evaluation of seismic performance of thereinforced...

Technical Journal of Engineering and Applied Sciences Available online at www.tjeas.com ©2013 TJEAS Journal-2013-3-24-3313-3324 ISSN 2051-0853 ©2013 TJEAS

Evaluation of Seismic Performance of theReinforced Concrete Buildings with Steel Bracing, Shear Wall and Column Jacketing

Masoud Ghaderi1, Hossein Ghafarzade2, Jalal Jamali3

1. Department of Civil Engineering, Germi Branch, Islamic Azad University, Germi, Iran 2. Assistant Professor, Faculty of Civil Engineering, University of Tabriz

3. Department of Civil Engineering, Ahar Branch, Islamic Azad University, Ahar, Iran.

Corresponding author email: [email protected]

ABSTRACT:In this study several reinforced concrete buildings with intermediate ductility and average 4, 8, 12 and 16 storeys were modeled which were designed for estimated seismic loads based on 2800 standard(2

ndedition) of Iran. In order to evaluate structures under modified seismic

loads models were reloaded based on 2800 standard (3rd

edition)of Iran. Repeated analysis of structures indicated that stress ratio exceeded from allowed limits of regulations and structures' lack of enough lateral resistance. Based on this, it was decided to seismically improve structures using three methods: addingconcrete shear wall, steel bracing and covering columns with steel jacket.In Iranian seismic design code (Standard 2800),similar to many other conventional codes, the design of structures is carried out using force-based methods. On the other hand, Iranian guidelines for seismic rehabilitation(Guide 360) have many similarities with Prestandard and Commentary for the Seismic Rehabilitation of Buildings (FEMA 356).In order to study the structures behavior in nonlinear scope, we used nonlinear static analysis. PERFORM-3D software was used to 3D simulation of structures and ETABS software was utilized in linear analysis and basic design. Keywords:Seismic retrofitting, shear wall, steel brace, seismic evaluation, nonlinear static analysis.

INTRODUCTION

Steel brace or shear walls are applied to increase the seismic resistance of concrete buildings. Shear walls are common in reinforced concrete buildings and steel brace are used in steel buildings. It is several decades that steel bracing are in use to increase lateral resistance and shear resistance of concrete frames. In past 30 years, many concrete buildings were severely damaged or destroyed by heavy earthquakes. In order to prevent these damages there is a logical and cost-effective method to retrofit buildings. Retrofitting is a set of operations done on a part or all structure so that it can bear more loads and overheads than initial condition and shows better behavior characteristics (Penelis and Kappos, 1997).Three major purposes are considered in retrofitting buildings: increasing resistance against lateral loads, increasing ductility and increasing resistance with ductility (Sugano, 1992). In 1991, Bush et.al placed a steel bracing in a concrete frame and obtained considerable increase in inter-plane shear resistance of frame. Ohishi et.al (1988) implemented a similar study on the application of V-shaped braces. In all researches, the steel bracing has been indirectly placed in a concrete frame. First, the steel bracing is placed in a steel frame, and then this steel frame was mounted into concrete frame. Therefore, shear force is transferred indirectly by a steel frame between steel bracing and concrete frame [3]. This is called indirect bracing which is a costly and uneconomic system. When increase in shear strength is desirable in a concrete frame, it is necessary to use a lateral steel frame. Another disadvantage of these frames is their sensitivity to various parameters especially interaction between concrete and steel frames under earthquake effects. In direct bracing, steel bracing is directly mounted to concrete frame. Dynamic interaction between bracing system and concrete frame is insignificant (Maheri and Sahebi, 1997). Maheri and Kosari (2003), after literature review about retrofitting concrete buildings using steel bracing, placed some stereotypes constructed by 1:3 scales as simple frame, braced frame with cross framing and knee-braced under the lateral load to failure phase. Results showed considerable increase in lateral stiffness of frame in the case of knee bracing.

