Abstract' Progressive collapse is the collapse of all or a big part of a structure caused by damage or failure of a relatively small part of it. The wonder is of particular concern since progressive collapse is often (though not always) disproportionate, i.e., the collapse is out of proportion to the event that activates as per Expansion in industry, the Public are elaborate towards, new ideas to plan the structures with the irregularities in plan as well as in elevation. On other side structural engineer's aim is to provide the structure safe against all the forces. The structural engineer's role becomes challenging when such buildings which are irregular in plan as well as in elevation.
All these structures are analysis and Design as per Indian Standard(IS800:2007,IS1893:2002) with all combination of loading after that these structure are again analysis for progressive collapse. These types of analysis are considered i.e. Linear static and long linear static with load load case and critical location Suggested by GSA Guidelines
From this study Following observation are made Height of structure affect the collapse behavior as height increases progressive collapse decreases which is seen from D.C.R.values, Joint Displacement, and Bending Moment.
Keywords' ProgressiveCollapse ,vertical irregular structure,linear static analysis,non linear static analysis,etabs.
Progressive collapse of structures is initiatedted by the loss of one or more load-carrying members. As a result, the structure will seek alternate load paths to transfer the load to structural elements, which may or may not have been designed to resist the additional loads. Failure of overloaded structural elements will cause further redistribution of loads, a process that may continue until stable equilibrium is reached. Equilibrium may be reached when a substantial part of the structure has already collapsed. The resulting overall damage may be disproportionate to the damage in the local region near the lost member..
There are two types of Irregularity of structure.but now a days there is an attraction of architectural view so people are focus to build a structure in different elevation shape hence irregularity of building will differ in horizontal regularity and vertical irregularity .these irregularities during temblor needs to be studied, so that satisfactory precautions can be taken. Progressive collapse is a relatively rare event. But after the remarkable partial collapse of the Ronan Point apartment tower in 1968 initiated an intellectual discussion among the engineering community on the possible ways to design buildings against such catastrophic progressive types of failure. While there have been several notable building collapses with similar characteristics in the years since Ronan Point, the debate considerably intensified after the World Trade Center disaster on 11 September 2001. Progressive collapse is characterized by the loss of the load carry ng capacity of a relatively small part of a structure due to an abnormal event due to a vehicle impact, fire, earthquake and or other man made hazard such as terrorist attack.
With the current scenario of increasing reasons for disaster like situation at industrial or residential workplace, its utmost important to design the structure to all factors leading to lessen loss of human life & reduce impact to productivity by implementing minimum strengthening measures or rectifying local failures. Hence Global collapse of the structure is of utmost importance.so for in this study simple frame work for progressive collapse analysis for sudden column loss design scenario is analyzed by using finite element software tabs 2015.and progressive collapse guide lines such as linear static and nonlinear static analysis were carried out for comparison.
II. LITURATURE SURVEY
There are lot of research carried out on many aspects of progressive collapse of steel buildings. To identify the clear objective of present research work & its scope, summary and review of the critical observations of some researches as under are presented R. Shankar Nair (March 2004) describing description of major collapse of previous structure and observation on progressive collapse and discorporate collapse.Swami Nathan Krishnan and Matthew Muto (2012) says that mechanism of collapse of tall structures of 2 building subjected to 18 stories under earthquake excitations through nonlinear static analysis. And Both fracture-susceptible and perfect-connection conditions are investigated. Osama A. Mohamed(2006) studied that limitation and difference between linear static and nonlinear static model. N.M. Youssef b, S. El-Tawil (2013) studied A parametric study is performed using the finite element models to assess the effect of location of damage, extent of damage, role of initial imperfection, as well as asymmetric damage on the stability of a steel column.Majid Mohammad, Bahram kordbagh(2015)For this researcher make a model of different height (4,8,12) stories and these model are designed for most severe zone area and also progressive collapse considered. For this Alternate load path method is considered.Jinkoo Kim and Sumin Hong(2009) studied that 30 story tilted building analyzed by using nonlinear static and dynamic analysis and concluded that tilted structures that the plastic hinges formed not only in the base from which a column was removed, but also in the nearby bays. Similar results were observed in the analysis of the twisted structures In the United States the Department of Defense (DoD)  and the General Services Administration (GSA)  provide detailed information and guidelines regarding methodologies to resist progressive collapse of building structures. Both employ the alternate path method (APM) to ensure that structural systems have adequate resistance to progressive collapses. Gerasimidis (2013) Author studied the approaches to the progressive collapse analysis of steel frames have focused so far on computational Methods which try to capture the solution of the system responding to localized damage.Bondala Mahendra Reddy And P.rajesh(2016)The researcher studied the comparison between the irregular Steel Structure frame with and without having cases of progressive collapse using nonlinear static analysis The results of the pushover analysis also confirmed that the irregular steel frames work with progressive collapse cases have significantly improved stability in seismic zones over their counterparts withoutprogressivecollapsecases.S.vardharajan,B.saini(2016)The researcher studied the different irregularity system, also they describe various types of irregularity The criteria and limits are defined for irregularity by different types of codes. they observe that plan and vertical irregularity are comparable the review of previous research works regarding different types of plan irregularities justify end the preference of multi-storey building models over single storey building models and concept of balanced. M. A. Hadianfard & M. Wassegh(2012)stuided steel moment resisting frame with intermediate steel moment resisting frame for different seismic zone in iran and results concluded that higher seismicity higher capacity of collapse and lower seismicity there is no that much redundancy to disperse load to adjacent element the potential of collapse increase with decreasing height of structure.
