Progressive Collapse Analysis of Moment Resisting Steel Frames for Failure Performance Improvement

1. INTRODUCTION

Progressive Collapse is the spread of an primary local failure from a structural element resulting, eventually, in the collapse of an entire structure. Progressive collapse involves a phenomenon of sequential failure of part of the structure or the complete structure initiated by sudden loss of vertical load carrying member i.e. column, failure of a member in the primary load resisting system leads to relocation of forces to the adjoining members and if redistributed load surpasses member capacity it fails. Nowadays Steel Frame Structure (buildings) are establishing, Building technique with a ‖skeleton frame‖ of vertical member and horizontal member of various I-beams, constructed in frame to support the floors, roof and elements attached to the frame.

Alternate load path method is the procedure in which structure is analyzed for a collapse potential after the exclusion of column. In this research work whole structure is designed and analyzed, bending moment results of vertical structural member were taken in consideration. The member which observes lowest bending moment should be removed this in result gives the lowest number of failed structural member after reanalyzing.

Jain and Patil [2018)] has done a research work on a linear static analysis method for progressive collapse analysis to determine strength against the local failure and accidental occurrences for a RC framed structure to calculate the demand capacity ratio and the safety of the structure. In this research, A finite element model had been is considered and analyzed for the G+9 storey building and then the analysis was carried under critical column removal consequence as per the guidelines provided in GSA (2003) considering the provisions of IS 1893:2002 to simulate dynamic collapse mechanism using ETABS software v16.2.1 (software for modelling or analysis of structure) to assess the exposure to progressive collapse of a representative RC framed structures.

Tavakoli et al. [2012] engrossed on gravity and explosion loading. Remarks of structures damaged by earthquake had shown that earthquake load also may cause local partial or complete failure of critical elements and may lead to progressive failure. This research was established on the three and two-dimensional forming and push-over analysis of seismically calculated special dual system steel frame structures with concentrically braced frames with complete loss of critical elements. Farzin Zareian, et. al. [2007] illustrates a probabilistic-based practice for measuring the collapse potential of structural systems, which can provide us with more precise estimates of losses prompted by earthquakes. Applications of this methodology for assessment of collapse potential of existing buildings and design for collapse safety are demonstrated by equations and example. The potential to collapse is signified by the probability of collapse at discrete the probability of collapse as a function of the selected ground motion intensity measure The execution encounters are to develop mathematical models for structural systems that can mimic performance close to collapse, identify structural parameters that suggestively affect the structure‘s collapse capacity

The United States General Service Authority (GSA) out a document permitted ―Progressive collapse analysis and design guidelines for new federal office building and major modernization projects‖ in November 2000 and revised in June 2003. The (GSA, 2003) guideline monitors a risk independent methodology for analysis and design of structures to moderate the threat of progressive collapse. This guideline was the first articles which signify explicit stepwise process to support the structural engineering to evaluate the potential of progressive collapse of federal facilities.

Analyze the structure after the notional removal for a load-carrying structural member for the first floor positioned at or near the mid of short side, intermediate of long side, or at the corner of the structure as shown in Figure

The (GSA, 2003) guideline states that only 25 percent of the live load essential to be applied in vertical load combination because of the probability of presence of the complete live load during the collapse being very low. A magnification factor of 2 is used in the static analysis approach to account for dynamic effects. Load Combination = 2(DL + 0.25LL) where, DL = dead load LL = live load

For the analysis work, three models of steel frame building (G+10) floors are made to know the realistic behavior of building during earthquake. The length of the steel frame structure is 12m and width is 8m. Height of typical story is 3.5m. Column sizes changes first at 5 storey, 8 story and 9 story. Building is asymmetrical. Material concrete grade M20 is used, while steel Fe 250 (mild steel) is used. Analytical modeling that contains all components which impact the mass, strength and stiffness. The non-structural element and components that do not considerably influence the behavior of structure were not modeled. Beams (horizontal structural member) and columns (vertical structural member) are modeled as frame ground level.