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Tech J Engin & App Sci., 3 (23): 3313-3324, 2013

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Youssef and Ghafarzade (2007) studied the behavior of concrete framed with concentric internal steel bracing. Results of this study showed that the design of RC sections in a braced RC frame can be carried out using conventional RC design methods. General reinforcement detailing requirements are adequate and there is no need to use special seismic detailing. The brace members and their connections can be designed using a similar procedure to that for braces in steel structures. On the other hand, braced concrete frames with reduction factor of load similar to concrete moment frame with moderate ductility shows appropriate behavior during earthquake. Jong-Wha et al. (2007) examined a new concrete building which was constructed in 1980s in US. They used three methods for seismic retrofitting including adding a shear wall in two spans of external frame to increase stiffness and buildings' resistance.Adding concrete jacket to columns and adding steel plates to columns in plastic joints in order to increases ductility of components. Comparing results of three techniques showed that shear wall is the best technique for seismic improvement in building. In the present study seismic vulnerability was evaluated for reinforced concrete buildings with different heights and various improvement techniques were tested to determine seismic performance improvement and finally, a suitable retrofit technique was selected for certain height. In order to reach these goals, several reinforced concrete buildings with similar plan and 4, 12, 8 and 16 storeys were evaluated based on second edition of 2800 standard of Iran and seismic regulations (3

rd edition). Nonlinear static analysis was used in

order to calculate overall parameters of structure like stiffness, strength and ductility capacity. Based on the nonlinear static analysis results seismic evaluation of structures was done regarding FEMA356 (2000) and rehabilitation instruction (Guide 360, 2006). Two evaluation criteria are in FEMA, one based on Member-level and the other on Global-level. In the Member-level, evaluation plastic rotation limitations in members are used and the global level is considered for structure's behavior curve. After required seismic evaluations of building, seismic vulnerabilityof structures were determined and retrofit techniques were used to improve this vulnerability. Many parameters are considered in selection of the techniques including stiffness, strength and ductility. Finally, the results of these techniques are compared with each other and initial structure. Modeling and evaluating existing structures Lateral resisting system of structures in this study is moment frame with moderate ductility. Height of all storeys is identical 3m and dead and live loads are 500kg/m

2 and 200kg/m

2 and roof’s dead and live loads are

600kg/m2 and 150kg/m

2, respectively. Compressive strength of concrete and Yield strength of longitudinal bars

were 250kg/cm2 and 400kg/cm

2, respectively. Dimensions of beams and columns and cross-section of

longitudinal bars in initial structures are based on seismic loads in standard 2800 second edition. Gravity loads are based on 519 Iran's standard. By studying primary structures and linear analysis with ETABS software, it was seen that relative dislocation of storeys is exceeded than allowed rate in regulations. In order to predict accurate seismic behavior, all structures were modeled in Perform-3D and undergone nonlinear static analysis. According to rehabilitation gridlines (Guide 360), two lateral load models must be considered in this analysis and these models must be imposed in both positive and negative directions on structures. Lateral loads pattern is compatible with the distributions as follow: 1) Even distribution in which lateral load is appropriated with storey's weight. 2) Appropriate distribution with lateral load in linear static method for structures with less than one second period and appropriate distribution for linear dynamic analysis for structures with higher than onesecond period. There are various methods for modeling inelastic elements in Performa-3D program. In this paper, rotation model was used for nonlinear elements modeling. The beam and columns elements behavior curves were introduced to software as figure (1).


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Figure 1. PERFORM Action-Deformation Relationship

In this figure, Y pointis the first yield point, where significant nonlinear behavior begins. U point is the ultimate strength point, where the maximumstrength is reached. L point is the ductile limit point, where significant strength loss begins. R pointis the residual strength point, where the minimum residual strength is reached. X Point is usually at a deformation that is so large that thereis no point in continuing the analysis. According to FEMA356, the break points were introduced in behavior curve as DL=9DY and DR=11DY. Because the sudden loss of strength which is suggested in FEMA356 is infrequent in real structures, the progressive loss of strength is considered as a real behavior. In this article we have used Guide 360 for modeling inelastic behavior of beam and column and PEER (2007) was used to calculate Yield strengthin reinforced concrete components (Curt et al., 2007). In push-over analysis, the structure is placed under a load with a specific shape, then the force increases. Crack forming process and plastic joints were examined and determined the failure of structure. With this analysis, we can determine vulnerability of the structure. The performance criteria in push-over analysis aredisplacement of the center of mass in roof storey. This displacement is called Target Displacement. The method used to determine displacement target in rigid diaphragms is known as Displacement Coefficient Method. In this method, first a nonlinear static analysis is done with the initialtarget displacement to obtain basic curve versus lateral dislocation of the control point. From push-over curve and other factors in rehabilitation instruction, we can determine the final target displacement.The target displacementis calculated by equation (1).