III. MODELLING OF STRUCTURE
In order to observation for structural behavior of building for progressive collapse .and it is useful to build up with 3D model by using finite element model. And to solve the First, confirm that you have the correct temple problem ETABS(15)
used to set up whole model geometrical
The model was created in etabs as shown in fig.2. which is having typical floor. And three models are built up with different height and spacing in X direction and Spacing in Y direction is 5meter. The floor to floor height of structure is 3 interform column different sizes of box section are headland for beam different I sections are used.
Our Study is based analysis of Vertical Irregular Steel Frame Structure such as 5X7,7X9,9X11 for on progressive collapse, Considering Sudden Loss of Column as a design Scenario and the structure analysis for effect of Vertical irregularity on progressive collapse that there are many codes and Guideline available worldwide but most of the research work uses the GSA guideline.
For our research work There are various methods to analyse the structures and investigate their response to the progressive collapse phenomenon, we use the latest GSA-2013 for further guideline. The main aim is to reduce Progressive Collapse over the loss of a Structural Element, Limiting the Extent of damage to a localised area and Redundant and balance structural system along the height of building.
There are many methods such as linear static analysis, on linear static analysis, linear dynamic analysis are given as per GSA guidelines. But for our research work we are analysing all three models for linear static and nonlinear static analysis.
A. Linear static analysis procedure
Linear static procedure is very effective for less than or equal to 10 stories. There are two cases deformation control can be calculated by using case I and force control action will be calculated by using case II. For ductile actions' analysis, the applied load is increased through the use of an LIF that considers dynamic and nonlinear effects both. linear static model, which has one removed column, wall section or another load-bearing member, for our study we used force control action .
' First of all model is created by using finite element software.
' Then apply loading as per guideline given by G.S.A.2013.
' Then analyses the model for forced control loading action.
' Find the result of models for demand capacity Ratio
B. Nom Linear static analysis
Once the nonlinear model, both materially and geometrically, is made, the loads are increased with a Dynamic Increase Factor (DIF) that takes into account the inertia effects only. The consequent load is then applied to the model when the column is eliminated. The preferred performance level indicates the deformation limits which are compared with the consequent member deformation from deformation- controlled actions. However, in the case of force controlled actions, modification of member strength does not occur. This member strength is compared with the maximum internal member forces (actions).
To model, analyze, and evaluate a building, employ a three-dimensional assembly of elements and components. Create one model for either framed or load-bearing wall structures, respectively. Inclusion of secondary components in the model is optional. However, if the second-ray components are omitted, they must be checked after the analysis, against the allowable deformation-controlled criteria.
' First of all model is created by using finite element software.
' Assign the property of non-linearity and multiply with the nonlinear factor
' Apply plastic hinges for structure as per describe in ASCE 41 and FEMA
' Apply load combination as per GSA guide lines
' Then apply loading as per guideline given by G.S.A.2013.
' Then analyses the model for forced control loading action and displacement control action.
' Find the results as per your consideration
C. Load cases for linear static and non linear static
Case I: Force Control action Qu for linear static
G LF = '' LF [1.2 D + (0.5 L or 0.2 S)] (1)
G LF = Increased gravity loads for force-controlled actions for Linear Static analysis
'' LF = Load increase factor for calculating force-controlled actions for Linear Static analysis; use appropriate value for framed or load-bearing wall structures
Case II: Force Control action Qu for nonlinear static
Apply the following increased
GN= 'N [1.2 D + (0.5 L or 0.2 S)] (2)
GN = Increased gravity loads for Nonlinear Static Analysis
S= Snow Load
'N = Dynamic increase factor for calculating deformation-controlled and force controlled actions for Nonlinear Static analysis.
