Assessment of Progressive Collapse of G+7 RC Building

Assessment of Progressive Collapse of G+7 RC Building

Sushilkumar M Bhoite1

1M.E (Structure) Student, Department of Civil Engineering,

JSPMs Rajarshi Shahu College of Engineering, Tathawade,

Pune-411033, India

Nilima Pote3

Seema Patil2

2Assistant Professor, Department of Civil Engineering,

JSPMs Rajarshi Shahu College of Engineering, Tathawade,

Pune-411033, India

3Assistant Professor, Department of Civil Engineering,

JSPMs Rajarshi Shahu College of Engineering, Tathawade, Pune-411033, India

Abstract A simplified framework is proposed for progressive collapse assessment of multi-storey buildings, considering sudden column loss as a design scenario. This framework can be applied at various levels of structural idealisation, and enables the quantification of structural robustness taking into account the combined influences of redundancy, ductility and energy absorption this study aims to provide the designer engineers with wider overview on this topic to minimize the consequences of buildings progressive collapse after the event of column removal scenario. A Seven storey reinforced concrete framed structure is considered in the study to evaluate the Demand Capacity Ratio (D.C.R.), the ratio of the member force and the member strength as per U.S. General Services Administration (GSA) guidelines. The Non Linear static analysis is carried out using software, STAAD PRO according to Indian Standard codes. To study the collapse, typical columns are removed one at a time, and continued with analysis and design. Many such columns are removed in different trials to know the effects of progressive analysis. Member forces and reinforcement details are calculated. From the analysis, DCR values of beams are calculated.

Keywords: RC building, progressive collapse, nonlinear static analysis

1. INTRODUCTION

   Progressive collapse is a situation where local failure of a primary structural component leads to the collapse of adjoining members which, in turn, leads to additional collapse. Hence, the total damage is disproportionate to the original cause. Progressive collapse the spread of local damage, from an initiating event, from element to element resulting, eventually, in the collapse of an entire structure or a disproportionately large part of it; also known as disproportionate collapse. This failure occurs when a building loses one or more of its vertical load carrying components. This loss could be the result of an unexpected loading, like a vehicle accident, an explosion, terroristic attack or a construction/ design error. The single element failure can lead to a larger damage in determinate structure, for that this structural system is not robust. In contrast to indeterminate structure, the collapse of one element will not cause building failure as other element can compensate the local damage and bridge out the load of damaged element to undamaged near

   elements. Structural robustness is a function of structural degree of redundancy, which represents the structure ability to redistribute loads after collapse to intact members.

   1. Aim and Objective

      To analyse, design G+7 RC structure by using different measures to sustain progressive collapse. To perform analysis for the proposed structure with removal of critical columns fully to know potential for progressive collapse.

      The objective of dissertation includes:

      • To analyse, design G+7 RC structure by using different measures to sustain progressive collapse.

      • To perform analysis for the proposed structure with removal of critical columns fully to know potential for progressive collapse.

      • To suggest effective method for design of new building to avoid progressive collapse.

2. OVERVIEW OF PROGRESSIVE COLLAPSE

   A. General

   All different guidelines identify three basic design methods for progressive collapse prevention: event control, direct design approach and indirect design approach; the three methods are explained as follows:

   1. Event control: Protection and isolation of the building from any accident loads that can cause progressive collapse.

   2. Direct design approach: focuses on providing building with resisting mechanisms: 1- Alternate Path Method by improving the structure ability to transfer the loads of the damaged elements to intact regions through two mechanisms; Vierendeel and Catenary/ membrane action. 2- Specific Local Resistance (SLR) Method, which focuses on providing sufficient strength to the key elements in the building to withstand these abnormal loads.

   3. Indirect design approach: This approach aims to guarantee the minimum level of strength, continuity and ductility for different buildings elements depending on selecting suitable plan layout, horizontal and vertical tie systems, and seismic ductile detailing. For that, indirect

   design method is the first line of defence towards catastrophic failures.