(1) gT

SCCCC eat 2

2

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In which: C0: Modification factor to relate spectraldisplacement of an equivalent SDOF systemto the roof displacement of the buildingMDOF system. C1: Modification factor to relate expectedmaximuminelastic displacements todisplacementscalculated for linear elasticresponse.C2:Modification factor to represent the effect ofpinched hysteretic shape, stiffness degradationand strength deterioration on maximumdisplacement response.C3:Modification factor to represent increaseddisplacements due to dynamic P-Δeffects.Sa:Response spectrum acceleration.Te: Effective fundamental period of the building. g: acceleration of gravity. In table (1) initial target displacement based on LS performance level is shown.

Table1. primary displacement target

t

(cm) Te Sa B A C3 C2 C1 C0

40 1.15 0.96 1.98 0.35 1 1.2 1

1.03 4-storey building

71.5 1.88 0.52 1.49 0.35 1 1.1

1


115 2.69 0.39 1.12 0.35 1 1.1

1


151 3.34 0.33 1.12 0.35 1 1.1

1


In figures (2) to (5) models behavior curves from nonlinear static analysis is shown,but it is observed that the difference in target displacement with final dislocation obtained from push-over curve is more and so, there is no need to calculate the target displacement accurately. None of the models has reached the performance point. Therefore, it is not necessary to study the acceptance criteria and overall vulnerability of structures and the need to improve is clear.


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Figure 2. storey building



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Retrofitting Techniques

Regarding the weakness in structures in reaching to the performance point and not meeting the acceptance criteria based on local performance, three retrofitting methods were used to increase the seismic performance of structures. Adding shear wall and steel bracing were used to increase stiffness and strength and column jacket was used to increase strength and ductility of structures. Use of the Shear Wall Adding the shear wall is a common method and this technique increases both stiffness and strength. Initial dimensions of shear wall were obtained for 1.5 times of seismic force and then static nonlinear analysis was used to reach to the target displacement and performance level. The first retrofit technique is adding shear wall to two span external of reinforced concrete frames in x and y directions in figure (6).

Figure 6. Shear wall and steel brace location in building

In order to model the shear wall in Perform-3D, the Shear wall, inelastic fiber section model was used which is based on Fiber model. Flexural reinforcement and concrete section of shear wall are introduced as fibers to Performa-3D software and behavior of shear wall. Use of the Cross Steel Bracing The second retrofit method is adding steel bracing with double cross into two external span of reinforced concrete frames and locating of figure (6) in x and y directions. This techniques increases stiffness and structure resistance like the previous technique. The difference between these two techniques is that the steel bracing imposes less weight than shear wall. The steel bracing dimensions were obtained for 1.5 times of earthquake force, then revised during static nonlinear analysis to reach target displacement and performance

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level. Because only the axial stiffness of bracing is considered, simple bar element in Performa-3D software was used. Details of these bracings are presented in table (2).