Gravity Loads for Floor Areas Away from Removed Column or Wall. Apply the gravity load combination in below Equation to those bays not loaded with GN
G = 1.2 D + (0.5 L or 0.2 S) (3)
For those bays not immediately adjacent to the removed element the load combination is the same for both deformation and force- controlled action.
The structures which are used in this study are a 5X7,7X9,9X11 stores with 7x7 bays steel frame structure. The Proposed plan of the buildings is typical (symmetrical). The typical structural bays are uniform in terms of dimension .
D. Loading data used for modelling
Progressive collapse analysis : In this analysis method we are 5X7,7X9,9X11 for these models following load cases are consider
Case1 : analyzed for sudden loss of corner column C1
Case2 : analyzed for sudden loss of middle column C4
Case3 : analyzed for sudden loss of center column C9
Case4 : analyzed for sudden loss of corner column C43
Case5 : analyzed for sudden loss of middle column C37
Case6 : analyzed for sudden loss of center column C47
V. RESULTS AND DISCUSSION
A. Comparison Of Results For Joint Displacement C43
From Result shows that as displacement before removal of columns very small after removal these displacement are largely increase in case of linear static analysis as compare to nonlinear static analysis because dynamic increasing factor so large
B. Comparison Of Results For Dcr For Adjecent Column
From graph 2,3 shows D.C.R. of adjacent column C2,C8 after removal of column C1.As we designed the structure for all combination we maintain DCR of all of structural element is in between 0.5 to 0.9.after Removal of Column C1 DCR in adjustment Column .D.C.R. increases suddenly in linear static analysis as compared to nonlinear static analysis.
C. comparison of results for dcr for beams
From Graph4,5 D.C.R. value of adjacent beam are considered and the structure for all combination we maintain DCR of all of structural element is in between 0.5 to 0.9.after Removal of Column C1 there is an drastic change in DCR of adjacent Beams in linear static analysis as compared to nonlinear static analysis.
D. Comparison Of Results For Bm
From Graph no 6 and graph no 7 shows that there is an gradual increase in bending moment before removal of column but there is an abruptly change in bending moment in linear static analysis as compared to nonlinear static analysis.
Graph. 7.Bending Moment For Beam No.B43
E. Comparison Of Results For Joint Displacement
Graph. 8. displacement for different story C43
Graph no 8 shows that as displacement before removal of columns very small after removal these displacement are largely increase in case of linear static analysis as compare to nonlinear static analysis because dynamic increasing factor so large
F. Comparison Of Results For Dcr For Ajecent Column
Graph no.9 and graph no. 10 shows Dacron column no.36 and column no.45 after removal of column column no.43
As we designed the structure for all combination we maintain DCR of all of structural element is in between 0.5 to 0.9.after Removal of Column C1 DCR in adjustment Column increases suddenly in linear static analysis as compared to nonlinear static analysis
G. Comparison Of Results For Dcr For Beams
Graph. 11. DCR for Beam No.B37
Graph. 12. Bending Moment For Beam No.48
Graph no.11 and graph no.12 shows that a structures designed for all combination we maintain DCR of all of structural element is in between 0.5 to 0.9.after Removal of Column C1 there is an sudden change in DCR of Beams in linear static analysis as compared to nonlinear static analysis.
H. Comparison Of Results For Bm For Beams
From Graph no 13 and graph no 14 shows that there is an gradual increase in bending moment before removal of column but there is sudden change in bending moment in linear static analysis as compared to nonlinear static analysis.
VI. SUMMURY AND CONCULSION
This study Discuss about effect of vertical Irregularity in special moment resisting steel frame structures. For that we consider three models having 5X7,7X9,9X11 vertical irregularity. Following observation are made.
Nodal Displacement for lower height of Structure is more as we increase the height of structure the displacement goes on reducing.
Demand Capacity Ratio of nearer to removal location is maximum for restructure changes with respect increasing height of structure.
Bending moment at corner location of lower storey structure is maximum as compare to other two cases.
Height of structure affect the collapse behavior as height increases progressive collapse decreases which is seen from D.C.R.values, Joint Displacement, and Bending Moment.
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