3. METHODOLOGY

   1. Building Configuration

      To study the effect of column removal condition on the structure, 7 storey building is considered. Progressive collapse analysis is based on the GSA guidelines. Structure considered in this analysis is hospital building, which is designed for an importance factor 1.5 (IS code 1893-2016).Figure shows typical floor plan

      Load Considered Are As Follows:

      1. Dead Load as per IS 875 (Part I).

      2. Live Load IS 875 (Part II) – on Roof 1.5 KN/m2 and on Floors 3.0 KN/m2

      3. Wind Load as per IS 875 (Part III).

      4. Self-weight of the Structural elements, Floor Finish =1.5 KN/m2.

      5. Seismic loading as per IS: 1893 (Part I): 2016 Zone III,

         Zone factor = 0.16,

         Soil Type = Type I, Rock or hard soil, Importance Factor = 1.5 and

         Response Reduction Factor = 5.0

         The characteristic compressive strength of concrete (fck) is 25 N/mm2 and yield strength of reinforcing steel (fy) is 500 N/mm2. Analysis and design of building for the loading is performed in the Staad pro. 7 storey building is designed for seismic loading in Staad pro according to the IS 456:2000.

         TABLE I. BASIC LOAD COMBINATION

         SR. No	LOAD COMBINATIONS
         1	1.5( DL + LL )
         2	1.2( DL + LL ± EQ)
         3	1.5(DL ± EQ )
         4	0.9DL ± 1.5EQ

         Fig. 1. Typical floor plan of hospital building

   2. Analysis

      To evaluate the potential for progressive collapse of a 7 storey reinforced concrete building using the nonlinear static analysis column removal conditions is considered. First building is designed in STAAD PRO for the IS 1893 (Part-I) load combinations. Demand capacity ratio for the moments and forces at all storeys is calculated for each cases of column failure. Capacity of the member at any section is calculated as per IS 456:2000 from the obtained reinforcement details after

      analysis and design. Member forces are obtained by analysis results carried out in Staad pro.

   3. Modeling

   The 7 storied reinforced concrete framed structures is modelled using Staad pro software.

   Fig. 2. Render view of 7 storied Hospital Building

   Fig. 3. Typical Floor Plan (Showing Beam & Column Numbering) Fig. 4.

   5 models will be prepared. Each separate model will be prepared by considering various preventive measures such as,

   Model 1 Wit corner removal column.

   Model 2 Providing inverted V type bracing at ground and roof floor level.

   Model 3- By considering beam above column removal to be designed as cantilever beam.

   Model 4- By considering load combination as suggested by GSA.

   Model 5- By increasing column and beam sizes by 20 % at column removal location.

   After analysis and design of the building by using above mentioned options nonlinear analysis will be carried out to check effectiveness of options against progressive collapse. After studying various literature survey it seems that corner column removal is quite critical case, so worked on only corner column removal case.

   Steps for analysis

   Step-l. First, the building is designed in Staad pro for the IS 1893 load combinations and the output results are obtained for moment and shear without removing any column.

   Step-2. A vertical support (column) is removed from the position under consideration and linear static analysis is carried out to the altered structure with above mentioned preventive measures.

   Step-3. The load combinations are entered into the staad pro program. Each case of different Column removal location on the model and the results are reviewed.

   Step-4. Further, from the analysis results are obtained and if the DCR for any member exceeds the allowable limit based upon moment and shear force, the member is expected as a failed member.

   Step-5. If DCR values surpass its criteria then it will lead to progressive collapse.

4. RESULT AND DISCUSSION

   1. General

      • Five building models of 7 storey are generated using software staad pro.

      • Each models of 7 storey are analysed for corner column removal case. The progressive collapse analysis is done according to the G.S.A. guidelines. Linear static analysis has been carried out.

      • Comparison of all cases is done on the basis of Demand Capacity Ratio.

      • Obtained results have been presented in form of graphs/charts, indicating the trends and pattern of Demand Capacity Ratio.

      • Four different mitigation approaches like providing bracing at bottom and top floors, by considering beam above column removal to be designed as cantilever beam, by considering load combination as suggested by GSA and by increasing column and beam sizes by 20 % at column removal location.

   2. Render view for different cases with 4 mitigation provided Case 1 With corner column removal

      Fig. 5. Render view showing corner column removal case (Front view)

      Fig. 6. Render view showing corner column removal case (Back view)

      Figure 4 & 5 shows the 100% corner column removal i.e. all corner column are removed at a time for considering the critical case.