Table2. Shear walls and bracing details

Cross section of braces Shear wall

storey AS(cm

2) T(cm)

2UNP22 147.5 20 1,2 4storey 2UNP14 65.5 15 3

2UNP12 65.5 10 4 2UNP28(1), 2UNP22(2), 2UNP18(3) 147.5 25 1,2,3

8storey 2UNP16 147.5 20 4,5 2UNP10 147.5 15 6 2UNP10 65.5 10 7,8 2UNP32 220.5 35 1,2

12storey

2UNP32(3), 2UNP28(4) 220.5 30 3,4 2UNP28 147.5 25 5,6 2UNP24 147.5 20 7,8 2UNP18 147.5 15 9,10 2UNP18 65.5 15 11,12 2UNP32 220.5 35 1,2,3,4

16storey

2UNP32 220.5 30 5,6,7 2UNP30 147.5 25 8,9 2UNP30 147.5 20 10 2UNP24 147.5 20 11 2UNP24 147.5 15 12 2UNP22 147.5 15 13 2UNP22 65.5 15 14 2UNP20 65.5 10 15,16

using steel column jack Based on the guidelines for seismic rehabilitation (Guide 360), inthe evaluation of the unretrofitted case study building, the columns had the most deficiencies in meeting the LS performance level to strengthen these vulnerable members and increase ductility, the column jacketing technique was selected as the thirdretrofit technique. The thickness of these steel jackets and numbers of columns reinforced with them is selected based on allowed displacement of LS performance level. An equivalent concrete cross-section was utilized to model these jackets. Seismic Evaluation of RetrofittedStructures As mentioned before, after modeling and nonlinear analysis,the lateral loads based on code360 should be calculated. By calculating the initial target displacement and nonlinear static analysis, structures' behavior curves were substituted by two-linear model and then, final value of target displacement is obtained. These steps are obtained with try and error. After the evaluation, final target displacementof structures was obtained and presented in table (3).

Table3. Final target displacement Retrofitting by steel jacket Retrofitting by steel brace Retrofitting by shear wall

24.8cm 10.7cm 6.9cm 4-storey 59.5cm 40.4cm 21.8cm 8-storey 119cm 48.1cm 34.7cm 12-storey 144.5cm 95cm 71cm 16-storey

Regarding push-over curves obtained from final non-linear static analysis, it can be observed that all improved structures except 16 storeys structure, has reached to performance point by column jacket. So acceptance criteria were studied in performance point which must not exceed from allowed rate before reaching plastic rotation. Tables (4) to (7) show acceptance criteria according to rehabilitation instructions. In these tables, technique (1)is referring to use of the reinforced concrete shear wall, technique (2) is the steel bracing and technique (3)is the column jacket.

Table4.Acceptance criteria of member in 4-story building Beams Columns

Technique (1)

Technique (2)

Technique (3)

IO LS Technique (1)

Technique (2)

Technique (3)

IO LS

Storey1 0.015 0.0147 0.0274 0.010 0.020 0.00810 0.0092 0.0164 0.005 0.015

Storey2 0.0120 0.0110 0.0271 0.010 0.020 0.00280 0.0018 0.0007 0.005 0.015 Storey3 0.0089 0.0139 0.0279 0.010 0.020 0.00063 0.0013 0.0051 0.005 0.015 Storey4 0.0036 0.0146 0.0260 0.010 0.020 0.00061 0.0007 0.0030 0.005 0.015 Number - - 48 - - - - 16 - -


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Table5. Acceptance criteria of member in 8-story building

Beams Columns Technique (1)

Technique (2)

Technique (3)

IO LS Technique (1)

Technique (2)

Technique (3)

IO LS

Storey1 0.0195 0.0190 0.0320 0.01 0.02 0.0103 0.0143 0.0220 0.005 0.015

Storey2 0.0203 0.0206 0.0370 0.01 0.02 0.0045 0.0070 0.0090 0.005 0.015 Storey3 0.0190 0.0201 0.0340 0.01 0.02 0.0020 0.0050 0.0060 0.005 0.015 Storey4 0.0149 0.0210 0.0320 0.01 0.02 0.0016 0.0044 0.0056 0.005 0.015 Storey5 0.0139 0.0170 0.0280 0.01 0.02 0.0120 0.0043 0.0076 0.005 0.015 Storey6 0.0130 0.0167 0.0260 0.01 0.02 0.0006 0.0038 0.0047 0.005 0.015 Storey7 0.0060 0.0162 0.0167 0.01 0.02 0.0007 0.0036 0.0030 0.005 0.015 Storey8 0.0050 0.0120 0.0140 0.01 0.02 0.0009 0.0021 0.0020 0.005 0.015 Number 2 8 72 - - - - 16 - -


beams columns Technique (1)

