreases the lateral loads or story displacement. During this investigation of the different types of steel-bracing are compered, to know the most irresistible during the seismic activities. So, X-bracing becomes the most useful and ethical reductions for story displacement. Therefore, the X

bracing was helpful to the structures, also as the height of the structure increase the range of the movement will decrease

Figure 7: The displacement curve of the five-story building

Figure 8: The displacement of five story building

Figure 9: Story drift curve for five-story building-x direction

International Journal of Engineering Research & Technology

ISSN: 2278-0181

Vol. 9 Issue 07, July-2020

Figure 10: Five story diagonal Figure 11: Five story inverted bracing

Figure 12: Five story x-bracing

Figure 13: Five story zipper bracing

International Journal of Engineering Research & Technology

ISSN: 2278-0181

Vol. 9 Issue 07, July-2020

CONCLUSION

During this study, various types of steel bracing systems have been analyzing as an effective method in the form of retrofitting an existing RC building. The different kinds of steel bracing that selected during this study are; (x bracing, inverted bracing, zipper bracing, and diagonal-bracing). This research of the various type of steel-bracing has been tested by checking their strength limit of the existing structure. During this study, there are differences in height models selected, but in this article, only five-story building is showed, which is utilized and analyzed by the SAP2000 program. The pushover method is applying through all the models. So, the result of this study indicates that the x bracing system was the most irresistible during this study compared with the others. X-bracing system increases the strength of the structure; also, it takes part in the energy dissipation of the frame.

REFERENCES

  1. Applied Technology Council, ATC 40: Seismic evaluation and retrofit of concrete buildings (the USA,1996).

  2. Federal Emergency Management Agency, FEMA 440: Improvement of non-linear static seismic analysis procedures (Washington, 2005).

  3. Federal Emergency Management Agency, FEMA 356: Pre-standard and commentary for the Seismic-rehabilitation of buildings (Wash- ington, 2000).

  4. Federal Emergency Management Agency (FEMA). (2000). "Prestandard And Commentary for The Rehabilitation of Buildings" FEMA- 356, Washington DC.

  5. Applied Technology Council, ATC-40 (1996)." Seismic evaluation and retrofit of concrete buildings" Vol 1-2, Redwood City, California.

  6. AVAD Turkish website.

  7. Federal Emergency Management Agency (FEMA). (2000). "Prestandard And Commentary for the rehabilitation of buildings" FEMA- 356, Washington DC.

  8. S. kawamata and M. OhnumaS. Kawamata and M. Ohnuma, "Strengthening effect of eccentric steel braces to existing reinforced concrete frames," in Proceedings of the 2nd Seminar on Repair and Retrofit of StructuresConference, NSF, AnnArbor, Mich, USA, 198.

  9. Kunnath, S.K., and E. Kalkan. (2011). "IDA capacity curves: The need for alternative intensity factors" University of California Davis, one shields avenue, Engineering III.

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