      Case 2 Providing inverted V type bracing at ground and roof floor level

      Fig. 7. Render view showing bracing member provided as ground and roof floor level

      Case 3 -By considering beam above column removal to be designed as cantilever beam.

      Fig. 8. Showing beam no B1, B4, B24, B30 released at end.

      Case 4:- By considering load combination as suggested by GSA

      LOAD COMBINATION AS PER GSA INCLUDED IN STAAD ANALYSIS

      LOAD COMB 301 2(DL+0.25LL) 3 2.0 4 2.0 5 2.0 6 0.5

      Case 5:- By increasing column and beam sizes by 20 % at column removal location.

      –

      Fig. 9. Showing increasing column sizes adjacent to column removal location

   3. Node displacement for various cases

      TABLE II. BASE MODEL

      TABLE III. CASE 1 CORNER COLUMN REMOVAL

      TABLE IV. CASE 2 PROVIDING INVERTED V TYPE BRACING AT GROUND AND ROOF FLOOR LEVEL

      TABLE V. CASE 3 BY CONSIDERING BEAM ABOVE COLUMN REMOVAL TO BE DESIGNED AS CANTILEVER BEAM.

      TABLE VI. BY CONSIDERING LOAD COMBINATION AS SUGGESTED BY

      GSA

      TABLE VII. TABLE 6.6 – CASE 5:- BY INCREASING COLUMN AND BEAM SIZES BY 20 % AT COLUMN REMOVAL

      LOCATION.

      Fig. 10. Showing node no 799 where maximum displacement occurs at column removal floor level

      Node displacement (mm)

      Node displacement (mm)

      30 26.524

      	4.587

      	4.587

      25

      26.98226.511

      24.228

      TABLE XI. FLEXURAL DEMAND FOR CASE 3 BY CONSIDERING BEAM ABOVE COLUMN REMOVAL TO BE DESIGNED AS CANTILEVER BEAM. (ALL VALUES IN KN-M)

      20

      15

      10

      5

      0 MODEL

      Case 1 Case2 Case 3 Case 4 Case 5

      TABLE XII. FLEXURAL DEMAND FOR CASE 4 BY CONSIDERING LOAD COMBINATION AS SUGGESTED BY GSA. (ALL VALUES IN KN-M)

      Fig. 11. Chart showing maximum displacement in node no 799

      Referring table II to VII, maximum displacement in node no 799 results are summarized in figure 10 which shows node displacement in respective 5 cases. Only in case 2 i.e by providing bracing, vertical displacement is within limit i.e 20 mm. In all other case vertical displacement is exceeding the limit.

   4. Flexural demand for various cases

      Obtained results have been presented in form of graphs, charts and tables indicating the trends and pattern of DCR ratio in flexure.

      TABLE VIII. FLEXURAL DEMAND FOR BASE MODEL (ALL VALUES IN KN- M)

      TABLE IX. FLEXURAL DEMAND FOR CASE 1CORNER COLUMN REMOVAL (ALL VALUES IN KN-M)

      TABLE X. FLEXURAL DEMAND FOR CASE 2 PROVIDING INVERTED V

      TYPE BRACING AT GROUND AND ROOF FLOOR LEVEL. (ALL VALUES IN KN-M)

      TABLE XIII. FLEXURAL DEMAND FOR CASE 5:- BY INCREASING COLUMN AND BEAM SIZES BY 20 % AT COLUMN REMOVAL LOCATION. (ALL VALUES IN KN-M)

   5. DCR for various cases

   From the analysis results demand at critical points are obtained and from the designed section the capacity of the member is determined. The DCR of each member is calculated from the following equation.

   DCR = QUD

   QCE

   Where,

   Qud = Acting force (demand) determined in member or connection.

   Qce = Expected ultimate, un-factored capacity of the member Qce = 0.133fck b d2 = 0.133 x 25 x 300 x 7122 =505.68 kN-m.