Technique (2)

Technique (3)

IO LS Technique (1)

Technique (2)

Technique (3)

IO LS

Storey1 0.015 0.018 0.0301 0.01 0.02 0.007 0.004 0.022 0.005 0.015 Storey2 0.016 0.023 0.039 0.01 0.02 0.0134 0.008 0.011 0.005 0.015 Storey3 0.022 0.026 0.043 0.01 0.02 0.0133 0.005 0.004 0.005 0.015 Storey4 0.022 0.0267 0.039 0.01 0.02 0.0090 0.0045 0.011 0.005 0.015 Storey5 0.013 0.024 0.027 0.01 0.02 0.003 0.003 0.001 0.005 0.015 Storey6 0.011 0.018 0.023 0.01 0.02 0.006 0.0017 0.0009 0.005 0.015 Storey7 0.011 0.017 0.020 0.01 0.02 0.003 0.0010 0.0008 0.005 0.015 Storey8 0.090 0.0163 0.017 0.01 0.02 0.002 0.0009 0.0007 0.005 0.015 Storey9 0.060 0.016 0.015 0.01 0.02 0.0019 0.0008 0.0006 0.005 0.015 Storey10

0.003 0.015 0.009 0.01 0.02 0.0017 0.0006 0.0026 0.005 0.015

Storey11

0.003 0.018 0.006 0.01 0.02 0.002 0.0065 0.0002 0.005 0.015

Storey12

0.002 0.013 0.003 0.01 0.02 0.0010 0.0006 0.0001 0.005 0.015

no 2 10 81 - - - - 16 - -


Beams Columns Technique (1)

Technique (2)

Technique (3)

IO LS Technique (1)

Technique (2)

Technique (3)

IO LS

Storey1 0.016 0.0210 - 0.01 0.02 0.0090 0.0150 - 0.005 0.015

Storey2 0.0220 0.0220 - 0.01 0.02 0.0160 0.0080 - 0.005

0.015

Storey3 0.0230 0.0230 - 0.01 0.02 0.0130 0.0050 - 0.005 0.015

Storey4 0.0250 0.0240 - 0.01 0.02 0.0090 0.0030 - 0.005 0.015

Storey5 0.0200 0.0200 - 0.01 0.02 0.0070 0.0030 - 0.005 0.015

Storey6 0.0210 0.0260 - 0.01 0.02 0.0060 0.0017 - 0.005

0.015

Storey7 0.0204 0.0210 - 0.01 0.02 0.0040 0.0010 - 0.005 0.015

Storey8 0.0200 0.0210 - 0.01 0.02 0.0050 0.0009 - 0.005 0.015

Storey9 0.0210 0.0220 - 0.01 0.02 0.0020 0.0008 - 0.005 0.015

Storey10

0.0210 0.0220 - 0.01 0.02 0.0016 0.0009 - 0.005 0.015

Storey11

0.0210 0.0190 - 0.01 0.02 0.0015 0.0040 - 0.005 0.015

Storey12

0.0210 0.0180 - 0.01 0.02 0.0020 0.0040 - 0.005 0.015

Storey13

0.0210 0.0170 - 0.01 0.02 0.0020 0.0010 - 0.005 0.015

Storey14

0.0220 0.0160 - 0.01 0.02 0.0030 0.0020 - 0.005 0.015

Storey15

0.0220 0.0150 - 0.01 0.02 0.0050 0.0020 - 0.005 0.015

Storey16

0.006 0.0090 - 0.01 0.02 0.0010 0.0010 - 0.005 0.015

Number 61 71 - - 1 - - - -


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Comparison of Results for Initial Structures and Improved Structures In this section,the push-over curves of initial and improved structures have been compared regarding stiffness, strength and ductility. In figures (7) to (10)the push-over curve were presented for both load distributions. The amount of basic shear increase on structure's weight is presented in tables (8) and (9) for distribution of type one and ductility factor.