Plan of the steel building which is used for the study is shown in figure 4.1.1

Member size used for beams, columns and bracing are shown in table 3.1

Concrete- M 20, Density-2400 Kg/m3, Young‘s Modulus E= 22360 N/mm2, Shear Modulus 8000N/mm2, Poisson‘s Ratio-0.2 Structural steel- Fe 250, Density-7850 Kg/m3, Young‘s Modulus E= 2.1x105N/mm2, Shear Modulus 80000N/mm2 Poisson‘s Ratio-0.3

Dead Load = DL = 1.5 kN/m2, Live Load = LL = 3.5 kN/m2 Load Combinations 1. 1.5 X DL : 1.5 X LL

4. 0.9 X LL (NOTE= ZONE – NON SEISMIC ZONE)

Analysis of above structure shows zero member failure which indicates structure observed safe in linear static analysis.

Which suggest? - Vertical member near centre to shortest side of structure (case 1) - Vertical member near centre to longest side of structure (case 2) - Any corner vertical member (case 3)

taken in consideration. The member who observes lowest bending moment should be removed this in result gives the lowest number of failed structural member after reanalyzing.

4.4 Overcome Failure and Improving Performance of Structure After finding location of failure to achieve this objective different remedial measures for improving

Strengthening can be done in different ways, Two Adopted Methods - 1) Strengthening of column by increasing its size.

2) Bracing added next to failed member was embraced. There are various types of bracings are as follows-

4.4.2. Graphs of Staad Pro Results: Bending moments of ground story are taken in consideration

1) Bracing added adjacent to failed member were adopted. There are different types of bracings are as follows-

Bending moments of ground story are taken in consideration

2) Bracing added adjacent to failed member were adopted. There are different types of bracings are as follows-

Bending moments of ground story are taken in consideration

We observed the three types of member failed conditions , in which case one shows minimum number of failed member as that of case two as that of case three. For other asymmetrical steel frames we can suggest case one that is removal of vertical member which is near to centre of shortest side of steel frame structure.

Discussion on results obtained by analysis of the 3D model of asymmetrical G+11 story‘s steel frame

Present study shows members adjacent to the damaged/removed vertical member joint experienced more destruction as compared to the beams which are away from the removed vertical member joint. Corner column removal (case 3) is found serious in the incident of progressive collapse. For reducing effect of progressive collapse strengthening of column become more difficult for structure having more than one failed member and for floor to floor failure. Bracing element acts as effective remedial measure to overcome progressive collapse

[1] Vikas Tiwari and Sambhav Gangwal (2019). ―Progressive Collapse Analysis for Asymmetrical G+11 Story Tall Building using STAAD PRO. For progressive Collapse Analysis GSA(2003)‖ International Journal of Engineering Research & Technology (IJERT) Published by : www.ijert.org Vol. 8 Issue 06, June-2019 [2] GSA. Progressive Collapse Analysis and Design Guidelines for New Federal Office Buildings and Major Modernization Projects. General Services Administration, Washington DC, 2003 [3] ASCE 7–05. Minimum Design Loads for Buildings and Other Structures. American Society of Civil Engineers (ASCE), Report: ASCE/SEI 7–05. Reston, VA, 2005 [4] A S Patil and P D Kumbhar (2013), ‗Time history analysis of multistore‘, International Journal of Structural and Civil Engineering research, Vol. 2, Issue No. 3. [5] Farzin Zareian et. al. (2007), Assessment of probability of collapse and design for collapse safety. Earthquake Engng Struct. Dyn.; 36: pp. 1901–1914 published online 11 May 2007 in Wiley InterScience (www.interscience.wiley.com). DOI: 10.1002/eqe.702 [6] Challa VRM, Hall JF (1994). Earthquake collapse analysis of steel frames. Earthquake Engineering and Structural Dynamics; 23(11): pp. 1199–1218. [7] Villaverde R (2007). Methods to assess the seismic collapse capacity of building structures: state of the art. Journal of Structural Engineering (ASCE); 133(1): pp. 57–66.

PG Student, Civil Engineering Department, SVERI‘S College of Engineering, Pandharpur, Maharashtra