   Referring table VIII to XIII, DCR values are calculated and results are summarized in figure 11 to 18

   Fig. 12. DCR for beam B1

   Fig. 13. DCR for beam B56

   Fig. 14. DCR for beam B4

   Fig. 15. DCR for beam B28

   Fig. 16. DCR for beam B30

   Fig. 17. DCR for beam B27

   Fig. 18. DCR for beam B24

   Fig. 19. Fig:-6.15 DCR for beam B57

5. 7.0 CONCLUSION

   1. Progressive Collapse Analysis of Building

      The analytical study on both 7-storey building is done by creating the 3D model and the analysis is done for all corner column removal cases by following GSA guidelines. Progressive collapse potential of building is found out by considering column removal cases. Demand Capacity Ratio in flexure is calculated for all the cases. From the study, the following conclusions can be drawn out:

      1. DCR in flexure of beam exceeds permissible limit of 2.0 in all storey of for case 3, 4 & 5. The DCR values in beams in case 2 i.e by providing inverted V type bracing at ground and roof floor level are within limit indicate that building considered for the study is having very low potential to resist the progressive collapse when column is considered as fully damage/removed.

      2. The adjacent beam to the damaged/removed column joint experienced more damage as compared to the beams which are away from the removed column joint.

      3. Corner column case is found critical in the event of progressive collapse.

      4. The beams adjacent to the damaged/removed column joint experienced more damae as compared to the beams which are away from the removed column joint.

      5. Four different alternatives are used to mitigate the progressive collapse. When mitigation alternatives are adopted, DCR value is reduced within permissible limit. From four mitigation alternatives presented, provision of bracing in the building is economical solution to reduce the potential of progressive collapse.

   2. Scope of Future Work

      There is a scope of extending this work to include the following for future:-

      1. The present work has been carried out to calculate the DCR for a symmetric building. The work can be extended to asymmetric buildings.

      2. In this study STAAD Pro has been used other software like SAP, and ANSYS etc. can be used.

      3. Here linear static and linear dynamic (response spectrum method) analysis have been performed; Push over Non-linear analysis can be done for same building.

6. REFERENCES

1. General Services Administration (GSA), Progressive Collapse Analysis and Design Guidelines for New Federal Office Buildings and Major Modernization Projects, U.S. General Services Administration, Washington, DC, 2013.

2. U. Starossek, Typology of progressive collapse, Eng. Struct. 29 (2007) pp. 2302 2307.

3. EN 1991-1-7, Eurocode 1: Actions on Structures Part 17: General Actions Accidental Actions, (2006).

4. Department of Defense (DoD), Design of Building to Resist Progressive Collapse, UFC 4-023-03, Washington, DC, 2010.

5. BSI. BS 6399: Loading for Buildings, British Standards Institution, London, UK, 1996.

6. IS 456-2000 Plain and Reinforced Concrete Code of Practice.

7. IS: 1893 (Part 1): 2002, Criteria for Earthquake Resistant Design of Structure

8. B. Abdelwahed (March 2019),A review on building progressive collapse, survey and discussion.

9. Kamal Alogla, Laurence Weekes, Levingshan Augusthus-Nelson (August 2016),A new mitigation scheme to resist progressive collapse of RC structures.

10. K. Qian and B. Li (2012), "Dynamic performance of RC beam-column substructures under the scenario of the loss of a comer column- experimental results," Engineering Structures, vol.42, pp. 154-167. May 2012.

11. Mohamed, O. A. (2009)," Assessment of progressive collapse potential in corner floor panels of reinforced concrete buildings". Engineering Structures, vol. 31, no. 3, pp. 749-757.

12. M. Sasani and J. Kropejnicki (2007). "Progressive collapse analysis of an RC structure," The Structural Design of Tall and Special Buildings, vol. 17, no.4. pp.757- 771,July2007.

13. Rakshith K G, Radhakrishna (2013), "Progressive Collapse Analysis of Reinforced Concrete Framed Structure", International Journal of Research in Engineering and Technology. IC-RICE Conference Issue, Nov-2013, pp. 36-40.

14. Tsai M. and Lin H., (2008). "Investigation of progressive collapse resistance and inelastic response for an earthquake-resistant RC building subjected to column failure" Engineering Structures, vol. 30, pp. 3619-3628

15. UFC 4-023-03, (2009), "Design of Building to Resist Progressive Collapse, Unified Facilities Criteria (UFC)", Department of Defence, USA (DoD