Figure 7. (a) push-over curve of 4-storey building

Figure 7. (b) push-over curve of 4-storey building

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Table8. Percentage of the basic shear ratio to structure's weight in distribution of type (1) Technique(1) Technique(2) Technique(3)

4-storey building 216% 215% 52% 8-storey building 152% 100% 41% 12-storey building 144% 74% 20% 16-storey building 96% 59% 10%

Table9. Ductilityof buildings in distribution of type (1)

Technique(1) Technique(2) Technique(3)

y∆ max ∆ µ y∆ max ∆ µ y∆ max ∆ µ

4-storey building 1.5 6.9 4.6 1.9 10.7 5.63 3.6 24.8 6.8 8-storey building 4.5 21.8 4.9 7.9 40 5.06 11 59.5 5.4 12-storey building 8.85 34.7 3.9 9.35 48.55 5.1 24 119 5 16-storey building 16.7 71 4.2 16 95 5.9 - - -

CONCLUSION

Using shear wall and steel bracing as retrofitting techniques,General weakness of all structures was resolved and they reached to performance point. There was considerable increase in stiffness and strength of structures. Regarding ductility, although steel bracing has better results than shear wall but none of them had great effects on ductility. Regarding behavior curves of nonlinear static analysis it was clear that with increase in storeys number the percentage of basic shear increase to thestructure weight is decreased. In order to investigate theacceptance criteria, it can be said that maximum plastic rotation of all members, except in 16 stories building, is lower than allowed level. In improved 16 stories building with shear wall about 15% of beams and in steel bracing about 20% of beams have exceeded allowed limits.Therefore both techniques are suitable for retrofitting concrete building but shear walls is recommended only forshort and average height buildings because of their high weight and too much work, so steel bracing is suitable for concrete buildings with accurate connection installation. Adding column jacket has reached structures of 12 stories to performance point but it has no great effect on increasing stiffness and strength and only has met the weakness of columns. 75% of columns in 4 stories, 88% in 8 stories and 90% in 12 stories buildings were improved but 50% of beams in 4 stories, 62% in 8 stories and 71% in 12 stories buildings need retrofitting. It can be said that this technique must be used with beams retrofitting in short buildings. Because by increase in stories more beams needs retrofit and there is not such an increase in basic shear.

REFERENCES Curt BH, Abbie BL, Sarah TL, Gregory GD. 2007. Beam-Column Element Model Calibrated for Predicting Flexural Response Leading to

Global Collapse of RC Frame Buildings. PEER Report 2007/03. FEMA 356. 2000. Prestandard and Commentary on the Seismic Rehabilitation of Buildings. Federal Emergency Management Agency.

Washington DC. Guide 360. 2006. Instruction for Seismic Rehabilitation for the Existing Buildings, Management and Planning Organization of Country,

Technical Office.

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Jong-Wha B, Mary BD, Hueste. 2007. Deterministic and Probabilisti Evaluation of Retrofit Alternatives for a Five-Story Flat-Slab RC Building. Texas A&M University Zachry Department of Civil Engineering.

Maheri MR, Sahebi A. Use of steel bracing in reinforced concrete frames. Engineering Structures. 04141-0296. Maheri MR, Kousari R. 1996. Push-over test on steel X-braced and knee braced RC frames. Engineering Structures. No 25:1697-1705. Penelis GG, Kappos AJ. 1997. Earthquake Resistant Concrete Structure. Thomson Press Ltd. Sugano S. 1992. Seismic Strengthening of Existing Reinforced Concrete Building in Japan. International Institute of Seismology and

Earthquake Engineering, Building Research Institute, Ministry of Construction. Tasnimi A. 2001. Retrofitting Reinforced Concrete Frames Using Steel Bracing. Publication of the Building and Housing Research Center.

Tehran. Youssef MA, Ghaffarzadeh H. 2003. Seismic performance of RC frames with concentric internal steel bracing. Engineering Structures. No

29: 1561-1568.

evaluation of seismic performance of thereinforced...

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